WEBVTT

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<v Speaker 1>Welcome to Bedtime Astronomy. Explore the wonders of the cosmos

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<v Speaker 1>with our soothing Bedtime Astronomi podcast. Each episode offers a

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<v Speaker 1>gentle journey through the stars, planets, and beyond, perfect for

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<v Speaker 1>unwinding after a long day. Let's travel through the mysteries

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<v Speaker 1>of the universe as you drift off into a peaceful

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<v Speaker 1>slumber under the night sky.

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<v Speaker 2>The universe is actively expanding, and this stretching of physical

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<v Speaker 2>space is governed by a precise mathematical value known as

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<v Speaker 2>the Hubble constant.

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<v Speaker 3>Right every single second, the very physical reality of the

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<v Speaker 3>cosmos is stretching.

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<v Speaker 2>The distance between distant galaxies is increasing in all directions,

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<v Speaker 2>and that exact rate of current expansion is what the

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<v Speaker 2>Hubble constant represents. It is the absolute fundamental metric of

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<v Speaker 2>our cosmos.

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<v Speaker 3>I mean, it's the ultimate cosmological ruler, really. But to

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<v Speaker 3>truly understand what that means, we have to completely separate

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<v Speaker 3>cosmic expansion from our everyday human intuition of movement.

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<v Speaker 2>Because when you think of things moving apart, you usually

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<v Speaker 2>imagine objects traveling through a pre existing empty room.

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<v Speaker 3>Exactly, if I throw a baseball, it moves through the

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<v Speaker 3>air in a static space. But when we talk about

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<v Speaker 3>galaxies moving apart, that is absolutely not what is happening.

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<v Speaker 2>We are not talking about objects moving through pre existing

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<v Speaker 2>empty space, like shrapnel flying outward from some localized explosion. No,

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<v Speaker 2>because the Big Bang wasn't an explosion in space, It

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<v Speaker 2>was an explosion of space.

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<v Speaker 3>That is a crucial distinction. According to Albert Einstein's general relativity,

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<v Speaker 3>space time itself is a malleable dynamic fabric. It can bend,

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<v Speaker 3>it can bend, it can warp, and critically it can stretch.

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<v Speaker 3>What is actually happening out there in the deep cosmos

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<v Speaker 3>is the continuous, ongoing creation of new physical space between

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<v Speaker 3>these massive objects.

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<v Speaker 2>So the galaxies themselves are relatively stationary in their local

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<v Speaker 2>pockets space.

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<v Speaker 3>Time rice exactly, but the tapestry there woven into is

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<v Speaker 3>being pulled apart.

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<v Speaker 2>The classic analogy here is always the raisin bread.

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<v Speaker 3>Baking in the oven, right the raisin break.

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<v Speaker 2>If you put a loaf of unbaked raisin bread in

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<v Speaker 2>the oven, the raisins represent the balaxies, and the dough

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<v Speaker 2>is space time, And as the dough bakes and rises,

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<v Speaker 2>it expands in all.

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<v Speaker 3>Directions, and the raisins aren't swimming through the dough.

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<v Speaker 2>No, they are just being carried along as the dough

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<v Speaker 2>itself gets bigger. So the distance between any two raisins increases,

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<v Speaker 2>and the.

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<v Speaker 3>Further apart two raisins are the faster they appear to

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<v Speaker 3>be moving away from each other.

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<v Speaker 2>And the hubble constant is the exact measurement of how

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<v Speaker 2>fast that dough is rising right now. It measures the

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<v Speaker 2>current rate of this stretching.

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<v Speaker 3>It's typically expressed in a rather clunky unit kilometers per

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<v Speaker 3>second per megaparsek, which is a mouthful. It is. A

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<v Speaker 3>megaparsec is an astronomical unit of distance equal to about

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<v Speaker 3>three point twenty six million light years.

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<v Speaker 2>Okay, so for every three point twenty six million light

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<v Speaker 2>years of distance between US and a galaxy, that galaxy

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<v Speaker 2>appears to be receding from us by a certain number

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<v Speaker 2>of kilometers every single.

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<v Speaker 3>Second, pearly due to the creation of new.

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<v Speaker 2>Space, right, which you know, sounds like a settled science.

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<v Speaker 2>We just measure the galaxies, get the number and write

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<v Speaker 2>it in the textbooks.

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<v Speaker 3>But it isn't not even.

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<v Speaker 2>Close, right, because right now we are investigating what is

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<v Speaker 2>undoubtedly the most critical unresolved paradox in modern astrophysics. It

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<v Speaker 2>is called the Hubble tension.

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<v Speaker 3>The Hubble tensions.

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<v Speaker 2>Yes, and for you listen right now. You might think

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<v Speaker 2>this is just a rounding error, some tiny disagreement in

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<v Speaker 2>the decimal points of a complex calculation that scientists are

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<v Speaker 2>just being pedantic about.

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<v Speaker 3>But it's really not.

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<v Speaker 2>It's not at all. It is a fundamental discrepancy threatening

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<v Speaker 2>the absolute axioms of cosmology.

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<v Speaker 3>It forces the entire discipline to confront a highly uncomfortable

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<v Speaker 3>objective scientific reality. Astrophysics is currently undergoing a foundational crisis.

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<v Speaker 2>A foundational crisis, yes.

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<v Speaker 3>The crisis arises from the massive dichotomy between two distinct,

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<v Speaker 3>highly pristine sets of precision measurements that simply refuse to align.

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<v Speaker 2>It's as if you hired two different teams of master

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<v Speaker 2>architects to measure the exact length of a bridge.

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<v Speaker 3>Right, They both used state of the art lasers, they

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<v Speaker 3>both check their mouth one hundred times, and they come

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<v Speaker 3>back with two completely different lengths.

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<v Speaker 2>Let's lay out that dichotomy, because the details of how

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<v Speaker 2>we get these numbers are absolutely fascinating.

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<v Speaker 3>Let's do it.

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<v Speaker 2>On one side, we have measurements derived from the early universe,

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<v Speaker 2>astrophysicists looked deep into the past by analyzing observations originating

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<v Speaker 2>from the cosmic microwave background, or the CMB.

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<v Speaker 3>The CMB is essentially the after glow of the Big Bang.

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<v Speaker 3>It is the absolute oldest like we can possibly detect

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<v Speaker 3>in the universe.

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<v Speaker 2>And to understand why it's the oldest light, you really

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<v Speaker 2>have to picture the universe just after the Big Bang.

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<v Speaker 3>It was a fiercely hot, unimaginably dense soup of plasma.

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<v Speaker 2>It was so hot that atoms couldn't even form yet exactly.

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<v Speaker 3>Electrons and protons were just zipping around independently. And because

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<v Speaker 3>of this dense fog of free electrons, light could not travel.

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<v Speaker 2>Because a photon would travel a microscopic distance and immediately

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<v Speaker 2>scatter off an electron.

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<v Speaker 3>Right, So the early universe was opaque. It was glowing,

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<v Speaker 3>but you couldn't see through it.

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<v Speaker 2>It was essentially an infinite cosmic fog bank.

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<v Speaker 3>A glowing fog bank. Yes. But then as the universe expanded,

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<v Speaker 3>it naturally cooled down.

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<v Speaker 2>It cooled for about three hundred and eighty thousand years.

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<v Speaker 3>And then it hit a critical temperature threshold. It became

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<v Speaker 3>cool enough for those free roaming electrons to finally bind

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<v Speaker 3>with protons and form the first stable, neutral hydrogen atoms.

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<v Speaker 2>This era is known as recombination.

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<v Speaker 3>Recombination exactly, and the moment those electrons were locked up

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<v Speaker 3>in atoms, the fog instantly.

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<v Speaker 2>Lifted, the universe became transparent.

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<v Speaker 3>And all those photons that had been bouncing around in

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<v Speaker 3>the plasma were suddenly free to travel in a straight

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<v Speaker 3>line across the cosmos.

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<v Speaker 2>And those exact same photons have been traveling through space

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<v Speaker 2>for the last thirteen point eight billion years.

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<v Speaker 3>But because the space they were traveling through has been

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<v Speaker 3>expanding this whole time, the actual wavelengths of that light

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<v Speaker 3>have been physically stretched out.

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<v Speaker 2>So it started as intensely hot high energy light has

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<v Speaker 2>been stretched all the way down into the microwave spectrum.

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<v Speaker 3>That's the cosmic microwave background. When we point our most

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<v Speaker 3>advanced satellites like the Plank Space Observatory of the empty sky,

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<v Speaker 3>we see this faint microwave hum everywhere we look.

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<v Speaker 2>And contained within that hum is a complete treasure trove

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<v Speaker 2>of data.

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<v Speaker 3>There are microscopic temperature fluctuations in that background, radiation hot

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<v Speaker 3>spots and cold spots.

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<v Speaker 2>And those represent the initial seeds of all the galaxies

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<v Speaker 2>and galaxy clusters that exist today.

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<v Speaker 3>Yes, by looking at the size and distribution of these

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<v Speaker 3>microscopic spots, cosmologists can plug that data into our standard

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<v Speaker 3>model of the universe.

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<v Speaker 2>And they basically fast forward the clock to figure out

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<v Speaker 2>how fast the universe should be expanding today.

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<v Speaker 3>And when they do that incredibly complex calculation, analyzing this

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<v Speaker 3>primordial light from the dawn of time, they calculate one

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<v Speaker 3>highly specific expansion rate.

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<v Speaker 2>Roughly sixty seven kilometers per second per mega parsec.

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<v Speaker 3>That is measurement number one, the early universe ruler.

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<v Speaker 2>Okay, so that's the first team of architects, right, But.

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<v Speaker 3>Then we look at the other side of the data,

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<v Speaker 3>the late universe ruler.

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<v Speaker 2>When scientists use entirely different observational methodologies to measure the local,

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<v Speaker 2>more recent observable universe.

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<v Speaker 3>Looking at galaxies and stars that exist relatively close to

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<v Speaker 3>us in cosmic.

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<v Speaker 2>Time, they arrive at a completely different rate.

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<v Speaker 3>This more recent measurement yields an expansion rate of about

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<v Speaker 3>seventy three kilometers per second per megaparsek.

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<v Speaker 2>Sixty seven versus seventy three.

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<v Speaker 3>That is the tension.

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<v Speaker 2>And here is where the crisis really solidifies. You might

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<v Speaker 2>look at those numbers and think, well, they are pretty close.

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<v Speaker 3>And twenty or thirty years ago, the error bars on

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<v Speaker 3>these megaments were.

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<v Speaker 2>Huge, right, sixty seven might have had an error margin

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<v Speaker 2>of plus or minus ten and seventy three might have

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<v Speaker 2>had an error margin of plus or minus ten.

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<v Speaker 3>So the margins overlapped, and scientists figured they would eventually

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<v Speaker 3>meet somewhere in the middle as our instruments got better.

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<v Speaker 2>But the technology evolved. The instruments got better, the mathematical

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<v Speaker 2>models became more rigorous, and.

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<v Speaker 3>The margins of error on these two massive, heavily cross

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<v Speaker 3>checked measurements shrank drastically.

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<v Speaker 2>They shrank so much they have become so staggeringly precise

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<v Speaker 2>that their error bars no longer overlap whatsoever.

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<v Speaker 3>They are statistically mathematically incompatible.

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<v Speaker 2>Which is terrifying for a physicist. It really is because

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<v Speaker 2>both of these methodologies rely on the identical fundamental laws

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<v Speaker 2>of physics.

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<v Speaker 3>The underlying math governing gravity, thermodynamics, and electromagnetism is exactly

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<v Speaker 3>the same for both the early Universe calculations and the

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<v Speaker 3>late Universe observations.

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<v Speaker 2>The physics and the CMB and the physics of the stars.

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<v Speaker 2>We look at today. Are supposed to be part of

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<v Speaker 2>one unified reality, so they absolutely should align perfectly.

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<v Speaker 3>The lack of alignment points directly to an axiomatic conflict.

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<v Speaker 3>We have two pristine rulers to measure the cosmos, built

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<v Speaker 3>on the exact same physical laws, yet giving entirely different dimensions.

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<v Speaker 2>And because our methodologies are logically sound and heavily cross

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<v Speaker 2>checked by thousands of independent researchers worldwide, we cannot simply

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<v Speaker 2>tweak our existing models or blame a dusty telescope lens.

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<v Speaker 3>No, we can't. This discrepancy means the standard model of cosmology,

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<v Speaker 3>known as the Lambda CDM model, has a massive glaring.

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<v Speaker 2>Deficit Lambda CDM. Lambda stands for dark energy and CDM

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<v Speaker 2>stands for cold dark matter.

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<v Speaker 3>That is the bedrock blueprint of astrophysics. It dictates the

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<v Speaker 3>inventory and behavior of the entire universe.

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<v Speaker 2>The fact that it cannot reconcile sixty seven and seventy

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<v Speaker 2>three implies a literal gap in our current framework of

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<v Speaker 2>physical reality.

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<v Speaker 3>It implies we are fundamentally misunderstanding something profound about how

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<v Speaker 3>the universe operates.

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<v Speaker 2>So what does this all mean? Let's look at the

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<v Speaker 2>fallout of this.

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<v Speaker 3>The fallout is significant.

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<v Speaker 2>If our baseline understanding of how the universe expands is

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<v Speaker 2>fundamentally flawed, then our calculations regarding the age of the

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<v Speaker 2>universe are wrong. Our calculations regarding its total geometric.

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<v Speaker 3>Size are wrong also, yes.

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<v Speaker 2>And our predictions for its ultimate cosmological fate, whether it

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<v Speaker 2>will expand forever into a cold, dark void or eventually

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<v Speaker 2>rip itself apart, are all built on incredibly shaky ground.

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<v Speaker 3>Establishing a unified Hubble constant is an absolute imperative.

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<v Speaker 2>If the established standard model is broken or incomplete, theoretical

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<v Speaker 2>physicists have to hypothesize what exactly we are missing.

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<v Speaker 3>And usually, when looking for missing pieces in cosmology, scientists

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<v Speaker 3>look to the dark sectors of the universe to patch

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<v Speaker 3>this cosmological hole.

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<v Speaker 2>The dark sectors being dark energy and dark matter.

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<v Speaker 3>Which together make up about ninety five percent of the

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<v Speaker 3>total mass energy content of the universe ninety five percent,

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<v Speaker 3>it's almost everything. We call them dark simply because they

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<v Speaker 3>do not interact with light. We can't see them directly.

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<v Speaker 2>We only know they exist because of their gravitational effects

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<v Speaker 2>on the five percent of normal matter that we can

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<v Speaker 2>actually see, like starred and gas.

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<v Speaker 3>Clothes, exactly, and that search for a theoretical patch brings

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<v Speaker 3>us to the first major hypothesis attempting to solve the

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<v Speaker 3>hubble tension early dark energy.

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<v Speaker 2>Let's break that down because it's a wild concept, it

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<v Speaker 2>really is.

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<v Speaker 3>To understand early dark energy, we need to quickly look

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<v Speaker 3>at regular dark energy as we know it today.

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<v Speaker 2>Dark energy is currently the dominant component of the universe.

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<v Speaker 2>It acts as a mysterious repulsive force, essentially anti gravity,

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<v Speaker 2>that is actively driving the accelerated expansion of the cosmos.

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<v Speaker 3>It's why the raisin bread is rising faster and faster

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<v Speaker 3>every minute.

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<v Speaker 2>But this new theoretical framework suggests there was a distinct,

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<v Speaker 2>entirely separate, temporary phase of early dark energy.

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<v Speaker 3>A phase that was active only during the universe's earliest epox,

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<v Speaker 3>long before the current era of dark energy dominance.

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<v Speaker 2>The hypothesis details that roughly one hundred thousand years after

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<v Speaker 2>the Big Bang, an entirely different scalar field emerged.

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<v Speaker 3>Right, and a scaler field is just a physical field

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<v Speaker 3>that has a specific value at every point in space,

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<v Speaker 3>like a temperature map of a room.

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<v Speaker 2>This early dark energy scalar field acted as a massive

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<v Speaker 2>temporary repelling force.

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<v Speaker 3>It significantly boosted the expansion rate when the universe was

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<v Speaker 3>incredibly young, dense, and hot.

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<v Speaker 2>So the universe is born, it's expanding at a certain rate,

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<v Speaker 2>and then suddenly this invisible force kicks in, hits the

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<v Speaker 2>gas pedal, and forces space to stretch out much faster

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<v Speaker 2>for a brief period, and.

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<v Speaker 3>In doing so, it fundamentally changed the size of something

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<v Speaker 3>cosmologists call the sound horizon.

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<v Speaker 2>The sound horizon, Yes, it's.

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<v Speaker 3>A brilliant, albeit complex concept. Remember that dense, hot soup

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<v Speaker 3>of plasma in the early universe before recombination the fog

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<v Speaker 3>bank right, Well, that soup wasn't perfectly smooth. Dark matter

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<v Speaker 3>was constantly trying to pull matter together through gravity, while

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<v Speaker 3>the intense radiation pressure of the photons was pushing matter apart.

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<v Speaker 2>This cosmic tug of war created literal acoustic waves, sound

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<v Speaker 2>waves that rippled through the primordial plasma.

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<v Speaker 3>It's incredible to think about the early universe ringing like.

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<v Speaker 2>A bell, massive deep sound waves propagating through a soup

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<v Speaker 2>of light and matter.

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<v Speaker 3>Those acoustic waves traveled outwards from areas of high density.

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<v Speaker 3>The sound horizon is simply the absolute maximum distance that

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<v Speaker 3>those acoustic waves could travel within that plasma before the

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<v Speaker 3>universe cooled enough for atoms to form.

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<v Speaker 2>Because once recombination happened and the fog lifted, the radiation

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<v Speaker 2>pressure dropped to zero, the.

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<v Speaker 3>Sound waves were instantly frozen in place.

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<v Speaker 2>They left a permanent spherical imprint on the distribution of

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<v Speaker 2>matter in the universe.

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<v Speaker 3>We can actually look out at the distribution of galaxies

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<v Speaker 3>today and see these massive spherical shells of galaxies millions

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<v Speaker 3>of light years across, which are the frozen echoes of

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<v Speaker 3>those primordial sound waves.

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<v Speaker 2>We call them baryon acoustic oscillations.

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<v Speaker 3>And because we know the physics of that early plasma,

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<v Speaker 3>we think we know exactly how far a sound wave

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<v Speaker 3>could have traveled in three hundred and eighty thousand years.

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<v Speaker 3>We use the size of that sound horizon as a

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<v Speaker 3>standard ruler to measure the cosmos.

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<v Speaker 2>But here is where the early dark energy hypothesis changes everything.

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<v Speaker 3>It really does. If this temporary burst of early dark

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<v Speaker 3>energy was present acting as a massive repelling force, it

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<v Speaker 3>altered the fundamental physics of that plasma.

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<v Speaker 2>It changed the expansion rate during that critical era, which

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<v Speaker 2>means it changed the physical distance those acoustic waves could

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<v Speaker 2>travel before the universe cooled. And froze them. Wait, so,

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<v Speaker 2>if early dark energy was secretly accelerating things the sound horizon,

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<v Speaker 2>our ultimate cosmic ruler is actually a different size than

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<v Speaker 2>we thought it was precisely.

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<v Speaker 3>And then, according to the theory, just as quickly as

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<v Speaker 3>it appeared, this early dark energy essentially decayed.

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<v Speaker 2>The scaler field lost its energy.

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<v Speaker 3>And the extrapulsive force faded away, leave the universe to

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<v Speaker 3>continue expanding at a more normal rate until regular dark

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<v Speaker 3>energy took over billions of years later.

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<v Speaker 2>Which means if our current LAMB to CDM models miss

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<v Speaker 2>this temporary ancient boost, any calculations we make bridging that

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<v Speaker 2>early cosmic microwave background data to the present day are

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<v Speaker 2>structurally skewed.

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<v Speaker 3>We are taking data from the baby universe, assuming a

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<v Speaker 3>steady growth curve and predicting how big the adult universe

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<v Speaker 3>should be.

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<v Speaker 2>But if we didn't know the baby had a massive

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<v Speaker 2>sudden growth spurt that altered its fundamental geometry before settling

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<v Speaker 2>back down, our predictions for its adult size are going

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<v Speaker 2>to be completely wrong.

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<v Speaker 3>That is exactly the implication of the early dark energy model.

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<v Speaker 3>The early universe data from the CMB isn't intrinsically wrong.

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<v Speaker 2>Our measurements of the microwave background are spectacular.

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<v Speaker 3>They are, but our mathematical bridge extrapolating that data to

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<v Speaker 3>the present day is missing a massive structural component. We

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<v Speaker 3>are extrapolating an expansion rate across thirteen point eight billion

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<v Speaker 3>years without accounting for a massive temporary acceleration that happened

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<v Speaker 3>at the very beginning.

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<v Speaker 2>It's a compelling fix. If you plug early dark energy

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<v Speaker 2>into the equations, the sixty seven number shifts upward closer

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<v Speaker 2>to the seventy three number. It bridges the gap.

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<v Speaker 3>It does, but it's not the only theory in town.

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<v Speaker 2>Right. If early dark energy isn't the culprit, what else

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<v Speaker 2>in the universe's massive invisible inventory could be messing with

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<v Speaker 2>the map.

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<v Speaker 3>That leads us directly to the second major hypothesis. Theoretical

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<v Speaker 3>physicists are heavily debating dark matter and neutrino interactions.

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<v Speaker 2>Okay, To frame this hypothesis accurately, you have to consider

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<v Speaker 2>the sheer scale of the universe's invisible inventory.

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<v Speaker 3>First, you have dark matter. As we noted, it is

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<v Speaker 3>entirely invisible. We cannot observe it electromagnetically. It doesn't emit,

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<v Speaker 3>reflect or absorb light.

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<v Speaker 2>But it possesses immense gravitational pull.

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<v Speaker 3>It forms this massive, invisible web like scaffolding that spans

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<v Speaker 3>the cosmos, and its gravity is literally what holds galaxies

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<v Speaker 3>and galaxy clusters together.

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<v Speaker 2>Without the extra gravitational glue of dark matter, galaxy spinning

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<v Speaker 2>as fast as ours would simply fly apart.

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<v Speaker 3>And then on the other end of the size spectrum

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<v Speaker 3>you have neutrinos.

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<v Speaker 2>Neutrinos are utterly fascinating elementary particles.

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<v Speaker 3>They are the most abundant particles in the universe that

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<v Speaker 3>actually possess mass, but they are incredibly elusive.

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<v Speaker 2>They are often categorized as ghostly particle.

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<v Speaker 3>Their cross section for interaction with normal matter is infinitesimally small.

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<v Speaker 3>We don't feel the strong nuclear force and they don't

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<v Speaker 3>feel electromagnetism.

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<v Speaker 2>To put that into perspective for you listening right now,

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<v Speaker 2>trillions of these neutrinos, generated by nuclear fusion in our

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<v Speaker 2>sun and by distant cosmic events, are passing through your

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<v Speaker 2>body every single.

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<v Speaker 3>Second, trillions every second, and.

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<v Speaker 2>They do so without interacting with a single atom of

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<v Speaker 2>your being. They pass through the entire Earth as easily

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<v Speaker 2>as light passes through a pane of glass staggering to

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<v Speaker 2>think about.

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<v Speaker 3>Now, under this standard model of cosmology, the established foundational

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<v Speaker 3>assumption is that dark matter is entirely collisionless.

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<v Speaker 2>It doesn't bump into itself, and it doesn't bump into

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<v Speaker 2>normal matter.

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<v Speaker 3>And the assumption is that neutrinos basically interact with nothing

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<v Speaker 3>except very rarely via the weak nuclear force.

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<v Speaker 2>But this new theory questions this.

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<v Speaker 3>It questions whether there are complex, unmapped theoretical interactions occurring

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<v Speaker 3>between the massive and visible scaffolding of dark matter and

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<v Speaker 3>this endless back ground sea of cosmic neutrinos.

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<v Speaker 2>Because both of these components were incredibly densely packed in

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<v Speaker 2>the early universe.

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<v Speaker 3>If dark matter particles and neutrinos scatter off each other,

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<v Speaker 3>even minutely, if they bounce off one another in ways

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<v Speaker 3>we haven't detected yet, the implications for the evolution of

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<v Speaker 3>the universe are profound.

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<v Speaker 2>Let's use an analogy here. Imagine playing a game of

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<v Speaker 2>pool in the dark.

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<v Speaker 3>Okay, pool in the dark.

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<v Speaker 2>You know where the pockets are, and you strike the cubeball.

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<v Speaker 2>Based on your math and your force, you calculate exactly

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<v Speaker 2>when the cube ball will hit the back of the pocket.

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00:18:29.319 --> 00:18:32.440
<v Speaker 2>But you don't realize someone has scattered thousands of invisible

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<v Speaker 2>marbles across the felt. As your cube ball rolls, it's

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<v Speaker 2>imperceptibly colliding with these marbles.

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<v Speaker 3>And with each tiny collision it transfers a fraction of

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<v Speaker 3>its energy and momentum, it slows down slightly, its path

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<v Speaker 3>is altered.

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00:18:46.240 --> 00:18:49.839
<v Speaker 2>In the cosmos. If these two immensely abundant components, dark

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<v Speaker 2>matter and neutrinos are interacting in ways that particle physics

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<v Speaker 2>has not yet quantified, those hidden physics would alter the

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<v Speaker 2>density perturbations of the early universe.

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<v Speaker 3>The dark matter is trying to clump together gravitationally to

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<v Speaker 3>form the seeds of galaxies.

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00:19:04.079 --> 00:19:08.000
<v Speaker 2>But if a sea of energetic neutrinos is constantly bombarding it,

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<v Speaker 2>scattering off it, it would suppress that gravitational clumping.

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<v Speaker 3>It would smooth out the early cosmic structures. And that

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<v Speaker 3>suppression is the key.

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00:19:16.200 --> 00:19:19.559
<v Speaker 2>If we are completely ignoring a major mechanism by which

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<v Speaker 2>the universe's primary ingredients behave and evolve, our mathematical understanding

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00:19:24.200 --> 00:19:26.680
<v Speaker 2>of cosmic expansion is heavily distorted.

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00:19:26.920 --> 00:19:30.160
<v Speaker 3>When cosmologists look at the CMB and calculate the expansion rate,

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00:19:30.480 --> 00:19:33.920
<v Speaker 3>they are assuming dark matter behaved perfectly smoothly without any

401
00:19:33.960 --> 00:19:35.039
<v Speaker 3>neutrino interference.

402
00:19:35.440 --> 00:19:38.640
<v Speaker 2>We would essentially be trying to balance a highly complex

403
00:19:38.720 --> 00:19:43.079
<v Speaker 2>cosmological equation while leaving out a massive structural variable.

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00:19:43.279 --> 00:19:46.480
<v Speaker 3>Ignoring this hidden physics distorts the mathematical bridge to the

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00:19:46.519 --> 00:19:49.599
<v Speaker 3>present day just as severely as missing a phase of

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00:19:49.640 --> 00:19:50.920
<v Speaker 3>early dark energy would.

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00:19:51.160 --> 00:19:54.160
<v Speaker 2>So we have a hypothetical new energy field, or we

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00:19:54.240 --> 00:19:57.279
<v Speaker 2>have invisible particles secretly crashing into each other.

409
00:19:57.480 --> 00:20:00.759
<v Speaker 3>And if those two variables weren't sufficiently complex, there is

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<v Speaker 3>a third major hypothesis attempting to patch the cosmological whole,

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<v Speaker 3>the temporal evolution of dark energy.

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<v Speaker 2>This one fundamentally challenges the most basic assumption of our

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00:20:10.599 --> 00:20:12.920
<v Speaker 2>current models regarding empty space itself.

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00:20:13.119 --> 00:20:16.119
<v Speaker 3>Currently, the standard view treats dark energy as a static,

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00:20:16.400 --> 00:20:21.480
<v Speaker 3>unchanging cosmological constant. It is represented by the Greek letter Lambda.

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<v Speaker 2>It is assumed to be an inherent property of space itself,

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<v Speaker 2>a steady, unyielding vacuum energy that pushes space apart at

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00:20:29.279 --> 00:20:33.359
<v Speaker 2>a constant exponential rate, completely unchanging over the billions of

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00:20:33.480 --> 00:20:34.680
<v Speaker 2>years of cosmic history.

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00:20:34.839 --> 00:20:37.400
<v Speaker 3>A cubic meter of space today has the exact same

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00:20:37.440 --> 00:20:40.079
<v Speaker 3>amount of repulsive dark energy as a cubic meter of

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00:20:40.119 --> 00:20:41.640
<v Speaker 3>space did ten billion years ago.

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00:20:41.960 --> 00:20:45.359
<v Speaker 2>But the dynamic alternative asks, what if it isn't static?

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00:20:45.799 --> 00:20:49.279
<v Speaker 2>What if dark energy is a dynamic, evolving phenomenon.

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00:20:49.480 --> 00:20:53.319
<v Speaker 3>What's fascinating here is how theoretical physicists model this mechanism.

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00:20:53.640 --> 00:20:56.960
<v Speaker 3>They use something called the equation of state parameter, usually

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00:20:56.960 --> 00:20:57.880
<v Speaker 3>denoted as W.

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00:20:58.200 --> 00:21:01.319
<v Speaker 2>In the standard LAMBA CDM model, W is assumed to

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00:21:01.359 --> 00:21:03.440
<v Speaker 2>be exactly minus one permanently.

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00:21:03.599 --> 00:21:06.359
<v Speaker 3>But if that equation of state parameter changes over time,

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00:21:06.440 --> 00:21:09.359
<v Speaker 3>if W is minus zero point nine or minus one

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00:21:09.400 --> 00:21:13.079
<v Speaker 3>point one in different epochs, it dictates that the actual

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00:21:13.200 --> 00:21:16.680
<v Speaker 3>energy density and the repulsive pressure of dark energy shifts.

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00:21:16.799 --> 00:21:20.000
<v Speaker 2>It's like a cosmic thermostat that someone is slowly turning up.

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00:21:19.960 --> 00:21:23.200
<v Speaker 3>Or down exactly. Dark energy might grow stronger, it might weaken,

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00:21:23.599 --> 00:21:26.920
<v Speaker 3>or it might fundamentally mutate over vast cosmic timescales.

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00:21:27.200 --> 00:21:31.319
<v Speaker 2>Models exploring this are sometimes called quintessence or phantom energy models.

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00:21:31.480 --> 00:21:34.799
<v Speaker 3>If dark energy is dynamic, its influence on universal expansion

439
00:21:34.839 --> 00:21:37.759
<v Speaker 3>is entirely temporal. The repulsive force today is different from

440
00:21:37.759 --> 00:21:39.119
<v Speaker 3>the repulsive force yesterday.

441
00:21:39.319 --> 00:21:42.960
<v Speaker 2>So the conclusion there is stark and incredibly elegant. In

442
00:21:43.000 --> 00:21:47.079
<v Speaker 2>its simplicity. If the equation of state parameter is evolving,

443
00:21:47.599 --> 00:21:50.599
<v Speaker 2>then comparing the expansion rate of the early universe to

444
00:21:50.680 --> 00:21:54.000
<v Speaker 2>the expansion rate of the recent universe is an exercise

445
00:21:54.119 --> 00:21:55.119
<v Speaker 2>in futility.

446
00:21:55.359 --> 00:21:57.519
<v Speaker 3>It's like trying to calculate the average speed of a

447
00:21:57.599 --> 00:21:59.920
<v Speaker 3>road trip by looking at the speedometer while you were

448
00:21:59.920 --> 00:22:02.599
<v Speaker 3>in a school zone and comparing it to the speedometer

449
00:22:02.680 --> 00:22:03.880
<v Speaker 3>while you are on the highway.

450
00:22:04.079 --> 00:22:07.599
<v Speaker 2>If you assume a static, unchanging speed limit, but the

451
00:22:07.640 --> 00:22:11.559
<v Speaker 2>actual rules of the expansion mechanism mutated over billions of years,

452
00:22:11.880 --> 00:22:13.359
<v Speaker 2>of course your numbers won't match.

453
00:22:13.839 --> 00:22:16.680
<v Speaker 3>The mechanism pushing the inniverse apart during the era of

454
00:22:16.720 --> 00:22:20.440
<v Speaker 3>the cosmic microwave background would be fundamentally different from the

455
00:22:20.480 --> 00:22:22.119
<v Speaker 3>mechanism pushing it apart today.

456
00:22:22.480 --> 00:22:26.200
<v Speaker 2>This perfectly explains the Hubble tension without needing to invalidate

457
00:22:26.319 --> 00:22:27.480
<v Speaker 2>either set of measurements.

458
00:22:27.559 --> 00:22:30.720
<v Speaker 3>They are both right. They're just measuring a universe governed

459
00:22:30.720 --> 00:22:31.640
<v Speaker 3>by shifting rules.

460
00:22:31.799 --> 00:22:34.279
<v Speaker 2>It's a brilliant way to solve the puzzle, but it

461
00:22:34.359 --> 00:22:39.119
<v Speaker 2>leaves astrophysics at a massive methodological impasse. We have these

462
00:22:39.160 --> 00:22:44.200
<v Speaker 2>three incredible theories early dark energy, neutrino scattering or dynamic

463
00:22:44.319 --> 00:22:45.039
<v Speaker 2>dark energy.

464
00:22:45.279 --> 00:22:48.319
<v Speaker 3>But to figure out which of these dark sector hypotheses

465
00:22:48.799 --> 00:22:51.839
<v Speaker 3>is the true culprit, we can't just keep staring at

466
00:22:51.839 --> 00:22:53.400
<v Speaker 3>the cosmic microwave background.

467
00:22:53.480 --> 00:22:56.039
<v Speaker 2>We have to rigorously scrutinize the other side of the equation.

468
00:22:56.440 --> 00:22:58.759
<v Speaker 2>We have to look at how we have historically measured

469
00:22:58.799 --> 00:23:02.359
<v Speaker 2>the expansion of the law local modern universe. To get

470
00:23:02.359 --> 00:23:03.880
<v Speaker 2>that seventy three number.

471
00:23:03.839 --> 00:23:06.480
<v Speaker 3>We need to analyze the mechanics of the tools that

472
00:23:06.640 --> 00:23:09.519
<v Speaker 3>yielded that higher rate, and that means looking at what

473
00:23:09.559 --> 00:23:11.519
<v Speaker 3>we can call the electromagnetic ceiling.

474
00:23:11.640 --> 00:23:15.000
<v Speaker 2>The electromagnetic ceiling, because practically everything we know about the

475
00:23:15.039 --> 00:23:16.599
<v Speaker 2>local universe comes from light.

476
00:23:17.079 --> 00:23:20.480
<v Speaker 3>Since the early twentieth century, practically all of our primary

477
00:23:20.519 --> 00:23:25.119
<v Speaker 3>astrophysical tools have relied on capturing photons. We rely on

478
00:23:25.160 --> 00:23:28.960
<v Speaker 3>a century old paradigm established by Edwin Hubble himself when

479
00:23:29.000 --> 00:23:31.839
<v Speaker 3>he first discovered the universe was expanding. In the nineteen twenties.

480
00:23:32.079 --> 00:23:35.000
<v Speaker 2>Hubble used the Hooker telescope in California to look at

481
00:23:35.039 --> 00:23:37.599
<v Speaker 2>Cepheide variable stars in the Andromeda galaxy.

482
00:23:37.799 --> 00:23:40.359
<v Speaker 3>He proved Andromeda wasn't just a gas cloud in our

483
00:23:40.400 --> 00:23:44.640
<v Speaker 3>Milky Way, but an entirely separate island universe, and that

484
00:23:44.720 --> 00:23:46.039
<v Speaker 3>it was moving away from us.

485
00:23:46.279 --> 00:23:49.000
<v Speaker 2>Since then, the entire methodology of astronomy has relied on

486
00:23:49.079 --> 00:23:55.000
<v Speaker 2>capturing these electromagnetic signals visible light, infrared, X rays, radio

487
00:23:55.000 --> 00:23:56.519
<v Speaker 2>waves from distant objects.

488
00:23:56.960 --> 00:24:00.319
<v Speaker 3>By analyzing the spectral lines and using the fundamental properies

489
00:24:00.359 --> 00:24:04.400
<v Speaker 3>of that light, we calculate both distance and recession velocity and.

490
00:24:04.359 --> 00:24:08.079
<v Speaker 2>The absolute anchor of this entire observational paradigm. The tool

491
00:24:08.160 --> 00:24:10.400
<v Speaker 2>that gives us the precision to claim the seventy three

492
00:24:10.480 --> 00:24:14.039
<v Speaker 2>rate is the mechanism known as the standard candle protocol.

493
00:24:14.240 --> 00:24:18.400
<v Speaker 3>To measure vast cosmic distances, you need a light source

494
00:24:18.480 --> 00:24:21.319
<v Speaker 3>with a known absolute intrinsic brightness.

495
00:24:21.559 --> 00:24:23.880
<v Speaker 2>Imagine you see a street lamp in the distance on

496
00:24:23.920 --> 00:24:25.920
<v Speaker 2>a foggy night. If you don't know how bright the

497
00:24:25.960 --> 00:24:27.960
<v Speaker 2>bulb in that street lamp is supposed to be, you

498
00:24:28.000 --> 00:24:30.079
<v Speaker 2>can't tell if it's a very dim bulb close to

499
00:24:30.119 --> 00:24:33.000
<v Speaker 2>you or a massively bright bulb very far away.

500
00:24:33.240 --> 00:24:34.960
<v Speaker 3>But if you know for a fact that the bulb

501
00:24:35.000 --> 00:24:37.680
<v Speaker 3>is exactly one hundred watts, you can measure how dim

502
00:24:37.759 --> 00:24:41.119
<v Speaker 3>it appears to your eye and easily calculate its exact distance.

503
00:24:41.279 --> 00:24:44.440
<v Speaker 2>That is a standard candle, and in astrophysics specifically, for

504
00:24:44.519 --> 00:24:48.559
<v Speaker 2>measuring the hubble constant. We utilize Type IA supernovae, and.

505
00:24:48.519 --> 00:24:51.839
<v Speaker 3>These aren't just random stellar explosions. When a massive star

506
00:24:51.960 --> 00:24:54.680
<v Speaker 3>runs out of fuel and dies, it explodes in a

507
00:24:54.759 --> 00:25:00.160
<v Speaker 3>core collapsed supernova. Those are messy, unpredictable, and they very

508
00:25:00.279 --> 00:25:01.359
<v Speaker 3>wildly in brightness.

509
00:25:01.440 --> 00:25:04.440
<v Speaker 2>You can't use them as standard candles. Type EA supernova

510
00:25:04.480 --> 00:25:09.559
<v Speaker 2>are entirely different beasts. They are highly precise, almost mathematical events.

511
00:25:09.640 --> 00:25:12.640
<v Speaker 3>The physics governing a Type YA supernova are tied directly

512
00:25:12.680 --> 00:25:16.119
<v Speaker 3>to a fundamental threshold known as the Chandrasekhar limit.

513
00:25:16.119 --> 00:25:20.720
<v Speaker 2>Named after the brilliant astrophysicist Subramanian chandrasecar who calculated it.

514
00:25:21.079 --> 00:25:24.640
<v Speaker 3>The process begins with a binary star system two stars

515
00:25:24.720 --> 00:25:27.680
<v Speaker 3>orbiting a common center of mass. One of these stars

516
00:25:27.680 --> 00:25:30.920
<v Speaker 3>has already exhausted its nuclear fuel, blown off its outer layers,

517
00:25:31.240 --> 00:25:34.400
<v Speaker 3>and died, leaving behind a dense hot core known as

518
00:25:34.440 --> 00:25:35.160
<v Speaker 3>a white dwarf.

519
00:25:35.440 --> 00:25:38.240
<v Speaker 2>A white dwarf is an insane object. It packs the

520
00:25:38.279 --> 00:25:40.240
<v Speaker 2>mass of our Sun into a sphere the size of

521
00:25:40.279 --> 00:25:42.599
<v Speaker 2>the Earth. It is incredibly dense.

522
00:25:42.480 --> 00:25:44.799
<v Speaker 3>And in this binary system, this white dwarf is locked

523
00:25:44.799 --> 00:25:47.359
<v Speaker 3>in a gravitational dance with its companion star, which is

524
00:25:47.480 --> 00:25:49.359
<v Speaker 3>usually a red giant that has swollen up and is

525
00:25:49.359 --> 00:25:50.440
<v Speaker 3>shedding its outer layers.

526
00:25:50.599 --> 00:25:53.640
<v Speaker 2>The immense gravity of the white dwarf starts siphoning off

527
00:25:53.680 --> 00:25:57.279
<v Speaker 2>that material. It slowly pulls gas and mass off its partner,

528
00:25:57.359 --> 00:26:00.920
<v Speaker 2>cannibalizing it and growing heavier over millions.

529
00:26:00.400 --> 00:26:03.599
<v Speaker 3>Of years, and it grows until it hits a very specific,

530
00:26:03.880 --> 00:26:07.359
<v Speaker 3>unbreakable mathematical wall, the Chendersucar limit.

531
00:26:07.480 --> 00:26:11.319
<v Speaker 2>At exactly approximately one point four to four times the

532
00:26:11.359 --> 00:26:15.759
<v Speaker 2>mass of our sun. A profound quantum mechanical failure occurs

533
00:26:15.759 --> 00:26:17.160
<v Speaker 2>within the white dwarf, and to.

534
00:26:17.160 --> 00:26:19.920
<v Speaker 3>Understand this failure, you have to know what keeps a

535
00:26:19.920 --> 00:26:22.559
<v Speaker 3>white dwarf from collapsing into a black hole under its

536
00:26:22.599 --> 00:26:25.680
<v Speaker 3>own immense gravity. It is a nuclear fusion.

537
00:26:25.720 --> 00:26:28.039
<v Speaker 2>Because the scar is dead, it is supported by something

538
00:26:28.039 --> 00:26:29.799
<v Speaker 2>called electron degeneracy pressure.

539
00:26:29.960 --> 00:26:32.680
<v Speaker 3>It's a concept rooted in the poly exclusion principle from

540
00:26:32.799 --> 00:26:36.240
<v Speaker 3>quantum mechanics, which states that two electrons cannot occupy the

541
00:26:36.319 --> 00:26:38.359
<v Speaker 3>exact same quantum state at the same time.

542
00:26:38.559 --> 00:26:41.680
<v Speaker 2>Imagine trying to pack an impossible number of commuters into

543
00:26:41.720 --> 00:26:43.079
<v Speaker 2>a tiny subway.

544
00:26:42.720 --> 00:26:44.920
<v Speaker 3>Car at a certain point. No matter how hard you

545
00:26:44.960 --> 00:26:48.400
<v Speaker 3>push from the outside, the people inside physically cannot be

546
00:26:48.400 --> 00:26:49.759
<v Speaker 3>compressed any further without.

547
00:26:49.519 --> 00:26:53.640
<v Speaker 2>Overlapping the repulsive force of the electrons. Violently resisting being

548
00:26:53.680 --> 00:26:57.000
<v Speaker 2>crushed into the same state is the electron degeneracy pressure.

549
00:26:57.599 --> 00:27:00.599
<v Speaker 2>It actively supports the entire mass of the dead star

550
00:27:00.720 --> 00:27:03.039
<v Speaker 2>against the crushing weight of its own gravity.

551
00:27:03.240 --> 00:27:06.680
<v Speaker 3>But gravity is relentless. As the white dwarf steals more

552
00:27:06.680 --> 00:27:10.160
<v Speaker 3>and more mass from its partner, the weight increases, and

553
00:27:10.240 --> 00:27:13.880
<v Speaker 3>at one point four to four solar masses, gravity finally wins.

554
00:27:13.599 --> 00:27:16.599
<v Speaker 2>And electron degeneracy pressure catastrophically fails.

555
00:27:16.680 --> 00:27:19.400
<v Speaker 3>On that quanto pressure fails, the star collapses inward. In

556
00:27:19.400 --> 00:27:22.599
<v Speaker 3>a fraction of second. The immense heat and pressure instantly

557
00:27:22.599 --> 00:27:25.839
<v Speaker 3>trigger a runaway thermonuclear fusion of the carbon and oxygen

558
00:27:25.839 --> 00:27:26.599
<v Speaker 3>making up the star.

559
00:27:26.960 --> 00:27:30.759
<v Speaker 2>The entire white dwarf detonates simultaneously. It doesn't just blow

560
00:27:30.799 --> 00:27:34.200
<v Speaker 2>off its outer layers. The star is completely obliterated in

561
00:27:34.240 --> 00:27:36.640
<v Speaker 2>one of the most violent explosions in the universe.

562
00:27:36.720 --> 00:27:39.319
<v Speaker 3>And here is why this is the ultimate standard candle.

563
00:27:39.559 --> 00:27:44.480
<v Speaker 3>Because this colossal detonation consistently, unfailingly happens at that exact

564
00:27:44.519 --> 00:27:46.960
<v Speaker 3>mass limit one point four to four solar masses. It

565
00:27:47.000 --> 00:27:49.400
<v Speaker 3>always involves the exact same amount of nuclear fuel.

566
00:27:49.640 --> 00:27:54.359
<v Speaker 2>Therefore, it has a strict known absolute intrinsic luminosity. It

567
00:27:54.400 --> 00:27:58.200
<v Speaker 2>is an explosion with a highly predictable, standardized peak brightness.

568
00:27:58.599 --> 00:28:04.119
<v Speaker 3>Every single type Vias supernova across the cosmos explodes with

569
00:28:04.279 --> 00:28:05.799
<v Speaker 3>roughly the same wattage.

570
00:28:05.440 --> 00:28:10.279
<v Speaker 2>Which gives us a brilliant, reliable diagnostic tool. When astronomers

571
00:28:10.279 --> 00:28:13.559
<v Speaker 2>spot one of these explosions in a distant galaxy, they

572
00:28:13.799 --> 00:28:15.359
<v Speaker 2>monitor it carefully for weeks.

573
00:28:15.519 --> 00:28:20.400
<v Speaker 3>They chart the light curve, that's specific mathematical rate at

574
00:28:20.400 --> 00:28:24.200
<v Speaker 3>which the supernova brightens to its peak luminosity and then

575
00:28:24.279 --> 00:28:25.960
<v Speaker 3>slowly fades away over time.

576
00:28:26.119 --> 00:28:30.079
<v Speaker 2>There's a known correlation called the Phillips relationship where slightly

577
00:28:30.119 --> 00:28:33.160
<v Speaker 2>brighter supernovae take a little longer to fade, allowing us

578
00:28:33.200 --> 00:28:34.680
<v Speaker 2>to standardize them even further.

579
00:28:35.079 --> 00:28:38.400
<v Speaker 3>So we know it's absolute intrinsic luminosity, we measure its

580
00:28:38.400 --> 00:28:41.559
<v Speaker 3>apparent magnitude, meaning how dim it hourly looks to us

581
00:28:41.599 --> 00:28:42.839
<v Speaker 3>through our telescopes here.

582
00:28:42.680 --> 00:28:44.720
<v Speaker 2>On Earth, and then we just apply a basic geometric

583
00:28:44.720 --> 00:28:48.480
<v Speaker 2>calculation through the Inversquare law of light, which dictates that

584
00:28:48.559 --> 00:28:51.920
<v Speaker 2>light dims predictably as it spreads out over distance. Comparing

585
00:28:51.960 --> 00:28:55.480
<v Speaker 2>its absolute known brightness to its apparent dimness gives us

586
00:28:55.480 --> 00:28:57.680
<v Speaker 2>a highly precise distance to that galaxy.

587
00:28:57.720 --> 00:29:00.440
<v Speaker 3>But if you remember the Hubble constant equation, distance is

588
00:29:00.480 --> 00:29:03.200
<v Speaker 3>only half the battle. You know exactly how far away

589
00:29:03.240 --> 00:29:06.200
<v Speaker 3>the supernova's host galaxy is, but you also need to

590
00:29:06.200 --> 00:29:08.640
<v Speaker 3>know how fast it is moving away from us due

591
00:29:08.680 --> 00:29:12.359
<v Speaker 3>to the expansion of cosmic space. That brings us to

592
00:29:12.440 --> 00:29:13.519
<v Speaker 3>recession velocity.

593
00:29:13.680 --> 00:29:15.960
<v Speaker 2>And to get that velocity you measure the red shift.

594
00:29:16.200 --> 00:29:18.640
<v Speaker 2>It's the visual equivalent of a Doppler effect.

595
00:29:18.799 --> 00:29:21.680
<v Speaker 3>If an angulance drives past you, the siren sounds high

596
00:29:21.680 --> 00:29:24.200
<v Speaker 3>pitched as it approaches because the sound waves are compressed,

597
00:29:24.440 --> 00:29:26.200
<v Speaker 3>and it drops to a lower pitch as it drives

598
00:29:26.240 --> 00:29:29.079
<v Speaker 3>away because the sound waves are stretched out. Like does

599
00:29:29.119 --> 00:29:30.039
<v Speaker 3>the exact same thing.

600
00:29:30.279 --> 00:29:33.119
<v Speaker 2>As the galaxy recedes away from us, carried by the

601
00:29:33.119 --> 00:29:38.200
<v Speaker 2>expanding fabric of space, the actual wavelengths of the electromagnetic

602
00:29:38.279 --> 00:29:40.680
<v Speaker 2>signals it emits are physically stretched out.

603
00:29:40.839 --> 00:29:45.440
<v Speaker 3>Shorter, bluer wavelengths are stretched into longer, redder wavelengths, shifting

604
00:29:45.480 --> 00:29:47.960
<v Speaker 3>the entire spectrum of light toward the red end of

605
00:29:47.960 --> 00:29:49.359
<v Speaker 3>the electromagnetic spectrum.

606
00:29:49.400 --> 00:29:53.119
<v Speaker 2>Astronomers look at the spectral lines. These are the specific

607
00:29:53.240 --> 00:29:57.200
<v Speaker 2>fingerprints of elements like hydrogen and helium embedded in the light,

608
00:29:57.759 --> 00:29:59.759
<v Speaker 2>and they see how far those lines have shifted toward

609
00:29:59.759 --> 00:29:59.960
<v Speaker 2>the r.

610
00:30:00.480 --> 00:30:03.119
<v Speaker 3>You measure the exact degree of that spectral stretching, and

611
00:30:03.160 --> 00:30:04.119
<v Speaker 3>you get your velocity.

612
00:30:04.359 --> 00:30:07.440
<v Speaker 2>So you have your pristine distance from the tupernova and

613
00:30:07.519 --> 00:30:11.559
<v Speaker 2>your precise velocity from the red shift. Distance plus redshift

614
00:30:11.839 --> 00:30:13.240
<v Speaker 2>equals the expansion rate.

615
00:30:13.680 --> 00:30:17.799
<v Speaker 3>It is an incredibly elegant, beautiful system. It is the

616
00:30:17.839 --> 00:30:21.039
<v Speaker 3>bedrock of modern observational astronomy.

617
00:30:21.119 --> 00:30:24.119
<v Speaker 2>But when it comes to resolving a paradox as tight

618
00:30:24.200 --> 00:30:27.680
<v Speaker 2>as the Hubble tension, we have fundamentally hit the precision

619
00:30:27.720 --> 00:30:31.960
<v Speaker 2>ceiling of electromagnetic observations. We have pushed light to the

620
00:30:32.119 --> 00:30:33.920
<v Speaker 2>absolute limit of its utility.

621
00:30:34.160 --> 00:30:37.960
<v Speaker 3>The critical flaw in this methodology is the inherent, unavoidable

622
00:30:38.000 --> 00:30:38.880
<v Speaker 3>fragility of light.

623
00:30:39.200 --> 00:30:44.920
<v Speaker 2>Electromagnetic signals over cosmic distances are incredibly vulnerable. Light interacts

624
00:30:44.960 --> 00:30:46.359
<v Speaker 2>with almost everything it touches.

625
00:30:46.480 --> 00:30:49.240
<v Speaker 3>When we use these standard candles to peer billions of

626
00:30:49.319 --> 00:30:52.119
<v Speaker 3>light years into the past, we are constantly at the

627
00:30:52.119 --> 00:30:55.519
<v Speaker 3>mercy of the interstellar and intergalactic medium. A photon has

628
00:30:55.559 --> 00:30:57.440
<v Speaker 3>to travel for a billion years to reach our.

629
00:30:57.319 --> 00:31:01.039
<v Speaker 2>Telescope, and over that immense journey, light is heavily obscured

630
00:31:01.079 --> 00:31:04.519
<v Speaker 2>by cosmic dust. It gets absorbed and scattered by intervening

631
00:31:04.559 --> 00:31:05.200
<v Speaker 2>gas clouds.

632
00:31:05.279 --> 00:31:07.839
<v Speaker 3>Think about driving on a dirt road behind a massive truck.

633
00:31:08.000 --> 00:31:09.920
<v Speaker 3>Your head lights hit the dust cloud, and the light

634
00:31:10.000 --> 00:31:12.279
<v Speaker 3>is scattered. It looks dimmer than it actually is.

635
00:31:12.640 --> 00:31:17.839
<v Speaker 2>In astronomy, this is called extinction. Cosmic dust specifically absorbs

636
00:31:17.880 --> 00:31:21.720
<v Speaker 2>blue light more readily than red light, a process called rettening.

637
00:31:21.960 --> 00:31:23.279
<v Speaker 3>We have to look at the red and light of

638
00:31:23.319 --> 00:31:27.640
<v Speaker 3>the supernova and try to mathematically guess exactly how much

639
00:31:27.720 --> 00:31:31.319
<v Speaker 3>dust it passed through to calculate its true original brightness.

640
00:31:31.640 --> 00:31:35.680
<v Speaker 2>Furthermore, the apparent luminosity can be altered by the metallicity

641
00:31:35.720 --> 00:31:39.680
<v Speaker 2>of the host galaxy itself. In astronomy, anything heavier than

642
00:31:39.680 --> 00:31:41.119
<v Speaker 2>helium is considered a metal.

643
00:31:41.640 --> 00:31:43.720
<v Speaker 3>If the white dwarf formed in a galaxy with a

644
00:31:43.799 --> 00:31:47.920
<v Speaker 3>very high concentration of heavy metals, that chemical composition fundamentally

645
00:31:47.920 --> 00:31:51.599
<v Speaker 3>affects the opacity of the supernova ejecta when it explodes.

646
00:31:51.880 --> 00:31:53.839
<v Speaker 3>It changes how the light escapes the explosion.

647
00:31:53.920 --> 00:31:55.920
<v Speaker 2>So we are looking at a light bulb trying to

648
00:31:56.000 --> 00:31:59.839
<v Speaker 2>judge its exact wattage, but we are looking through a dirty, scratched,

649
00:32:00.039 --> 00:32:03.000
<v Speaker 2>foggy window, and the bulb itself might have a slightly

650
00:32:03.039 --> 00:32:06.480
<v Speaker 2>different chemical tint depending on where it was manufactured exactly.

651
00:32:06.720 --> 00:32:11.640
<v Speaker 3>An enormous, massive computational and observational effort goes into simply

652
00:32:11.680 --> 00:32:16.640
<v Speaker 3>calibrating out these confounding variables. Thousands of hours of telescope

653
00:32:16.680 --> 00:32:20.680
<v Speaker 3>time and supercomputer modeling are dedicated to estimating the extinction

654
00:32:20.839 --> 00:32:23.039
<v Speaker 3>caused by an endless ocean of cosmic dust.

655
00:32:23.240 --> 00:32:26.519
<v Speaker 2>But eventually you hit a wall of systemic uncertainty. We

656
00:32:26.559 --> 00:32:31.680
<v Speaker 2>cannot completely eradicate the systemic uncertainties inherent to capturing photons.

657
00:32:31.160 --> 00:32:34.720
<v Speaker 3>If we want to definitively solve a paradox as mathematically

658
00:32:34.759 --> 00:32:38.480
<v Speaker 3>precise and foundational as the hubble tension, relying on fragile

659
00:32:38.519 --> 00:32:39.680
<v Speaker 3>light is no longer.

660
00:32:39.480 --> 00:32:45.079
<v Speaker 2>Sufficient, independent non electromagnetic measurement modalities are mathematically necessary. We

661
00:32:45.160 --> 00:32:48.720
<v Speaker 2>need an entirely separate physical channel of information to measure

662
00:32:48.720 --> 00:32:50.039
<v Speaker 2>the cosmos.

663
00:32:49.480 --> 00:32:52.319
<v Speaker 3>The channel that doesn't care about dust, that isn't affected

664
00:32:52.319 --> 00:32:55.799
<v Speaker 3>by metallicity, and that doesn't scatter off gas clouds. And

665
00:32:55.880 --> 00:32:59.759
<v Speaker 3>this establishes the absolute critical necessity of shifting our focus

666
00:32:59.759 --> 00:33:03.079
<v Speaker 3>to a pristine metric gravitational waves Okay.

667
00:33:02.880 --> 00:33:05.839
<v Speaker 2>Let's unpack this. This is where the science fiction becomes reality.

668
00:33:05.920 --> 00:33:08.759
<v Speaker 2>This is a massive paradigm shift in how human beings

669
00:33:08.799 --> 00:33:09.799
<v Speaker 2>perceive the universe.

670
00:33:09.920 --> 00:33:14.000
<v Speaker 3>We are moving away from observing photons, away from light entirely,

671
00:33:14.480 --> 00:33:18.720
<v Speaker 3>to measuring literal ripples propagating through the physical fabric of

672
00:33:18.839 --> 00:33:20.039
<v Speaker 3>four dimensional space time.

673
00:33:20.119 --> 00:33:23.160
<v Speaker 2>It's almost impossible to visualize. We're used to thinking of

674
00:33:23.200 --> 00:33:26.400
<v Speaker 2>space as the empty container where things happen, but space

675
00:33:26.440 --> 00:33:29.000
<v Speaker 2>itself is a flexible, dynamic medium.

676
00:33:29.279 --> 00:33:32.400
<v Speaker 3>Think of it like a physical object displacing water to

677
00:33:32.519 --> 00:33:36.640
<v Speaker 3>create radiating wavefronts. But on a cosmic scale, when massive

678
00:33:36.720 --> 00:33:40.480
<v Speaker 3>objects accelerate, they don't just move through space. They literally

679
00:33:40.599 --> 00:33:42.880
<v Speaker 3>alter the curve of space time around them.

680
00:33:42.680 --> 00:33:45.839
<v Speaker 2>And as they move, that alteration, that distortion of the

681
00:33:45.839 --> 00:33:49.200
<v Speaker 2>geometric fabric moves outward in all directions at the speed

682
00:33:49.200 --> 00:33:51.839
<v Speaker 2>of light. Those are gravitational waves.

683
00:33:51.599 --> 00:33:54.039
<v Speaker 3>But the fabric of space time is incredibly stiff. It

684
00:33:54.039 --> 00:33:56.119
<v Speaker 3>takes an immense amount of energy to warp it. You

685
00:33:56.200 --> 00:33:59.680
<v Speaker 3>do not get detectable gravitational waves from a star simply burning,

686
00:34:00.160 --> 00:34:03.519
<v Speaker 3>or a planet orbiting, or even a normal supernova exploding.

687
00:34:03.599 --> 00:34:05.720
<v Speaker 2>To generate these spacetime ripples in a way that we

688
00:34:05.759 --> 00:34:08.199
<v Speaker 2>can detect them on Earth. You need an environment of

689
00:34:08.400 --> 00:34:12.039
<v Speaker 2>almost unimaginable catastrophic gravitational violence.

690
00:34:12.480 --> 00:34:16.239
<v Speaker 3>You need the densest objects in the universe interacting. We

691
00:34:16.280 --> 00:34:20.280
<v Speaker 3>are talking about the inspiral and ultimate merger of exceedingly massive,

692
00:34:20.639 --> 00:34:26.360
<v Speaker 3>compact astronomical bodies, primarily binary systems composed of two black

693
00:34:26.360 --> 00:34:28.280
<v Speaker 3>holes or two neutron stars.

694
00:34:28.480 --> 00:34:31.440
<v Speaker 2>Let's focus on black holes. These are objects of immense

695
00:34:31.519 --> 00:34:35.559
<v Speaker 2>mass containing the gravitational pull of dozens of suns packed

696
00:34:35.599 --> 00:34:36.679
<v Speaker 2>into a singularity.

697
00:34:36.840 --> 00:34:39.760
<v Speaker 3>When two black holes get caught in each other's gravitational grip,

698
00:34:39.840 --> 00:34:42.280
<v Speaker 3>they begin to orbit one another, and as they orbit,

699
00:34:42.480 --> 00:34:44.920
<v Speaker 3>they stir up the fabric of space time around them.

700
00:34:45.360 --> 00:34:47.360
<v Speaker 3>They shed their orbital energy in the form of these

701
00:34:47.400 --> 00:34:49.800
<v Speaker 3>gravitational waves radiating outward.

702
00:34:49.559 --> 00:34:53.039
<v Speaker 2>And because they are losing orbital energy, they slowly spiral

703
00:34:53.119 --> 00:34:56.199
<v Speaker 2>closer and closer together. As they get closer, the gravitational

704
00:34:56.239 --> 00:34:58.519
<v Speaker 2>pull intensifies and they accelerate.

705
00:34:58.639 --> 00:35:02.159
<v Speaker 3>They whip around each other fast, turn faster, reaching significant

706
00:35:02.199 --> 00:35:04.800
<v Speaker 3>fractions of the speed of light. Finally, in the last

707
00:35:04.880 --> 00:35:07.719
<v Speaker 3>fraction of a second, they violently merge into a single,

708
00:35:07.880 --> 00:35:08.760
<v Speaker 3>larger black hole.

709
00:35:09.079 --> 00:35:12.320
<v Speaker 2>This final merger event converts several sons worth of pure

710
00:35:12.360 --> 00:35:16.199
<v Speaker 2>mass directly into gravitational wave energy in an instant Sending

711
00:35:16.199 --> 00:35:19.960
<v Speaker 2>out a massive catastrophic shock wave of space time distortion

712
00:35:20.079 --> 00:35:21.440
<v Speaker 2>across the universe.

713
00:35:21.119 --> 00:35:24.840
<v Speaker 3>And capturing that specific microscopic distortion as it washes over

714
00:35:24.840 --> 00:35:28.880
<v Speaker 3>the Earth requires arguably the most precise engineering in human history.

715
00:35:29.639 --> 00:35:32.320
<v Speaker 3>This is the domain of the LVK Collaboration.

716
00:35:32.159 --> 00:35:35.559
<v Speaker 2>That stands for LEGO in the United States, VIRGO in Italy,

717
00:35:35.760 --> 00:35:40.119
<v Speaker 2>and CAGRA in Japan. This is an international global consortionum

718
00:35:40.159 --> 00:35:44.039
<v Speaker 2>of over two thousand scientific members dedicated to hearing the universe.

719
00:35:44.360 --> 00:35:48.559
<v Speaker 3>The engineering behind these detectors is staggering. They operate massive innerferometers.

720
00:35:48.960 --> 00:35:51.880
<v Speaker 3>These are l shaped facilities with vacuum tubes extending out

721
00:35:51.880 --> 00:35:54.199
<v Speaker 3>for several kilometers in perpendicular directions.

722
00:35:54.239 --> 00:35:57.920
<v Speaker 2>Inside these incredibly pure vacuum tubes, they fire ultra stable,

723
00:35:58.039 --> 00:35:58.960
<v Speaker 2>high powered lasers.

724
00:35:59.000 --> 00:36:00.719
<v Speaker 3>The laser beam is split at the corner of the

725
00:36:00.840 --> 00:36:04.840
<v Speaker 3>l travels down both arms, hits massive perfectly polished mirrors

726
00:36:04.840 --> 00:36:08.320
<v Speaker 3>suspended by complex pendulum systems, and bounces back to a

727
00:36:08.360 --> 00:36:09.159
<v Speaker 3>central detector.

728
00:36:09.440 --> 00:36:11.960
<v Speaker 2>And the mirrors are isolated from the Earth in ways

729
00:36:12.000 --> 00:36:15.800
<v Speaker 2>that defy belief. They have to dampen the seismic noise

730
00:36:15.800 --> 00:36:18.480
<v Speaker 2>of the planet. They have to account for the rumble

731
00:36:18.519 --> 00:36:21.800
<v Speaker 2>of ocean waves miles away, the vibration of a truck

732
00:36:21.920 --> 00:36:24.400
<v Speaker 2>driving on a nearby highway, even.

733
00:36:24.239 --> 00:36:27.880
<v Speaker 3>The microscopic thermal vibrations of the atoms within the mirrors themselves.

734
00:36:28.320 --> 00:36:32.559
<v Speaker 3>They even use advanced quantum optics techniques injecting squeeze light

735
00:36:32.639 --> 00:36:35.760
<v Speaker 3>into the vacuum to reduce the inherent quantum noise of

736
00:36:35.760 --> 00:36:37.239
<v Speaker 3>the photons hitting the mirrors.

737
00:36:37.639 --> 00:36:40.440
<v Speaker 2>All of this is done for one specific purpose, to

738
00:36:40.519 --> 00:36:42.840
<v Speaker 2>detect the microscopic stretching of space.

739
00:36:43.519 --> 00:36:46.079
<v Speaker 3>When a gravitational wave passes through the Earth, it is

740
00:36:46.119 --> 00:36:49.920
<v Speaker 3>a quadrupole wave. It literally stretches physical space in one

741
00:36:50.000 --> 00:36:53.559
<v Speaker 3>direction while simultaneously compressing it in the perpendicular direction.

742
00:36:53.920 --> 00:36:57.239
<v Speaker 2>So as the wayer washes over the Lego facility, one

743
00:36:57.239 --> 00:36:59.719
<v Speaker 2>of the four kilometer arms gets physically longer and the

744
00:36:59.719 --> 00:37:01.239
<v Speaker 2>other arm gets physically shorter.

745
00:37:01.639 --> 00:37:04.280
<v Speaker 3>The light traveling down the longer arm takes a fraction

746
00:37:04.320 --> 00:37:06.639
<v Speaker 3>of a second longer to return than the light in

747
00:37:06.639 --> 00:37:10.039
<v Speaker 3>the shorter arm. When the two laser beams recombine, they

748
00:37:10.039 --> 00:37:13.079
<v Speaker 3>are slightly out of phase, creating an interference pattern.

749
00:37:13.320 --> 00:37:16.719
<v Speaker 2>The LVK instruments measure that fractional change in the distance.

750
00:37:16.760 --> 00:37:20.639
<v Speaker 3>And the scale of what they are measuring is almost incomprehensible.

751
00:37:21.079 --> 00:37:23.440
<v Speaker 3>By the time a gravitational wave from a black hole

752
00:37:23.519 --> 00:37:27.639
<v Speaker 3>merger a billion light years away reaches Earth, the amplitude

753
00:37:27.639 --> 00:37:29.719
<v Speaker 3>of the wave is infinitesimally small.

754
00:37:30.199 --> 00:37:33.239
<v Speaker 2>The LVK detectors are sensing changes in the length of

755
00:37:33.280 --> 00:37:37.599
<v Speaker 2>their four kilometal arms that are smaller than one thousandth

756
00:37:37.599 --> 00:37:39.400
<v Speaker 2>the diameter of a single.

757
00:37:39.119 --> 00:37:40.920
<v Speaker 3>Proton, smaller than a proton.

758
00:37:40.719 --> 00:37:43.239
<v Speaker 2>Let that sink in. They are measuring a change in

759
00:37:43.320 --> 00:37:46.000
<v Speaker 2>distance across four kilometers that is a fraction of the

760
00:37:46.039 --> 00:37:49.400
<v Speaker 2>width of a subatomic particle, and because the sensitivity is

761
00:37:49.440 --> 00:37:54.199
<v Speaker 2>so phenomenally high, astrophysicists realize they could use this technology

762
00:37:54.280 --> 00:37:55.599
<v Speaker 2>to solve the Huddle tension.

763
00:37:55.840 --> 00:37:59.199
<v Speaker 3>They developed a gravitational wave counterpart to the standard candle

764
00:38:00.159 --> 00:38:01.760
<v Speaker 3>as the Standard Siren protocol.

765
00:38:02.039 --> 00:38:05.400
<v Speaker 2>This is where the sheer mathematical beauty of general relativity shines.

766
00:38:05.920 --> 00:38:09.159
<v Speaker 2>With standard candles, we have to rely on complex calibration

767
00:38:09.280 --> 00:38:11.320
<v Speaker 2>and empirical observations of supernovae.

768
00:38:11.360 --> 00:38:15.239
<v Speaker 3>With standard sirens, the physics are entirely self contained. By

769
00:38:15.280 --> 00:38:19.000
<v Speaker 3>closely analyzing the specific morphology of the gravitational wave signal

770
00:38:19.039 --> 00:38:23.679
<v Speaker 3>captured by the interferometer, scientists can extract the exact absolute

771
00:38:23.719 --> 00:38:27.039
<v Speaker 3>physical properties of the black hole collision without needing any

772
00:38:27.039 --> 00:38:27.960
<v Speaker 3>outside information.

773
00:38:28.480 --> 00:38:31.719
<v Speaker 2>They analyze the chirp as the black holes spiral inward

774
00:38:31.760 --> 00:38:35.519
<v Speaker 2>and accelerate the frequency and amplitude of the gravitational waves

775
00:38:35.639 --> 00:38:39.679
<v Speaker 2>rapidly increase, creating a signal that, if converted to sound,

776
00:38:40.239 --> 00:38:42.519
<v Speaker 2>literally sounds like a bird chirping.

777
00:38:42.639 --> 00:38:45.440
<v Speaker 3>They look at the phase evolution, the exact frequency of

778
00:38:45.480 --> 00:38:48.199
<v Speaker 3>the chirp, and the absolute amplitude of the space time stretching.

779
00:38:48.360 --> 00:38:52.800
<v Speaker 3>From those highly specific waveform characteristics, general relativity allows them

780
00:38:52.840 --> 00:38:56.559
<v Speaker 3>to mathematically calculate exactly how massive the two black holes were.

781
00:38:56.679 --> 00:38:59.400
<v Speaker 2>They extract what is called the intrinsic Chirk mass of

782
00:38:59.440 --> 00:39:00.639
<v Speaker 2>the binary.

783
00:39:00.119 --> 00:39:04.000
<v Speaker 3>System, and because Einstein's equations perfectly predict exactly how loud

784
00:39:04.000 --> 00:39:06.679
<v Speaker 3>a gravitational wave should be based purely on that intrinsic

785
00:39:06.760 --> 00:39:11.000
<v Speaker 3>mass and orbital frequency, we automatically know it's absolute intrinsic amplitude.

786
00:39:11.000 --> 00:39:11.519
<v Speaker 3>At the source.

787
00:39:11.800 --> 00:39:14.920
<v Speaker 2>We instantly know the wattage of the bulb just by

788
00:39:14.960 --> 00:39:17.639
<v Speaker 2>listening to the exact pitch and volume of the church.

789
00:39:17.719 --> 00:39:23.000
<v Speaker 3>Precisely, we simply compare that intrinsic theoretical amplitude calculated from

790
00:39:23.039 --> 00:39:27.559
<v Speaker 3>the waveform to the actual incredibly faint signal strength detected

791
00:39:27.559 --> 00:39:29.639
<v Speaker 3>by the LVK interferometers on Earth.

792
00:39:29.920 --> 00:39:33.079
<v Speaker 2>Using the inverse square law of gravity, which dictates how

793
00:39:33.079 --> 00:39:36.920
<v Speaker 2>the wave dissipates over space, That comparison yields an exact

794
00:39:37.000 --> 00:39:38.159
<v Speaker 2>luminosity distance.

795
00:39:38.440 --> 00:39:41.519
<v Speaker 3>And crucially, this measurement is completely pristine. There is no

796
00:39:41.679 --> 00:39:45.719
<v Speaker 3>cosmic dust blocking the gravitational wave space time ripples don't

797
00:39:45.719 --> 00:39:46.719
<v Speaker 3>get absorbed by.

798
00:39:46.599 --> 00:39:50.440
<v Speaker 2>Gas clouds, There is no metallicity interfering with the signal.

799
00:39:50.880 --> 00:39:54.480
<v Speaker 2>The distortion pass is completely unhindered through all intervening matter,

800
00:39:54.599 --> 00:39:57.760
<v Speaker 2>through stars, through galaxies, through the Earth itself. It is

801
00:39:57.800 --> 00:40:01.280
<v Speaker 2>a perfect, uninterrupted ruler measuring the geometry of the universe.

802
00:40:01.400 --> 00:40:04.800
<v Speaker 3>It sounds like the perfect solution, but standard sirens have

803
00:40:04.840 --> 00:40:08.199
<v Speaker 3>a glaring flaw. They suffer from a massive bottleneck problem.

804
00:40:08.360 --> 00:40:12.639
<v Speaker 2>You have this pristine, incredibly accurate, mathematically perfect distance measurement,

805
00:40:13.119 --> 00:40:16.039
<v Speaker 2>but if you remember the Hubble formula to measure the constant,

806
00:40:16.320 --> 00:40:18.599
<v Speaker 2>you need both distance and recession velocity.

807
00:40:18.920 --> 00:40:22.079
<v Speaker 3>You need to know how fast that specific black hole

808
00:40:22.119 --> 00:40:25.760
<v Speaker 3>merger is physically receding from Earth due to the expansion

809
00:40:25.760 --> 00:40:26.199
<v Speaker 3>of space.

810
00:40:26.719 --> 00:40:30.599
<v Speaker 2>And here's the brutal paradox that astrophysicists ran into. Black

811
00:40:30.639 --> 00:40:33.159
<v Speaker 2>holes do not emit light. They are black.

812
00:40:33.400 --> 00:40:38.039
<v Speaker 3>Their gravity is so intense that nothing, not even electromagnetic radiation,

813
00:40:38.239 --> 00:40:41.039
<v Speaker 3>escapes the event horizon. If there is no light, there

814
00:40:41.039 --> 00:40:43.400
<v Speaker 3>are no spectral lines for our telescopes to measure.

815
00:40:43.519 --> 00:40:46.440
<v Speaker 2>If you have no spectral lines, you absolutely cannot measure

816
00:40:46.440 --> 00:40:48.559
<v Speaker 2>the red shift, and with no red shift, you have

817
00:40:48.599 --> 00:40:49.320
<v Speaker 2>no velocity.

818
00:40:49.400 --> 00:40:52.639
<v Speaker 3>You are left holding a massive, pristine catalog of highly

819
00:40:52.679 --> 00:40:56.800
<v Speaker 3>precise distances to black hole mergers, but absolutely no speeds

820
00:40:56.800 --> 00:40:58.920
<v Speaker 3>to pair them with. You have half of the equation

821
00:40:59.159 --> 00:41:01.559
<v Speaker 3>and it's useless for solving the Hubble attension on its own.

822
00:41:01.800 --> 00:41:06.079
<v Speaker 2>So how do you bypass this bottleneck? Traditionally, using standard

823
00:41:06.079 --> 00:41:09.880
<v Speaker 2>sirens requires an incredible stroke of astronomical luck. You require

824
00:41:09.880 --> 00:41:12.679
<v Speaker 2>the simultaneous detection of an electromagnetic counterpart.

825
00:41:12.840 --> 00:41:16.400
<v Speaker 3>For instance, if two neutron stars collide rather than two

826
00:41:16.480 --> 00:41:19.599
<v Speaker 3>black holes, the intense violence of the merger not only

827
00:41:19.639 --> 00:41:22.880
<v Speaker 3>emits a massive burst of gravitational waves, but it also

828
00:41:23.119 --> 00:41:27.400
<v Speaker 3>violently rips the neutron stars apart, emitting a blindingly bright

829
00:41:27.480 --> 00:41:29.519
<v Speaker 3>flash of gamma rays and visible light.

830
00:41:29.880 --> 00:41:32.639
<v Speaker 2>This is called a killinova. If the LVK detects the

831
00:41:32.639 --> 00:41:36.760
<v Speaker 2>gravitational chirp and optical telescopes simultaneously catch the flash of light,

832
00:41:37.159 --> 00:41:40.039
<v Speaker 2>you have hit the jackpot. You use the gravitational waves

833
00:41:40.039 --> 00:41:42.559
<v Speaker 2>for the perfect distance, and you use the light flash

834
00:41:42.559 --> 00:41:45.239
<v Speaker 2>to measure the red shift and get the perfect velocity.

835
00:41:45.400 --> 00:41:48.320
<v Speaker 3>But neutron star mergers are relatively rare compared to black

836
00:41:48.320 --> 00:41:51.360
<v Speaker 3>hole mergers, and catching the light flash before it fades

837
00:41:51.559 --> 00:41:55.599
<v Speaker 3>is incredibly difficult. Alternatively, if you just have black holes,

838
00:41:55.920 --> 00:41:58.360
<v Speaker 3>you would need a small enough localization volume in the

839
00:41:58.400 --> 00:42:01.760
<v Speaker 3>sky to pinpoint the exact host galaxy where the black

840
00:42:01.760 --> 00:42:02.440
<v Speaker 3>holes lived.

841
00:42:02.599 --> 00:42:05.840
<v Speaker 2>The LVK network triangulates the signal to find out roughly

842
00:42:05.880 --> 00:42:08.079
<v Speaker 2>where in the sky it came from. If that search

843
00:42:08.119 --> 00:42:10.360
<v Speaker 2>area is small enough, you can look at the galaxies

844
00:42:10.360 --> 00:42:13.960
<v Speaker 2>in that patch, find the host, and measure the galaxy's redshift.

845
00:42:14.280 --> 00:42:17.519
<v Speaker 3>But the reality is finding that exact host galaxy among

846
00:42:17.599 --> 00:42:21.519
<v Speaker 3>millions in a localized patch of sky is rarely feasible.

847
00:42:21.960 --> 00:42:24.639
<v Speaker 3>The LVK network gives us error boxes on the sky

848
00:42:24.719 --> 00:42:28.239
<v Speaker 3>map indicating where the signal originated, but those boxes are

849
00:42:28.239 --> 00:42:28.960
<v Speaker 3>often massive.

850
00:42:29.119 --> 00:42:32.119
<v Speaker 2>They cover huge swaths of the sky containing tens of

851
00:42:32.239 --> 00:42:35.760
<v Speaker 2>thousands of potential host galaxies. You can't guess which one

852
00:42:35.760 --> 00:42:39.039
<v Speaker 2>holds the black holes, so the traditional standard siren protocol

853
00:42:39.159 --> 00:42:42.280
<v Speaker 2>hits a wall. The data is too sparse to decisively

854
00:42:42.320 --> 00:42:43.159
<v Speaker 2>solve the tension.

855
00:42:43.320 --> 00:42:47.039
<v Speaker 3>That is, until a massive conceptual leap occurred recently, a

856
00:42:47.039 --> 00:42:49.400
<v Speaker 3>paradigm shift developed by a team of researchers at the

857
00:42:49.480 --> 00:42:52.840
<v Speaker 3>University of Illinois or Bana Champagne and the University of Chicago,

858
00:42:53.280 --> 00:42:59.000
<v Speaker 3>involving prominent theoretical physicists and astrophysicists like Nicholas June's, Daniel Holtz,

859
00:42:59.199 --> 00:43:00.000
<v Speaker 3>and Bryce Cousins.

860
00:43:00.440 --> 00:43:04.079
<v Speaker 2>What they realized was profound. They realized that the entire

861
00:43:04.199 --> 00:43:09.239
<v Speaker 2>field's intense focus on individual perfectly resolved standard sirens chasing

862
00:43:09.320 --> 00:43:12.400
<v Speaker 2>the loud, clear chirps was fundamentally blinding them to an

863
00:43:12.400 --> 00:43:16.280
<v Speaker 2>even larger, vastly more powerful data set hidden right beneath

864
00:43:16.280 --> 00:43:17.320
<v Speaker 2>their noses.

865
00:43:17.000 --> 00:43:19.760
<v Speaker 3>Hidden in the noise itself. They moved away from looking

866
00:43:19.840 --> 00:43:22.519
<v Speaker 3>for individual ripples in the pond and started looking at

867
00:43:22.559 --> 00:43:23.360
<v Speaker 3>the entire ocean.

868
00:43:23.519 --> 00:43:25.440
<v Speaker 2>To understand their breakthrough, you have to look at how

869
00:43:25.480 --> 00:43:29.400
<v Speaker 2>the LVK data is structured. There is a strict mathematical

870
00:43:29.440 --> 00:43:33.920
<v Speaker 2>bifurcation in the data between observable events and unobservable events.

871
00:43:34.039 --> 00:43:37.199
<v Speaker 3>Let's clearly differentiate those two, because this is the hinge

872
00:43:37.199 --> 00:43:40.760
<v Speaker 3>of the whole theory. An observable event is a massive,

873
00:43:41.119 --> 00:43:46.239
<v Speaker 3>relatively nearby binary black hole merger two giant black holes

874
00:43:46.280 --> 00:43:49.039
<v Speaker 3>crashing together somewhat close to our cosmic neighborhood.

875
00:43:49.079 --> 00:43:52.039
<v Speaker 2>Because they're massive and close, the gravitational wave they produce

876
00:43:52.079 --> 00:43:55.159
<v Speaker 2>has a high signal to noise ratio. The signal is

877
00:43:55.239 --> 00:43:58.679
<v Speaker 2>loud enough to stand out clearly and unmistakably above the

878
00:43:58.719 --> 00:44:02.039
<v Speaker 2>inherent instrumental and quantum noise of the LVK detectors.

879
00:44:02.280 --> 00:44:05.320
<v Speaker 3>The algorithms scan the data stream, find the distinct chirp,

880
00:44:05.400 --> 00:44:07.960
<v Speaker 3>and flag it as a confirmed merger. These are the

881
00:44:08.000 --> 00:44:10.760
<v Speaker 3>observable events. We've detected dozens.

882
00:44:10.360 --> 00:44:13.239
<v Speaker 2>Of them, but the universe is incredibly vast and star

883
00:44:13.400 --> 00:44:16.599
<v Speaker 2>formation has been happening for billions of years. For every

884
00:44:16.639 --> 00:44:20.280
<v Speaker 2>one of those loud, observable nearby events, there is a vast,

885
00:44:20.480 --> 00:44:24.440
<v Speaker 2>almost innumerable multitude of smaller collisions or vastly more distant

886
00:44:24.480 --> 00:44:27.840
<v Speaker 2>collisions happening constantly throughout the deep universe, and.

887
00:44:27.840 --> 00:44:31.760
<v Speaker 3>Those distant ancient collisions register is far too faint to

888
00:44:31.760 --> 00:44:34.920
<v Speaker 3>be observed individually. Their signal to noise ratio is simply

889
00:44:34.960 --> 00:44:35.400
<v Speaker 3>too low.

890
00:44:35.679 --> 00:44:38.000
<v Speaker 2>The chirp is buried beneath the quantum static of the

891
00:44:38.079 --> 00:44:41.719
<v Speaker 2>lasers and the thermal vibrations of the mirrors. The LVK

892
00:44:41.960 --> 00:44:46.599
<v Speaker 2>pipeline algorithm cannot confidently flag them as distinct individual mergers.

893
00:44:46.800 --> 00:44:49.000
<v Speaker 2>They are classified as unobservable.

894
00:44:49.239 --> 00:44:52.960
<v Speaker 3>But they don't just disappear. They are still physically stretching

895
00:44:53.039 --> 00:44:55.760
<v Speaker 3>and compressing the Earth. And because there are so many

896
00:44:55.840 --> 00:44:59.599
<v Speaker 3>of them happening constantly all across the cosmos, these unresolved

897
00:44:59.599 --> 00:45:03.159
<v Speaker 3>signals blend together. They overlap in time and frequency.

898
00:45:03.280 --> 00:45:05.559
<v Speaker 2>Here's where it gets really interesting. Think of it like

899
00:45:05.599 --> 00:45:09.239
<v Speaker 2>being in a massive, crowded sports stadium. You can clearly

900
00:45:09.320 --> 00:45:11.880
<v Speaker 2>hear the voice of the person sitting directly next to you.

901
00:45:12.039 --> 00:45:13.920
<v Speaker 2>That is your observable event, but.

902
00:45:13.920 --> 00:45:17.039
<v Speaker 3>You are also surrounded by eighty thousand other people talking, shouting,

903
00:45:17.119 --> 00:45:20.280
<v Speaker 3>and moving. You cannot make out a single distinct word

904
00:45:20.320 --> 00:45:22.119
<v Speaker 3>from the crowd on the other side of the stadium,

905
00:45:22.559 --> 00:45:25.840
<v Speaker 3>but their collective voices overlap and merge into a continuous

906
00:45:25.880 --> 00:45:29.360
<v Speaker 3>low frequency roar, a stadium wide background noise.

907
00:45:29.639 --> 00:45:34.880
<v Speaker 2>In astrophysics, these unresolved distant gravitational wave signals blend together

908
00:45:34.920 --> 00:45:38.199
<v Speaker 2>into what is formally defined as the gravitational wave background.

909
00:45:38.559 --> 00:45:40.360
<v Speaker 2>It is a stochastic.

910
00:45:39.760 --> 00:45:44.280
<v Speaker 3>Hump stochastic meaning randomly determined, having a random probability distribution.

911
00:45:44.639 --> 00:45:49.960
<v Speaker 3>It's the cumulative overlapping spacetime ripples generated by countless unresolved

912
00:45:50.000 --> 00:45:53.800
<v Speaker 3>black hole collisions occurring continuously throughout the cosmos since the

913
00:45:53.840 --> 00:45:56.679
<v Speaker 3>era of peak star formation billions of years ago.

914
00:45:56.880 --> 00:46:00.719
<v Speaker 2>It is a pervasive, continuous background noise of ground itself,

915
00:46:00.840 --> 00:46:02.960
<v Speaker 2>constantly vibrating the entire universe.

916
00:46:03.119 --> 00:46:05.599
<v Speaker 3>So the immense challenge this research team face was this,

917
00:46:06.559 --> 00:46:11.119
<v Speaker 3>if the highly advanced interferometers cannot resolve these individual differant mergers,

918
00:46:11.360 --> 00:46:13.920
<v Speaker 3>how can we possibly use them to measure the Hubble constant.

919
00:46:14.280 --> 00:46:18.400
<v Speaker 2>The key is mathematical statistical extrapolation. The researchers developed a

920
00:46:18.400 --> 00:46:21.519
<v Speaker 2>brilliant methodology to formally harness the stochastic hum.

921
00:46:21.519 --> 00:46:24.079
<v Speaker 3>They start by working with what they actually know. They

922
00:46:24.119 --> 00:46:27.440
<v Speaker 3>carefully quantify the precise rate and mass distribution of the

923
00:46:27.480 --> 00:46:31.280
<v Speaker 3>observable individual black hole collisions, the loud ones that LVK

924
00:46:31.440 --> 00:46:33.159
<v Speaker 3>can clearly detect and measure perfectly.

925
00:46:33.400 --> 00:46:37.119
<v Speaker 2>From those clear local events, the physicists build a robust

926
00:46:37.159 --> 00:46:41.079
<v Speaker 2>demographic profile of black hole populations in the local universe.

927
00:46:41.519 --> 00:46:44.679
<v Speaker 2>They figure out the average masses, the ratio of big

928
00:46:44.719 --> 00:46:47.360
<v Speaker 2>mergers to small mergers, and how often they occur.

929
00:46:47.880 --> 00:46:50.679
<v Speaker 3>It's akin to taking a highly detailed census of a

930
00:46:50.719 --> 00:46:54.440
<v Speaker 3>single typical neighborhood to understand the demographics of an entire

931
00:46:54.519 --> 00:46:58.960
<v Speaker 3>massive city. Once they have that localized demographic profile secured,

932
00:46:59.360 --> 00:47:00.880
<v Speaker 3>they statistic extrapolate.

933
00:47:01.159 --> 00:47:04.960
<v Speaker 2>They modeled the sheer massive volume of unobservable events occurring

934
00:47:04.960 --> 00:47:08.440
<v Speaker 2>across the broader universe that must be actively contributing to

935
00:47:08.480 --> 00:47:09.960
<v Speaker 2>the background hum.

936
00:47:09.639 --> 00:47:14.039
<v Speaker 3>It requires immense computational modeling. They integrate the expected merger

937
00:47:14.119 --> 00:47:17.199
<v Speaker 3>rates of these black hole populations over vast spans of

938
00:47:17.239 --> 00:47:20.400
<v Speaker 3>cosmic time. They know roughly when the universe was churning

939
00:47:20.440 --> 00:47:22.360
<v Speaker 3>out the most stars, which tells them when the most

940
00:47:22.400 --> 00:47:25.119
<v Speaker 3>black holes were born, and consequently when the most mergers

941
00:47:25.119 --> 00:47:25.840
<v Speaker 3>should be happening.

942
00:47:25.920 --> 00:47:28.719
<v Speaker 2>They combine all this data and project the total gravitational

943
00:47:28.760 --> 00:47:33.239
<v Speaker 2>wave energy density those countless unobservable mergers would logically produce.

944
00:47:33.239 --> 00:47:38.440
<v Speaker 3>And this mathematical projection yields a highly predictable theoretical stochastic

945
00:47:38.480 --> 00:47:41.880
<v Speaker 3>background spectrum. They can predict exactly how loud the hum

946
00:47:41.960 --> 00:47:44.519
<v Speaker 3>should be and at what frequencies it should be humming.

947
00:47:44.920 --> 00:47:48.639
<v Speaker 2>This theoretical framework is the birth of the stochastic siren methodology,

948
00:47:49.320 --> 00:47:51.360
<v Speaker 2>and the brilliance of it is that it bypasses the

949
00:47:51.360 --> 00:47:55.639
<v Speaker 2>need for individual light flashes or host galaxy redshifts entirely.

950
00:47:55.960 --> 00:48:00.760
<v Speaker 3>It completely sidesteps the electromagnetic bottleneck. It solves the paradox

951
00:48:00.800 --> 00:48:03.800
<v Speaker 3>through a rigorous, incredibly tight gmeter correlation.

952
00:48:03.960 --> 00:48:07.639
<v Speaker 2>The entire method hinges on a diagnostic geometry, a precise

953
00:48:07.840 --> 00:48:11.079
<v Speaker 2>inverse relationship between the physical value of the hubble constant

954
00:48:11.320 --> 00:48:14.559
<v Speaker 2>and the physical volume the literal loudness of the gravitational

955
00:48:14.599 --> 00:48:15.360
<v Speaker 2>wave background.

956
00:48:15.480 --> 00:48:18.119
<v Speaker 3>Let's walk through this logical sequence step by step, because

957
00:48:18.119 --> 00:48:21.039
<v Speaker 3>it is arguably one of the most elegant conceptual leaps

958
00:48:21.079 --> 00:48:24.679
<v Speaker 3>in modern cosmology. Step A requires us to postulate a

959
00:48:24.719 --> 00:48:26.760
<v Speaker 3>scenario where the hubble constant is smaller.

960
00:48:27.000 --> 00:48:29.519
<v Speaker 2>Let's assume the lower value derived from the early universe

961
00:48:29.559 --> 00:48:33.079
<v Speaker 2>cosmic microwave background data is the correct one. We adopt

962
00:48:33.119 --> 00:48:35.599
<v Speaker 2>the scenario where the universe is expanding at roughly that

963
00:48:35.679 --> 00:48:37.440
<v Speaker 2>sixty seven kilometers per second rate.

964
00:48:37.719 --> 00:48:40.360
<v Speaker 3>We pretend the early universe math is one hundred percent right,

965
00:48:40.639 --> 00:48:43.800
<v Speaker 3>and we see what physical consequences that forces onto the universe.

966
00:48:44.440 --> 00:48:48.239
<v Speaker 3>A smaller Hubble constant of sixty seven definitively means a

967
00:48:48.280 --> 00:48:51.400
<v Speaker 3>slower overall rate of universal expansion over time.

968
00:48:51.639 --> 00:48:54.920
<v Speaker 2>Now, moving to step B, we have to logically deduce

969
00:48:54.960 --> 00:48:57.679
<v Speaker 2>the geometric consequences of that slower expansion rate.

970
00:48:58.000 --> 00:49:00.519
<v Speaker 3>If the universe has been expanding more slowly for the

971
00:49:00.599 --> 00:49:03.360
<v Speaker 3>last thirteen point eight billion years to reach its current

972
00:49:03.440 --> 00:49:07.679
<v Speaker 3>observable state, then the total geometric volume of the observable

973
00:49:07.760 --> 00:49:10.719
<v Speaker 3>universe at any given distance at any given red shift

974
00:49:10.719 --> 00:49:14.159
<v Speaker 3>in the past must mathematically be smaller.

975
00:49:14.320 --> 00:49:16.880
<v Speaker 2>To picture this, imagine two balloons being blown up for

976
00:49:16.960 --> 00:49:20.199
<v Speaker 2>exactly ten seconds. One is blown up slowly, representing the

977
00:49:20.239 --> 00:49:23.280
<v Speaker 2>sixty seven rate, the other is blown up incredibly fast,

978
00:49:23.400 --> 00:49:24.880
<v Speaker 2>representing the seventy three rate.

979
00:49:25.239 --> 00:49:27.079
<v Speaker 3>If you stop them at ten seconds and look back

980
00:49:27.079 --> 00:49:28.920
<v Speaker 3>at how big they were at the five second mark,

981
00:49:29.199 --> 00:49:32.159
<v Speaker 3>the slower expanding balloon was physically much smaller at that

982
00:49:32.199 --> 00:49:34.639
<v Speaker 3>point in its history than the fast expanding balloon.

983
00:49:34.840 --> 00:49:38.800
<v Speaker 2>The actual cosmological container of space stretching back into the

984
00:49:38.800 --> 00:49:42.280
<v Speaker 2>deep past where these unobservable black hole mergers are happening,

985
00:49:42.760 --> 00:49:45.159
<v Speaker 2>is physically more compact than it would be in a

986
00:49:45.159 --> 00:49:46.719
<v Speaker 2>faster expanding model.

987
00:49:46.559 --> 00:49:48.880
<v Speaker 3>Which brings us to the critical inflection point of the

988
00:49:48.880 --> 00:49:53.480
<v Speaker 3>theory step C. If the universe's geometric volume is significantly

989
00:49:53.599 --> 00:49:58.360
<v Speaker 3>smaller at those distant redshifts, but the intrinsic statistical number

990
00:49:58.400 --> 00:50:02.159
<v Speaker 3>of black hole mergers occurring remains exactly constantly.

991
00:50:02.199 --> 00:50:04.679
<v Speaker 2>Wait, let me pause you there. Why does the number

992
00:50:04.719 --> 00:50:08.280
<v Speaker 2>of black hole mergers remain constant. Wouldn't a smaller universe

993
00:50:08.320 --> 00:50:09.559
<v Speaker 2>have fewer black holes?

994
00:50:09.880 --> 00:50:12.559
<v Speaker 3>That's a great question, But no, it wouldn't. The rate

995
00:50:12.599 --> 00:50:15.159
<v Speaker 3>of black hole mergers is strictly dictated by the star

996
00:50:15.280 --> 00:50:18.440
<v Speaker 3>formation history of the universe. How many stars were born,

997
00:50:18.800 --> 00:50:21.280
<v Speaker 3>how fast they burned out, and how many collapse into

998
00:50:21.320 --> 00:50:21.760
<v Speaker 3>black hole.

999
00:50:21.800 --> 00:50:25.199
<v Speaker 2>Well, we measure that star formation history independently, primarily using

1000
00:50:25.239 --> 00:50:28.079
<v Speaker 2>electromagnetic observations of distant galaxies.

1001
00:50:28.400 --> 00:50:31.880
<v Speaker 3>That history doesn't change based on the Hubble constant. We

1002
00:50:31.920 --> 00:50:35.239
<v Speaker 3>know how many catastrophic black hole collisions are happening out there.

1003
00:50:35.360 --> 00:50:37.519
<v Speaker 2>Okay, I see, so the number of events is locked in.

1004
00:50:37.960 --> 00:50:41.599
<v Speaker 2>You have the exact same vast number of catastrophic black

1005
00:50:41.599 --> 00:50:45.320
<v Speaker 2>hole collisions happening, but because of the slower expansion rate,

1006
00:50:45.400 --> 00:50:48.519
<v Speaker 2>they are occurring in a much smaller geometric volume of space.

1007
00:50:48.760 --> 00:50:51.679
<v Speaker 3>Exactly right, you have the same amount of catastrophic events

1008
00:50:51.760 --> 00:50:55.920
<v Speaker 3>compressed into a much tighter region of comoving space. Therefore,

1009
00:50:56.440 --> 00:51:01.079
<v Speaker 3>a profound Sneichel compression occurs. This rafacial density of these

1010
00:51:01.159 --> 00:51:04.840
<v Speaker 3>massive gravitational wave events spikes significantly.

1011
00:51:04.920 --> 00:51:07.920
<v Speaker 2>Think about that you are cramming the exact same number

1012
00:51:07.920 --> 00:51:10.960
<v Speaker 2>of massive fireworks into a much smaller room, and.

1013
00:51:10.880 --> 00:51:14.599
<v Speaker 3>That increased density leads directly to Step D. We can

1014
00:51:14.639 --> 00:51:18.000
<v Speaker 3>mathematically dictate that this increased batial density of black hole

1015
00:51:18.039 --> 00:51:22.079
<v Speaker 3>collisions unequivocally amplifies the overall strength and volume of the

1016
00:51:22.079 --> 00:51:23.400
<v Speaker 3>gravitational wave background.

1017
00:51:23.480 --> 00:51:26.480
<v Speaker 2>Because the active sources of gravitational waves are packed much

1018
00:51:26.480 --> 00:51:30.679
<v Speaker 2>closer together in a geometrically smaller universe, the cumulative spacetime

1019
00:51:30.760 --> 00:51:33.679
<v Speaker 2>ripples they produce compound upon each other much more intensely.

1020
00:51:33.920 --> 00:51:37.400
<v Speaker 3>The resulting stochastic hum the roar of the stadium would

1021
00:51:37.400 --> 00:51:41.000
<v Speaker 3>be significantly louder and physically stronger. The waves wouldn't have

1022
00:51:41.039 --> 00:51:43.920
<v Speaker 3>as much space to dissipate before overlapping.

1023
00:51:43.559 --> 00:51:47.360
<v Speaker 2>So the analytical tool is complete and rigorous. A smaller

1024
00:51:47.440 --> 00:51:52.000
<v Speaker 2>Hubble constant strictly mandates a louder gravitational wave background. The

1025
00:51:52.039 --> 00:51:55.679
<v Speaker 2>inverse relationship is the master key to the entire method.

1026
00:51:55.480 --> 00:51:59.559
<v Speaker 3>And this inverse relationship functions as an extraordinarily potent analytical

1027
00:51:59.599 --> 00:52:04.119
<v Speaker 3>tool through the classic scientific process of elimination. The methodology

1028
00:52:04.119 --> 00:52:07.360
<v Speaker 3>relies on constraining the parameter space of the Hubble tension

1029
00:52:07.679 --> 00:52:09.679
<v Speaker 3>using hard empirical constraints.

1030
00:52:09.840 --> 00:52:13.400
<v Speaker 2>The Illinois and Chicago research team applied this geometric logic

1031
00:52:13.480 --> 00:52:17.079
<v Speaker 2>directly to the existing raw LVK data, and the massive

1032
00:52:17.119 --> 00:52:19.760
<v Speaker 2>power of this application lies purely in non detection.

1033
00:52:20.159 --> 00:52:22.880
<v Speaker 3>This is where doing nothing is actually doing something. The

1034
00:52:22.960 --> 00:52:25.880
<v Speaker 3>highly sensitive LVK instruments, running for months and years at

1035
00:52:25.920 --> 00:52:29.760
<v Speaker 3>a time did not detect a massive deafening stochastic signal.

1036
00:52:29.880 --> 00:52:32.960
<v Speaker 2>The interferometers were not overwhelmed by a massive background hum

1037
00:52:33.039 --> 00:52:36.840
<v Speaker 2>dominating their low frequency sensitivity bands. They detected the loud

1038
00:52:36.880 --> 00:52:40.760
<v Speaker 2>close chirps, but the baseline static was relatively quiet, and.

1039
00:52:40.719 --> 00:52:44.679
<v Speaker 3>In astrophysics, a non detection like this is absolutely crucial

1040
00:52:44.719 --> 00:52:48.440
<v Speaker 3>empirical data. It is proof of absence if the lower

1041
00:52:48.480 --> 00:52:51.800
<v Speaker 3>bounds of the Hubble tension the extremely slow sixty seven

1042
00:52:51.840 --> 00:52:55.119
<v Speaker 3>expansion models derived from the early universe were strictly true

1043
00:52:55.159 --> 00:52:58.840
<v Speaker 3>without any modifications. The spatial compression of black holes would

1044
00:52:58.880 --> 00:53:02.320
<v Speaker 3>be so intense that the stochastic hum would have been

1045
00:53:02.400 --> 00:53:04.800
<v Speaker 3>theoretically deafening to the LVK sensors.

1046
00:53:05.280 --> 00:53:08.440
<v Speaker 2>It would have saturated the data, but it didn't. By

1047
00:53:08.480 --> 00:53:12.159
<v Speaker 2>proving definitively how loud the background is not, the researchers

1048
00:53:12.239 --> 00:53:15.840
<v Speaker 2>utilized the absence of a massive signal to establish firm

1049
00:53:16.039 --> 00:53:17.519
<v Speaker 2>mathematical upper limits.

1050
00:53:17.719 --> 00:53:21.840
<v Speaker 3>They carefully quantified the absolute maximum possible volume the background

1051
00:53:21.880 --> 00:53:25.000
<v Speaker 3>hume could be producing without triggering a massive detection in

1052
00:53:25.079 --> 00:53:29.239
<v Speaker 3>the current incredibly sensitive LVK data streams, and by establishing

1053
00:53:29.280 --> 00:53:32.960
<v Speaker 3>those rigorous limits, they mathematically ruled out the slowest expansion

1054
00:53:32.960 --> 00:53:33.719
<v Speaker 3>models outright.

1055
00:53:33.800 --> 00:53:36.800
<v Speaker 2>Furthermore, they heavily constrained the most extreme variance of the

1056
00:53:36.840 --> 00:53:41.320
<v Speaker 2>early dark energy hypotheses. They placed a rigid, unyielding mathematical

1057
00:53:41.360 --> 00:53:44.480
<v Speaker 2>ceiling on what models of cosmology are physically permissible in

1058
00:53:44.519 --> 00:53:45.159
<v Speaker 2>our reality.

1059
00:53:45.440 --> 00:53:48.440
<v Speaker 3>But the research didn't stop at simply ruling out the

1060
00:53:48.519 --> 00:53:52.599
<v Speaker 3>extreme models. They took the methodology further to fundamentally refine

1061
00:53:52.639 --> 00:53:58.159
<v Speaker 3>the Hubble constant itself. The methodology elegantly synthesizes two completely

1062
00:53:58.199 --> 00:54:00.719
<v Speaker 3>independent streams of gravitational data.

1063
00:54:00.760 --> 00:54:03.880
<v Speaker 2>They combine the strict upper limits of the unresolved background

1064
00:54:04.000 --> 00:54:08.000
<v Speaker 2>hum with the pristine distance data extracted from the isolated

1065
00:54:08.199 --> 00:54:10.719
<v Speaker 2>individual standard sirens we discussed earlier.

1066
00:54:11.000 --> 00:54:15.280
<v Speaker 3>By combining the massive statistical, unobservable data set that dictates

1067
00:54:15.320 --> 00:54:18.519
<v Speaker 3>the volume of the universe with a perfectly resolved local

1068
00:54:18.599 --> 00:54:21.920
<v Speaker 3>data set that acts as our perfect localized ruler, they

1069
00:54:22.000 --> 00:54:26.199
<v Speaker 3>mathematically extract a highly refined, entirely independent estimate of the

1070
00:54:26.280 --> 00:54:27.519
<v Speaker 3>Hubble constant.

1071
00:54:27.440 --> 00:54:30.760
<v Speaker 2>And the result is staggering. This new estimate, derived purely

1072
00:54:30.800 --> 00:54:33.840
<v Speaker 2>from space time ripples, falls directly within the parameter space

1073
00:54:33.880 --> 00:54:36.639
<v Speaker 2>of the Hubble tension. It doesn't use standard candles, it

1074
00:54:36.679 --> 00:54:38.599
<v Speaker 2>doesn't use the cousmic microwave background.

1075
00:54:38.639 --> 00:54:42.559
<v Speaker 3>It provides a highly constrained, completely independent physical measurement utilizing

1076
00:54:42.599 --> 00:54:46.960
<v Speaker 3>a fundamentally distinct physical force, gravity instead of electromagnetism.

1077
00:54:47.159 --> 00:54:49.960
<v Speaker 2>If we connect this to the bigger picture, the technological

1078
00:54:49.960 --> 00:54:54.639
<v Speaker 2>horizon over the next decade points toward a definitive, monumental

1079
00:54:54.719 --> 00:54:56.159
<v Speaker 2>resolution to this crisis.

1080
00:54:56.559 --> 00:55:00.800
<v Speaker 3>The LVK network is not static. It is continuous undergoing

1081
00:55:00.920 --> 00:55:06.280
<v Speaker 3>significant multimillion dollars sensitivity upgrades. The engineering teams are actively

1082
00:55:06.320 --> 00:55:09.719
<v Speaker 3>reducing the quantum noise within the lasers even further and

1083
00:55:09.840 --> 00:55:13.679
<v Speaker 3>drastically improving the physical isolation of the mirrors from terrestrial

1084
00:55:13.719 --> 00:55:14.719
<v Speaker 3>seismic interference.

1085
00:55:14.920 --> 00:55:17.840
<v Speaker 2>They are making the most sensitive instrument ever built even

1086
00:55:17.880 --> 00:55:21.480
<v Speaker 2>more sensitive. The data predicts that within just six years,

1087
00:55:21.840 --> 00:55:26.239
<v Speaker 2>scientific consensus dictates that the interferometers will have increased in

1088
00:55:26.280 --> 00:55:28.880
<v Speaker 2>sensitivity enough to cross the critical threshold.

1089
00:55:28.960 --> 00:55:33.320
<v Speaker 3>Within six years, detectors will definitively detect, isolate, and precisely

1090
00:55:33.360 --> 00:55:36.639
<v Speaker 3>constrain the exact volume and spectral shape of the gravitational

1091
00:55:36.639 --> 00:55:39.239
<v Speaker 3>wave background. They won't just set upper limits, they will

1092
00:55:39.239 --> 00:55:42.079
<v Speaker 3>hear the hump perfectly. They will definitively isolate it from

1093
00:55:42.079 --> 00:55:43.000
<v Speaker 3>the instrumental noise.

1094
00:55:43.159 --> 00:55:46.480
<v Speaker 2>The ultimate objective of modern astrophysics is resolving the Hubble

1095
00:55:46.519 --> 00:55:51.719
<v Speaker 2>tension purely through gravity. Securing this independent, ultra precise measurement

1096
00:55:51.840 --> 00:55:54.440
<v Speaker 2>via the aggregate space time ripples of millions of black

1097
00:55:54.440 --> 00:55:59.920
<v Speaker 2>holes will definitively solve the foundational physical paradoxes that localize

1098
00:56:00.199 --> 00:56:04.000
<v Speaker 2>isolated electromagnetic measurements simply cannot reconcile.

1099
00:56:04.440 --> 00:56:07.159
<v Speaker 3>It will tell us once and for all whether our

1100
00:56:07.239 --> 00:56:10.639
<v Speaker 3>standard model of the universe is fundamentally broken or if

1101
00:56:10.760 --> 00:56:12.599
<v Speaker 3>dark energy is mutating over time.

1102
00:56:12.920 --> 00:56:16.599
<v Speaker 2>It remains an unresolved cosmic paradigm today, but the sheer

1103
00:56:16.639 --> 00:56:21.280
<v Speaker 2>elegance of the stochastic siren method is unparalleled. It possesses

1104
00:56:21.320 --> 00:56:25.719
<v Speaker 2>the profound capacity to leverage the macroscopic, unresolved dynamics of

1105
00:56:25.760 --> 00:56:27.880
<v Speaker 2>the cosmos to solve a local problem.

1106
00:56:27.960 --> 00:56:32.239
<v Speaker 3>It relies on the massive statistical aggregation of unobservable invisible

1107
00:56:32.239 --> 00:56:35.960
<v Speaker 3>events to precisely calibrate the geometric expansion of the universe.

1108
00:56:36.039 --> 00:56:39.400
<v Speaker 2>It entirely bypasses the limitations of standard candles. We don't

1109
00:56:39.400 --> 00:56:42.159
<v Speaker 2>have to worry about the cosmic dust, the light extinction rates,

1110
00:56:42.239 --> 00:56:44.559
<v Speaker 2>or the metallicity of distinct galaxies ever again.

1111
00:56:44.880 --> 00:56:49.719
<v Speaker 3>And it completely bypasses the recession velocity bottleneck that plagued

1112
00:56:49.880 --> 00:56:54.480
<v Speaker 3>individual standard sirens. It is a masterful, pure application of

1113
00:56:54.519 --> 00:56:57.079
<v Speaker 3>statistical mechanics and general relativity.

1114
00:56:57.199 --> 00:56:59.599
<v Speaker 2>As we synthesize the power of this entire method, o dotage,

1115
00:56:59.679 --> 00:57:02.639
<v Speaker 2>there's a highly provocative extrapolation. We must leave you with

1116
00:57:02.880 --> 00:57:06.400
<v Speaker 2>a thought experiment about the distant future of cosmology.

1117
00:57:06.079 --> 00:57:09.079
<v Speaker 3>When the LVK network or the next future generation of

1118
00:57:09.159 --> 00:57:13.079
<v Speaker 3>highly advanced space based or massive ground based detectors like

1119
00:57:13.079 --> 00:57:17.960
<v Speaker 3>the proposed Cosmic Explorer eventually detect and fully map this

1120
00:57:18.079 --> 00:57:22.440
<v Speaker 3>gravitational wave background. They won't merely be recording its overall amplitude.

1121
00:57:22.440 --> 00:57:24.079
<v Speaker 2>They won't just measure how loud the HUM is.

1122
00:57:24.119 --> 00:57:27.320
<v Speaker 3>With enough sensitivity and time, they will eventually map its

1123
00:57:27.360 --> 00:57:30.039
<v Speaker 3>specific directional anisas anesotropies.

1124
00:57:30.119 --> 00:57:32.079
<v Speaker 2>That's a complex term, but we've actually talked about it

1125
00:57:32.119 --> 00:57:35.159
<v Speaker 2>already today. Just as the cosmic microwave background has those

1126
00:57:35.199 --> 00:57:39.079
<v Speaker 2>microscopic temperature fluctuations across different regions of the sky, the

1127
00:57:39.119 --> 00:57:41.760
<v Speaker 2>hot spots and cold spots that form the seeds of galaxies,

1128
00:57:42.000 --> 00:57:45.320
<v Speaker 2>the gravitational wave background will also possess anisotropies.

1129
00:57:45.679 --> 00:57:49.039
<v Speaker 3>There will be a subtle distinct unevenness in the gravitational

1130
00:57:49.119 --> 00:57:53.719
<v Speaker 3>hum originating from different cosmological coordinates. The roar of the

1131
00:57:53.719 --> 00:57:57.280
<v Speaker 3>stadium won't be perfectly uniform, will be slightly louder coming

1132
00:57:57.280 --> 00:57:59.559
<v Speaker 3>from the north bleachers than the south bleachers.

1133
00:58:00.119 --> 00:58:04.760
<v Speaker 2>Consider the immense reality altering implications of mapping that gravitational topography.

1134
00:58:05.480 --> 00:58:10.239
<v Speaker 2>The precise spatial distribution of these microscopic spacetime ripples arriving

1135
00:58:10.280 --> 00:58:14.440
<v Speaker 2>from all directions could theoretically map the density of matter

1136
00:58:14.480 --> 00:58:17.519
<v Speaker 2>in the universe before the cosmic dark ages even began.

1137
00:58:17.920 --> 00:58:22.000
<v Speaker 3>Because gravitational waves pass unhindered through the primordial plasma that

1138
00:58:22.039 --> 00:58:24.880
<v Speaker 3>trapped light. We could see further back than the cosmic

1139
00:58:24.920 --> 00:58:28.480
<v Speaker 3>microwave background. We could map the true dawn of the universe.

1140
00:58:28.800 --> 00:58:31.440
<v Speaker 2>But it goes even further than that. Variations in this

1141
00:58:31.480 --> 00:58:35.679
<v Speaker 2>gravitational background might reveal entirely new pre Big Bang structures

1142
00:58:35.719 --> 00:58:40.119
<v Speaker 2>predicted by fringe highly theoretical cyclic cosmology models.

1143
00:58:40.480 --> 00:58:44.440
<v Speaker 3>If the universe expands, collapses, and bangs again, the gravitational

1144
00:58:44.440 --> 00:58:48.679
<v Speaker 3>echoes of previous universes might be permanently imprinted in the stochasticom.

1145
00:58:49.559 --> 00:58:53.360
<v Speaker 3>This mapping of anisotropes could expose phenomena that our current

1146
00:58:53.519 --> 00:58:57.239
<v Speaker 3>LAMB to CDM expansion models cannot even mathematically formulate.

1147
00:58:57.440 --> 00:59:01.840
<v Speaker 2>We might expose the gravitational signatures of previously theorized higher

1148
00:59:01.840 --> 00:59:05.280
<v Speaker 2>dimensions of space time. If string theory is correct and

1149
00:59:05.400 --> 00:59:09.559
<v Speaker 2>gravity is leaking into our observable universe from higher hidden dimensions,

1150
00:59:10.199 --> 00:59:14.119
<v Speaker 2>the evidence of that multidimensional leakage would be inscribed directly

1151
00:59:14.199 --> 00:59:17.559
<v Speaker 2>into the uneven fluctuations of the gravitational wave background.

1152
00:59:17.679 --> 00:59:18.880
<v Speaker 3>It's an incredible frontier.

1153
00:59:19.159 --> 00:59:22.599
<v Speaker 2>Just consider the absolute magnitude of what humanity is attempting

1154
00:59:22.639 --> 00:59:26.159
<v Speaker 2>to map here by isolating the microscopic stretching of lasers

1155
00:59:26.159 --> 00:59:28.840
<v Speaker 2>in a vacuum tube. We are listening to the invisible

1156
00:59:28.880 --> 00:59:31.639
<v Speaker 2>geometry of the universe. We are listening to a symphony

1157
00:59:31.639 --> 00:59:35.400
<v Speaker 2>of catastrophic violence stretching across billion year epochs. We are

1158
00:59:35.480 --> 00:59:38.079
<v Speaker 2>using the invisible force of gravity to peel back the

1159
00:59:38.159 --> 00:59:41.760
<v Speaker 2>veil of the cosmos, revealing structures, dimensions, and ancient histories

1160
00:59:42.039 --> 00:59:45.760
<v Speaker 2>far beyond the fragile, dusty limits of light itself. Allow

1161
00:59:45.840 --> 00:59:48.039
<v Speaker 2>the profound magnitude of that thought to sit with you.

1162
01:00:00.079 --> 01:00:33.800
<v Speaker 3>The school most us