# Massive Stellar Survey Tests the Age of the Universe

An episode of [Bedtime Astronomy](https://invisiblenetwork.ai/podcast/1736397134), 5 Aug 2026, 39 min.

Audio: https://dts.podtrac.com/redirect.mp3/api.spreaker.com/download/episode/73024520/ancientp.mp3

A study of more than 155,000 Milky Way stars offers compelling new clues about the universe's true age. By examining some of the galaxy's oldest stars, astronomers provide an independent test of leading cosmological theories while revealing new insights into the ongoing Hubble tension. The findings strengthen our understanding of the universe's earliest history without fully resolving one of astronomy's biggest mysteries. Thank you for listening to Bedtime Astronomy — your guide to the cosmos. New episodes on space exploration, NASA missions & the latest astronomy breakthroughs.

## Transcript

[0:03] Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
[0:07] Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
[0:12] Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
[0:16] Speaker 1: unwinding after a long day. Let's travel through the mysteries
[0:20] Speaker 1: of the universe as you drift off into a peaceful
[0:22] Speaker 1: slumber under the night sky.
[0:27] Speaker 2: So, if you look at the absolute oldest light in
[0:29] Speaker 2: the universe, the grand cosmic math says, reality is thirteen
[0:33] Speaker 2: point eight billion years old.
[0:34] Speaker 3: Right.
[0:35] Speaker 2: But and this is where it gets crazy. If you
[0:37] Speaker 2: look at your cosmic window right now, at the stars
[0:40] Speaker 2: and galaxies relatively close to us, the local math insists
[0:44] Speaker 2: the universe is a billion years younger.
[0:46] Speaker 3: Yeah, it's a massive discrepancy.
[0:48] Speaker 2: Like, let that sink in for a second. We haven't
[0:50] Speaker 2: just misplaced your car keys. We have somehow misplaced an
[0:55] Speaker 2: entire billion year era of cosmic history and.
[0:58] Speaker 3: Losing a billion year I mean that isn't a mere
[1:01] Speaker 3: rounding error. It fundamentally shatters our entire timeline. It throws
[1:05] Speaker 3: into question really our understanding of how galaxies assembled, when
[1:08] Speaker 3: the first star is ignited, and even how the very
[1:11] Speaker 3: fabric of space and time behaves on a macroscopic scale.
[1:14] Speaker 3: We are dealing with highly precise data sets here, and
[1:17] Speaker 3: they are pointing in two completely contradictory directions.
[1:20] Speaker 2: It is a massive crisis in modern astronomy. They often
[1:24] Speaker 2: refer to it as the Hubble tension. So for everyone listening,
[1:28] Speaker 2: our mission today is to break down a really fascinating
[1:31] Speaker 2: new approach to solving this exact standoff. There's this massive
[1:35] Speaker 2: research effort led by dron Old Bannock at the University
[1:37] Speaker 2: of Portsmouth, and they submitted a study this past July
[1:41] Speaker 2: that tries to finally settle.
[1:42] Speaker 3: The debate, which is incredibly exciting, right but.
[1:44] Speaker 2: Instead of peering out to the very edge of the
[1:46] Speaker 2: observable universe, they are looking inward. They're hunting for the
[1:51] Speaker 2: absolute oldest, most pristine cosmic fossils right here in our
[1:55] Speaker 2: own galactic backyard, the Milky Way. So we are going
[1:58] Speaker 2: to explore these two conflict tape measures of the cosmos,
[2:01] Speaker 2: break down how a staggeringly massive senses of over one
[2:04] Speaker 2: hundred and fifty five thousand ancient stars is acting as
[2:06] Speaker 2: a tie breaker, and explore the incredibly wild possibility that
[2:11] Speaker 2: our local neighborhood of space might just be completely distorting
[2:14] Speaker 2: our view of reality.
[2:15] Speaker 3: The shift in methodology here is crucial to understand because
[2:18] Speaker 3: for decades cosmology has relied really heavily on measuring the
[2:21] Speaker 3: stretching of space itself, exactly the container. This new approach
[2:26] Speaker 3: entirely abandons the attempt to measure the container, so to speak,
[2:29] Speaker 3: and instead focuses on finding the oldest possible objects sitting
[2:33] Speaker 3: inside that container.
[2:34] Speaker 2: But let's start with the container, though, because I feel
[2:36] Speaker 2: like you need to understand the standoff before you can
[2:38] Speaker 2: appreciate the solution. The core of this crisis revolves around
[2:43] Speaker 2: measuring how fast the universe is expanding, which is a
[2:47] Speaker 2: metric known as the Hubble constant. Right, And the tension
[2:50] Speaker 2: exists because we have this nine percent mismatch between two
[2:53] Speaker 2: historically bulletproof methods of measuring that expansion. Let's talk about
[2:57] Speaker 2: tape measure number one, the early universe.
[3:00] Speaker 3: So the early universe method relies on something called the
[3:02] Speaker 3: cosmic microwave background, or the CMB. To picture this, you
[3:06] Speaker 3: have to imagine the universe about three hundred and eighty
[3:09] Speaker 3: thousand years after the Big Bank.
[3:10] Speaker 2: Okay, pretty early on, very early.
[3:12] Speaker 3: Before this point. The universe was so intensely hot and
[3:15] Speaker 3: dense that it was essentially a thick fog of plasma.
[3:18] Speaker 3: Photons of light couldn't travel freely. They just you know,
[3:21] Speaker 3: constantly smashed into free electrons.
[3:23] Speaker 2: So the universe was effectively opaque, right, just a giant, glowing,
[3:27] Speaker 2: superheated cloud where light was totally trapped precisely.
[3:31] Speaker 3: But as space expanded, it naturally cooled, and right around
[3:34] Speaker 3: that three hundred and eighty thousand year mark, the temperature
[3:37] Speaker 3: dropped just enough for electrons to finally bind to protons,
[3:41] Speaker 3: which formed the first neutral hydrogen.
[3:43] Speaker 2: Atoms, and that's when the fog lifted.
[3:45] Speaker 3: The fog lifted, light could suddenly travel unimpeded, and that
[3:49] Speaker 3: first burst of free light has literally been traveling through
[3:53] Speaker 3: space for billions of years. As the universe has expanded,
[3:57] Speaker 3: those ancient light waves have been stretched out into the
[4:00] Speaker 3: microwave spectrum.
[4:01] Speaker 2: So when we point speralized radio telescopes at the sky today,
[4:05] Speaker 2: we can actually see the afterglow of this exact event.
[4:08] Speaker 2: It's like we're looking at a baby picture.
[4:10] Speaker 3: Of the universe we are, and that baby picture, interestingly,
[4:14] Speaker 3: is not perfectly uniform. It has microscopic temperature fluctuations these
[4:18] Speaker 3: tiny hot and cold spots. By analyzing the physical size
[4:21] Speaker 3: and distribution of those temperature ripples, cosmologists can apply our
[4:25] Speaker 3: standard model of the universe.
[4:26] Speaker 2: Which is known as the Lambda CDM model. Hold on,
[4:29] Speaker 2: let's not let that acronym just slide by Lambda CDM.
[4:33] Speaker 2: What physically are we talking about there, because I know
[4:35] Speaker 2: that model is doing a whole lot of heavy lifting
[4:36] Speaker 2: in this measurement.
[4:37] Speaker 3: Sure, so, Lambda represents dark energy. This is the mysterious
[4:41] Speaker 3: intrinsic energy of space itself that is causing the expansion
[4:45] Speaker 3: of the universe to accelerate.
[4:46] Speaker 2: It pushes things apart.
[4:47] Speaker 3: Yes, it acts like a repulsive gravity, pushing space apart.
[4:51] Speaker 3: Then CDM stands for cold dark matter. This is the invisible,
[4:57] Speaker 3: slow moving matter that doesn't interact with light at all,
[5:00] Speaker 3: but it exerts a massive gravitational pull. It acts as
[5:04] Speaker 3: the invisible staffolding for galaxies.
[5:07] Speaker 2: So we basically have dark energy pushing everything apart on
[5:09] Speaker 2: one side, in cold dark matter trying to pull it
[5:12] Speaker 2: all together on the other.
[5:13] Speaker 3: Exactly. The LAMB to CDM model perfectly balances those two
[5:17] Speaker 3: opposing forces by plugging the temperature fluctuations of the CMB
[5:21] Speaker 3: baby picture. Into this mathematical model, cosmologists can calculate exactly
[5:25] Speaker 3: how fast the universe was expanding in its earliest moments,
[5:28] Speaker 3: and then they can project that math forward to the
[5:31] Speaker 3: present day. When you run that simulation all the way
[5:34] Speaker 3: to its conclusion, the math dictates that the universe has
[5:38] Speaker 3: been expanding for thirteen point eight billion years.
[5:41] Speaker 2: Okay, so that is tape measure number one, giving us
[5:44] Speaker 2: the universe that is thirteen point eight billion years old.
[5:48] Speaker 2: It is an incredibly sophisticated deduction based on the oldest
[5:52] Speaker 2: light in existence. But then we have tape measure number two,
[5:55] Speaker 2: and this one doesn't look at ancient stretched out microwaves.
[5:59] Speaker 2: It looks at the local, present day universe right outside
[6:01] Speaker 2: our cosmic front door.
[6:03] Speaker 3: Right The local measurements rely on a completely different astrophysical tool.
[6:07] Speaker 3: They use standard candles. Standard candles, specifically, astronomers look at
[6:11] Speaker 3: pulsating stars called cepheides and exploding stars known as type
[6:15] Speaker 3: ia supernovae. The fundamental principle of a standard candle is
[6:19] Speaker 3: that we know its exact intrinsic true brightness.
[6:23] Speaker 2: Let me make sure I'm wrapping my head around this.
[6:24] Speaker 2: If I look out my window at night and I
[6:26] Speaker 2: see a dim street lamp, it might be a tiny
[6:28] Speaker 2: flashlight one hundred feet away, or it could be a
[6:30] Speaker 2: massive stadium floodlight a mile away. Without knowing its true brightness,
[6:34] Speaker 2: I can't determine its distance at all.
[6:35] Speaker 3: That is the fundamental problem of all astronomical observation. You
[6:40] Speaker 3: can't just take a literal tape measure to the stars,
[6:43] Speaker 3: but standard candles solve this. Back in the early twentieth century,
[6:47] Speaker 3: astronomer Henrietta swan Livett discovered that cephed variable stars pulse
[6:52] Speaker 3: at a rate that is directly tied to their true brightness,
[6:56] Speaker 3: so they basically blink yes, and a slower pulse means
[7:00] Speaker 3: a brighter star. Once you measure the pulse rate, you
[7:03] Speaker 3: know exactly how bright the star truly is at its source.
[7:06] Speaker 2: So, going back to my streetline analogy, the star essentially
[7:10] Speaker 2: tells you, hey, I am exactly as bright as a
[7:13] Speaker 2: hundred watt bulb. So when you look at it in
[7:15] Speaker 2: the telescope and it looks incredibly dim, you can use
[7:18] Speaker 2: a simple inverse square law of light to calculate precisely
[7:21] Speaker 2: how far away it must be to appear that dim
[7:23] Speaker 2: to us.
[7:24] Speaker 3: You've got the distance. That's half the puzzle. Now you
[7:26] Speaker 3: need the speed because the Hubble constant is all about
[7:28] Speaker 3: distance and speed. To get the speed, astronomers measure the
[7:31] Speaker 3: red shift of that star's light. Yeah, as the star
[7:35] Speaker 3: moves away from us, due to the expansion of space,
[7:39] Speaker 3: the light waves it emits get stretched out. Over that distance.
[7:42] Speaker 3: The wavelength becomes longer, shifting toward the red end of
[7:45] Speaker 3: the light spectrum.
[7:46] Speaker 2: Oh, it's like the visual version of the Doppler effect.
[7:48] Speaker 2: Like when an ambulance speeds away from you, the sand
[7:50] Speaker 2: waves stretch out and the pitch drops in space. As
[7:54] Speaker 2: a galaxy speeds away, the light waves stretch out and
[7:57] Speaker 2: the color reddens.
[7:58] Speaker 3: That's a perfect analogy. Combining the precise distance from the
[8:01] Speaker 3: standard candle with the precise speed from the red shift,
[8:05] Speaker 3: astronomers can calculate the local expansion rate of the universe today,
[8:09] Speaker 3: and here is where the crisis erpts the tension. The
[8:12] Speaker 3: local measurement reveals a noticeably higher expansion rate than the
[8:16] Speaker 3: early universe. CMB measurement predicts.
[8:18] Speaker 2: The universe right around as appears to be flying apart,
[8:21] Speaker 2: roughly nine percent faster than the early universe. Baby pictures
[8:24] Speaker 2: said it should be, and that brings us to the
[8:27] Speaker 2: mathematical nightmare here. If space has been expanding at this
[8:31] Speaker 2: faster rate for almost all of cosmic history, it wouldn't
[8:34] Speaker 2: have taken thirteen point eight billion years to reach its
[8:37] Speaker 2: current size, not at all.
[8:39] Speaker 3: It would have reached its current volume much much faster.
[8:42] Speaker 3: If you apply the local expansion rate retroactively, the universe
[8:46] Speaker 3: is suddenly only twelve point five to roughly twelve point
[8:49] Speaker 3: nine billion.
[8:50] Speaker 2: Years old, thirteen point eight billion on one side, twelve
[8:54] Speaker 2: point five billion on the other. That is a gap
[8:57] Speaker 2: of over a billion years. Now I have to ask
[8:59] Speaker 2: the obvious question that anyone listening is probably you know,
[9:02] Speaker 2: shouting out to speakers right now. Why can't we just
[9:04] Speaker 2: split the difference? Why not just average the two numbers,
[9:06] Speaker 2: say the universes, I don't know, thirteen point two billion
[9:09] Speaker 2: years old, and call it a day.
[9:11] Speaker 3: Splitting the difference is intellectually dishonest. In physics, it is
[9:14] Speaker 3: equivalent to taking a thermometer that says water boils at
[9:17] Speaker 3: one hundred degrees and another that says it boils at
[9:20] Speaker 3: ninety degrees, and just deciding water boils at ninety five degrees.
[9:23] Speaker 2: Right, It doesn't work that way.
[9:24] Speaker 3: No, these aren't sloppy approximations. The instruments measuring the CMB,
[9:28] Speaker 3: like the Plank satellite, are total marvels of engineering. The
[9:31] Speaker 3: telescopes observing the cepheeds, like the Hubble Space telescope, have
[9:34] Speaker 3: been calibrated relentlessly for decades. The nine percent discrepancy is
[9:39] Speaker 3: significantly larger than the combined margin of error for both methods, so.
[9:43] Speaker 2: We absolutely cannot chalk this up to like a smudge
[9:46] Speaker 2: on a telescope lens or a bad line of code
[9:48] Speaker 2: in the software. A nine percent discrepancy on a cosmic
[9:52] Speaker 2: scale means there has to be a physical reason for
[9:54] Speaker 2: the mismatch, which leaves us with two pretty terrifying possibilities.
[9:59] Speaker 3: Yeah.
[9:59] Speaker 2: First, there could be some entirely new physics, some exotic
[10:03] Speaker 2: energy field or particle behavior that shape the universe's expansion
[10:07] Speaker 2: from its earliest moments that our LAMB to CDM model
[10:09] Speaker 2: is completely blind to. Or conversely, this fast local expansion
[10:14] Speaker 2: rate is an illusion created by something weird in our
[10:17] Speaker 2: local neighborhood.
[10:18] Speaker 3: The scientific community has been at a total impasse over this.
[10:21] Speaker 3: Are we missing a fundamental piece of the cosmological puzzle?
[10:24] Speaker 3: Or is our tape measure skewed by where we live?
[10:27] Speaker 3: And to break a deadlock like this, you cannot keep
[10:29] Speaker 3: using the same tools. You can't just run another CMB
[10:32] Speaker 3: scan or catalog another thousand supernovae.
[10:35] Speaker 2: You need a totally independent referee, which brings us to
[10:38] Speaker 2: Indronobanic and the University of Portsmouth team. They realize that
[10:42] Speaker 2: you have to stop measuring the stretching of the container.
[10:44] Speaker 2: If you want to know how old a house is,
[10:46] Speaker 2: you don't necessarily measure how far the wooden beams have
[10:49] Speaker 2: warped over time. Right, you look for a newspaper stuffed
[10:52] Speaker 2: in the walls during construction. You date the objects inside
[10:55] Speaker 2: the space.
[10:56] Speaker 3: This relies on what is formally called the minimum age principle,
[11:00] Speaker 3: and the logic is as robust as it is simple.
[11:03] Speaker 3: The universe cannot possibly be younger than the oldest object
[11:06] Speaker 3: within it.
[11:07] Speaker 2: I love this concept. It's like paleontology, but for the cosmos.
[11:12] Speaker 2: If a geologist is trying to determine the age of
[11:14] Speaker 2: a rock formation, they look for fossils. If they dig
[11:17] Speaker 2: into a canyon wall and find a trilobyte fossil, that
[11:20] Speaker 2: carbon and radiometric dating proves as say, five hundred million
[11:23] Speaker 2: years old. Then they know for an absolute, undeniable fact
[11:27] Speaker 2: that the canyon rock must be at least five hundred
[11:29] Speaker 2: million years old. Exactly, the rock cannot be younger than
[11:32] Speaker 2: the fossil trapped inside it.
[11:34] Speaker 3: Stars act as these exact cosmic fossils. If you can
[11:37] Speaker 3: accurately isolate and date the absolute oldest star in our galaxy,
[11:41] Speaker 3: you establish a hard physical floor for the age of
[11:44] Speaker 3: the universe. Of course, you have to add a small
[11:46] Speaker 3: buffer of time to account for how long it took
[11:48] Speaker 3: that start of physically form after the Big Bang, but
[11:51] Speaker 3: it gives you a definitive baseline.
[11:52] Speaker 2: And this methodology is a direct attack on the younger
[11:56] Speaker 2: twelve point five billion year estimate. Right If the local
[12:00] Speaker 2: expansion rate is correct and the universe is only twelve
[12:03] Speaker 2: point five billion years old, then it should be physically
[12:06] Speaker 2: impossible to find a star that is thirteen billion years old.
[12:10] Speaker 2: Finding a thirteen billion year old star would immediately bust
[12:13] Speaker 2: the local expansion theory. At least as a universal constant
[12:16] Speaker 2: rule for all of space.
[12:18] Speaker 3: The theory is flawless. The challenge is the execution. The
[12:22] Speaker 3: Milky Way contains anywhere from one hundred to four hundred
[12:25] Speaker 3: billion stars. You are searching for the absolute oldest members
[12:28] Speaker 3: of a population that vast. You cannot merely point a
[12:31] Speaker 3: telescope and estimate the age of a star just by
[12:33] Speaker 3: looking at its color size on the main sequence.
[12:36] Speaker 2: Main sequence being the long stable middle age of a
[12:39] Speaker 2: star's life right like what our sun is doing right now.
[12:41] Speaker 3: Yes, for the vast majority of its existence, a star
[12:44] Speaker 3: is in hydrostatic equilibrium. Gravity is constantly trying to crush
[12:48] Speaker 3: the star inward, but the immense heat and pressure from
[12:51] Speaker 3: nuclear fusion in the core where it's fusing hydrogen into
[12:53] Speaker 3: helium creates an.
[12:55] Speaker 2: Outward pressure it pushes back.
[12:56] Speaker 3: Exactly as long as the star has hydrogen to burn,
[13:00] Speaker 3: those forces are perfectly balanced. It remains stable, its brightness
[13:04] Speaker 3: barely changes, and its temperature remains relatively constant for billions
[13:08] Speaker 3: of years.
[13:08] Speaker 2: So if I'm trying to find a star's exact age,
[13:11] Speaker 2: looking at it during this phase is basically useless. It's
[13:14] Speaker 2: like trying to tell the difference between a thirty year
[13:16] Speaker 2: old human and a thirty five year old human just
[13:18] Speaker 2: by looking at them sitting on a couch. The physical
[13:22] Speaker 2: changes over that five year span are too subtle to
[13:24] Speaker 2: measure accurately.
[13:26] Speaker 3: That's a great way to put it. To accurately data star.
[13:28] Speaker 3: You need to catch it at a moment of extreme
[13:30] Speaker 3: structural transition. And this brings us to the specific focus
[13:34] Speaker 3: of Banick's team, a very precise evolutionary stage known as
[13:38] Speaker 3: the subgiant phase.
[13:39] Speaker 2: Okay, walk us through the astrophysics of a subgiant. Why
[13:42] Speaker 2: do we care about this specific kind of awkward teenage
[13:45] Speaker 2: transition phase of a star? What is physically happening inside
[13:49] Speaker 2: the star that makes it a perfect clock.
[13:51] Speaker 3: A star enters the subgiant phase the very moment it
[13:54] Speaker 3: exhausts the hydrogen fuel in its core, the fusion engine
[13:58] Speaker 3: at the very center just shuts down because that outward
[14:01] Speaker 3: thermal pressure disappears. Gravity instantly starts winning the battle. Oh wow, Yeah,
[14:06] Speaker 3: the helium core begins to collapse in on itself under
[14:08] Speaker 3: its own weight.
[14:09] Speaker 2: That sounds catastrophic for the star.
[14:11] Speaker 3: It is a massive physical crisis. As the core collapses inward,
[14:15] Speaker 3: the extreme compression generates an immense amount of new heat.
[14:19] Speaker 3: This heat radiates outward and actually ignites a fresh shell
[14:23] Speaker 3: of unfused hydrogen that surrounds the dead core. So now
[14:27] Speaker 3: you have fusion happening in a shell around the core
[14:30] Speaker 3: rather than right in the center. Yes, shell burning, and
[14:34] Speaker 3: the energy generated by this new shell burning is so
[14:36] Speaker 3: intense that it forces the outer gaseous layers of the
[14:39] Speaker 3: star to rapidly expand and cool. The star begins to
[14:43] Speaker 3: balloon in size. It has left the stable main sequence
[14:46] Speaker 3: and is well on its way to becoming a massive
[14:48] Speaker 3: red giant. The subgiant phase is that incredibly brief vauldatle
[14:52] Speaker 3: window caught right in between.
[14:54] Speaker 2: But wait, I'm confused here. You're telling me a star
[14:57] Speaker 2: going through a massive structural crisis. Its core is collapsing
[15:02] Speaker 2: a new shell of fire, igniting its outer layers ballooning
[15:05] Speaker 2: out of control. That makes it easier to date. If
[15:08] Speaker 2: I'm trying to figure out how old a car is,
[15:10] Speaker 2: I don't photograph it while the engine block is actively exploding.
[15:13] Speaker 2: Doesn't that volatility make it a terrible clock?
[15:16] Speaker 3: It's a completely fair question. But the instability is exactly
[15:19] Speaker 3: the feature we need. Because the star's structure is changing
[15:22] Speaker 3: so rapidly during this phase, its surface temperature and its
[15:26] Speaker 3: overall luminosity, its true brightness changed dramatically over a relatively
[15:31] Speaker 3: short period of cosmic time.
[15:32] Speaker 2: Ah I see it's moving fast on.
[15:34] Speaker 3: The graph exactly When a star is on the stable
[15:37] Speaker 3: main sequence, its brightness changes at a glacial pace, but
[15:40] Speaker 3: during the subgiant phase, the luminosity becomes hypersensitive to the
[15:44] Speaker 3: star's precise mass and its age. By mapping the exact
[15:47] Speaker 3: surface temperature and the exact luminosity of a subgiant, astrophysicists
[15:52] Speaker 3: can run stellar evolution models backward with incredible precision. The
[15:56] Speaker 3: rapid physical changes give us a much tighter temporal window.
[16:00] Speaker 2: Subgiants are the perfect cosmic clocks because they are in
[16:03] Speaker 2: the middle of a highly visible, mathematically predictable growth spurt.
[16:07] Speaker 2: Now we need the data, and you can't just comb
[16:10] Speaker 2: through a few hundred stars to find the absolute oldest fossils.
[16:13] Speaker 2: The researchers pulled data from two of the most monumental
[16:16] Speaker 2: astronomical surveys ever conducted, Gaya and la Most.
[16:20] Speaker 3: These two surveys provide complementary data sets that are fundamentally
[16:24] Speaker 3: altering our understanding of the galaxy. Let's start with Gaya.
[16:28] Speaker 3: The Gaia Space Observatory is engaged in the most ambitious
[16:31] Speaker 3: astrometry mission in human history. It is precisely measuring the positions, distances,
[16:36] Speaker 3: and proper motions of over a billion stars.
[16:39] Speaker 2: Astrometry is essentially the three D mapping of the galaxy. Right, Yeah,
[16:43] Speaker 2: but how does it actually know how far away a
[16:45] Speaker 2: star is? Without using those standard candles we.
[16:47] Speaker 3: Talked about earlier, Guya uses a geometric principle called parallax.
[16:51] Speaker 3: As the Earth orbits the Sun, our vantage point in
[16:53] Speaker 3: space shifts by about one hundred and eighty six million
[16:55] Speaker 3: miles from one side of the orbit to the other.
[16:58] Speaker 2: Oh like, if you hold your thumb up in front
[17:00] Speaker 2: of your face and close your left eye, then open
[17:02] Speaker 2: it and close your right eye, your thumb appears to
[17:04] Speaker 2: jump back and forth against the background of the wall.
[17:07] Speaker 2: That's parallax.
[17:08] Speaker 3: Precisely, Gaya takes incredibly precise measurements of a star's position
[17:13] Speaker 3: against the background of distant, unmoving galaxies. Six months later,
[17:17] Speaker 3: it takes the measurement again from the other side of
[17:19] Speaker 3: the Solar System. By measuring that tiny apparent shift, which
[17:23] Speaker 3: is microscopically small equivalent to measuring the width of a
[17:27] Speaker 3: human hair from miles away, Guya can calculate the exact
[17:30] Speaker 3: distance to the star using simple trigonometry.
[17:33] Speaker 2: So Gaya gives us the perfect three D position and distance.
[17:36] Speaker 2: What does LAWMOS do. That's the large sky area multi
[17:40] Speaker 2: object fiber spectroscopic telescope. A total mouthful of an acronym.
[17:44] Speaker 3: Lams provides spectroscopy. If GUYA is the map, most is
[17:48] Speaker 3: the chemical laboratory. A spectroscope takes the light emitted from
[17:51] Speaker 3: a star and splits it into its component colors like
[17:54] Speaker 3: a highly advanced prism. But when you look at that
[17:56] Speaker 3: resulting rainbow, there are tiny dark lines.
[17:59] Speaker 2: Missing from the spectrum, the absorption lines.
[18:01] Speaker 3: Yes, different chemical elements in the star's atmosphere absorb very
[18:05] Speaker 3: specific wavelengths of light. By looking at which specific lines
[18:08] Speaker 3: of color are missing, astronomers get a literal chemical barcode.
[18:12] Speaker 3: LUMOS reads that barcode to tell us exactly what elements
[18:15] Speaker 3: a star is made of.
[18:16] Speaker 2: Which is absolutely crucial for dating a star. I want
[18:19] Speaker 2: to really dig into this because how does reading a
[18:22] Speaker 2: chemical barcode of a star actually tell you how old
[18:24] Speaker 2: it is?
[18:25] Speaker 3: This involves the concept of metallicity, and it requires a
[18:28] Speaker 3: really quick history of the elemental universe. In the immediate
[18:31] Speaker 3: aftermath of the Big Bang, during the first few hundred
[18:34] Speaker 3: million years, the universe consisted almost entirely of hydrogen and helium,
[18:38] Speaker 3: with just trace amounts of lithium. That was it.
[18:41] Speaker 2: The periodic table was basically just two blogs correct.
[18:44] Speaker 3: So the very first generation of stars, which astronomers call
[18:47] Speaker 3: population third stars, were forged purely out of this pristine
[18:51] Speaker 3: hydrogen and helium gas. Inside the extreme pressure of their cores,
[18:56] Speaker 3: these massive early stars fuse those basic elements into heavier
[19:00] Speaker 3: elements carbon, oxygen, nitrogen, all the way up to iron.
[19:03] Speaker 2: And when astronomers say metals, they don't just mean iron
[19:06] Speaker 2: or gold. In astrophysics, anything heavier than helium is lazily
[19:11] Speaker 2: referred to as a metal, right.
[19:12] Speaker 3: A charming quirk of astronomical jargon. Yes, oxygen, carbon, neon,
[19:17] Speaker 3: astronomers consider them all metals. Now, when those massive first
[19:22] Speaker 3: generation stars dyed in spectacular supernova explosions, they violently scattered
[19:27] Speaker 3: all those newly forged heavy metals out into the surrounding
[19:30] Speaker 3: interstellar gas clouds, so.
[19:32] Speaker 2: They seated the universe with the heavy stuff.
[19:34] Speaker 3: Exactly. The next generation of stars, population two stars formed
[19:37] Speaker 3: from those seated gas clouds, so they incorporated a small
[19:40] Speaker 3: amount of those heavier metals into their structure. They lived,
[19:43] Speaker 3: they died, They exploded, seating the universe with even more metals. Finally,
[19:47] Speaker 3: you get two population I stars like our own Sun,
[19:50] Speaker 3: which formed relatively recently from heavily enriched gas. Our Sun
[19:54] Speaker 3: has a high metallicity because it is essentially made from
[19:57] Speaker 3: the recycled, polluted douts of multiple dead star GA generations.
[20:00] Speaker 2: This is an incredible detective story. So if you were
[20:03] Speaker 2: hunting for an ancient cosmic fossil, you do not want
[20:06] Speaker 2: a star with a lot of carbon or iron. You
[20:08] Speaker 2: want a star that is fundamentally devoid of heavy metals,
[20:11] Speaker 2: because that proves it formed back when the universe was
[20:14] Speaker 2: incredibly young and chemically pure.
[20:16] Speaker 3: A true ancient fossil will have an exceedingly low metallicity.
[20:20] Speaker 3: By utilizing Lamost's chemical bar codes, Bannick's team could filter
[20:24] Speaker 3: their massive data set. They started with two hundred and
[20:27] Speaker 3: forty seven thousand, one hundred and three subgiant stars identified
[20:31] Speaker 3: by Gaya and Lamost, but they needed to brutally sift
[20:34] Speaker 3: through this catalog to ensure absolute purity.
[20:37] Speaker 2: They executed a massive purge of the data. They systematically
[20:40] Speaker 2: removed any star whose chemical bar code didn't perfectly match
[20:43] Speaker 2: the expected low metallicity signature of an ancient star. But
[20:46] Speaker 2: they didn't just stop at chemistry, did they. They applied
[20:48] Speaker 2: multiple layers of quality cuts.
[20:50] Speaker 3: They did. They removed stars that had anomalous velocity readings,
[20:55] Speaker 3: stars were parallax data from Gaya had a high margin
[20:57] Speaker 3: of error, and stars that might be part of binary
[21:00] Speaker 3: systems where gravitational interactions could completely skew the numinosity readings.
[21:04] Speaker 3: They even ran cross checks using completely independent statistical methods
[21:08] Speaker 3: to verify the integrity of the data points.
[21:11] Speaker 2: By the end of this grueling filtration process, that initial
[21:14] Speaker 2: massive haul of two hundred and forty seven one hundred
[21:17] Speaker 2: and three stars was brutally whittled down to a final
[21:21] Speaker 2: verified sample of one hundred and fifty five thousand, six
[21:24] Speaker 2: hundred stars. I just want to pause and appreciate the
[21:27] Speaker 2: immense rigor of that. They intentionally threw out nearly one
[21:30] Speaker 2: hundred thousand perfectly good data points simply because those points
[21:34] Speaker 2: had a tiny fraction of a percent of uncertainty attached
[21:36] Speaker 2: to them.
[21:36] Speaker 3: Right, they had to be serious.
[21:37] Speaker 2: They sacrificed enormous raw quantity to guarantee that the remaining
[21:41] Speaker 2: one hundred and fifty five thousand, six hundred stars were structurally, chemically,
[21:44] Speaker 2: and physically bulletproof.
[21:45] Speaker 3: It is a true masterclass in data hygiene. When your
[21:48] Speaker 3: conclusion threatens to rewrite the fundamental age of the cosmos,
[21:51] Speaker 3: your foundation cannot have a single crack in it.
[21:54] Speaker 2: So the foundation is set. We have one hundred and
[21:56] Speaker 2: fifty five thousand, six hundred meticulously verified sub giant stars
[22:01] Speaker 2: functioning as hyper accurate cosmic clocks, all guaranteed to be
[22:04] Speaker 2: low metallicity fossils from the dawn of time. The team
[22:07] Speaker 2: analyzes the exact luminosity, surface temperature, and chemical composition of
[22:12] Speaker 2: every single one. What time do the clocks actually say
[22:14] Speaker 2: it is?
[22:15] Speaker 3: After running the stellar evolution models backward on this pristine sample,
[22:18] Speaker 3: the team reached a highly definitive conclusion. The oldest long
[22:22] Speaker 3: lived star in the Milky Way galaxy, based on this
[22:25] Speaker 3: vast census, is approximately thirteen point seven three billion years old.
[22:29] Speaker 2: Thirteen point seven three billion years old. That number alone
[22:32] Speaker 2: feels like a massive victory for the early Universe tape measure.
[22:35] Speaker 2: But before we just declare a winner, how tight is
[22:37] Speaker 2: the margin of error on that number? Is it thirteen
[22:39] Speaker 2: point seven three billion, give or take a billion years?
[22:41] Speaker 3: The precision is what makes the study so compelling. The
[22:44] Speaker 3: calculated age comes with an incredibly tight uncertainty window roughly
[22:49] Speaker 3: plus point one eight or minus point one five billion years.
[22:52] Speaker 2: That's nothing.
[22:53] Speaker 3: We are talking about a margin of error of barely
[22:55] Speaker 3: over one hundred million years on a timescale of nearly
[22:57] Speaker 3: fourteen billion.
[22:58] Speaker 2: Okay, so the oldest in the Milky Way is definitively
[23:02] Speaker 2: thirteen point seventy three billion years old. But looping back
[23:06] Speaker 2: to the minimum age principle we discussed earlier, the oldest
[23:08] Speaker 2: star is not the exact age of the universe itself.
[23:12] Speaker 2: The universe had to exist for some amount of time
[23:14] Speaker 2: before this star could physically form.
[23:16] Speaker 3: This is a critical cosmological phase known as the Dark Ages.
[23:20] Speaker 3: When the Big Bang occurred, space expanded and the plasma cooled,
[23:23] Speaker 3: which gave us the cosmic microwave background, But the universe
[23:26] Speaker 3: was completely devoid of stars. It was a vast, pitch
[23:30] Speaker 3: black expanse filled almost entirely with neutral hydrogen gas, just.
[23:34] Speaker 2: Dark clouds of gas expanding into nothingness. How long did
[23:38] Speaker 2: it take for gravity to actually do something with that gas?
[23:41] Speaker 3: It takes an immense amount of time for gravity to
[23:43] Speaker 3: overcome the kinetic energy of the expanding gas, gravity has
[23:46] Speaker 3: to slowly pull microscopic clumps of hydrogen together. The clumps
[23:50] Speaker 3: gain mass, their gravitational pull increases, they draw in more gas.
[23:53] Speaker 3: The pressure builds, the core temperature rises to millions of degrees,
[23:56] Speaker 3: until finally the density is so extreme that clear fusion ignites.
[24:01] Speaker 2: The first light turns on. How long does our standard
[24:04] Speaker 2: model say that process took from the moment of the
[24:07] Speaker 2: Big Bang?
[24:07] Speaker 3: Based on the physics of gas dynamics and gravitational collapse,
[24:11] Speaker 3: specifically calculating what's called the genes mass, the most robust
[24:15] Speaker 3: cosmological models assume this dark age period lasted roughly two
[24:19] Speaker 3: hundred million years or zero point two billion years.
[24:22] Speaker 2: All right, let's do the final arithmetic. We take the
[24:25] Speaker 2: definitive age of our oldest subgiant fossil thirteen point seven
[24:28] Speaker 2: three billion years. We add the two hundred million years
[24:32] Speaker 2: of the dark age is required for that star's hydrogen
[24:34] Speaker 2: gas to coalace and ignite. Thirteen point seventy three plus
[24:38] Speaker 2: zero point two gives us roughly thirteen point nine billion years.
[24:41] Speaker 3: Which represents a monumental validation of the standard Lambda CDM model.
[24:46] Speaker 3: Thirteen point nine billion years aligns almost perfectly with the
[24:49] Speaker 3: thirteen point eight billion year age predicted by analyzing the
[24:52] Speaker 3: cosmic microwave background.
[24:53] Speaker 2: It is stunning. The container is thirteen point eight billion
[24:56] Speaker 2: years old, and we know this because the ancient subgiant
[24:58] Speaker 2: fossil sitting right here in our own galaxy demands a
[25:01] Speaker 2: timeline of nearly thirteen point eight billion years to exist.
[25:04] Speaker 2: This completely decimates the local expansion theory as a universal baseline,
[25:07] Speaker 2: doesn't it. Oh Absolutely like if the local measurements of
[25:10] Speaker 2: Cepheid's and supernovae were universally true and the universe was
[25:14] Speaker 2: only twelve point five billion years old, these subgiant stars
[25:18] Speaker 2: simply could not exist. They would be older than time itself,
[25:22] Speaker 2: which breaks every law of causality.
[25:24] Speaker 3: It reinforces the early universe measurements profoundly. The team also
[25:29] Speaker 3: noted that this thirteen point nine billion year figure perfectly
[25:32] Speaker 3: aligns with prior independent studies that attempted to date globular
[25:36] Speaker 3: clusters right, which are incredibly dense spherical collections of millions
[25:40] Speaker 3: of very old stars orbiting the galactic core. Multiple independent
[25:45] Speaker 3: physical phenomena, the ancient microwave afterglow, the dating of globular clusters,
[25:50] Speaker 3: and now the precise stellar modeling of one hundred and
[25:53] Speaker 3: fifty five thousand subgiants are all converging on the exact
[25:56] Speaker 3: same chronological baseline.
[25:57] Speaker 2: Okay, as much as I want to celebrate this perfectly
[25:59] Speaker 2: new conclusion, true scientific rigor isn't about slapping a bow
[26:03] Speaker 2: and a result and walking away. We have to violently
[26:05] Speaker 2: poke holes in this. If I'm a skeptic advocating for
[26:07] Speaker 2: the younger twelve point five billion year universe, ye, how
[26:10] Speaker 2: do I attack this thirteen point seventy three billion year
[26:13] Speaker 2: stellar age. The research team must have published their own uncertainties.
[26:16] Speaker 3: They absolutely did. Transparency regarding the limits of measurement is
[26:20] Speaker 3: the hallmark of robust science. The team explicitly codified five
[26:24] Speaker 3: specific sources of potential error, five pillars of uncertainty that
[26:28] Speaker 3: could systematically shift their final calculation.
[26:31] Speaker 2: Let's put these pillars on trial. I really want to
[26:33] Speaker 2: challenge them. Number one on their list is sample size. Now,
[26:35] Speaker 2: they started with two hundred and forty seven thousand stars
[26:38] Speaker 2: and whittled it down to one hundred and fifty five thousand,
[26:40] Speaker 2: six hundred. That is a massive data set. Why is
[26:43] Speaker 2: sample size still a massive pillar of uncertainty?
[26:46] Speaker 3: Because the Milky Way galaxy contains up to four hundred
[26:48] Speaker 3: billion stars. Even a pristine sample of one hundred and
[26:51] Speaker 3: fifty five thousand stars is a microscopic fraction of the
[26:54] Speaker 3: total population. The statistical reality is that they may have
[26:58] Speaker 3: simply missed an older outlier. Perhaps the true oldest star
[27:02] Speaker 3: is sitting in a quadrant of the galaxy heavily obscured
[27:04] Speaker 3: by interstellar dust, completely invisible to the Gaya and loamost sensors.
[27:09] Speaker 2: So the true age could theoretically be even older, pushing
[27:11] Speaker 2: the thirteen point seventy three number higher. What about pillar
[27:14] Speaker 2: number two quality cuts? This refers to the great sifting,
[27:17] Speaker 2: and we talk about removing the high metallicity stars and
[27:20] Speaker 2: the binary systems. How does making the data cleaner introduce uncertainty.
[27:24] Speaker 3: Because every time you define a parameter to cut data,
[27:27] Speaker 3: you are imposing a human made threshold on nature. For instance,
[27:31] Speaker 3: determining the exact cutoff point for what constitutes low metallicity
[27:35] Speaker 3: is a theoretical decision. If they set that threshold slightly
[27:39] Speaker 3: too high or slightly too low, they could accidentally exclude
[27:42] Speaker 3: older stars or falsely include younger stars, skewing the overall
[27:46] Speaker 3: age distribution.
[27:47] Speaker 2: I see the scalpel might have been a millimeter off.
[27:50] Speaker 2: Moving to the third uncertainty stellar model assumptions, this one
[27:55] Speaker 2: seems like a huge vulnerability. We're relying entirely on complex
[27:59] Speaker 2: computer simulations of how the cores of subgiant stars collapse
[28:02] Speaker 2: and ignite hydrogen shells. What if our fundamental understanding of
[28:06] Speaker 2: subgiant astrophysics is just flawed. What if the fusion mechanics
[28:10] Speaker 2: operate slightly differently under extreme low metallicity conditions.
[28:14] Speaker 3: It is a very valid critique. If our thermal dynamic
[28:16] Speaker 3: equations modeling the core collapse phase have a blind spot,
[28:20] Speaker 3: then our physical clock is inherently biased. The star might
[28:23] Speaker 3: be ticking through its subgiant phase five percent faster or
[28:26] Speaker 3: slower than our algorithms assume, which would.
[28:28] Speaker 2: Throw off the entire age calculation. Okay, fourth on their
[28:31] Speaker 2: list star formation timescales. This targets that two hundred million
[28:35] Speaker 2: year buffer we added for the dark ages. Let me
[28:37] Speaker 2: push back on this. We assumed it took two hundred
[28:39] Speaker 2: million years for the first gas clouds to ignite. But
[28:42] Speaker 2: what if the early universe was vastly denser than we
[28:45] Speaker 2: think and gravity worked much faster. What if the population
[28:49] Speaker 2: through stars formed in just fifty million years.
[28:52] Speaker 3: The timeframe of early star formation is highly debated because
[28:55] Speaker 3: we cannot directly observe the first generation of stars. We
[28:58] Speaker 3: can only model their formation view fluid dynamics and dark
[29:01] Speaker 3: matter clustering theories. If the first star is ignited much faster,
[29:05] Speaker 3: say in fifty million years, it reduces the total age
[29:08] Speaker 3: of the universe. Conversely, if it took four hundred million
[29:11] Speaker 3: years for gravity to overcome the kinetic energy of the
[29:13] Speaker 3: early plasma, the universe must.
[29:15] Speaker 2: Be older, and the final pillar of uncertainty theoretical predictions.
[29:20] Speaker 2: This feels a bit like a catch all safety net.
[29:22] Speaker 3: It acknowledges the overarching reality that our macroscopic cosmological frameworks,
[29:27] Speaker 3: including the lambasidim model itself, are merely mathematical approximations of reality.
[29:32] Speaker 3: They are not reality itself.
[29:33] Speaker 2: Okay, so they've listed these five major vulnerabilities. From a
[29:37] Speaker 2: skeptics point of view, it sounds like this study is
[29:39] Speaker 2: built on a very shaky foundation of assumptions.
[29:42] Speaker 3: Here is where the brilliance of their self analysis comes
[29:45] Speaker 3: into play. The team mathematically quantified the impact of each
[29:49] Speaker 3: of these uncertainties. They calculated that every single one of
[29:53] Speaker 3: these five factors limits the overall precision by roughly point
[29:57] Speaker 3: one five to point two gidde years. A flaw in
[30:01] Speaker 3: any one of these pillars only shifts the final age
[30:04] Speaker 3: by about one hundred and fifty to two hundred million years.
[30:06] Speaker 2: Oh, that completely flips the narrative. That means their methodology
[30:10] Speaker 2: is incredibly robust. It's not relying on one massive, fragile assumption.
[30:14] Speaker 2: It's balancing several small, highly constrained variables.
[30:17] Speaker 3: Precisely, they noted that because the uncertainties are distributed evenly
[30:21] Speaker 3: across these five factors, no single magical improvement in observation
[30:25] Speaker 3: technology or theoretical physics which sharply refine the result overnight.
[30:28] Speaker 2: And here is the fatal blow to the local expansion theory.
[30:33] Speaker 2: Even if you stack all five of these uncertainties against
[30:36] Speaker 2: the thirteen point eight billion year model, even if you
[30:39] Speaker 2: push every single margin of error to its absolute maximum
[30:42] Speaker 2: limit to force a younger calculation, the estimated age of
[30:46] Speaker 2: the universe still lands notably higher than twelve point nine
[30:48] Speaker 2: billion years. The absolute floor of reality holds firm.
[30:52] Speaker 3: The universe simply cannot be twelve point five billion years
[30:54] Speaker 3: old if it contains a massive, statistically unassailable population of
[30:59] Speaker 3: subgiant stars whose physical structures demand they are at least
[31:02] Speaker 3: thirteen point five billion years old. The astrophysics of the
[31:05] Speaker 3: stars forbid it.
[31:06] Speaker 2: The Early Universe tape measure was right, the universe is
[31:09] Speaker 2: about thirteen point eight billion years old. But this leaves
[31:12] Speaker 2: us with a galaxy sized elephant in the room. If
[31:14] Speaker 2: the universe is definitively thirteen point eight billion years old,
[31:17] Speaker 2: and the land of CDM model is fundamentally correct about
[31:20] Speaker 2: the early universe, why on Earth do our local measurements
[31:23] Speaker 2: of Cepheid's and supernovae insist that the space right around
[31:26] Speaker 2: us is expanding nine percent faster? What is actually causing
[31:29] Speaker 2: the Hubble tension.
[31:30] Speaker 3: This is where the implications of Bannock's stellar census force
[31:34] Speaker 3: us into incredibly bizarre territory. Because this study mathematically demands
[31:39] Speaker 3: an older universe, it allows us to completely rule out
[31:42] Speaker 3: an entire category of theoretical physics. For years, theorists proposed
[31:47] Speaker 3: that the Hubble tension was caused by early Universe new physics.
[31:51] Speaker 3: They suggested some exotic, undiscovered energy field was present immediately
[31:55] Speaker 3: after the Big Bang, altering the initial expansion rate universally.
[31:59] Speaker 2: But because these agent stars exist, we know the early
[32:02] Speaker 2: universe must have behaved exactly as the LAMB to CDM
[32:05] Speaker 2: model predicted. If weird new physics was universally accelerating expansion
[32:10] Speaker 2: from day one, the universe would have reached its current
[32:12] Speaker 2: size far too quickly, the timeline would be compressed, and
[32:15] Speaker 2: those thirteen point seven billion year old subgiants just wouldn't
[32:19] Speaker 2: have had time to form exactly.
[32:21] Speaker 3: The existence of the fossils proves the early climate was stable,
[32:24] Speaker 3: so the research team pivots entirely. If the early universe
[32:27] Speaker 3: was behaving normally. They favor what is called a late universe.
[32:30] Speaker 2: Solution, meaning the rules of the game changed recently.
[32:33] Speaker 3: It posits that whatever fundamental mechanism is causing the Hubble tension,
[32:37] Speaker 3: it is a relatively recent phenomenon. In cosmic history. The
[32:41] Speaker 3: universal rate of expansion hasn't been a smooth constant. Something
[32:45] Speaker 3: has actively altered it, perhaps only within the last few
[32:48] Speaker 3: billion years.
[32:50] Speaker 2: The idea that the very fabric of space and time
[32:52] Speaker 2: is behaving differently today than it did for the first
[32:55] Speaker 2: ten billion years of its existence is profoundly unsettling. The
[33:00] Speaker 2: researchers didn't stop at a late time universal shift. They
[33:03] Speaker 2: proposed a wildly different structural alternative, and frankly, this hypothesis
[33:08] Speaker 2: is even more staggering. They suggest the hubble tension might
[33:11] Speaker 2: be a purely local illusion caused by a massive local
[33:14] Speaker 2: under density.
[33:15] Speaker 3: The void hypothesis.
[33:16] Speaker 2: Yes, okay, let's build a visual for this. Imagine you
[33:19] Speaker 2: are driving on a massive, densely packed super highway. You
[33:22] Speaker 2: are completely boxed in by thousands of heavy semi trucks
[33:25] Speaker 2: and cars. The combined mass and traffic flow force everyone
[33:28] Speaker 2: to move at a grinding, steady fifty five miles per hour.
[33:31] Speaker 2: That dense traffic represents the universe expanding normally, where the
[33:34] Speaker 2: gravitational pull of all the mass in the universe constantly
[33:37] Speaker 2: acts as a break on the expansion of space.
[33:39] Speaker 3: A perfect analogy for the lambda CDM balance.
[33:43] Speaker 2: But suddenly, your specific lane clears out, you break through
[33:46] Speaker 2: the pack. The heavy semi trucks surrounding you vanish, and
[33:50] Speaker 2: you find yourself in a massive, empty stretch of open road,
[33:54] Speaker 2: with nothing boxing you in and no traffic dictating your speed.
[33:57] Speaker 2: You naturally slam on the gas and accelerate to eighty
[34:00] Speaker 2: miles per hour. You feel like you are moving much
[34:02] Speaker 2: faster than the rest of the highway, But it is
[34:04] Speaker 2: only because your immediate surroundings are totally empty.
[34:07] Speaker 3: This is precisely the physical mechanics of the void hypothesis.
[34:11] Speaker 3: If our local cosmic neighborhood, the Milky Way galaxy and
[34:14] Speaker 3: the local group of galaxies surrounding us, is actually situated
[34:17] Speaker 3: deep inside a giant cosmic void, it drastically alters our
[34:21] Speaker 3: local physics. A void is a massive region of space
[34:24] Speaker 3: with a remarkably low density of matter compared to the
[34:27] Speaker 3: universal average.
[34:28] Speaker 2: Less matter phyfically means less gravity.
[34:31] Speaker 3: Exactly, gravity is the fundamental breaking mechanism countering the expansion
[34:35] Speaker 3: of the universe. If we happen to live in an
[34:38] Speaker 3: immense bubble that contains significantly fewer galaxies, less gas, and
[34:42] Speaker 3: critically less cold dark matter, there is simply less local
[34:46] Speaker 3: gravity to pull inward. Without that gravitational anchor, the space
[34:50] Speaker 3: immediately inside this void would literally expand outward faster than
[34:54] Speaker 3: the space and denser regions of the universe.
[34:56] Speaker 2: So when our telescopes measure the Cepheide standard candles in
[34:59] Speaker 2: the exploding supernovae right around us, they are objectively moving
[35:03] Speaker 2: away nine percent faster. Our local tape measure isn't broken.
[35:07] Speaker 2: Our astronomers haven't made a mistake. They are accurately measuring
[35:10] Speaker 2: a local anomaly. It is the equivalent of trying to
[35:13] Speaker 2: calculate the average global temperature of the Earth by only
[35:16] Speaker 2: using the thermometer mounted inside a running sauna. The instrument
[35:19] Speaker 2: is giving you a perfectly accurate reading of its immediate environment,
[35:22] Speaker 2: but a terribly distorted reading of the entire planet.
[35:25] Speaker 3: Which brings up the KBC Void. Some astronomers have actively
[35:29] Speaker 3: hypothesized the existence of a massive local under density known
[35:33] Speaker 3: as the KBC Void, named after Keenan, Barger and Cowie,
[35:37] Speaker 3: who proposed it in twenty thirteen. They suggested we might
[35:41] Speaker 3: be sitting near the center of a roughly spherical region
[35:43] Speaker 3: of space that is vastly larger and emptier than standard
[35:47] Speaker 3: cosmological models predict.
[35:49] Speaker 2: If the void hypothesis is true, it is an incredible
[35:52] Speaker 2: resolution to the crisis. We don't need to invent exotic
[35:55] Speaker 2: new physics to fix the math. We don't have to
[35:57] Speaker 2: throw away the LAMB to CDM model. We just have
[36:00] Speaker 2: to accept that our neighborhood is weird.
[36:01] Speaker 3: But excepting that our neighborhood is weird, violates one of
[36:04] Speaker 3: the most sacred philosophical pillars of astronomy, the Copernican principle.
[36:08] Speaker 2: Explain the Copernican principle in this context, because I think
[36:11] Speaker 2: this is where the physics bleeds into pure philosophy.
[36:14] Speaker 3: Ever since Nicholas Copernicus proved the Earth was not the
[36:17] Speaker 3: center of the Solar System, science has operated on the
[36:20] Speaker 3: assumption that humanity does not occupy a special, privileged, or
[36:24] Speaker 3: highly unusual place in the universe. We assume our vantage
[36:27] Speaker 3: point is completely average when we look out from the
[36:30] Speaker 3: Milky Way. We assume the physics we observe locally applies
[36:33] Speaker 3: uniformly to the rest of the cosmos.
[36:35] Speaker 2: But the void hypothesis violently shatters that assumption. It suggests
[36:40] Speaker 2: that out of all the incredibly dense, bustling galactic superclusters
[36:43] Speaker 2: we could have evolved in, we just so happened to
[36:46] Speaker 2: spawn in the cosmic equivalent of a deserted cul de sac.
[36:50] Speaker 2: Our view of the universe's expansion is artificially inflated, purely
[36:53] Speaker 2: because of our deeply unusual zip code.
[36:56] Speaker 3: It is a humbling realization. Our localized measurements of reality
[36:59] Speaker 3: are perfectly precise, yet entirely unrepresentative of the cosmic hole.
[37:03] Speaker 2: It's an incredible synthesis of disciplines. Let's just step back
[37:07] Speaker 2: and trace the arc of this journey. We started with
[37:10] Speaker 2: a fundamental crisis threatening modern astrophysics, two tape measures giving
[37:15] Speaker 2: two wildly incompatible ages for reality itself, threatening a missing
[37:20] Speaker 2: billion year era of time. To solve this, astronomers didn't
[37:23] Speaker 2: launch a bigger telescope to look further back in time.
[37:26] Speaker 2: They looked closely at the ancient low metallicity subgiant stars
[37:30] Speaker 2: caught in their volatile transitional phase right here in the
[37:33] Speaker 2: Milky Way.
[37:34] Speaker 3: By understanding the delicate thermodynamics of a collapsing stellar core,
[37:38] Speaker 3: they transformed these one hundred and fifty five thousand subgiants
[37:41] Speaker 3: into hyper precise temporal checkpoints. They verified the existence of
[37:46] Speaker 3: hard cosmic floor, definitively proving the universe is roughly thirteen
[37:49] Speaker 3: point eight billion years old, entirely vindicating the early universe
[37:53] Speaker 3: microwave background measurements.
[37:54] Speaker 2: It proves that sometimes to understand the sheer vastness of
[37:57] Speaker 2: the cosmos, we don't need to look billions of light
[37:59] Speaker 2: years away. Sometimes the most profound answers are encoded in
[38:02] Speaker 2: the chemical barcodes of the ancient relics float and right
[38:05] Speaker 2: in our own backyard.
[38:06] Speaker 3: But solving one mystery has fully exposed another. The hubble
[38:10] Speaker 3: tension remains a reality of observation, but its fundamental nature
[38:13] Speaker 3: has shifted. It is no longer an existential debate about
[38:17] Speaker 3: the age of the universe. It is a debate about
[38:19] Speaker 3: the recent structural behavior of our localized.
[38:21] Speaker 2: Space, which leaves us with a truly lingering, almost unsettling thought.
[38:26] Speaker 2: If this hubble tension is indeed caused by our solar
[38:29] Speaker 2: system existing in a massive cosmic void, a localized bubble
[38:33] Speaker 2: of under density, where the physical rules of expansion are
[38:36] Speaker 2: slightly tweaked just for us, it means our immediate perspective
[38:40] Speaker 2: on reality is fundamentally skewed simply by where we are standing.
[38:44] Speaker 2: If our very mathematical measure of space and time is
[38:46] Speaker 2: distorted because of the specific empty neighborhood we happen to occupy,
[38:50] Speaker 2: what else about our human viewpoint, our scientific models, or
[38:52] Speaker 2: our daily lives is completely distorted simply because we assume
[38:56] Speaker 2: our local experience represents universal truth.

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