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How Large Is the Hercules Corona Borealis Really · Boring Science

• 0:00
  Speaker 1: In 2013, a group of astronomers was combing through a
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  Speaker 1: map of the most violent explosions in the known universe,
• 0:08
  Speaker 1: and they found something that should not have been there.
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  Speaker 1: These explosions are called gamma-ray bursts. Each one outshines entire galaxies.
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  Speaker 2: For a few seconds.
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  Speaker 1: They are the brightest events the universe produces, and astronomers
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  Speaker 1: have been cataloguing them for decades. The plan was straightforward.
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  Speaker 1: Map where the bursts fall in the sky. Check whether
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  Speaker 1: they are evenly spread. Standard statistical work. The kind of
• 0:35
  Speaker 1: analysis that usually returns a clean result and gets far
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  Speaker 1: the way. This one did not return a clean result.
• 0:43
  Speaker 1: In a specific patch of sky, at a specific range
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  Speaker 1: of distances, the bursts were clustering. Not randomly, not subtly.
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  Speaker 1: They were piling up in a region of space in
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  Speaker 1: a way that a smooth, evenly distributed universe simply should
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  Speaker 1: not produce. The team looked for an error. They checked
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  Speaker 1: the instruments. They looked for a bias in how the
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  Speaker 1: data had been collected.
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  Speaker 2: The clustering held. What they were looking at, if it
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  Speaker 2: was real.
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  Speaker 1: Was a structure roughly 10 billion light years across. 10
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  Speaker 1: billion light years. The entire observable universe is about 93
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  Speaker 1: billion light years wide. The thing they had found stretched
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  Speaker 1: across one tenth of that. Everything humanity has ever seen,
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  Speaker 1: every galaxy we have ever mapped, every signal we have
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  Speaker 1: ever received from space, all of it fits inside a sphere.
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  Speaker 1: And this structure spans a tenth of that sphere's diameter.
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  Speaker 1: Cosmology has rules about how large things are allowed to be.
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  Speaker 1: Those rules come from some of the most carefully tested
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  Speaker 1: theory in.
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  Speaker 2: All of science.
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  Speaker 1: They predict a ceiling on structure size. That ceiling sits
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  Speaker 1: at roughly 1.2 billion light years. Anything coherent, anything you
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  Speaker 1: could point to and call a single object, should be
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  Speaker 1: smaller than that. The structure these astronomers were looking at
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  Speaker 1: was not slightly above the ceiling. It was not twice
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  Speaker 1: the ceiling, not five times, it was more than eight
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  Speaker 1: times the size that the standard model of cosmology says
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  Speaker 1: a structure can reach. It has no business being that large.
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  Speaker 1: That is not a casual observation.
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  Speaker 2: It is a.
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  Speaker 1: Direct challenge to the framework that modern cosmology is built on.
• 2:34
  Speaker 1: The cosmological principle, the assumption that the universe is uniform
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  Speaker 1: on large enough scales, is not just a background belief.
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  Speaker 1: It is a load-bearing wall in the standard model. Pull
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  Speaker 1: it out, and a significant amount of what we think
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  Speaker 1: we understand about the universe has to be re-examined. The
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  Speaker 1: discovery triggered immediate debate. Some researchers accepted it, others pushed
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  Speaker 1: back hard on the method. The argument has not been
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  Speaker 1: fully settled, and the stakes are real. Because if the
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  Speaker 1: structure is genuine, the universe built something that the current
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  Speaker 1: rulebook explicitly says it cannot. That is where this begins.
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  Speaker 1: A map of the most violent explosions in existence, and
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  Speaker 1: somewhere in the data, something vast enough to rewrite the textbooks,
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  Speaker 1: and to understand why it matters. You first have to
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  Speaker 1: understand what 10 billion light years actually is. The number
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  Speaker 1: 10 billion light years does not mean anything to most people.
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  Speaker 1: And that is not a failure of imagination. It is
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  Speaker 1: just that nothing in ordinary human experience prepares you for
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  Speaker 1: what it points at. Start with the basic unit. A
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  Speaker 1: light year is not a measure of time. It is
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  Speaker 1: a measure of distance. Specifically, it is the distance light
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  Speaker 1: travels in one year. moving at roughly 186,000 miles per second.
• 4:01
  Speaker 1: In a single second, light crosses the distance between New
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  Speaker 1: York and Los Angeles about 62 times. In one year,
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  Speaker 1: traveling at that speed without stopping, light covers about 5.88
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  Speaker 1: trillion miles. That is the unit, one light year, nearly
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  Speaker 1: 6 trillion miles. Hold that number in your head because
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  Speaker 1: we are going to need it. The nearest star to
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  Speaker 1: our sun is Proxima Centauri. It sits roughly 4.2 light
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  Speaker 1: years away. That means the light arriving at your eyes
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  Speaker 1: from Proxima Centauri tonight left that star in the year 2021.
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  Speaker 1: If you wanted to send a message there at the
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  Speaker 1: speed of light and wait for a reply, that conversation
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  Speaker 1: would take more than 8 years to complete. No spacecraft
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  Speaker 1: humanity has ever built could reach it within a human lifetime.
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  Speaker 1: Four light years is by any practical measure unreachable, and
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  Speaker 1: four light years is the smallest gap between stars.
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  Speaker 2: In our neighborhood. Now scale up.
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  Speaker 1: Our galaxy, the Milky Way, contains somewhere between 100 and
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  Speaker 1: 400 billion stars. It is shaped roughly like a flattened
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  Speaker 1: spiral disc with a dense bulge at the center. Across
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  Speaker 1: its widest point, it measures about 100,000 light years. If
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  Speaker 1: you could somehow travel at the speed of light from
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  Speaker 1: one edge to the other without stopping, the journey would
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  Speaker 1: take 100,000 years. The civilization that launched you would be
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  Speaker 1: unrecognizable by the time you arrived, if it still existed
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  Speaker 1: at all. The Milky Way is enormous by every standard
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  Speaker 1: that matters to a human being, but we are just
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  Speaker 1: getting started. Beyond the Milky Way, the nearest large galaxy
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  Speaker 1: is Andromeda. It hangs about 2.5 million light years away.
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  Speaker 1: The light reaching you from Andromeda tonight has been traveling
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  Speaker 1: since before the earliest stone tools were made on Earth.
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  Speaker 1: Two and a half million years in transit, crossing empty space,
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  Speaker 1: arriving now at your eye or at a telescope lens
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  Speaker 1: somewhere on this planet. Andromeda is close by cosmic standards.
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  Speaker 1: It is our nearest significant neighbor. The Milky Way in
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  Speaker 1: Andromeda are both members of a collection of galaxies called
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  Speaker 1: the Local Group. It contains more than 50 galaxies in total,
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  Speaker 1: including both large spirals and dozens of smaller dwarf galaxies.
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  Speaker 1: The Local Group spans roughly 10 million light years from
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  Speaker 1: one edge to the other. 10 million light years. That
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  Speaker 1: is 100 Milky Ways laid end to end. The whole thing,
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  Speaker 1: every galaxy we are gravitationally bound to, fits inside a
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  Speaker 1: bubble 10 million light years across. The Local Group is
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  Speaker 1: itself just one small knot in a larger structure called
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  Speaker 1: the Virgo Supercluster, which stretches about 110 million light years
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  Speaker 1: across and contains dozens of galaxy groups and clusters. And
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  Speaker 1: the Virgo Supercluster is just one lobe of an even
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  Speaker 1: larger supercluster called Laniakea, which spans roughly 500 million light
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  Speaker 1: years and contains the mass of a hundred million billion suns.
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  Speaker 1: These are the structures that feel staggeringly large when you
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  Speaker 1: first encounter them. They are the things that make astronomers pause.
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  Speaker 1: But even Laniakea is not close to the scale we.
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  Speaker 2: Are working toward.
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  Speaker 1: The observable universe, the entire sphere of space from which
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  Speaker 1: light has had time to reach us since the Big Bang,
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  Speaker 1: spans approximately 93 billion light years in diameter. Not the
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  Speaker 1: whole universe, Not all of space, just the portion we
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  Speaker 1: can see from here. The region bounded by the distance
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  Speaker 1: light could travel in 13.8 billion years through an expanding cosmos.
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  Speaker 1: 93 billion light years. Everything we have ever observed, every galaxy,
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  Speaker 1: every quasar, every faint smudge in the deepest telescope images,
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  Speaker 1: fits inside that sphere. Here is a scale model worth
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  Speaker 1: holding in your mind. If you shrink the observable universe
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  Speaker 1: down to the size of a regulation football field, the
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  Speaker 1: Milky Way becomes a grain of salt somewhere near the
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  Speaker 1: middle of it.
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  Speaker 2: Not a pebble.
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  Speaker 1: Not a speck of dust.
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  Speaker 2: A grain of salt.
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  Speaker 1: The entire galaxy containing our sun and 400 billion other stars,
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  Speaker 1: all the stars you can see on any clear night
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  Speaker 1: from anywhere on Earth, compressed to the size of something
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  Speaker 1: that falls off a pretzel, That is the relationship between
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  Speaker 1: our galaxy and the full scope of what we can observe.
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  Speaker 1: This perspective reveals something profoundly humbling about human existence. We
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  Speaker 1: inhabit one planet around one star, in one galaxy that
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  Speaker 1: occupies one grain of salt on a football field sized
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  Speaker 1: model of the observable universe. The vastness is not merely large,
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  Speaker 1: it is systematically indifferent to our presence. Yet this grain
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  Speaker 1: of salt contains everything we have ever known, every human thought,
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  Speaker 1: every discovery, every moment of meaning or beauty we have experienced.
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  Speaker 1: The scale disparity is so extreme that it borders on absurdity,
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  Speaker 1: and yet we discovered it. Some arrangement of atoms on
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  Speaker 1: that grain of salt figured out how to measure and
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  Speaker 1: map structures so large they defy intuition. This contradiction, our
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  Speaker 1: smallness and our ability to comprehend smallness, sits at the
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  Speaker 1: heart of why the cosmic scale matters at all now
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  Speaker 1: introduce the structure the thing the astronomers found in 2013
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  Speaker 1: measures approximately 10 billion light years along its longest dimension 7.2
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  Speaker 1: billion light years wide nearly 1 billion light years thick
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  Speaker 1: These are not the dimensions of a thin sheet or
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  Speaker 1: a narrow filament. This is a three-dimensional region of space
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  Speaker 1: with substantial depth in every direction. 94,000 Milky Way galaxies
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  Speaker 1: placed side by side would barely span the length of it.
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  Speaker 1: That is not a comparison that helps much. because 94,000
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  Speaker 1: of anything is hard to picture. But try it another way.
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  Speaker 1: The distance from Proxima Centauri to our Sun, that four
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  Speaker 1: light-year gap we started with, is completely invisible at the
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  Speaker 1: scale of this structure. So is the Milky Way itself.
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  Speaker 1: So is the Local Group. So is Lanakaia. Every structure
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  Speaker 1: we described on the way up here, every step in
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  Speaker 1: the ladder from nearest star to nearest galaxy to nearest supercluster,
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  Speaker 1: disappears into the noise when you try to mark it
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  Speaker 1: on a map of the Hercules-Corona-Borealis Great Wall. The structure
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  Speaker 1: does not contain multiples of our galaxy, it contains multiples
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  Speaker 1: of everything we have ever considered large. On that football
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  Speaker 1: field model, where the Milky Way was a grain of salt,
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  Speaker 1: the Hercules-Corona-Borealis Great Wall would stretch across roughly 10 yards
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  Speaker 1: of the field, one-tenth of the entire length, not a
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  Speaker 1: faint smear near one end zone. a visible, substantial portion
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  Speaker 1: of everything the model contains. That is the number.
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  Speaker 2: One tenth.
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  Speaker 1: The structure they found stretches across roughly one tenth of
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  Speaker 1: everything we can observe from Earth. And it has no
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  Speaker 1: business being that large. To understand what the Hercules-Corona-Borealis Great
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  Speaker 1: Wall actually is, you have to understand what kind of
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  Speaker 1: universe it lives in. The universe is not a smooth,
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  Speaker 1: uniform spread of matter.
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  Speaker 2: It never was.
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  Speaker 1: If you could pull back far enough to see the
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  Speaker 1: whole observable universe at once, what you would find is
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  Speaker 1: not a fog of evenly distributed galaxies. What you would
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  Speaker 1: find looks more like a sponge, or foam sitting in
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  Speaker 1: a bathtub. Enormous empty bubbles surrounded by thin walls and
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  Speaker 1: threads of matter. Dark voids so large that entire galaxy
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  Speaker 1: clusters would seem tiny against their interiors. And running through everything,
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  Speaker 1: connecting the dense patches to each other, a network of
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  Speaker 1: long filaments carrying the overwhelming majority of.
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  Speaker 2: The matter in the universe.
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  Speaker 1: This is the cosmic web, and it is the fundamental
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  Speaker 1: architecture of everything at the largest scales. To understand how
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  Speaker 1: it got there, you have to go back almost 14
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  Speaker 1: billion years. The universe just after the Big Bang was
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  Speaker 1: not perfectly smooth. Close, but not perfectly. Tiny quantum fluctuations
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  Speaker 1: in the density of the early universe meant that some
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  Speaker 1: regions had slightly more matter packed into them than others.
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  Speaker 1: Not dramatically more. The differences were extraordinarily small. But gravity
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  Speaker 1: does not care how small the difference is. Gravity is patient.
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  Speaker 1: Over millions of years, the slightly denser regions pulled in
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  Speaker 1: more matter from their surroundings. The slightly less dense regions
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  Speaker 1: gave matter away. That feedback loop ran for hundreds of
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  Speaker 1: millions of years, then billions of years, and the small
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  Speaker 1: differences compounded. Dense regions became denser. Empty regions became emptier.
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  Speaker 1: What started as a barely perceptible ripple across the fabric
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  Speaker 1: of the young universe grew into the web structure you
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  Speaker 1: see mapped in modern galaxy surveys. The nodes of that
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  Speaker 1: web are the places where the densest threads cross.
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  Speaker 2: Galaxy clusters form there.
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  Speaker 1: These are not single galaxies, but collections of hundreds or
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  Speaker 1: thousands of galaxies, all bound together by gravity, sitting in
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  Speaker 1: vast halos of dark matter, the hottest and most massive
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  Speaker 1: concentrations of normal matter in the universe. Between the nodes,
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  Speaker 1: the filaments stretch outward. These are long, relatively narrow highways
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  Speaker 1: of matter, sometimes hundreds of millions of light years from
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  Speaker 1: end to end. Galaxies form inside the filaments. Gas flows
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  Speaker 1: along them. They are not static structures but active channels.
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  Speaker 1: Funneling matter toward the dense nodes where clusters sit. Between
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  Speaker 1: the filaments and walls there is almost nothing. These empty
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  Speaker 1: regions are called voids. A typical void might be a
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  Speaker 1: few hundred million light years across.
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  Speaker 2: Some are larger.
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  Speaker 1: Inside a void you might find a handful of galaxies
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  Speaker 1: spread so thinly across such enormous volumes. that the average
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  Speaker 1: density is a fraction of what you would measure inside
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  Speaker 1: a filament. If you were a hypothetical observer sitting in
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  Speaker 1: the middle of a cosmic void, the nearest galaxy cluster
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  Speaker 1: might be hundreds of millions of light years away in
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  Speaker 1: every direction. The night sky would look sparse in a
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  Speaker 1: way that is hard to imagine from our position inside
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  Speaker 1: a filament. The walls are somewhere between the filaments and
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  Speaker 1: the voids. flat, sheet-like arrangements of galaxies forming the surfaces
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  Speaker 1: of the large empty bubbles. When you look at a
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  Speaker 1: cross-section of a galaxy survey, these are the boundaries you see.
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  Speaker 1: The sponge analogy works because the voids are the holes
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  Speaker 1: and the walls and filaments are the material surrounding them.
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  Speaker 1: The foam analogy works too because the bubbles press against
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  Speaker 1: each other and their boundaries.
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  Speaker 2: Are the walls. Either way, the picture is the same.
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  Speaker 1: A connected network of structure separated by enormous emptiness. Now,
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  Speaker 1: here is something worth holding onto. Most of the ordinary
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  Speaker 1: matter in the universe, the atoms, the gas, the stars,
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  Speaker 1: the galaxies, lives inside the filaments and walls. The voids
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  Speaker 1: are genuinely empty by comparison. This means the cosmic web
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  Speaker 1: is not just a description of how galaxies are arranged,
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  Speaker 1: It is a description of where almost everything is. If
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  Speaker 1: you want to find a galaxy, look in a filament.
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  Speaker 1: If you want to find a galaxy cluster, look where
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  Speaker 1: the filaments cross. The voids contain almost nothing, and they
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  Speaker 1: make up most of the volume of the universe. Galaxy
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  Speaker 1: filaments come in a range of sizes. Some are relatively modest,
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  Speaker 1: connecting a few clusters across a few hundred million light years.
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  Speaker 1: Others are larger, more substantial. part of what astronomers call superclusters.
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  Speaker 1: Our own Milky Way lives inside a supercluster called Lanakaia,
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  Speaker 1: which stretches roughly 500 million light years across and contains
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  Speaker 1: the mass of more than 100 million billion suns. That
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  Speaker 1: sounds enormous, and by any human measure it is. Lanakaia
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  Speaker 1: is one of the largest named structures in our immediate
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  Speaker 1: cosmic neighborhood, but it is still a local feature of
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  Speaker 1: the web. Zoom out far enough. and Lanakea is just
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  Speaker 1: one node among many. This is the framework that makes
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  Speaker 1: the Hercules-Corona-Borealis Great Wall legible. It is a filament, an
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  Speaker 1: extreme one, but the same kind of structure that shows
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  Speaker 1: up everywhere in the web, built by the same process,
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  Speaker 1: driven by the same physics. Gravity gathered matter into threads.
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  Speaker 1: Threads formed walls, walls enclosed voids. The web emerged. What
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  Speaker 1: makes the Hercules-Corona-Borealis Great Wall remarkable is not what it is,
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  Speaker 1: but how large it is, because the web was not
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  Speaker 1: supposed to keep growing at that scale. Standard cosmological models
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  Speaker 1: predict that the web reaches a natural ceiling. At large
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  Speaker 1: enough scales, the density fluctuations that seeded the structure in
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  Speaker 1: the first place were too small, and the time available
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  Speaker 1: for gravity to amplify them was too short. Above a
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  Speaker 1: certain size threshold, the web should look smooth. The large
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  Speaker 1: over densities and under densities that define the filaments and
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  Speaker 1: voids at smaller scales should average out. The universe at
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  Speaker 1: sufficiently large scales should look the same in every direction,
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  Speaker 1: roughly uniform, roughly featureless. The scale where this smoothing was
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  Speaker 1: expected to have taken hold is somewhere in the range
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  Speaker 1: of a few hundred million to perhaps a billion light years.
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  Speaker 1: Above that, Organized structure should not exist. The Hercules-Corona-Borealis Great
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  Speaker 1: Wall sits somewhere in that web, but at a scale
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  Speaker 1: that the web was never supposed to reach. The tool
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  Speaker 1: that made this discovery possible is one of the strangest
• 18:43
  Speaker 1: instruments in astronomy. Not a telescope, exactly. Not a detector
• 18:48
  Speaker 1: pointed patiently at a single target. The instrument is the
• 18:52
  Speaker 1: universe itself. scattered with the most violent explosions that physics allows,
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  Speaker 1: each one going off once and never again, each one
• 19:01
  Speaker 1: briefly outshining everything around it by a factor that defies
• 19:06
  Speaker 1: easy comparison. Gamma ray bursts are the most energetic explosions
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  Speaker 1: in the known universe. When a massive star runs out
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  Speaker 1: of fuel, its core can collapse in under a second,
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  Speaker 1: triggering a catastrophic implosion that drives a jet of energy
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  Speaker 1: outward and nearly the speed of light. The result is
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  Speaker 1: a flash of gamma radiation so intense that a single
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  Speaker 1: burst lasting anywhere from a fraction of a second to
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  Speaker 1: several minutes can briefly outshine the entire observable universe in
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  Speaker 1: high energy light. Some are caused by collapsing stars. Others
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  Speaker 1: come from two neutron stars spiraling together over billions of
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  Speaker 1: years and finally merging in a collision. that releases more
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  Speaker 1: energy in milliseconds than our sun will produce across its
• 19:54
  Speaker 1: entire 10 billion year life. Either way, the explosion is brief,
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  Speaker 1: ferocious and unrepeatable. It happens once and then it is gone.
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  Speaker 1: What makes this relevant to mapping cosmic structure? is where
• 20:10
  Speaker 1: these explosions happen. Gamma ray bursts tied to collapsing massive
• 20:15
  Speaker 1: stars occur in galaxies where new stars are actively forming.
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  Speaker 1: Massive stars burn fast. They live tens of millions of
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  Speaker 1: years at most. That means they die close to where
• 20:27
  Speaker 1: they were born, inside the dense star forming regions of
• 20:31
  Speaker 1: their host galaxies. Because star formation traces the distribution of
• 20:35
  Speaker 1: matter across the universe. The locations of gamma ray bursts
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  Speaker 1: serve as markers for where matter has concentrated. Plot them
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  Speaker 1: on a map of the sky, and you are, in
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  Speaker 1: a rough sense, plotting the skeleton of large-scale structure. The
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  Speaker 1: other thing that makes gamma ray bursts uniquely powerful as
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  Speaker 1: a tool is how far away.
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  Speaker 2: They can be seen.
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  Speaker 1: An optical survey of galaxies runs into a hard limit.
• 21:02
  Speaker 1: The farther away a galaxy is, the fainter it appears. Eventually,
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  Speaker 1: even the largest telescopes lose the signal. The deepest galaxy
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  Speaker 1: surveys reach out perhaps a few billion light years with
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  Speaker 1: reasonable completeness. Gamma ray bursts punch through that limit because
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  Speaker 1: they are not steady faint objects, but sudden, violent flares.
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  Speaker 1: At their peak, the brightest of them can be detected
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  Speaker 1: from halfway across the observable universe. Some have been measured
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  Speaker 1: at redshifts above 9, meaning the light left them when
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  Speaker 1: the universe was less than 500 million years old. No
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  Speaker 1: galaxy survey comes close to that depth. If you want
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  Speaker 1: a tracer of structure that reaches back toward the earliest
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  Speaker 1: epochs of cosmic history, gamma ray bursts are one of
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  Speaker 1: the very few options available. NASA recognized this potential and
• 21:57
  Speaker 1: launched the Swift Gamma Ray Burst Mission in 2004. Swift
• 22:01
  Speaker 1: was designed to do something no previous satellite had managed reliably.
• 22:06
  Speaker 1: When its burst alert telescope detected a gamma ray burst,
• 22:10
  Speaker 1: the satellite could pivot its more sensitive instruments toward the
• 22:13
  Speaker 1: source within about a minute, catching the afterglow before it faded.
• 22:18
  Speaker 1: That afterglow is the key. The initial flash of gamma
• 22:21
  Speaker 1: radiation carries energy but not much spectral detail. The afterglow,
• 22:27
  Speaker 1: glowing in X-ray optical, Sometimes radio light as the explosion
• 22:31
  Speaker 1: shockwave plows into surrounding gas contains identifiable spectral features. Specific
• 22:38
  Speaker 1: emission and absorption lines from known elements appear shifted toward
• 22:42
  Speaker 1: longer wavelengths depending on how far the light has traveled
• 22:45
  Speaker 1: through an expanding universe. Measure that shift and you have
• 22:49
  Speaker 1: the redshift.
• 22:50
  Speaker 2: From the redshift you can calculate the distance.
• 22:54
  Speaker 1: This is how a three-dimensional map gets built. Each burst
• 22:58
  Speaker 1: Swift detected, and whose afterglow was followed up by ground-based telescopes,
• 23:03
  Speaker 1: gave astronomers a single point in space, a position on
• 23:07
  Speaker 1: the sky combined with a distance derived from the redshift.
• 23:11
  Speaker 1: Stack enough of these points, and you have a scatterplot
• 23:14
  Speaker 1: of explosions distributed across billions of light-years in three dimensions.
• 23:19
  Speaker 1: The question you can then ask is whether those points
• 23:22
  Speaker 1: are distributed randomly, as a smooth and featureless universe would predict.
• 23:27
  Speaker 1: or whether they cluster, piling up in some regions and
• 23:31
  Speaker 1: leaving others comparatively empty. This is exactly the question the
• 23:35
  Speaker 1: team studying the Hercules-Corona-Borealis Great Wall was asking. The depth
• 23:41
  Speaker 1: of the Swift catalog is what set this approach apart
• 23:44
  Speaker 1: from earlier work. Previous gamma-ray burst missions had detected bursts
• 23:49
  Speaker 1: but could not pivot fast enough to catch the afterglows reliably.
• 23:53
  Speaker 1: That meant redshifts were hard to measure. Without redshifts, you
• 23:57
  Speaker 1: have positions on the sky, but no distances. A two-dimensional
• 24:01
  Speaker 1: map of the sky tells you almost nothing about three-dimensional structure.
• 24:06
  Speaker 1: Swift changed that. By the time the Hungarian and American
• 24:10
  Speaker 1: team began their analysis, they had access to a catalog
• 24:14
  Speaker 1: of hundreds of bursts with measured redshifts spread across a
• 24:18
  Speaker 1: huge range of distances. That was enough to start looking
• 24:22
  Speaker 1: for patterns. This observation demands your sustained attention. The most
• 24:27
  Speaker 1: powerful of these explosions have been detected from distances so
• 24:31
  Speaker 1: extreme that their light left the source more than 13
• 24:35
  Speaker 1: billion years ago. One burst, recorded in 2009, was so
• 24:41
  Speaker 1: far away that the universe had not yet finished its
• 24:45
  Speaker 1: first billion years when the explosion occurred. The light crossed
• 24:49
  Speaker 1: the entire subsequent history of the cosmos to reach a
• 24:53
  Speaker 1: satellite in Earth orbit. You could argue that gamma ray
• 24:58
  Speaker 1: bursts are less instruments than time machines, each one delivering
• 25:02
  Speaker 1: a message from a universe that no longer exists in
• 25:05
  Speaker 1: the form it had when the message was sent. That
• 25:09
  Speaker 1: is the power of the tool. But power comes with limitations,
• 25:14
  Speaker 1: and the limitation here is significant. The Swift Catalog and
• 25:18
  Speaker 1: every catalogue built before or alongside it was assembled under
• 25:23
  Speaker 1: conditions that were never perfectly controlled. Different satellites with different
• 25:28
  Speaker 1: detection thresholds covered the sky at different times, with different
• 25:33
  Speaker 1: sensitivities to bursts at different energies. Ground-based follow-up observations required
• 25:39
  Speaker 1: to measure the redshift from the afterglow depended on which
• 25:43
  Speaker 1: telescopes happened to be available and pointing in the right
• 25:46
  Speaker 1: direction when the burst occurred. Some bursts were followed up thoroughly,
• 25:51
  Speaker 1: others were not. Some parts of the sky were watched
• 25:54
  Speaker 1: more carefully than others. Some redshift ranges were sampled more
• 25:59
  Speaker 1: densely than the data's apparent coverage implied. The result is
• 26:03
  Speaker 1: a catalogue that is not a clean, uniform sampling of
• 26:06
  Speaker 1: the universe. It is a patchwork, stitched together from dozens
• 26:11
  Speaker 1: of observing campaigns with different characteristics and uneven coverage. The
• 26:16
  Speaker 1: catch is that gamma ray bursts are not perfectly uniform
• 26:19
  Speaker 1: traces of the universe. That single limitation sits at the
• 26:24
  Speaker 1: center of everything that came next. In late 2013, a
• 26:29
  Speaker 1: team of Hungarian and American astronomers was doing something that
• 26:33
  Speaker 1: sounds fairly routine, running a statistical check on the sky
• 26:37
  Speaker 1: positions of gamma ray bursts in a large data catalog.
• 26:41
  Speaker 1: Istvan Holvath, John Hakala and Zolt Bagali had been working
• 26:46
  Speaker 1: through data collected by NASA's Swift mission, cross-referencing it with
• 26:50
  Speaker 1: redshift measurements pulled from ground-based telescopes around the world.
• 26:55
  Speaker 2: The goal was straightforward.
• 26:57
  Speaker 1: Were these explosions scattered evenly across the sky, or were
• 27:01
  Speaker 1: they clustering?
• 27:02
  Speaker 2: Routine work.
• 27:04
  Speaker 1: The kind of analysis that usually produces a clean result
• 27:07
  Speaker 1: and gets filed away. It did not produce a clean result.
• 27:11
  Speaker 1: The team was sorting the bursts by redshift, grouping them
• 27:15
  Speaker 1: by distance, and examining whether each distance slice showed a
• 27:19
  Speaker 1: uniform sky distribution. Most of the slices looked normal. The
• 27:24
  Speaker 1: explosions spread out roughly evenly, no suspicious concentrations, nothing that
• 27:29
  Speaker 1: demanded attention. Then they reached the slice corresponding to a
• 27:33
  Speaker 1: redshift of approximately two. That is a distance so vast
• 27:38
  Speaker 1: it corresponds to light that left its source when the
• 27:41
  Speaker 1: universe was only about 3 billion years old, roughly a
• 27:45
  Speaker 1: fifth of its current age. At that distance range, the
• 27:49
  Speaker 1: map changed. A section of sky spanning the constellations Hercules
• 27:53
  Speaker 1: and Corona Borealis was packed with gamma ray bursts, not
• 27:57
  Speaker 1: slightly elevated, not a gentle statistical bump, packed. Picture what
• 28:03
  Speaker 1: a uniform map of these explosions should look like. If
• 28:07
  Speaker 1: you scatter points randomly across a sphere, you expect rough evenness,
• 28:12
  Speaker 1: some small clusters here and there, the way random noise
• 28:16
  Speaker 1: always looks a little clumpy up close. What you do
• 28:19
  Speaker 1: not expect is a dense concentration covering a substantial arc
• 28:24
  Speaker 1: of the sky, sitting against a background that shows nothing
• 28:27
  Speaker 1: comparable anywhere else in the same distant slice. That is
• 28:31
  Speaker 1: what the team was looking at, a patch of sky
• 28:34
  Speaker 1: that was clearly dramatically different from everything around it. The
• 28:39
  Speaker 1: first instinct in that situation is not excitement, it is suspicion.
• 28:44
  Speaker 1: Harvath and his colleagues knew immediately that before they could
• 28:47
  Speaker 1: say anything meaningful about the universe, they had to.
• 28:50
  Speaker 2: Rule out themselves.
• 28:52
  Speaker 1: Was the swift satellite observing certain parts of the sky
• 28:56
  Speaker 1: more than others? Were there biases in which bursts received
• 28:59
  Speaker 1: optical follow-up? which is what produces the redshift measurements needed
• 29:03
  Speaker 1: to place them at a specific distance, were there systematic
• 29:07
  Speaker 1: differences in how the ground-based telescopes had been operating during
• 29:11
  Speaker 1: the period the data covered. These are not exotic concerns.
• 29:16
  Speaker 1: They are the standard checklist for any anomaly in survey data,
• 29:20
  Speaker 1: and they had to be worked through carefully before the
• 29:23
  Speaker 1: result meant anything at all.
• 29:25
  Speaker 2: They worked through it. The clustering survived.
• 29:28
  Speaker 1: Adjusting for known observational biases in the SWIFT catalog, restricting
• 29:33
  Speaker 1: the sample to bursts with the most reliable redshift measurements,
• 29:37
  Speaker 1: checking whether the concentration held up when the analysis was
• 29:41
  Speaker 1: approached from different angles each test left the signal standing
• 29:46
  Speaker 1: something in that region of sky at that distance was
• 29:49
  Speaker 1: genuinely over dense the team could not make it disappear
• 29:53
  Speaker 1: what they had found spanned roughly 10 billion light years
• 29:56
  Speaker 1: in its longest dimension 7 billion wide, nearly a billion
• 30:01
  Speaker 1: light years deep. Those numbers were already hard to absorb
• 30:05
  Speaker 1: in isolation. In context, they were staggering. The previous record
• 30:10
  Speaker 1: for the largest known structure in the observable universe stood
• 30:14
  Speaker 1: at just under 4 billion light years. This was more
• 30:17
  Speaker 1: than twice that. It was nearly eight times the size
• 30:21
  Speaker 1: of the Sloan Great Wall, which had itself been considered
• 30:25
  Speaker 1: astonishing when it was announced. The clustering signal in that
• 30:29
  Speaker 1: single redshift band was pointing at something so large that
• 30:33
  Speaker 1: the comparison to anything previously known felt almost meaningless. The
• 30:38
  Speaker 1: team published their findings in November 2013. The structure needed
• 30:43
  Speaker 1: a name. In astronomy, naming rights for a discovery typically
• 30:48
  Speaker 1: belong to the people who made it, but occasionally a
• 30:51
  Speaker 1: name emerges from somewhere unexpected. In this case, The name
• 30:56
  Speaker 1: came from a Filipino teenager named Yondric Valdez, who had
• 31:00
  Speaker 1: been following the astronomical literature and aspired to become an astronomer.
• 31:05
  Speaker 1: He proposed the name Hercules Corona Borealis Great Wall, drawing
• 31:11
  Speaker 1: on the constellations that mark the region of sky where
• 31:14
  Speaker 1: the over-density sits.
• 31:16
  Speaker 2: The name stuck.
• 31:18
  Speaker 1: It carries something of the old tradition of naming the
• 31:21
  Speaker 1: sky's features after patterns humans drew in the stars. except
• 31:25
  Speaker 1: that what the name now points at is not a
• 31:27
  Speaker 1: handful of stars arranged in a shape. It is the
• 31:31
  Speaker 1: largest known object in the universe. News of the discovery
• 31:35
  Speaker 1: moved quickly through the astronomical community, and the reaction was
• 31:39
  Speaker 1: not uniform.
• 31:42
  Speaker 2: Some researchers found the signal compelling.
• 31:45
  Speaker 1: Others were more cautious, pointing immediately to the limitations of
• 31:49
  Speaker 1: gamma-ray burst data as a tool for mapping large-scale structure.
• 31:54
  Speaker 1: The Swift satellite had not been designed as a cosmological
• 31:57
  Speaker 1: survey instrument. Its burst catalogue was a byproduct of a
• 32:01
  Speaker 1: mission aimed at understanding the explosions themselves, not at mapping
• 32:06
  Speaker 1: matter distribution across the universe. The data it produced was real,
• 32:11
  Speaker 1: but it was also uneven, assembled over years of observations
• 32:15
  Speaker 1: with varying conditions, varying sky coverage, and varying availability of
• 32:22
  Speaker 1: the follow-up observations needed to measure redshifts. Whether that unevenness
• 32:27
  Speaker 1: could produce a false clustering signal was a question that
• 32:31
  Speaker 1: could not be answered quickly. The implications, if the structure
• 32:35
  Speaker 1: was genuine, were profound. Current models of structure formation suggested
• 32:41
  Speaker 1: a universe where large structures grew through gravitational attraction over
• 32:45
  Speaker 1: cosmic time. Something this size, at this distance, presented a
• 32:50
  Speaker 1: significant challenge to existing theory. If confirmed, it would mean
• 32:55
  Speaker 1: the observable universe contained at least one structure so vast
• 33:00
  Speaker 1: that it approached theoretical limits of what could coherently exist
• 33:04
  Speaker 1: given the universe's age and expansion rate. These were not
• 33:08
  Speaker 1: minor complications. They were fundamental problems that could require new
• 33:14
  Speaker 1: physics or a complete rethinking of how cosmic structures assembled themselves.
• 33:20
  Speaker 1: The stakes of verification had become clear to the entire
• 33:24
  Speaker 1: astronomical community. What the team had done was find something.
• 33:29
  Speaker 1: Whether that something was a genuine physical structure or an
• 33:33
  Speaker 1: artifact of how the data had been collected was a
• 33:36
  Speaker 1: separate question entirely. The discovery and the verification were two
• 33:41
  Speaker 1: different problems and the announcement in 2013 only resolved the
• 33:46
  Speaker 1: first one. The second was going to take years different teams,
• 33:51
  Speaker 1: different methods and a great deal of argument. What nobody
• 33:56
  Speaker 1: disputed was that the signal was there in the data.
• 33:59
  Speaker 1: What it meant and what it was had not been settled.
• 34:04
  Speaker 1: The question now was whether what they were looking at
• 34:07
  Speaker 1: was real. When the team laid out the positions of
• 34:10
  Speaker 1: the gamma ray bursts in that particular redshift band and
• 34:13
  Speaker 1: looked at where they fell on the sky, what came
• 34:16
  Speaker 1: back was not what a smooth, evenly distributed universe should produce.
• 34:22
  Speaker 1: Think about what a uniform distribution looks like. If gamma
• 34:26
  Speaker 1: ray bursts are scattered randomly across the sky, the way
• 34:29
  Speaker 1: you would expect from a universe with no large structures
• 34:32
  Speaker 1: at the scale being surveyed, the dots on the map
• 34:35
  Speaker 1: should look roughly even. Some patches will have slightly more,
• 34:40
  Speaker 1: some slightly fewer, the way raindrops falling on a sidewalk
• 34:44
  Speaker 1: are not perfectly spaced, but still spread out.
• 34:47
  Speaker 2: What you should.
• 34:48
  Speaker 1: Not see is a dense, obvious clump concentrated in one
• 34:52
  Speaker 1: region with the surrounding area conspicuously emptier. That is not random.
• 34:59
  Speaker 1: That is a signal. The signal was there. It was
• 35:03
  Speaker 1: hard to miss. At the redshift range the team was examining,
• 35:08
  Speaker 1: corresponding to a slice of the universe roughly 10 billion
• 35:12
  Speaker 1: light years from Earth, the gamma ray bursts were not
• 35:15
  Speaker 1: behaving randomly. They were piling up. The overdensity was not subtle.
• 35:22
  Speaker 1: In the region of sky covering the constellations Hercules and
• 35:25
  Speaker 1: Corona Borealis, the concentration of gamma ray bursts ran significantly
• 35:31
  Speaker 1: higher than the surrounding background. The team ran the statistics.
• 35:35
  Speaker 1: Under their analysis, the probability of that clustering appearing by
• 35:39
  Speaker 1: chance in a genuinely uniform distribution was less than one
• 35:44
  Speaker 1: in a thousand. Some estimates put it closer to less
• 35:48
  Speaker 1: than 1 in 2000. Numbers like that do not mean impossible.
• 35:53
  Speaker 1: They mean that if you ran this survey a thousand
• 35:56
  Speaker 1: times on a truly random universe, you would almost never
• 35:59
  Speaker 1: see something this concentrated in this small A patch of sky.
• 36:04
  Speaker 1: The angular footprint of the overdensity was not small either.
• 36:08
  Speaker 1: It did not confine itself neatly to two constellations. The
• 36:13
  Speaker 1: clustering extended outward, spreading toward Beortes in one direction and
• 36:18
  Speaker 1: toward Gemini in another. The full angular extent of the
• 36:22
  Speaker 1: dense region covered a substantial arc of the northern sky.
• 36:26
  Speaker 1: That angular size, combined with the distance is where the
• 36:30
  Speaker 1: physical dimension started to become staggering. Distance turns angular size
• 36:35
  Speaker 1: into actual size. When you are measuring something 10 billion
• 36:39
  Speaker 1: light years away, even a moderate angular span corresponds to
• 36:44
  Speaker 1: an almost incomprehensible physical width. The team worked through the numbers.
• 36:50
  Speaker 1: Along its longest dimension, the structure measured approximately 10 billion
• 36:54
  Speaker 1: light years across. That is not a typo. 10 billion
• 36:59
  Speaker 1: light years. In the perpendicular direction, its width measured roughly 7.2
• 37:05
  Speaker 1: billion light years. Its depth, the extent along the line
• 37:09
  Speaker 1: of sight, ran close to 1 billion light years. This
• 37:13
  Speaker 1: is not a flat sheet. It is not a two-dimensional wall.
• 37:17
  Speaker 2: In any meaningful sense.
• 37:19
  Speaker 1: It has substantial three-dimensional volume. A depth of nearly a
• 37:23
  Speaker 1: billion light years means the structure has real thickness. You
• 37:28
  Speaker 1: are not looking at a cosmic pancake. You are looking
• 37:31
  Speaker 1: at something more like an enormous dense region of space
• 37:35
  Speaker 1: with mass and extent in every direction. To get a
• 37:39
  Speaker 1: feel for what those numbers mean, consider the Milky Way.
• 37:43
  Speaker 1: Our galaxy stretches roughly 100,000 light years from edge to edge.
• 37:48
  Speaker 1: That feels enormous when you are thinking about it in
• 37:50
  Speaker 1: human terms. Light traveling for 100,000 years just across from
• 37:55
  Speaker 1: one side to the other. Now try to place that
• 37:58
  Speaker 1: galaxy against the length of this structure. To span 10
• 38:02
  Speaker 1: billion light years by lining up Milky Way galaxies side
• 38:06
  Speaker 1: by side, you would need roughly 94,000 of them, not 94.
• 38:12
  Speaker 1: Not 940, 94,000 galaxies, each one 100,000 light years wide,
• 38:19
  Speaker 1: placed end to end before you reach the other side.
• 38:22
  Speaker 1: The original paper included exactly that comparison. And it does
• 38:26
  Speaker 1: not get easier to absorb no matter how many times
• 38:29
  Speaker 1: you read it. Now hold the width in your mind
• 38:32
  Speaker 1: alongside the observable universe. The full sphere of the observable universe.
• 38:38
  Speaker 1: Everything humanity has ever been able to see or detect
• 38:42
  Speaker 1: or infer extends roughly 93 billion light years in diameter.
• 38:47
  Speaker 1: The structure found in that data runs 10 billion light
• 38:51
  Speaker 1: years along its longest axis. That is more than one-tenth
• 38:55
  Speaker 1: of the entire observable universe spanned by a single coherent overdensity.
• 39:00
  Speaker 1: If you shrank the observable universe down to the size
• 39:03
  Speaker 1: of a standard classroom, this structure would stretch across more
• 39:07
  Speaker 1: than one full wall. floor to ceiling, corner to corner.
• 39:12
  Speaker 1: Something worth understanding is what the team was actually measuring.
• 39:16
  Speaker 1: They were not looking at a picture of this structure.
• 39:19
  Speaker 1: They were looking at a statistical excess in the positions
• 39:22
  Speaker 1: of gamma ray bursts. An overdensity in a distribution is
• 39:26
  Speaker 1: not the same as a photograph. What it means is
• 39:29
  Speaker 1: that something in that region of the universe caused more
• 39:32
  Speaker 1: massive stars to form and explode than you would expect
• 39:35
  Speaker 1: if matter was spread evenly. More explosions in a given
• 39:39
  Speaker 1: region means more matter. More matter means structure. The team
• 39:43
  Speaker 1: was reading the skeleton of something enormous from the footprints
• 39:47
  Speaker 1: it left in the death counts of distant stars. That
• 39:50
  Speaker 1: is a remarkable piece of inference. The extent of the
• 39:53
  Speaker 1: structure was striking enough on its own. What compounded it
• 39:57
  Speaker 1: was the depth.
• 39:58
  Speaker 2: A depth of.
• 39:59
  Speaker 1: Nearly a billion light years is not a thin coincidence
• 40:02
  Speaker 1: of alignment. When objects at similar distances pile up across
• 40:07
  Speaker 1: a broad sky region, one possible explanation is that separate,
• 40:12
  Speaker 1: unrelated structures happen to sit at similar distances and overlap
• 40:16
  Speaker 1: in projection. But a billion light-year depth makes that explanation
• 40:21
  Speaker 1: difficult to sustain. Objects a billion light-years apart in depth
• 40:26
  Speaker 1: are genuinely separated in space. They're not casually superimposed. Something
• 40:33
  Speaker 1: had to account for why that entire volume was denser
• 40:36
  Speaker 1: than the surrounding regions at.
• 40:38
  Speaker 2: The same distance.
• 40:40
  Speaker 1: The team was not claiming a thin wall seen face-on.
• 40:44
  Speaker 1: They were claiming a thick three-dimensional excess of matter spanning
• 40:48
  Speaker 1: billions of light years in every direction. Put all of
• 40:52
  Speaker 1: those dimensions together and the conclusion is not ambiguous. The
• 40:57
  Speaker 1: structure being described was the largest discrete thing anyone had
• 41:01
  Speaker 1: ever proposed existed anywhere in the observable universe. Nothing in
• 41:06
  Speaker 1: the catalogue of known cosmic structures came close. A cluster
• 41:10
  Speaker 1: of that size, if genuine, would be the largest thing
• 41:13
  Speaker 1: anyone had ever found. To understand why the numbers stopped
• 41:17
  Speaker 1: the astronomical community cold, you need to know what had
• 41:20
  Speaker 1: been considered large before 2013. Astronomy has a habit of
• 41:25
  Speaker 1: humbling itself. Every generation of researchers draws a mental map
• 41:29
  Speaker 1: of the universe, decides where the edges of things are,
• 41:33
  Speaker 1: and then watches a new instrument or a new survey
• 41:36
  Speaker 1: erase those edges. Large-scale structure is where this pattern has
• 41:41
  Speaker 1: played out most dramatically. The story of how big the
• 41:44
  Speaker 1: universe's biggest features are is not a story of gradual refinement.
• 41:50
  Speaker 1: It is a story of repeated shocks, each one arriving
• 41:54
  Speaker 1: before the field had fully absorbed the last. The first
• 41:58
  Speaker 1: chapter starts in 1989. Margaret Geller and John Hutra were
• 42:03
  Speaker 1: mapping the positions of thousands of galaxies, building one of
• 42:07
  Speaker 1: the first real three-dimensional pictures of.
• 42:10
  Speaker 2: The nearby universe.
• 42:12
  Speaker 1: What came back from that survey was not what most
• 42:15
  Speaker 1: astronomers expected. Instead of a roughly uniform scattering of galaxies,
• 42:20
  Speaker 1: the map showed something long and coherent. A sheet of
• 42:24
  Speaker 1: galaxies stretching roughly 500 million light years across.
• 42:29
  Speaker 2: They called it the Great Wall.
• 42:31
  Speaker 1: Nothing that large had been identified before. The reaction was
• 42:36
  Speaker 1: not uniform excitement. Some researchers thought the feature was genuine.
• 42:41
  Speaker 1: Others argued it was an artifact of the survey's geometry,
• 42:45
  Speaker 1: a boundary effect, something that would dissolve if you extended
• 42:49
  Speaker 1: the map far enough in the right direction. The debate
• 42:53
  Speaker 1: had that particular texture that shows up whenever a discovery
• 42:57
  Speaker 1: is both surprising and hard to immediately confirm. But the
• 43:01
  Speaker 1: structure did not dissolve. It stayed in the data. 500
• 43:07
  Speaker 1: million light years is a number that does not announce
• 43:10
  Speaker 1: itself well. It needs a frame of reference. The Milky
• 43:14
  Speaker 1: Way is roughly 100,000 light years across. The distance to
• 43:19
  Speaker 1: the Andromeda Galaxy, our nearest large neighbor, is about 2.5
• 43:24
  Speaker 1: million light years. The distance to the nearest significant galaxy
• 43:28
  Speaker 1: cluster is tens of millions of light years. 500 million
• 43:33
  Speaker 1: light years is 5,000 times the diameter of the galaxy
• 43:38
  Speaker 1: you live in. That was the Great Wall. The field
• 43:41
  Speaker 1: absorbed it, eventually, and moved on. Then, in 2005, a
• 43:46
  Speaker 1: team analyzing data from the Sloan Digital Sky Survey found
• 43:51
  Speaker 1: something bigger. The Sloan Great Wall came in at 1.37
• 43:56
  Speaker 1: billion light years in length, nearly three times the size
• 44:00
  Speaker 1: of the Galahadra structure. It stretched across a much larger
• 44:04
  Speaker 1: slice of sky than anything previously cataloged. It held the
• 44:08
  Speaker 1: record for nearly a decade. A billion light years plus.
• 44:13
  Speaker 1: The field absorbed this too, not without debate, but eventually
• 44:17
  Speaker 1: it settled into the textbooks as the largest confirmed structure
• 44:21
  Speaker 1: in the universe. For ten years that designation stuck. Here
• 44:26
  Speaker 1: is something worth noticing about that progression. Each record holder
• 44:30
  Speaker 1: was not just incrementally larger than the previous one. Going
• 44:34
  Speaker 1: from the Great Wall to the Sloan Great Wall meant
• 44:36
  Speaker 1: nearly tripling the size of the largest known structure in
• 44:39
  Speaker 1: the span of about 15 years. That is not gradual refinement.
• 44:44
  Speaker 1: That is the survey getting deeper and wider and revealing
• 44:48
  Speaker 1: something the older surveys could not reach. It raised an
• 44:51
  Speaker 1: uncomfortable background question, one that most researchers preferred not to
• 44:55
  Speaker 1: press too hard, which was whether the records would keep
• 44:59
  Speaker 1: falling as the surveys kept improving. In 2012, they fell
• 45:02
  Speaker 1: again A team led by Roger Klaus announced the huge
• 45:07
  Speaker 1: large quasar group, a clustering of 73 quasars spread across
• 45:11
  Speaker 1: a region roughly 4 billion light years, in its longest dimension.
• 45:16
  Speaker 1: Quasars are the extremely luminous cores of distant galaxies, powered
• 45:21
  Speaker 1: by supermassive black holes consuming enormous amounts of material. They
• 45:26
  Speaker 1: can be seen from much farther away than ordinary galaxies,
• 45:30
  Speaker 1: which makes them useful for mapping structure at greater depths.
• 45:34
  Speaker 1: The huge LQG was three times larger than the Sloan
• 45:38
  Speaker 1: Great Wall. It arrived in the literature like a stone
• 45:42
  Speaker 1: thrown into still water. Reactions ranged from fascination to outright skepticism.
• 45:48
  Speaker 1: Some researchers argued that quasar groups are not the same
• 45:51
  Speaker 1: kind of structure as a galaxy wall, that they are
• 45:54
  Speaker 1: looser and less physically coherent, and that calling the huge
• 45:58
  Speaker 1: LQG a single structure was a question of definition as
• 46:03
  Speaker 1: much as observation. Others pointed out that even accounting for
• 46:07
  Speaker 1: those objections, the clustering was real and the scale was
• 46:11
  Speaker 1: difficult to explain away. The huge LQG controversy had barely
• 46:16
  Speaker 1: settled into a low simmer when the 2013 results arrived.
• 46:21
  Speaker 1: The Hercules-Corona-Borealis Great Wall was not found through galaxy surveys
• 46:26
  Speaker 1: or quasar catalogues. It came from a completely different kind
• 46:30
  Speaker 1: of observation. which made direct comparison slightly complicated. But the
• 46:36
  Speaker 1: size was not complicated at all. 10 billion light years
• 46:40
  Speaker 1: in its longest dimension. 7 billion wide. Nearly a billion thick.
• 46:46
  Speaker 1: Against the previous record of 4 billion light years, that
• 46:50
  Speaker 1: number does not feel like a new entry in the
• 46:52
  Speaker 1: same list. It feels like a different list entirely. Put
• 46:56
  Speaker 1: it in plain terms. The Sloan Great Wall. which had
• 47:00
  Speaker 1: held the record for a decade, measured 1.37 billion light
• 47:05
  Speaker 1: years across. The Hercules-Corona-Borealis Great Wall measured roughly 10 billion.
• 47:13
  Speaker 1: That is not 10 or 20% larger, it is almost
• 47:16
  Speaker 1: 8 times larger. The huge LQG, which was already controversial
• 47:22
  Speaker 1: for being too big to sit comfortably in standard models,
• 47:26
  Speaker 1: measured about 4 billion light years. The Hercules-Corona-Borealis Great Wall
• 47:32
  Speaker 1: was more than twice that size. The community had spent
• 47:35
  Speaker 1: years debating whether a 4 billion might-year structure could be real.
• 47:40
  Speaker 1: Now there was a structure claiming to be 10 billion,
• 47:43
  Speaker 1: found through a different method, in a different kind of data,
• 47:47
  Speaker 1: at a different depth in the universe. The pattern of
• 47:51
  Speaker 1: shock and absorption that had played out with the Great
• 47:54
  Speaker 1: Wall and the Sloan Great Wall had always involved some
• 47:57
  Speaker 1: time to process. Each new record arrived, triggered debate, and
• 48:02
  Speaker 1: eventually settled into the accepted picture. What made 2013 different
• 48:08
  Speaker 1: was the size of the gap. You could plausibly trace
• 48:11
  Speaker 1: a line of discovery from 500 million to 1.37 billion
• 48:16
  Speaker 1: to 4 billion and tell a story of gradual expansion.
• 48:20
  Speaker 1: You could not easily extend that line to 10 billion
• 48:24
  Speaker 1: without stopping to ask whether something was fundamentally wrong with
• 48:27
  Speaker 1: the picture. The Hercules-Corona-Borealis Great War was not slightly bigger
• 48:32
  Speaker 1: than these previous record holders. It was several times larger,
• 48:37
  Speaker 1: and that gap was exactly the problem. At the heart
• 48:40
  Speaker 1: of modern cosmology is an assumption so fundamental that most
• 48:44
  Speaker 1: of the people working in the field barely stop to
• 48:47
  Speaker 1: examine it consciously. It does not have a dramatic name.
• 48:52
  Speaker 1: does not come with a story of its discovery. It
• 48:55
  Speaker 1: is simply called the cosmological principle and it says that
• 48:59
  Speaker 1: the universe, smoothed out over large enough scales, is homogeneous
• 49:04
  Speaker 1: and isotropic. Homogeneous means the same everywhere. Isotropic means the
• 49:11
  Speaker 1: same in every direction. If you could take a big
• 49:14
  Speaker 1: enough chunk of the universe and compare it to any
• 49:17
  Speaker 1: other chunk of the same size, they would look essentially identical.
• 49:22
  Speaker 1: No special places, no special directions, everywhere, roughly, equal. That
• 49:29
  Speaker 1: idea did not come from a single observation or a
• 49:32
  Speaker 1: single experiment. It came from something older and more philosophical.
• 49:37
  Speaker 1: When Copernicus argued that Earth was not the center of
• 49:40
  Speaker 1: the solar system, he was making a claim that went
• 49:43
  Speaker 1: beyond orbital mechanics. He was saying that we are not special,
• 49:48
  Speaker 1: that the place we happen to occupy does not hold
• 49:51
  Speaker 1: a privileged position in the structure of things. Astronomers inherited
• 49:55
  Speaker 1: that logic and applied it to the universe itself.
• 49:58
  Speaker 2: If you follow it.
• 49:59
  Speaker 1: To its conclusion, it tells you that any sufficiently large
• 50:03
  Speaker 1: piece of the cosmos should be representative of the whole.
• 50:07
  Speaker 1: No region should be dramatically richer or emptier than any other,
• 50:11
  Speaker 1: once you zoom out far enough. That is the Copernican
• 50:14
  Speaker 1: argument extended to its limit, and it became the philosophical
• 50:18
  Speaker 1: backbone of modern cosmology. It is not just philosophy though.
• 50:23
  Speaker 1: The cosmological principle has evidence behind it. The most powerful
• 50:28
  Speaker 1: piece of that evidence is the cosmic microwave background. This
• 50:32
  Speaker 1: is the faint flow of radiation left over from the
• 50:35
  Speaker 1: early universe. about 380,000 years after the Big Bang, when
• 50:40
  Speaker 1: the cosmos cooled enough for atoms to form and light
• 50:43
  Speaker 1: to travel freely for the first time. When you map
• 50:46
  Speaker 1: this radiation across the entire sky, it is extraordinarily uniform.
• 50:52
  Speaker 1: The temperature barely varies by more than one part in 100,000
• 50:56
  Speaker 1: from one region to the next. That smoothness is not
• 51:00
  Speaker 1: an accident. It is exactly what you expect from a
• 51:03
  Speaker 1: universe that started homogenous. and has stayed broadly homogenous ever since.
• 51:08
  Speaker 1: The cosmic microwave background is one of the most precisely
• 51:12
  Speaker 1: measured things in all of science and it tells you
• 51:15
  Speaker 1: in the most direct terms possible that the early universe
• 51:19
  Speaker 1: was not lumpy in any dramatic way. The standard cosmological
• 51:23
  Speaker 1: model known as Lambda CDM is built directly on top
• 51:28
  Speaker 1: of this principle. Lambda refers to the cosmological constant which
• 51:32
  Speaker 1: drives the accelerating expansion of the universe CDM stands for
• 51:37
  Speaker 1: Cold Dark Matter. Together, they form a framework that has
• 51:41
  Speaker 1: been stunningly successful. It correctly predicts the large-scale distribution of galaxies.
• 51:47
  Speaker 1: It accounts for the observed abundance of light elements.
• 51:51
  Speaker 2: It matches the.
• 51:51
  Speaker 1: Precise details of the microwave background's temperature fluctuations. Every major
• 51:57
  Speaker 1: observational test that astronomers have thrown at it over the
• 52:00
  Speaker 1: past few decades has come back more or less confirming
• 52:03
  Speaker 1: the model. That is an extraordinary track record. And the
• 52:08
  Speaker 1: cosmological principle is not a peripheral assumption in that model.
• 52:12
  Speaker 2: It is the foundation.
• 52:14
  Speaker 1: Pull it out and the entire mathematical structure built on
• 52:17
  Speaker 1: top of it requires rethinking from the ground up. So
• 52:21
  Speaker 1: the question becomes practical. At what scale does the principle
• 52:25
  Speaker 1: actually hold? At the scale of a single galaxy, the
• 52:29
  Speaker 1: universe is obviously not homogenous. Galaxies are dense. The space
• 52:34
  Speaker 1: between them is nearly empty. At the scale of galaxy clusters,
• 52:38
  Speaker 1: still not homogenous. Clusters are denser than the voids surrounding them.
• 52:43
  Speaker 1: At the scale of superclusters and filaments, still lumpy. The
• 52:48
  Speaker 1: cosmic web, with all its threads and nodes and enormous
• 52:52
  Speaker 1: empty spaces, is visibly structured. But cosmologists have expected all
• 52:57
  Speaker 1: of this to average out above a certain threshold. Run
• 53:00
  Speaker 1: the numbers on the standard model. you get a prediction
• 53:04
  Speaker 1: somewhere around 300 to 400 million light years the universe
• 53:09
  Speaker 1: should stop looking structured and start looking smooth above that
• 53:14
  Speaker 1: scale any large cube of space you sam please should
• 53:18
  Speaker 1: contain roughly the same density of matter as any other
• 53:22
  Speaker 1: large cube the lumps wash out the web fades into
• 53:27
  Speaker 1: a uniform background This is what most of the field
• 53:30
  Speaker 1: has taken as the working answer to the question. 3
• 53:33
  Speaker 1: to 400 million light years is the scale of homogeneity.
• 53:38
  Speaker 1: Below it, structure exists and is expected. Above it, the
• 53:43
  Speaker 1: universe irons itself flat. And when you look at the
• 53:46
  Speaker 1: data from galaxy surveys on those scales, this is broadly
• 53:50
  Speaker 1: what you see. The largest known structures before the Hercules-Corona-Borealis
• 53:56
  Speaker 1: Great Wall fell in the range of 1 to 4
• 53:58
  Speaker 1: billion light years, which already stretched the expectation uncomfortably. But
• 54:04
  Speaker 1: they were debated, they were absorbed, and the model survived.
• 54:08
  Speaker 1: Now here is the problem. Standard inflationary models, which describe
• 54:13
  Speaker 1: the very first moments of the universe's existence, make a
• 54:17
  Speaker 1: specific prediction about how large coherent structures can get.
• 54:21
  Speaker 2: Inflation was a.
• 54:22
  Speaker 1: Period of extraordinarily rapid expansion in the first fractions of
• 54:27
  Speaker 1: a second after the Big Bang. It stretched quantum scale
• 54:31
  Speaker 1: fluctuations to cosmological sizes, seeding the density variations that would
• 54:37
  Speaker 1: eventually grow into everything you see when you look at.
• 54:40
  Speaker 2: The night sky.
• 54:42
  Speaker 1: Those fluctuations had a particular statistical character. and that character
• 54:47
  Speaker 1: places a hard ceiling on the size of structures that
• 54:50
  Speaker 1: gravity can assemble from them. Most calculations put that ceiling
• 54:55
  Speaker 1: at roughly 1.2 billion light years. That is not a
• 54:59
  Speaker 1: round number chosen for convenience. It falls out of the
• 55:03
  Speaker 1: mathematics of how inflationary perturbations evolve. The Sloan Great Wall
• 55:08
  Speaker 1: at 1.37 billion light years was already nudging that boundary.
• 55:14
  Speaker 1: that made people uncomfortable. But 1.37 billion is close enough
• 55:19
  Speaker 1: to 1.2 billion that you could argue the models were
• 55:23
  Speaker 1: still roughly right. You could accommodate it with some adjustment
• 55:27
  Speaker 1: at the margins. What you cannot accommodate with a margin
• 55:31
  Speaker 1: adjustment is a structure 10 billion light years across. That
• 55:36
  Speaker 1: is not a small violation of the boundary. It is
• 55:40
  Speaker 1: a violation by nearly an order of magnitude A structure
• 55:44
  Speaker 1: that large cannot grow out of the density fluctuations that
• 55:47
  Speaker 1: inflation is supposed.
• 55:49
  Speaker 2: To have produced.
• 55:50
  Speaker 1: The initial conditions required to form something so coherent across
• 55:55
  Speaker 1: such a vast scale are not consistent with the smooth,
• 55:59
  Speaker 1: nearly uniform early universe that the microwave background shows us.
• 56:04
  Speaker 1: For both things to be true simultaneously, something in the
• 56:08
  Speaker 1: picture has to be wrong. That is what makes this
• 56:11
  Speaker 1: discovery so uncomfortable for theoretical cosmology. It is not that
• 56:16
  Speaker 1: the Hercules-Coronaborialis Great Wall is merely large. It is that
• 56:20
  Speaker 1: its existence, if confirmed, demands an explanation that the standard
• 56:25
  Speaker 1: framework does not currently provide. The Hercules-Coronaborialis Great Wall, if
• 56:31
  Speaker 1: it is real, sits well outside the scale where homogeneity
• 56:35
  Speaker 1: is supposed to have taken hold. And that is not
• 56:38
  Speaker 1: a comfortable place for something to sit. Not everyone accepted
• 56:42
  Speaker 1: the discovery. The reaction inside the astronomical community was not
• 56:48
  Speaker 1: simple amazement. It was complicated, fractured, and in some corners
• 56:53
  Speaker 1: genuinely hostile. Not toward the researchers personally, but toward the
• 56:58
  Speaker 1: claim itself. A structure 10 billion light years across sits
• 57:03
  Speaker 1: so far outside the boundaries of what the standard model permits.
• 57:07
  Speaker 1: that accepting it at face value would mean accepting that
• 57:10
  Speaker 1: something fundamental about cosmology is broken. For a field built
• 57:14
  Speaker 1: on the cosmological principle, that is not a small concession.
• 57:18
  Speaker 1: The first wave of skepticism came from theorists. If the
• 57:22
  Speaker 1: universe is supposed to be homogeneous above roughly 300 to
• 57:26
  Speaker 1: 400 million light years, then a coherent structure 10 billion
• 57:30
  Speaker 1: light years long is not just an outlier, it is
• 57:33
  Speaker 1: a different category of object entirely. Some researchers pointed out
• 57:38
  Speaker 1: that no known physical mechanism could plausibly organize matter on
• 57:42
  Speaker 1: that scale in the time the universe has had.
• 57:44
  Speaker 2: To work with.
• 57:45
  Speaker 1: Gravity builds structure, but it builds it slowly, seeding small
• 57:50
  Speaker 1: over densities and growing them over billions of years into filaments, walls.
• 57:55
  Speaker 2: And clusters.
• 57:57
  Speaker 1: To produce something the size of the Hercules-Corona-Borealis Great Wall,
• 58:02
  Speaker 1: through ordinary gravitational collapse would require initial conditions that the
• 58:06
  Speaker 1: Big Bang simply does not appear to have provided. Were
• 58:10
  Speaker 1: the observations correct, or was the interpretation the problem? But
• 58:15
  Speaker 1: the deeper and more pointed criticism was not about the physics.
• 58:20
  Speaker 1: It was about the tool. Gamma ray bursts are not
• 58:23
  Speaker 1: galaxy surveys, and that difference matters more than it might
• 58:27
  Speaker 1: first appear. A galaxy survey maps the sky by detecting
• 58:31
  Speaker 1: light from millions of galaxies. Using carefully characterized instruments with
• 58:36
  Speaker 1: well-understood selection effects, the surveys are designed from the start
• 58:41
  Speaker 1: to be as uniform as possible. GRB catalogs are built
• 58:45
  Speaker 1: from nothing like that process. A gamma-ray burst is detected
• 58:49
  Speaker 1: when a satellite happens to be looking in the right
• 58:52
  Speaker 1: direction at the right moment. and when the burst is
• 58:55
  Speaker 1: bright enough to cross the detection threshold of whichever instrument
• 58:59
  Speaker 1: is operating at the time. That last part is important.
• 59:03
  Speaker 1: Different satellites have different sensitivities. NASA's Swift Gamma Ray Burst
• 59:09
  Speaker 1: mission was the primary source of the data behind this discovery.
• 59:13
  Speaker 1: But the catalog also incorporated observations from other instruments and
• 59:18
  Speaker 1: ground based optical telescopes used to measure redshifts from afterglows.
• 59:23
  Speaker 1: Each of those instruments has its own observing history, its
• 59:27
  Speaker 1: own biases, its own gaps, Swift does not stare at
• 59:31
  Speaker 1: one part of the sky. It sweeps, responds to triggers,
• 59:36
  Speaker 1: and follows up on alerts. Its coverage is episodic and uneven.
• 59:41
  Speaker 1: Some regions of the sky simply accumulate more burst detections
• 59:45
  Speaker 1: over time because of how the satellite's orbit and pointing
• 59:49
  Speaker 1: history interact with what happens to be out there. Others
• 59:53
  Speaker 1: are systematically undersampled. What this means in practice is that
• 59:58
  Speaker 1: the raw number of gamma ray bursts detected in any
• 1:00:01
  Speaker 1: patch of sky is not a clean measurement of how
• 1:00:04
  Speaker 1: many gamma ray bursts actually occurred there. It is a
• 1:00:07
  Speaker 1: measurement of how many bursts occurred there and were detectable
• 1:00:11
  Speaker 1: by the instruments that were running and were bright enough
• 1:00:13
  Speaker 1: to trigger the detectors and were followed up quickly enough
• 1:00:17
  Speaker 1: to get a redshift. Each of those filters introduces a
• 1:00:20
  Speaker 1: potential bias. if those biases happen to concentrate detections in
• 1:00:25
  Speaker 1: one region of the sky at one range of redshifts,
• 1:00:28
  Speaker 1: the result can look like a genuine overdensity even when
• 1:00:32
  Speaker 1: the underlying distribution of gamma ray bursts is perfectly uniform.
• 1:00:36
  Speaker 1: This is what skeptics called observer bias, and the concern
• 1:00:40
  Speaker 1: was specific. At a redshift of around 2, The ability
• 1:00:44
  Speaker 1: to measure a reliable redshift from a burst's optical afterglow
• 1:00:48
  Speaker 1: depends heavily on whether ground-based telescopes could respond quickly enough
• 1:00:53
  Speaker 1: after the initial detection. That response time is not uniform
• 1:00:57
  Speaker 1: around the sky. Some observatories are better positioned to catch
• 1:01:02
  Speaker 1: afterglows from certain sky regions. Others have gaps in their coverage.
• 1:01:07
  Speaker 1: If the Hercules and Corona Borealis region happened to be
• 1:01:10
  Speaker 1: better covered by follow-up telescopes during the period of the survey,
• 1:01:14
  Speaker 1: more bursts in that region would accumulate confirmed redshifts. More
• 1:01:19
  Speaker 1: confirmed redshifts means more data points. More data points in
• 1:01:24
  Speaker 1: one patch of sky looks exactly like a clustering signal.
• 1:01:28
  Speaker 1: The researchers who raised these concerns were not dismissing the work.
• 1:01:32
  Speaker 1: Most of them acknowledged that the original team had done
• 1:01:35
  Speaker 1: careful analysis had cross-checked their results and had tried to
• 1:01:39
  Speaker 1: account for known biases. The dispute was about whether the
• 1:01:43
  Speaker 1: accounting had gone far enough. It is genuinely difficult to
• 1:01:47
  Speaker 1: correct for selection effects you cannot fully characterize. Some of
• 1:01:52
  Speaker 1: the biases built into GRB catalogs are well understood and.
• 1:01:56
  Speaker 2: Can be modeled.
• 1:01:57
  Speaker 1: Others are subtle, buried in the specific history of how
• 1:02:01
  Speaker 1: each instrument operated. and how follow-up campaigns were coordinated across
• 1:02:06
  Speaker 1: different facilities over more than a decade. Digging all of
• 1:02:09
  Speaker 1: that out and removing its fingerprint from the data is
• 1:02:13
  Speaker 1: not straightforward. Reasonable people can look at the same catalogue
• 1:02:17
  Speaker 1: and disagree about whether the corrections applied were sufficient. There
• 1:02:22
  Speaker 1: was also a quieter question running underneath all of this.
• 1:02:26
  Speaker 1: Even setting aside the observational concerns, what would it mean
• 1:02:30
  Speaker 1: for a structure this large to exist? If you accept
• 1:02:34
  Speaker 1: the Hercules-Corona-Borealis Great Wall as a genuine physical object, you
• 1:02:39
  Speaker 1: are not just adding a new entry to the record books.
• 1:02:43
  Speaker 1: You are acknowledging that the universe organized itself on a
• 1:02:46
  Speaker 1: scale where the standard model says organization should not be possible.
• 1:02:51
  Speaker 1: That is not a conclusion most cosmologists reach easily. The
• 1:02:55
  Speaker 1: cosmological principle is not a minor convenience. It is the
• 1:02:59
  Speaker 1: scaffolding that holds together almost every major result in modern cosmology.
• 1:03:05
  Speaker 1: Pulling it loose at 10 billion light years has consequences
• 1:03:08
  Speaker 1: that ripple through decades of theory. So the mood in
• 1:03:12
  Speaker 1: the field was something like cautious refusal. Not rejection, not acceptance,
• 1:03:17
  Speaker 1: but a sustained demand for a higher standard of evidence
• 1:03:20
  Speaker 1: before anyone was prepared to start rewriting the textbooks.
• 1:03:24
  Speaker 2: The data was interesting.
• 1:03:26
  Speaker 1: The signal was real in some sense, but whether it
• 1:03:29
  Speaker 1: pointed at a genuine physical structure or at the imperfect
• 1:03:33
  Speaker 1: fingerprint of how the survey was assembled, that remained an
• 1:03:37
  Speaker 1: open question. What researchers needed was not more argument from
• 1:03:41
  Speaker 1: either side.
• 1:03:42
  Speaker 2: But better data, and that had not yet arrived.
• 1:03:46
  Speaker 1: The core of the scientific dispute came down to something
• 1:03:49
  Speaker 1: that sounds dry and technical, but turns out to be
• 1:03:52
  Speaker 1: genuinely consequential. The original team placed the probability of the
• 1:03:57
  Speaker 1: observed clustering happening by random chance at less than 1
• 1:04:00
  Speaker 1: tenth of 1%. That is a number that sounds decisive.
• 1:04:05
  Speaker 1: In most scientific contexts, a result that strong would end
• 1:04:08
  Speaker 1: the argument. You found something.
• 1:04:11
  Speaker 2: Move on.
• 1:04:12
  Speaker 1: But critics looked at how that number was calculated and
• 1:04:16
  Speaker 1: argued the methodology had buried several assumptions that, once pulled
• 1:04:20
  Speaker 1: into the open, changed everything. The debate that followed was
• 1:04:24
  Speaker 1: not about whether the data existed. The data existed. It
• 1:04:28
  Speaker 1: was about what the data actually meant. And that turned
• 1:04:31
  Speaker 1: out to be a much harder question. Here is where
• 1:04:34
  Speaker 1: the numbers came from. When you want to test whether
• 1:04:37
  Speaker 1: a cluster of objects is real, you compare what you
• 1:04:40
  Speaker 1: observed to what you would expect from a uniform, random distribution.
• 1:04:45
  Speaker 1: The gap between those two things is your signal. The
• 1:04:49
  Speaker 1: bigger the gap, the less likely it is that chance
• 1:04:52
  Speaker 1: produced it. This sounds straightforward. The problem is that the
• 1:04:56
  Speaker 1: expected background is not something you measure directly. You calculate it.
• 1:05:02
  Speaker 1: And the way you calculate it depends on choices that
• 1:05:05
  Speaker 1: are not written in the laws of physics. They are
• 1:05:08
  Speaker 1: judgment calls. How large a region of sky do you
• 1:05:12
  Speaker 1: use to define the background? Which redshift range do you include?
• 1:05:17
  Speaker 1: How do you weight bursts from regions of sky with
• 1:05:20
  Speaker 1: better or worse observational coverage? Each of these decisions shifts
• 1:05:25
  Speaker 1: the baseline. Shift the bar dars, saline and the gap
• 1:05:29
  Speaker 1: between expected and observed changes. Change the gap and the
• 1:05:34
  Speaker 1: probability changes with it. The 2015 critical paper zeroed in
• 1:05:39
  Speaker 1: on exactly this problem. The authors argued that the original
• 1:05:43
  Speaker 1: analysis had used a method for estimating the background distribution
• 1:05:48
  Speaker 1: that did not properly account for non-uniform sky coverage. Gamma
• 1:05:52
  Speaker 1: ray burst surveys are not clean. Different parts of the
• 1:05:56
  Speaker 1: sky have been watched more carefully than others. Some regions
• 1:06:00
  Speaker 1: have dense observational histories going back years. Others are sparsely sampled.
• 1:06:05
  Speaker 1: If you calculate your expected background assuming uniform coverage and
• 1:06:10
  Speaker 1: the actual coverage was not uniform, your signal can look
• 1:06:14
  Speaker 1: stronger than it really is. Patches of sky that were
• 1:06:17
  Speaker 1: observed more often will naturally contain more detected bursts. That
• 1:06:22
  Speaker 1: is not clustering. That is just telescope time. The critics recalculated.
• 1:06:28
  Speaker 1: After correcting for what they saw as these methodological problems,
• 1:06:32
  Speaker 1: the probability of the clustering occurring by chance came out
• 1:06:35
  Speaker 1: somewhere between 5 and 20%, not less than a fraction
• 1:06:39
  Speaker 1: of a percent, between 5 and 20. That range does
• 1:06:44
  Speaker 1: not sound like a discovery. That range sounds like noise
• 1:06:47
  Speaker 1: you cannot explain yet. It is the kind of number
• 1:06:51
  Speaker 1: that makes scientists shrug and ask for more data, rather
• 1:06:55
  Speaker 1: than call a press conference. What makes this genuinely difficult
• 1:06:59
  Speaker 1: is that neither side was wrong in any simple sense.
• 1:07:02
  Speaker 1: The original team had made defensible choices. The critics had
• 1:07:06
  Speaker 1: made equally defensible corrections. The disagreement was not about arithmetic.
• 1:07:12
  Speaker 1: It was about what the right setup for the problem
• 1:07:14
  Speaker 1: actually was. You can think of it like measuring the
• 1:07:17
  Speaker 1: temperature in a room. If you hold the thermometer near
• 1:07:20
  Speaker 1: a window, you get one number. If you hold it
• 1:07:23
  Speaker 1: in the center of the room, you get another. Both
• 1:07:26
  Speaker 1: numbers are accurate. Which one represents the room depends on
• 1:07:30
  Speaker 1: what you are trying to measure, and that question requires
• 1:07:33
  Speaker 1: judgment that the thermometer itself cannot answer. The redshift bin
• 1:07:38
  Speaker 1: choice was another fault line. The original analysis concentrated on
• 1:07:43
  Speaker 1: bursts at a particular redshift range, roughly Z equals 2.
• 1:07:48
  Speaker 1: where the clustering appeared strongest. Critics pointed out that if
• 1:07:52
  Speaker 1: you go looking for clustering in a specific slice of
• 1:07:55
  Speaker 1: the universe and then calculate how unlikely that clustering is
• 1:07:59
  Speaker 1: without accounting for the fact that you chose that slice
• 1:08:02
  Speaker 1: because it looked unusual, you are going to underestimate the
• 1:08:06
  Speaker 1: probability of finding something by chance. Statisticians call this the
• 1:08:11
  Speaker 1: look elsewhere effect. It is the same problem that makes
• 1:08:14
  Speaker 1: it easy to find patterns in random data when you
• 1:08:17
  Speaker 1: are free to search wherever you want and only report
• 1:08:20
  Speaker 1: what you found. The original team disputed the severity of
• 1:08:24
  Speaker 1: this concern in their specific case, but the point was Lee,
• 1:08:28
  Speaker 1: get him it enough, that it could not simply be
• 1:08:31
  Speaker 1: waved away. The original researchers responded to the criticism carefully.
• 1:08:37
  Speaker 1: They stood behind their methodology. They had not, in their view,
• 1:08:41
  Speaker 1: made the errors they were being accused of. They had
• 1:08:45
  Speaker 1: considered sky coverage. They had not simply mined the data
• 1:08:49
  Speaker 1: for the strongest signal without accounting for the search, but
• 1:08:53
  Speaker 1: they also acknowledged that the uncertainties were real. This is
• 1:08:58
  Speaker 1: what honest science looks like when the data is imperfect
• 1:09:02
  Speaker 1: you defend what you did while recognizing that reasonable people
• 1:09:06
  Speaker 1: looking at the same data set are going to arrive
• 1:09:10
  Speaker 1: at different answers depending on the choices they make neither
• 1:09:14
  Speaker 1: side was being reckless both sides were wrestling with the
• 1:09:18
  Speaker 1: genuine difficulty of extracting a clean signal from a messy, incomplete,
• 1:09:24
  Speaker 1: human-assembled sea of cosmic explosions.
• 1:09:29
  Speaker 2: What it came down to was this.
• 1:09:32
  Speaker 1: A probability below 0.1% tells you the universe almost certainly
• 1:09:37
  Speaker 1: contains a real structure. A probability of 15% tells you
• 1:09:42
  Speaker 1: the universe might contain a real structure, or you might
• 1:09:45
  Speaker 1: just be looking at an imperfect dataset from an unlucky angle.
• 1:09:49
  Speaker 1: These are not the same conclusion. The entire scientific weight
• 1:09:53
  Speaker 1: of the discovery pivots on which of those numbers is
• 1:09:56
  Speaker 1: closer to the truth. And the answer depends on statistical
• 1:10:00
  Speaker 1: choices that the data itself cannot adjudicate. That is the
• 1:10:04
  Speaker 1: situation the field was left in.
• 1:10:07
  Speaker 2: Not fraud. Not error. Not a failure of imagination.
• 1:10:12
  Speaker 1: Just a set of legitimate, unresolved technical disagreements about how
• 1:10:17
  Speaker 1: to handle data that was never designed to answer this
• 1:10:20
  Speaker 1: specific question. The clustering was there, whether it meant something real,
• 1:10:26
  Speaker 1: or whether it was an artifact of how the sky
• 1:10:29
  Speaker 1: had been watched, remained genuinely open. In science, a disagreement
• 1:10:35
  Speaker 1: this sustained, without a clean resolution, is often where the
• 1:10:39
  Speaker 1: most important work eventually happens. While the critics were making
• 1:10:43
  Speaker 1: their arguments, separate groups of researchers went back to the
• 1:10:47
  Speaker 1: same data with different methods and found the same thing
• 1:10:51
  Speaker 1: this is worth pausing on because it matters how science
• 1:10:55
  Speaker 1: actually works here when a single team produces a single
• 1:10:59
  Speaker 1: result using a single method skepticism is the correct response
• 1:11:04
  Speaker 1: one set of hands one set of choices one chance
• 1:11:07
  Speaker 1: for something to go subtly wrong what changes the picture
• 1:11:11
  Speaker 1: is independent confirmation different teams different tools, different assumptions, and
• 1:11:17
  Speaker 1: if they all keep landing in the same place, that
• 1:11:20
  Speaker 1: is no longer a methodology story. That is starting to look.
• 1:11:24
  Speaker 2: Like a real signal.
• 1:11:25
  Speaker 1: Several groups took that exact approach. They pulled the gamma
• 1:11:29
  Speaker 1: ray burst catalogs, applied their own statistical frameworks, went looking
• 1:11:35
  Speaker 1: for the overdensity the original team had reported. Some used
• 1:11:39
  Speaker 1: nearest neighbor tests, comparing the distance between observed bursts, to
• 1:11:44
  Speaker 1: what a random distribution would produce. Others used angular correlation functions.
• 1:11:50
  Speaker 1: That measure whether bursts at similar redshifts cluster together more
• 1:11:54
  Speaker 1: tightly than expected across the sky. These are not small
• 1:11:58
  Speaker 1: variations on the same method. They are fundamentally different ways
• 1:12:03
  Speaker 1: of asking the same question. And they kept returning the
• 1:12:06
  Speaker 1: same answer. Something in that region of the sky was
• 1:12:10
  Speaker 1: denser than background. The clustering was there. What made this
• 1:12:14
  Speaker 1: striking was not just that the signal survived a different test,
• 1:12:18
  Speaker 1: it was that the signal survived attempts to break it.
• 1:12:22
  Speaker 1: Researchers tried restricting the sample to only the brightest gamma
• 1:12:25
  Speaker 1: ray bursts, the ones most reliably detected regardless of which
• 1:12:30
  Speaker 1: satellite happened to be watching. The clustering was still there.
• 1:12:34
  Speaker 1: They tried the opposite, dropping the brightest events and keeping
• 1:12:38
  Speaker 1: only the moderate ones. reducing the influence of any particularly
• 1:12:43
  Speaker 1: dramatic outliers.
• 1:12:44
  Speaker 2: Still there. They looked at subsets based on the quality.
• 1:12:48
  Speaker 1: Of the redshift measurement, keeping only the bursts whose distances
• 1:12:53
  Speaker 1: were most precisely known and discarding the ambiguous cases.
• 1:12:57
  Speaker 2: Still there.
• 1:12:59
  Speaker 1: Each time someone tightened the sample in a way that
• 1:13:01
  Speaker 1: should have weakened a statistical artifact, the clustering. Gee. Held.
• 1:13:07
  Speaker 1: That pattern is exactly what distinguishes a real physical structure
• 1:13:12
  Speaker 1: from an observational bias. A sampling artefact is fragile. It
• 1:13:17
  Speaker 1: depends on the specific quirks of the dataset that produced it,
• 1:13:21
  Speaker 1: the particular satellites involved, the particular sky coverage gaps, the
• 1:13:27
  Speaker 1: particular years of observation. Pull on it in the right way,
• 1:13:32
  Speaker 1: restrict the sample, change the selection criteria. it tends to
• 1:13:36
  Speaker 1: fall apart. A genuine overdensity in the distribution of matter
• 1:13:41
  Speaker 1: does not care how you slice the catalogue. It is
• 1:13:45
  Speaker 1: there because the matter is there, and no amount of
• 1:13:48
  Speaker 1: methodological pruning makes it disappear. One group pushed further and
• 1:13:53
  Speaker 1: looked at whether the angular shape of the overdensity was
• 1:13:56
  Speaker 1: consistent across different statistical approaches. The original team had described
• 1:14:02
  Speaker 1: a region spanning roughly the constellations Hercules and Corona Borealis,
• 1:14:07
  Speaker 1: but extending in the angular direction toward Boötes and Gemini
• 1:14:11
  Speaker 1: as well. When independent researchers mapped the overdensity using their
• 1:14:16
  Speaker 1: own boundary definitions, they were not drawing identical outlines. But
• 1:14:21
  Speaker 1: the core of the excess, the region where the gamma
• 1:14:25
  Speaker 1: ray burst density was highest relative to background, came back
• 1:14:29
  Speaker 1: in essentially the same part of the sky. The shape
• 1:14:32
  Speaker 1: was not perfectly reproducible because different methods define edges differently,
• 1:14:38
  Speaker 1: but the center held.
• 1:14:40
  Speaker 2: This is not the same as proof. It has to
• 1:14:42
  Speaker 2: be said plainly.
• 1:14:44
  Speaker 1: None of these independent analyses closed the case. The core uncertainty,
• 1:14:49
  Speaker 1: whether gamma-ray burst surveys are uniform enough to support this
• 1:14:53
  Speaker 1: kind of structural inference at all, did not evaporate. because
• 1:14:57
  Speaker 1: multiple teams found the same clustering. If there is a
• 1:15:00
  Speaker 1: systematic bias baked into the catalogs themselves, independent teams working
• 1:15:06
  Speaker 1: from those same catalogs will reproduce it faithfully. Finding the
• 1:15:10
  Speaker 1: same pattern in the same flawed dataset is better than
• 1:15:14
  Speaker 1: finding it once, but it is not the same as
• 1:15:17
  Speaker 1: finding it in a completely independent dataset collected through a
• 1:15:21
  Speaker 1: different method entirely. That test has not yet been run
• 1:15:24
  Speaker 1: in any definitive way. Still, robustness under this kind of
• 1:15:29
  Speaker 1: pressure is significant. The researchers who remained skeptical after 2013
• 1:15:35
  Speaker 1: had argued that the original analysis was fragile, that specific
• 1:15:39
  Speaker 1: choices made by the original team were doing the heavy lifting,
• 1:15:44
  Speaker 1: that different reasonable choices would make the signal weaker or
• 1:15:47
  Speaker 1: disappear entirely. What the follow-up analyses showed was that this
• 1:15:52
  Speaker 1: was not quite right. The choices mattered at the margins.
• 1:15:57
  Speaker 1: Different methods gave somewhat different estimates of the structure's boundaries
• 1:16:01
  Speaker 1: and significance, but.
• 1:16:03
  Speaker 2: None of them gave nothing.
• 1:16:06
  Speaker 1: The absence of the result under independent scrutiny, which is
• 1:16:10
  Speaker 1: what you would expect if the original detection was a
• 1:16:13
  Speaker 1: statistical artifact tied to one team's particular approach, did not materialize.
• 1:16:20
  Speaker 1: One analysis took a particularly careful look.
• 1:16:23
  Speaker 2: At the redshift range involved.
• 1:16:25
  Speaker 1: The original detection had concentrated on a specific band around
• 1:16:30
  Speaker 1: Z is approximately equal to 2. Researchers asked whether the
• 1:16:35
  Speaker 1: clustering was genuinely confined to that range or whether it
• 1:16:39
  Speaker 1: was bleeding into adjacent redshift bins in a way that
• 1:16:43
  Speaker 1: suggested edge effects from the statistical window used. What they
• 1:16:47
  Speaker 1: found was that the overdensity did have some extension beyond
• 1:16:52
  Speaker 1: the original reported range. which some took as evidence for
• 1:16:56
  Speaker 1: a broader structure. Others took as a reason to question
• 1:17:00
  Speaker 1: whether the boundaries had been defined correctly in the first place.
• 1:17:05
  Speaker 1: What it did not look like was a clean artifact
• 1:17:08
  Speaker 1: sitting neatly at the edges of a redshift bin and
• 1:17:11
  Speaker 1: vanishing the moment you looked outside it. By the middle
• 1:17:14
  Speaker 1: of the decade following the discovery, the scientific situation had
• 1:17:19
  Speaker 1: reached a state that is both uncomfortable and genuinely interesting.
• 1:17:24
  Speaker 2: The skeptics had made real points.
• 1:17:27
  Speaker 1: The statistical debate had not resolved cleanly in the original
• 1:17:31
  Speaker 1: team's favor. The methodological concerns about GRB surveys as structural
• 1:17:36
  Speaker 1: traces remained legitimate and unresolved. But the signal had also
• 1:17:41
  Speaker 1: proven more durable than a fragile artifact should be. Multiple
• 1:17:46
  Speaker 1: teams had handled it, tested it, restricted it, and tried
• 1:17:50
  Speaker 1: to make it go away. It had not gone away.
• 1:17:54
  Speaker 1: What this suggested, and what made some of the skeptics
• 1:17:57
  Speaker 1: quieter than they had been, was that the clustering was
• 1:18:01
  Speaker 1: not going away under pressure. A lot of the confusion
• 1:18:04
  Speaker 1: around this discovery traces back to a question most people
• 1:18:08
  Speaker 1: have never had reason to think about. How do astronomers
• 1:18:11
  Speaker 1: know how far away a gamma-ray burst actually is? These
• 1:18:15
  Speaker 1: explosions happen in an instant. They leave no address. There
• 1:18:19
  Speaker 1: is no ruler you can stretch across 10 billion light years.
• 1:18:23
  Speaker 1: The answer is redshift. And once you understand what redshift is,
• 1:18:29
  Speaker 1: the whole architecture of this discovery starts to make more sense.
• 1:18:33
  Speaker 1: Start with the universe expanding. Every galaxy is moving away
• 1:18:38
  Speaker 1: from every other galaxy. Not because the galaxies themselves are
• 1:18:42
  Speaker 1: flying outward through space like shrapnel, but because the space
• 1:18:46
  Speaker 1: between them is stretching. The fabric itself is growing. Light
• 1:18:51
  Speaker 1: traveling through that stretching space gets stretched along with it.
• 1:18:55
  Speaker 1: Its wavelength increases. And when a wavelength increases, the light
• 1:19:01
  Speaker 1: shifts toward the red end of the visible spectrum. That
• 1:19:05
  Speaker 1: shift is the redshift. The longer the light has been traveling,
• 1:19:09
  Speaker 1: the more the universe has expanded around it, and the
• 1:19:13
  Speaker 1: more its wavelength has been pulled apart. So, a high
• 1:19:17
  Speaker 1: redshift tells you the light is old, and old light
• 1:19:21
  Speaker 1: means distant source. This is not a metaphor. It is
• 1:19:25
  Speaker 1: a direct physical consequence of living inside an expanding universe.
• 1:19:30
  Speaker 1: The light does not know it is being stretched. It
• 1:19:33
  Speaker 1: just travels, and the space it travels through keeps getting bigger.
• 1:19:38
  Speaker 1: And by the time it reaches your detector, it carries
• 1:19:41
  Speaker 1: a record of exactly how much expansion it lived through.
• 1:19:45
  Speaker 1: That record is readable. That is the key thing. Astronomers
• 1:19:49
  Speaker 1: can open that record and extract a number. Here is
• 1:19:53
  Speaker 1: how they do it in practice. Every element in the
• 1:19:56
  Speaker 1: periodic table absorbs and emits light at specific wavelengths. Hydrogen
• 1:20:01
  Speaker 1: absorbs at one precise set of wavelengths. Oxygen at another.
• 1:20:06
  Speaker 1: magnesium at another. These are fixed, laboratory measured values. They
• 1:20:12
  Speaker 1: do not change. When a gamma ray burst goes off
• 1:20:15
  Speaker 1: and leaves behind a glowing afterglow, that afterglow shines through
• 1:20:20
  Speaker 1: whatever gas and dust exists along the line of sight,
• 1:20:24
  Speaker 1: and those elements leave their fingerprints in the spectrum, absorbing
• 1:20:28
  Speaker 1: light at their characteristic wavelengths. An astronomer points a telescope
• 1:20:33
  Speaker 1: at the afterglow breaks the light into its component wavelengths,
• 1:20:38
  Speaker 1: and looks for those fingerprints. The fingerprints are there, but
• 1:20:42
  Speaker 1: they are not at the wavelengths the laboratory says.
• 1:20:45
  Speaker 2: They should be. They are shifted. Move toward the red.
• 1:20:50
  Speaker 1: The size of that shift is the redshift value, written
• 1:20:54
  Speaker 1: as Z. Measure the shift, calculate Z, and you have
• 1:20:59
  Speaker 1: a distance. This sounds straightforward, but the window for doing
• 1:21:03
  Speaker 1: it is narrow. Gamma ray bursts fade fast. Hours, sometimes less.
• 1:21:09
  Speaker 1: Ground based telescopes have to pivot quickly after a satellite alert,
• 1:21:14
  Speaker 1: before the afterglow disappears entirely. Not every burst gets a
• 1:21:19
  Speaker 1: measured redshift. Some are too faint. Some set before their
• 1:21:23
  Speaker 1: host galaxy is above the horizon clacks. Some simply fade
• 1:21:27
  Speaker 1: before anyone can get a spectrum. This is one of
• 1:21:31
  Speaker 1: the reasons GRB surveys are not perfectly uniform. and it
• 1:21:35
  Speaker 1: feeds directly into the statistical debates around the Hercules-Corona-Borealis Great Wall.
• 1:21:41
  Speaker 1: Redshift coverage is uneven, and uneven coverage creates headaches when
• 1:21:46
  Speaker 1: you are trying to decide whether a clustering signal is real.
• 1:21:50
  Speaker 1: The Hercules-Corona-Borealis Great Wall sits at roughly Z equals two.
• 1:21:55
  Speaker 1: That number requires some unpacking. The universe today is roughly 13.8
• 1:22:01
  Speaker 1: billion years old. A redshift of two corresponds to a
• 1:22:05
  Speaker 1: look back time of about 10 to 11 billion years.
• 1:22:09
  Speaker 1: The light arriving from those gamma ray bursts left its
• 1:22:13
  Speaker 1: source when the universe was somewhere around 3 billion years old,
• 1:22:17
  Speaker 1: roughly a fifth of its current age. The universe at
• 1:22:20
  Speaker 1: that point was physically smaller, hotter and denser. Galaxies were
• 1:22:26
  Speaker 1: forming aggressively. Star formation rates were near their peak. The
• 1:22:30
  Speaker 1: conditions were nothing like what surrounds us now. What this
• 1:22:34
  Speaker 1: means for the structure itself is significant. When astronomers say
• 1:22:38
  Speaker 1: the Hercules-Corona Borealis Great Wall is 10 billion light years across,
• 1:22:44
  Speaker 1: they are not describing something.
• 1:22:45
  Speaker 2: That exists in the present.
• 1:22:47
  Speaker 1: They are describing a pattern in the distribution of ancient explosions,
• 1:22:52
  Speaker 1: a snapshot of where matter was concentrated at a specific
• 1:22:55
  Speaker 1: moment in cosmic history.
• 1:22:58
  Speaker 2: The structure, if real, existed then.
• 1:23:01
  Speaker 1: Whether anything coherent remains in that region today, whether it
• 1:23:05
  Speaker 1: has merged, dispersed, evolved into something unrecognizable, is a separate
• 1:23:11
  Speaker 1: question that the data cannot answer. You are looking at
• 1:23:15
  Speaker 1: a fossil arrangement, not a living one. This is worth sitting.
• 1:23:19
  Speaker 2: With for a moment.
• 1:23:21
  Speaker 1: Every observation in astronomy is observation of the past. The
• 1:23:25
  Speaker 1: sun you see in the sky is 8 minutes old.
• 1:23:29
  Speaker 1: The Andromeda Galaxy you can barely make out on a
• 1:23:32
  Speaker 1: dark night is 2.5 million years old. At z equals 2,
• 1:23:38
  Speaker 1: the delay is measured in billions of years. The universe
• 1:23:42
  Speaker 1: that produced those gamma ray bursts was so different from
• 1:23:45
  Speaker 1: the one we inhabit that it barely resembles the same place.
• 1:23:49
  Speaker 1: And yet the light still carries the information. The expansion
• 1:23:53
  Speaker 1: of space encoded itself into the spectrum.
• 1:23:56
  Speaker 2: Of each burst.
• 1:23:57
  Speaker 1: And modern instruments can read that encoding with enough precision
• 1:24:01
  Speaker 1: to place each explosion at a specific distance and a
• 1:24:04
  Speaker 1: specific moment in time. This is also why the statistical
• 1:24:09
  Speaker 1: analysis is so demanding. Building a three-dimensional map from redshift
• 1:24:13
  Speaker 1: data requires combining position on the sky, which is straightforward,
• 1:24:18
  Speaker 1: with distance estimated from redshift, which depends on a cosmological model.
• 1:24:23
  Speaker 1: The model connects Z to physical distance using parameters like
• 1:24:27
  Speaker 1: the Hubble constant and the density of dark matter and
• 1:24:30
  Speaker 1: dark energy. If those parameters shift slightly, every distance in
• 1:24:34
  Speaker 1: the map shifts with them. The structure does not disappear,
• 1:24:39
  Speaker 1: but its exact dimensions depend on choices about cosmology that
• 1:24:43
  Speaker 1: are themselves still being refined. Every distance in that map
• 1:24:47
  Speaker 1: is a calculation, not a direct measurement. and every calculation
• 1:24:52
  Speaker 1: rests on a model of the universe that is still
• 1:24:54
  Speaker 1: being tested. Every gamma ray burst in that survey is
• 1:24:59
  Speaker 1: a fossil signal from an explosion that happened billions of
• 1:25:02
  Speaker 1: years ago, arriving at our instruments with the entire history
• 1:25:06
  Speaker 1: of an expanding universe baked into its spectrum. Standard cosmological
• 1:25:11
  Speaker 1: models make a specific prediction about the largest structures that
• 1:25:14
  Speaker 1: should exist in the universe, and it is a prediction
• 1:25:18
  Speaker 1: that can be calculated precisely. That is what makes this
• 1:25:21
  Speaker 1: particular problem so hard to dismiss. This is not a
• 1:25:25
  Speaker 1: case where theorists shrug and say the models are vague.
• 1:25:29
  Speaker 1: The models are specific. They give you a number. And
• 1:25:32
  Speaker 1: the number the Hercules-Corona-Borealis Great Wall comes back with is
• 1:25:37
  Speaker 1: so far outside what the models allow that the gap
• 1:25:40
  Speaker 1: is difficult to look at without stopping to ask what
• 1:25:43
  Speaker 1: it means. To understand why, you have to go back
• 1:25:46
  Speaker 1: to a fraction of a second after the Big Bang.
• 1:25:49
  Speaker 1: when something happened to the universe that set the rules
• 1:25:52
  Speaker 1: for everything that came after it. The event is called inflation.
• 1:25:57
  Speaker 1: In the first unimaginably brief interval after the Big Bang,
• 1:26:01
  Speaker 1: fractions of a second so small that normal language does
• 1:26:04
  Speaker 1: not have useful words for them, the universe expanded at
• 1:26:08
  Speaker 1: an extraordinary rate. Not the ordinary expansion that continues today,
• 1:26:14
  Speaker 1: but something far more violent, an exponential stretching of space,
• 1:26:19
  Speaker 1: that took whatever was there and smoothed it out across
• 1:26:22
  Speaker 1: enormous scales. Think of a wrinkled sheet being pulled flat
• 1:26:27
  Speaker 1: in every direction simultaneously, fast enough that any large-scale clumping
• 1:26:33
  Speaker 1: in the original distribution gets erased. That is roughly what
• 1:26:37
  Speaker 1: inflation did to the early universe.
• 1:26:40
  Speaker 2: It took the.
• 1:26:40
  Speaker 1: Initial conditions and ironed them out, leaving behind something close
• 1:26:45
  Speaker 1: to uniform. What it did not erase were tiny quantum fluctuations,
• 1:26:51
  Speaker 1: microscopic ripples in the density of energy that inflation stretched
• 1:26:55
  Speaker 1: and preserved. Those tiny ripples became the seeds of everything
• 1:27:00
  Speaker 1: that followed. Here is why those seeds matter. Once inflation
• 1:27:05
  Speaker 1: ended and the universe began cooling, matter started gathering in
• 1:27:10
  Speaker 1: the regions where those density fluctuations had left a slightly
• 1:27:14
  Speaker 1: higher concentration of materials. Gravity pulled more matter toward those
• 1:27:19
  Speaker 1: overdense spots. Over hundreds of millions of years, and then billions,
• 1:27:24
  Speaker 1: the overdensities grew. Galaxies formed in the denser regions. Clusters
• 1:27:30
  Speaker 1: of galaxies formed where multiple overdensities were close enough to
• 1:27:34
  Speaker 1: pull together. The filaments and walls of the cosmic web
• 1:27:38
  Speaker 1: grew along the same lines. Every structure in the universe
• 1:27:42
  Speaker 1: traces its ancestry back to those original quantum fluctuations. And
• 1:27:47
  Speaker 1: because the fluctuations came from a specific physical process, inflation,
• 1:27:53
  Speaker 1: they carry a specific statistical fingerprint. The spectrum of those
• 1:27:57
  Speaker 1: fluctuations is not random. It follows rules that can be
• 1:28:02
  Speaker 1: calculated and tested against observation. That spectrum has a ceiling
• 1:28:07
  Speaker 1: built into it. the fluctuations that inflation produced were not
• 1:28:11
  Speaker 1: equally powerful at all scales. On very large scales, the
• 1:28:16
  Speaker 1: primordial variations in density were small enough that gravity could
• 1:28:20
  Speaker 1: not pull together coherent structures above a certain size. The
• 1:28:25
  Speaker 1: universe started too smooth at large scales for anything truly
• 1:28:29
  Speaker 1: enormous to grow into a single bound or semi-bound object.
• 1:28:34
  Speaker 1: Run the numbers through the standard inflationary framework, account for
• 1:28:38
  Speaker 1: the rate of structure growth under gravity factor in dark
• 1:28:42
  Speaker 1: matter and dark energy and what you get is a
• 1:28:45
  Speaker 1: hard upper limit most careful calculations put the maximum expected
• 1:28:50
  Speaker 1: size of a coherent large-scale structure at roughly 1.2 billion
• 1:28:55
  Speaker 1: light years above that threshold The density variations are simply
• 1:29:01
  Speaker 1: too weak and too uncorrelated to produce something you could
• 1:29:04
  Speaker 1: point to and call a single structure. Now consider what
• 1:29:08
  Speaker 1: already existed before 2013. The Sloan Great Wall, at roughly 1.37
• 1:29:15
  Speaker 1: billion light years, was already sitting uncomfortably close to that boundary.
• 1:29:21
  Speaker 1: Some researchers argued it was slightly over the line. Others
• 1:29:24
  Speaker 1: contended that because it was not a gravitationally bound object,
• 1:29:28
  Speaker 1: a loose filamentary arrangement, the standard limit did not quite
• 1:29:33
  Speaker 1: apply in the same way. The debate was real and
• 1:29:36
  Speaker 1: it had not fully resolved itself when the next discovery arrived.
• 1:29:40
  Speaker 1: The huge large quasar group at around 4 billion light
• 1:29:44
  Speaker 1: years pushed the problem further. Each of these discoveries arrived
• 1:29:50
  Speaker 1: at the edge of what the models were comfortable with
• 1:29:52
  Speaker 1: and each triggered a version of the same argument. Then
• 1:29:56
  Speaker 1: the Hercules-Corona-Borealis Great Wall entered the picture. At 10 billion
• 1:30:02
  Speaker 1: light-years across, it is not nudging against the boundary. It
• 1:30:06
  Speaker 1: is not slightly outside it. It is more than 8
• 1:30:09
  Speaker 1: times the size of the Sloan Great Wall and roughly 2.5
• 1:30:13
  Speaker 1: times the size of the huge LQG. The 1.2 billion
• 1:30:18
  Speaker 1: light-year ceiling is not a distant memory from this vantage point.
• 1:30:22
  Speaker 1: It is not even visible in the rear-view mirror. What
• 1:30:26
  Speaker 1: would have to change for something this large to exist?
• 1:30:29
  Speaker 1: There are a few possibilities, and none of them are comfortable.
• 1:30:33
  Speaker 1: The first is that the primordial density fluctuations on these
• 1:30:37
  Speaker 1: scales were significantly stronger than inflation predicts. If the initial
• 1:30:41
  Speaker 1: seeds were larger, the resulting structures could in principle be
• 1:30:45
  Speaker 1: larger too, but this would require a modification to inflationary
• 1:30:49
  Speaker 1: theory that has no other observational support. The cosmic microwave background,
• 1:30:54
  Speaker 1: which maps those primordial fluctuations in extraordinary detail, does not
• 1:30:59
  Speaker 1: show the kind of enhanced power on large scales that
• 1:31:01
  Speaker 1: this explanation would require. Changing inflation to accommodate the wall
• 1:31:06
  Speaker 1: means breaking something else that the models currently get right.
• 1:31:10
  Speaker 1: The second possibility is that structure grew faster under gravity
• 1:31:14
  Speaker 1: than the standard model allows. Dark matter drives the growth
• 1:31:18
  Speaker 1: of structure.
• 1:31:19
  Speaker 2: If there was.
• 1:31:19
  Speaker 1: More of it in certain regions, or if it clustered
• 1:31:23
  Speaker 1: differently than expected. Maybe gravity had more to work with,
• 1:31:27
  Speaker 1: but the scale of the discrepancy makes this hard to close.
• 1:31:31
  Speaker 1: You would need an unusual concentration of dark matter on
• 1:31:35
  Speaker 1: extraordinary scales, and there is no independent evidence for that either.
• 1:31:40
  Speaker 1: The third possibility is something outside the current framework entirely,
• 1:31:46
  Speaker 1: an unknown physical process operating on cosmological scales. something that
• 1:31:51
  Speaker 1: is not dark matter, not dark energy is currently understood,
• 1:31:56
  Speaker 1: not inflation is currently modelled, something new. Astronomers are cautious
• 1:32:02
  Speaker 1: about invoking unknown physics without strong evidence, and reasonably so,
• 1:32:07
  Speaker 1: but the absence of a clean explanation inside the existing
• 1:32:11
  Speaker 1: framework is itself a signal worth taking seriously.
• 1:32:15
  Speaker 2: When the best.
• 1:32:15
  Speaker 1: Models fail to account for an observation by a factor
• 1:32:19
  Speaker 1: of eight or more, That is not a rounding error.
• 1:32:22
  Speaker 2: That is a problem.
• 1:32:24
  Speaker 1: What the Sloan Great Wall showed was that the models
• 1:32:26
  Speaker 1: had limits. What the huge LQG showed was that those
• 1:32:30
  Speaker 1: limits were being reached more often than expected. What the
• 1:32:34
  Speaker 1: Hercules Corona Borealis Great Wall showed was something different in kind.
• 1:32:39
  Speaker 1: Not a structure that nudges against the theoretical ceiling, but
• 1:32:43
  Speaker 1: one that, if it is real, stands so far outside
• 1:32:47
  Speaker 1: that ceiling that no obvious path exists from the current
• 1:32:50
  Speaker 1: framework to the observation. The gap cannot be closed by
• 1:32:54
  Speaker 1: adjusting parameters. It cannot be explained away by pointing to
• 1:32:59
  Speaker 1: measurement uncertainty. If the wall is real, it means the
• 1:33:03
  Speaker 1: universe managed to construct something far larger than the standard
• 1:33:07
  Speaker 1: recipe allows, and nobody has a clean explanation for how.
• 1:33:12
  Speaker 1: One of the stranger developments in the story of the
• 1:33:14
  Speaker 1: Hercules-Corona-Borealis Great Wall is that subsequent analysis has not made
• 1:33:20
  Speaker 1: it smaller. When a controversial discovery comes under sustained pressure
• 1:33:24
  Speaker 1: from the scientific community, the usual outcome is one of
• 1:33:28
  Speaker 1: two things. Either the signal fades under closer inspection and
• 1:33:32
  Speaker 1: the original estimate shrinks, or the evidence collapses entirely. What
• 1:33:38
  Speaker 1: happened here was neither. Researchers who went back to the
• 1:33:42
  Speaker 1: gamma-ray burst catalog with fresh methods and wider redshift windows
• 1:33:47
  Speaker 1: did not find a smaller structure, they.
• 1:33:49
  Speaker 2: Found a larger one.
• 1:33:51
  Speaker 1: That outcome is strange enough that it is worth sitting
• 1:33:54
  Speaker 1: with for a moment, because it changes the shape of
• 1:33:57
  Speaker 1: the problem considerably. The original 2013 analysis placed the Hercules-Corona-Borealis
• 1:34:05
  Speaker 1: Great Wall at a redshift of roughly Z equals 2.
• 1:34:08
  Speaker 1: That redshift corresponds to a time when the universe was
• 1:34:12
  Speaker 1: about 3 billion years old, roughly a fifth of its
• 1:34:16
  Speaker 1: current age. The structure appeared to occupy a relatively well-defined
• 1:34:20
  Speaker 1: band in redshift space, concentrated around that value. That was
• 1:34:25
  Speaker 1: already a staggering result. But subsequent work, including analyses published
• 1:34:31
  Speaker 1: around 2020 and afterward, started finding that the overdense region
• 1:34:36
  Speaker 1: did not stay neatly inside that band. It extended outward
• 1:34:40
  Speaker 1: in both directions along the line of sight. reaching redshifts
• 1:34:45
  Speaker 1: as low as roughly 0.33 and as high as roughly 2.43.
• 1:34:52
  Speaker 1: Those are very different distances. The lower end of that
• 1:34:55
  Speaker 1: range corresponds to a universe that is already several billion
• 1:35:00
  Speaker 1: years old, meaning some of the structure's components are much
• 1:35:04
  Speaker 1: closer to Earth than anyone initially suspected. the upper end
• 1:35:10
  Speaker 1: pushes even deeper into the early universe than the original
• 1:35:14
  Speaker 1: discovery had mapped. What does it mean to stretch the
• 1:35:17
  Speaker 1: redshift range from 0.33 to 2.43? In physical terms, it
• 1:35:24
  Speaker 1: is dramatic. A structure that was already 10 billion light
• 1:35:28
  Speaker 1: years across in its original estimate now appears to span
• 1:35:32
  Speaker 1: a volume that, along its depth alone, covers an enormous
• 1:35:36
  Speaker 1: fraction of cosmic history. The components closest to Earth sit
• 1:35:41
  Speaker 1: in a universe that has had billions of years more
• 1:35:43
  Speaker 1: time to evolve than the components at the far end
• 1:35:46
  Speaker 1: of the range. If these are genuinely connected, the structure
• 1:35:51
  Speaker 1: is not just physically enormous, it is cosmologically deep in
• 1:35:55
  Speaker 1: a way that almost nothing else we have ever observed
• 1:35:58
  Speaker 1: can match. The team conducting this reanalysis was explicit about
• 1:36:02
  Speaker 1: one thing. The expansion of the apparent size did not
• 1:36:07
  Speaker 1: look like a statistical fluctuation. It did not look like
• 1:36:11
  Speaker 1: a sampling artifact. They went through the same checklist that
• 1:36:15
  Speaker 1: had fueled the original debate. Sky coverage biases, redshift measurement reliability,
• 1:36:22
  Speaker 1: whether certain GRBs were easier to detect in certain redshift ranges,
• 1:36:28
  Speaker 1: and the expanded signal survived those checks. The clustering was
• 1:36:32
  Speaker 1: real enough in their analysis to remain standing after the
• 1:36:36
  Speaker 1: standard pressure tests. What they also found was that the
• 1:36:39
  Speaker 1: structure is not a single, clean, monolithic wall. The original name,
• 1:36:45
  Speaker 1: the Great Wall, conjures an image of something unified and continuous,
• 1:36:50
  Speaker 1: like a vast sheet of galaxies stretching in one direction.
• 1:36:54
  Speaker 1: That picture is probably too simple. The reanalysis found evidence
• 1:36:58
  Speaker 1: that the Hercules Corona Borealis Great Wall encompasses several smaller,
• 1:37:03
  Speaker 1: distinct overdense clusters. These clusters are not randomly scattered. They
• 1:37:09
  Speaker 1: appear to be embedded within, or associated with, the broader
• 1:37:13
  Speaker 1: overdense region rather than sitting outside it. Think of it
• 1:37:17
  Speaker 1: less like a flat wall, and more like a sponge
• 1:37:20
  Speaker 1: with dense nodes connected by thinner threads. all of it
• 1:37:24
  Speaker 1: sitting inside a region of space that is overall denser
• 1:37:28
  Speaker 1: than its surroundings. This distinction matters for the physics. A
• 1:37:32
  Speaker 1: single monolithic structure would require something specific, a coherent density
• 1:37:38
  Speaker 1: enhancement that formed and evolved as a unit across a
• 1:37:41
  Speaker 1: vast stretch of space. A complex of related over densities
• 1:37:46
  Speaker 1: is a different kind of object and in some ways
• 1:37:49
  Speaker 1: a more plausible one. Gravity works locally, It can build clusters.
• 1:37:55
  Speaker 1: It can connect clusters along filaments. A hierarchy of over-dense regions,
• 1:38:00
  Speaker 1: each formed through its own history but collectively concentrated in
• 1:38:04
  Speaker 1: one region of the sky and one range of redshifts,
• 1:38:08
  Speaker 1: is at least conceptually more approachable than a single uniform wall.
• 1:38:13
  Speaker 1: But here is the catch. Even under this more complex interpretation,
• 1:38:18
  Speaker 1: the overall region those clusters occupy is still enormous. The
• 1:38:23
  Speaker 1: footprint does not shrink just because the intern. All structure
• 1:38:27
  Speaker 1: is more complicated. In fact, a web of overdense clusters
• 1:38:31
  Speaker 1: spread across an even wider redshift range occupies more volume,
• 1:38:36
  Speaker 1: not less. This is the uncomfortable situation that the reanalysis
• 1:38:40
  Speaker 1: left the field with. The debate had been partly framed
• 1:38:44
  Speaker 1: around whether the original number, 10 billion light years, was reliable.
• 1:38:49
  Speaker 1: Critics had reasonable grounds to push back on that estimate,
• 1:38:53
  Speaker 1: given the limitations of the data. But the subsequent work
• 1:38:57
  Speaker 1: did not resolve the controversy by bringing the number down.
• 1:39:01
  Speaker 1: It moved the number in the other direction. The region
• 1:39:04
  Speaker 1: appears to be larger than originally reported, more complex in
• 1:39:08
  Speaker 1: its internal structure, and it extends closer to Earth than
• 1:39:12
  Speaker 1: anyone had initially measured. For cosmology, this progression is hard
• 1:39:17
  Speaker 1: to absorb. Structures that start large and grow under additional
• 1:39:21
  Speaker 1: scrutiny are structures that the standard models have an increasingly
• 1:39:25
  Speaker 1: difficult time explaining away. The inflation argument, the one that
• 1:39:29
  Speaker 1: places a hard ceiling of roughly 1.2 billion light years
• 1:39:33
  Speaker 1: on coherent cosmic structure, does not become more comfortable when
• 1:39:37
  Speaker 1: the anomaly doubles in apparent size. It becomes less comfortable.
• 1:39:42
  Speaker 1: Every additional billion light years of extent, every additional cluster
• 1:39:46
  Speaker 1: embedded in the system, adds to the difficulty of fitting
• 1:39:50
  Speaker 1: the observation into the existing framework. The questions that surrounded
• 1:39:54
  Speaker 1: the original discovery are still open. Whether the structure is real,
• 1:39:58
  Speaker 1: whether it violates the cosmological principle, whether inflation needs revision,
• 1:40:04
  Speaker 1: none of those questions has a settled answer. But the
• 1:40:07
  Speaker 1: geometry of the problem has shifted. The thing being questioned
• 1:40:11
  Speaker 1: is now bigger than it was. The structure that was
• 1:40:14
  Speaker 1: already too large to fit comfortably into the models turned out,
• 1:40:18
  Speaker 1: on closer inspection, to be larger still. The cleanest path
• 1:40:22
  Speaker 1: to settling this debate runs through a telescope that does
• 1:40:26
  Speaker 1: not exist yet. Every major argument about the Hercules-Corona-Borealis Great
• 1:40:31
  Speaker 1: Wall eventually circles back to the same problem. The data
• 1:40:35
  Speaker 1: is imperfect. The GRB catalogues that revealed the clustering in
• 1:40:39
  Speaker 1: the first place were built from observations gathered by multiple
• 1:40:43
  Speaker 1: satellites operating across different years, each with its own sensitivity thresholds,
• 1:40:49
  Speaker 1: its own sky coverage patterns, its own blind spots. SWIFT
• 1:40:54
  Speaker 1: was never designed to map large-scale cosmic structure. It was
• 1:40:58
  Speaker 1: designed to catch gamma-ray bursts fast and point other telescopes
• 1:41:02
  Speaker 1: at them before the afterglow faded. That it produced data
• 1:41:06
  Speaker 1: useful for structure mapping at all was a kind of
• 1:41:09
  Speaker 1: fortunate accident. But fortunate accidents leave marks. The sample is uneven.
• 1:41:15
  Speaker 1: Some patches of sky are better covered than others. Some
• 1:41:18
  Speaker 1: redshift ranges are easier to F, OLO up than others.
• 1:41:22
  Speaker 1: These irregularities sit inside every analysis anyone has ever run
• 1:41:27
  Speaker 1: on this dataset.
• 1:41:28
  Speaker 2: And no amount of.
• 1:41:29
  Speaker 1: Statistical correction fully removes them. You cannot correct for something
• 1:41:34
  Speaker 1: you cannot fully characterize.
• 1:41:36
  Speaker 2: This is where Theseus comes in.
• 1:41:39
  Speaker 1: The full name is the Transient High Energy Sky and
• 1:41:42
  Speaker 1: Early Universe Surveyor. It is a proposed European Space Agency
• 1:41:47
  Speaker 1: mission and the whole point of it from the ground
• 1:41:50
  Speaker 1: up is to do what Swift was never built to do.
• 1:41:53
  Speaker 1: Detect gamma ray bursts across a wider range of energies,
• 1:41:57
  Speaker 1: cover the sky more uniformly and critically, measure redshifts directly
• 1:42:02
  Speaker 1: from the burst itself rather than waiting for ground-based telescopes
• 1:42:07
  Speaker 1: to catch the afterglow at a random moment under whatever
• 1:42:10
  Speaker 1: weather conditions happened to exist that night. Theseus carries an
• 1:42:14
  Speaker 1: onboard infrared telescope specifically for this purpose. Infrared light penetrates
• 1:42:20
  Speaker 1: the dust and gas that can obscure the afterglows of
• 1:42:23
  Speaker 1: distant bursts from optical telescopes. You get a redshift for
• 1:42:28
  Speaker 1: more bursts, not just the ones that were bright enough
• 1:42:32
  Speaker 1: and lucky enough to be followed up under good conditions.
• 1:42:35
  Speaker 1: That last part matters more than it might sound. One
• 1:42:39
  Speaker 1: of the persistent worries about the current GRB catalogues is
• 1:42:42
  Speaker 1: that redshift measurements are not available for every burst in
• 1:42:46
  Speaker 1: the sample. The bursts without confirmed redshifts have to be
• 1:42:50
  Speaker 1: excluded from structure analyses or handled with statistical assumptions about
• 1:42:55
  Speaker 1: where they might fall. Either way, You are working with
• 1:42:59
  Speaker 1: an incomplete picture. A mission that delivers redshifts for a
• 1:43:02
  Speaker 1: far higher fraction of detected bursts gives you something.
• 1:43:06
  Speaker 2: Far more powerful.
• 1:43:07
  Speaker 1: A sample where you actually know where things are rather
• 1:43:11
  Speaker 1: than inferring it. Think of what the current situation looks
• 1:43:14
  Speaker 1: like from an engineer's standpoint. You want to know whether
• 1:43:18
  Speaker 1: a signal in a data set is real or an
• 1:43:21
  Speaker 1: artifact of your instrument. The most direct test is to
• 1:43:24
  Speaker 1: build a better instrument. one whose biases you understand completely,
• 1:43:29
  Speaker 1: and run the measurement again. If the signal survives a
• 1:43:32
  Speaker 1: clean instrument, it.
• 1:43:33
  Speaker 2: Was probably real.
• 1:43:35
  Speaker 1: If it disappears, it was probably the old instrument talking
• 1:43:39
  Speaker 1: to itself. That is exactly what Theseus offers this particular problem.
• 1:43:44
  Speaker 1: A single, well-characterized uniform survey from a single mission. No
• 1:43:48
  Speaker 1: patchwork of satellite archives from different eras. No gaps in
• 1:43:53
  Speaker 1: sky coverage that vary from year to year based on
• 1:43:55
  Speaker 1: which observatories were operational. One data set, built to a
• 1:43:59
  Speaker 1: consistent standard, designed specifically to answer the kind of question
• 1:44:04
  Speaker 1: the Hercules-Corona-Borealis Great Wall is asking. Researchers directly involved in
• 1:44:09
  Speaker 1: the original discovery have said this plainly. Theseus is what
• 1:44:13
  Speaker 1: the field needs to decide. That is not a vague
• 1:44:17
  Speaker 1: hope about future technology. It is a specific statement.
• 1:44:21
  Speaker 2: About what the problem requires.
• 1:44:23
  Speaker 1: The uncertainty is not coming from ambiguity in the physics
• 1:44:26
  Speaker 1: or disagreement about theory. It is coming from the limitations
• 1:44:30
  Speaker 1: of the data. Fix the data and the answer becomes legible.
• 1:44:35
  Speaker 1: Theseus is the fix. What would a definitive result actually
• 1:44:39
  Speaker 1: look like? If the Hercules-Corona Borealis Great Wall is a
• 1:44:44
  Speaker 1: genuine physical structure, A properly uniformed GRB survey should detect it,
• 1:44:49
  Speaker 1: without ambiguity. The over-density in that region of the sky
• 1:44:54
  Speaker 1: at that redshift range should appear in the new data
• 1:44:57
  Speaker 1: just as it appeared in the old, but cleaner, sharper,
• 1:45:01
  Speaker 1: no longer dependent on statistical corrections that skeptics can dispute.
• 1:45:07
  Speaker 1: The argument dies. The structure goes into the catalogue as real.
• 1:45:11
  Speaker 1: and the theoretical headache of explaining it becomes the field's
• 1:45:15
  Speaker 1: primary obligation. If the wall is an artifact, the reverse happens.
• 1:45:20
  Speaker 1: A uniform survey with no selection effects should produce a
• 1:45:25
  Speaker 1: distribution of gamma-ray bursts that looks roughly the way a smooth,
• 1:45:29
  Speaker 1: homogenous universe predicts. The clustering fades. The apparent great wall
• 1:45:35
  Speaker 1: dissolves into background noise. The community moves on, somewhat relieved,
• 1:45:41
  Speaker 1: and the cosmological principle survives intact at this scale.
• 1:45:46
  Speaker 2: Either outcome is valuable.
• 1:45:48
  Speaker 1: Science does not only advance by confirming things. Ruling out
• 1:45:52
  Speaker 1: a 10 billion light-year structure that was never there would
• 1:45:55
  Speaker 1: be its own contribution. A cautionary lesson in how systematically
• 1:46:00
  Speaker 1: biased data can masquerade as discovery even under careful analysis.
• 1:46:05
  Speaker 1: That lesson would be worth having. The timeline for Theseus
• 1:46:09
  Speaker 1: has shifted over the years, as proposed missions tend to do.
• 1:46:13
  Speaker 1: ESA has considered it in multiple mission selection cycles, and
• 1:46:17
  Speaker 1: its advocates have continued making the scientific case with each iteration.
• 1:46:22
  Speaker 1: The technical capability is not speculative. The infrared spectrometer that
• 1:46:27
  Speaker 1: would measure burst redshifts, the wide-field X-ray monitor that would
• 1:46:31
  Speaker 1: detect the bursts in the first place, the architecture that
• 1:46:34
  Speaker 1: would allow rapid follow-up within the same spacecraft rather than
• 1:46:38
  Speaker 1: depending on a relay to ground-based observatories. None of this
• 1:46:42
  Speaker 1: is beyond current engineering. The challenge is priority and funding,
• 1:46:46
  Speaker 1: not physics. Other missions compete for the same resources. The
• 1:46:51
  Speaker 1: argument for Theseus has to be made against the backdrop
• 1:46:54
  Speaker 1: of everything else the field wants to build. What makes
• 1:46:58
  Speaker 1: that argument compelling is that Theseus is not a single-purpose instrument.
• 1:47:03
  Speaker 1: Gamma ray bursts are interesting for dozens of reasons beyond
• 1:47:07
  Speaker 1: large-scale structure. They probe the early universe. They mark the
• 1:47:12
  Speaker 1: deaths of massive stars. They test general relativity under extreme conditions.
• 1:47:17
  Speaker 1: They illuminate the history of star formation across cosmic time.
• 1:47:22
  Speaker 1: A mission that captures all of that, while also resolving
• 1:47:25
  Speaker 1: one of the most consequential structural debates in modern cosmology,
• 1:47:29
  Speaker 1: is a strong case. But the Hercules-Corona-Borealis Great Wall gives
• 1:47:34
  Speaker 1: it a particular urgency. There is a specific, answerable question
• 1:47:39
  Speaker 1: sitting in the data. An instrument exists that could answer it.
• 1:47:44
  Speaker 1: Until something like Theseus flies and delivers the data the
• 1:47:47
  Speaker 1: field is waiting for, whether the largest known staff, Uksha
• 1:47:51
  Speaker 1: in the universe, is genuinely real remains one of the
• 1:47:55
  Speaker 1: most consequential open problems in modern cosmology. The Hercules Corona
• 1:48:00
  Speaker 1: Borealis Great Wall did not arrive in isolation. To understand
• 1:48:06
  Speaker 1: what its existence actually means, you have to see it
• 1:48:09
  Speaker 1: against the background of everything else that came before it.
• 1:48:13
  Speaker 1: Because there is a pattern here, and the pattern is strange.
• 1:48:18
  Speaker 2: Go back to 1989.
• 1:48:20
  Speaker 1: A pair of astronomers named Margaret Geller and John Hutra
• 1:48:24
  Speaker 1: were mapping the positions of galaxies out to a relatively
• 1:48:27
  Speaker 1: modest distance, roughly 600 million light years. What they found
• 1:48:32
  Speaker 1: inside that volume was a thin sheet of galaxies stretching
• 1:48:35
  Speaker 1: across their maps like a wall.
• 1:48:38
  Speaker 2: They called it the Great Wall.
• 1:48:40
  Speaker 1: At the time, it was the largest known structure in
• 1:48:42
  Speaker 1: the universe, measuring somewhere around 500 million light years across.
• 1:48:48
  Speaker 1: The field stopped and stared. Nothing in the standard picture
• 1:48:52
  Speaker 1: of how galaxies cluster had predicted something that large.
• 1:48:56
  Speaker 2: There was a debate. Papers were written.
• 1:48:58
  Speaker 1: The structure survived scrutiny and was eventually absorbed into the
• 1:49:02
  Speaker 1: cosmological literature without anyone fully explaining why it was allowed
• 1:49:07
  Speaker 1: to be that big. The models were adjusted sly. Work continued.
• 1:49:13
  Speaker 1: What made this discovery particularly troubling was not just the scale,
• 1:49:18
  Speaker 1: but what it implied about the universe's organization. The cosmological principle,
• 1:49:24
  Speaker 1: a foundational assumption in modern cosmology, holds that matter should
• 1:49:28
  Speaker 1: be distributed roughly uniformly across the larger scales. A structure
• 1:49:34
  Speaker 1: of this magnitude suggested the universe had more inherent organization
• 1:49:39
  Speaker 1: than the models accounted for. The tension remained unresolved. A
• 1:49:44
  Speaker 1: theoretical puzzle filed away as observations continued. Then came 2003.
• 1:49:51
  Speaker 1: A new survey, the Sloan Digital Sky Survey, was producing
• 1:49:57
  Speaker 1: the most detailed three-dimensional map of galaxies that had ever
• 1:50:01
  Speaker 1: been assembled. Inside that map, a team led by J.
• 1:50:06
  Speaker 1: Richard Gott found another wall, longer than the first, stretching
• 1:50:10
  Speaker 1: roughly 1.37 billion light years.
• 1:50:14
  Speaker 2: The Sloan Great Wall.
• 1:50:16
  Speaker 1: It was nearly three times the size of what Geller
• 1:50:19
  Speaker 1: and Hutra had found, and it immediately claimed the record.
• 1:50:23
  Speaker 2: Same story. The field stopped. There was a debate.
• 1:50:27
  Speaker 1: Some researchers argued the Sloan Great Wall was not a
• 1:50:30
  Speaker 1: single coherent structure but a chance alignment of separate clusters
• 1:50:35
  Speaker 1: along the line of sight.
• 1:50:37
  Speaker 2: Others disagreed.
• 1:50:39
  Speaker 1: The structure survived partial scrutiny, the record was updated, and
• 1:50:44
  Speaker 1: the theoretical tension it created quietly accumulated without resolution. The
• 1:50:49
  Speaker 1: huge large quasar group arrived next.
• 1:50:53
  Speaker 2: Quasars are the.
• 1:50:54
  Speaker 1: Extremely luminous cores of active galaxies, powered by supermassive black
• 1:50:59
  Speaker 1: holes consuming material at enormous rates. They shine so brightly
• 1:51:04
  Speaker 1: that they can be seen across billions of light years,
• 1:51:07
  Speaker 1: which makes them useful for mapping large-scale structure in the
• 1:51:11
  Speaker 1: distant universe in the same way that gamma ray bursts
• 1:51:14
  Speaker 1: would later be used. In 2013, a team led by
• 1:51:19
  Speaker 1: Roger Clowes identified a clustering of 73 quasars spanning roughly
• 1:51:24
  Speaker 1: 4 billion light years. This was the huge LQG, and
• 1:51:30
  Speaker 1: it pushed against the cosmological principle just as hard as
• 1:51:33
  Speaker 1: the structures before it had. The debate it triggered was
• 1:51:37
  Speaker 1: still running when the Hercules-Corona-Borealis Great War was published later
• 1:51:42
  Speaker 1: that same year. It is worth pausing on the Klaus
• 1:51:45
  Speaker 1: Camposano Large Quasar Group, which came even earlier. Klaus and
• 1:51:50
  Speaker 1: his colleague Luis Camposano found a grouping of quasars in
• 1:51:54
  Speaker 1: the early 1990s that itself seemed too large when first reported.
• 1:51:59
  Speaker 1: That structure was roughly 2 billion light years across, smaller
• 1:52:03
  Speaker 1: than the huge LQG, but it carried the same pattern.
• 1:52:08
  Speaker 1: Too big, unexpected, debated, partially absorbed, unresolved. The Klaus Camposano
• 1:52:16
  Speaker 1: group barely registers as remarkable now, because every structure that
• 1:52:21
  Speaker 1: followed it was larger. Two years after the Hercules-Corona-Borealis Great
• 1:52:26
  Speaker 1: War was announced, team at the University of Hawaii found
• 1:52:31
  Speaker 1: something else using similar gamma-ray burst mapping methods. They called
• 1:52:36
  Speaker 1: it the giant GRB ring. It measured roughly 5.6 billion
• 1:52:42
  Speaker 1: light years across, making it one of the largest known
• 1:52:46
  Speaker 1: structures by angular extent, and it appeared as a ring-shaped
• 1:52:50
  Speaker 1: overdensity of gamma-ray bursts in a particular region of sky.
• 1:52:54
  Speaker 1: The giant GRB ring was debated immediately Was it a
• 1:52:59
  Speaker 1: genuine physical structure or a statistical quirk in the data?
• 1:53:04
  Speaker 1: Sound familiar. The methods that found it were related to
• 1:53:07
  Speaker 1: the methods that found the Hercules-Corona-Borealis Great Wall. So the
• 1:53:12
  Speaker 1: same methodological questions applied. The same unresolved tensions settled in.
• 1:53:19
  Speaker 1: Then in 2021 came the giant arc. A PhD student
• 1:53:24
  Speaker 1: named Alexia Lopez working through quasar spectra from the Sloan
• 1:53:28
  Speaker 1: Digital Sky Survey, identified an enormous arc-shaped concentration of material
• 1:53:35
  Speaker 1: stretching about 3.3 billion light-years, sitting roughly 9.2 billion light-years away.
• 1:53:42
  Speaker 1: Lopez was not looking.
• 1:53:43
  Speaker 2: For a megastructure.
• 1:53:45
  Speaker 1: She was examining a particular spectral feature, the magnesium absorption
• 1:53:49
  Speaker 1: signature found in quasar light as it passes through intervening materials.
• 1:53:55
  Speaker 1: and the signal of something enormous showed up in the data.
• 1:53:58
  Speaker 1: The giant arc is not a gamma-ray burst result. It
• 1:54:02
  Speaker 1: uses an entirely different tracer, different data, different methods, and
• 1:54:07
  Speaker 1: it found the same category of thing, a structure far
• 1:54:11
  Speaker 1: larger than standard models comfortably allow, located in a universe
• 1:54:16
  Speaker 1: that was not supposed to be producing objects of that scale.
• 1:54:20
  Speaker 1: The consistency was striking. Multiple independent discovery methods, spanning decades
• 1:54:26
  Speaker 1: and using entirely different types of astronomical data, were all
• 1:54:31
  Speaker 1: pointing toward the same troubling conclusion about cosmic structure. What
• 1:54:35
  Speaker 1: connects all of these discoveries is not the structures themselves,
• 1:54:40
  Speaker 1: but the reaction they each produced. Every decade, at least once,
• 1:54:45
  Speaker 1: something has appeared in a survey that stopped the field cold.
• 1:54:49
  Speaker 1: The structure was too big. The debate started. Researchers attacked
• 1:54:54
  Speaker 1: the methods. Other researchers defended them. The signal proved stubborn.
• 1:55:00
  Speaker 1: No clean theoretical explanation arrived. The record was updated. The
• 1:55:06
  Speaker 1: tension was filed away. And then the next survey ran.
• 1:55:10
  Speaker 1: And the next structure arrived. Bigger than the last one.
• 1:55:14
  Speaker 1: The Hercules-Corona-Borealis Great Wall is the most extreme entry in
• 1:55:18
  Speaker 1: this sequence. It is not slightly larger than the structures
• 1:55:22
  Speaker 1: that preceded it. It dwarfs most of them by factors
• 1:55:25
  Speaker 1: of two or three or more, but it is recognizably
• 1:55:29
  Speaker 1: part of the same family. Following the same pattern of discovery, debate,
• 1:55:34
  Speaker 1: partial survival, and unresolved theoretical weight, the universe appears to
• 1:55:40
  Speaker 1: manufacture large coherent structures more readily than the models prefer.
• 1:55:45
  Speaker 1: and it has been doing this consistently across decades of
• 1:55:49
  Speaker 1: observations and improvements in survey technology. The signal has not
• 1:55:53
  Speaker 1: gone away as the data have gotten better. If anything,
• 1:55:58
  Speaker 1: the signal has gotten stronger. Each of those structures arrived
• 1:56:02
  Speaker 1: as a surprise, and each one nudged the field a
• 1:56:05
  Speaker 1: little further toward asking whether the models were capturing something
• 1:56:09
  Speaker 1: true or missing something large. Step back from the data
• 1:56:14
  Speaker 1: for a moment. and look at what this argument is
• 1:56:16
  Speaker 1: actually about. On one side, you have the cosmological principle,
• 1:56:22
  Speaker 1: not just a working assumption, not just a convenience, a
• 1:56:26
  Speaker 1: foundational claim about the nature of reality itself. The universe
• 1:56:32
  Speaker 1: at large enough scales is the same everywhere and in
• 1:56:36
  Speaker 1: all directions. This is the bedrock on which modern cosmology
• 1:56:40
  Speaker 1: is built. The Lambda CDM model which is the standard
• 1:56:44
  Speaker 1: framework for describing how the universe evolved from a hot,
• 1:56:48
  Speaker 1: dense state to the web of galaxies we see today,
• 1:56:51
  Speaker 1: inherits everything from this principle. Predictions about the cosmic microwave background,
• 1:56:57
  Speaker 1: the expansion rate of the universe, the distribution of dark matter,
• 1:57:02
  Speaker 1: the behavior of dark energy, all of it traces back
• 1:57:05
  Speaker 1: at some level to the assumption that space is homogenous
• 1:57:09
  Speaker 1: and isotropic above a certain scale. That model has been
• 1:57:13
  Speaker 1: tested against observation after observation for decades, and it keeps working.
• 1:57:19
  Speaker 1: That is not nothing. That is a strong argument for
• 1:57:22
  Speaker 1: taking the principle seriously. On the other side, you have
• 1:57:26
  Speaker 1: the data. A region of the sky at redshift z
• 1:57:30
  Speaker 1: is approximately equal to 2 where gamma ray bursts cluster
• 1:57:34
  Speaker 1: so densely that the structure implied by that clustering spans
• 1:57:38
  Speaker 1: roughly 10 billion light years. Multiple independent analyses looking at
• 1:57:43
  Speaker 1: the same region with different methods and finding the same signal.
• 1:57:48
  Speaker 1: Subsequent reanalysis not shrinking the structure but expanding it. A
• 1:57:53
  Speaker 1: feature that does not dissolve under scrutiny the way statistical
• 1:57:56
  Speaker 1: artifacts typically do. The universe apparently built something. Whether that
• 1:58:02
  Speaker 1: something is as large as the data suggest is still
• 1:58:05
  Speaker 1: being argued. But the arguing has been going on for
• 1:58:08
  Speaker 1: over a decade now. The signal has not gone away.
• 1:58:12
  Speaker 1: The stakes of that conflict are genuinely large. If the
• 1:58:15
  Speaker 1: cosmological principle fails at the scale of the Hercules-Corona-Borealis Great Wall,
• 1:58:21
  Speaker 1: it does not fail quietly. Everything downstream of it becomes suspect.
• 1:58:27
  Speaker 1: The way cosmologists interpret the faint ripples in the cosmic
• 1:58:31
  Speaker 1: microwave background depends on the assumption that those ripples represent
• 1:58:35
  Speaker 1: a statistically uniform field across the whole sky. If the
• 1:58:39
  Speaker 1: universe has large-scale inhomogeneities at the scale of 10 billion
• 1:58:43
  Speaker 1: light years, then different patches of the CMB might be
• 1:58:47
  Speaker 1: telling different stories. Averaging them together would produce a number
• 1:58:51
  Speaker 1: that does not accurately describe any particular region. The calculated
• 1:58:56
  Speaker 1: age of the universe, 13.8 billion years, comes from models
• 1:59:01
  Speaker 1: built on homogeneity. Dark energy, the term cosmologists use for
• 1:59:06
  Speaker 1: whatever is driving the accelerating expansion of the universe, is
• 1:59:10
  Speaker 1: quantified using observations spread across different directions and depths on
• 1:59:16
  Speaker 1: the assumption that the underlying distribution of matter is roughly uniform.
• 1:59:21
  Speaker 1: All of this interconnects. Pull one thread. and the fabric shifts.
• 1:59:27
  Speaker 1: That is a lot to put at risk on GRB
• 1:59:29
  Speaker 1: clustering data alone. The critics who raised methodological concerns were
• 1:59:34
  Speaker 1: not being obstructionist.
• 1:59:36
  Speaker 2: They were being careful.
• 1:59:38
  Speaker 1: Careful is exactly what you want scientists to be when
• 1:59:41
  Speaker 1: the stakes are this high. A 5-20% probability that the
• 1:59:46
  Speaker 1: signal is noise is not a ringing endorsement of a
• 1:59:50
  Speaker 1: discovery that would require rewriting the foundations of cosmology. The
• 1:59:54
  Speaker 1: field was right to demand more before drawing sweeping conclusions.
• 1:59:59
  Speaker 1: But the other side of that cuts just as hard.
• 2:00:02
  Speaker 1: Science does not get to selectively ignore observations because they
• 2:00:05
  Speaker 1: are inconvenient. The history of cosmology is full of moments
• 2:00:09
  Speaker 1: where the data arrived before the theory was ready. The
• 2:00:13
  Speaker 1: honest response was not to dismiss the data but to
• 2:00:15
  Speaker 1: go find out what was generating it. When the universe's
• 2:00:19
  Speaker 1: expansion was found to be accelerating in the late 1990s.
• 2:00:24
  Speaker 1: Nobody demanded that the result be ignored because it contradicted
• 2:00:28
  Speaker 1: a cleaner picture. They labelled the unknown driving force and
• 2:00:32
  Speaker 1: kept working. The Hercules-Corona Borealis Great Wall presents a version
• 2:00:39
  Speaker 1: of that same challenge. If the clustering is real, the
• 2:00:43
  Speaker 1: question is not whether to accept it, but what to
• 2:00:46
  Speaker 1: do with it. What would it take for the models
• 2:00:49
  Speaker 1: to accommodate a structure this large? The short answer is
• 2:00:53
  Speaker 1: that nobody has a fully worked out version yet. Some
• 2:00:56
  Speaker 1: researchers have explored whether inflation models with non-standard parameters could
• 2:01:01
  Speaker 1: produce density fluctuations large enough on these scales to seed
• 2:01:05
  Speaker 1: such a structure. The numbers are difficult. Others have raised
• 2:01:09
  Speaker 1: the possibility that the structure is not a single coherent
• 2:01:13
  Speaker 1: object but a complex of related overdensities. that what looks
• 2:01:17
  Speaker 1: like one enormous thing from our particular vantage point is
• 2:01:21
  Speaker 1: actually several large things roughly aligned. That would make it
• 2:01:25
  Speaker 1: slightly less catastrophic for the models, though structures of several
• 2:01:29
  Speaker 1: billion light years each would themselves require explanation. The possibility
• 2:01:34
  Speaker 1: that we are seeing a genuine alignment, et of separate structures,
• 2:01:38
  Speaker 1: rather than one continuous object, has not been ruled out,
• 2:01:43
  Speaker 1: but it has also not been demonstrated convincingly The honest position,
• 2:01:48
  Speaker 1: the one most researchers working in this field will give
• 2:01:51
  Speaker 1: you if you push them, is that the data are real,
• 2:01:55
  Speaker 1: the signal is persistent, the theoretical framework for explaining it
• 2:01:59
  Speaker 1: is incomplete. The instrument that would settle the question has
• 2:02:03
  Speaker 1: not been built yet. That is not a satisfying place
• 2:02:07
  Speaker 1: to land. It is, however, an accurate one. What the
• 2:02:11
  Speaker 1: Hercules-Corona-Borealis Great Wall has already done regardless of how the
• 2:02:16
  Speaker 1: debate resolves, is change the terms of the conversation. Before 2013,
• 2:02:23
  Speaker 1: the cosmological principle sat largely unchallenged as a working assumption.
• 2:02:28
  Speaker 1: The structures that had been found up to that point,
• 2:02:31
  Speaker 1: the Sloan Great Wall, the large quasar groups were large
• 2:02:35
  Speaker 1: enough to raise eyebrows, but not large enough to constitute
• 2:02:39
  Speaker 1: a crisis. The Hercules-Corona-Borealis Great Wall moved the needle. It
• 2:02:45
  Speaker 1: forced cosmologists to take seriously the possibility that the universe's
• 2:02:50
  Speaker 1: large-scale structure has not converged to uniformity at the scales
• 2:02:54
  Speaker 1: we assumed it had. It prompted new analyses of the
• 2:02:58
  Speaker 1: existing data, new proposals for future instruments, new theoretical work
• 2:03:04
  Speaker 1: exploring what the models would look like if homogeneity holds
• 2:03:07
  Speaker 1: only at larger scales than currently assumed. All of that
• 2:03:11
  Speaker 1: is productive, regardless of the final answer. Whether the answer
• 2:03:16
  Speaker 1: turns out to require new physics, or simply a deeper
• 2:03:19
  Speaker 1: understanding of what we already have, the Hercules-Corona-Borealis Great Wall
• 2:03:25
  Speaker 1: has made the universe a stranger and more unsettling place
• 2:03:29
  Speaker 1: than it was before anyone noticed that clustering in the data.