Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Imagine standing outside on a really dark night, just looking
Speaker 2: up at the stars. You've probably been told that everything
Speaker 2: up there is accelerating away from us, right, push by
Speaker 2: this mysterious invisible force called dark energy, right.
Speaker 3: Which supposedly makes up roughly what seventy percent of our universe?
Speaker 2: Exactly seventy percent. But uh, what if I told you
Speaker 2: that dark energy just doesn't actually exist? Like, what if
Speaker 2: it's just a mathematical ghoth that we invented to cover
Speaker 2: up a gaping hole in our understanding of gravity.
Speaker 3: I mean that fundamentally depends how we view reality. If
Speaker 3: dark energy is just a phantom placeholder, it means the
Speaker 3: standard model of cosmology, the whole framework we use to
Speaker 3: understand the origin and fate of the universe, it has
Speaker 3: a massive flaw right at its center.
Speaker 2: Yeah, it's wild to think about. So today's deep dive
Speaker 2: is going to explore a really radical new framework from
Speaker 2: theoretical physicists Walmagueyo and re Out of Imperial College London.
Speaker 3: Oh, this is such an exciting theory.
Speaker 2: It really is. They published a theory attempting to explain
Speaker 2: the acceleration of the cosmos without a single drop of
Speaker 2: dark energy. Instead, they're looking at the universe entirely through
Speaker 2: the lens of thermodynamics, you know, like the physics of
Speaker 2: heat and engines and energy transfer.
Speaker 3: Which is a completely entirely different paradigm completely.
Speaker 2: Okay, let's unpack this, because if we want to throw
Speaker 2: out dark energy, we really have to start with the
Speaker 2: problem that forced us to invent it in the first place.
Speaker 3: Right to understand why we're even looking at a new theory,
Speaker 3: we have to look at why the absolute gold standard
Speaker 3: of physics is currently failing us. I mean, Albert Einstein's
Speaker 3: theory of general relativity is arguably one of the most
Speaker 3: successful scientific theories of all time. Absolutely, it tells us
Speaker 3: that gravity isn't just some invisible tether pulling planets together.
Speaker 3: It is the actual curving and warping of a four
Speaker 3: dimensional fabric called space time.
Speaker 2: Right, So, heavy objects like stars essentially bend this fabric,
Speaker 2: and that curvature dictates how other objects.
Speaker 3: Move exactly, and it works wonderfully almost everywhere we look.
Speaker 3: It predicts the weird orbit of mercury around our sun.
Speaker 3: It explains how light bends around a black hole.
Speaker 2: I mean, it's the only reason the GPS satellites orbiting
Speaker 2: the Earth can successfully pinpoint your phone on a map.
Speaker 3: Right, Yeah, without general relativity, your GPS would be off
Speaker 3: by miles every single day. But the problem is, when
Speaker 3: you zoom out to the scale of the entire universe,
Speaker 3: Einstein's framework just hits a wall.
Speaker 2: And this is what's known as the cosmological constant problem.
Speaker 3: Right, that's the one, and honestly, it is arguably the
Speaker 3: most embarrassing mismatch in the history of theoretical physics.
Speaker 2: Okay, so I know this involves empty space, But why
Speaker 2: is measuring literally nothing so incredibly complicated?
Speaker 3: Well, because empty space isn't actually empty.
Speaker 2: Wait, what do you mean If.
Speaker 3: You take a patch of space and just remove every
Speaker 3: single atom, every photon of light, every trace of matter,
Speaker 3: you might think you're left with zero energy, But quantum
Speaker 3: mechanics tells us a very different story.
Speaker 2: H Right, The quantum world is always.
Speaker 3: Messy, very messy. It operates on a principle of constant fluctuation.
Speaker 3: Even in a perfect vacuum, these virtual particles are constantly
Speaker 3: bubbling into existence and popping back out. Empty space is
Speaker 3: basically a boiling, turbulent sea of quantum energy.
Speaker 2: Okay, so quantum physicists can actually calculate how much energy
Speaker 2: is bubbling in this cosmic vacuum, right.
Speaker 3: They can. But when they run the math to predict
Speaker 3: how much energy should be an empty space, the number
Speaker 3: they get is just unimaginably huge. It is a one
Speaker 3: followed by one hundred and twenty zeros.
Speaker 2: Fee to one. With one hundred and twenty zeros, that's
Speaker 2: I can't even fathom a number that large.
Speaker 3: Nobody can. It's absurdly huge.
Speaker 2: But when astronomers actually point their telescopes out into the darkest,
Speaker 2: emptiest patches of the night sky, we don't see an explosive,
Speaker 2: boiling universe. The observed energy of empty space is microscopic.
Speaker 3: It's absolutely tiny. So we have this unbridgable gap between
Speaker 3: the quantum world, which predicts a violently energetic vacuum and
Speaker 3: the cosmic world, which observes a very calm.
Speaker 2: One in general relativity just simply cannot reconcile these two realities.
Speaker 3: No, the math totally breaks down, And this huge discrepancy
Speaker 3: is exactly why physicists introduce dark energy. It was basically
Speaker 3: a way to mathematically balance the cosmic books, just to.
Speaker 2: Explain why the universe is expanding the way it is
Speaker 2: without tossing out Einstein.
Speaker 3: Entirely precisely, they needed a patch for the whole.
Speaker 2: But if Einstein's math is creating this unbridgable gap, it
Speaker 2: means we can't just tweak general relativity, right, We have
Speaker 2: to derive gravity from a completely different starting point. Has
Speaker 2: anyone actually tried to build gravity from scratch using something else?
Speaker 3: They have? Actually, Back in nineteen ninety five, a physicist
Speaker 3: named Ted Jacobson published a seminal paper doing exactly that.
Speaker 2: Okay, nineteen ninety five, that's a while ago. What was
Speaker 2: his approach?
Speaker 3: Well before Jacobson, the physicists like Stephen Hawking had already
Speaker 3: proven that black holes have a temperature and they have entropy.
Speaker 2: Oh right, Hawking radiation.
Speaker 3: Exactly So, in other words, Einstein's gravity possesses thermal properties.
Speaker 3: Jackson looked at that relationship and wondered if it could
Speaker 3: be a two way street.
Speaker 2: Oh I see, he ran the logic in reverse. Instead
Speaker 2: of saying gravity has a temperature, he asked if temperature
Speaker 2: and heat can actually create gravity.
Speaker 3: That is the crucial pivot right there. Jacobson started with
Speaker 3: the foundational laws of thermodynamics. Think about what entropy really is.
Speaker 3: It's a measure of hidden information or disorder in a system.
Speaker 2: Right like a shattered coffee mug has more entropy than
Speaker 2: a whole one exactly.
Speaker 3: Jacobson connected the entropy of a patch of space to
Speaker 3: the actual surface area of that space. He showed mathematically
Speaker 3: that if heat flows across a boundary in space, the
Speaker 3: entropy changes. Okay, To accommodate that change in entropy, the
Speaker 3: actual geometry of the space has to warp and bend.
Speaker 2: And warping space time is the literal definition of gravity.
Speaker 2: So he used the laws of heat to mathematically derive
Speaker 2: Einstein's equations of general relativity.
Speaker 3: He really did. He built Einstein's theory using nothing but thermodynamics.
Speaker 2: It is amazing.
Speaker 3: What's fascinating here is that it proved gravity might not
Speaker 3: be a fundamental force at all. It might just be
Speaker 3: a large scale emergent property of heat and energy, much
Speaker 3: like how the temperature of a room is just an
Speaker 3: emergent property of billions of invisible air molecules bouncing off
Speaker 3: each other.
Speaker 2: Wow. So if Jacobs improved gravity is thermodynamic back in
Speaker 2: nineteen ninety five, why are we only getting this new
Speaker 2: dark energy killing framework right now? What took almost thirty years?
Speaker 3: Because the math is agonizingly difficult and physicists just got stuck.
Speaker 3: Jean Maguejo, the senior author of this new paper, read
Speaker 3: Jacobson's work right after finishing his PhD, and he was
Speaker 3: utterly captivated by it.
Speaker 2: He couldn't figure out.
Speaker 3: He spent years decades really trying to build on it
Speaker 3: and feeling every single time he tried to push the
Speaker 3: idea forward the equations just fell apart.
Speaker 2: What was the roadblock? What was he doing wrong?
Speaker 3: Well, he, along with almost everyone else in the field,
Speaker 3: was trying to take Jacobson's thermodynamic construction and retrofit it
Speaker 3: to match existing theories.
Speaker 2: Oh, because they already knew what the final picture of
Speaker 2: gravity was supposed to look like. They had Einstein's template right.
Speaker 3: So they were trying to force these new thermodynamic puzzle
Speaker 3: pieces into Einstein's predetermined box.
Speaker 2: It sounds like trying to write a song where you
Speaker 2: already know you have to end on a specific chord progression,
Speaker 2: and it's just making the whole creative process feel unnatural
Speaker 2: and broken.
Speaker 3: That's a perfect analogy. The turning point didn't actually come
Speaker 3: until mcgueo was on holiday on a remote Greek island,
Speaker 3: a Greek island, nice, yeah, and he had absolutely no
Speaker 3: Internet access, no distractions, and he suddenly realized his underlying
Speaker 3: approach was flawed. He needed to wipe the slate clean.
Speaker 2: So he stopped trying to force the math to recreate
Speaker 2: standard gravity exactly.
Speaker 3: He decided to start purely with thermal physics, follow the
Speaker 3: equations blindly, and just accept whatever weird, unprecedented theory of
Speaker 3: gravity naturally emerged on the other side.
Speaker 2: I mean, that is a massive leap of faith for
Speaker 2: a theoretical physicist. You're basically saying, I'm going to abandon
Speaker 2: the most elegant, proven theory of the twentieth century just
Speaker 2: to see where this raw thermal math takes me.
Speaker 3: It requires an incredible amount of intellectual bravery. Honestly, general
Speaker 3: relativity works so perfectly on the local scale that letting
Speaker 3: go of it to follow thermodynamic equations requires you to
Speaker 3: accept that the universe might look entirely alien compared to
Speaker 3: what we currently believe.
Speaker 2: Okay, So mcguasho gets back from his island epiphany, he
Speaker 2: teams up with his PhD student Race at Shay, and
Speaker 2: they start building a brand new theory of gravity purely
Speaker 2: from thermal physics.
Speaker 3: Right.
Speaker 2: But they don't look at colliding galaxies or supermassive black holes.
Speaker 2: They look at engines. Specifically, they frame the gravity of
Speaker 2: the universe as an autocycle.
Speaker 3: Yep, an autocycle.
Speaker 2: Waits up an autocycle like the internal combustion engine sitting
Speaker 2: under the hood of a standard gasoline.
Speaker 3: Car, the very same engine.
Speaker 2: Let me visualize this because it sounds completely absurd. In
Speaker 2: my car, I have fuel injecting into a cylinder, A
Speaker 2: spark plug ignites it. The resulting explosion pushes a physical
Speaker 2: metal piston down, which turns a crank shaft, which spins
Speaker 2: my wheels.
Speaker 3: That's the basic mechanics. Y.
Speaker 2: How on earth do you apply a mechanical car engine
Speaker 2: to the four dimensional fabric of space time, like, what
Speaker 2: is the piston in the universe?
Speaker 3: Well, it helps to step back and look at what
Speaker 3: an engine is doing on a thermodynamic level. When physicists
Speaker 3: previously tried to link gravity and heat, they were essentially
Speaker 3: only looking at heat flowing from a hot place to
Speaker 3: a cold place. Okay, but that is the simplest, most
Speaker 3: passive form of thermodynamics. Think of a hot cup of
Speaker 3: coffee cooling down on a desk. That's just basic heat transfer.
Speaker 3: An engine is different. An engine involves actual work.
Speaker 2: Right, The heat in a car engine is being actively
Speaker 2: converted into mechanical work to move a two ton vehicle
Speaker 2: down the highway exactly.
Speaker 3: And Mgueo andysa Kai realized that previous cosmic models were
Speaker 3: completely ignoring the work aspect. They were treating the universe
Speaker 3: like a cooling cup of coffee rather than a dynamic machine.
Speaker 2: So they injected these missing elements into the math.
Speaker 3: Yes, and to do this they set up a theoretical
Speaker 3: framework using something called a causal diamond.
Speaker 2: Okay, a causal diamond are we talking about like actual
Speaker 2: geometry floating in space.
Speaker 3: Not a physical object. No, think of a causal diamond
Speaker 3: as a localized bubble of space time A bubble, got it,
Speaker 3: Because the speed of light is the absolute speed limit
Speaker 3: of the universe. There is a strict boundary on how
Speaker 3: far a signal or ray of light can travel in
Speaker 3: a set amount of time.
Speaker 2: Right, nothing can go faster than.
Speaker 3: Life exactly, So a causal diamond represents that limit. It
Speaker 3: is an isolated bubble representing the maximum region of space
Speaker 3: where events can actually influence each other. They use this
Speaker 3: bubble as a tiny theoretical laboratory.
Speaker 2: So they let heat flow in and out of the
Speaker 2: boundaries of this space time bubble. But they also calculated
Speaker 2: the thermodynamic work happening inside it. That's right, But I'm
Speaker 2: still stuck on my question from earlier. What is the
Speaker 2: universe's version of a piston? What is the work actually doing.
Speaker 3: So the gas inside the cosmic engine is the energy
Speaker 3: of the universe itself, and the piston is the physical
Speaker 3: boundary of that space time bubble. Okay, when the internal
Speaker 3: combustion happens in this thermodynamic sense, the energy does work
Speaker 3: to physically stretch the fabric of space time. The universe
Speaker 3: doing the work to expand its own boundaries is the
Speaker 3: mathematical equivalent of the hot gas pushing the metal piston
Speaker 3: in your car.
Speaker 2: Okay, that actually makes sense. The expansion of space itself
Speaker 2: is the mechanical work exactly. But when they ran the
Speaker 2: math on this cosmic engine treating gravity this way, they
Speaker 2: hit a result so shocking they almost threw the whole
Speaker 2: paper in the trash. The mass revealed a gravitational theory
Speaker 2: where matter and energy could be continuously created or destroyed.
Speaker 3: Which is usually a massive, massive red flag.
Speaker 2: Here's where it gets really interesting, though, because you and
Speaker 2: I both know the conservation of mass and energy is
Speaker 2: basically rule number one in physics. You can't just break
Speaker 2: a fundamental law of the universe.
Speaker 3: Well, you really can.
Speaker 2: It is drilled into every science student from day one.
Speaker 2: Energy cannot be created or destroyed, only transformed. If I
Speaker 2: turned in a high school physics test where I just
Speaker 2: magically conjured new matter out of nowhere, I would fail.
Speaker 3: You definitely fail.
Speaker 2: How did this not immediately get thrown out as a
Speaker 2: fundamental math error.
Speaker 3: Because normally it would be. If your equations violate the
Speaker 3: conservation of energy, you almost always assume you dropped a
Speaker 3: minus sign or you carried a zero wrong somewhere Migueo
Speaker 3: and Ech felt exactly the same way. Their immediate instinct
Speaker 3: was that their theory was fundamentally broken.
Speaker 2: They thought they just messed up the calculations.
Speaker 3: But they checked the math, and they checked it again.
Speaker 3: It was sound. The thermodynamic engine model absolutely demanded that
Speaker 3: the conservation laws be modified.
Speaker 2: So instead of throwing it away, they decided to follow
Speaker 2: the math and apply this broken rule to the universe
Speaker 2: as a hole to see what would happen.
Speaker 3: They asked a terrifying question, what if this isn't a
Speaker 3: bug but a feature. To understand why this is so profound,
Speaker 3: we really have to look at the standard model of
Speaker 3: cosmology again. Okay, In our normal universe, matter has positive
Speaker 3: mass and it exerts gravity. Gravity pulls things together. So
Speaker 3: as the universe expands from the Big Bang, all the
Speaker 3: galaxy stars in dark matter should be pulling on each
Speaker 3: other gravitationally.
Speaker 2: Right, this collective poll should be acting like a giant
Speaker 2: brake pedal, slowing the expansion of the universe down.
Speaker 3: It should be decelerating.
Speaker 2: But we know from observing distant supernovas that the universe
Speaker 2: isn't decelerating, It is accelerating. The brake pedal isn't working
Speaker 2: someone is actively slamming on the gas. Yes, and that
Speaker 2: is why we invented dark energy to begin with, to
Speaker 2: act as a mysterious anti gravity force pushing everything apart
Speaker 2: to counteract the pulling of normal matter.
Speaker 3: Right. So, now let's apply Mguejo and Isaka's engine model
Speaker 3: to that scenario. In their thermodynamic gravity, the strict conservation
Speaker 3: law is modified. It allows for the continuous creation of
Speaker 3: new matter and energy as the universe hums along. If
Speaker 3: matter is continuously being generated while the universe expands, it
Speaker 3: fundamentally alters how the thermodynamics of the cosmos operate.
Speaker 2: Would I need to wrap my head around this. If
Speaker 2: you are creating more matter, wouldn't you just have more
Speaker 2: gravity pulling things together. Wouldn't more matter hit the brake
Speaker 2: pedal even harder?
Speaker 3: That is the intuitive assumption. Yes, yes, but thermodynamics operates differently.
Speaker 3: It all comes down to pressure. Yeah. In a closed system,
Speaker 3: if you suddenly start continuously generating new material to keep
Speaker 3: your engine running, that continuous generation actually alters the thermodynamic
Speaker 3: equation of state. Instead of acting like normal passive matter
Speaker 3: that just polls this continuously generated matter exerts a global
Speaker 3: negative pressure.
Speaker 2: Negative pressure, What does that even mean in space?
Speaker 3: Think of a dry sponge. If you let it soak
Speaker 3: up water, the sponge expands outward. Right The act of
Speaker 3: drawing in new material pushes the boundaries of the sponge apart.
Speaker 3: Oh wow, and the cosmic engine, the continuous mathematical creation
Speaker 3: of energy required to satisfy this modified autocycle, produces a
Speaker 3: negative pressure that physically pushes the boundaries of space time outward.
Speaker 2: So the matter itself, through the act of its own
Speaker 2: continuous creation, drives the acceleration exactly. My mind is genuinely
Speaker 2: blown right now, because if the modified nature of matter itself,
Speaker 2: functioning through this engine like cycle, is generating that outward
Speaker 2: negative pressure, you don't need dark energy at all.
Speaker 3: The phantom placeholder vanishes completely.
Speaker 2: That is wild. You solve the cosmological constant problem, You
Speaker 2: explain the accelerating universe, and you get rid of a
Speaker 2: mysterious force making up seventy percent of reality, all just
Speaker 2: by treating gravity as a thermodynamic engine.
Speaker 3: It is a beautifully elegant, incredibly clean mathematical fix.
Speaker 2: It really is incredibly elegant. It links the mundane physics
Speaker 2: of a combustion engine with the grand mysteries of astronomy.
Speaker 2: But in modern physics, elegant math doesn't automatically rewrite the textbooks.
Speaker 3: No, it definitely doesn't. If we connect this to the
Speaker 3: bigger picture, we have to bring this back down to reality,
Speaker 3: because creating a gorgeous theoretical model on a whiteboard is very,
Speaker 3: very different from proving it exists in nature. Mcgueo himself
Speaker 3: is very candid about this. Actually, he pointed out that
Speaker 3: back in nineteen ninety when he was just starting out
Speaker 3: in physics, cosmology was a very loose field. We didn't
Speaker 3: have the ultrasensitive detectors or the massive space telescopes we
Speaker 3: have today.
Speaker 2: So because there was a severe lack of hard data,
Speaker 2: theoretical physicists could hypothesize almost anything pretty much.
Speaker 3: Yeah, you could build these beautiful mathematical castles in the sky,
Speaker 3: and because the telescopes weren't powerful enough to check your work,
Speaker 3: no one could definitely prove you wrong.
Speaker 2: But today you cannot get away with building castles in
Speaker 2: the sky. Cosmology is a ruthless, rigidly data driven field.
Speaker 3: It really is. We have mapped the microscopic tricher fluctuations
Speaker 3: in the cosmic microwave background, you know, the leftover heat
Speaker 3: from the Big Bang. We have instruments like DSi, the
Speaker 3: Dark Energy Spectroscopic Instrument, meticulously tracking how millions of galaxies
Speaker 3: are moving and clustering over time. We just have mountains
Speaker 3: of high precision observational.
Speaker 2: Data now, which means this thermodynamic engine theory has to
Speaker 2: go to war. I think MCGUEO calls it the gauntlet
Speaker 2: of observation.
Speaker 3: Exactly the gauntlet this model is in its absolute infancy.
Speaker 3: It is highly speculative. For it to survive, it must
Speaker 3: be rigorously tested against the data we are pulling down
Speaker 3: from the James Web Space Telescope and other observatories.
Speaker 2: So the researchers now have to calculate exactly how their
Speaker 2: modified matter would behave over billions of years.
Speaker 3: Right, They have to ask does it perfectly predict the
Speaker 3: expansion rates we actually measure, does the continuous creation of
Speaker 3: matter leave a signature in the cosmic microwave.
Speaker 2: Background, or does it align with how galaxies actually clump
Speaker 2: together in the real universe exactly?
Speaker 3: All that has to match up.
Speaker 2: So what does this all mean? We started this journey
Speaker 2: looking up at the night sky, assuming everything was being
Speaker 2: pushed apart by an invisible ghost called dark energy. But
Speaker 2: by tracking the work of physicists willing to abandon assumptions,
Speaker 2: we've seen a totally different.
Speaker 3: Possibility, a really fascinating one from.
Speaker 2: Ted Jacobson proving you can build gravity from heat to
Speaker 2: a Greek Island epiphany that told us to stop forcing
Speaker 2: puzzle pieces to fit. We've seen how treating the fabric
Speaker 2: of space time like an internal combustion engine, focusing on
Speaker 2: mechanical work, not just heat flow, leads to a universe
Speaker 2: where the rules of conservation are literally rewritten. By allowing
Speaker 2: matter and energy to be continuously created, we arrive at
Speaker 2: a universe that accelerates itself through negative pressure cleanly and elegantly,
Speaker 2: without a single drop of dark energy.
Speaker 3: Whether it survives the gauntlet of hard data or gets
Speaker 3: discarded like so many theories before it, it is a
Speaker 3: profound reminder that we must constantly question our most basic assumptions.
Speaker 3: Sometimes the fundamental rules we learn in high school are
Speaker 3: the very things preventing us from seeing the true pattern
Speaker 3: of reality.
Speaker 2: It really is a massive paradigm shift, and it leaves
Speaker 2: you with a truly staggering thought to mull over the
Speaker 2: next time you are standing outside looking up at those stars.
Speaker 2: Under the old model of dark energy, the universe just
Speaker 2: expands faster and faster until everything freezes in a lonely
Speaker 2: isolated darkness. You know, big freeze, right. But if this
Speaker 2: new theory holds true, if the universe truly operates via
Speaker 2: a thermodynamic cycle, functioning like a colossal cosmic engine that
Speaker 2: continuously generates matter to fuel its own endless expansion, it
Speaker 2: happens to an engine over time. Even the best design
Speaker 2: car eventually reaches its limit. Does a universe built like
Speaker 2: an engine eventually run out of whatever underlying fuel drives
Speaker 2: the cycle? Does the thermodynamic machinery eventually stall out and
Speaker 2: break down? Or is this cosmic engine perfectly engineered to
Speaker 2: just keep running, generating itself forever