Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomi 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: The universe is actively expanding, and this stretching of physical
Speaker 2: space is governed by a precise mathematical value known as
Speaker 2: the Hubble constant.
Speaker 3: Right every single second, the very physical reality of the
Speaker 3: cosmos is stretching.
Speaker 2: The distance between distant galaxies is increasing in all directions,
Speaker 2: and that exact rate of current expansion is what the
Speaker 2: Hubble constant represents. It is the absolute fundamental metric of
Speaker 2: our cosmos.
Speaker 3: I mean, it's the ultimate cosmological ruler, really. But to
Speaker 3: truly understand what that means, we have to completely separate
Speaker 3: cosmic expansion from our everyday human intuition of movement.
Speaker 2: Because when you think of things moving apart, you usually
Speaker 2: imagine objects traveling through a pre existing empty room.
Speaker 3: Exactly, if I throw a baseball, it moves through the
Speaker 3: air in a static space. But when we talk about
Speaker 3: galaxies moving apart, that is absolutely not what is happening.
Speaker 2: We are not talking about objects moving through pre existing
Speaker 2: empty space, like shrapnel flying outward from some localized explosion. No,
Speaker 2: because the Big Bang wasn't an explosion in space, It
Speaker 2: was an explosion of space.
Speaker 3: That is a crucial distinction. According to Albert Einstein's general relativity,
Speaker 3: space time itself is a malleable dynamic fabric. It can bend,
Speaker 3: it can bend, it can warp, and critically it can stretch.
Speaker 3: What is actually happening out there in the deep cosmos
Speaker 3: is the continuous, ongoing creation of new physical space between
Speaker 3: these massive objects.
Speaker 2: So the galaxies themselves are relatively stationary in their local
Speaker 2: pockets space.
Speaker 3: Time rice exactly, but the tapestry there woven into is
Speaker 3: being pulled apart.
Speaker 2: The classic analogy here is always the raisin bread.
Speaker 3: Baking in the oven, right the raisin break.
Speaker 2: If you put a loaf of unbaked raisin bread in
Speaker 2: the oven, the raisins represent the balaxies, and the dough
Speaker 2: is space time, And as the dough bakes and rises,
Speaker 2: it expands in all.
Speaker 3: Directions, and the raisins aren't swimming through the dough.
Speaker 2: No, they are just being carried along as the dough
Speaker 2: itself gets bigger. So the distance between any two raisins increases,
Speaker 2: and the.
Speaker 3: Further apart two raisins are the faster they appear to
Speaker 3: be moving away from each other.
Speaker 2: And the hubble constant is the exact measurement of how
Speaker 2: fast that dough is rising right now. It measures the
Speaker 2: current rate of this stretching.
Speaker 3: It's typically expressed in a rather clunky unit kilometers per
Speaker 3: second per megaparsek, which is a mouthful. It is. A
Speaker 3: megaparsec is an astronomical unit of distance equal to about
Speaker 3: three point twenty six million light years.
Speaker 2: Okay, so for every three point twenty six million light
Speaker 2: years of distance between US and a galaxy, that galaxy
Speaker 2: appears to be receding from us by a certain number
Speaker 2: of kilometers every single.
Speaker 3: Second, pearly due to the creation of new.
Speaker 2: Space, right, which you know, sounds like a settled science.
Speaker 2: We just measure the galaxies, get the number and write
Speaker 2: it in the textbooks.
Speaker 3: But it isn't not even.
Speaker 2: Close, right, because right now we are investigating what is
Speaker 2: undoubtedly the most critical unresolved paradox in modern astrophysics. It
Speaker 2: is called the Hubble tension.
Speaker 3: The Hubble tensions.
Speaker 2: Yes, and for you listen right now. You might think
Speaker 2: this is just a rounding error, some tiny disagreement in
Speaker 2: the decimal points of a complex calculation that scientists are
Speaker 2: just being pedantic about.
Speaker 3: But it's really not.
Speaker 2: It's not at all. It is a fundamental discrepancy threatening
Speaker 2: the absolute axioms of cosmology.
Speaker 3: It forces the entire discipline to confront a highly uncomfortable
Speaker 3: objective scientific reality. Astrophysics is currently undergoing a foundational crisis.
Speaker 2: A foundational crisis, yes.
Speaker 3: The crisis arises from the massive dichotomy between two distinct,
Speaker 3: highly pristine sets of precision measurements that simply refuse to align.
Speaker 2: It's as if you hired two different teams of master
Speaker 2: architects to measure the exact length of a bridge.
Speaker 3: Right, They both used state of the art lasers, they
Speaker 3: both check their mouth one hundred times, and they come
Speaker 3: back with two completely different lengths.
Speaker 2: Let's lay out that dichotomy, because the details of how
Speaker 2: we get these numbers are absolutely fascinating.
Speaker 3: Let's do it.
Speaker 2: On one side, we have measurements derived from the early universe,
Speaker 2: astrophysicists looked deep into the past by analyzing observations originating
Speaker 2: from the cosmic microwave background, or the CMB.
Speaker 3: The CMB is essentially the after glow of the Big Bang.
Speaker 3: It is the absolute oldest like we can possibly detect
Speaker 3: in the universe.
Speaker 2: And to understand why it's the oldest light, you really
Speaker 2: have to picture the universe just after the Big Bang.
Speaker 3: It was a fiercely hot, unimaginably dense soup of plasma.
Speaker 2: It was so hot that atoms couldn't even form yet exactly.
Speaker 3: Electrons and protons were just zipping around independently. And because
Speaker 3: of this dense fog of free electrons, light could not travel.
Speaker 2: Because a photon would travel a microscopic distance and immediately
Speaker 2: scatter off an electron.
Speaker 3: Right, So the early universe was opaque. It was glowing,
Speaker 3: but you couldn't see through it.
Speaker 2: It was essentially an infinite cosmic fog bank.
Speaker 3: A glowing fog bank. Yes. But then as the universe expanded,
Speaker 3: it naturally cooled down.
Speaker 2: It cooled for about three hundred and eighty thousand years.
Speaker 3: And then it hit a critical temperature threshold. It became
Speaker 3: cool enough for those free roaming electrons to finally bind
Speaker 3: with protons and form the first stable, neutral hydrogen atoms.
Speaker 2: This era is known as recombination.
Speaker 3: Recombination exactly, and the moment those electrons were locked up
Speaker 3: in atoms, the fog instantly.
Speaker 2: Lifted, the universe became transparent.
Speaker 3: And all those photons that had been bouncing around in
Speaker 3: the plasma were suddenly free to travel in a straight
Speaker 3: line across the cosmos.
Speaker 2: And those exact same photons have been traveling through space
Speaker 2: for the last thirteen point eight billion years.
Speaker 3: But because the space they were traveling through has been
Speaker 3: expanding this whole time, the actual wavelengths of that light
Speaker 3: have been physically stretched out.
Speaker 2: So it started as intensely hot high energy light has
Speaker 2: been stretched all the way down into the microwave spectrum.
Speaker 3: That's the cosmic microwave background. When we point our most
Speaker 3: advanced satellites like the Plank Space Observatory of the empty sky,
Speaker 3: we see this faint microwave hum everywhere we look.
Speaker 2: And contained within that hum is a complete treasure trove
Speaker 2: of data.
Speaker 3: There are microscopic temperature fluctuations in that background, radiation hot
Speaker 3: spots and cold spots.
Speaker 2: And those represent the initial seeds of all the galaxies
Speaker 2: and galaxy clusters that exist today.
Speaker 3: Yes, by looking at the size and distribution of these
Speaker 3: microscopic spots, cosmologists can plug that data into our standard
Speaker 3: model of the universe.
Speaker 2: And they basically fast forward the clock to figure out
Speaker 2: how fast the universe should be expanding today.
Speaker 3: And when they do that incredibly complex calculation, analyzing this
Speaker 3: primordial light from the dawn of time, they calculate one
Speaker 3: highly specific expansion rate.
Speaker 2: Roughly sixty seven kilometers per second per mega parsec.
Speaker 3: That is measurement number one, the early universe ruler.
Speaker 2: Okay, so that's the first team of architects, right, But.
Speaker 3: Then we look at the other side of the data,
Speaker 3: the late universe ruler.
Speaker 2: When scientists use entirely different observational methodologies to measure the local,
Speaker 2: more recent observable universe.
Speaker 3: Looking at galaxies and stars that exist relatively close to
Speaker 3: us in cosmic.
Speaker 2: Time, they arrive at a completely different rate.
Speaker 3: This more recent measurement yields an expansion rate of about
Speaker 3: seventy three kilometers per second per megaparsek.
Speaker 2: Sixty seven versus seventy three.
Speaker 3: That is the tension.
Speaker 2: And here is where the crisis really solidifies. You might
Speaker 2: look at those numbers and think, well, they are pretty close.
Speaker 3: And twenty or thirty years ago, the error bars on
Speaker 3: these megaments were.
Speaker 2: Huge, right, sixty seven might have had an error margin
Speaker 2: of plus or minus ten and seventy three might have
Speaker 2: had an error margin of plus or minus ten.
Speaker 3: So the margins overlapped, and scientists figured they would eventually
Speaker 3: meet somewhere in the middle as our instruments got better.
Speaker 2: But the technology evolved. The instruments got better, the mathematical
Speaker 2: models became more rigorous, and.
Speaker 3: The margins of error on these two massive, heavily cross
Speaker 3: checked measurements shrank drastically.
Speaker 2: They shrank so much they have become so staggeringly precise
Speaker 2: that their error bars no longer overlap whatsoever.
Speaker 3: They are statistically mathematically incompatible.
Speaker 2: Which is terrifying for a physicist. It really is because
Speaker 2: both of these methodologies rely on the identical fundamental laws
Speaker 2: of physics.
Speaker 3: The underlying math governing gravity, thermodynamics, and electromagnetism is exactly
Speaker 3: the same for both the early Universe calculations and the
Speaker 3: late Universe observations.
Speaker 2: The physics and the CMB and the physics of the stars.
Speaker 2: We look at today. Are supposed to be part of
Speaker 2: one unified reality, so they absolutely should align perfectly.
Speaker 3: The lack of alignment points directly to an axiomatic conflict.
Speaker 3: We have two pristine rulers to measure the cosmos, built
Speaker 3: on the exact same physical laws, yet giving entirely different dimensions.
Speaker 2: And because our methodologies are logically sound and heavily cross
Speaker 2: checked by thousands of independent researchers worldwide, we cannot simply
Speaker 2: tweak our existing models or blame a dusty telescope lens.
Speaker 3: No, we can't. This discrepancy means the standard model of cosmology,
Speaker 3: known as the Lambda CDM model, has a massive glaring.
Speaker 2: Deficit Lambda CDM. Lambda stands for dark energy and CDM
Speaker 2: stands for cold dark matter.
Speaker 3: That is the bedrock blueprint of astrophysics. It dictates the
Speaker 3: inventory and behavior of the entire universe.
Speaker 2: The fact that it cannot reconcile sixty seven and seventy
Speaker 2: three implies a literal gap in our current framework of
Speaker 2: physical reality.
Speaker 3: It implies we are fundamentally misunderstanding something profound about how
Speaker 3: the universe operates.
Speaker 2: So what does this all mean? Let's look at the
Speaker 2: fallout of this.
Speaker 3: The fallout is significant.
Speaker 2: If our baseline understanding of how the universe expands is
Speaker 2: fundamentally flawed, then our calculations regarding the age of the
Speaker 2: universe are wrong. Our calculations regarding its total geometric.
Speaker 3: Size are wrong also, yes.
Speaker 2: And our predictions for its ultimate cosmological fate, whether it
Speaker 2: will expand forever into a cold, dark void or eventually
Speaker 2: rip itself apart, are all built on incredibly shaky ground.
Speaker 3: Establishing a unified Hubble constant is an absolute imperative.
Speaker 2: If the established standard model is broken or incomplete, theoretical
Speaker 2: physicists have to hypothesize what exactly we are missing.
Speaker 3: And usually, when looking for missing pieces in cosmology, scientists
Speaker 3: look to the dark sectors of the universe to patch
Speaker 3: this cosmological hole.
Speaker 2: The dark sectors being dark energy and dark matter.
Speaker 3: Which together make up about ninety five percent of the
Speaker 3: total mass energy content of the universe ninety five percent,
Speaker 3: it's almost everything. We call them dark simply because they
Speaker 3: do not interact with light. We can't see them directly.
Speaker 2: We only know they exist because of their gravitational effects
Speaker 2: on the five percent of normal matter that we can
Speaker 2: actually see, like starred and gas.
Speaker 3: Clothes, exactly, and that search for a theoretical patch brings
Speaker 3: us to the first major hypothesis attempting to solve the
Speaker 3: hubble tension early dark energy.
Speaker 2: Let's break that down because it's a wild concept, it
Speaker 2: really is.
Speaker 3: To understand early dark energy, we need to quickly look
Speaker 3: at regular dark energy as we know it today.
Speaker 2: Dark energy is currently the dominant component of the universe.
Speaker 2: It acts as a mysterious repulsive force, essentially anti gravity,
Speaker 2: that is actively driving the accelerated expansion of the cosmos.
Speaker 3: It's why the raisin bread is rising faster and faster
Speaker 3: every minute.
Speaker 2: But this new theoretical framework suggests there was a distinct,
Speaker 2: entirely separate, temporary phase of early dark energy.
Speaker 3: A phase that was active only during the universe's earliest epox,
Speaker 3: long before the current era of dark energy dominance.
Speaker 2: The hypothesis details that roughly one hundred thousand years after
Speaker 2: the Big Bang, an entirely different scalar field emerged.
Speaker 3: Right, and a scaler field is just a physical field
Speaker 3: that has a specific value at every point in space,
Speaker 3: like a temperature map of a room.
Speaker 2: This early dark energy scalar field acted as a massive
Speaker 2: temporary repelling force.
Speaker 3: It significantly boosted the expansion rate when the universe was
Speaker 3: incredibly young, dense, and hot.
Speaker 2: So the universe is born, it's expanding at a certain rate,
Speaker 2: and then suddenly this invisible force kicks in, hits the
Speaker 2: gas pedal, and forces space to stretch out much faster
Speaker 2: for a brief period, and.
Speaker 3: In doing so, it fundamentally changed the size of something
Speaker 3: cosmologists call the sound horizon.
Speaker 2: The sound horizon, Yes, it's.
Speaker 3: A brilliant, albeit complex concept. Remember that dense, hot soup
Speaker 3: of plasma in the early universe before recombination the fog
Speaker 3: bank right, Well, that soup wasn't perfectly smooth. Dark matter
Speaker 3: was constantly trying to pull matter together through gravity, while
Speaker 3: the intense radiation pressure of the photons was pushing matter apart.
Speaker 2: This cosmic tug of war created literal acoustic waves, sound
Speaker 2: waves that rippled through the primordial plasma.
Speaker 3: It's incredible to think about the early universe ringing like.
Speaker 2: A bell, massive deep sound waves propagating through a soup
Speaker 2: of light and matter.
Speaker 3: Those acoustic waves traveled outwards from areas of high density.
Speaker 3: The sound horizon is simply the absolute maximum distance that
Speaker 3: those acoustic waves could travel within that plasma before the
Speaker 3: universe cooled enough for atoms to form.
Speaker 2: Because once recombination happened and the fog lifted, the radiation
Speaker 2: pressure dropped to zero, the.
Speaker 3: Sound waves were instantly frozen in place.
Speaker 2: They left a permanent spherical imprint on the distribution of
Speaker 2: matter in the universe.
Speaker 3: We can actually look out at the distribution of galaxies
Speaker 3: today and see these massive spherical shells of galaxies millions
Speaker 3: of light years across, which are the frozen echoes of
Speaker 3: those primordial sound waves.
Speaker 2: We call them baryon acoustic oscillations.
Speaker 3: And because we know the physics of that early plasma,
Speaker 3: we think we know exactly how far a sound wave
Speaker 3: could have traveled in three hundred and eighty thousand years.
Speaker 3: We use the size of that sound horizon as a
Speaker 3: standard ruler to measure the cosmos.
Speaker 2: But here is where the early dark energy hypothesis changes everything.
Speaker 3: It really does. If this temporary burst of early dark
Speaker 3: energy was present acting as a massive repelling force, it
Speaker 3: altered the fundamental physics of that plasma.
Speaker 2: It changed the expansion rate during that critical era, which
Speaker 2: means it changed the physical distance those acoustic waves could
Speaker 2: travel before the universe cooled. And froze them. Wait, so,
Speaker 2: if early dark energy was secretly accelerating things the sound horizon,
Speaker 2: our ultimate cosmic ruler is actually a different size than
Speaker 2: we thought it was precisely.
Speaker 3: And then, according to the theory, just as quickly as
Speaker 3: it appeared, this early dark energy essentially decayed.
Speaker 2: The scaler field lost its energy.
Speaker 3: And the extrapulsive force faded away, leave the universe to
Speaker 3: continue expanding at a more normal rate until regular dark
Speaker 3: energy took over billions of years later.
Speaker 2: Which means if our current LAMB to CDM models miss
Speaker 2: this temporary ancient boost, any calculations we make bridging that
Speaker 2: early cosmic microwave background data to the present day are
Speaker 2: structurally skewed.
Speaker 3: We are taking data from the baby universe, assuming a
Speaker 3: steady growth curve and predicting how big the adult universe
Speaker 3: should be.
Speaker 2: But if we didn't know the baby had a massive
Speaker 2: sudden growth spurt that altered its fundamental geometry before settling
Speaker 2: back down, our predictions for its adult size are going
Speaker 2: to be completely wrong.
Speaker 3: That is exactly the implication of the early dark energy model.
Speaker 3: The early universe data from the CMB isn't intrinsically wrong.
Speaker 2: Our measurements of the microwave background are spectacular.
Speaker 3: They are, but our mathematical bridge extrapolating that data to
Speaker 3: the present day is missing a massive structural component. We
Speaker 3: are extrapolating an expansion rate across thirteen point eight billion
Speaker 3: years without accounting for a massive temporary acceleration that happened
Speaker 3: at the very beginning.
Speaker 2: It's a compelling fix. If you plug early dark energy
Speaker 2: into the equations, the sixty seven number shifts upward closer
Speaker 2: to the seventy three number. It bridges the gap.
Speaker 3: It does, but it's not the only theory in town.
Speaker 2: Right. If early dark energy isn't the culprit, what else
Speaker 2: in the universe's massive invisible inventory could be messing with
Speaker 2: the map.
Speaker 3: That leads us directly to the second major hypothesis. Theoretical
Speaker 3: physicists are heavily debating dark matter and neutrino interactions.
Speaker 2: Okay, To frame this hypothesis accurately, you have to consider
Speaker 2: the sheer scale of the universe's invisible inventory.
Speaker 3: First, you have dark matter. As we noted, it is
Speaker 3: entirely invisible. We cannot observe it electromagnetically. It doesn't emit,
Speaker 3: reflect or absorb light.
Speaker 2: But it possesses immense gravitational pull.
Speaker 3: It forms this massive, invisible web like scaffolding that spans
Speaker 3: the cosmos, and its gravity is literally what holds galaxies
Speaker 3: and galaxy clusters together.
Speaker 2: Without the extra gravitational glue of dark matter, galaxy spinning
Speaker 2: as fast as ours would simply fly apart.
Speaker 3: And then on the other end of the size spectrum
Speaker 3: you have neutrinos.
Speaker 2: Neutrinos are utterly fascinating elementary particles.
Speaker 3: They are the most abundant particles in the universe that
Speaker 3: actually possess mass, but they are incredibly elusive.
Speaker 2: They are often categorized as ghostly particle.
Speaker 3: Their cross section for interaction with normal matter is infinitesimally small.
Speaker 3: We don't feel the strong nuclear force and they don't
Speaker 3: feel electromagnetism.
Speaker 2: To put that into perspective for you listening right now,
Speaker 2: trillions of these neutrinos, generated by nuclear fusion in our
Speaker 2: sun and by distant cosmic events, are passing through your
Speaker 2: body every single.
Speaker 3: Second, trillions every second, and.
Speaker 2: They do so without interacting with a single atom of
Speaker 2: your being. They pass through the entire Earth as easily
Speaker 2: as light passes through a pane of glass staggering to
Speaker 2: think about.
Speaker 3: Now, under this standard model of cosmology, the established foundational
Speaker 3: assumption is that dark matter is entirely collisionless.
Speaker 2: It doesn't bump into itself, and it doesn't bump into
Speaker 2: normal matter.
Speaker 3: And the assumption is that neutrinos basically interact with nothing
Speaker 3: except very rarely via the weak nuclear force.
Speaker 2: But this new theory questions this.
Speaker 3: It questions whether there are complex, unmapped theoretical interactions occurring
Speaker 3: between the massive and visible scaffolding of dark matter and
Speaker 3: this endless back ground sea of cosmic neutrinos.
Speaker 2: Because both of these components were incredibly densely packed in
Speaker 2: the early universe.
Speaker 3: If dark matter particles and neutrinos scatter off each other,
Speaker 3: even minutely, if they bounce off one another in ways
Speaker 3: we haven't detected yet, the implications for the evolution of
Speaker 3: the universe are profound.
Speaker 2: Let's use an analogy here. Imagine playing a game of
Speaker 2: pool in the dark.
Speaker 3: Okay, pool in the dark.
Speaker 2: You know where the pockets are, and you strike the cubeball.
Speaker 2: Based on your math and your force, you calculate exactly
Speaker 2: when the cube ball will hit the back of the pocket.
Speaker 2: But you don't realize someone has scattered thousands of invisible
Speaker 2: marbles across the felt. As your cube ball rolls, it's
Speaker 2: imperceptibly colliding with these marbles.
Speaker 3: And with each tiny collision it transfers a fraction of
Speaker 3: its energy and momentum, it slows down slightly, its path
Speaker 3: is altered.
Speaker 2: In the cosmos. If these two immensely abundant components, dark
Speaker 2: matter and neutrinos are interacting in ways that particle physics
Speaker 2: has not yet quantified, those hidden physics would alter the
Speaker 2: density perturbations of the early universe.
Speaker 3: The dark matter is trying to clump together gravitationally to
Speaker 3: form the seeds of galaxies.
Speaker 2: But if a sea of energetic neutrinos is constantly bombarding it,
Speaker 2: scattering off it, it would suppress that gravitational clumping.
Speaker 3: It would smooth out the early cosmic structures. And that
Speaker 3: suppression is the key.
Speaker 2: If we are completely ignoring a major mechanism by which
Speaker 2: the universe's primary ingredients behave and evolve, our mathematical understanding
Speaker 2: of cosmic expansion is heavily distorted.
Speaker 3: When cosmologists look at the CMB and calculate the expansion rate,
Speaker 3: they are assuming dark matter behaved perfectly smoothly without any
Speaker 3: neutrino interference.
Speaker 2: We would essentially be trying to balance a highly complex
Speaker 2: cosmological equation while leaving out a massive structural variable.
Speaker 3: Ignoring this hidden physics distorts the mathematical bridge to the
Speaker 3: present day just as severely as missing a phase of
Speaker 3: early dark energy would.
Speaker 2: So we have a hypothetical new energy field, or we
Speaker 2: have invisible particles secretly crashing into each other.
Speaker 3: And if those two variables weren't sufficiently complex, there is
Speaker 3: a third major hypothesis attempting to patch the cosmological whole,
Speaker 3: the temporal evolution of dark energy.
Speaker 2: This one fundamentally challenges the most basic assumption of our
Speaker 2: current models regarding empty space itself.
Speaker 3: Currently, the standard view treats dark energy as a static,
Speaker 3: unchanging cosmological constant. It is represented by the Greek letter Lambda.
Speaker 2: It is assumed to be an inherent property of space itself,
Speaker 2: a steady, unyielding vacuum energy that pushes space apart at
Speaker 2: a constant exponential rate, completely unchanging over the billions of
Speaker 2: years of cosmic history.
Speaker 3: A cubic meter of space today has the exact same
Speaker 3: amount of repulsive dark energy as a cubic meter of
Speaker 3: space did ten billion years ago.
Speaker 2: But the dynamic alternative asks, what if it isn't static?
Speaker 2: What if dark energy is a dynamic, evolving phenomenon.
Speaker 3: What's fascinating here is how theoretical physicists model this mechanism.
Speaker 3: They use something called the equation of state parameter, usually
Speaker 3: denoted as W.
Speaker 2: In the standard LAMBA CDM model, W is assumed to
Speaker 2: be exactly minus one permanently.
Speaker 3: But if that equation of state parameter changes over time,
Speaker 3: if W is minus zero point nine or minus one
Speaker 3: point one in different epochs, it dictates that the actual
Speaker 3: energy density and the repulsive pressure of dark energy shifts.
Speaker 2: It's like a cosmic thermostat that someone is slowly turning up.
Speaker 3: Or down exactly. Dark energy might grow stronger, it might weaken,
Speaker 3: or it might fundamentally mutate over vast cosmic timescales.
Speaker 2: Models exploring this are sometimes called quintessence or phantom energy models.
Speaker 3: If dark energy is dynamic, its influence on universal expansion
Speaker 3: is entirely temporal. The repulsive force today is different from
Speaker 3: the repulsive force yesterday.
Speaker 2: So the conclusion there is stark and incredibly elegant. In
Speaker 2: its simplicity. If the equation of state parameter is evolving,
Speaker 2: then comparing the expansion rate of the early universe to
Speaker 2: the expansion rate of the recent universe is an exercise
Speaker 2: in futility.
Speaker 3: It's like trying to calculate the average speed of a
Speaker 3: road trip by looking at the speedometer while you were
Speaker 3: in a school zone and comparing it to the speedometer
Speaker 3: while you are on the highway.
Speaker 2: If you assume a static, unchanging speed limit, but the
Speaker 2: actual rules of the expansion mechanism mutated over billions of years,
Speaker 2: of course your numbers won't match.
Speaker 3: The mechanism pushing the inniverse apart during the era of
Speaker 3: the cosmic microwave background would be fundamentally different from the
Speaker 3: mechanism pushing it apart today.
Speaker 2: This perfectly explains the Hubble tension without needing to invalidate
Speaker 2: either set of measurements.
Speaker 3: They are both right. They're just measuring a universe governed
Speaker 3: by shifting rules.
Speaker 2: It's a brilliant way to solve the puzzle, but it
Speaker 2: leaves astrophysics at a massive methodological impasse. We have these
Speaker 2: three incredible theories early dark energy, neutrino scattering or dynamic
Speaker 2: dark energy.
Speaker 3: But to figure out which of these dark sector hypotheses
Speaker 3: is the true culprit, we can't just keep staring at
Speaker 3: the cosmic microwave background.
Speaker 2: We have to rigorously scrutinize the other side of the equation.
Speaker 2: We have to look at how we have historically measured
Speaker 2: the expansion of the law local modern universe. To get
Speaker 2: that seventy three number.
Speaker 3: We need to analyze the mechanics of the tools that
Speaker 3: yielded that higher rate, and that means looking at what
Speaker 3: we can call the electromagnetic ceiling.
Speaker 2: The electromagnetic ceiling, because practically everything we know about the
Speaker 2: local universe comes from light.
Speaker 3: Since the early twentieth century, practically all of our primary
Speaker 3: astrophysical tools have relied on capturing photons. We rely on
Speaker 3: a century old paradigm established by Edwin Hubble himself when
Speaker 3: he first discovered the universe was expanding. In the nineteen twenties.
Speaker 2: Hubble used the Hooker telescope in California to look at
Speaker 2: Cepheide variable stars in the Andromeda galaxy.
Speaker 3: He proved Andromeda wasn't just a gas cloud in our
Speaker 3: Milky Way, but an entirely separate island universe, and that
Speaker 3: it was moving away from us.
Speaker 2: Since then, the entire methodology of astronomy has relied on
Speaker 2: capturing these electromagnetic signals visible light, infrared, X rays, radio
Speaker 2: waves from distant objects.
Speaker 3: By analyzing the spectral lines and using the fundamental properies
Speaker 3: of that light, we calculate both distance and recession velocity and.
Speaker 2: The absolute anchor of this entire observational paradigm. The tool
Speaker 2: that gives us the precision to claim the seventy three
Speaker 2: rate is the mechanism known as the standard candle protocol.
Speaker 3: To measure vast cosmic distances, you need a light source
Speaker 3: with a known absolute intrinsic brightness.
Speaker 2: Imagine you see a street lamp in the distance on
Speaker 2: a foggy night. If you don't know how bright the
Speaker 2: bulb in that street lamp is supposed to be, you
Speaker 2: can't tell if it's a very dim bulb close to
Speaker 2: you or a massively bright bulb very far away.
Speaker 3: But if you know for a fact that the bulb
Speaker 3: is exactly one hundred watts, you can measure how dim
Speaker 3: it appears to your eye and easily calculate its exact distance.
Speaker 2: That is a standard candle, and in astrophysics specifically, for
Speaker 2: measuring the hubble constant. We utilize Type IA supernovae, and.
Speaker 3: These aren't just random stellar explosions. When a massive star
Speaker 3: runs out of fuel and dies, it explodes in a
Speaker 3: core collapsed supernova. Those are messy, unpredictable, and they very
Speaker 3: wildly in brightness.
Speaker 2: You can't use them as standard candles. Type EA supernova
Speaker 2: are entirely different beasts. They are highly precise, almost mathematical events.
Speaker 3: The physics governing a Type YA supernova are tied directly
Speaker 3: to a fundamental threshold known as the Chandrasekhar limit.
Speaker 2: Named after the brilliant astrophysicist Subramanian chandrasecar who calculated it.
Speaker 3: The process begins with a binary star system two stars
Speaker 3: orbiting a common center of mass. One of these stars
Speaker 3: has already exhausted its nuclear fuel, blown off its outer layers,
Speaker 3: and died, leaving behind a dense hot core known as
Speaker 3: a white dwarf.
Speaker 2: A white dwarf is an insane object. It packs the
Speaker 2: mass of our Sun into a sphere the size of
Speaker 2: the Earth. It is incredibly dense.
Speaker 3: And in this binary system, this white dwarf is locked
Speaker 3: in a gravitational dance with its companion star, which is
Speaker 3: usually a red giant that has swollen up and is
Speaker 3: shedding its outer layers.
Speaker 2: The immense gravity of the white dwarf starts siphoning off
Speaker 2: that material. It slowly pulls gas and mass off its partner,
Speaker 2: cannibalizing it and growing heavier over millions.
Speaker 3: Of years, and it grows until it hits a very specific,
Speaker 3: unbreakable mathematical wall, the Chendersucar limit.
Speaker 2: At exactly approximately one point four to four times the
Speaker 2: mass of our sun. A profound quantum mechanical failure occurs
Speaker 2: within the white dwarf, and to.
Speaker 3: Understand this failure, you have to know what keeps a
Speaker 3: white dwarf from collapsing into a black hole under its
Speaker 3: own immense gravity. It is a nuclear fusion.
Speaker 2: Because the scar is dead, it is supported by something
Speaker 2: called electron degeneracy pressure.
Speaker 3: It's a concept rooted in the poly exclusion principle from
Speaker 3: quantum mechanics, which states that two electrons cannot occupy the
Speaker 3: exact same quantum state at the same time.
Speaker 2: Imagine trying to pack an impossible number of commuters into
Speaker 2: a tiny subway.
Speaker 3: Car at a certain point. No matter how hard you
Speaker 3: push from the outside, the people inside physically cannot be
Speaker 3: compressed any further without.
Speaker 2: Overlapping the repulsive force of the electrons. Violently resisting being
Speaker 2: crushed into the same state is the electron degeneracy pressure.
Speaker 2: It actively supports the entire mass of the dead star
Speaker 2: against the crushing weight of its own gravity.
Speaker 3: But gravity is relentless. As the white dwarf steals more
Speaker 3: and more mass from its partner, the weight increases, and
Speaker 3: at one point four to four solar masses, gravity finally wins.
Speaker 2: And electron degeneracy pressure catastrophically fails.
Speaker 3: On that quanto pressure fails, the star collapses inward. In
Speaker 3: a fraction of second. The immense heat and pressure instantly
Speaker 3: trigger a runaway thermonuclear fusion of the carbon and oxygen
Speaker 3: making up the star.
Speaker 2: The entire white dwarf detonates simultaneously. It doesn't just blow
Speaker 2: off its outer layers. The star is completely obliterated in
Speaker 2: one of the most violent explosions in the universe.
Speaker 3: And here is why this is the ultimate standard candle.
Speaker 3: Because this colossal detonation consistently, unfailingly happens at that exact
Speaker 3: mass limit one point four to four solar masses. It
Speaker 3: always involves the exact same amount of nuclear fuel.
Speaker 2: Therefore, it has a strict known absolute intrinsic luminosity. It
Speaker 2: is an explosion with a highly predictable, standardized peak brightness.
Speaker 3: Every single type Vias supernova across the cosmos explodes with
Speaker 3: roughly the same wattage.
Speaker 2: Which gives us a brilliant, reliable diagnostic tool. When astronomers
Speaker 2: spot one of these explosions in a distant galaxy, they
Speaker 2: monitor it carefully for weeks.
Speaker 3: They chart the light curve, that's specific mathematical rate at
Speaker 3: which the supernova brightens to its peak luminosity and then
Speaker 3: slowly fades away over time.
Speaker 2: There's a known correlation called the Phillips relationship where slightly
Speaker 2: brighter supernovae take a little longer to fade, allowing us
Speaker 2: to standardize them even further.
Speaker 3: So we know it's absolute intrinsic luminosity, we measure its
Speaker 3: apparent magnitude, meaning how dim it hourly looks to us
Speaker 3: through our telescopes here.
Speaker 2: On Earth, and then we just apply a basic geometric
Speaker 2: calculation through the Inversquare law of light, which dictates that
Speaker 2: light dims predictably as it spreads out over distance. Comparing
Speaker 2: its absolute known brightness to its apparent dimness gives us
Speaker 2: a highly precise distance to that galaxy.
Speaker 3: But if you remember the Hubble constant equation, distance is
Speaker 3: only half the battle. You know exactly how far away
Speaker 3: the supernova's host galaxy is, but you also need to
Speaker 3: know how fast it is moving away from us due
Speaker 3: to the expansion of cosmic space. That brings us to
Speaker 3: recession velocity.
Speaker 2: And to get that velocity you measure the red shift.
Speaker 2: It's the visual equivalent of a Doppler effect.
Speaker 3: If an angulance drives past you, the siren sounds high
Speaker 3: pitched as it approaches because the sound waves are compressed,
Speaker 3: and it drops to a lower pitch as it drives
Speaker 3: away because the sound waves are stretched out. Like does
Speaker 3: the exact same thing.
Speaker 2: As the galaxy recedes away from us, carried by the
Speaker 2: expanding fabric of space, the actual wavelengths of the electromagnetic
Speaker 2: signals it emits are physically stretched out.
Speaker 3: Shorter, bluer wavelengths are stretched into longer, redder wavelengths, shifting
Speaker 3: the entire spectrum of light toward the red end of
Speaker 3: the electromagnetic spectrum.
Speaker 2: Astronomers look at the spectral lines. These are the specific
Speaker 2: fingerprints of elements like hydrogen and helium embedded in the light,
Speaker 2: and they see how far those lines have shifted toward
Speaker 2: the r.
Speaker 3: You measure the exact degree of that spectral stretching, and
Speaker 3: you get your velocity.
Speaker 2: So you have your pristine distance from the tupernova and
Speaker 2: your precise velocity from the red shift. Distance plus redshift
Speaker 2: equals the expansion rate.
Speaker 3: It is an incredibly elegant, beautiful system. It is the
Speaker 3: bedrock of modern observational astronomy.
Speaker 2: But when it comes to resolving a paradox as tight
Speaker 2: as the Hubble tension, we have fundamentally hit the precision
Speaker 2: ceiling of electromagnetic observations. We have pushed light to the
Speaker 2: absolute limit of its utility.
Speaker 3: The critical flaw in this methodology is the inherent, unavoidable
Speaker 3: fragility of light.
Speaker 2: Electromagnetic signals over cosmic distances are incredibly vulnerable. Light interacts
Speaker 2: with almost everything it touches.
Speaker 3: When we use these standard candles to peer billions of
Speaker 3: light years into the past, we are constantly at the
Speaker 3: mercy of the interstellar and intergalactic medium. A photon has
Speaker 3: to travel for a billion years to reach our.
Speaker 2: Telescope, and over that immense journey, light is heavily obscured
Speaker 2: by cosmic dust. It gets absorbed and scattered by intervening
Speaker 2: gas clouds.
Speaker 3: Think about driving on a dirt road behind a massive truck.
Speaker 3: Your head lights hit the dust cloud, and the light
Speaker 3: is scattered. It looks dimmer than it actually is.
Speaker 2: In astronomy, this is called extinction. Cosmic dust specifically absorbs
Speaker 2: blue light more readily than red light, a process called rettening.
Speaker 3: We have to look at the red and light of
Speaker 3: the supernova and try to mathematically guess exactly how much
Speaker 3: dust it passed through to calculate its true original brightness.
Speaker 2: Furthermore, the apparent luminosity can be altered by the metallicity
Speaker 2: of the host galaxy itself. In astronomy, anything heavier than
Speaker 2: helium is considered a metal.
Speaker 3: If the white dwarf formed in a galaxy with a
Speaker 3: very high concentration of heavy metals, that chemical composition fundamentally
Speaker 3: affects the opacity of the supernova ejecta when it explodes.
Speaker 3: It changes how the light escapes the explosion.
Speaker 2: So we are looking at a light bulb trying to
Speaker 2: judge its exact wattage, but we are looking through a dirty, scratched,
Speaker 2: foggy window, and the bulb itself might have a slightly
Speaker 2: different chemical tint depending on where it was manufactured exactly.
Speaker 3: An enormous, massive computational and observational effort goes into simply
Speaker 3: calibrating out these confounding variables. Thousands of hours of telescope
Speaker 3: time and supercomputer modeling are dedicated to estimating the extinction
Speaker 3: caused by an endless ocean of cosmic dust.
Speaker 2: But eventually you hit a wall of systemic uncertainty. We
Speaker 2: cannot completely eradicate the systemic uncertainties inherent to capturing photons.
Speaker 3: If we want to definitively solve a paradox as mathematically
Speaker 3: precise and foundational as the hubble tension, relying on fragile
Speaker 3: light is no longer.
Speaker 2: Sufficient, independent non electromagnetic measurement modalities are mathematically necessary. We
Speaker 2: need an entirely separate physical channel of information to measure
Speaker 2: the cosmos.
Speaker 3: The channel that doesn't care about dust, that isn't affected
Speaker 3: by metallicity, and that doesn't scatter off gas clouds. And
Speaker 3: this establishes the absolute critical necessity of shifting our focus
Speaker 3: to a pristine metric gravitational waves Okay.
Speaker 2: Let's unpack this. This is where the science fiction becomes reality.
Speaker 2: This is a massive paradigm shift in how human beings
Speaker 2: perceive the universe.
Speaker 3: We are moving away from observing photons, away from light entirely,
Speaker 3: to measuring literal ripples propagating through the physical fabric of
Speaker 3: four dimensional space time.
Speaker 2: It's almost impossible to visualize. We're used to thinking of
Speaker 2: space as the empty container where things happen, but space
Speaker 2: itself is a flexible, dynamic medium.
Speaker 3: Think of it like a physical object displacing water to
Speaker 3: create radiating wavefronts. But on a cosmic scale, when massive
Speaker 3: objects accelerate, they don't just move through space. They literally
Speaker 3: alter the curve of space time around them.
Speaker 2: And as they move, that alteration, that distortion of the
Speaker 2: geometric fabric moves outward in all directions at the speed
Speaker 2: of light. Those are gravitational waves.
Speaker 3: But the fabric of space time is incredibly stiff. It
Speaker 3: takes an immense amount of energy to warp it. You
Speaker 3: do not get detectable gravitational waves from a star simply burning,
Speaker 3: or a planet orbiting, or even a normal supernova exploding.
Speaker 2: To generate these spacetime ripples in a way that we
Speaker 2: can detect them on Earth. You need an environment of
Speaker 2: almost unimaginable catastrophic gravitational violence.
Speaker 3: You need the densest objects in the universe interacting. We
Speaker 3: are talking about the inspiral and ultimate merger of exceedingly massive,
Speaker 3: compact astronomical bodies, primarily binary systems composed of two black
Speaker 3: holes or two neutron stars.
Speaker 2: Let's focus on black holes. These are objects of immense
Speaker 2: mass containing the gravitational pull of dozens of suns packed
Speaker 2: into a singularity.
Speaker 3: When two black holes get caught in each other's gravitational grip,
Speaker 3: they begin to orbit one another, and as they orbit,
Speaker 3: they stir up the fabric of space time around them.
Speaker 3: They shed their orbital energy in the form of these
Speaker 3: gravitational waves radiating outward.
Speaker 2: And because they are losing orbital energy, they slowly spiral
Speaker 2: closer and closer together. As they get closer, the gravitational
Speaker 2: pull intensifies and they accelerate.
Speaker 3: They whip around each other fast, turn faster, reaching significant
Speaker 3: fractions of the speed of light. Finally, in the last
Speaker 3: fraction of a second, they violently merge into a single,
Speaker 3: larger black hole.
Speaker 2: This final merger event converts several sons worth of pure
Speaker 2: mass directly into gravitational wave energy in an instant Sending
Speaker 2: out a massive catastrophic shock wave of space time distortion
Speaker 2: across the universe.
Speaker 3: And capturing that specific microscopic distortion as it washes over
Speaker 3: the Earth requires arguably the most precise engineering in human history.
Speaker 3: This is the domain of the LVK Collaboration.
Speaker 2: That stands for LEGO in the United States, VIRGO in Italy,
Speaker 2: and CAGRA in Japan. This is an international global consortionum
Speaker 2: of over two thousand scientific members dedicated to hearing the universe.
Speaker 3: The engineering behind these detectors is staggering. They operate massive innerferometers.
Speaker 3: These are l shaped facilities with vacuum tubes extending out
Speaker 3: for several kilometers in perpendicular directions.
Speaker 2: Inside these incredibly pure vacuum tubes, they fire ultra stable,
Speaker 2: high powered lasers.
Speaker 3: The laser beam is split at the corner of the
Speaker 3: l travels down both arms, hits massive perfectly polished mirrors
Speaker 3: suspended by complex pendulum systems, and bounces back to a
Speaker 3: central detector.
Speaker 2: And the mirrors are isolated from the Earth in ways
Speaker 2: that defy belief. They have to dampen the seismic noise
Speaker 2: of the planet. They have to account for the rumble
Speaker 2: of ocean waves miles away, the vibration of a truck
Speaker 2: driving on a nearby highway, even.
Speaker 3: The microscopic thermal vibrations of the atoms within the mirrors themselves.
Speaker 3: They even use advanced quantum optics techniques injecting squeeze light
Speaker 3: into the vacuum to reduce the inherent quantum noise of
Speaker 3: the photons hitting the mirrors.
Speaker 2: All of this is done for one specific purpose, to
Speaker 2: detect the microscopic stretching of space.
Speaker 3: When a gravitational wave passes through the Earth, it is
Speaker 3: a quadrupole wave. It literally stretches physical space in one
Speaker 3: direction while simultaneously compressing it in the perpendicular direction.
Speaker 2: So as the wayer washes over the Lego facility, one
Speaker 2: of the four kilometer arms gets physically longer and the
Speaker 2: other arm gets physically shorter.
Speaker 3: The light traveling down the longer arm takes a fraction
Speaker 3: of a second longer to return than the light in
Speaker 3: the shorter arm. When the two laser beams recombine, they
Speaker 3: are slightly out of phase, creating an interference pattern.
Speaker 2: The LVK instruments measure that fractional change in the distance.
Speaker 3: And the scale of what they are measuring is almost incomprehensible.
Speaker 3: By the time a gravitational wave from a black hole
Speaker 3: merger a billion light years away reaches Earth, the amplitude
Speaker 3: of the wave is infinitesimally small.
Speaker 2: The LVK detectors are sensing changes in the length of
Speaker 2: their four kilometal arms that are smaller than one thousandth
Speaker 2: the diameter of a single.
Speaker 3: Proton, smaller than a proton.
Speaker 2: Let that sink in. They are measuring a change in
Speaker 2: distance across four kilometers that is a fraction of the
Speaker 2: width of a subatomic particle, and because the sensitivity is
Speaker 2: so phenomenally high, astrophysicists realize they could use this technology
Speaker 2: to solve the Huddle tension.
Speaker 3: They developed a gravitational wave counterpart to the standard candle
Speaker 3: as the Standard Siren protocol.
Speaker 2: This is where the sheer mathematical beauty of general relativity shines.
Speaker 2: With standard candles, we have to rely on complex calibration
Speaker 2: and empirical observations of supernovae.
Speaker 3: With standard sirens, the physics are entirely self contained. By
Speaker 3: closely analyzing the specific morphology of the gravitational wave signal
Speaker 3: captured by the interferometer, scientists can extract the exact absolute
Speaker 3: physical properties of the black hole collision without needing any
Speaker 3: outside information.
Speaker 2: They analyze the chirp as the black holes spiral inward
Speaker 2: and accelerate the frequency and amplitude of the gravitational waves
Speaker 2: rapidly increase, creating a signal that, if converted to sound,
Speaker 2: literally sounds like a bird chirping.
Speaker 3: They look at the phase evolution, the exact frequency of
Speaker 3: the chirp, and the absolute amplitude of the space time stretching.
Speaker 3: From those highly specific waveform characteristics, general relativity allows them
Speaker 3: to mathematically calculate exactly how massive the two black holes were.
Speaker 2: They extract what is called the intrinsic Chirk mass of
Speaker 2: the binary.
Speaker 3: System, and because Einstein's equations perfectly predict exactly how loud
Speaker 3: a gravitational wave should be based purely on that intrinsic
Speaker 3: mass and orbital frequency, we automatically know it's absolute intrinsic amplitude.
Speaker 3: At the source.
Speaker 2: We instantly know the wattage of the bulb just by
Speaker 2: listening to the exact pitch and volume of the church.
Speaker 3: Precisely, we simply compare that intrinsic theoretical amplitude calculated from
Speaker 3: the waveform to the actual incredibly faint signal strength detected
Speaker 3: by the LVK interferometers on Earth.
Speaker 2: Using the inverse square law of gravity, which dictates how
Speaker 2: the wave dissipates over space, That comparison yields an exact
Speaker 2: luminosity distance.
Speaker 3: And crucially, this measurement is completely pristine. There is no
Speaker 3: cosmic dust blocking the gravitational wave space time ripples don't
Speaker 3: get absorbed by.
Speaker 2: Gas clouds, There is no metallicity interfering with the signal.
Speaker 2: The distortion pass is completely unhindered through all intervening matter,
Speaker 2: through stars, through galaxies, through the Earth itself. It is
Speaker 2: a perfect, uninterrupted ruler measuring the geometry of the universe.
Speaker 3: It sounds like the perfect solution, but standard sirens have
Speaker 3: a glaring flaw. They suffer from a massive bottleneck problem.
Speaker 2: You have this pristine, incredibly accurate, mathematically perfect distance measurement,
Speaker 2: but if you remember the Hubble formula to measure the constant,
Speaker 2: you need both distance and recession velocity.
Speaker 3: You need to know how fast that specific black hole
Speaker 3: merger is physically receding from Earth due to the expansion
Speaker 3: of space.
Speaker 2: And here's the brutal paradox that astrophysicists ran into. Black
Speaker 2: holes do not emit light. They are black.
Speaker 3: Their gravity is so intense that nothing, not even electromagnetic radiation,
Speaker 3: escapes the event horizon. If there is no light, there
Speaker 3: are no spectral lines for our telescopes to measure.
Speaker 2: If you have no spectral lines, you absolutely cannot measure
Speaker 2: the red shift, and with no red shift, you have
Speaker 2: no velocity.
Speaker 3: You are left holding a massive, pristine catalog of highly
Speaker 3: precise distances to black hole mergers, but absolutely no speeds
Speaker 3: to pair them with. You have half of the equation
Speaker 3: and it's useless for solving the Hubble attension on its own.
Speaker 2: So how do you bypass this bottleneck? Traditionally, using standard
Speaker 2: sirens requires an incredible stroke of astronomical luck. You require
Speaker 2: the simultaneous detection of an electromagnetic counterpart.
Speaker 3: For instance, if two neutron stars collide rather than two
Speaker 3: black holes, the intense violence of the merger not only
Speaker 3: emits a massive burst of gravitational waves, but it also
Speaker 3: violently rips the neutron stars apart, emitting a blindingly bright
Speaker 3: flash of gamma rays and visible light.
Speaker 2: This is called a killinova. If the LVK detects the
Speaker 2: gravitational chirp and optical telescopes simultaneously catch the flash of light,
Speaker 2: you have hit the jackpot. You use the gravitational waves
Speaker 2: for the perfect distance, and you use the light flash
Speaker 2: to measure the red shift and get the perfect velocity.
Speaker 3: But neutron star mergers are relatively rare compared to black
Speaker 3: hole mergers, and catching the light flash before it fades
Speaker 3: is incredibly difficult. Alternatively, if you just have black holes,
Speaker 3: you would need a small enough localization volume in the
Speaker 3: sky to pinpoint the exact host galaxy where the black
Speaker 3: holes lived.
Speaker 2: The LVK network triangulates the signal to find out roughly
Speaker 2: where in the sky it came from. If that search
Speaker 2: area is small enough, you can look at the galaxies
Speaker 2: in that patch, find the host, and measure the galaxy's redshift.
Speaker 3: But the reality is finding that exact host galaxy among
Speaker 3: millions in a localized patch of sky is rarely feasible.
Speaker 3: The LVK network gives us error boxes on the sky
Speaker 3: map indicating where the signal originated, but those boxes are
Speaker 3: often massive.
Speaker 2: They cover huge swaths of the sky containing tens of
Speaker 2: thousands of potential host galaxies. You can't guess which one
Speaker 2: holds the black holes, so the traditional standard siren protocol
Speaker 2: hits a wall. The data is too sparse to decisively
Speaker 2: solve the tension.
Speaker 3: That is, until a massive conceptual leap occurred recently, a
Speaker 3: paradigm shift developed by a team of researchers at the
Speaker 3: University of Illinois or Bana Champagne and the University of Chicago,
Speaker 3: involving prominent theoretical physicists and astrophysicists like Nicholas June's, Daniel Holtz,
Speaker 3: and Bryce Cousins.
Speaker 2: What they realized was profound. They realized that the entire
Speaker 2: field's intense focus on individual perfectly resolved standard sirens chasing
Speaker 2: the loud, clear chirps was fundamentally blinding them to an
Speaker 2: even larger, vastly more powerful data set hidden right beneath
Speaker 2: their noses.
Speaker 3: Hidden in the noise itself. They moved away from looking
Speaker 3: for individual ripples in the pond and started looking at
Speaker 3: the entire ocean.
Speaker 2: To understand their breakthrough, you have to look at how
Speaker 2: the LVK data is structured. There is a strict mathematical
Speaker 2: bifurcation in the data between observable events and unobservable events.
Speaker 3: Let's clearly differentiate those two, because this is the hinge
Speaker 3: of the whole theory. An observable event is a massive,
Speaker 3: relatively nearby binary black hole merger two giant black holes
Speaker 3: crashing together somewhat close to our cosmic neighborhood.
Speaker 2: Because they're massive and close, the gravitational wave they produce
Speaker 2: has a high signal to noise ratio. The signal is
Speaker 2: loud enough to stand out clearly and unmistakably above the
Speaker 2: inherent instrumental and quantum noise of the LVK detectors.
Speaker 3: The algorithms scan the data stream, find the distinct chirp,
Speaker 3: and flag it as a confirmed merger. These are the
Speaker 3: observable events. We've detected dozens.
Speaker 2: Of them, but the universe is incredibly vast and star
Speaker 2: formation has been happening for billions of years. For every
Speaker 2: one of those loud, observable nearby events, there is a vast,
Speaker 2: almost innumerable multitude of smaller collisions or vastly more distant
Speaker 2: collisions happening constantly throughout the deep universe, and.
Speaker 3: Those distant ancient collisions register is far too faint to
Speaker 3: be observed individually. Their signal to noise ratio is simply
Speaker 3: too low.
Speaker 2: The chirp is buried beneath the quantum static of the
Speaker 2: lasers and the thermal vibrations of the mirrors. The LVK
Speaker 2: pipeline algorithm cannot confidently flag them as distinct individual mergers.
Speaker 2: They are classified as unobservable.
Speaker 3: But they don't just disappear. They are still physically stretching
Speaker 3: and compressing the Earth. And because there are so many
Speaker 3: of them happening constantly all across the cosmos, these unresolved
Speaker 3: signals blend together. They overlap in time and frequency.
Speaker 2: Here's where it gets really interesting. Think of it like
Speaker 2: being in a massive, crowded sports stadium. You can clearly
Speaker 2: hear the voice of the person sitting directly next to you.
Speaker 2: That is your observable event, but.
Speaker 3: You are also surrounded by eighty thousand other people talking, shouting,
Speaker 3: and moving. You cannot make out a single distinct word
Speaker 3: from the crowd on the other side of the stadium,
Speaker 3: but their collective voices overlap and merge into a continuous
Speaker 3: low frequency roar, a stadium wide background noise.
Speaker 2: In astrophysics, these unresolved distant gravitational wave signals blend together
Speaker 2: into what is formally defined as the gravitational wave background.
Speaker 2: It is a stochastic.
Speaker 3: Hump stochastic meaning randomly determined, having a random probability distribution.
Speaker 3: It's the cumulative overlapping spacetime ripples generated by countless unresolved
Speaker 3: black hole collisions occurring continuously throughout the cosmos since the
Speaker 3: era of peak star formation billions of years ago.
Speaker 2: It is a pervasive, continuous background noise of ground itself,
Speaker 2: constantly vibrating the entire universe.
Speaker 3: So the immense challenge this research team face was this,
Speaker 3: if the highly advanced interferometers cannot resolve these individual differant mergers,
Speaker 3: how can we possibly use them to measure the Hubble constant.
Speaker 2: The key is mathematical statistical extrapolation. The researchers developed a
Speaker 2: brilliant methodology to formally harness the stochastic hum.
Speaker 3: They start by working with what they actually know. They
Speaker 3: carefully quantify the precise rate and mass distribution of the
Speaker 3: observable individual black hole collisions, the loud ones that LVK
Speaker 3: can clearly detect and measure perfectly.
Speaker 2: From those clear local events, the physicists build a robust
Speaker 2: demographic profile of black hole populations in the local universe.
Speaker 2: They figure out the average masses, the ratio of big
Speaker 2: mergers to small mergers, and how often they occur.
Speaker 3: It's akin to taking a highly detailed census of a
Speaker 3: single typical neighborhood to understand the demographics of an entire
Speaker 3: massive city. Once they have that localized demographic profile secured,
Speaker 3: they statistic extrapolate.
Speaker 2: They modeled the sheer massive volume of unobservable events occurring
Speaker 2: across the broader universe that must be actively contributing to
Speaker 2: the background hum.
Speaker 3: It requires immense computational modeling. They integrate the expected merger
Speaker 3: rates of these black hole populations over vast spans of
Speaker 3: cosmic time. They know roughly when the universe was churning
Speaker 3: out the most stars, which tells them when the most
Speaker 3: black holes were born, and consequently when the most mergers
Speaker 3: should be happening.
Speaker 2: They combine all this data and project the total gravitational
Speaker 2: wave energy density those countless unobservable mergers would logically produce.
Speaker 3: And this mathematical projection yields a highly predictable theoretical stochastic
Speaker 3: background spectrum. They can predict exactly how loud the hum
Speaker 3: should be and at what frequencies it should be humming.
Speaker 2: This theoretical framework is the birth of the stochastic siren methodology,
Speaker 2: and the brilliance of it is that it bypasses the
Speaker 2: need for individual light flashes or host galaxy redshifts entirely.
Speaker 3: It completely sidesteps the electromagnetic bottleneck. It solves the paradox
Speaker 3: through a rigorous, incredibly tight gmeter correlation.
Speaker 2: The entire method hinges on a diagnostic geometry, a precise
Speaker 2: inverse relationship between the physical value of the hubble constant
Speaker 2: and the physical volume the literal loudness of the gravitational
Speaker 2: wave background.
Speaker 3: Let's walk through this logical sequence step by step, because
Speaker 3: it is arguably one of the most elegant conceptual leaps
Speaker 3: in modern cosmology. Step A requires us to postulate a
Speaker 3: scenario where the hubble constant is smaller.
Speaker 2: Let's assume the lower value derived from the early universe
Speaker 2: cosmic microwave background data is the correct one. We adopt
Speaker 2: the scenario where the universe is expanding at roughly that
Speaker 2: sixty seven kilometers per second rate.
Speaker 3: We pretend the early universe math is one hundred percent right,
Speaker 3: and we see what physical consequences that forces onto the universe.
Speaker 3: A smaller Hubble constant of sixty seven definitively means a
Speaker 3: slower overall rate of universal expansion over time.
Speaker 2: Now, moving to step B, we have to logically deduce
Speaker 2: the geometric consequences of that slower expansion rate.
Speaker 3: If the universe has been expanding more slowly for the
Speaker 3: last thirteen point eight billion years to reach its current
Speaker 3: observable state, then the total geometric volume of the observable
Speaker 3: universe at any given distance at any given red shift
Speaker 3: in the past must mathematically be smaller.
Speaker 2: To picture this, imagine two balloons being blown up for
Speaker 2: exactly ten seconds. One is blown up slowly, representing the
Speaker 2: sixty seven rate, the other is blown up incredibly fast,
Speaker 2: representing the seventy three rate.
Speaker 3: If you stop them at ten seconds and look back
Speaker 3: at how big they were at the five second mark,
Speaker 3: the slower expanding balloon was physically much smaller at that
Speaker 3: point in its history than the fast expanding balloon.
Speaker 2: The actual cosmological container of space stretching back into the
Speaker 2: deep past where these unobservable black hole mergers are happening,
Speaker 2: is physically more compact than it would be in a
Speaker 2: faster expanding model.
Speaker 3: Which brings us to the critical inflection point of the
Speaker 3: theory step C. If the universe's geometric volume is significantly
Speaker 3: smaller at those distant redshifts, but the intrinsic statistical number
Speaker 3: of black hole mergers occurring remains exactly constantly.
Speaker 2: Wait, let me pause you there. Why does the number
Speaker 2: of black hole mergers remain constant. Wouldn't a smaller universe
Speaker 2: have fewer black holes?
Speaker 3: That's a great question, But no, it wouldn't. The rate
Speaker 3: of black hole mergers is strictly dictated by the star
Speaker 3: formation history of the universe. How many stars were born,
Speaker 3: how fast they burned out, and how many collapse into
Speaker 3: black hole.
Speaker 2: Well, we measure that star formation history independently, primarily using
Speaker 2: electromagnetic observations of distant galaxies.
Speaker 3: That history doesn't change based on the Hubble constant. We
Speaker 3: know how many catastrophic black hole collisions are happening out there.
Speaker 2: Okay, I see, so the number of events is locked in.
Speaker 2: You have the exact same vast number of catastrophic black
Speaker 2: hole collisions happening, but because of the slower expansion rate,
Speaker 2: they are occurring in a much smaller geometric volume of space.
Speaker 3: Exactly right, you have the same amount of catastrophic events
Speaker 3: compressed into a much tighter region of comoving space. Therefore,
Speaker 3: a profound Sneichel compression occurs. This rafacial density of these
Speaker 3: massive gravitational wave events spikes significantly.
Speaker 2: Think about that you are cramming the exact same number
Speaker 2: of massive fireworks into a much smaller room, and.
Speaker 3: That increased density leads directly to Step D. We can
Speaker 3: mathematically dictate that this increased batial density of black hole
Speaker 3: collisions unequivocally amplifies the overall strength and volume of the
Speaker 3: gravitational wave background.
Speaker 2: Because the active sources of gravitational waves are packed much
Speaker 2: closer together in a geometrically smaller universe, the cumulative spacetime
Speaker 2: ripples they produce compound upon each other much more intensely.
Speaker 3: The resulting stochastic hum the roar of the stadium would
Speaker 3: be significantly louder and physically stronger. The waves wouldn't have
Speaker 3: as much space to dissipate before overlapping.
Speaker 2: So the analytical tool is complete and rigorous. A smaller
Speaker 2: Hubble constant strictly mandates a louder gravitational wave background. The
Speaker 2: inverse relationship is the master key to the entire method.
Speaker 3: And this inverse relationship functions as an extraordinarily potent analytical
Speaker 3: tool through the classic scientific process of elimination. The methodology
Speaker 3: relies on constraining the parameter space of the Hubble tension
Speaker 3: using hard empirical constraints.
Speaker 2: The Illinois and Chicago research team applied this geometric logic
Speaker 2: directly to the existing raw LVK data, and the massive
Speaker 2: power of this application lies purely in non detection.
Speaker 3: This is where doing nothing is actually doing something. The
Speaker 3: highly sensitive LVK instruments, running for months and years at
Speaker 3: a time did not detect a massive deafening stochastic signal.
Speaker 2: The interferometers were not overwhelmed by a massive background hum
Speaker 2: dominating their low frequency sensitivity bands. They detected the loud
Speaker 2: close chirps, but the baseline static was relatively quiet, and.
Speaker 3: In astrophysics, a non detection like this is absolutely crucial
Speaker 3: empirical data. It is proof of absence if the lower
Speaker 3: bounds of the Hubble tension the extremely slow sixty seven
Speaker 3: expansion models derived from the early universe were strictly true
Speaker 3: without any modifications. The spatial compression of black holes would
Speaker 3: be so intense that the stochastic hum would have been
Speaker 3: theoretically deafening to the LVK sensors.
Speaker 2: It would have saturated the data, but it didn't. By
Speaker 2: proving definitively how loud the background is not, the researchers
Speaker 2: utilized the absence of a massive signal to establish firm
Speaker 2: mathematical upper limits.
Speaker 3: They carefully quantified the absolute maximum possible volume the background
Speaker 3: hume could be producing without triggering a massive detection in
Speaker 3: the current incredibly sensitive LVK data streams, and by establishing
Speaker 3: those rigorous limits, they mathematically ruled out the slowest expansion
Speaker 3: models outright.
Speaker 2: Furthermore, they heavily constrained the most extreme variance of the
Speaker 2: early dark energy hypotheses. They placed a rigid, unyielding mathematical
Speaker 2: ceiling on what models of cosmology are physically permissible in
Speaker 2: our reality.
Speaker 3: But the research didn't stop at simply ruling out the
Speaker 3: extreme models. They took the methodology further to fundamentally refine
Speaker 3: the Hubble constant itself. The methodology elegantly synthesizes two completely
Speaker 3: independent streams of gravitational data.
Speaker 2: They combine the strict upper limits of the unresolved background
Speaker 2: hum with the pristine distance data extracted from the isolated
Speaker 2: individual standard sirens we discussed earlier.
Speaker 3: By combining the massive statistical, unobservable data set that dictates
Speaker 3: the volume of the universe with a perfectly resolved local
Speaker 3: data set that acts as our perfect localized ruler, they
Speaker 3: mathematically extract a highly refined, entirely independent estimate of the
Speaker 3: Hubble constant.
Speaker 2: And the result is staggering. This new estimate, derived purely
Speaker 2: from space time ripples, falls directly within the parameter space
Speaker 2: of the Hubble tension. It doesn't use standard candles, it
Speaker 2: doesn't use the cousmic microwave background.
Speaker 3: It provides a highly constrained, completely independent physical measurement utilizing
Speaker 3: a fundamentally distinct physical force, gravity instead of electromagnetism.
Speaker 2: If we connect this to the bigger picture, the technological
Speaker 2: horizon over the next decade points toward a definitive, monumental
Speaker 2: resolution to this crisis.
Speaker 3: The LVK network is not static. It is continuous undergoing
Speaker 3: significant multimillion dollars sensitivity upgrades. The engineering teams are actively
Speaker 3: reducing the quantum noise within the lasers even further and
Speaker 3: drastically improving the physical isolation of the mirrors from terrestrial
Speaker 3: seismic interference.
Speaker 2: They are making the most sensitive instrument ever built even
Speaker 2: more sensitive. The data predicts that within just six years,
Speaker 2: scientific consensus dictates that the interferometers will have increased in
Speaker 2: sensitivity enough to cross the critical threshold.
Speaker 3: Within six years, detectors will definitively detect, isolate, and precisely
Speaker 3: constrain the exact volume and spectral shape of the gravitational
Speaker 3: wave background. They won't just set upper limits, they will
Speaker 3: hear the hump perfectly. They will definitively isolate it from
Speaker 3: the instrumental noise.
Speaker 2: The ultimate objective of modern astrophysics is resolving the Hubble
Speaker 2: tension purely through gravity. Securing this independent, ultra precise measurement
Speaker 2: via the aggregate space time ripples of millions of black
Speaker 2: holes will definitively solve the foundational physical paradoxes that localize
Speaker 2: isolated electromagnetic measurements simply cannot reconcile.
Speaker 3: It will tell us once and for all whether our
Speaker 3: standard model of the universe is fundamentally broken or if
Speaker 3: dark energy is mutating over time.
Speaker 2: It remains an unresolved cosmic paradigm today, but the sheer
Speaker 2: elegance of the stochastic siren method is unparalleled. It possesses
Speaker 2: the profound capacity to leverage the macroscopic, unresolved dynamics of
Speaker 2: the cosmos to solve a local problem.
Speaker 3: It relies on the massive statistical aggregation of unobservable invisible
Speaker 3: events to precisely calibrate the geometric expansion of the universe.
Speaker 2: It entirely bypasses the limitations of standard candles. We don't
Speaker 2: have to worry about the cosmic dust, the light extinction rates,
Speaker 2: or the metallicity of distinct galaxies ever again.
Speaker 3: And it completely bypasses the recession velocity bottleneck that plagued
Speaker 3: individual standard sirens. It is a masterful, pure application of
Speaker 3: statistical mechanics and general relativity.
Speaker 2: As we synthesize the power of this entire method, o dotage,
Speaker 2: there's a highly provocative extrapolation. We must leave you with
Speaker 2: a thought experiment about the distant future of cosmology.
Speaker 3: When the LVK network or the next future generation of
Speaker 3: highly advanced space based or massive ground based detectors like
Speaker 3: the proposed Cosmic Explorer eventually detect and fully map this
Speaker 3: gravitational wave background. They won't merely be recording its overall amplitude.
Speaker 2: They won't just measure how loud the HUM is.
Speaker 3: With enough sensitivity and time, they will eventually map its
Speaker 3: specific directional anisas anesotropies.
Speaker 2: That's a complex term, but we've actually talked about it
Speaker 2: already today. Just as the cosmic microwave background has those
Speaker 2: microscopic temperature fluctuations across different regions of the sky, the
Speaker 2: hot spots and cold spots that form the seeds of galaxies,
Speaker 2: the gravitational wave background will also possess anisotropies.
Speaker 3: There will be a subtle distinct unevenness in the gravitational
Speaker 3: hum originating from different cosmological coordinates. The roar of the
Speaker 3: stadium won't be perfectly uniform, will be slightly louder coming
Speaker 3: from the north bleachers than the south bleachers.
Speaker 2: Consider the immense reality altering implications of mapping that gravitational topography.
Speaker 2: The precise spatial distribution of these microscopic spacetime ripples arriving
Speaker 2: from all directions could theoretically map the density of matter
Speaker 2: in the universe before the cosmic dark ages even began.
Speaker 3: Because gravitational waves pass unhindered through the primordial plasma that
Speaker 3: trapped light. We could see further back than the cosmic
Speaker 3: microwave background. We could map the true dawn of the universe.
Speaker 2: But it goes even further than that. Variations in this
Speaker 2: gravitational background might reveal entirely new pre Big Bang structures
Speaker 2: predicted by fringe highly theoretical cyclic cosmology models.
Speaker 3: If the universe expands, collapses, and bangs again, the gravitational
Speaker 3: echoes of previous universes might be permanently imprinted in the stochasticom.
Speaker 3: This mapping of anisotropes could expose phenomena that our current
Speaker 3: LAMB to CDM expansion models cannot even mathematically formulate.
Speaker 2: We might expose the gravitational signatures of previously theorized higher
Speaker 2: dimensions of space time. If string theory is correct and
Speaker 2: gravity is leaking into our observable universe from higher hidden dimensions,
Speaker 2: the evidence of that multidimensional leakage would be inscribed directly
Speaker 2: into the uneven fluctuations of the gravitational wave background.
Speaker 3: It's an incredible frontier.
Speaker 2: Just consider the absolute magnitude of what humanity is attempting
Speaker 2: to map here by isolating the microscopic stretching of lasers
Speaker 2: in a vacuum tube. We are listening to the invisible
Speaker 2: geometry of the universe. We are listening to a symphony
Speaker 2: of catastrophic violence stretching across billion year epochs. We are
Speaker 2: using the invisible force of gravity to peel back the
Speaker 2: veil of the cosmos, revealing structures, dimensions, and ancient histories
Speaker 2: far beyond the fragile, dusty limits of light itself. Allow
Speaker 2: the profound magnitude of that thought to sit with you.
Speaker 3: The school most us