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LANIAKEA SUPERCLUSTER_ The Milky Way Is Just a Tiny Part of This · Boring Science

• 0:00
  Speaker 1: Most people can tell you their street address, their city,
• 0:04
  Speaker 1: their country, and if they are paying attention in school,
• 0:08
  Speaker 1: maybe even the name of the galaxy they live in,
• 0:11
  Speaker 1: but ask them to go one level higher, one step
• 0:15
  Speaker 1: further out, and almost everyone goes quiet. There is a
• 0:20
  Speaker 1: structure above the galaxy. There is a structure above the
• 0:24
  Speaker 1: galaxy cluster. There is an address most people have never
• 0:28
  Speaker 1: been given. And it belongs to a place so enormous
• 0:32
  Speaker 1: that the number of galaxies inside it runs to roughly 100,000.
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  Speaker 1: We live inside it right now. Most people have never
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  Speaker 1: heard its name. That silence matters. It is not a
• 0:46
  Speaker 1: gap in trivia. It is a gap in something more basic.
• 0:50
  Speaker 1: The question of where, exactly, you are. Humans have spent
• 0:56
  Speaker 1: thousands of years getting better at answering that question. We
• 0:59
  Speaker 1: mapped the continents. We tracked the planets. We measured the
• 1:04
  Speaker 1: distance to the sun, to nearby stars, to the edge
• 1:08
  Speaker 1: of our own galaxy. Every generation pushed the answer a
• 1:12
  Speaker 1: little further out. And then for a long stretch, the
• 1:17
  Speaker 1: answer stalled. The galaxy was as far as most people got,
• 1:21
  Speaker 1: and the Milky Way became the edge of the mental map.
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  Speaker 1: Beyond it, in this informal accounting, was just space, undifferentiated, unmapped, vast.
• 1:40
  Speaker 1: The truth is stranger and more structured than that. The
• 1:43
  Speaker 1: universe at its largest scales is not a smooth, even
• 1:47
  Speaker 1: fog of galaxies scattered randomly in every direction. It has bones.
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  Speaker 1: It has architecture. Galaxies cluster together. clusters gather into super clusters.
• 2:01
  Speaker 1: Super clusters are themselves embedded in a web of filaments
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  Speaker 1: and voids stretching across hundreds of millions of light years.
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  Speaker 1: This structure exists whether or not we know about it
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  Speaker 1: and we are inside it. The question was never whether
• 2:18
  Speaker 1: there was a larger address. The question was whether anyone
• 2:23
  Speaker 1: would ever figure out what it was. In 2014 A
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  Speaker 1: team of astronomers did. What they published that year was
• 2:33
  Speaker 1: not just a new measurement or a refined catalog. It
• 2:38
  Speaker 1: was a map of something that had never been mapped before.
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  Speaker 1: The full supercluster that contains the Milky Way, defined for
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  Speaker 1: the first time with a clear boundary, a coherent shape,
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  Speaker 1: and a name. The structure stretches 520 million light years across.
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  Speaker 1: Its total mass runs to something like a hundred quadrillion suns.
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  Speaker 1: It holds roughly 100,000 large galaxies inside it, all of
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  Speaker 1: them flowing, slowly and gravitationally, toward a common center. And
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  Speaker 1: almost nobody outside of astronomy has heard of it. The
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  Speaker 1: name comes from Hawaiian. The team behind the discovery was
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  Speaker 1: based at the University of Hawaii. And when the time
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  Speaker 1: came to name the structure, they consulted with Hawaiian language experts,
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  Speaker 1: rather than reaching for the usual Latin or Greek. The
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  Speaker 1: word they settled on is Laniakea. Lani means heaven or sky.
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  Speaker 1: Akea means spacious, open, immeasurable. Together the phrase means something
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  Speaker 1: close to immense heaven. There is something right about that.
• 3:54
  Speaker 1: Polynesian navigators once crossed the open Pacific with no instruments
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  Speaker 1: and no landmarks, reading the sky to find where they
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  Speaker 1: were in the world. The name given to our supercluster
• 4:06
  Speaker 1: reaches back to those same navigators, and it carries that
• 4:09
  Speaker 1: same orientation, looking up to understand your place. Most people
• 4:15
  Speaker 1: have a cosmic address they have never been told. Street, city, country, planet,
• 4:22
  Speaker 1: solar system, galaxy. galaxy cluster, supercluster. That last entry is
• 4:29
  Speaker 1: the missing one. That is the level where the address has,
• 4:33
  Speaker 1: until recently, been blank. For decades, astronomers thought the Virgo
• 4:39
  Speaker 1: supercluster was the best answer, a structure about 100 million
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  Speaker 1: light years across that the Milky Way sat on the
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  Speaker 1: edge of. But that picture was incomplete. The Virgo supercluster
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  Speaker 1: turned out to be a small piece of something much larger.
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  Speaker 1: What replaced it is deeper, wider, stranger, and harder to picture.
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  Speaker 1: It took a new way of thinking about the problem entirely,
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  Speaker 1: not just pointing telescopes but rethinking what a supercluster even is,
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  Speaker 1: before anyone could see it clearly. That discovery, how it
• 5:19
  Speaker 1: was made, what it revealed about the structure we are
• 5:22
  Speaker 1: embedded in, and what it means for the question of
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  Speaker 1: where you are. That is what the rest of this
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  Speaker 1: is about. The name is Laniakea, and understanding what it
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  Speaker 1: is changes everything about how you think about where you are.
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  Speaker 1: For decades, if you asked an astronomer where the Milky
• 5:45
  Speaker 1: Way sat in the largest known structure, the answer was
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  Speaker 1: the Virgo supercluster. That was the official answer. That was
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  Speaker 1: what the textbooks said. And for a long time, it
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  Speaker 1: felt like enough. To understand why that answer seemed satisfying,
• 6:06
  Speaker 1: you have to walk through the hierarchy that astronomers had
• 6:09
  Speaker 1: assembled piece by piece over the 20th century. Start at
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  Speaker 1: the bottom. Earth orbits the Sun. The Sun is one
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  Speaker 1: star among several hundred billion in the Milky Way. The
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  Speaker 1: Milky Way, a barred spiral galaxy roughly 100,000 light-years across,
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  Speaker 1: belongs to a small cluster of galaxies called the Local Group.
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  Speaker 1: The Local Group contains around 80 galaxies in total, most
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  Speaker 1: of them small and dim, gravitationally bound to each other
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  Speaker 1: and to the two dominant members, the Milky Way and
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  Speaker 1: the Andromeda Galaxy. That cluster spans roughly 10 million light years.
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  Speaker 1: Beyond the local group, things get larger, much larger. The
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  Speaker 1: Virgo supercluster was the next rung on that ladder. It
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  Speaker 1: stretched roughly 100 million light years across, an enormous region
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  Speaker 1: of space containing thousands of galaxies organized into smaller clusters
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  Speaker 1: and groups, all loosely associated around a gravitational center. At
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  Speaker 1: that centre sat the Virgo Cluster itself, one of the
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  Speaker 1: nearest large galaxy clusters to us, holding several thousand galaxies
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  Speaker 1: packed into a region roughly 8 million light-years wide. The
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  Speaker 1: local group sat on the outer edge of this structure,
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  Speaker 1: a minor outpost well away from the dense central regions.
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  Speaker 1: That was the address. That was the picture. The man
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  Speaker 1: most responsible for assembling it was a French-American astronomer named
• 7:55
  Speaker 1: Gérard de Vaucouleur. Working in the 1950s, de Vaucouleur noticed
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  Speaker 1: something that had been hiding in plain sight. When he
• 8:05
  Speaker 1: plotted the positions of nearby galaxies across the sky, they
• 8:10
  Speaker 1: weren't scattered randomly. They clustered preferentially along a flattened plane.
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  Speaker 1: a great disk of galaxies tilted roughly six degrees relative
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  Speaker 1: to the celestial equator. He called this the local supercluster.
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  Speaker 1: Other astronomers were skeptical. The concept of superclusters, enormous structures
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  Speaker 1: containing multiple clusters of galaxies, was not universally accepted at
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  Speaker 1: the time. Some researchers argued that what de Vaucouleur was
• 8:43
  Speaker 1: seeing was just a statistical accident, a coincidence in the
• 8:48
  Speaker 1: distribution of nearby galaxies rather than a genuine physical structure.
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  Speaker 1: The debate went on for decades. Gradually, as observations improved
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  Speaker 1: and galaxy catalogues grew larger, the reality of the local
• 9:04
  Speaker 1: supercluster became harder to dismiss. By the 1980s, most astronomers
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  Speaker 1: had accepted that de Vaucouleurs had been right. The Virgo
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  Speaker 1: supercluster was real. And once it was accepted, the picture
• 9:18
  Speaker 1: felt remarkably complete. You had a clean hierarchy. Planets orbited stars.
• 9:25
  Speaker 1: Stars gathered in galaxies. Galaxies gathered in clusters. Clusters gathered
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  Speaker 1: in superclusters. The universe was organized, nested, logical. The Virgo
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  Speaker 1: supercluster was the top of that nesting, the largest box
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  Speaker 1: that contained our box. and it had a sensible size,
• 9:46
  Speaker 1: about 100 million light years, and a sensible shape. It
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  Speaker 1: was centered on a visible, well-studied cluster of galaxies. You
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  Speaker 1: could point to it on a map. Cosmologically speaking, the
• 10:01
  Speaker 1: address problem seemed solved. Then the data started behaving strangely.
• 10:07
  Speaker 1: The universe is expanding. Edwin Hubble established this in 1929,
• 10:13
  Speaker 1: and by the second half of the 20th century, It
• 10:18
  Speaker 1: was one of the most thoroughly confirmed facts in all
• 10:21
  Speaker 1: of science. Galaxies are receding from us, and from each other,
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  Speaker 1: at speeds proportional to their distances. The further away a
• 10:32
  Speaker 1: galaxy is, the faster it appears to move away. This
• 10:37
  Speaker 1: is not galaxies moving through space so much as space
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  Speaker 1: itself stretching, carrying galaxies along with it. If you know
• 10:46
  Speaker 1: a galaxy's recession speed, you can calculate its distance. This relationship,
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  Speaker 1: called the Hubble flow, forms the backbone of how astronomers
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  Speaker 1: measure the large-scale universe. The problem was that real galaxies
• 11:01
  Speaker 1: didn't follow the Hubble flow exactly. When astronomers measured individual
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  Speaker 1: galaxy velocities carefully and compared them to what pure Hubble
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  Speaker 1: expansion predicted, there were systematic leftovers. Galaxies were moving at
• 11:17
  Speaker 1: speeds and in directions that pure expansion could not account for.
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  Speaker 1: These deviations had a name, peculiar velocities, and in small amounts,
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  Speaker 1: peculiar velocities were expected. Local gravity, the pull of a
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  Speaker 1: nearby galaxy cluster, the tug of a neighboring group, would
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  Speaker 1: naturally push galaxies slightly off the smooth expansion baseline. That
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  Speaker 1: was normal. that was understood. What was not understood was
• 11:48
  Speaker 1: the scale of what astronomers were beginning to see. By
• 11:53
  Speaker 1: the 1970s and into the 1980s, galaxy surveys were growing
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  Speaker 1: large enough that a troubling pattern was becoming visible. Galaxies
• 12:04
  Speaker 1: across an enormous volume of space, far larger than any
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  Speaker 1: individual cluster, far larger even than the Virgo supercluster, seemed
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  Speaker 1: to be drifting coherently in roughly the same direction. Not
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  Speaker 1: just a handful of galaxies, not just one cluster. Thousands
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  Speaker 1: of galaxies spread across hundreds of millions of light years
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  Speaker 1: were showing a systematic motion that pointed toward a particular
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  Speaker 1: region of the sky, somewhere in the direction of the
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  Speaker 1: constellations Centaurus and Norma. The motion was subtle, but it
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  Speaker 1: was measurable, and it was consistent. Something was pulling on
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  Speaker 1: a scale the existing maps would not explain. The Virgo
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  Speaker 1: supercluster alone could not account for it. The gravitational influence
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  Speaker 1: of the Virgo cluster and its surrounding structure was well understood,
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  Speaker 1: and yes, it tugged on the local group. But this
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  Speaker 1: new signal was different, larger, deeper, coming from a direction
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  Speaker 1: and on a scale that pointed to something much more
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  Speaker 1: massive sitting further out, something that had never been properly
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  Speaker 1: identified or mapped. The clean hierarchy began to look incomplete.
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  Speaker 1: The top rung of the ladder seemed to be missing something,
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  Speaker 1: or rather, it seemed to be sitting on top of
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  Speaker 1: something larger that nobody had noticed. For a generation of astronomers,
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  Speaker 1: this was the uncomfortable feeling at the edge of the
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  Speaker 1: The Virgo supercluster was real. The hierarchy was real. But
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  Speaker 1: the hierarchy wasn't the whole story. The galaxies weren't just
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  Speaker 1: expanding outward uniformly. They were being pulled, subtly but unmistakably,
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  Speaker 1: towards something nobody had fully mapped. In the 1970s, when
• 14:04
  Speaker 1: astronomers first produced detailed maps of the cosmic microwave background radiation,
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  Speaker 1: something immediately looked wrong. The CMB is the oldest light
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  Speaker 1: in the universe, a faint glow left over from roughly 380,000
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  Speaker 1: years after the Big Bang, spread almost perfectly uniformly across
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  Speaker 1: the sky. Almost. When scientists looked carefully at their new maps,
• 14:33
  Speaker 1: they noticed that one side of the sky was slightly
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  Speaker 1: warmer than the other. Not dramatically. Not in a way
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  Speaker 1: that leapt off the page. But the asymmetry was real,
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  Speaker 1: and it was consistent, and it meant something specific. The
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  Speaker 1: Milky Way was moving, not just spinning in place, not
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  Speaker 1: just orbiting the center of our galaxy. The entire local
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  Speaker 1: group was being carried in a direction, at a speed
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  Speaker 1: of roughly 600 kilometers per second, toward a regi, on
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  Speaker 1: of the sky nobody had properly investigated. 600 kilometers per
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  Speaker 1: second is not a small number. That is fast enough
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  Speaker 1: to cross the continental United States in under 10 seconds.
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  Speaker 1: At that speed, something is doing the pulling. The simple
• 15:24
  Speaker 1: model of cosmic expansion, galaxies moving apart uniformly in all directions,
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  Speaker 1: like raisins in a rising loaf of bread, predicted no
• 15:35
  Speaker 1: such drift. Everything should be moving outward from everything else.
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  Speaker 1: no preferred direction, no net flow toward any particular point.
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  Speaker 1: What the CMB maps were showing was a deviation from
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  Speaker 1: that picture. The local group had what astronomers call a
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  Speaker 1: peculiar velocity, meaning a velocity that cannot be accounted for
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  Speaker 1: by the ordinary expansion of space alone. Something gravitational was
• 16:06
  Speaker 1: adding an extra tug. Peculiar velocities are the fingerprints of structure.
• 16:12
  Speaker 1: In a perfectly smooth universe, galaxies would have no peculiar
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  Speaker 1: velocities at all. They would simply ride the expansion of
• 16:20
  Speaker 1: space outward, evenly, in all directions. But the universe is
• 16:26
  Speaker 1: not smooth. Matter is clumped into galaxies, clusters, filaments. Wherever
• 16:34
  Speaker 1: mass concentrates, it pulls neighboring objects toward it. giving those
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  Speaker 1: objects a velocity component that points toward the mass, rather
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  Speaker 1: than simply away from everything else. Measure enough peculiar velocities
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  Speaker 1: across a large enough volume of space, and you can
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  Speaker 1: reconstruct where the hidden mass is sitting. The CMB dipole
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  Speaker 1: was the first crude map of a peculiar velocity on
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  Speaker 1: the largest scale anyone had yet considered. It was telling
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  Speaker 1: astronomers that a significant mass concentration XI stead somewhere in
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  Speaker 1: the direction the local group was streaming toward, and that
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  Speaker 1: this concentration was large enough to accelerate thousands of galaxies simultaneously.
• 17:21
  Speaker 1: Through the late 1970s and into the 1980s, several independent
• 17:27
  Speaker 1: teams began measuring peculiar velocities for galaxies beyond the local group.
• 17:33
  Speaker 1: What they found was alarming in its consistency. Galaxies in
• 17:38
  Speaker 1: our general neighborhood were not just drifting outward with the
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  Speaker 1: Hubble flow. They were streaming. Hundreds of galaxies, spread across
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  Speaker 1: enormous distances, were all showing a common component of motion,
• 17:53
  Speaker 1: pointed in roughly the same direction. This was not noise.
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  Speaker 1: This was a coherent bulk flow. a river of galaxies
• 18:02
  Speaker 1: being carried together towards something. Astronomers called this the Great Attractor,
• 18:08
  Speaker 1: and the name was chosen carefully. Whatever was out there
• 18:13
  Speaker 1: was not a single object. It was a region, a
• 18:17
  Speaker 1: concentration of matter so vast and so massive that its
• 18:22
  Speaker 1: gravity was reaching hundreds of millions. of light years in
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  Speaker 1: every direction and bending the trajectories of everything it touched.
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  Speaker 1: The 1986 paper that gave the Great Attractor its name
• 18:36
  Speaker 1: came from a group of seven astronomers who would become
• 18:39
  Speaker 1: known informally as the Seven Samurai. Donald Lyndon Bell, Sandra
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  Speaker 1: Faber and five colleagues had spent years building a catalogue
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  Speaker 1: of elliptical galaxies with measured distances and velocities. When they
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  Speaker 1: analysed the streaming motions in their data, they found that
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  Speaker 1: the bulk flow pointed toward a specific region of the sky,
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  Speaker 1: the direction of the constellations Norma and Centaurus Crux, roughly
• 19:11
  Speaker 1: in the southern sky. Their best estimate placed the source
• 19:15
  Speaker 1: of the gravitational pull at somewhere between 150 and 250
• 19:19
  Speaker 1: million light-years away. mass required to produce the observed streaming
• 19:28
  Speaker 1: was staggering. 10 million billion solar masses. That is a 10,
• 19:36
  Speaker 1: followed by 15 zeros. That is T. And quadrillion suns
• 19:42
  Speaker 1: concentrated into one region of space, exerting gravitational influence across
• 19:47
  Speaker 1: a volume that makes our entire local group look like
• 19:51
  Speaker 1: a single grain of sand on a beach. Stop and
• 19:54
  Speaker 1: hold that number for a moment. 10 million billion solar masses.
• 20:00
  Speaker 1: Our sun is already so large that a million Earths
• 20:03
  Speaker 1: would fit inside it. The Milky Way contains somewhere around
• 20:08
  Speaker 1: 200 to 400 billion stars. The entire mass of everything
• 20:13
  Speaker 1: in the Local Group, every star, every galaxy, all the
• 20:18
  Speaker 1: dark matter, all the gas, is perhaps a few trillion
• 20:23
  Speaker 1: solar masses. The Greater Tractor was something altogether different. It
• 20:29
  Speaker 1: was not a cluster of galaxies in the ordinary sense.
• 20:33
  Speaker 1: It was a concentration of mass that dwarfed entire superclusters,
• 20:38
  Speaker 1: pulling the Milky Way and everything around it toward it
• 20:42
  Speaker 1: at hundreds of kilometers per second. And it had apparently
• 20:46
  Speaker 1: been doing this for billions of years. And yet, for
• 20:50
  Speaker 1: most of the 1980s, nobody could see it properly. This
• 20:54
  Speaker 1: is where the story gets genuinely strange. The greater tractor
• 20:59
  Speaker 1: was not a subtle signal buried in noisy data. Its
• 21:03
  Speaker 1: gravitational effect was measurable across hundreds of millions of light years.
• 21:09
  Speaker 1: Thousands of galaxies were streaming toward it. The CMB dipole
• 21:14
  Speaker 1: was pointing at it. And yet when astronomers turned their
• 21:18
  Speaker 1: telescopes toward the region of Norma and Centaurus and tried
• 21:22
  Speaker 1: to actually observe this gravitational engine directly, they ran into
• 21:27
  Speaker 1: a wall. Not a metaphorical wall. Something physical. sitting between
• 21:34
  Speaker 1: us and the attractor, blocking the view. The Milky Way itself.
• 21:39
  Speaker 1: Our galaxy is a disk. We are embedded inside that disk,
• 21:45
  Speaker 1: roughly two-thirds of the way out from the center. When
• 21:49
  Speaker 1: we look outward in the plane of the disk, toward
• 21:52
  Speaker 1: what we see as the band of the Milky Way
• 21:55
  Speaker 1: stretching across the night sky, We are looking through the
• 21:59
  Speaker 1: maximum concentration of our own galaxy's stars, gas and dust.
• 22:06
  Speaker 1: There are hundreds of billions of stars between us and
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  Speaker 1: the edge of the galactic disk in that direction, along
• 22:13
  Speaker 1: with enormous clouds of molecular gas and thick lanes of
• 22:18
  Speaker 1: interstellar dust that absorb and scatter visible light almost completely.
• 22:24
  Speaker 1: Anything sitting behind that disk invisible wavelengths is essentially invisible.
• 22:31
  Speaker 1: Astronomers have a name for this region of the sky.
• 22:34
  Speaker 1: They call it the zone of avoidance. The zone of
• 22:38
  Speaker 1: avoidance covers a significant band across the entire sky. It
• 22:42
  Speaker 1: is not a narrow slit. In some directions it extends
• 22:46
  Speaker 1: 20 to 30 degrees above and below the galactic plane.
• 22:51
  Speaker 1: A substantial fraction of the entire sky Perhaps 20% or
• 22:55
  Speaker 1: more of the observable universe as seen from Earth is
• 22:59
  Speaker 1: obscured or seriously compromised in optical wavelengths by our own
• 23:04
  Speaker 1: galaxy's disk. This would be merely inconvenient if the objects
• 23:09
  Speaker 1: behind it were distributed randomly. But they are not. The
• 23:14
  Speaker 1: greater tractor sits squarely in this zone. The densest, most
• 23:20
  Speaker 1: consequential structure in our corner of the universe happens to
• 23:24
  Speaker 1: lie almost perfectly behind the thickest part of the galactic plane,
• 23:29
  Speaker 1: as seen from our position within the Milky Way. You
• 23:33
  Speaker 1: could not design a more effective obstacle if you tried.
• 23:37
  Speaker 1: Astronomers throughout the 1980s and into the 1990s pushed hard
• 23:43
  Speaker 1: against this limitation. They turned to radio telescopes, which can
• 23:48
  Speaker 1: detect the 21cm emission line of neutral hydrogen through almost
• 23:54
  Speaker 1: any amount of dust. They used X-ray observatories, which can
• 23:59
  Speaker 1: detect the hot gas in galaxy clusters even through substantial obscuration.
• 24:05
  Speaker 1: They developed infrared surveys that could cut through dust far
• 24:09
  Speaker 1: more effectively than optical light. Slowly, painfully, the picture behind
• 24:16
  Speaker 1: the Zone of Avoidance began to clarify. The Norma Cluster
• 24:21
  Speaker 1: emerged from the A rich cluster of galaxies sitting right
• 24:26
  Speaker 1: at the heart of the attractor region, dense with thousands
• 24:30
  Speaker 1: of galaxies, threaded through with hot gas. It was not
• 24:35
  Speaker 1: the totality of the great attractor, but it was a
• 24:38
  Speaker 1: confirmation that something mass, sieve was genuinely there. The gravitational
• 24:44
  Speaker 1: signal was real. The streaming was real. The thing causing
• 24:48
  Speaker 1: it was real. What was almost absurd about the situation
• 24:53
  Speaker 1: was the irony embedded in it. Here was the most
• 24:57
  Speaker 1: gravitationally dominant structure within hundreds of millions of light years
• 25:02
  Speaker 1: of the Milky Way, something pulling our entire galactic neighborhood
• 25:06
  Speaker 1: toward it at enormous speed, something that had been shaping
• 25:11
  Speaker 1: the large-scale motion of galaxies in our region for billions
• 25:15
  Speaker 1: of years. And the reason we could barely study it
• 25:19
  Speaker 1: was not a technological limitation, or a fundamental physical barrier.
• 25:25
  Speaker 1: It was us. The very galaxy we live in was
• 25:29
  Speaker 1: blocking our view of the gravitational engine at the center
• 25:33
  Speaker 1: of our cosmic home. Imagine trying to map a city
• 25:36
  Speaker 1: while standing in the middle of a thick forest that
• 25:39
  Speaker 1: circles the entire downtown core. You can see what is
• 25:43
  Speaker 1: directly around you. You can see patches of sky above.
• 25:48
  Speaker 1: But the buildings at the center, the streets, the whole
• 25:52
  Speaker 1: layout of the place you are trying to understand. All
• 25:56
  Speaker 1: of it is blocked by the trees. That is roughly
• 26:00
  Speaker 1: the situation astronomers face when they try to observe the
• 26:04
  Speaker 1: region of the universe sitting behind the plane of the
• 26:07
  Speaker 1: Milky Way. The forest is our own galaxy, and it
• 26:12
  Speaker 1: does not move. The problem has a name. Astronomers call
• 26:17
  Speaker 1: it the zone of avoidance. which sounds like something you
• 26:20
  Speaker 1: would find on a nautical chart warning ships away from
• 26:24
  Speaker 1: shallow water. The name fits. It is a band running
• 26:29
  Speaker 1: all the way around the sky, tracing the galactic plane,
• 26:34
  Speaker 1: where the Milky Way's own stars, gas, and dust absorb
• 26:39
  Speaker 1: and scatter the light coming from anything beyond. In optical wavelengths,
• 26:45
  Speaker 1: the kind of light human eyes can see This band
• 26:49
  Speaker 1: is essentially opaque. Galaxies that sit behind it are not dimmed.
• 26:55
  Speaker 1: They are gone. Their light never makes it through. The
• 26:59
  Speaker 1: zone of avoidance covers roughly 20% of the entire sky.
• 27:05
  Speaker 1: That is not a narrow strip you can work around.
• 27:08
  Speaker 1: That is a fifth of everything, running in a continuous
• 27:12
  Speaker 1: band around the full equator of our celestial sphere. What
• 27:17
  Speaker 1: makes this strange is that the obscuring material is not
• 27:21
  Speaker 1: particularly thick by cosmic standards. The dust and gas clouds
• 27:26
  Speaker 1: responsible for the blockage are relatively diffuse, but they are
• 27:31
  Speaker 1: spread across tens of thousands of light years of galactic disk,
• 27:36
  Speaker 1: and when you stack that much material between yourself and
• 27:40
  Speaker 1: a distant galaxy, even thin stuff adds up. The total
• 27:45
  Speaker 1: extinction in some parts of the galactic plane is enormous.
• 27:49
  Speaker 1: Light from distant objects gets absorbed, scattered, and reddened into
• 27:54
  Speaker 1: invisibility long before it reaches a telescope on Earth. Astronomers
• 28:00
  Speaker 1: are not helpless. They found workarounds, and the workarounds are clever.
• 28:07
  Speaker 1: Infrared light has longer wavelengths than visible light. and longer
• 28:12
  Speaker 1: wavelengths cut through dust far more effectively. An infrared telescope
• 28:18
  Speaker 1: can detect galaxies behind the galactic plane that are completely
• 28:23
  Speaker 1: invisible to an optical instrument. X-ray observations help as well.
• 28:30
  Speaker 1: High-energy X-rays punch through interstellar dust with relatively little scattering.
• 28:36
  Speaker 1: which is how some of the galaxy clusters lurking behind
• 28:39
  Speaker 1: the zone of avoidance were first identified. Radio wavelengths work too.
• 28:46
  Speaker 1: The 21 cm emission line from neutral hydrogen passes straight
• 28:50
  Speaker 1: through the galactic dust without any significant absorption, which means
• 28:56
  Speaker 1: radio surveys can map hydrogen in distant galaxies even when
• 29:00
  Speaker 1: those galaxies are sitting directly behind the Milky Way's thickest regions.
• 29:05
  Speaker 1: These tools opened up parts of the Zone of Avoidance
• 29:08
  Speaker 1: that had been completely dark before. The Norma Cluster, one
• 29:13
  Speaker 1: of the major structures near the Greater Tractor, was partly
• 29:17
  Speaker 1: mapped through these techniques. Several previously unknown galaxy clusters were
• 29:23
  Speaker 1: found hiding in the obscured region during the 1990s and 2000s,
• 29:29
  Speaker 1: when systematic infrared and radio surveys swept across the galactic
• 29:34
  Speaker 1: plane for the first time. Each discovery reminded astronomers how
• 29:40
  Speaker 1: much had been missed simply because of where they happened
• 29:44
  Speaker 1: to be sitting. But here is the thing, even with infrared,
• 29:49
  Speaker 1: x-ray and radio data combined, the zone of avoidance remains
• 29:54
  Speaker 1: the worst characterized region of the nearby universe. The tools
• 29:58
  Speaker 1: that cut through dust come with their own limitations. Infrared
• 30:04
  Speaker 1: surveys still struggle with the bright emission from our own
• 30:07
  Speaker 1: galaxy's stars, which floods the detectors and makes faint background
• 30:13
  Speaker 1: sources hard to extract. Radio surveys measure hydrogen, but miss
• 30:18
  Speaker 1: galaxies with little neutral gas. X-ray observations pick up hot
• 30:23
  Speaker 1: cluster gas, but not the full picture of galaxy distribution.
• 30:29
  Speaker 1: No single alternative method gives you what optical astronomy gives
• 30:33
  Speaker 1: you everywhere else. The coverage is patchier. The catalogues are
• 30:38
  Speaker 1: less complete. The distance measurements are harder to make and
• 30:43
  Speaker 1: less reliable. When Brent Tully's team built the Cosmic Flows
• 30:47
  Speaker 1: 2 catalogue, the one that would eventually define Laniakea, the
• 30:52
  Speaker 1: data thinned out and degraded precisely in the directions behind
• 30:56
  Speaker 1: the galactic plane. The map had a hole in it,
• 31:01
  Speaker 1: and the hole sat right over one of the most
• 31:03
  Speaker 1: gravitationally significant regions in the local universe. There is a
• 31:08
  Speaker 1: particular irony in all of this that is hard to ignore.
• 31:12
  Speaker 1: The Milky Way is not a distant obstacle. It is
• 31:16
  Speaker 1: not some intervening object that happens to lie in an
• 31:19
  Speaker 1: unfortunate direction. It is the galaxy we live inside. The
• 31:25
  Speaker 1: stars blocking our view of the Great Attractor are the
• 31:29
  Speaker 1: same stars that make up the bright band of the
• 31:31
  Speaker 1: Milky Way that humans have looked up at for all
• 31:35
  Speaker 1: of recorded history. The dust blocking the light from thousands
• 31:40
  Speaker 1: of background galaxies is the same dust that fills the
• 31:44
  Speaker 1: spiral arms of our own home. We are embedded so
• 31:49
  Speaker 1: deeply inside this structure that it wraps completely around us
• 31:54
  Speaker 1: and because of that There is a ring around our
• 31:57
  Speaker 1: entire sky, where the universe is functionally hidden. The very
• 32:03
  Speaker 1: thing that makes us astronomers, having a galaxy to stand in,
• 32:08
  Speaker 1: is the same they, none that blinds us to a
• 32:11
  Speaker 1: fifth of what surrounds us. For years, the great attractor
• 32:16
  Speaker 1: sat squarely behind this veil, its true nature hidden behind
• 32:21
  Speaker 1: the very structure that contains every star you can see
• 32:25
  Speaker 1: on a clear night. The breakthrough that produced Laniakea was
• 32:29
  Speaker 1: not a new telescope or a new piece of hardware.
• 32:32
  Speaker 1: It was a new idea about what astronomers should be measuring.
• 32:37
  Speaker 1: For most of the 20th century, when astronomers tried to
• 32:40
  Speaker 1: map the large-scale structure of the universe, they did it
• 32:44
  Speaker 1: by counting. They would survey a region of sky, catalog
• 32:48
  Speaker 1: the galaxies they found and draw boundaries around the densest concentrations.
• 32:54
  Speaker 1: Where galaxies clumped together, that was a cluster. Where clusters
• 32:59
  Speaker 1: grouped together, that was a supercluster. It was a logical approach.
• 33:05
  Speaker 1: It was also, it turned out, incomplete. Density maps can
• 33:11
  Speaker 1: tell you where matter piled up, but they cannot tell
• 33:14
  Speaker 1: you what belongs together gravitationally. A city map that only
• 33:20
  Speaker 1: shows population density misses the fact that commuters from far-flung
• 33:25
  Speaker 1: suburbs are functionally part of the same metropolitan system, even
• 33:30
  Speaker 1: if they live in a sparse neighborhood at the edge.
• 33:33
  Speaker 1: Brent Tully understood this problem. Tully is an astronomer at
• 33:38
  Speaker 1: the University of Hawaii's Institute for Astronomy, and by He
• 33:45
  Speaker 1: had spent decades building the most precise catalogues of galaxy
• 33:49
  Speaker 1: distances and velocities that the field had ever produced. He
• 33:53
  Speaker 1: had already made his name decades earlier, co-developing the Tully-Fisher relation,
• 33:59
  Speaker 1: the technique that links a spiral galaxy's rotation speed to
• 34:03
  Speaker 1: its true brightness and allows astronomers to infer distances from
• 34:08
  Speaker 1: observations alone. That earlier work was groundbreaking. But by the 2000s,
• 34:16
  Speaker 1: Tully was working on something with even larger implications. He
• 34:21
  Speaker 1: was thinking about what the motions of galaxies could reveal,
• 34:25
  Speaker 1: not just their positions. Here is the key concept. When
• 34:29
  Speaker 1: astronomers measure the velocity of a distant galaxy, they typically
• 34:34
  Speaker 1: get two signals mixed together. One is the velocity from
• 34:38
  Speaker 1: the expansion of the universe, the background hum of space
• 34:43
  Speaker 1: itself stretching, which makes every galaxy appear to be moving
• 34:47
  Speaker 1: away from us, faster with distance. The second signal is
• 34:53
  Speaker 1: something subtler. It is the galaxy's individual motion on top
• 34:59
  Speaker 1: of that expansion, caused by the gravitational tug of everything
• 35:04
  Speaker 1: around it. Astronomers call this the peculiar velocity. It is
• 35:09
  Speaker 1: the deviation from pure expansion, and it is a direct
• 35:13
  Speaker 1: fingerprint of the local gravitational field. If you could map
• 35:18
  Speaker 1: the peculiar velocities of thousands of galaxies across hundreds of
• 35:22
  Speaker 1: millions of light years, you would not be looking at
• 35:26
  Speaker 1: where galaxies happen to be sitting right now. You would
• 35:30
  Speaker 1: be looking at where gravity is pulling them. You would
• 35:34
  Speaker 1: see the underlying skeleton of the mass distribution. not just
• 35:39
  Speaker 1: its surface appearance. This is what Tully and his collaborators
• 35:44
  Speaker 1: set out to do. The analogy that makes this clearest
• 35:48
  Speaker 1: is a watershed. Stand somewhere in the Rocky Mountains, and
• 35:53
  Speaker 1: the rain that falls on your left flows eventually toward
• 35:57
  Speaker 1: the Pacific. The rain that falls on your right flows
• 36:01
  Speaker 1: toward the Atlantic or the Gulf of Mexico. There is
• 36:05
  Speaker 1: a dividing line running along the mountain ridges where these
• 36:09
  Speaker 1: drainage basins meet. On either side of that line, water
• 36:14
  Speaker 1: flows in fundamentally different directions. Neither side knows anything about
• 36:20
  Speaker 1: the other. They belong to different systems. Now imagine the
• 36:25
  Speaker 1: same thing at cosmic scale. Galaxies are not sitting still.
• 36:30
  Speaker 1: They are flowing, very slowly by human standards. toward the
• 36:34
  Speaker 1: nearest major gravitational concentration. In one region, they flow toward
• 36:40
  Speaker 1: one center of mass. In an adjacent region, they flow
• 36:45
  Speaker 1: toward a different one. The boundary between those two regions,
• 36:50
  Speaker 1: the cosmic equivalent of the continental divide, is where the
• 36:54
  Speaker 1: peculiar velocities reverse direction. That boundary defines where one supercluster
• 37:01
  Speaker 1: ends and another begins. not a density threshold, a watershed.
• 37:08
  Speaker 1: This was the conceptual breakthrough. A supercluster, under Tully's definition,
• 37:13
  Speaker 1: is not simply a region where galaxies are dense. It
• 37:17
  Speaker 1: is a basin of attraction, a volume of space inside
• 37:21
  Speaker 1: which all galaxy motions, once you subtract the background expansion,
• 37:27
  Speaker 1: are directed inward toward the same gravitational center. The boundaries
• 37:32
  Speaker 1: are determined not by how many galaxies you can count
• 37:36
  Speaker 1: per cubic megaparsec, but by where the flow changes direction.
• 37:41
  Speaker 1: The method required data, enormous amounts of it. To construct
• 37:47
  Speaker 1: a meaningful map of peculiar velocities across hundreds of millions
• 37:51
  Speaker 1: of light years, you need precise independent distances for thousands
• 37:56
  Speaker 1: of galaxies. Redshift alone does not work. Because redshift conflates
• 38:02
  Speaker 1: the expansion velocity with the peculiar velocity, you cannot separate
• 38:08
  Speaker 1: them without an independent distance measurement. Tully and his colleagues
• 38:14
  Speaker 1: had been building toward this for years. The result was
• 38:18
  Speaker 1: the Cosmic Flows 2 catalog containing measured distances for more
• 38:23
  Speaker 1: than 8,100 galaxies spread across a substantial volume of the
• 38:29
  Speaker 1: nearby universe. Each distance was derived using one or more
• 38:34
  Speaker 1: of the established techniques, primarily the Tully-Fisher relation for spirals,
• 38:40
  Speaker 1: along with other methods for other galaxy types. The Kata
• 38:46
  Speaker 1: log represented the most complete and precise dataset of its
• 38:49
  Speaker 1: kind ever assembled. With those distances, The team could calculate
• 38:54
  Speaker 1: each galaxy's peculiar velocity directly, subtract the expected expansion velocity,
• 39:01
  Speaker 1: and what remains is real motion, gravitational flow. When you
• 39:06
  Speaker 1: plot those flow vectors across thousands of galaxies, patterns emerge,
• 39:12
  Speaker 1: filaments of flow converging toward the same point, boundaries where
• 39:17
  Speaker 1: flow directions diverge. The invisible architecture of gravity made visible
• 39:23
  Speaker 1: through the motion of light. The computation was not trivial.
• 39:29
  Speaker 1: Converting raw distance and velocity measurements for thousands of galaxies
• 39:34
  Speaker 1: into a coherent three-dimensional flow map required sophisticated mathematical reconstruction.
• 39:42
  Speaker 1: The team had to account for gaps in coverage, errors
• 39:46
  Speaker 1: in individual distance measurements, and the contaminating effects of the
• 39:51
  Speaker 1: zone of avoidance, where peculiar velocity data was thin or absent.
• 39:57
  Speaker 1: They developed techniques to smooth and reconstruct the flow field
• 40:01
  Speaker 1: across poorly sampled regions, using the surrounding data to fill
• 40:06
  Speaker 1: in the gaps as accurately as possible. It was as
• 40:10
  Speaker 1: much mathematical craft as astronomical observation. When the paper landed
• 40:16
  Speaker 1: in Nature on September 4th, 2014, it presented not just
• 40:22
  Speaker 1: a new structure, but a new framework. Every previous map
• 40:27
  Speaker 1: of the local supercluster had drawn its borders based on
• 40:31
  Speaker 1: galaxy density. Tully's map drew borders based on gravitational coherence.
• 40:38
  Speaker 1: The result was a structure vastly larger than anyone had
• 40:42
  Speaker 1: previously outlined. one that absorbed the old Virgo supercluster as
• 40:47
  Speaker 1: a single component, that stretched 520 million light years from
• 40:52
  Speaker 1: one side to the other, and that contained roughly 100,000
• 40:57
  Speaker 1: large galaxies, all flowing, however slowly, toward a common gravitational center.
• 41:05
  Speaker 1: The Great Attractor, which had mystified astronomers for decades, turned
• 41:11
  Speaker 1: out to be the heart of this basin. It was
• 41:14
  Speaker 1: not a strange anomaly in an otherwise simple universe. It
• 41:19
  Speaker 1: was the gravitational floor of the largest structure any of
• 41:23
  Speaker 1: us had ever lived inside. What made the work genuinely
• 41:27
  Speaker 1: significant was not the size of what it found, though
• 41:31
  Speaker 1: the size was staggering. It was the redefinition of the
• 41:35
  Speaker 1: thing being measured. Tully's team did not discover that the
• 41:40
  Speaker 1: universe was bigger than we thought. They changed the questions.
• 41:44
  Speaker 1: Instead of asking where the galaxies are, they asked where
• 41:48
  Speaker 1: the galaxies are going. That shift in question produced a
• 41:53
  Speaker 1: shift in structure, a new way of drawing the map
• 41:57
  Speaker 1: of our cosmic address that nobody had managed before. When
• 42:02
  Speaker 1: they applied it to over 8,000 galaxies with measured distances
• 42:08
  Speaker 1: and velocities, the shape that emerged from the data was enormous, coherent,
• 42:14
  Speaker 1: and unlike anything on the existing maps. The structure that
• 42:19
  Speaker 1: emerged from Tully's maps was 520 million light years across.
• 42:25
  Speaker 1: That number is easy to type and almost impossible to
• 42:29
  Speaker 1: hold in your mind. But let's try. The Milky Way,
• 42:34
  Speaker 1: our galaxy, the one containing our sun and every star
• 42:39
  Speaker 1: visible on a clear night, stretches roughly 100,000 light years
• 42:44
  Speaker 1: from one edge to the other. That already sounds enormous. Light,
• 42:50
  Speaker 1: traveling at 186,000 miles per second, takes 100,000 years just
• 42:57
  Speaker 1: to cross it. Yet if you wanted to line up
• 43:01
  Speaker 1: Milky Way-sized galaxies end to end and span the full
• 43:05
  Speaker 1: width of Laniakea, you would need 5,000 of them. Not five.
• 43:11
  Speaker 1: not 50, 5,000 galaxies, each containing hundreds of billions of stars,
• 43:18
  Speaker 1: laid side by side, and you still haven't reached the
• 43:21
  Speaker 1: other end. That is what 520 million light years means
• 43:26
  Speaker 1: in practical terms. It is a number that defeats ordinary
• 43:31
  Speaker 1: intuition entirely. The mass locked up inside this structure is
• 43:35
  Speaker 1: just as staggering. Laniakea contains roughly 100,000 large galaxies. Each
• 43:42
  Speaker 1: of those galaxies is, by any human measure, incomprehensibly large.
• 43:49
  Speaker 1: But the total mass of Laniakea isn't just the mass
• 43:52
  Speaker 1: of the stars inside those galaxies. It includes the dark
• 43:57
  Speaker 1: matter halos wrapped around each one, the hot gas filling
• 44:02
  Speaker 1: the space between galaxies. and the gravitational glue holding clusters together.
• 44:09
  Speaker 1: Add it all up, and you get something in the
• 44:11
  Speaker 1: range of 10 to the power of 17 solar masses.
• 44:16
  Speaker 1: That's a 1 followed by 17 zeros, measured in suns.
• 44:21
  Speaker 1: A hundred quadrillion suns. Written out as a number, it
• 44:25
  Speaker 1: has so many digits that the number itself becomes meaningless
• 44:29
  Speaker 1: to read. The human brain simply doesn't have a reference
• 44:33
  Speaker 1: frame for it. There is no analogy that fully survives
• 44:37
  Speaker 1: contact with this scale. What does Laniakea actually look like?
• 44:42
  Speaker 1: This is where it gets genuinely strange. It is not
• 44:46
  Speaker 1: a sphere. It is not a uniform cloud. It does
• 44:49
  Speaker 1: not have smooth edges or a clean center. If you
• 44:53
  Speaker 1: could somehow generate an image of it in three dimensions
• 44:57
  Speaker 1: and step back far enough to see the whole thing
• 45:00
  Speaker 1: at once, What you would see looks something like a crumpled,
• 45:05
  Speaker 1: sprawling web. Dense bright knots mark where massive galaxy clusters sit.
• 45:13
  Speaker 1: Thin threads connect them, filaments made of galaxies and gas,
• 45:18
  Speaker 1: stretching for hundreds of millions of light years between the nodes.
• 45:23
  Speaker 1: And between those filaments, there is almost nothing. vast regions
• 45:28
  Speaker 1: of dark empty space where galaxies are rare or absent entirely.
• 45:34
  Speaker 1: The structure has shape and anatomy, but nothing about that
• 45:38
  Speaker 1: shape is neat or symmetrical. Think of it less like
• 45:42
  Speaker 1: a ball and more like a handful of soap bubbles
• 45:45
  Speaker 1: smashed together and stretched. The walls of the bubbles are
• 45:49
  Speaker 1: the filaments, the places where galaxies concentrate. The air inside
• 45:55
  Speaker 1: each bubble is a void. Where multiple bubbles meet, the
• 46:00
  Speaker 1: concentration of matter is highest. Those are the clusters. Laniakea
• 46:06
  Speaker 1: is the region defined by one connected system of these
• 46:10
  Speaker 1: filaments and flows, all of it draining gravitationally toward a
• 46:15
  Speaker 1: common center. That center is what astronomers call the Great Attractor,
• 46:21
  Speaker 1: a region deep inside Laniakea where the gravitational pull is strongest.
• 46:28
  Speaker 1: galaxies across the full 520 million light-year span of the
• 46:33
  Speaker 1: structure are moving slowly in that direction. Not because they
• 46:39
  Speaker 1: are being pushed, but because gravity has been pulling on
• 46:42
  Speaker 1: them for billions of years and they have built up adrift.
• 46:47
  Speaker 1: This motion is subtle, you would not notice it over
• 46:51
  Speaker 1: a human lifetime, but measured in kilometers per second, The
• 46:56
  Speaker 1: infall toward the greater tractor is real and detectable. It
• 47:01
  Speaker 1: is what allowed Tully's team to define the structure in
• 47:04
  Speaker 1: the first place. The watershed flows all run toward this
• 47:09
  Speaker 1: gravitational basin. That's where the center of Laniakea is. Now
• 47:15
  Speaker 1: here is the part that changes how you think about
• 47:18
  Speaker 1: where you are. The Milky Way does not sit anywhere
• 47:22
  Speaker 1: near that center. It sits on the edge. the outskirts,
• 47:27
  Speaker 1: the rim. Depending on how you measure it, our local
• 47:32
  Speaker 1: group is somewhere around 150 to 250 million light years
• 47:38
  Speaker 1: from the greater tractor. That means we are not in
• 47:41
  Speaker 1: the middle of Laniakea. We are roughly halfway to the
• 47:44
  Speaker 1: edge on the outer fringe in a relatively sparse and
• 47:48
  Speaker 1: quiet part of the structure. There are no major galaxy
• 47:53
  Speaker 1: clusters nearby. there is no dramatic concentration of matter in
• 47:57
  Speaker 1: our immediate vicinity. We are in the low density outer
• 48:02
  Speaker 1: region of an enormous gravitational basin, and the heart of
• 48:06
  Speaker 1: that basin is hundreds of millions of light years away.
• 48:11
  Speaker 1: This should be a genuinely disorienting realization. For most of
• 48:16
  Speaker 1: human history, humans assumed they occupied a special or central
• 48:21
  Speaker 1: place in the cosmos. Copernicus moved the Earth away from
• 48:26
  Speaker 1: the center of the solar system. Later work moved the
• 48:30
  Speaker 1: Sun away from the center of the galaxy. Now, Laniakea
• 48:35
  Speaker 1: moves us away from the center of our own supercluster.
• 48:39
  Speaker 1: Whatever the center of things might be, we are not
• 48:42
  Speaker 1: near it. We are peripheral in every structure we have
• 48:46
  Speaker 1: ever managed to identify. There is something worth sitting with there.
• 48:52
  Speaker 1: The greater tractor is pulling us toward it. Our local
• 48:56
  Speaker 1: group is drifting, incredibly slowly, in that direction. But we
• 49:01
  Speaker 1: are not falling fast. The distance is so enormous, and
• 49:06
  Speaker 1: the drift so gradual, that it will take billions of
• 49:10
  Speaker 1: years to cover even a fraction of it. And dark energy,
• 49:15
  Speaker 1: the force accelerating the expansion of the universe, will likely
• 49:19
  Speaker 1: pull the outer regions of Laniakea apart before any dramatic
• 49:24
  Speaker 1: convergence happens. We are moving toward the center of our supercluster,
• 49:30
  Speaker 1: but the supercluster itself is dissolving as we go. It
• 49:35
  Speaker 1: is not a destination we will ever reach. The overall
• 49:39
  Speaker 1: architecture of Laniakea, when you map it out with the
• 49:42
  Speaker 1: flows and the clusters and the filaments, divides into several
• 49:47
  Speaker 1: major regions. There is the part containing the Virgo cluster
• 49:51
  Speaker 1: and our local group, the part containing the Hydra and
• 49:55
  Speaker 1: Centaurus clusters, the region around the Norma cluster near the
• 50:00
  Speaker 1: greater tractor itself, and the Parvo-Indus supercluster region further out.
• 50:08
  Speaker 1: These are not cleanly separated neighborhoods. They are connected by filaments,
• 50:14
  Speaker 1: blending into each other the way the suburbs of a
• 50:16
  Speaker 1: city blend into its outskirts. But the rough anatomy is there,
• 50:23
  Speaker 1: and it all connects into a single, coherent, gravitational basin.
• 50:29
  Speaker 1: One thing that the three-dimensional maps make very clear is
• 50:33
  Speaker 1: how much empty space there is. The filaments are thin,
• 50:38
  Speaker 1: the clusters are relatively compact. Most of the volume of
• 50:42
  Speaker 1: Laniakea is void. If you were a traveler moving through
• 50:46
  Speaker 1: this structure at random, you would spend the vast majority
• 50:50
  Speaker 1: of your journey in near-empty darkness, far from any galaxy.
• 50:55
  Speaker 1: The bright connected web that shows up on the maps
• 50:59
  Speaker 1: represents a tiny fraction of the total volume. Most of
• 51:03
  Speaker 1: Laniakea is nothing. And yet, even knowing all that, 100,000
• 51:10
  Speaker 1: large galaxies is not a small number. Spread across 520
• 51:16
  Speaker 1: million light years, they fill this structure with an almost
• 51:20
  Speaker 1: uncountable number of stars, planets, and everything else. The Milky
• 51:27
  Speaker 1: Way alone has somewhere between 100 and 400 billion stars.
• 51:30
  Speaker 1: Multiply that by 100,000 galaxies, and even a rough estimate
• 51:39
  Speaker 1: becomes a number that no human can meaningfully visualize. Whatever
• 51:43
  Speaker 1: is out there in Laniakea, whatever is in those galaxies,
• 51:48
  Speaker 1: on those planets, around those stars, it exists at a
• 51:53
  Speaker 1: scale that makes the entire history of human civilization look
• 51:57
  Speaker 1: like a footnote written in pencil on the last page
• 52:01
  Speaker 1: of a book inside a library that fills a continent.
• 52:06
  Speaker 1: The structure is real. It is not a theoretical construct
• 52:10
  Speaker 1: or a statistical artifact. It is a physical feature of
• 52:14
  Speaker 1: the universe we live in, defined by the actual motions
• 52:18
  Speaker 1: of actual galaxies across actual space. And the Milky Way,
• 52:24
  Speaker 1: with all its hundreds of billions of stars, sits near
• 52:28
  Speaker 1: the outer edge of this. a small dot on the
• 52:31
  Speaker 1: rim of something almost too large to picture. When the
• 52:36
  Speaker 1: time came to name the structure, Brent Tully did not
• 52:39
  Speaker 1: reach for Greek or Latin. Most astronomical discoveries get named
• 52:44
  Speaker 1: after their discoverers, or after constellations, or after the catalogues
• 52:49
  Speaker 1: they appeared in. Tully's team was working at the University
• 52:53
  Speaker 1: of Hawaii. They were embedded in a place with its
• 52:57
  Speaker 1: own deep language its own history of navigating enormous and
• 53:02
  Speaker 1: featureless expanses, and its own tradition of reading the sky.
• 53:09
  Speaker 1: So Tully did something unusual. He consulted with Hawaiian language
• 53:14
  Speaker 1: experts to find a name that fit what they had
• 53:17
  Speaker 1: actually found. The word they landed on was Laniakea. It
• 53:22
  Speaker 1: comes from two Hawaiian roots. Lani means heaven or sky
• 53:27
  Speaker 1: or the celestial realm above. Akea means spacious, open, immeasurable.
• 53:34
  Speaker 1: Together the phrase means something like immense heaven, or the
• 53:37
  Speaker 1: expansive sky, a realm of stars so vast it resists
• 53:42
  Speaker 1: ordinary description. The name was suggested by Nawa'a Napoleon, an
• 53:48
  Speaker 1: associate professor of Hawaiian language at Kapiolani Community College. It
• 53:54
  Speaker 1: was not a casual choice. it captured something real about
• 53:58
  Speaker 1: the scale of the thing being named a structure 520
• 54:03
  Speaker 1: million light years across containing a hundred thousand galaxies bigger
• 54:09
  Speaker 1: than anything our nearest ancestors could have conceived immense heaven
• 54:15
  Speaker 1: is not an exaggeration it is barely adequate but there
• 54:19
  Speaker 1: is something stranger and more interesting here than just a
• 54:23
  Speaker 1: well-chosen word The name carries a cultural weight that runs
• 54:28
  Speaker 1: directly parallel to the science behind it. Polynesian navigators crossed
• 54:34
  Speaker 1: the Pacific Ocean, the largest body of water on Earth,
• 54:39
  Speaker 1: without compasses, without GPS, without charts in the modern sense.
• 54:45
  Speaker 1: They crossed it by reading the sky. They memorized the
• 54:49
  Speaker 1: rising and setting points of hundreds of stars. They understood
• 54:54
  Speaker 1: how ocean swells move relative to wind and island chains.
• 54:58
  Speaker 1: They tracked the color of the water, the flight paths
• 55:02
  Speaker 1: of birds, the feeling of current against a hull. But
• 55:06
  Speaker 1: above all, they read the heavens. The sky was their map.
• 55:11
  Speaker 1: The sky told them where they were. These were not
• 55:15
  Speaker 1: short journeys. The Pacific spans more than 12,000 miles at
• 55:19
  Speaker 1: its widest. Ancient Polynesian navigators reached Hawaii, New Zealand, Easter Island,
• 55:27
  Speaker 1: and dozens of other island groups separated by thousands of
• 55:30
  Speaker 1: miles of open ocean, with no landmarks visible from the water.
• 55:36
  Speaker 1: They did it by knowing the sky better than any
• 55:39
  Speaker 1: civilization in history. The sky was not decoration to them.
• 55:44
  Speaker 1: It was orientation. It told you which way was home.
• 55:48
  Speaker 1: Now consider what Tully's team actually did. They spent years
• 55:53
  Speaker 1: mapping how 8,000 galaxies move through space. They tracked the flows,
• 55:59
  Speaker 1: the convergences, the divergences, the subtle gravitational currents running beneath
• 56:05
  Speaker 1: the smooth expansion of the universe. And by reading those flows,
• 56:11
  Speaker 1: they found our address. Not our street address. Not our galaxy.
• 56:16
  Speaker 1: Our supercluster. They used the motion of the cosmos to
• 56:20
  Speaker 1: figure out where we are inside it. They navigated by
• 56:24
  Speaker 1: reading the sky. The parallel is not decorative, it is exact.
• 56:30
  Speaker 1: The navigators who crossed the Pacific were doing something that looks,
• 56:34
  Speaker 1: from the outside, like it should be impossible. How do
• 56:38
  Speaker 1: you find a small island in an ocean that wide
• 56:42
  Speaker 1: using only the sky? The answer is that you know
• 56:46
  Speaker 1: the sky well enough that it becomes a coordinate system,
• 56:50
  Speaker 1: a live map of your position and heading. Tully's team
• 56:55
  Speaker 1: was doing something that also looks, from the outside, like
• 56:59
  Speaker 1: it should be impossible. How do you find the shape
• 57:02
  Speaker 1: of a structure 520 million light-years across when you are
• 57:07
  Speaker 1: inside it and can only observe from a single point?
• 57:11
  Speaker 1: The answer is that you read the flows well enough
• 57:15
  Speaker 1: that they reveal the shape of the basin you are
• 57:18
  Speaker 1: sitting in. There is something almost too fitting about this.
• 57:23
  Speaker 1: The name Laniakea honors a tradition of navigation that solved
• 57:28
  Speaker 1: the same fundamental problem at a completely different scale. Where
• 57:34
  Speaker 1: are we? Which way is home? How do you find
• 57:38
  Speaker 1: your position in a featureless expanse with no obvious landmarks?
• 57:43
  Speaker 1: The Polynesian answer was, the stars? Tully's answer was the
• 57:48
  Speaker 1: motion of galaxies. Both are forms of reading the sky
• 57:52
  Speaker 1: to find your place within it. Noir Napoleon's suggestion was
• 57:57
  Speaker 1: not just linguistically appropriate, it was philosophically accurate. The sky
• 58:03
  Speaker 1: to Polynesian navigators was not a background, it was a
• 58:07
  Speaker 1: location system. And that is precisely what Laniakea is, a location.
• 58:14
  Speaker 1: a place in the cosmos that has a structure, a shape,
• 58:18
  Speaker 1: a center, a set of flows defining its edges. For
• 58:22
  Speaker 1: the first time in history, we have a name for
• 58:25
  Speaker 1: the largest structure we belong to, and that name comes
• 58:29
  Speaker 1: from a people whose entire civilization was built around the
• 58:33
  Speaker 1: idea that the sky tells you where you are. That
• 58:37
  Speaker 1: is a strange kind of symmetry. The navigators who crossed
• 58:41
  Speaker 1: the Pacific by reading the heavens had no way of
• 58:44
  Speaker 1: knowing what those heavens were embedded in. They knew the
• 58:48
  Speaker 1: stars as guides. They did not know those stars were
• 58:52
  Speaker 1: part of a galaxy, or that the galaxy was part
• 58:56
  Speaker 1: of a supercluster, or that the supercluster had a name.
• 59:01
  Speaker 1: Now it does. The people who learned to cross the
• 59:04
  Speaker 1: Pacific by reading the sky gave their language to the
• 59:08
  Speaker 1: discovery of what that sky actually sits in the universe.
• 59:13
  Speaker 1: The Virgo supercluster did not disappear when Laniakea was defined,
• 59:19
  Speaker 1: it simply shrank in significance. For decades, the Virgo supercluster
• 59:24
  Speaker 1: was the best answer astronomers had to the question of
• 59:28
  Speaker 1: our large-scale cosmic home. It was a genuine structure. It
• 59:33
  Speaker 1: was real. Roughly 100 million light-years across, centered on a
• 59:39
  Speaker 1: dense knot of galaxies in the direction of the constellation Virgo,
• 59:44
  Speaker 1: it had been identified in the 1950s by astronomer Gérard
• 59:49
  Speaker 1: de Vaucouleur and refined by generations of researchers who followed him.
• 59:56
  Speaker 1: If you had asked a cosmologist in 1990 whether Milky
• 1:00:00
  Speaker 1: Way lived in the largest known structure, the answer was
• 1:00:04
  Speaker 1: the Virgo supercluster. And that answer felt solid. It felt complete.
• 1:00:11
  Speaker 1: It had been tested and mapped and written into textbooks.
• 1:00:16
  Speaker 1: When Laniakea arrived in 2014, it did not invalidate any
• 1:00:19
  Speaker 1: of that work. It just revealed that the work had
• 1:00:25
  Speaker 1: been describing a neighbourhood without, realising the city extended far
• 1:00:30
  Speaker 1: beyond it. The Virgo Cluster itself sits near the heart
• 1:00:35
  Speaker 1: of this older structure, and it is worth pausing on
• 1:00:38
  Speaker 1: what that cluster actually is. Several thousand galaxies, packed into
• 1:00:44
  Speaker 1: a region roughly 15 million light-years across. Not a loose scattering,
• 1:00:51
  Speaker 1: but a genuine gravitational city, one of the richest concentrations
• 1:00:56
  Speaker 1: of galaxies within several hundred million light-years of Earth. It
• 1:01:02
  Speaker 1: anchors the Virgo supercluster the way a downtown core anchors
• 1:01:06
  Speaker 1: a metropolitan region. Its mass pulls on everything around it.
• 1:01:13
  Speaker 1: The local group, the small collection of roughly 80 galaxies
• 1:01:17
  Speaker 1: that includes the Milky Way and Andromeda, is moving toward
• 1:01:21
  Speaker 1: the Virgo cluster right now. very slowly, tugged by its
• 1:01:26
  Speaker 1: gravity across 50 to 60 million light-years of intervening space.
• 1:01:34
  Speaker 1: The Virgo Cluster is not abstract. It is a real gravitati,
• 1:01:40
  Speaker 1: onal presence, something our entire galactic neighbourhood feels. But the
• 1:01:45
  Speaker 1: Local Group's position in all of this is worth examining closely.
• 1:01:49
  Speaker 1: Roughly 80 galaxies most of them small satellites orbiting either
• 1:01:54
  Speaker 1: the Milky Way or Andromeda. The two dominant members, our
• 1:01:59
  Speaker 1: galaxy and its large neighbor, are themselves unremarkable spiral galaxies
• 1:02:06
  Speaker 1: by the standards of the broader universe. The local group
• 1:02:10
  Speaker 1: sits in the outer regions of the Virgo supercluster, not
• 1:02:14
  Speaker 1: near its center. Then the Virgo supercluster itself, as Laniakea revealed,
• 1:02:21
  Speaker 1: occupies an outer region of Laniakea. Stack these positions together
• 1:02:26
  Speaker 1: and a clear picture forms. We are not near the
• 1:02:30
  Speaker 1: centre of our galaxy cluster. Our cluster is not near
• 1:02:35
  Speaker 1: the centre of the Virgo supercluster. The Virgo supercluster is
• 1:02:40
  Speaker 1: not near the centre of Laniakea. At every level of
• 1:02:44
  Speaker 1: the hierarchy we are somewhere on the periphery, a pattern
• 1:02:49
  Speaker 1: that seems almost deliberate but is simply what the data shows.
• 1:02:54
  Speaker 1: The conceptual demotion this represents is worth sitting with. Every
• 1:02:59
  Speaker 1: level of our cosmic address that had felt like a
• 1:03:03
  Speaker 1: meaningful designation, Virgo supercluster, home, the largest structure we belong to,
• 1:03:11
  Speaker 1: turned out to be a subdivision of something larger. It
• 1:03:15
  Speaker 1: is like being told that the city you have lived
• 1:03:18
  Speaker 1: in your whole life The city whose name you gave
• 1:03:22
  Speaker 1: when people asked where you were from is not a
• 1:03:26
  Speaker 1: city at all. It is a district, and the actual
• 1:03:31
  Speaker 1: city is five times bigger, extends in directions you were
• 1:03:36
  Speaker 1: not looking, and contains structures in its other districts you
• 1:03:40
  Speaker 1: have never seen. The name on your driver's license did
• 1:03:43
  Speaker 1: not change. You did not move, but your sense of
• 1:03:48
  Speaker 1: where you are shifted completely. This kind of conceptual reshuffling
• 1:03:53
  Speaker 1: has happened before in astronomy. Earth was not the center
• 1:03:58
  Speaker 1: of the solar system. The Sun was not the center
• 1:04:01
  Speaker 1: of the galaxy. The Milky Way was not the only galaxy.
• 1:04:07
  Speaker 1: Each revision followed the same pattern. A structure that seemed
• 1:04:11
  Speaker 1: like the largest relevant frame turned out to be a
• 1:04:14
  Speaker 1: component of something larger. The Virgo supercluster joining this list
• 1:04:20
  Speaker 1: was not a shock to anyone paying attention to the
• 1:04:23
  Speaker 1: history of the field, but it was still a genuine
• 1:04:27
  Speaker 1: revision of the scientific record. Every textbook that had listed
• 1:04:32
  Speaker 1: the Virgo supercluster as our supercluster needed an asterisk, if
• 1:04:37
  Speaker 1: not a rewrite. What Laniakea absorbed was not just a
• 1:04:41
  Speaker 1: name on a map. The Virgo supercluster had been associated
• 1:04:46
  Speaker 1: with a specific picture of cosmic structure a set of boundaries,
• 1:04:51
  Speaker 1: a hierarchy. That picture was not wrong, exactly. The galaxies
• 1:04:57
  Speaker 1: are still where they were. The flows are real. The
• 1:05:01
  Speaker 1: Virgo cluster still dominates its local region of space. But
• 1:05:05
  Speaker 1: the boundaries that defined the Virgo supercluster as an independent
• 1:05:10
  Speaker 1: entity were revealed to be permeable, artificial in a certain sense,
• 1:05:16
  Speaker 1: drawn around a density peak rather than around a true
• 1:05:20
  Speaker 1: gravitational basin. When Tully's team redrew those boundaries using flow
• 1:05:26
  Speaker 1: patterns instead of density, the Virgo supercluster was absorbed. It
• 1:05:31
  Speaker 1: became one region in a much larger structure, like a
• 1:05:35
  Speaker 1: burrow absorbed into a growing metropolis that had expanded far
• 1:05:40
  Speaker 1: beyond its original limits. There is something almost vertiginous about
• 1:05:45
  Speaker 1: this if you follow it all the way down. The
• 1:05:49
  Speaker 1: Milky Way is one of roughly 80 galaxies in the
• 1:05:52
  Speaker 1: Local Group. The Local Group is one of perhaps a
• 1:05:56
  Speaker 1: thousand groups and clusters in the Virgo Supercluster. The Virgo
• 1:06:01
  Speaker 1: Supercluster is one of several major components within Laniakea. Laniakea
• 1:06:08
  Speaker 1: contains something on the order of 100,000 large galaxies spread
• 1:06:11
  Speaker 1: across 520 million light years. At each step, the scale
• 1:06:20
  Speaker 1: multiplies and the previous frame of reference shrinks. Our galaxy,
• 1:06:26
  Speaker 1: which contains hundreds of billions of stars, is a minor
• 1:06:30
  Speaker 1: entry in a minor cluster on the outer edge of
• 1:06:34
  Speaker 1: a supercluster component that is itself an outer region of
• 1:06:39
  Speaker 1: the structure we actually live in. None of this diminishes
• 1:06:43
  Speaker 1: what the Virgo supercluster is. it is still a real
• 1:06:48
  Speaker 1: and massive structure. The gravitational influence of the Virgo cluster
• 1:06:53
  Speaker 1: on our local group is real and measurable. But calling
• 1:06:58
  Speaker 1: the Virgo supercluster our home supercluster, the way astronomers did
• 1:07:03
  Speaker 1: for half a century, was like calling a suburb the city.
• 1:07:09
  Speaker 1: What we had called home for half a century turned
• 1:07:12
  Speaker 1: out to be one small corner of a much larger room.
• 1:07:16
  Speaker 1: Laniakea is not a smooth, uniform cloud of galaxies. It
• 1:07:20
  Speaker 1: has bones. If you could somehow pull back far enough
• 1:07:24
  Speaker 1: to see the whole structure at once. The way you
• 1:07:27
  Speaker 1: might look down at a city from altitude on a
• 1:07:30
  Speaker 1: clear night, what you would see is not a featureless glow.
• 1:07:35
  Speaker 1: You would see something more like a nervous system. Bright
• 1:07:39
  Speaker 1: knots of light where clusters sit. Long, faint threads connecting them.
• 1:07:45
  Speaker 1: And between those threads, enormous darkness, not empty by accident,
• 1:07:52
  Speaker 1: but empty because gravity spent billions of years pulling matter
• 1:07:56
  Speaker 1: away from those regions and piling it somewhere else. The
• 1:08:01
  Speaker 1: voids are not gaps in the data. They are real features,
• 1:08:05
  Speaker 1: as much a part of the structure as the clusters themselves.
• 1:08:10
  Speaker 1: The major galaxy clusters inside Laniakea red like a catalogue
• 1:08:15
  Speaker 1: of the southern and equatorial sky. Virgo is the closest
• 1:08:20
  Speaker 1: significant one to us. Hydra and Centaurus sit deeper in,
• 1:08:25
  Speaker 1: part of a dense complex that blends into the gravitational
• 1:08:28
  Speaker 1: centre of the whole structure. The norma cluster lies close
• 1:08:32
  Speaker 1: to the greater tractor itself, embedded in the most crowded
• 1:08:36
  Speaker 1: region of Laniakea's interior. Ophiuchus is one of the most
• 1:08:41
  Speaker 1: massive clusters in the entire supercluster, holding an enormous concentration
• 1:08:46
  Speaker 1: of hot gas and hundreds of galaxies bound tightly together.
• 1:08:52
  Speaker 1: Fornax and Eridanus anchor a separate region of the structure,
• 1:08:57
  Speaker 1: part of the southern extension of the filamentary web. These
• 1:09:02
  Speaker 1: are not just names on a list. Each one represents
• 1:09:06
  Speaker 1: a gravitational knot that has been accumulating matter for most
• 1:09:11
  Speaker 1: of the age of the universe. A galaxy cluster forms
• 1:09:15
  Speaker 1: because the universe was never perfectly smooth. In the earliest
• 1:09:19
  Speaker 1: moments after the Big Bang, there were tiny variations in density.
• 1:09:25
  Speaker 1: Some regions had slightly more matter, some slightly less. Those
• 1:09:31
  Speaker 1: differences were almost imperceptibly small. But gravity is patient. Over
• 1:09:38
  Speaker 1: hundreds of millions of years, the slightly denser regions pulled
• 1:09:42
  Speaker 1: more matter toward themselves. That made them denser still. Other
• 1:09:48
  Speaker 1: matter fell in from surrounding areas. Eventually, those regions collapsed
• 1:09:53
  Speaker 1: into the first galaxies. Galaxies fell toward each other, grouping
• 1:09:59
  Speaker 1: into clusters, and clusters gathered into superclusters. What you see
• 1:10:05
  Speaker 1: in Laniakea now is the result of that process running
• 1:10:08
  Speaker 1: for roughly 13 billion years. The clusters are where gravity
• 1:10:14
  Speaker 1: won most decisively. The voids are where it why, too
• 1:10:18
  Speaker 1: thinly spread to win at all. The assembly process did
• 1:10:22
  Speaker 1: not stop once the initial clusters formed. Smaller clusters and
• 1:10:27
  Speaker 1: galaxy groups continued falling into larger ones throughout cosmic history,
• 1:10:33
  Speaker 1: their mergers releasing tremendous energy. A massive cluster like Virgo
• 1:10:38
  Speaker 1: or Centaurus did not reach its present configuration until relatively recently.
• 1:10:45
  Speaker 1: on cosmic time scales. Clusters continue to grow and evolve
• 1:10:51
  Speaker 1: incorporating isolated galaxies that venture too close to their gravitational influence.
• 1:10:58
  Speaker 1: The largest clusters have been accumulating matter steadily for billions
• 1:11:02
  Speaker 1: of years and some are still in the process of
• 1:11:05
  Speaker 1: merging with neighboring structures today. This ongoing accretion gradually reshapes
• 1:11:12
  Speaker 1: the cluster environment and increases total mass. The clusters visible
• 1:11:18
  Speaker 1: in Laniakea are not static monuments to ancient gravity, b.
• 1:11:23
  Speaker 1: are dynamic systems still assembling and growing, drawing matter inward
• 1:11:28
  Speaker 1: through the cosmic web. Inside a cluster like Virgo or Norma,
• 1:11:33
  Speaker 1: individual galaxies are not sitting still. They move at speeds
• 1:11:38
  Speaker 1: of hundreds or even thousands of kilometers per second. orbiting
• 1:11:43
  Speaker 1: the cluster's center of mass the way bees circle a hive.
• 1:11:47
  Speaker 1: The space between them is filled with extremely hot, diffuse gas,
• 1:11:52
  Speaker 1: so hot it emits x-rays, and all of it is
• 1:11:56
  Speaker 1: held together by the combined gravity of the galaxies, the gas,
• 1:12:01
  Speaker 1: the dark matter that makes up the majority of the
• 1:12:04
  Speaker 1: cluster's total mass. A rich cluster can contain anywhere from
• 1:12:09
  Speaker 1: hundreds to several thousand galaxies, The Virgo cluster alone holds
• 1:12:15
  Speaker 1: several thousand. That kind of density is genuinely strange when
• 1:12:20
  Speaker 1: you think about what galaxies are. Each one of those
• 1:12:25
  Speaker 1: is a structure containing hundreds of billions of stars. They
• 1:12:30
  Speaker 1: are packed together tightly enough to interact, distort each other,
• 1:12:34
  Speaker 1: and occasionally merge. The filaments that connect these clusters are
• 1:12:39
  Speaker 1: harder to see, but just as real. They are elongated structures,
• 1:12:44
  Speaker 1: rivers of galaxies flowing between the dense nodes of the web.
• 1:12:49
  Speaker 1: A single filament inside Laniakea might stretch for a hundred
• 1:12:53
  Speaker 1: million light years or more, containing thousands of galaxies arranged
• 1:12:59
  Speaker 1: loosely along its length. These are not solid structures. There
• 1:13:05
  Speaker 1: is enormous space between the galaxies inside a filament, but statistically,
• 1:13:11
  Speaker 1: The galaxy density along a filament is meaningfully higher than
• 1:13:16
  Speaker 1: in the surrounding voids. Gravity draws matter toward the filaments,
• 1:13:22
  Speaker 1: and the filaments drain toward the clusters at their ends.
• 1:13:26
  Speaker 1: The whole thing flows, slowly, toward the densest concentrations. Then
• 1:13:33
  Speaker 1: there are the voids. Cosmological voids are among the strangest
• 1:13:38
  Speaker 1: objects in the universe, if you can call an absence
• 1:13:41
  Speaker 1: an object. They range in diameter from about 30 million
• 1:13:46
  Speaker 1: light years on the small end to 300 million light
• 1:13:50
  Speaker 1: years for the largest known examples. Inside a void, the
• 1:13:55
  Speaker 1: mean density of matter is less than a tenth of
• 1:13:58
  Speaker 1: the cosmic average. Galaxies are not absent entirely. There are
• 1:14:04
  Speaker 1: isolated galaxies and small groups scattered through void regions, but
• 1:14:09
  Speaker 1: they are so sparse that the void is, on cosmic terms,
• 1:14:14
  Speaker 1: essentially empty. If you lived in a galaxy inside one
• 1:14:18
  Speaker 1: of the large voids bordering Laniakea, your view of the
• 1:14:23
  Speaker 1: night sky would be far lonelier than ours. The nearest
• 1:14:27
  Speaker 1: large galaxy cluster might be a hundred million light-years away.
• 1:14:33
  Speaker 1: the universe would look far emptier than it do, as
• 1:14:36
  Speaker 1: from our position. What makes this architecture striking is that
• 1:14:41
  Speaker 1: it is not unique to Laniakea. The same pattern, clusters
• 1:14:46
  Speaker 1: at the nodes, filaments connecting them, voids filling the space between,
• 1:14:53
  Speaker 1: appears everywhere in the observable universe at these scales. Cosmologists
• 1:14:59
  Speaker 1: call it the cosmic web. It is the large-scale structure
• 1:15:03
  Speaker 1: of the universe, and it was not designed. It emerged
• 1:15:08
  Speaker 1: naturally from gravity, acting on the tiny density fluctuations left
• 1:15:13
  Speaker 1: over from the earliest moments of cosmic history. Simulations that
• 1:15:18
  Speaker 1: start from the conditions of the early universe and run
• 1:15:22
  Speaker 1: the physics forward reproduce this filamentary structure automatically. The web
• 1:15:28
  Speaker 1: was always going to form this way. given those initial conditions.
• 1:15:34
  Speaker 1: Laniakea is one node in that larger web, surrounded by
• 1:15:38
  Speaker 1: neighboring superclusters that have the same e-internal architecture of clusters, filaments, voids,
• 1:15:47
  Speaker 1: each one connected to others across distances that dwarf even
• 1:15:51
  Speaker 1: Laniakea itself. This matters for how you think about what
• 1:15:55
  Speaker 1: Laniakea is. It is not a bounded object floating in
• 1:16:00
  Speaker 1: empty space. It is a region of the cosmic web
• 1:16:04
  Speaker 1: that has a coherent gravitational basin, a region where galaxy
• 1:16:09
  Speaker 1: motions converge toward a common center, but its edges blend
• 1:16:13
  Speaker 1: into surrounding structures that are themselves organized the same way.
• 1:16:19
  Speaker 1: The filaments inside Laniakea connect outward to filaments in neighboring superclusters.
• 1:16:26
  Speaker 1: The voids inside Laniakea open onto voids that extend far
• 1:16:31
  Speaker 1: beyond its defined boundary. The structure has no sharp walls.
• 1:16:36
  Speaker 1: It fades, bleeds outward, continues. From inside, living in a
• 1:16:42
  Speaker 1: galaxy on the outer edge of one of the smaller
• 1:16:45
  Speaker 1: filamentary extensions, you see almost none of this. You see
• 1:16:51
  Speaker 1: a sky full of stars that all belong to your galaxy.
• 1:16:56
  Speaker 1: you see a handful of nearby galaxies with a telescope.
• 1:17:00
  Speaker 1: If you look at the distribution of distant galaxies across
• 1:17:04
  Speaker 1: the whole sky with a powerful enough survey, you start
• 1:17:09
  Speaker 1: to see hints of the filamentary structure, overdense regions in
• 1:17:13
  Speaker 1: some directions, underdense regions in others. But the full three-dimensional picture,
• 1:17:21
  Speaker 1: the bones of Laniakea, only becomes visible when you map
• 1:17:26
  Speaker 1: thousands of galaxies across hundreds of millions of light years
• 1:17:30
  Speaker 1: and trace how they are moving. This is not a
• 1:17:34
  Speaker 1: structure you would recognize from the inside. That is exactly
• 1:17:39
  Speaker 1: why it took until 2014 for anyone to draw its
• 1:17:43
  Speaker 1: full outline. Here is the strange part. Laniakea is not
• 1:17:48
  Speaker 1: actually held together. There is a difference between a gravitationally
• 1:17:52
  Speaker 1: bound structure and a basin of attraction A gravitationally bound
• 1:17:57
  Speaker 1: structure is one where gravity wins, where the objects inside
• 1:18:02
  Speaker 1: it are locked together tightly enough that expansion cannot pull
• 1:18:07
  Speaker 1: them apart. Galaxy clusters are bound. The Virgo Cluster, sitting
• 1:18:13
  Speaker 1: near the centre of our local corner of Laniakea, holds
• 1:18:17
  Speaker 1: thousands of galaxies in a gravitational grip they will never escape.
• 1:18:23
  Speaker 1: Those galaxies are not going anywhere. They will continue orbiting, colliding,
• 1:18:29
  Speaker 1: eventually merging over tens of billions of years into something unrecognizable,
• 1:18:35
  Speaker 1: but they will stay together. Our own local group is bound.
• 1:18:41
  Speaker 1: The Milky Way and the Andromeda Galaxy are falling toward
• 1:18:45
  Speaker 1: each other right now, closing the gap at roughly 110 kilometers.
• 1:18:50
  Speaker 1: per second. In about 4.5 billion years, they will collide.
• 1:18:57
  Speaker 1: That is a gravitationally bound system behaving exactly as bound
• 1:19:01
  Speaker 1: systems do. Laniakea is something different. Its galaxies are not
• 1:19:07
  Speaker 1: locked to each other. They are simply flowing in the
• 1:19:10
  Speaker 1: same direction, pulled toward the greater tractor the way water
• 1:19:15
  Speaker 1: flows toward the lowest point in a valley. The structure
• 1:19:19
  Speaker 1: has coherence because the flows are real and measurable. But
• 1:19:24
  Speaker 1: coherence is not the same as a bond. A river
• 1:19:28
  Speaker 1: has coherence. The water moves together in a shared direction,
• 1:19:34
  Speaker 1: following the same gradient. But the river does not hold
• 1:19:38
  Speaker 1: itself together. It flows because the landscape underneath it slopes
• 1:19:43
  Speaker 1: a certain way. Remove the slope, and the river stops.
• 1:19:49
  Speaker 1: Laniakea is similar. Its structure exists because the gravitational landscape
• 1:19:54
  Speaker 1: of this region of space slopes inward toward the greater tractor.
• 1:20:00
  Speaker 1: The galaxies follow that slope. Right now, in this epoch
• 1:20:05
  Speaker 1: of cosmic history, T, hat slope is real enough to
• 1:20:09
  Speaker 1: define an enormous coherent supercluster, but there is something else
• 1:20:14
  Speaker 1: shaping that landscape. Dark energy is real, it is the
• 1:20:19
  Speaker 1: dominant energy component of the universe, and it is working
• 1:20:23
  Speaker 1: against gravity at every scale large enough for the expansion
• 1:20:28
  Speaker 1: of space to matter. On the scale of galaxy clusters,
• 1:20:33
  Speaker 1: gravity wins. On the scale of superclusters, the contest is closer.
• 1:20:40
  Speaker 1: On the scale of Laniakea, dark energy is already winning
• 1:20:44
  Speaker 1: at the outer edges. The expansion of the universe is
• 1:20:48
  Speaker 1: not uniform in its effects. Galaxies that are gravitationally bound
• 1:20:53
  Speaker 1: to each other are immune. The expansion of space does
• 1:20:57
  Speaker 1: not reach in and tear apart structures that are already
• 1:21:00
  Speaker 1: gravitationally locked. But galaxies on the outer fringes of Laniakea,
• 1:21:06
  Speaker 1: where the gravitational pull from the center is weaker and
• 1:21:10
  Speaker 1: the distances are greater, are in a different situation. For
• 1:21:15
  Speaker 1: those galaxies, the outward push of cosmic expansion is already
• 1:21:20
  Speaker 1: comparable to, or greater than, the inward pull of gravity.
• 1:21:26
  Speaker 1: Over time, that balance tips further toward expansion. The outer
• 1:21:32
  Speaker 1: galaxies drift. Then they accelerate away. The boundary of the
• 1:21:38
  Speaker 1: structure does not hold. Think about what this means practically.
• 1:21:43
  Speaker 1: Right now, a galaxy near the edge of Laniakea is
• 1:21:47
  Speaker 1: technically part of the supercluster. Its motion, if you subtract
• 1:21:53
  Speaker 1: out the general expansion of the universe, points inward. It
• 1:21:57
  Speaker 1: is part of the flow. But over hundreds of billions
• 1:22:01
  Speaker 1: of years, the expansion rate increases relative to the gravitational attraction,
• 1:22:08
  Speaker 1: and at some point, that galaxy's peculiar velocity, the inward
• 1:22:13
  Speaker 1: drift that makes it part of Laniakea, gets overwhelmed by
• 1:22:18
  Speaker 1: the expanding universe carrying it away. The galaxy tips over
• 1:22:23
  Speaker 1: the watershed divide and effectively leaves the supercluster. Not dramatically,
• 1:22:29
  Speaker 1: Not suddenly, just gradually, inexorably, as cosmic expansion stretches the
• 1:22:36
  Speaker 1: space between it and the greater tractor until gravity can
• 1:22:41
  Speaker 1: no longer bridge the gap. This happens first at the
• 1:22:45
  Speaker 1: edges and works inward. The filaments connecting distant clusters weaken
• 1:22:51
  Speaker 1: and eventually dissolve. The clusters themselves remain intact. They are bound.
• 1:22:59
  Speaker 1: but the threads linking them across hundreds of millions of
• 1:23:02
  Speaker 1: light years slowly break. The supercluster's architecture, that web of
• 1:23:08
  Speaker 1: bright nodes connected by strands of galaxies, gradually loses its connections.
• 1:23:15
  Speaker 1: The nodes persist. The web does not. The greater tractor
• 1:23:21
  Speaker 1: does not switch off. It remains a massive concentration of matter,
• 1:23:26
  Speaker 1: and it continues pulling nearby galaxies toward it. But its
• 1:23:30
  Speaker 1: gravitational reach has a limit, and that limit gets shorter
• 1:23:34
  Speaker 1: as dark energy drives space to expand faster. Currently, the
• 1:23:40
  Speaker 1: Great Attractor's influence extends across the full scale of Laniakea,
• 1:23:45
  Speaker 1: roughly 250 million light years in all directions. Over hundreds
• 1:23:51
  Speaker 1: of billions of years, the region where its gravity beats
• 1:23:55
  Speaker 1: out expansion contracts. More and more of the supercluster's outer
• 1:24:00
  Speaker 1: volume crosses over into territory where expansion wins. What you
• 1:24:05
  Speaker 1: are left with, eventually, is not Laniakea. You are left
• 1:24:10
  Speaker 1: with a collection of bound galaxy clusters, each isolated, each
• 1:24:15
  Speaker 1: intact within itself, but separated from all the others. by
• 1:24:20
  Speaker 1: expanding voids too large for gravity to bridge. The Great
• 1:24:25
  Speaker 1: Attractor's neighborhood survives as a dense core. The outlying regions
• 1:24:31
  Speaker 1: drift away into the darkness. Nothing remains to show that
• 1:24:35
  Speaker 1: these clusters were ever connected, that galaxies across 520 million
• 1:24:41
  Speaker 1: light-years once all flowed toward the same gravitational basin. This
• 1:24:47
  Speaker 1: is the strange status Laniakea holds. It is real. The
• 1:24:52
  Speaker 1: flows that define it are measurable. The structure that Brent
• 1:24:56
  Speaker 1: Tully's team drew in 2014 is coherent and meaningful. And
• 1:25:01
  Speaker 1: yet it is not permanent in the way that a
• 1:25:04
  Speaker 1: galaxy is permanent, or a star, or a planet. It
• 1:25:09
  Speaker 1: exists as a structure only because we happen to be
• 1:25:11
  Speaker 1: living in an epoch when its coherence is intact. when
• 1:25:16
  Speaker 1: the gravitational flows are strong enough relative to expansion to
• 1:25:20
  Speaker 1: give it definable shape and definable borders. In a universe
• 1:25:26
  Speaker 1: older than ours by a factor of ten or a hundred,
• 1:25:30
  Speaker 1: there would be no Laniakea to find. There would be
• 1:25:34
  Speaker 1: no flow to map. We mapped it just in time,
• 1:25:39
  Speaker 1: in a sense, a structure coherent enough to define today
• 1:25:44
  Speaker 1: but destined to dissolve over time scales longer than the
• 1:25:47
  Speaker 1: current age of the universe. To define a structure by
• 1:25:51
  Speaker 1: how galaxies move, you first have to know where those
• 1:25:54
  Speaker 1: galaxies actually are. That sounds obvious. It is, in practice,
• 1:26:00
  Speaker 1: one of the hardest problems in observational astronomy, and solving
• 1:26:05
  Speaker 1: it took the better part of five decades. Here is
• 1:26:08
  Speaker 1: the core difficulty. You cannot lay a measuring tape across space.
• 1:26:13
  Speaker 1: You cannot bounce a signal off a galaxy a hundred
• 1:26:16
  Speaker 1: million light years away and time the echo. Every method
• 1:26:21
  Speaker 1: astronomers have for measuring cosmic distances is indirect. Each one
• 1:26:27
  Speaker 1: rests on a physical relationship, something that connects a property
• 1:26:31
  Speaker 1: you can observe to a property you cannot directly measure.
• 1:26:35
  Speaker 1: And each one carries error. Small errors in distance, when
• 1:26:40
  Speaker 1: converted into peculiar velocities, produce large errors in the flow maps.
• 1:26:46
  Speaker 1: The flow maps are only as clean as the distances
• 1:26:50
  Speaker 1: underneath them. Everything that makes Laniakea real and mappable and
• 1:26:55
  Speaker 1: coherent traces back to this unglamorous problem of actually pinning
• 1:27:00
  Speaker 1: down where things are. The way astronomers approach this is
• 1:27:04
  Speaker 1: through what they call the distance ladder. The idea is
• 1:27:08
  Speaker 1: to build outward in steps, Each step uses a method
• 1:27:12
  Speaker 1: that works reliably over a certain range of distances, but
• 1:27:17
  Speaker 1: fails beyond it. Each new method gets calibrated against the
• 1:27:21
  Speaker 1: previous one, before you trust it at greater distances. The
• 1:27:27
  Speaker 1: bottom rungs of the ladder are close enough that geometry
• 1:27:30
  Speaker 1: alone can do the work. Parallax, the tiny apparent shift
• 1:27:36
  Speaker 1: in a nearby star's position as Earth orbits the sun,
• 1:27:40
  Speaker 1: works out to a few thousand light years. Above that,
• 1:27:44
  Speaker 1: you switch to a different technique. At each transition, you
• 1:27:49
  Speaker 1: are trusting that the calibration between methods is solid, because
• 1:27:53
  Speaker 1: any error there propagates upward through every measurement you make
• 1:27:57
  Speaker 1: at greater distances. To reach galaxies hundreds of millions of
• 1:28:02
  Speaker 1: light years away, you need methods that work at truly
• 1:28:07
  Speaker 1: enormous scales. Two of the most important are the Tully-Fisher
• 1:28:12
  Speaker 1: relation and the fundamental plane, and together they are responsible
• 1:28:17
  Speaker 1: for most of the data that went into defining Laniakea.
• 1:28:22
  Speaker 1: The Tully-Fisher relation applies to spiral galaxies. It was noticed
• 1:28:28
  Speaker 1: in 1977 by Brent Tully and J. Richard Fisher, and
• 1:28:34
  Speaker 1: the same Tully would later lead the Laniakea team. What
• 1:28:38
  Speaker 1: they found was the time. correlation between how fast a
• 1:28:42
  Speaker 1: spiral galaxy rotates and how intrinsically luminous it is. A
• 1:28:47
  Speaker 1: galaxy spinning faster is more massive, and more massive galaxies
• 1:28:52
  Speaker 1: are brighter. If you measure a spiral galaxy's rotation speed
• 1:28:57
  Speaker 1: you can infer how bright it truly is. Then you
• 1:29:01
  Speaker 1: compare that true brightness to how bright it appears in
• 1:29:05
  Speaker 1: the sky. The difference tells you how far away the
• 1:29:09
  Speaker 1: light must have travelled to look as faint as it does.
• 1:29:13
  Speaker 1: It's the same logic as knowing how powerful a light
• 1:29:16
  Speaker 1: bulb is and using its apparent dimness to estimate how
• 1:29:20
  Speaker 1: far down the street it sits. The challenge is precision.
• 1:29:26
  Speaker 1: Small uncertainties in the rotation speed measurement translate into distance errors.
• 1:29:32
  Speaker 1: Calibrating the relation required extensive work across nearby galaxies where
• 1:29:38
  Speaker 1: independent checks were possible. For elliptical galaxies, which don't rotate
• 1:29:44
  Speaker 1: the same way, a different method applies. Elliptical galaxies follow
• 1:29:50
  Speaker 1: what astronomers call the fundamental plane. a relationship involving three
• 1:29:56
  Speaker 1: observable quantities, the galaxy's size, its surface brightness, and the
• 1:30:02
  Speaker 1: velocity dispersion of its stars, basically how fast the stars
• 1:30:07
  Speaker 1: are moving relative to each other internally. These three properties
• 1:30:13
  Speaker 1: are not independent. They are linked by the underlying physics
• 1:30:17
  Speaker 1: of how elliptical galaxies form and evolve. If you measure
• 1:30:22
  Speaker 1: two of them, you can infer the third, and from
• 1:30:25
  Speaker 1: the inferred properties you can extract the true luminosity, which
• 1:30:30
  Speaker 1: again gives you distance. The fundamental plane is messier than
• 1:30:34
  Speaker 1: Tully-Fisher in some respects, with more scatter in the relationship,
• 1:30:39
  Speaker 1: but it extends the distance ladder to galaxy types that
• 1:30:42
  Speaker 1: Tully-Fisher cannot reach. The Cosmic Flows project, led by Tully
• 1:30:48
  Speaker 1: and his team, was built to gather these measurements in systematic,
• 1:30:53
  Speaker 1: large numbers. The Cosmic Flows 2 catalog, which fed directly
• 1:30:58
  Speaker 1: into the 2014 Laniakea paper, contained distances for more than 8,100 galaxies.
• 1:31:08
  Speaker 1: That number sounds large until you realize how vast the
• 1:31:11
  Speaker 1: volume of space being mapped actually is. At the outer
• 1:31:16
  Speaker 1: edges of the survey, the coverage was thin. individual galaxies
• 1:31:21
  Speaker 1: were separated by gaps where no measurements existed. The flow
• 1:31:26
  Speaker 1: maps in those regions were smooth interpolations between real data points.
• 1:31:32
  Speaker 1: Every boundary on the Laniakea map is only as sharp
• 1:31:36
  Speaker 1: as the data density behind it allows. What Cosmic Flows 4,
• 1:31:41
  Speaker 1: released years later, brought was scale. Nearly 56,000 galaxy distances
• 1:31:49
  Speaker 1: gathered using eight separate methodologies cross-checked against each other. The
• 1:31:54
  Speaker 1: expanded catalog allowed the flow maps to extend further and
• 1:31:59
  Speaker 1: resolve structure more finely. It also allowed genuine tests of
• 1:32:05
  Speaker 1: whether the 2014 boundaries held up under scrutiny from a
• 1:32:09
  Speaker 1: data set seven times larger. Mostly they did, which is
• 1:32:16
  Speaker 1: itself a statement about how solid the original analysis was,
• 1:32:20
  Speaker 1: despite the sparse coverage. It is worth being specific about
• 1:32:26
  Speaker 1: how much human effort this represents. Measuring rotation curves for
• 1:32:30
  Speaker 1: thousands of spiral galaxies requires deep spectroscopic observations, long nights
• 1:32:37
  Speaker 1: at large telescopes, careful sky subtraction, and painstaking reduction of
• 1:32:43
  Speaker 1: the raw data. It requires doing this for galaxies that
• 1:32:47
  Speaker 1: appear as faint smudges in the sky. It requires going
• 1:32:52
  Speaker 1: back and re-measuring, checking for systematic errors, updating calibrations as
• 1:32:58
  Speaker 1: better nearby anchor points become available. The Cosmic Flows catalogs
• 1:33:05
  Speaker 1: reflect observational campaigns stretching back to the 1970s, accumulated across
• 1:33:12
  Speaker 1: hundreds of telescope nights at facilities from Hawaii to the
• 1:33:17
  Speaker 1: Canary Islands to Chile. Nobody did this in a single
• 1:33:22
  Speaker 1: coordinated push. It accumulated piece by piece, researcher by researcher,
• 1:33:28
  Speaker 1: over four decades, until the database was large enough and
• 1:33:33
  Speaker 1: reliable enough to trace the flows that outlined Laniakea. The
• 1:33:38
  Speaker 1: map of Laniakea is only as reliable as the distances
• 1:33:42
  Speaker 1: that went into building it. which means it rests on
• 1:33:46
  Speaker 1: decades of unglamorous observational work that most people never hear about.
• 1:33:53
  Speaker 1: If Laniakea had a neighbourhood, the Shapley Supercluster would be
• 1:33:58
  Speaker 1: its nearest significant neighbour, and the relationship between them is
• 1:34:03
  Speaker 1: not simple. The Shapley Supercluster sits roughly 650 million light-years away,
• 1:34:12
  Speaker 1: that is several hundred million light years further out than
• 1:34:16
  Speaker 1: the Great Attractor, which already sits 150 to 250 million
• 1:34:23
  Speaker 1: light years from the Milky Way. By any measure, Shapley
• 1:34:28
  Speaker 1: is distant, but distant does not mean irrelevant. Shapley is
• 1:34:34
  Speaker 1: one of the most massive concentrations of matter in the
• 1:34:37
  Speaker 1: observable universe, and its gravitational influence reaches far beyond its
• 1:34:43
  Speaker 1: own boundaries. When astronomers began measuring the peculiar velocities of
• 1:34:49
  Speaker 1: galaxies throughout and around Laniakea, something strange kept showing up
• 1:34:54
  Speaker 1: in the data. The Great Attractor was not just pulling
• 1:34:59
  Speaker 1: nearby galaxies toward itself, it was also moving. The entire
• 1:35:05
  Speaker 1: gravitational center of Laniakea was drifting, being pulled in Shapley's
• 1:35:11
  Speaker 1: This is where the picture gets complicated. Laniakea was defined
• 1:35:16
  Speaker 1: as a basin of attraction, a region where galaxy motions
• 1:35:20
  Speaker 1: converge inward toward a shared gravitational center. That definition worked
• 1:35:27
  Speaker 1: cleanly within its mapped boundaries. But the greater tractor at
• 1:35:31
  Speaker 1: Laniakea's core is itself part of a larger flow. Something
• 1:35:37
  Speaker 1: with even more mass is pulling on it from further out.
• 1:35:41
  Speaker 1: The Shapley concentration, as astronomers sometimes call it, generates a
• 1:35:47
  Speaker 1: gravitational pull strong enough to tug on a structure containing
• 1:35:51
  Speaker 1: a hundred quadrillion solar masses. Which raises a real question.
• 1:35:57
  Speaker 1: Is Laniakea truly an independent basin, or is it a
• 1:36:02
  Speaker 1: smaller valley inside a larger one, one that drains ultimately
• 1:36:06
  Speaker 1: towards Shapley? there is no clean answer yet. Some analyses
• 1:36:12
  Speaker 1: suggest Laniakea and the Ophiuchus cluster region form a combined
• 1:36:16
  Speaker 1: basin that flows towards Shapley, which would make Laniakea a
• 1:36:21
  Speaker 1: sub-basin rather than a top-level structure. Others maintain that the
• 1:36:26
  Speaker 1: flow patterns are distinct enough to treat them separately. The
• 1:36:31
  Speaker 1: boundary is fuzzy. That fuzziness is not a failure of science.
• 1:36:37
  Speaker 1: It reflects the fact that the universe does not organize
• 1:36:40
  Speaker 1: itself into tidy boxes. Gravity does not stop at the
• 1:36:45
  Speaker 1: edges of whatever structure we choose to name. Then something
• 1:36:49
  Speaker 1: else turned up entirely. In 2020, a team of astronomers
• 1:36:54
  Speaker 1: announced the discovery of a massive structure lying just beyond
• 1:36:58
  Speaker 1: Laniakea's boundaries. They called it the South Pole Wall. The
• 1:37:04
  Speaker 1: name comes from its orientation in the sky. concentrated near
• 1:37:08
  Speaker 1: the South Celestial Pole and extending outward in a great
• 1:37:13
  Speaker 1: sweeping arc. The scale of it is hard to take in.
• 1:37:18
  Speaker 1: The South Pole wall stretches across roughly 200 degrees of sky,
• 1:37:23
  Speaker 1: more than a semicircle. It wraps around Laniakea like an arm.
• 1:37:29
  Speaker 1: The densest part of the structure sits about 500 million
• 1:37:33
  Speaker 1: light years from the Milky Way, but following the arc
• 1:37:36
  Speaker 1: northward It curves inward to within 300 million light years
• 1:37:41
  Speaker 1: of us. It is not some distant background feature. It
• 1:37:46
  Speaker 1: is immediately adjacent. What makes the South Pole Wall particularly
• 1:37:50
  Speaker 1: striking is how long it went unnoticed. Part of the
• 1:37:55
  Speaker 1: answer is the zone of avoidance. A significant portion of
• 1:38:00
  Speaker 1: this structure lies behind the galactic plane, hidden behind the
• 1:38:04
  Speaker 1: dust and gas of the Milky Way. The tools that
• 1:38:08
  Speaker 1: revealed it, the same peculiar velocity mapping technique used to
• 1:38:13
  Speaker 1: define Laniakea, are better at seeing through that obstruction than
• 1:38:18
  Speaker 1: optical surveys. The South Pole Wall is a reminder that
• 1:38:23
  Speaker 1: Laniakea does not float in empty space. It sits within
• 1:38:28
  Speaker 1: a rich, dense cosmic environment. bordered by enormous structures that
• 1:38:33
  Speaker 1: we are still in the process of cataloguing. In 2023,
• 1:38:38
  Speaker 1: a study using the Cosmic Flows 4 catalogue pushed this
• 1:38:42
  Speaker 1: work further. Cosmic Flows 4 contains distances for nearly 56,000
• 1:38:47
  Speaker 1: galaxies compared to the 8100 used in the original 2014
• 1:38:55
  Speaker 1: Laniakea paper. With that much more data, the watershed technique
• 1:39:01
  Speaker 1: could be applied at larger scales and with better precision.
• 1:39:06
  Speaker 1: The result was a map that confirmed Laniakea's size and shape,
• 1:39:11
  Speaker 1: and simultaneously identified five neighbouring superclusters using the same method.
• 1:39:17
  Speaker 1: Those neighbours are Shapley, Perseus Pisces, Hercules, Lepus, and Apus.
• 1:39:24
  Speaker 1: Each one is a distinct gravitational basin in its own right,
• 1:39:28
  Speaker 1: a region where galaxy motions converge inward, just as they
• 1:39:32
  Speaker 1: do within Laniakea. Each one is enormous, and each one
• 1:39:37
  Speaker 1: sits adjacent to Laniakea in a way that makes the
• 1:39:41
  Speaker 1: entire local region of the universe feel increasingly crowded and interconnected.
• 1:39:48
  Speaker 1: Perseus Pisces is one of the largest concentrations of matter
• 1:39:53
  Speaker 1: in the nearby universe, a long filamentary structure stretching across
• 1:39:58
  Speaker 1: hundreds of millions of light years in a completely different
• 1:40:03
  Speaker 1: direction from Shapley. Hercules sits further out, a less concentrated
• 1:40:09
  Speaker 1: but still massive structure. Lepus and Apus are less studied,
• 1:40:15
  Speaker 1: less well-characterized, identified primarily through the flow signatures in the
• 1:40:20
  Speaker 1: Cosmic Flows 4 data, rather than through dense optical surveys.
• 1:40:26
  Speaker 1: These are not minor footnotes. They are superclusters. And Laniakea
• 1:40:32
  Speaker 1: sits among them, not at the edge of organized structure,
• 1:40:36
  Speaker 1: but deep inside a web of it. This brings in
• 1:40:39
  Speaker 1: the Pisces-Cetus supercluster complex. This is an even larger organizational level.
• 1:40:46
  Speaker 1: a structure that contains Laniakea, Perseus Pisces, Cetus, and several
• 1:40:52
  Speaker 1: other components in a single elongated complex stretching across roughly
• 1:40:57
  Speaker 1: a billion light years. The Pisces-Cetus complex is among the
• 1:41:02
  Speaker 1: largest known structures in the observable universe. Laniakea is its
• 1:41:08
  Speaker 1: inner component, its central region, which means the structure we
• 1:41:13
  Speaker 1: spent so much effort defining the one that took decades
• 1:41:17
  Speaker 1: of observational work to map, is itself a neighbourhood inside
• 1:41:22
  Speaker 1: something far larger. There is a pattern here. Before 2014,
• 1:41:27
  Speaker 1: our largest named home was the Virgo supercluster. Then Laniakea
• 1:41:34
  Speaker 1: absorbed it and grew the answer by a factor of
• 1:41:36
  Speaker 1: five in diameter. Now Laniakea sits inside the Pisces-Cetus complex
• 1:41:43
  Speaker 1: and flows towards Shapley. Each time astronomers step back and
• 1:41:47
  Speaker 1: look at a larger volume, the structure does not end.
• 1:41:51
  Speaker 1: It continues. New walls, new clusters, new basins of attraction
• 1:41:57
  Speaker 1: keep appearing at the edges of whatever map was just completed.
• 1:42:02
  Speaker 1: This is not a coincidence. It is what the physics predicts.
• 1:42:06
  Speaker 1: Gravity has been operating on matter for 13 billion years,
• 1:42:11
  Speaker 1: pulling density enhancements into galaxy clusters. pulling clusters toward each
• 1:42:17
  Speaker 1: other along filaments, pulling superclusters into still larger flows. There
• 1:42:23
  Speaker 1: is no obvious scale at which this process terminates. The
• 1:42:28
  Speaker 1: cosmic web extends across the entire observable universe, 93 billion
• 1:42:34
  Speaker 1: light years in diameter, and on that scale, the largest
• 1:42:38
  Speaker 1: structures observable are only a small fraction of the whole. Laniakea,
• 1:42:45
  Speaker 1: at 520 million light years is enormous by human standards
• 1:42:50
  Speaker 1: and unremarkable by universal ones. What lies beyond Laniakea, then,
• 1:42:56
  Speaker 1: is not emptiness. It is more structure, more flow, more
• 1:43:01
  Speaker 1: mass concentrations pulling on each other across distances that make
• 1:43:06
  Speaker 1: Laniakea itself look modest. The South Pole wall wraps around it.
• 1:43:12
  Speaker 1: Shapley pulls on it from one direction, Perseus Pisces anchors
• 1:43:17
  Speaker 1: a different gravitational basin nearby. The Cosmic Flows 4 catalog
• 1:43:22
  Speaker 1: has already pushed the frontier outward, and the catalogs that
• 1:43:26
  Speaker 1: follow will push it further still. Every boundary we draw
• 1:43:30
  Speaker 1: around our cosmic home turns out to have something larger
• 1:43:34
  Speaker 1: just outside it. From far enough out, the universe looks
• 1:43:39
  Speaker 1: like a net. Not a metaphor. Not a poetic approximation.
• 1:43:46
  Speaker 1: When astronomers map the distribution of galaxies across hundreds of
• 1:43:50
  Speaker 1: millions of light years, the actual image that comes back
• 1:43:54
  Speaker 1: looks like a three-dimensional mesh. Bright filaments running between dense nodes,
• 1:44:01
  Speaker 1: with vast dark holes where almost nothing lives. Superclusters sit
• 1:44:07
  Speaker 1: at the intersections. Filaments run between them. And the space
• 1:44:12
  Speaker 1: in between, most of the volume of the universe, is
• 1:44:16
  Speaker 1: nearly empty. This is the cosmic web, and Laniakea is
• 1:44:22
  Speaker 1: one small piece of it. The scale of the observable
• 1:44:26
  Speaker 1: universe is roughly 93 billion light years across. Laniakea spans
• 1:44:32
  Speaker 1: about 520 million light years. Do the math. Our entire supercluster,
• 1:44:40
  Speaker 1: with its 100,000 galaxies and mass equivalent to 100 quadrillion
• 1:44:46
  Speaker 1: occupies less than 1% of the observable universe's diameter. Drop
• 1:44:52
  Speaker 1: it into the full cosmic map and it becomes difficult
• 1:44:55
  Speaker 1: to find. The web extends in every direction, repeating its
• 1:45:00
  Speaker 1: pattern of filaments and voids and dense nodes, all the
• 1:45:04
  Speaker 1: way to the edge of what we can see. Laniakea
• 1:45:08
  Speaker 1: is one node in that pattern. Nothing about its location
• 1:45:13
  Speaker 1: is obviously special, Nothing marks it as unusual among the
• 1:45:17
  Speaker 1: thousands of similar structures scattered across the cosmic map. The
• 1:45:22
  Speaker 1: voids are the part that most people don't expect. When
• 1:45:27
  Speaker 1: you picture the universe packed with galaxies, you are picturing
• 1:45:31
  Speaker 1: the bright parts, the filaments and clusters. But the voids,
• 1:45:36
  Speaker 1: those enormous dark regions between the filaments, are not exceptions
• 1:45:41
  Speaker 1: to the rule. They are the rule. The voids dominate.
• 1:45:47
  Speaker 1: A single void can stretch 100 to 300 million light
• 1:45:51
  Speaker 1: years across. Some of the largest, the supervoids, are even bigger.
• 1:45:57
  Speaker 1: The density inside them is less than a tenth of
• 1:46:00
  Speaker 1: the average density of the universe. Galaxy after galaxy, cluster
• 1:46:06
  Speaker 1: after cluster, essentially nothing for hundreds of millions of light
• 1:46:11
  Speaker 1: years in any direction. The universe, by volume, is mostly darkness.
• 1:46:18
  Speaker 1: The bright web we trace is a thin skeleton stretched
• 1:46:21
  Speaker 1: across an enormous emptiness. What makes this structure strange is
• 1:46:27
  Speaker 1: that it was predictable. Scientists did not discover the cosmic
• 1:46:31
  Speaker 1: web by looking at the sky and then scrambling to
• 1:46:34
  Speaker 1: explain what they saw. They predicted it first, from the
• 1:46:39
  Speaker 1: mathematics of gravity and the initial conditions of the early universe,
• 1:46:44
  Speaker 1: and then confirmed it through observation. The Millennium Simulation, run
• 1:46:50
  Speaker 1: in 2005 by a team including Volker Springl and hundreds
• 1:46:55
  Speaker 1: of collaborators, started with conditions matching the early universe and
• 1:47:00
  Speaker 1: ran gravity forward across 13 billion years of simulated time.
• 1:47:06
  Speaker 1: The result was a filamentary web of structure that matched
• 1:47:10
  Speaker 1: the observed distribution of galaxies with uncomfortable precision. Uncomfortable because
• 1:47:17
  Speaker 1: nothing about the early universe looked like it was headed
• 1:47:21
  Speaker 1: toward this. The early universe was almost perfectly smooth. Almost.
• 1:47:27
  Speaker 1: Not quite. The temperature variations in the cosmic microwave background
• 1:47:32
  Speaker 1: are tiny. One part in a hundred thousand. But they
• 1:47:36
  Speaker 1: were there, baked into the universe by quantum fluctuations in
• 1:47:40
  Speaker 1: the first fraction of a second after the Big Bang.
• 1:47:44
  Speaker 1: Inflation stretched those quantum variations to macroscopic scales. Gravity did
• 1:47:51
  Speaker 1: the rest. Regions that were slightly denser than average pulled
• 1:47:55
  Speaker 1: in more matter. Regions that were slightly less dense lost
• 1:48:00
  Speaker 1: matter to their neighbors. Over hundreds of millions of years,
• 1:48:05
  Speaker 1: the slight variations grew. Dense regions became filaments. The densest
• 1:48:11
  Speaker 1: intersections of filaments became clusters and superclusters. The under-dense regions
• 1:48:17
  Speaker 1: became voids. The same process, operating on the same initial conditions,
• 1:48:23
  Speaker 1: produces the same web pattern every time you run the simulation.
• 1:48:27
  Speaker 1: The cosmic web is not accidental. It is the inevitable
• 1:48:32
  Speaker 1: output of simple physics applied to a nearly uniform starting state.
• 1:48:37
  Speaker 1: The Illustrious simulation, and its successor, Illustrious TNG, pushed this further.
• 1:48:45
  Speaker 1: These models incorporated not just gravity, but gas dynamics, star formation,
• 1:48:51
  Speaker 1: black hole feedback, and the influence of dark energy. The
• 1:48:56
  Speaker 1: resulting simulated universes looked, at large scales, almost indistinguishable from
• 1:49:02
  Speaker 1: what we observe. Filaments in the right places, voids of
• 1:49:07
  Speaker 1: roughly the right size, clusters of roughly the right mass.
• 1:49:13
  Speaker 1: The match is not perfect. There are still open questions
• 1:49:17
  Speaker 1: about the precise distribution of matter on small scales. But
• 1:49:22
  Speaker 1: the broad architecture of the cosmic web has been reproduced
• 1:49:26
  Speaker 1: repeatedly from first principles. This is one of the more
• 1:49:30
  Speaker 1: remarkable facts in all of modern cosmology. The largest structures
• 1:49:35
  Speaker 1: we can observe were written into the universe before the
• 1:49:39
  Speaker 1: first star ever formed. Laniakea sits in this web the
• 1:49:44
  Speaker 1: way any other supercluster does. It is a gravitational basin,
• 1:49:50
  Speaker 1: a node where filaments converge and matter has pooled over
• 1:49:54
  Speaker 1: billions of years. On the full cosmic map, at the
• 1:49:58
  Speaker 1: scale where Laniakea becomes a recognizable object, dozens of similar
• 1:50:03
  Speaker 1: structures are visible in every direction. the Shapley supercluster, the
• 1:50:09
  Speaker 1: Perseus-Pisces chain, the Hercules supercluster, each one a basin like Laniakea,
• 1:50:16
  Speaker 1: each one pulling its local collection of galaxies inward, each
• 1:50:20
  Speaker 1: one connected to its neighbors by filaments and separated by voids.
• 1:50:26
  Speaker 1: The cosmic web at this scale looks almost biological, dense
• 1:50:30
  Speaker 1: nodes connected by thin bright threads, vast dark cavities in between.
• 1:50:38
  Speaker 1: If you have ever seen an image of neurons under
• 1:50:40
  Speaker 1: a microscope, or a leaf's vein structure, or the foam
• 1:50:44
  Speaker 1: that forms when soap bubbles crowd together, those images all
• 1:50:49
  Speaker 1: resemble the cosmic web for the same mathematical reason that
• 1:50:54
  Speaker 1: different physical systems, driven by similar branching processes, tend to
• 1:51:00
  Speaker 1: produce similar geometric patterns. There is nothing cosmologically remarkable about
• 1:51:05
  Speaker 1: Laniakea's position in this web. It is not at the
• 1:51:09
  Speaker 1: center of anything. It is not the most massive node
• 1:51:13
  Speaker 1: within reach. It is one of many similar structures spread
• 1:51:17
  Speaker 1: across a universe that extends unimaginably far beyond what any
• 1:51:22
  Speaker 1: current telescope can probe. The only thing that makes Laniakea
• 1:51:27
  Speaker 1: unusual is our location inside it. Because we are here,
• 1:51:32
  Speaker 1: We can study it in detail that is impossible for
• 1:51:35
  Speaker 1: any other supercluster. We know its shape, its mass, its
• 1:51:40
  Speaker 1: internal flows, the positions of its major clusters, the behavior
• 1:51:45
  Speaker 1: of its filaments. We have mapped it at a resolution
• 1:51:49
  Speaker 1: no other supercluster will achieve in any telescope that currently exists.
• 1:51:55
  Speaker 1: That is the advantage of being inside something. rather than
• 1:52:00
  Speaker 1: looking at it from across the universe. Laniakea is one
• 1:52:04
  Speaker 1: knot in that net, not special in any obvious cosmological sense,
• 1:52:10
  Speaker 1: but the knot we happen to be able to examine
• 1:52:13
  Speaker 1: from the inside. One of the earliest clues that something
• 1:52:17
  Speaker 1: was pulling our region of the universe came not from
• 1:52:21
  Speaker 1: counting galaxies, but from measuring temperature. In the 1970s When
• 1:52:27
  Speaker 1: physicists first mapped the cosmic microwave background in fine detail,
• 1:52:33
  Speaker 1: they expected to find something close to uniform. The CMB
• 1:52:38
  Speaker 1: is the afterglow of the Big Bang. Light released roughly 380,000
• 1:52:44
  Speaker 1: years after the universe began. Now cool to just a
• 1:52:49
  Speaker 1: few degrees above absolute zero, arriving at our detectors from
• 1:52:54
  Speaker 1: every direction in the sky. If the universe were perfectly smooth,
• 1:53:00
  Speaker 1: and we were sitting still relative to that background, the
• 1:53:04
  Speaker 1: temperature would be essentially the same in every direction. It
• 1:53:08
  Speaker 1: is not. One side of the sky runs slightly warmer,
• 1:53:12
  Speaker 1: the opposite side runs slightly cooler. The difference is tiny,
• 1:53:18
  Speaker 1: on the order of a thousandth of a degree, but
• 1:53:21
  Speaker 1: it is real, clean, and impossible to ignore. That asymmetry
• 1:53:26
  Speaker 1: is called the CMB dipole, and what it tells you
• 1:53:30
  Speaker 1: is motion. When you move toward a source of light,
• 1:53:33
  Speaker 1: the waves compress slightly and shift toward higher energy, higher temperature,
• 1:53:39
  Speaker 1: move away, and they stretch, cooling down. The dipole in
• 1:53:44
  Speaker 1: the CMB is a Doppler signature. Our entire region of
• 1:53:49
  Speaker 1: the universe is moving, moving fast, roughly 600 kilometers per second,
• 1:53:55
  Speaker 1: relative to the background radiation that fills all of space.
• 1:53:59
  Speaker 1: That number raised an immediate question. 600 kilometers per second
• 1:54:04
  Speaker 1: is not slow. It is not something you can attribute
• 1:54:08
  Speaker 1: to the gravity of a nearby galaxy cluster or even
• 1:54:11
  Speaker 1: a modest supercluster. Something with enormous gravitational pull had to
• 1:54:17
  Speaker 1: be responsible. And when astronomers try to account for all
• 1:54:21
  Speaker 1: the known mass in the local universe, all the visible
• 1:54:25
  Speaker 1: galaxy clusters within a few hundred million light years, they
• 1:54:30
  Speaker 1: could not explain it. The pull of known structures was
• 1:54:34
  Speaker 1: not enough. There was a missing source. That gap was
• 1:54:39
  Speaker 1: one of the first signs pointing toward what would eventually
• 1:54:43
  Speaker 1: be called the Greater Tractor, the gravitational engine sitting near
• 1:54:49
  Speaker 1: the center of Laniakea. Pulling our local group and thousands
• 1:54:54
  Speaker 1: of other galaxies toward a common point hundreds of millions
• 1:54:58
  Speaker 1: of light years away. What made this early evidence particularly
• 1:55:02
  Speaker 1: strange was that the bulk flow was not just ours.
• 1:55:07
  Speaker 1: Individual galaxies nearby were showing anomalous velocities in the same
• 1:55:12
  Speaker 1: general direction. Galaxy clusters across a wide region of space
• 1:55:17
  Speaker 1: were all drifting toward the same part of the sky.
• 1:55:21
  Speaker 1: faster than the cosmic expansion alone could explain. This is
• 1:55:26
  Speaker 1: what peculiar velocities look like in practice, not random noise
• 1:55:31
  Speaker 1: scattered in all directions, but a coherent drift, a tide,
• 1:55:37
  Speaker 1: millions of galaxies all leaning the same way. The CMB
• 1:55:42
  Speaker 1: dipole was the loudest signal, but the galaxy velocities were
• 1:55:47
  Speaker 1: the confirmation that the effect was real and widespread. The
• 1:55:52
  Speaker 1: problem with early peculiar velocity data was that it depended
• 1:55:56
  Speaker 1: entirely on galaxy distance measurements. That carry their own uncertainties.
• 1:56:02
  Speaker 1: If your distances are slightly wrong, your inferred velocities are wrong.
• 1:56:08
  Speaker 1: A pattern that looks coherent might dissolve under better measurements.
• 1:56:13
  Speaker 1: Astronomers needed a way to check the velocity field independently.
• 1:56:18
  Speaker 1: using a completely different physical process. That check eventually arrived
• 1:56:23
  Speaker 1: in the form of a phenomenon called the Kinetic Sunyaev-Zeldovich Effect.
• 1:56:28
  Speaker 1: Here is the basic picture. Galaxy clusters contain enormous clouds
• 1:56:33
  Speaker 1: of hot gas plasma at tens of millions of degrees
• 1:56:38
  Speaker 1: threaded through the space between individual galaxies. When CMB photons
• 1:56:44
  Speaker 1: travel through this hot gas they interact with the fast
• 1:56:47
  Speaker 1: moving electrons. If the cluster itself is moving relative to
• 1:56:52
  Speaker 1: the CMB rest frame, this interaction leaves a subtle imprint
• 1:56:56
  Speaker 1: on those photons. Moving toward us, the cluster slightly boosts
• 1:57:02
  Speaker 1: the energy of passing photons. Moving away, it slightly reduces it.
• 1:57:09
  Speaker 1: The effect is extraordinarily small. Detecting it requires precise microwave
• 1:57:14
  Speaker 1: observations careful subtraction of other signals, and large statistical samples
• 1:57:20
  Speaker 1: of clusters. But it is physically distinct from anything in
• 1:57:25
  Speaker 1: the galaxy distance measurements. No Tully-Fisher relations, no fundamental P,
• 1:57:32
  Speaker 1: lane corrections, no distance ladder. Just microwave photons and hot
• 1:57:38
  Speaker 1: gas and the Doppler shift of a moving cluster, read
• 1:57:42
  Speaker 1: directly from the sky. When researchers began applying kinetic Sunyaev-Zeldovich
• 1:57:47
  Speaker 1: measurements to galaxy clusters across the local universe, the results
• 1:57:51
  Speaker 1: were striking. The clusters showed bulk motion, not random velocities
• 1:57:57
  Speaker 1: pointing in scattered directions, but a coherent flow in roughly
• 1:58:02
  Speaker 1: the direction of the greater tractor, consistent with what the
• 1:58:06
  Speaker 1: peculiar velocity surveys had been showing for decades. This was
• 1:58:12
  Speaker 1: not a marginal overlap. The independent probe, built on entirely
• 1:58:17
  Speaker 1: different physics, pointed toward the same gravitational basin that Tully's
• 1:58:22
  Speaker 1: watershed analysis had defined using galaxy flows. What this convergence
• 1:58:28
  Speaker 1: means is important. A recurring concern whenever a large-scale structure
• 1:58:34
  Speaker 1: gets mapped from peculiar velocities is that the result might
• 1:58:38
  Speaker 1: be an artifact, a product of which galaxies happen to
• 1:58:42
  Speaker 1: be measured. That surveys covered which parts of the sky,
• 1:58:47
  Speaker 1: which distance methods were applied. Laniakea was defined using a
• 1:58:52
  Speaker 1: specific catalog of roughly 8,000 galaxies. That is a finite
• 1:58:58
  Speaker 1: sample with finite coverage. If the pattern were statistical noise,
• 1:59:04
  Speaker 1: independent probes using different physics on different objects should produce
• 1:59:09
  Speaker 1: a different picture. They do not. The CMB dipole, the
• 1:59:15
  Speaker 1: bulk flow studies of the 1980s and 1990s, the kinetic
• 1:59:20
  Speaker 1: Sunyaev-Zeldovich measurements from large microwave surveys, all describe the same
• 1:59:27
  Speaker 1: motion across the same enormous volume of space. Multiple independent
• 1:59:32
  Speaker 1: methods of measuring motion at cosmic scales now point toward
• 1:59:37
  Speaker 1: the same picture, a coherent flow of galaxies across hundreds
• 1:59:42
  Speaker 1: of millions of light years, converging on the same gravitational basin.
• 1:59:48
  Speaker 1: We do not live near the heart of Laniakea. The
• 1:59:52
  Speaker 1: Milky Way sits out near the edge, somewhere on the
• 1:59:56
  Speaker 1: outer rim of a structure 520 million light years across,
• 2:00:01
  Speaker 1: pulled slowly but measurably toward the gravitational center. Slowly is
• 2:00:07
  Speaker 1: the key word. The distance between us and the greater
• 2:00:12
  Speaker 1: tractor is somewhere between 150 and 250 million light years.
• 2:00:16
  Speaker 1: At our current infall velocity, Reaching it would take far
• 2:00:23
  Speaker 1: longer than the current age of the universe, and dark
• 2:00:27
  Speaker 1: energy will almost certainly intervene before any arrival is possible.
• 2:00:32
  Speaker 1: So we are falling inward, technically, but we are never
• 2:00:36
  Speaker 1: going to get there. We are permanent residents of the outskirts.
• 2:00:41
  Speaker 1: What would it look like to live somewhere else? Imagine
• 2:00:46
  Speaker 1: the Milky Way had formed closer to the dense core
• 2:00:49
  Speaker 1: of Laniakea, near one of the major clusters at the
• 2:00:52
  Speaker 1: heart of the structure. The sky would look different in
• 2:00:57
  Speaker 1: ways that are hard to fully picture. Galaxy density near
• 2:01:01
  Speaker 1: the center is dramatically higher. Neighboring galaxies would be closer.
• 2:01:08
  Speaker 1: Interactions and mergers between galaxies happen far more frequently in
• 2:01:13
  Speaker 1: dense environments, and those collisions drive bursts of star formation,
• 2:01:18
  Speaker 1: reshape spiral arms, heat the surrounding gas, and feed supermassive
• 2:01:23
  Speaker 1: black holes into periods of intense activity. A galaxy in
• 2:01:28
  Speaker 1: that environment would be a different kind of place. Noisier.
• 2:01:33
  Speaker 1: More active. More frequently disrupted. The quiet spiral structure of
• 2:01:39
  Speaker 1: the Milky Way, which has remained relatively undisturbed for billions
• 2:01:43
  Speaker 1: of years, is partly a product of where we ended up.
• 2:01:47
  Speaker 1: The outskirts are calm. Out here, the galaxy density drops.
• 2:01:53
  Speaker 1: In some directions, the voids open up, regions tens of
• 2:01:58
  Speaker 1: millions or hundreds of millions of light years across, where
• 2:02:02
  Speaker 1: almost nothing lives. These are not empty in an absolute sense,
• 2:02:07
  Speaker 1: but the density of matter is less than a tenth
• 2:02:10
  Speaker 1: of the universe's average, and galaxies in voids are rare
• 2:02:14
  Speaker 1: and isolated things. We have voids opening up around us
• 2:02:19
  Speaker 1: in certain directions right now. The local group is not
• 2:02:23
  Speaker 1: completely alone, but it is a small association of galaxies
• 2:02:28
  Speaker 1: in a relatively sparse region, far from the nearest major cluster.
• 2:02:34
  Speaker 1: That is just the reality of living on the periphery
• 2:02:37
  Speaker 1: of a supercluster. The closest large cluster to us, the
• 2:02:42
  Speaker 1: Virgo Cluster, is still 50 to 60 million light years away.
• 2:02:48
  Speaker 1: In cosmic terms, that is a neighbor. In any other terms,
• 2:02:54
  Speaker 1: it is an almost meaningless distance. There is something worth
• 2:02:58
  Speaker 1: sitting with here. The fact that we ended up in
• 2:03:01
  Speaker 1: this particular location, on the quiet edge rather than the
• 2:03:05
  Speaker 1: turbulent core, is not a coincidence in the way luck
• 2:03:10
  Speaker 1: is a coincidence. It is the outcome of processes that
• 2:03:14
  Speaker 1: were set in motion almost 14 billion years ago. And
• 2:03:19
  Speaker 1: this is where the story gets genuinely strange. The structure
• 2:03:24
  Speaker 1: of Laniakea, the reason the greater tractor exists where it does,
• 2:03:29
  Speaker 1: the reason the Milky Way formed in the specific region
• 2:03:33
  Speaker 1: of space it occupies, all of it traces back to
• 2:03:36
  Speaker 1: conditions in the first fractions of a second after the
• 2:03:40
  Speaker 1: Big Bang. The early universe was almost perfectly uniform. Almost.
• 2:03:47
  Speaker 1: There were tiny fluctuations in density, variations so small that
• 2:03:52
  Speaker 1: the temperature difference they created in the cosmic microwave background
• 2:03:57
  Speaker 1: is measured in hundred thousandths of a degree. These fluctuations
• 2:04:02
  Speaker 1: were not random in the classical sense. They were quantum mechanical.
• 2:04:07
  Speaker 1: At the smallest scales imaginable, Quantum uncertainty produces unavoidable variations
• 2:04:14
  Speaker 1: in energy density. In the very early universe, during the
• 2:04:19
  Speaker 1: period cosmologists call inflation, space expanded so violently and so
• 2:04:25
  Speaker 1: fast that those microscopic quantum fluctuations were stretched to cosmic scales.
• 2:04:32
  Speaker 1: A variation that existed across a distance smaller than a
• 2:04:35
  Speaker 1: proton became, after inflation, a variation spread across what would
• 2:04:41
  Speaker 1: eventually be millions of light years. T, he universe locked
• 2:04:46
  Speaker 1: those fluctuations in as it expanded. Gravity did the rest.
• 2:04:51
  Speaker 1: Over billions of years, regions that were even slightly denser
• 2:04:55
  Speaker 1: than average pulled in surrounding matter. The denser they got,
• 2:05:00
  Speaker 1: the more they pulled. The emptier regions got emptier as
• 2:05:05
  Speaker 1: matter drained away toward the denser ones. What started as
• 2:05:09
  Speaker 1: a near-uniform gas of hydrogen and helium slowly organized itself
• 2:05:15
  Speaker 1: into the cosmic web, filaments and clusters and voids, over
• 2:05:19
  Speaker 1: time scales measured in billions of years. The greater tractor,
• 2:05:25
  Speaker 1: the dense concentration of mass at the heart of Laniakea,
• 2:05:29
  Speaker 1: formed because gravity amplified a slight overdensity that had its
• 2:05:34
  Speaker 1: origin in a quantum event that happened before a single
• 2:05:38
  Speaker 1: atom existed, that is not a small claim. The reason
• 2:05:43
  Speaker 1: the Milky Way is where it is, the reason we
• 2:05:46
  Speaker 1: are on the outskirts of this particular structure rather than
• 2:05:50
  Speaker 1: somewhere else, traces back to a quantum fluctuation that was
• 2:05:55
  Speaker 1: inflated to cosmic scales before the Universe was a second old.
• 2:06:01
  Speaker 1: There was no inevitability to the specific location. If the
• 2:06:06
  Speaker 1: fluctuations had been arranged slightly differently, the large-scale structure would
• 2:06:11
  Speaker 1: have assembled differently. The greater tractor would be somewhere else.
• 2:06:17
  Speaker 1: The Milky Way would be somewhere else. The whole map
• 2:06:22
  Speaker 1: changes with tiny differences in those initial conditions. We are
• 2:06:27
  Speaker 1: here because of randomness that occurred at the very bottom
• 2:06:31
  Speaker 1: of physical reality. and was then enlarged to a scale
• 2:06:35
  Speaker 1: of hundreds of millions of light years. This is not
• 2:06:39
  Speaker 1: philosophy drifting away from the science. It is the science.
• 2:06:44
  Speaker 1: Cosmologists can take the measured fluctuations in the cosmic microwave background,
• 2:06:50
  Speaker 1: run them forward through simulations using known physics, and reproduce
• 2:06:55
  Speaker 1: structures that look like the cosmic web we actually observe.
• 2:06:59
  Speaker 1: The simulations produce filaments, voids, clusters and superclusters in roughly
• 2:07:06
  Speaker 1: the right proportions and at roughly the right scales. The
• 2:07:11
  Speaker 1: structure is predictable. The specific arrangement is not. The quantum
• 2:07:17
  Speaker 1: randomness of the earliest moments of the universe, amplified by
• 2:07:22
  Speaker 1: gravity over 13 billion years, is what put us where
• 2:07:26
  Speaker 1: we are, on the quiet edge of an immense heaven.
• 2:07:32
  Speaker 1: If you wanted to write out where you live in
• 2:07:34
  Speaker 1: the most complete way possible, the address would be longer
• 2:07:38
  Speaker 1: than most people expect. Start with the obvious part. Earth.
• 2:07:44
  Speaker 1: A rocky planet about 8,000 miles across, orbiting an average
• 2:07:49
  Speaker 1: star roughly 93 million miles away. That star is the Sun,
• 2:07:55
  Speaker 1: and the Sun sits inside a solar system that stretches
• 2:07:59
  Speaker 1: roughly four to five light hours out to Neptune, and
• 2:08:03
  Speaker 1: considerably further if you count the loose halo of comets
• 2:08:07
  Speaker 1: at its outer edge. That whole region, every planet, every moon,
• 2:08:14
  Speaker 1: every chunk of rock and ice that gravitationally belongs to
• 2:08:18
  Speaker 1: our star, fits inside a bubble perhaps two light years
• 2:08:22
  Speaker 1: across at its most generous estimate. That is your street address.
• 2:08:29
  Speaker 1: A two light year bubble in a cosmos 93 billion
• 2:08:33
  Speaker 1: light years wide. Step outward. The Sun is one of
• 2:08:38
  Speaker 1: somewhere between 200 and 400 billion stars in the Milky
• 2:08:42
  Speaker 1: Way galaxy. The Milky Way is a barred spiral, a
• 2:08:47
  Speaker 1: flat rotating disc, about 100,000 light years across and roughly 1,000
• 2:08:54
  Speaker 1: light years thick through much of its disk. The Sun
• 2:08:58
  Speaker 1: sits about 26,000 light years from the galactic centre, out
• 2:09:03
  Speaker 1: in one of the spiral arms, in a fairly quiet
• 2:09:07
  Speaker 1: and unremarkable neighbourhood. The solar system is so small compared
• 2:09:13
  Speaker 1: to the Milky Way that if you shrunk the galaxy
• 2:09:16
  Speaker 1: to the size of North America, the entire solar system
• 2:09:20
  Speaker 1: would be smaller than a dime. The Milky Way is
• 2:09:25
  Speaker 1: your city, and it is already almost incomprehensibly large. But
• 2:09:30
  Speaker 1: the Milky Way is not alone. It belongs to a
• 2:09:34
  Speaker 1: collection of galaxies called the Local Group, a gravitationally bound
• 2:09:39
  Speaker 1: cluster of roughly 80 known galaxies spread across approximately 10
• 2:09:44
  Speaker 1: million light years. Most of these 80 galaxies are small.
• 2:09:50
  Speaker 1: The dominant members are the Milky Way and Andromeda, two
• 2:09:55
  Speaker 1: large spirals falling toward each other at several hundred kilometers
• 2:09:59
  Speaker 1: per second, expected to collide in about 4 billion years.
• 2:10:05
  Speaker 1: The local group is your region, your county, if you're
• 2:10:09
  Speaker 1: keeping the metaphor running. 10 million light years is 100
• 2:10:14
  Speaker 1: times the width of the Milky Way. Hold that ratio
• 2:10:18
  Speaker 1: in your head, because it is about to repeat itself.
• 2:10:23
  Speaker 1: The Local Group is one small cluster among many in
• 2:10:27
  Speaker 1: the Virgo Supercluster. This structure, which astronomers had considered our
• 2:10:33
  Speaker 1: home supercluster for decades before 2014, stretches roughly 100 million
• 2:10:36
  Speaker 1: light-years across. It contains something on the order of 100
• 2:10:45
  Speaker 1: galaxy groups and clusters. The Virgo cluster itself, a dense
• 2:10:51
  Speaker 1: concentration of several thousand galaxies sitting roughly 50 to 60
• 2:10:57
  Speaker 1: million light years from the Milky Way, anchors the structure.
• 2:11:02
  Speaker 1: The Virgo supercluster is 10 times wider than the local group.
• 2:11:08
  Speaker 1: Each step outward in this address multiplies the scale by
• 2:11:12
  Speaker 1: a factor that should feel staggering, but somehow keeps arriving
• 2:11:16
  Speaker 1: as a routine number in the equations. This is part
• 2:11:20
  Speaker 1: of what makes cosmic scales genuinely difficult. The jumps are
• 2:11:25
  Speaker 1: not gradual. They are sudden and enormous. And then there
• 2:11:30
  Speaker 1: is Laniakea. The Virgo supercluster, it turns out, is not
• 2:11:35
  Speaker 1: a standalone structure. It is one subdivision, one lobe, of Laniakea,
• 2:11:42
  Speaker 1: the supercluster defined in 2014 by tracing the gravitational flow
• 2:11:47
  Speaker 1: of galaxies rather than just their density. Laniakea stretches 520
• 2:11:54
  Speaker 1: million light years across. It contains roughly 100,000 large galaxies.
• 2:12:01
  Speaker 1: Its total mass is something in the neighborhood of 10.
• 2:12:05
  Speaker 1: to the power of 17 solar masses, which is a
• 2:12:09
  Speaker 1: hundred quadrillion suns, a number that stops being a number
• 2:12:14
  Speaker 1: and becomes a symbol. The Virgo supercluster, which felt enormous
• 2:12:19
  Speaker 1: when it was considered the top of the hierarchy, is
• 2:12:22
  Speaker 1: approximately one fifth the width of Laniakea. What we called
• 2:12:28
  Speaker 1: the largest structure we belonged to was a suburb, a
• 2:12:32
  Speaker 1: small neighborhood in something vastly larger that nobody had successfully
• 2:12:38
  Speaker 1: outlined until fairly recently. Beyond Laniakea, the address continues. The
• 2:12:45
  Speaker 1: Great Attractor at Laniakea's centre is itself moving toward the
• 2:12:49
  Speaker 1: Shapley Supercluster, several hundred million light-years further out. Laniakea is
• 2:12:55
  Speaker 1: likely part of the Pisces-Cetus Supercluster Complex, a structure so
• 2:13:01
  Speaker 1: large it dwarfs even Laniakea. The south pole wall wraps
• 2:13:06
  Speaker 1: around Laniakea's edge like an arm. These structures together form
• 2:13:11
  Speaker 1: part of the cosmic web, the large scale architecture of
• 2:13:16
  Speaker 1: the observable universe. Filaments of galaxies hundreds of millions of
• 2:13:21
  Speaker 1: light years long, connecting nodes like Laniakea, surrounding voids up
• 2:13:27
  Speaker 1: to 300 million light years across, where almost nothing lives.
• 2:13:33
  Speaker 1: The full observable universe spans roughly 93 billion light years. Laniakea,
• 2:13:42
  Speaker 1: at 520 million light years, represents less than 1% of
• 2:13:47
  Speaker 1: that diameter. The challenge of communicating all of this is real.
• 2:13:52
  Speaker 1: The human mind handles a few orders of magnitude comfortably.
• 2:13:56
  Speaker 1: It can picture a city being larger than a neighborhood,
• 2:13:59
  Speaker 1: a country being larger than a city. But the jump
• 2:14:03
  Speaker 1: from the solar system to the Milky Way is a
• 2:14:06
  Speaker 1: factor of roughly a billion in linear scale. The jump
• 2:14:11
  Speaker 1: from there to Laniakea is another factor of 5 million.
• 2:14:16
  Speaker 1: These are not differences in degree, they are differences that
• 2:14:20
  Speaker 1: exhaust the imagination. It is the same problem physicists face
• 2:14:26
  Speaker 1: when trying to hold atoms and solar systems in the
• 2:14:30
  Speaker 1: same mental picture simultaneously. The scale range is simply too
• 2:14:35
  Speaker 1: large for intuition to carry without breaking. What astronomers mean
• 2:14:41
  Speaker 1: when they talk about a cosmic address is something genuinely
• 2:14:45
  Speaker 1: new in human history. For most of our existence as
• 2:14:48
  Speaker 1: a species, the question of where exactly we sat in
• 2:14:52
  Speaker 1: the universe had no real answer. The sky was overhead.
• 2:14:58
  Speaker 1: Beyond that, The answers were stories. Even 100 years ago,
• 2:15:04
  Speaker 1: astronomers were still debating whether the Milky Way was the
• 2:15:07
  Speaker 1: entire universe or just one of many island galaxies. The
• 2:15:13
  Speaker 1: idea that those galaxies organized into groups, clusters, and superclusters
• 2:15:19
  Speaker 1: came later. The idea that those superclusters were themselves components
• 2:15:25
  Speaker 1: of even larger basins of gravitational came later still in
• 2:15:31
  Speaker 1: 2014 in a paper in Nature. Each generation has extended
• 2:15:36
  Speaker 1: the address by one more line. This is not trivia.
• 2:15:42
  Speaker 1: It is the most complete answer to the question of
• 2:15:44
  Speaker 1: where we are that any human civilization has ever been
• 2:15:48
  Speaker 1: able to give. Dark energy is the reason Laniakea will
• 2:15:52
  Speaker 1: not survive. That sentence sounds dramatic, but it is just physics.
• 2:15:59
  Speaker 1: To understand what it means, you have to understand what
• 2:16:02
  Speaker 1: dark energy actually is. And the honest answer is that
• 2:16:06
  Speaker 1: nobody fully does. What astronomers know is this. Dark energy
• 2:16:13
  Speaker 1: is the dominant energy component of the universe, accounting for
• 2:16:17
  Speaker 1: roughly 68% of everything. It does not clump. It does
• 2:16:22
  Speaker 1: not interact with light or matter in any detectable way.
• 2:16:27
  Speaker 1: It is invisible. massless and spread perfectly uniformly across all
• 2:16:32
  Speaker 1: of space. The only thing it appears to do is
• 2:16:36
  Speaker 1: cause space itself to expand, and it does this with
• 2:16:40
  Speaker 1: a persistence that nothing in the universe can overcome at
• 2:16:44
  Speaker 1: large enough scales. For most of the 20th century, physicists
• 2:16:48
  Speaker 1: assumed the expansion of the universe was slowing down. This
• 2:16:53
  Speaker 1: made intuitive sense. The Big Bang flung matter outward gravity
• 2:16:58
  Speaker 1: pulls matter together. Over time, gravity should gradually win, decelerating
• 2:17:04
  Speaker 1: the expansion the way a ball thrown upward gradually loses speed.
• 2:17:11
  Speaker 1: The only real question was whether gravity would win completely,
• 2:17:16
  Speaker 1: stopping the expansion and reversing it into an eventual collapse,
• 2:17:21
  Speaker 1: or whether the universe would expand forever at a diminishing rate.
• 2:17:26
  Speaker 1: Both options assumed the same direction, expansion slowing over time. Then,
• 2:17:33
  Speaker 1: in 1998, two independent teams of astronomers studying distant Type
• 2:17:39
  Speaker 1: Ia supernovae published results that were almost impossible to believe.
• 2:17:46
  Speaker 1: The supernovae were fainter than they should have been. They
• 2:17:49
  Speaker 1: were farther away than the models predicted. The expansion was
• 2:17:54
  Speaker 1: not slowing down. It was speeding up. Space was not
• 2:17:59
  Speaker 1: fighting gravity to a standstill. Something was actively pushing it
• 2:18:04
  Speaker 1: apart faster with every passing era. That discovery earned its
• 2:18:09
  Speaker 1: lead researchers the Nobel Prize in Physics in 2011, and
• 2:18:14
  Speaker 1: it rewrote cosmology in a single year. The force responsible
• 2:18:20
  Speaker 1: for this acceleration is what physicists called dark energy, a
• 2:18:25
  Speaker 1: label that carries a lot of honesty in it. The
• 2:18:28
  Speaker 1: word dark here means unknown. It is not dark matter,
• 2:18:33
  Speaker 1: which at least has well understood gravitational effects. dark energy
• 2:18:39
  Speaker 1: is stranger than that. It behaves like a property of
• 2:18:42
  Speaker 1: empty space itself, a baseline energy that the vacuum carries,
• 2:18:48
  Speaker 1: sometimes called the cosmological constant, a term Einstein introduced and
• 2:18:54
  Speaker 1: then famously abandoned and then turned out to be correct
• 2:18:57
  Speaker 1: about after all. As space expands, a new volume of
• 2:19:02
  Speaker 1: empty space is created. The total amount of dark energy
• 2:19:06
  Speaker 1: grows with it. This is why the expansion accelerates over time,
• 2:19:12
  Speaker 1: rather than settling into a constant rate. More space means
• 2:19:16
  Speaker 1: more dark energy, which drives more expansion, which creates more space.
• 2:19:23
  Speaker 1: The feedback loop is slow by human standards, but relentless
• 2:19:26
  Speaker 1: on cosmological timescales. Now here is where Laniakea enters the picture.
• 2:19:33
  Speaker 1: Gravity and dark energy are in a continuous contest. and
• 2:19:37
  Speaker 1: which one wins depends on scale. On small scales, gravity
• 2:19:43
  Speaker 1: wins easily. The atoms in your body are not being
• 2:19:46
  Speaker 1: pulled apart by dark energy. Planets, solar systems, galaxies, even
• 2:19:53
  Speaker 1: galaxy clusters, these are all gravitationally bound. The matter in
• 2:19:59
  Speaker 1: them is locked together tightly enough that the gentle outward
• 2:20:03
  Speaker 1: pressure of dark energy is irrelevant. But as you move
• 2:20:07
  Speaker 1: to larger and larger scales, gravity becomes weaker and dark
• 2:20:12
  Speaker 1: energy becomes more significant. Superclusters occupy exactly the zone where
• 2:20:18
  Speaker 1: this contest becomes interesting. Laniakea is not gravitationally bound. This
• 2:20:25
  Speaker 1: was established when it was first defined in 2014, and
• 2:20:30
  Speaker 1: it is worth sitting with. The structure is real. The
• 2:20:34
  Speaker 1: galaxy flows are real. The inward motion toward the Great
• 2:20:39
  Speaker 1: Attractor is real. The Basin of Attraction exists, but the
• 2:20:43
  Speaker 1: outer regions of Laniakea do not have enough gravitational connection
• 2:20:48
  Speaker 1: to the center to resist the expansion of space indefinitely.
• 2:20:53
  Speaker 1: The Great Attractor exerts a genuine gravitational pull, estimated at
• 2:20:59
  Speaker 1: roughly 10 million billion solar masses of influence. That sounds enormous.
• 2:21:05
  Speaker 1: Against dark energy operating across 500 million light years, it
• 2:21:10
  Speaker 1: is not enough. The outer galaxies of Laniakea are already
• 2:21:15
  Speaker 1: in a kind of slow tug of war. Right now,
• 2:21:19
  Speaker 1: for our epoch of cosmic history, the gravity of the
• 2:21:23
  Speaker 1: greater tractor remains strong enough to draw our local group
• 2:21:28
  Speaker 1: and billions of nearby galaxies toward its basins. This infall
• 2:21:33
  Speaker 1: will continue for billions of years. But the boundary of
• 2:21:38
  Speaker 1: that influence is not fixed. As the Universe expands and
• 2:21:42
  Speaker 1: the distances between outer regions of Laniakea and its gravitational
• 2:21:47
  Speaker 1: centre grow, the gravitational force between them weakens. Dark energy's
• 2:21:54
  Speaker 1: push does not weaken with distance the way gravity does.
• 2:21:58
  Speaker 1: So the balance tips. Galaxies near Laniakea's periphery will eventually
• 2:22:04
  Speaker 1: cross a threshold where expansion carries them away faster than
• 2:22:09
  Speaker 1: gravity can draw them back. The filaments at the edges
• 2:22:13
  Speaker 1: will thin. The outer clusters will drift. The structure will
• 2:22:18
  Speaker 1: not collapse or explode. It will simply dissolve, gradually and quietly,
• 2:22:24
  Speaker 1: over timescales that are hard to write down meaningfully. What
• 2:22:30
  Speaker 1: does the far future universe actually look like? Astronomers have
• 2:22:35
  Speaker 1: modelled this and the picture is striking in its emptiness.
• 2:22:39
  Speaker 1: The local group itself, the Milky Way, Andromeda and roughly
• 2:22:44
  Speaker 1: 80 smaller companions, is bound. In several billion years, the
• 2:22:50
  Speaker 1: Milky Way and Andromeda will merge into a single massive galaxy.
• 2:22:56
  Speaker 1: That merged structure will remain gravitationally locked But beyond the
• 2:23:01
  Speaker 1: Local Group, the rest of Laniakea will gradually recede. The
• 2:23:06
  Speaker 1: Virgo Cluster will eventually pass beyond the boundary where gravitational
• 2:23:11
  Speaker 1: connection is possible. The Hydra and Centaurus Clusters, the Norma Cluster,
• 2:23:19
  Speaker 1: the hundreds of groups that today participate in the infall
• 2:23:22
  Speaker 1: toward the Greater Tractor, all of them will drift beyond reach.
• 2:23:27
  Speaker 1: On timescales of hundreds of billions of years, what remains
• 2:23:32
  Speaker 1: will be isolated islands of gravitationally bound matter, separated from
• 2:23:37
  Speaker 1: each other by expanding voids that grow wider with every
• 2:23:41
  Speaker 1: passing eon. The universe will still exist. Stars will still
• 2:23:47
  Speaker 1: burn for a while. But the large-scale structure we can
• 2:23:51
  Speaker 1: see today, the filaments, the clusters, the flowing basins of attraction,
• 2:23:58
  Speaker 1: The shape that Brent Tully's team mapped in 2014, none
• 2:24:03
  Speaker 1: of that will be visible. An observer in that far
• 2:24:07
  Speaker 1: future universe, looking outward from whatever remains of our local group,
• 2:24:12
  Speaker 1: would see nothing but darkness in all directions. No neighbouring
• 2:24:17
  Speaker 1: galaxies close enough to identify. No structure at all. The
• 2:24:23
  Speaker 1: cosmic web will have stretched beyond any possible detection. Whatever
• 2:24:29
  Speaker 1: civilization existed then would have no way of knowing that
• 2:24:33
  Speaker 1: a supercluster had once surrounded them, half a billion light-years
• 2:24:38
  Speaker 1: of galaxies flowing together in a coherent structure with a
• 2:24:42
  Speaker 1: name that meant immense heaven. In the far future, nothing
• 2:24:48
  Speaker 1: observable will remain to show that hundreds of thousands of
• 2:24:52
  Speaker 1: Galar ZEISS once flowed together toward a common center across
• 2:24:56
  Speaker 1: half a billion light years of space. The 2014 paper
• 2:25:00
  Speaker 1: that named Laniakea was not the end of the story.
• 2:25:04
  Speaker 1: It was more like the first reliable map of a
• 2:25:07
  Speaker 1: territory that had previously been described only in rumors. Tully's
• 2:25:12
  Speaker 1: team had used a catalog of roughly 8,100 galaxies with
• 2:25:17
  Speaker 1: measured distances and velocities. That number sounds large. For a
• 2:25:23
  Speaker 1: structure 520 million light years across, it is actually quite
• 2:25:28
  Speaker 1: thin coverage, like trying to map an entire continent from
• 2:25:32
  Speaker 1: a few hundred survey points scattered unevenly across it. The
• 2:25:37
  Speaker 1: researchers knew this. The paper itself acknowledged the gaps. What
• 2:25:43
  Speaker 1: they had produced was a framework, a first outline, and
• 2:25:47
  Speaker 1: the work of filling it in had barely started. Cosmic
• 2:25:51
  Speaker 1: Flows 3 came next. Released in 2016, it pushed the
• 2:25:56
  Speaker 1: galaxy count to around 18,000. More galaxies meant denser sampling,
• 2:26:03
  Speaker 1: which meant the flow patterns could be traced with finer resolution.
• 2:26:07
  Speaker 1: The boundaries of Laniakea didn't collapse under the new data.
• 2:26:11
  Speaker 1: The basic shape held, but the details shifted. Some filaments
• 2:26:17
  Speaker 1: resolved more clearly. Some previously ambiguous regions near the edges
• 2:26:22
  Speaker 1: snapped into focus. The watershed boundaries, which in the original
• 2:26:28
  Speaker 1: paper had been somewhat blurry in certain directions, tightened in
• 2:26:33
  Speaker 1: some places and softened in others. This is how science
• 2:26:38
  Speaker 1: actually works. Not a single revelation, but a slow accumulation
• 2:26:44
  Speaker 1: of better measurements, each one adjusting the picture slightly. The
• 2:26:50
  Speaker 1: 2014 map wasn't wrong. It was coarse. Then Cosmic Flows
• 2:26:56
  Speaker 1: 4 arrived in 2023, and the number jumped to nearly 56,000 galaxies.
• 2:27:04
  Speaker 1: That is roughly seven times the original dataset. Eight different
• 2:27:08
  Speaker 1: distance measurement techniques fed into the catalogue. The Tully-Fisher relation
• 2:27:13
  Speaker 1: for spiral galaxies, the fundamental plane for ellipticals, and several
• 2:27:19
  Speaker 1: others all cross-checked against each other. The result was a
• 2:27:24
  Speaker 1: peculiar velocity map of the local universe with a level
• 2:27:28
  Speaker 1: of detail that would have been unthinkable in 2014. The
• 2:27:31
  Speaker 1: 2023 analysis confirmed Laniakea's overall size and shape. 520 million
• 2:27:42
  Speaker 1: light-years across, roughly 100,000 large galaxies, mass sitting around 10
• 2:27:49
  Speaker 1: to the 17th solar masses. The original outline held But
• 2:27:56
  Speaker 1: the same watershed technique that had defined Laniakea in 2014
• 2:28:01
  Speaker 1: now revealed five neighbouring superclusters in comparable detail. Shapley, Perseus-Pisces, Hercules,
• 2:28:10
  Speaker 1: Lepus and Apus, each one its own basin of gravitational attraction,
• 2:28:16
  Speaker 1: each one adjacent to Laniakea in the larger cosmic web.
• 2:28:21
  Speaker 1: the local universe suddenly had neighbors with names and borders.
• 2:28:25
  Speaker 1: There are debates though. Not everyone agrees that Laniakea's boundaries
• 2:28:30
  Speaker 1: are drawn in exactly the right places. Some researchers argue
• 2:28:35
  Speaker 1: that the edges of the structure are sensitive to which
• 2:28:38
  Speaker 1: galaxies are included in the catalog, and how distances are
• 2:28:42
  Speaker 1: weighted at large radii. The zone of avoidance still creates
• 2:28:47
  Speaker 1: real gaps in the data, Galaxies behind the Milky Way's
• 2:28:51
  Speaker 1: disk are underrepresented in every version of cosmic flows, which
• 2:28:56
  Speaker 1: means the flow maps in those directions are less reliable.
• 2:29:01
  Speaker 1: If significant structures are hidden in those gaps, the boundary
• 2:29:05
  Speaker 1: of Laniakea in that region of sky could shift when
• 2:29:08
  Speaker 1: better data eventually fills the blind spot. These are not
• 2:29:13
  Speaker 1: fatal objections. They are exactly the kind of edge case
• 2:29:17
  Speaker 1: uncertainties you expect at the frontier of a measurement campaign.
• 2:29:23
  Speaker 1: The core of the structure is solid. The edges are
• 2:29:26
  Speaker 1: still being negotiated. What comes next is more data, orders
• 2:29:32
  Speaker 1: of magnitude more. Spectroscopic surveys now underway or in planning
• 2:29:38
  Speaker 1: will measure galaxy redshifts for tens of millions of objects.
• 2:29:43
  Speaker 1: The Dark Energy Spectroscopic Instrument, already operating in Arizona, is
• 2:29:48
  Speaker 1: accumulating galaxy spectra at a rate that would have seemed
• 2:29:52
  Speaker 1: impossible a decade ago. Surveys like these won't just extend
• 2:29:58
  Speaker 1: the cosmic flow's approach, they will transform it. Peculiar velocity
• 2:30:03
  Speaker 1: maps derive from millions of galaxies instead of tens of thousands.
• 2:30:08
  Speaker 1: will resolve structures that currently appear as vague suggestions in
• 2:30:12
  Speaker 1: the data. The flow patterns around Laniakea's edges, where the
• 2:30:18
  Speaker 1: supercluster's influence fades, and the influence of neighboring structures takes over,
• 2:30:24
  Speaker 1: will become far clearer. The extremely large telescope, currently under
• 2:30:29
  Speaker 1: construction in Chile's Atacama Desert, will add something different. Its
• 2:30:35
  Speaker 1: light-gathering power is so far beyond existing instruments that it
• 2:30:39
  Speaker 1: will be able to measure distances and velocities for galaxies
• 2:30:44
  Speaker 1: that are simply too faint for current surveys to handle reliably.
• 2:30:50
  Speaker 1: This reaches further out and fills in the picture at
• 2:30:53
  Speaker 1: larger scales. Weather structures like the South Pole Wall, the
• 2:30:59
  Speaker 1: enormous arc discovered in 2020 just beyond Laniakea, connect to
• 2:31:05
  Speaker 1: Laniakea's flow patterns or belong to entirely separate basins is
• 2:31:11
  Speaker 1: exactly the kind of question that next-generation instruments are positioned
• 2:31:17
  Speaker 1: to answer. The map of our cosmic neighborhood is not finished.
• 2:31:23
  Speaker 1: That might sound like a limitation, but it is also
• 2:31:26
  Speaker 1: the honest state of things, and it means the most
• 2:31:30
  Speaker 1: interesting results may not be the ones already published. Every
• 2:31:34
  Speaker 1: time the catalogue has expanded, something unexpected has appeared at
• 2:31:39
  Speaker 1: the new resolution. More galaxies revealed cleaner filaments. Better coverage
• 2:31:46
  Speaker 1: revealed neighbouring superclusters that the original data could only hint at.
• 2:31:52
  Speaker 1: There is no obvious reason to expect that pattern to stop.
• 2:31:57
  Speaker 1: The outline that Tully's team drew in 2014 has held up.
• 2:32:01
  Speaker 1: but the details inside it are still being filled in,
• 2:32:05
  Speaker 1: and the territory just outside it keeps turning out to
• 2:32:08
  Speaker 1: be larger than anyone expected. Every civilization that ever looked
• 2:32:12
  Speaker 1: up at the sky had some answer to the question
• 2:32:15
  Speaker 1: of where they were in it. The Babylonians placed themselves
• 2:32:19
  Speaker 1: beneath a dome of gods. Medieval astronomers put Earth at
• 2:32:24
  Speaker 1: the center of nested crystalline spheres. Polynesian navigators read the
• 2:32:29
  Speaker 1: sky not as theology, but as a map, and they
• 2:32:33
  Speaker 1: used it to cross the largest ocean on the planet
• 2:32:36
  Speaker 1: without instruments, without landmarks, without anything except an extraordinarily precise
• 2:32:43
  Speaker 1: knowledge of the heavens above them. Every one of those
• 2:32:48
  Speaker 1: civilizations had an answer. None of them had the right one.
• 2:32:54
  Speaker 1: We are the first generation in human history that does.
• 2:32:59
  Speaker 1: That answer is strange enough to stop you cold if
• 2:33:02
  Speaker 1: you sit with it. You are not at the center
• 2:33:05
  Speaker 1: of your galaxy. You are not at the center of
• 2:33:08
  Speaker 1: your galaxy cluster. You are not at the center of
• 2:33:12
  Speaker 1: your supercluster. The Milky Way sits near the outer edge
• 2:33:17
  Speaker 1: of Laniakea, in a relatively quiet, relatively sparse region, far
• 2:33:23
  Speaker 1: from the dense clusters where galaxy interactions are frequent and
• 2:33:28
  Speaker 1: the cosmic environment is violent. We are on the rim.
• 2:33:33
  Speaker 1: We are in the suburbs of an immense structure that
• 2:33:36
  Speaker 1: stretches 520 million light years from one side to the other,
• 2:33:42
  Speaker 1: and we are being slowly pulled toward its heart by
• 2:33:45
  Speaker 1: a gravitational concentration so massive it took decades just to
• 2:33:51
  Speaker 1: find it. That pull will never complete. Dark energy will
• 2:33:57
  Speaker 1: likely win before we get anywhere near the center. We
• 2:34:02
  Speaker 1: are drifting outward, even as we fall inward, passengers in
• 2:34:06
  Speaker 1: a structure that is quietly dissolving at its edges. And
• 2:34:10
  Speaker 1: yet this unremarkable outpost is the only place, as far
• 2:34:14
  Speaker 1: as anyone knows, where the question has ever been asked.
• 2:34:19
  Speaker 1: That asymmetry is strange. The greater tractor sits at the
• 2:34:25
  Speaker 1: gravitational heart of Laniakea, surrounded by some of the densest
• 2:34:30
  Speaker 1: concentrations of galaxies in our cosmic neighborhood nobody there is
• 2:34:36
  Speaker 1: asking anything the rich clusters of the norma supercluster region
• 2:34:41
  Speaker 1: the dense nodes where filaments converge silent the vast empty
• 2:34:47
  Speaker 1: voids that occupy most of laniakea's volume silent one minor
• 2:34:53
  Speaker 1: spiral galaxy far from anything particularly remarkable, produced the only
• 2:34:59
  Speaker 1: observers in the known universe who looked outward and wanted
• 2:35:03
  Speaker 1: to understand the structure they were part of. That is
• 2:35:07
  Speaker 1: not an answer to anything. It is just the fact,
• 2:35:12
  Speaker 1: and the fact is strange. Think about what Tully's team
• 2:35:16
  Speaker 1: actually did. The Polynesian navigators used the sky to find
• 2:35:20
  Speaker 1: their place in the ocean. They read the stars, the swells,
• 2:35:25
  Speaker 1: the flight paths of birds, and they triangulated themselves into
• 2:35:29
  Speaker 1: a location. Tully's team did something that rhymes with that,
• 2:35:34
  Speaker 1: but runs deeper. They didn't use the sky to find
• 2:35:37
  Speaker 1: their place in the world. They used the motion of 100,000
• 2:35:41
  Speaker 1: galaxies to find their place within the structure that contains
• 2:35:45
  Speaker 1: the sky itself. The navigators crossed the Pacific. The astronomers
• 2:35:51
  Speaker 1: mapped the Pacific. and discovered it was part of a
• 2:35:54
  Speaker 1: continent they hadn't known existed. The Hawaiian name connects those
• 2:35:59
  Speaker 1: two acts across centuries. The same language, the same sky,
• 2:36:05
  Speaker 1: an entirely different scale of understanding. What that understanding gives
• 2:36:11
  Speaker 1: us is a complete address. Not just Earth, not just
• 2:36:15
  Speaker 1: the solar system, not just the Milky Way or the
• 2:36:19
  Speaker 1: local group, but the full hierarchy extending outward to Laniakea
• 2:36:24
  Speaker 1: and beyond. For most of human history, that address was
• 2:36:28
  Speaker 1: unknown past the level of a few nearby stars. A
• 2:36:32
  Speaker 1: century ago, we didn't know other galaxies existed. 50 years ago,
• 2:36:38
  Speaker 1: we didn't know what was pulling our region of the
• 2:36:40
  Speaker 1: universe off course. 10 years ago, we didn't have a
• 2:36:44
  Speaker 1: name for the supercluster we live in. The discovery is
• 2:36:48
  Speaker 1: genuinely recent. The picture is genuinely incomplete. There are structures
• 2:36:54
  Speaker 1: beyond Laniakea still being traced, boundaries still being debated, catalogues
• 2:37:00
  Speaker 1: being extended from 8,000 galaxies to 56,000, and eventually further still.
• 2:37:09
  Speaker 1: The 2014 paper was a door opening, not a door closing.
• 2:37:15
  Speaker 1: What sits on the other side of that door is
• 2:37:18
  Speaker 1: uncomfortable and astonishing in equal measure. We are peripheral, we
• 2:37:24
  Speaker 1: are temporary, in the sense that the structure we belong
• 2:37:27
  Speaker 1: to will not survive on consciousness. timescales. The outer filaments
• 2:37:34
  Speaker 1: of Laniakea are already losing coherence to dark energy. In
• 2:37:39
  Speaker 1: hundreds of billions of years, the flows that define our
• 2:37:42
  Speaker 1: cosmic home will disperse into an expanding void. Laniakea will
• 2:37:48
  Speaker 1: not exist in any meaningful sense. The immense heaven will dissolve.
• 2:37:54
  Speaker 1: This is not a reason for distress. It is just
• 2:37:58
  Speaker 1: the physics. The structure was real. The flows were real.
• 2:38:04
  Speaker 1: The answer to where we are is real, even if
• 2:38:07
  Speaker 1: the structure itself is temporary. Somewhere on the outer rim
• 2:38:11
  Speaker 1: of an immense heaven, there is a small spiral galaxy.
• 2:38:15
  Speaker 1: and on one of its unremarkable arms, something learned to
• 2:38:19
  Speaker 1: ask where it was, and is only now beginning to
• 2:38:23
  Speaker 1: find out.