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Dark Energy – Why the Universe Is Flying Apart · Talking Science

0:00
Imagine you're driving down the highway at 80
0:02
miles an hour. You suddenly see a massive concrete
0:05
wall ahead, so you just slam on the brakes with
0:08
everything you have. Like full panic mode. Right,
0:10
full panic. But instead of slowing down, your
0:14
car instantly accelerates to a million miles
0:16
an hour and just launches into the sky. Which
0:19
is... you know completely absurd it's completely
0:21
absurd that absolute defiance of logic that complete
0:24
shattering of what we think we know about how
0:27
physical objects behave that is exactly what
0:29
is happening to our entire universe right now
0:31
yeah it really is the definition of a paradigm
0:33
shift i mean we live in a cosmos that is actively
0:37
breaking the foundational rules we thought governed
0:40
it it's just wild so welcome to the deep dive
0:42
everyone today we're taking you into uh honestly
0:46
the single strangest observation modern science
0:49
has ever made. Without a doubt. The universe
0:51
isn't just expanding, it's getting bigger, faster,
0:54
and faster. And to be completely transparent
0:56
with you up front, nobody has a definitive answer
0:59
for why it's happening. No, we really don't.
1:01
The source material we're looking at today zeroes
1:03
in on this cosmic mystery, which scientists call
1:06
dark energy. But, uh... A key takeaway from our
1:10
readings is that dark energy isn't an answer.
1:13
It's just a placeholder name for a mystery that
1:16
makes up most of our reality. Exactly. I mean,
1:18
calling it dark energy implies we understand
1:20
it, right? The way we understand electrical energy
1:23
or thermal energy, we don't. Not even a little
1:26
bit. But to fully grasp why this acceleration
1:29
is causing such a crisis in modern physics. we
1:33
first need to trace the steps back to what astronomers
1:36
firmly believed was the undisputed truth. Right,
1:38
the old baseline. So before we get to the shock
1:41
of the acceleration, let's look at why everyone
1:43
assumed the universe was slowing down. Why were
1:46
they so confident? Well, the foundation of that
1:48
confidence goes all the way back to the 1920s
1:50
with Edwin Hubble. The telescope guy. The very
1:53
same. He observed that galaxies are, on average,
1:56
receding from one another. So the universe is
1:58
expanding. And if you rewind that expansion,
2:01
logically... Everything must have been packed
2:03
tightly together in the past. Which gives us
2:05
the Big Bang. Exactly, that initial outward push.
2:08
I want to make sure we're visualizing this correctly
2:10
for you listening, because the sources use an
2:12
analogy that really helps. They describe it like
2:14
a loaf of raisin bread baking in an oven. It's
2:19
a classic analogy for a reason. Yeah, so the
2:21
dough is space itself, and the raisins are the
2:23
galaxies. As the dough bakes and swells, the
2:26
raisins just get further apart. That's a perfect
2:29
way to picture it, because the galaxies aren't...
2:32
you know, firing thrusters and flying through
2:34
space. Right. The space between them is physically
2:37
stretching and that carries them along. Okay,
2:39
so I'm following the expanding dough. But here
2:42
is my confusion with the classical model. The
2:44
universe is filled with matter, right? Absolutely.
2:48
Galaxies, dust clouds, stars, planets. And all
2:52
of that matter has mass. And mass exerts gravity.
2:56
So if you have all these objects pulling on each
2:58
other gravitationally across the universe, shouldn't
3:01
that mutual attraction counteract the stretching?
3:05
You would assume that, yes. I mean, I'd assume
3:06
gravity would act like a massive brake on the
3:09
entire system. And so did every prominent physicist
3:12
for decades. It's completely logical. If you
3:15
have the initial explosive expansion from the
3:17
Big Bang pushing outward, but you have the collective
3:20
gravity of all the matter in the universe pulling
3:23
inward. The expansion has to lose momentum. It
3:26
has to. So the scientific community wasn't debating
3:29
if the expansion was decelerating. Oh, they assumed
3:32
it was a given? Totally a given. They were only
3:34
debating the ultimate outcome of that deceleration.
3:37
Right, like how the story ends. Yeah. Option
3:40
one was that there was enough matter in the universe
3:43
that gravity eventually wins, stops the expansion
3:46
completely, and pulls everything back together
3:48
in a big crunch. The ultimate collapse. And option
3:51
two. Option two was that there isn't quite enough
3:54
matter to stop it entirely. So the universe just
3:56
coasts outward forever, continually slowing down,
3:59
but never fully stopping. OK, so if the math
4:01
was so flawless and literally everyone agreed
4:04
gravity was putting on the brakes, why did anyone
4:06
even bother checking? Well, because scientists
4:09
want to know the exact parameters of the reality
4:11
they live in, you know. Fair enough. So in the
4:13
1990s, two independent teams of astronomers wanted
4:16
to settle the debate. They wanted to measure
4:18
the precise rate of deceleration to figure out
4:21
which fate awaited us, the Big Crunch or the
4:24
Infinite Coast. Right. To do that, they needed
4:26
a way to measure extreme distances across the
4:28
universe. So they use something called a Type
4:31
Ia supernova. Let me stop you there because the
4:34
sources call that a standard candle. What exactly
4:36
makes an exploding star standard? Okay, so a
4:40
Type Ia supernova starts with a white dwarf.
4:42
That's the super dense leftover core of a dead
4:45
star. Just a glowing ember of a star. Right,
4:47
and sometimes a white dwarf will... Siphon gas
4:51
off a nearby companion star. As it steals this
4:54
material, it gets heavier and heavier until it
4:57
hits a very specific mathematical mass limit.
5:00
Oh, like a tripwire. Exactly as a tripwire. When
5:02
it crosses that exact threshold, it triggers
5:04
a runaway nuclear fusion reaction and detonates.
5:07
Wow. Because they always explode at that precise
5:09
mass limit, the resulting explosion peaks at
5:12
almost exactly the same true intrinsic brightness
5:15
every single time. Ah, I see. So it's like having
5:18
a literal candle in a dark field. Exactly. If
5:22
you know exactly how bright a candle is up close,
5:25
and you walk, say, a mile away, you can measure
5:28
how dim it looks to your eye to calculate the
5:30
exact distance. That's the principle, yeah. So
5:32
because we know the true brightness of these
5:34
supernovae, measuring their apparent brightness
5:37
from Earth tells us exactly how far away they
5:40
are. Precisely. But just knowing the distance
5:43
isn't enough to track the expansion. Yeah. We
5:46
also have to know how fast that particular piece
5:49
of space is moving away from us. Okay, and how
5:51
do we figure that out? The sources talk about
5:53
the universe stretching their light, but I'm
5:55
not clear on the mechanics of that. Think of
5:57
light as a wave, like ripples on a pond. Okay.
6:00
As light from that distant supernova travels
6:02
toward Earth across billions of light years,
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the space it's traveling through is constantly
6:07
expanding. The dough is baking. Right. As space
6:11
stretches, the light wave itself physically gets
6:13
stretched out. The wavelength gets longer. And
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longer wavelengths mean what? In physics, longer
6:19
wavelengths of visible light appear red to our
6:22
eyes. This phenomenon is called redshift. So
6:26
the more the light is stretched out, the more
6:28
red it looks to our telescopes. And that tells
6:30
us how much the universe expanded while that
6:33
light was in transit. You've got it. Because
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looking far out into space means looking back
6:37
in time. since light takes billions of years
6:40
to reach us, these teams could look at supernovae
6:43
at different distances and map out the universe's
6:46
expansion speed across different eras. Oh, they
6:49
were building a historical timeline of the cosmos.
6:51
Yes, exactly. And they fully expected the timeline
6:54
to show that the expansion was much faster in
6:56
the deep past and slower recently. Because gravity
6:59
was pumping the brakes? Right. But in 1998, they
7:02
looked at the final data. and the results were
7:05
completely backward. Backward, meaning the supernovae
7:08
were fainter than they should have been. Fainter,
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which means further away. Which means? The expansion
7:13
of the universe hadn't been slowing down at all.
7:16
When they plotted the data points, they saw that
7:19
for the first several billion years of the universe's
7:22
life, the expansion did slow down. So gravity
7:25
was doing its job initially. It was. But roughly
7:28
5 billion years ago, the universe shifted gears.
7:31
The deceleration stopped, the universe hit the
7:34
gas pedal, and the expansion started accelerating
7:37
outward. That is completely wild. I mean, I can
7:40
just imagine the teams looking at their computer
7:42
screens thinking they had a software bug. Oh,
7:44
they spent months trying to find the error in
7:47
their own work. They tested every possible interference,
7:50
like maybe intergalactic dust was dimming the
7:53
supernovae or maybe they calibrated their sensors
7:55
wrong. But the data held up. It held up. The
7:58
universe is speeding up. It fundamentally broke
8:00
our understanding of cosmology. And the leaders
8:03
of those teams, they were actually jointly awarded
8:05
the Nobel Prize in physics. Okay, so if we accept
8:11
the observation that the universe hit the accelerator
8:13
about 5 billion years ago, the immediate burning
8:16
question has to be, what's the fuel? What is
8:20
the engine providing the repulsive voice to physically
8:23
push the fabric of space apart? Yeah, that is
8:26
the multi -billion dollar question right there.
8:28
The leading theoretical candidate we have, which
8:31
is heavily featured in our source text, is called
8:34
vacuum energy. vacuum energy yes and this requires
8:37
us to fundamentally rethink what empty means.
8:40
In classical physics, a vacuum is just a void
8:43
with nothing in it. Just empty space. Right.
8:46
But in modern quantum mechanics, empty space
8:48
isn't truly empty. It's a boiling, seething soup
8:51
of virtual particles popping into and out of
8:53
existence constantly. Okay, that sounds like
8:55
sci -fi. It does. But this activity means that
8:58
space itself has an inherent baseline energy.
9:01
Hold on, I need to stop you there because I am
9:02
genuinely getting tripped up by this. The text
9:04
uses an analogy of a box of gas to explain this.
9:07
So if I have a one cubic foot box filled with
9:10
gas, and I suddenly expand that box to two cubic
9:12
feet, the gas inside spreads out to fill the
9:14
new volume. Right, it dilutes. The density drops.
9:17
Are you saying vacuum energy doesn't do that?
9:19
That's exactly what I'm saying. Normal matter
9:20
dilutes when you expand the volume. Vacuum energy,
9:24
though, is a property of space itself. Okay.
9:26
So if every cubic foot of space contains a specific
9:29
amount of vacuum energy, and you suddenly create
9:32
a second cubic foot of space, You don't dilute
9:36
the energy. Because you just made more space.
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Exactly. Which means you now have twice as much
9:41
vacuum energy. That completely breaks my brain.
9:43
It violates every intuitive rule of how physical
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stuff is supposed to behave. It is highly counterintuitive.
9:50
But it elegantly explains the timeline the astronomers
9:54
found in 1998. It creates a cosmic feedback loop.
9:58
Let me see if I can trace the loop here. the
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universe expands which creates more space yes
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because there is more space there is more vacuum
10:05
energy that extra energy pushes the universe
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apart even faster which creates even more space
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which creates even more vacuum energy which pushes
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even harder so it's a runaway train and meanwhile
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all the normal matter the galaxies the stars
10:20
the stuff exerting inward gravity that is acting
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like the gas in the box right it's diluting as
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the universe gets bigger The matter gets spread
10:28
thinner and thinner, so its collective gravitational
10:30
pull just gets weaker. That's the mechanism.
10:33
So for the first 8 billion years after the Big
10:36
Bang, matter was dense enough that its gravity
10:39
overpowered the push of the vacuum energy, slowing
10:43
the expansion down. Oh, I see. But as the universe
10:45
kept growing, matter diluted and vacuum energy
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accumulated. Roughly 5 billion years ago, the
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outward push finally eclipsed the inward pull.
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The cosmic scale tipped and the universe began
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accelerating. You know, there's a detail in the
11:00
reading that I find just incredibly ironic. This
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idea that space has a built -in outward pressure.
11:05
It wasn't cooked up in the 1990s to explain this
11:07
acceleration. Not at all. Albert Einstein actually
11:10
invented it nearly a century earlier. He did,
11:12
yeah. Back in 1917 while he was finalizing his
11:15
general theory of relativity. Einstein's original
11:17
equations actually suggested that the universe
11:20
must be dynamic, like it had to be either expanding
11:23
or collapsing under its own gravity. But at the
11:25
time. Right. At the time, the entire scientific
11:27
establishment believed the universe was static
11:29
and eternal. It didn't move. So rather than trusting
11:33
his own math. Einstein added a brand new variable
11:36
to his equations to force them to be static.
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Yes. He called it the cosmological constant.
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A mathematical anti -gravity. Exactly. It was
11:45
a repulsive force of space itself, calibrated
11:48
perfectly to balance out the inward pull of matter.
11:51
So he introduced a fudge factor to match the
11:53
prevailing bias of his era? He did. But 12 years
11:56
later, Edwin Hubble discovered the universe was
11:59
actually expanding. The static universe was a
12:02
total myth. Oops. Yeah, Einstein realized he
12:05
hadn't needed to alter his equations at all,
12:07
and he famously referred to the cosmological
12:09
constant as his greatest blunder. Yet, fast forward
12:13
to today, and physicists are pulling Einstein's
12:15
blunder right out of the trash can. I mean, when
12:18
we try to mathematically describe the dark energy
12:21
pushing our universe apart, the cosmological
12:24
constant is the simplest, most elegant fit. He
12:27
was right for the completely wrong reasons. It's
12:30
a fascinating quirk of scientific history, isn't
12:32
it? But we have to be very careful not to just
12:35
slap Einstein's name on it and call the mystery
12:37
solved. Because when we actually try to combine
12:41
Einstein's constant with our modern quantum mechanics,
12:45
the entire theoretical framework, just collapses.
12:49
I'm really glad you brought this up because the
12:51
sources dedicate a significant amount of time
12:52
to this problem. We know dark energy is there.
12:55
We can measure its effects. Let's look at the
12:57
actual inventory of the universe today. According
13:00
to the measurements, dark energy accounts for
13:02
about 68 % of everything in the cosmos. It is
13:05
the overwhelmingly dominant ingredient of reality.
13:08
68%. And dark matter, which is the invisible
13:11
material providing extra gravity to hold galaxies
13:13
together, that makes up roughly 27%. An ordinary,
13:17
everyday matter, everything we can see, every
13:20
star, planet, tree, and person, accounts for
13:23
a measly 5%. Just 5%. It's wild to think about.
13:26
Okay, so if we can measure the universe at precisely
13:29
68 % dark energy, 27 % dark matter, 5 % normal
13:33
matter, why does the math collapse? What is the
13:38
actual problem? The problem arises when theorists
13:42
try to calculate how much vacuum energy there
13:44
should be. Using the fundamental rules of quantum
13:46
mechanics. Yeah. When they add up all the seething
13:49
quantum fields that we know exist in empty space,
13:51
they get a theoretical number for the cosmological
13:54
constant. Right. Then they compare that theoretical
13:57
prediction to the actual observed acceleration
13:59
measured by our telescopes. The two numbers don't
14:02
match. Well, I mean, science deals with margins
14:04
of error all the time, right? How far off are
14:06
the theorists? It is widely considered the single
14:09
worst prediction in the history of physics. The
14:11
quantum calculation is too high by a factor of
14:14
10 to the power of 120. Wait, like a 1 with 120
14:18
zeros behind it? Yes. 10 to the 120th power.
14:23
It's an error so unfathomably massive that it
14:27
really defies human comprehension. That is, I
14:30
mean, that's catastrophically wrong. If the theory
14:33
was correct, It predicts an energy density so
14:36
intense that it would have ripped the universe
14:38
apart completely before galaxies or atoms could
14:42
even form. So that's not a rounding error. That
14:44
is a flashing red siren that our understanding
14:46
of reality is fundamentally broken somewhere.
14:49
Definitely. If quantum mechanics says the vacuum
14:52
energy should be astronomically huge, but our
14:54
telescopes say it's just strong enough to gently
14:56
accelerate the universe, we are missing a major
14:59
puzzle piece. And this colossal mismatch is exactly
15:02
why many physicists are actively exploring alternatives
15:05
to Einstein's cosmological constant. Maybe dark
15:08
energy isn't a constant fixed property of space
15:10
at all. Right. The source mentions a concept
15:12
called quintessence. Could you explain how that
15:15
differs from the cosmological constant? Sure.
15:17
So the cosmological constant assumes the energy
15:19
density of a cubic foot of space is exactly the
15:22
same today as it was 10 billion years ago and
15:25
will be the same 10 billion years from now. It's
15:27
rigid. Exactly. But quintessence proposes that
15:30
dark energy is dynamic. It's an energy field
15:34
permeating space that can change over time. Oh,
15:37
interesting. It could slowly lose strength or
15:39
gain strength. almost like a shifting cosmic
15:42
weather pattern. Or maybe the problem is even
15:44
deeper. I saw one suggestion in the reading that
15:46
maybe Einstein's theory of general relativity,
15:49
you know, our core theory of gravity, is just
15:51
incomplete. That's another major possibility.
15:53
Because it works perfectly when we test it around
15:55
our sun or black holes, but maybe on the grandest
15:58
scale of the entire universe, gravity doesn't
16:01
act the way we think it does. All these hypotheses
16:04
are on the table right now. But science requires
16:06
evidence, and gathering that evidence requires
16:09
mapping the cosmos with unprecedented precision.
16:13
Right. This is why the European Space Agency
16:14
recently launched the Euclid Space Telescope,
16:17
and why massive ground -based projects like the
16:20
Dark Energy Spectroscopic Instrument, or DSAI,
16:23
are currently operating. How does drawing a map
16:26
solve a quantum math problem? By reconstructing
16:29
the precise history of the universe's expansion.
16:32
These telescopes are mapping the three -dimensional
16:35
positions of billions of distant galaxies to
16:38
trace exactly how the expansion rate has changed
16:41
over the last 10 billion years. If dark energy
16:44
is truly a cosmological constant, the timeline
16:47
of acceleration will follow a very specific,
16:50
rigid mathematical curve. But if it's quintessence...
16:54
Yeah. If the dark energy is shifting or drifting
16:57
over time, the expansion curve will wobble. Exactly.
17:00
And a shifting field will leave a different imprint
17:02
on the structure of the universe. In fact, some
17:05
of the initial data releases from these mega
17:07
-surveys in the mid -2020s have shown faint,
17:10
tantalizing hints that dark energy might actually
17:13
be drifting. Wait, really? Yeah, the measurements
17:15
are showing slight deviations from a perfect
17:17
cosmological constant. Wow. If that holds true,
17:20
it would completely rewrite physics. It would
17:21
be a monumental paradigm shift. But I want to
17:23
stress to you, the listener, that in science,
17:26
extraordinary claims require extraordinary evidence.
17:29
The statistical confidence isn't high enough
17:31
yet to declare a revolution. We need more data,
17:34
more observations over the next several years
17:37
to know for sure. Well, while we wait for Euclid
17:40
and other observatories to deliver their final
17:43
verdicts, I think we have to confront what this
17:45
acceleration actually means for the deep future
17:48
of the universe. The source paints a picture
17:51
that is... Frankly, chilling. It is a very sobering
17:55
reality. If dark energy remains dominant and
17:58
the universe continues to accelerate its expansion
18:00
forever, it dictates a very lonely fate for the
18:03
cosmos. Right now, we can look up and see hundreds
18:07
of billions of galaxies. But as the universe
18:09
expands faster and faster, the space between
18:12
us and those distant galaxies is stretching.
18:14
Stretching faster every second. And eventually
18:17
that space will be stretching so rapidly that
18:19
it actually exceeds the speed of light. which
18:21
means the light from those distant galaxies will
18:23
no longer be able to reach us. It's like trying
18:27
to run up a down escalator that's moving faster
18:29
than you can sprint. You'll never reach the top.
18:31
You'll just never make progress. So over billions
18:34
and billions of years, those galaxies will just
18:36
blink out of our observable universe. They will
18:39
cross a cosmic horizon and vanish forever. Vanish
18:42
without a trace. To an astronomer living 100
18:45
billion years from now, the night sky will be
18:47
almost entirely black. They will only be able
18:50
to see the stars of our own Milky Way and maybe
18:53
a few neighboring galaxies that were close enough
18:55
for gravity to hold them together. Everything
18:58
else will be gone. They will have absolutely
19:00
no observational evidence that a wider universe
19:03
ever existed. The cosmic microwave background,
19:06
the distant supernovae, all the clues that gave
19:09
us the Big Bang Theory wiped clean. just erased.
19:12
It makes you incredibly grateful that we happen
19:14
to be living in the exact sliver of cosmic time
19:17
where we can still see the evidence. We get to
19:19
map the galaxies before they run away from us.
19:21
It is incredibly humbling. I mean, it reminds
19:23
us that 68 % of our universe was found completely
19:26
by accident and defies explanation by our most
19:29
successful theories. And it's described by a
19:31
term Einstein invented and disowned. Science
19:34
is just an ongoing, beautifully unfinished project.
19:37
It really is. And as we wrap up today's deep
19:40
dive, I want to leave you with one final thought
19:42
to mull over, building on this idea of the universe
19:46
hiding its own history. We know the universe
19:48
has been accelerating for the past five billion
19:50
years, right? Slowly pulling the curtain shut
19:53
on the cosmos. Right. We worry about future astronomers
19:57
not being able to see what we see today. But
19:59
consider this. What if there were magnificent
20:02
grand cosmic structures out there that have already
20:05
been carried away? Are we, right now, looking
20:07
up at a universe that has already been partially
20:09
erased, long before human eyes even evolved to
20:12
look at it? Something to think about the next
20:14
time you look at the stars. Thanks for listening.