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Scientists Think Dark Energy May Be Changing Over Time · The Quark Side - Quantum Physics Podcast

• 0:01
  Speaker 1: Welcome to the quart Side Quantum Physics Podcast, an exploration
• 0:05
  Speaker 1: of the fundamental structure of reality, where quantum laws govern matter, energy,
• 0:11
  Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
• 0:16
  Speaker 1: and understanding begins with the smallest scales.
• 0:27
  Speaker 2: So I want you to just, uh imagine the entire
• 0:31
  Speaker 2: history of the universe for a second, like that simple
• 0:33
  Speaker 2: story you probably learned back in grade school, right.
• 0:36
  Speaker 3: The whole big bang expanding outward kind of thing.
• 0:38
  Speaker 2: Exactly, There's big bang and then gravity slowly starts pulling
• 0:43
  Speaker 2: everything back together. It's you know, it's like throwing a
• 0:46
  Speaker 2: baseball straight up into the air.
• 0:47
  Speaker 3: It shoots up, but eventually it has to slow down.
• 0:50
  Speaker 2: Right, But here is the massive twist that changes literally everything.
• 0:54
  Speaker 2: The baseball isn't slowing down.
• 0:56
  Speaker 3: Yeah, it's actually shooting upward faster and.
• 0:58
  Speaker 2: Faster, faster and faster. And the invisible force that's driving
• 1:02
  Speaker 2: this crazy acceleration is what we call dark energy. And
• 1:06
  Speaker 2: the scale of this is just mind bending because it
• 1:09
  Speaker 2: makes up what nearly seventy percent of the entire cosmos, Yeah.
• 1:12
  Speaker 3: Right around sixty eight to seventy percent. I mean, it
• 1:14
  Speaker 3: is the dominant feature of reality.
• 1:17
  Speaker 2: Which is wild and For the longest time, science just
• 1:19
  Speaker 2: thought this mysterious energy was a fixed, unchanging background feature
• 1:25
  Speaker 2: of the universe.
• 1:25
  Speaker 3: It's constant cosmological constant. Yeah, that was the absolute bedrock
• 1:29
  Speaker 3: assumption for decades.
• 1:31
  Speaker 2: But and this is why we're talking about this today.
• 1:34
  Speaker 2: Recent discoveries are suggesting that it might not be constant
• 1:36
  Speaker 2: at all, might actually be alive in a sense dynamic evolving, which.
• 1:41
  Speaker 3: Is a terrifying and thrilling prospect for astrophysics honestly, totally.
• 1:46
  Speaker 2: So our mission right now is to figure out what
• 1:48
  Speaker 2: happens when the foundation of reality turns out to be
• 1:51
  Speaker 2: shifting beneath our feet. And you know how this evolving
• 1:55
  Speaker 2: mystery might actually determine the ultimate destiny of existence itself.
• 1:59
  Speaker 3: Yeah, it literally rewrites how the world ends.
• 2:02
  Speaker 2: Right, But before we get into how dark energy is changing,
• 2:06
  Speaker 2: we probably need to talk about what we actually thought
• 2:08
  Speaker 2: it was doing in the first.
• 2:09
  Speaker 3: Place, the whole illusion of the constant exactly.
• 2:12
  Speaker 2: So walk me through this. What is the establishment view here?
• 2:14
  Speaker 3: Well, it's all anchored in what we call the standard
• 2:17
  Speaker 3: cosmological model. And understand it, you really have to go
• 2:20
  Speaker 3: back to.
• 2:20
  Speaker 2: Albert Einstein always, back to Einstein.
• 2:22
  Speaker 3: Always, so he had this concept called the cosmological constant,
• 2:26
  Speaker 3: and the idea was that empty space itself possesses a
• 2:30
  Speaker 3: fixed energy density.
• 2:31
  Speaker 2: Okay, so empty space isn't just nothing, it has an
• 2:34
  Speaker 2: energy to it.
• 2:35
  Speaker 3: Right. When Einstein was working on his field equations for
• 2:39
  Speaker 3: general relativity, the math basically showed that a universe filled
• 2:43
  Speaker 3: with matter should be dynamically unstable, like it should either
• 2:47
  Speaker 3: be collapsing in on itself or blowing apart.
• 2:49
  Speaker 2: Because gravity's pulling all the matter together.
• 2:51
  Speaker 3: Yeah, exactly. But back in the nineteen tens, everyone including Einstein,
• 2:56
  Speaker 3: just assumed the universe was static, eternal, and unmoving. So
• 3:01
  Speaker 3: to make his equations work with the static universe, he
• 3:04
  Speaker 3: threw in this cosmological constant, a mathematical fix. Essentially, it
• 3:09
  Speaker 3: acted as the steady, uniform outward push to perfectly balance
• 3:13
  Speaker 3: out the inward pull of gravity.
• 3:15
  Speaker 2: Oh wow, So he just added it to make the
• 3:17
  Speaker 2: math match what people believed at the time pretty much.
• 3:20
  Speaker 3: And of course, a few years later Edwin Hubble realizes
• 3:23
  Speaker 3: the universe is actually expanding, and Einstein calls the constant
• 3:27
  Speaker 3: his biggest blunder. He just drops it.
• 3:29
  Speaker 2: That's so funny. But then we brought it back didn't.
• 3:31
  Speaker 3: We We had to because in the late nineteen nineties
• 3:34
  Speaker 3: we realized the expansion of the universe was accelerating. So
• 3:37
  Speaker 3: physicists resurrected Einstein's constant. But this time it wasn't just
• 3:41
  Speaker 3: balancing gravity, it was completely overpowering it.
• 3:44
  Speaker 2: So in this model, does the energy ever change?
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  Speaker 3: No, that's the key. In this constant model, dark energy
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  Speaker 3: remains perfectly identical across all of time. As the universe expands,
• 3:56
  Speaker 3: you get more empty space, which just means you get
• 3:59
  Speaker 3: proportionally or dark energy.
• 4:01
  Speaker 2: Huh. So it's a steady, uniform push that just causes
• 4:04
  Speaker 2: galaxies to drift apart faster and faster forever exactly.
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  Speaker 3: It offered this incredible mathematical elegance for decades. The equations
• 4:13
  Speaker 3: aligned perfectly with everything we observed distant supernovae, how galaxies
• 4:18
  Speaker 3: are distributed, even the cosmic microwave background.
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  Speaker 2: I mean, I get why scientists love that. It makes
• 4:24
  Speaker 2: the universe predictable. It's like setting your cruise control on
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  Speaker 2: the highway.
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  Speaker 3: You know, it's a great way to put it.
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  Speaker 2: You said it to sixty five. You expect the car
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  Speaker 2: to maintain the exact same steady push forward. We basically
• 4:34
  Speaker 2: thought the universe was on cosmic cruise control.
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  Speaker 3: We really did, and they're psychological comfort in that.
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  Speaker 2: But if the equations work so remarkably well for so long,
• 4:42
  Speaker 2: what made us start questioning the dashboard like why did
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  Speaker 2: the cruise control start flashing warning lights?
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  Speaker 3: Well, it really comes down to our instruments getting better.
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  Speaker 3: The universe wasn't on cruise control, and the transition happened
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  Speaker 3: when the math just literally stopped adding up.
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  Speaker 2: And this is what we call the Hubble tension.
• 5:00
  Speaker 3: Yes, the Hubble tension. It is arguably the most famous
• 5:03
  Speaker 3: and frankly most frustrating inconsistency in modern astronomy today.
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  Speaker 2: Break that down for me, what exactly is the tension?
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  Speaker 3: So we're trying to measure the expansion rate of the universe,
• 5:14
  Speaker 3: and to do that we have two completely different, highly
• 5:18
  Speaker 3: precise methods. Okay, the first method looks at the really
• 5:21
  Speaker 3: early universe. We look at the cosmic microwave background, which
• 5:24
  Speaker 3: is basically the afterglow of the Big Bang.
• 5:27
  Speaker 2: Right from when the universe was super young.
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  Speaker 3: Exactly just a few hundred thousand years old. We take
• 5:32
  Speaker 3: that data, apply our standard model of a constant dark energy,
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  Speaker 3: and fast forward to predict how fast the universe should
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  Speaker 3: be expanding.
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  Speaker 2: Today, and we get a specific number.
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  Speaker 3: We do around sixty seven kilometers per second per megaparsec.
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  Speaker 2: Okay, sixty seven, got it.
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  Speaker 3: And the second method, the second method ignores the early
• 5:49
  Speaker 3: universe completely. It just looks at nearby galaxies. Right now,
• 5:53
  Speaker 3: we use a cosmic distance ladder looking at specific stars
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  Speaker 3: and supernovae to directly measure how fast the look universe
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  Speaker 3: is stretching out today.
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  Speaker 2: And that gives us a different number, a.
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  Speaker 3: Completely different number, around seventy three kilometers per second per megaparsec.
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  Speaker 2: Wait, really, it's a huge gap.
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  Speaker 3: It's about a nine percent difference. And initially everyone just
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  Speaker 3: assumed it was human error, right, like a calibration glitch
• 6:17
  Speaker 3: or something exactly, a smudge on a telescope lens, some
• 6:21
  Speaker 3: dust obscuring the stars, just some kind of experimental mistake.
• 6:25
  Speaker 2: It's imagine you're measuring your living room to buy a rug, right, yeah,
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  Speaker 2: and you use two different highly precise tape measures. One
• 6:34
  Speaker 2: says the room is ten feet wide and the other says.
• 6:36
  Speaker 3: It's twelve feet and you check it again and again.
• 6:38
  Speaker 2: Right, no matter how many times you check, they give
• 6:40
  Speaker 2: different answers. So at some point you have to admit
• 6:43
  Speaker 2: the tape measures are fine, the room itself is changing.
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  Speaker 3: That's exactly the disturbing implication of the Hubble tension. The
• 6:50
  Speaker 3: measurements have become insanely precise over the last decade, the
• 6:54
  Speaker 3: Hubble space telescope, the Plank satellite. They've practically eliminated the
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  Speaker 3: chance of this being a statistical fluke.
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  Speaker 2: So the error is not in the tools.
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  Speaker 3: No, the tools are fine, which means the universe has
• 7:06
  Speaker 3: evolved differently than our foundational theory is assumed.
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  Speaker 2: Okay, So if the early universe in the modern universe
• 7:11
  Speaker 2: are playing by different speed limits, the underlying engine, dark
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  Speaker 2: energy must be shifting gears.
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  Speaker 3: It has to be. It can't be a constant.
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  Speaker 2: So what kind of shifting room are we actually dealing
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  Speaker 2: with here? If the walls are stretching at varying speeds,
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  Speaker 2: what is causing that?
• 7:26
  Speaker 3: Well, this is where we get into some really radical
• 7:28
  Speaker 3: new theories. Recent large scale surveys are hinting that dark
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  Speaker 3: energy was actually weaker or stronger at different periods in
• 7:35
  Speaker 3: cosmic history.
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  Speaker 2: Which totally breaks the Einstein.
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  Speaker 3: Model, completely shatters it, and the leading concept to replace
• 7:42
  Speaker 3: it is something called quintessence.
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  Speaker 2: Quintessence, it sounds like a sci fi movie.
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  Speaker 3: I know, it sounds a bit mystical, but it's grounded
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  Speaker 3: in quantum physics. The theory of quintessence is that dark
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  Speaker 3: energy is not a property of empty space itself. Instead,
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  Speaker 3: it's a dynamic quantum field that permeates the entire universe.
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  Speaker 2: A field like magnetic field kind of.
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  Speaker 3: It's a scaler field. And the important thing is that
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  Speaker 3: it can slowly fluctuate and evolve over billions of years.
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  Speaker 2: Okay, so it's not a rigid law. It's more like
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  Speaker 2: a physical substance.
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  Speaker 3: Yes, exactly. It treats dark energy like a fluid that
• 8:17
  Speaker 3: can have shifting properties like variations in pressure density over time.
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  Speaker 2: But wait, how does empty space have a fluctuating field
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  Speaker 2: in it? Isn't it you know? Empty?
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  Speaker 3: Ah? Well, from a quantum physics perspective, empty space is
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  Speaker 3: never truly.
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  Speaker 2: Empty, right, because of quantum mechanics.
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  Speaker 3: Yeah, the vacuum of space is actually filled with fluctuating energies.
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  Speaker 3: You have these virtual particles just constantly bubbling in and
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  Speaker 3: out of existence.
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  Speaker 2: It's it's almost like a boiling pot of water. Yes,
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  Speaker 2: empty space is less like a blank canvas and more
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  Speaker 2: like this boiling pot, just constantly bubbling with energy.
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  Speaker 3: That's a perfect analogy, and so physicists thought, hey, maybe
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  Speaker 3: the energy from all this bubbling quantum vacuum is the
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  Speaker 3: dark energy.
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  Speaker 2: That makes logical sense. Yeah, it provides the mechanism for
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  Speaker 2: the push it.
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  Speaker 3: Does until you actually try to calculate it. And this
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  Speaker 3: leads to what physicists call the quantum catastrophe.
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  Speaker 2: The catastrophe that sounds bad.
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  Speaker 3: It's widely considered the most embarrassing mismatch in the entire
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  Speaker 3: history of science.
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  Speaker 2: Oh wow, how bad is it?
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  Speaker 3: Well, when physicists theoretically calculate how much energy should be
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  Speaker 3: in this bubbling quantum vacuum, the answer they get is
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  Speaker 3: larger than the observed dark energy by a factor of
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  Speaker 3: ten to the one hundred and twentieth power.
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  Speaker 2: Wait, ten to the one hundred and twentieth that's not
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  Speaker 2: just a rounding error.
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  Speaker 3: No, it's a one followed by one hundred and twenty zeros.
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  Speaker 3: If the quantum vacuum actually had that much energy, the
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  Speaker 3: repulsive force would be so violent that the entire universe
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  Speaker 3: would have ripped itself apart before a single atom could
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  Speaker 3: even form.
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  Speaker 2: That's insane. So our calculations are just catastrophically.
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  Speaker 3: Wrong, fundamentally broken. We are missing something profoundly important about
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  Speaker 3: the fundamental nature of reality.
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  Speaker 2: But if our calculations are that wrong, why do we
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  Speaker 2: trust our understanding of quantum fields at all when it
• 9:58
  Speaker 2: comes to the cosmos, Like, maybe we're barking up the
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  Speaker 2: completely wrong tree.
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  Speaker 3: And that is exactly what some physicists are saying. Because
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  Speaker 3: the calculations are so badly misaligned, some people are abandoning
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  Speaker 3: the idea of an energy field altogether.
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  Speaker 2: Really, so if it's not an energy field, what else
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  Speaker 2: could it be.
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  Speaker 3: Well, they're looking for even stranger explanations, like what if
• 10:19
  Speaker 3: cosmic acceleration isn't a new energy at all, but a
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  Speaker 3: sign that we need to modify the laws of gravity.
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  Speaker 2: Modify gravity? You mean Einstein was wrong about that too.
• 10:27
  Speaker 3: Potentially, the idea is that gravity might behave fundamentally differently
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  Speaker 3: across enormous intergalactic distances than general relativity predicts.
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  Speaker 2: So on a small scale like our solar system, gravity
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  Speaker 2: works normally, but when you zoom out to billions of
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  Speaker 2: light years, it starts acting weird.
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  Speaker 3: Exactly the attractive force might weaken faster than we thought,
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  Speaker 3: or maybe it even becomes repulsive at those massive scales.
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  Speaker 2: But modifying gravity feels, i don't know, almost like.
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  Speaker 3: Cheating, like a mathematical cop out.
• 10:56
  Speaker 2: Yeah, it's like looking at a mirage on a highway. Right.
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  Speaker 2: You see this wavy stuff in the distance, and you
• 11:00
  Speaker 2: think you're seeing a puddle of water, like a brand
• 11:02
  Speaker 2: new physical thing. But actually it's just the laws of
• 11:06
  Speaker 2: light bending in a way you didn't expect over a
• 11:08
  Speaker 2: long distance. So are we just seeing a gravitational mirage.
• 11:14
  Speaker 3: That's a huge area of debate, differentiating between adding a
• 11:18
  Speaker 3: new ingredient like dark energy, versus changing the rules of
• 11:23
  Speaker 3: the game itself, like modified gravity is really difficult.
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  Speaker 2: Are there other options besides just changing gravity?
• 11:29
  Speaker 3: Oh, it gets weirder. We get into extra dimensions beyond
• 11:32
  Speaker 3: ordinary space time.
• 11:33
  Speaker 2: Oh man, like string theory.
• 11:35
  Speaker 3: Stuff exactly like string theory. There are models suggesting our
• 11:39
  Speaker 3: universe is just interacting with a much larger multiversal structure,
• 11:42
  Speaker 3: like we are a three dimensional membrane floating in a
• 11:45
  Speaker 3: higher dimensional space.
• 11:46
  Speaker 2: Okay, you caa have to slow down a membrane.
• 11:49
  Speaker 3: Yeah, they call them brains. And the idea is that
• 11:52
  Speaker 3: while forces like light and electromagnetism are stuck on our brain,
• 11:56
  Speaker 3: Gravity isn't Gravity might be leaking out into these extra dimensions.
• 12:00
  Speaker 2: Wait, gravity's leaking out of our universe.
• 12:02
  Speaker 3: That's the theory, and over huge cosmological distances, that leakage
• 12:07
  Speaker 3: dilutes the strength of gravity, which makes it look like
• 12:10
  Speaker 3: the universe is accelerating its expansion.
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  Speaker 2: Because the rubber band pulling it together is losing its snap.
• 12:15
  Speaker 3: Exactly, it mimics dark energy perfectly without actually needing a
• 12:19
  Speaker 3: new energy field. Or the universe might be transitioning through
• 12:23
  Speaker 3: vast landscapes of possible energy states over cosmic time.
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  Speaker 2: So what does it actually mean for our understanding of
• 12:30
  Speaker 2: reality if gravity itself is just like a shape shifter,
• 12:35
  Speaker 2: or if we're bleeding into extra dimensions.
• 12:37
  Speaker 3: Well, whether it's an evolving quantum field like quintessence or
• 12:41
  Speaker 3: changing gravity or multiverse interactions, a fluctuating dark energy doesn't
• 12:46
  Speaker 3: just change our past, it completely rewrites the end of.
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  Speaker 2: The world, ah the ultimate fate of the universe.
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  Speaker 3: Right, because if this energy isn't constant, the ending isn't fixed.
• 12:55
  Speaker 2: Okay, So let's walk through these doomsday scenarios. Because if
• 12:57
  Speaker 2: the standard model was right, and dark energy is constant,
• 13:01
  Speaker 2: we get what's called the heat death, right, correct.
• 13:03
  Speaker 3: The heat death is basically a slow freezing fade to black.
• 13:07
  Speaker 2: Right. Constant dark energy just keeps pushing things apart forever.
• 13:11
  Speaker 2: Galaxies drift away from each other until they vanish from
• 13:14
  Speaker 2: the night sky.
• 13:15
  Speaker 3: Yeah, the stars eventually burnout. Gas for new stars gets exhausted.
• 13:20
  Speaker 3: Matter decays into this cold, dark, near eternal emptiness, absolute zero.
• 13:27
  Speaker 2: It's like stretching a giant rubber band and it just
• 13:29
  Speaker 2: freezes in that stretched position forever.
• 13:31
  Speaker 3: Exactly. It's bleak, but it's stable.
• 13:34
  Speaker 2: But if dark energy is evolving, we get some different options. Yeah,
• 13:37
  Speaker 2: like the big rip. Tell me about the big rip.
• 13:39
  Speaker 3: The big rip happens if this evolving dark energy actually
• 13:42
  Speaker 3: gets stronger over time? Oh no, Yeah, the expansion doesn't
• 13:46
  Speaker 3: just push galaxies apart. It becomes so violent that it
• 13:49
  Speaker 3: eventually overcomes gravity entirely. First it tears apart galaxy clusters,
• 13:54
  Speaker 3: Then it strips stars away from their galaxies.
• 13:56
  Speaker 2: And it doesn't stop there, does it.
• 13:58
  Speaker 3: No. Months before the end, planetary orbits destabilize, planets are
• 14:02
  Speaker 3: ripped away from their suns. Minutes before the end, the
• 14:05
  Speaker 3: planets themselves are torn apart.
• 14:07
  Speaker 2: The rubber band gets buled so hard that the rubber
• 14:09
  Speaker 2: itself dissolves into nothing.
• 14:11
  Speaker 3: Literally. Eventually, the expansion outpaces the electromagnetic forces holding molecules together,
• 14:17
  Speaker 3: and then the strong nuclear force holding atoms together. Individual
• 14:22
  Speaker 3: atoms are shredded.
• 14:23
  Speaker 2: So total sub atomic dissolution. That's horrifying. But there's a
• 14:27
  Speaker 2: third option, right, the big crunch.
• 14:29
  Speaker 3: Right, This is the opposite. This happens if dark energy
• 14:32
  Speaker 3: weakens over time or actually reverses its polarity.
• 14:35
  Speaker 2: So the rubber band snaps back exactly.
• 14:38
  Speaker 3: The expansion slows down, stops, and the universe starts collapsing
• 14:41
  Speaker 3: inward on itself.
• 14:42
  Speaker 2: It hits you in the hand and hits hard.
• 14:45
  Speaker 3: Galaxies collide, the background radiation of the universe heats up,
• 14:48
  Speaker 3: basically roasting everything until all matter and energy are crushed
• 14:52
  Speaker 3: into a single, infinitely dense singularity.
• 14:55
  Speaker 2: But a lot of physicists think a big crunch wouldn't
• 14:58
  Speaker 2: just be the end, right, like it could a cyclic rebirth.
• 15:01
  Speaker 3: Yeah, cyclic models. The idea is that the big crunch
• 15:04
  Speaker 3: bounces back and triggers a new big bang. The universe
• 15:07
  Speaker 3: dies and is reborn over and.
• 15:09
  Speaker 2: Over, which is fascinating. We're gonna have to ask if
• 15:12
  Speaker 2: the universe is this evolving dynamic system. Does a cyclic
• 15:16
  Speaker 2: rebirth actually make more physic sense or is that just
• 15:20
  Speaker 2: human bias? Like we like seasons, we like the idea
• 15:23
  Speaker 2: of life and death and rebirth. Does a cyclic model
• 15:27
  Speaker 2: just feel better than a one way trip to oblivion?
• 15:30
  Speaker 3: That is a phenomenal question. There is definitely a philosophical
• 15:33
  Speaker 3: comfort in cyclic models. It avoids the messy problem of
• 15:37
  Speaker 3: an absolute beginning or an absolute end. It's poetic, it
• 15:41
  Speaker 3: is poetic, but theoretical physics isn't built on poetry. Models
• 15:45
  Speaker 3: like the ex pyrotic universe, which uses those colliding brains
• 15:48
  Speaker 3: we talked about to explain the bounce. They are mathematically rigorous, so.
• 15:52
  Speaker 2: They aren't just wishful thinking.
• 15:53
  Speaker 3: No, not at all. But ultimately, the only way to
• 15:56
  Speaker 3: strip away the human bias and figure out which of
• 15:58
  Speaker 3: these three apocalypses is our actual destiny is through observation.
• 16:01
  Speaker 3: We have to map the exact evolutionary curve of dark energy.
• 16:04
  Speaker 2: Which brings us to the ultimate problem. We're hunting ghosts
• 16:07
  Speaker 2: pretty much because to figure out which doom awaits us,
• 16:10
  Speaker 2: we need proof. Ah, but how do you measure something
• 16:13
  Speaker 2: you literally can't see, touch, or isolate in a lab.
• 16:18
  Speaker 2: Dark energy is entirely invisible.
• 16:20
  Speaker 3: It's the ultimate forensic astronomy. We are looking for the
• 16:23
  Speaker 3: invisible shadows and wakes left behind by this force.
• 16:27
  Speaker 2: So how do we actually do that well?
• 16:29
  Speaker 3: Cosmologists and for its existence by looking for tiny, tiny
• 16:33
  Speaker 3: deviations in large scale cosmic behavior, like what like looking
• 16:37
  Speaker 3: at distant supernovae, how galaxies cluster together over billions of years,
• 16:41
  Speaker 3: and something called gravitational lensing.
• 16:44
  Speaker 2: Gravitational lensing, that's when the gravity of huge objects bends light.
• 16:48
  Speaker 3: Around them, right, exactly, Massive structures like filaments of dark
• 16:52
  Speaker 3: matter distort the space time around them. As light from
• 16:55
  Speaker 3: background galaxies travels to us, it passes through these distortions,
• 16:59
  Speaker 3: and the shape of those distant galaxies look slightly stretched
• 17:02
  Speaker 3: or smeared.
• 17:03
  Speaker 2: But the distortion has to be microscopic.
• 17:05
  Speaker 3: It's incredibly subtle.
• 17:08
  Speaker 2: It's like trying to prove the wind exists, right, but
• 17:10
  Speaker 2: you're not allowed to feel it on your skin. You
• 17:12
  Speaker 2: can only look at photographs of trees bending in the distance.
• 17:15
  Speaker 3: That is exactly what it's like. We look at the
• 17:17
  Speaker 3: bending of light to map out where the dark matter
• 17:19
  Speaker 3: is because dark matter pulls things together while dark energy pushes.
• 17:23
  Speaker 2: Them apart, a cosmic tug of war.
• 17:25
  Speaker 3: Yes, and by mapping this tug of war across billions
• 17:29
  Speaker 3: of years of cosmic history, we can reconstruct exactly how
• 17:33
  Speaker 3: strong dark energy was at different epochs.
• 17:36
  Speaker 2: Okay, so why does mapping the history of the universe's
• 17:39
  Speaker 2: structure help us predict its future shape?
• 17:42
  Speaker 3: Because if we can see that the push of dark
• 17:44
  Speaker 3: energy was weaker five billion years ago than it is today,
• 17:47
  Speaker 3: we have proven it's an evolving field. We can plot
• 17:50
  Speaker 3: that curve and project it forward to see if we're
• 17:52
  Speaker 3: headed for a rip, a crunch, or a freeze.
• 17:56
  Speaker 2: Wow. And we have new instruments coming online to do this.
• 17:59
  Speaker 3: Right, Yes, and they are completely transforming the science. We
• 18:01
  Speaker 3: have the James Web Space Telescope, obviously, but there's also
• 18:04
  Speaker 3: the European Space Agency's EUCLID mission.
• 18:07
  Speaker 2: EUCLID is up there now mapping the dark universe exactly.
• 18:10
  Speaker 3: Its entire goal is to map the cosmic web out
• 18:12
  Speaker 3: to ten billion light years. And then on the ground
• 18:15
  Speaker 3: we have the Vera Reuben Observatory in Chile.
• 18:17
  Speaker 2: I've heard about this one. It's taking a massive time
• 18:20
  Speaker 2: lapse of the sky.
• 18:21
  Speaker 3: It's unprecedented. It will capture the entire southern sky every
• 18:24
  Speaker 3: few nights, generating petabytes of data. It will catalog millions
• 18:28
  Speaker 3: of supernovae. By combining data from Euclid and Reuben, we
• 18:33
  Speaker 3: are finally going to get the precision we need.
• 18:35
  Speaker 2: It's so much data. We're talking about measuring the shapes
• 18:38
  Speaker 2: of billions of galaxies.
• 18:39
  Speaker 3: Billions. It requires supercomputers just to process the images, but
• 18:44
  Speaker 3: it's the only way to pin down exactly what dark
• 18:46
  Speaker 3: energy is doing.
• 18:47
  Speaker 2: It really forces a philosophical paradigm shift, doesn't it. The
• 18:50
  Speaker 2: pursuit of these invisible forces leads to this really profound
• 18:54
  Speaker 2: realization about our own limitations as a species.
• 18:57
  Speaker 3: It's incredibly humbling.
• 18:58
  Speaker 2: Because, I mean, you think about evolutionary biology. Human brains
• 19:01
  Speaker 2: evolve to survive on Earth. We evolve to dodge predators,
• 19:05
  Speaker 2: fine food, build shelters, right.
• 19:07
  Speaker 3: We didn't evolve to instinctively understand the quantum architecture of
• 19:11
  Speaker 3: space time across billions of light years exactly.
• 19:15
  Speaker 2: And the humbling truth is that all the visible stuff,
• 19:18
  Speaker 2: the stars, the planets, the galaxies, everything we can see
• 19:21
  Speaker 2: with our eyes is just a tiny surface layer. It's
• 19:24
  Speaker 2: less than five percent of the universe.
• 19:26
  Speaker 3: The real mechanics of reality are governed by invisible structures
• 19:30
  Speaker 3: dark matter and dark energy that are currently beyond our comprehension.
• 19:34
  Speaker 2: It's historically parallel to every major scientific revolution, right No, Oh, absolutely,
• 19:39
  Speaker 2: like discovering the Earth isn't the center of the universe,
• 19:42
  Speaker 2: or that space and time aren't absolute, or that solid
• 19:45
  Speaker 2: matter is mostly empty space. Every single time our basic
• 19:50
  Speaker 2: assumptions get shattered.
• 19:51
  Speaker 3: And dark energy is forcing the next great conceptual transformation.
• 19:56
  Speaker 3: It's introducing the idea of a living universe.
• 19:58
  Speaker 2: I love that phrase living universe.
• 20:01
  Speaker 3: If dark energy evolves, the cosmos isn't just a passive
• 20:04
  Speaker 3: mechanical backdrop where galaxies drift around like dust motes. It's
• 20:07
  Speaker 3: an unfolding dynamic system. There are hidden processes actively shaping reality.
• 20:13
  Speaker 2: It means reality itself is profoundly unfinished.
• 20:16
  Speaker 3: Yes. From the perspective of human knowledge, we are barely
• 20:19
  Speaker 3: scratching the surface.
• 20:20
  Speaker 2: We walk around thinking we've got the universe pretty much
• 20:22
  Speaker 2: figured out. I mean, we have smartphones, we split the atom,
• 20:25
  Speaker 2: we put rovers on Mars, but we literally cannot explain
• 20:30
  Speaker 2: seventy percent of the room we're sitting in.
• 20:32
  Speaker 3: It's wild when you phrase it like that.
• 20:34
  Speaker 2: How do scientists deal with the psychological weight of that?
• 20:38
  Speaker 2: Knowing that every new observation like the Hubble tension just
• 20:42
  Speaker 2: seems to reveal deeper mysteries rather than final answers.
• 20:46
  Speaker 3: Honestly, most physicists thrive on it. If we had all
• 20:50
  Speaker 3: the final answers, the job would be boring. The mystery
• 20:53
  Speaker 3: means the universe is still scientifically vibrant. It means there
• 20:57
  Speaker 3: is still profound fundamental physics to be discovered.
• 21:01
  Speaker 2: It's job security for astrophysicists exactly.
• 21:03
  Speaker 3: But it also means we have to stay humble and
• 21:06
  Speaker 3: be willing to throw out our most cherished theories when
• 21:09
  Speaker 3: the universe tells us we're wrong.
• 21:11
  Speaker 2: Well, let's bring this all back down to Earth for
• 21:12
  Speaker 2: a second and just recap the incredible journey we've been on.
• 21:15
  Speaker 3: It's been a lot to process.
• 21:17
  Speaker 2: It, really is. We started with this simple, predictable universe
• 21:21
  Speaker 2: driven by a constant, elegant force. The cruise control was set,
• 21:25
  Speaker 2: but as our tools got better, we realized the math
• 21:28
  Speaker 2: was breaking. The Hubble tension showed us that the universe
• 21:31
  Speaker 2: is stretching at different speeds we explored how this might
• 21:34
  Speaker 2: be a fluctuating quantum field like quintessence, causing massive headaches
• 21:39
  Speaker 2: for quantum physicists.
• 21:40
  Speaker 3: The ten to the one hundred and twenty is power mistake.
• 21:42
  Speaker 2: Exactly the worst prediction in science, and that led us
• 21:46
  Speaker 2: to the truly mind bending possibilities that maybe gravity itself
• 21:50
  Speaker 2: is changing, or that our universe is bleeding out into
• 21:53
  Speaker 2: extra dimensions.
• 21:54
  Speaker 3: And all of this dictates whether we freeze and a
• 21:57
  Speaker 3: heat death, tear apart in a big rip, or collapse
• 21:59
  Speaker 3: in a big crunch.
• 22:00
  Speaker 2: Which is why we have to build these massive observatories
• 22:03
  Speaker 2: like Euclid and Reuben, just to hunt for the invisible
• 22:06
  Speaker 2: clues left behind. It's an amazing time for cosmology. But
• 22:10
  Speaker 2: before we wrap up, I want to leave you with
• 22:12
  Speaker 2: a thought that really builds on all this. Okay, am
• 22:14
  Speaker 2: ready we talk about the universe evolving, right, We've seen
• 22:17
  Speaker 2: that dark energy might be a mutating, shifting force over
• 22:20
  Speaker 2: billions of years, almost like a living organism adapting. Well,
• 22:24
  Speaker 2: if the underlying forces of our universe are capable of evolving,
• 22:29
  Speaker 2: does that mean the laws of physics themselves have a lifespan?
• 22:31
  Speaker 3: Oh?
• 22:32
  Speaker 2: Wow, think about it. We treat the laws of physics
• 22:34
  Speaker 2: as immortal. But if the rules of reality can die
• 22:37
  Speaker 2: and be replaced as these quantum fields shift, what unimaginable
• 22:42
  Speaker 2: physics might govern the next version of the cosmos after
• 22:44
  Speaker 2: our dark energy has finished its work. Are we just
• 22:47
  Speaker 2: living in one temporary iteration of reality?
• 22:50
  Speaker 3: That is something that will keep me awake tonight.
• 22:52
  Speaker 2: It's crazy to think about a universe that is still
• 22:55
  Speaker 2: actively deciding what it wants to be until next time.
• 22:58
  Speaker 2: Keep looking up