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