Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Imagine looking up at the night sky, I mean really
Speaker 2: looking and asking that huge question, what's the ultimate fate
Speaker 2: of well.
Speaker 3: Everything, It's the biggest question really.
Speaker 2: For decades, the answer seemed pretty set, if a bit
Speaker 2: uh chilling. The universe is expanding faster and faster.
Speaker 3: Right heading towards this sort of cold, dark, lonely end,
Speaker 3: driven by this mysterious anti gravity.
Speaker 2: Stuff dark energy. Yeah, but what if what if the
Speaker 2: very measurements that led us there had a kind of
Speaker 2: hidden flaw, a systematic bias. What if everything we thought
Speaker 2: we knew about the future of the cosmos is suddenly well,
Speaker 2: maybe wrong.
Speaker 3: That's exactly what we're digging into today.
Speaker 2: We are diving into a challenge to a cosmological idea
Speaker 2: that's been around for what thirty years?
Speaker 3: About that?
Speaker 2: Yeah, and it's a challenge so deep it basically pulls
Speaker 2: the rugout from under the discovery that won the twenty
Speaker 2: eleven Nobel Prize in physics.
Speaker 3: It really does question that foundation.
Speaker 2: There's this new, really meticulously researched study suggesting the universe
Speaker 2: isn't speeding up anymore. Might have actually switched gears and
Speaker 2: started slowing down right now today.
Speaker 3: Which is a huge turnaround.
Speaker 2: So our mission today is to unpack these frankly remarkable findings.
Speaker 2: It all seems to hinge on correcting a subtle, maybe
Speaker 2: but absolutely critical, systematic bias in one of astronomy's most
Speaker 2: trusted tools.
Speaker 3: The type IA supernova, the standard candle exactly.
Speaker 2: And this isn't just tweaking a number here or there.
Speaker 2: This could fundamentally you write the cosmic timeline and maybe
Speaker 2: change our whole understanding of the dominant force in the universe.
Speaker 3: It's fascinating because of the sheer scale of what might
Speaker 3: need reorienting. We're talking about dark energy, yeah, Mysteryes, this
Speaker 3: unseen influence that makes up what roughly seventy percent of
Speaker 3: everything in the universe. Our standard picture, the Lambda cold
Speaker 3: dark matter model or SCDM for short. It's built on
Speaker 3: one massive assumption that dark energy is a cosmological constant.
Speaker 3: Its strength never changes, it's just there, uniformly dense through
Speaker 3: space and.
Speaker 2: Time like a background hum kind of.
Speaker 3: But now we've got evidence, pretty robust evidence, actually suggesting
Speaker 3: that this foundational pillar might be seriously flawed. Well, the
Speaker 3: analysis shows that what we interpreted purely as a cosmological effect,
Speaker 3: this accelerated expansion, might actually be tangled up with stellar astrophysics,
Speaker 3: specifically how stars age.
Speaker 2: So not just space stretching, but the stars themselves exactly.
Speaker 3: It means our note isn't just evolving, it's being fundamentally reoriented.
Speaker 3: By looking really carefully at the data we already have,
Speaker 3: you really can't overstate the implications if you start questioning
Speaker 3: the gold standard of cosmic measurement like this.
Speaker 2: Okay, let's definitely unpack that ranting cosmology first, because to
Speaker 2: grasp how big this challenge is, we need to understand
Speaker 2: the foundation it's questioning. Let's go back to the mid
Speaker 2: nineties and that incredible discovery announced in ninety eight.
Speaker 3: Right before then, the expectation was pretty straightforward. You have
Speaker 3: the Big Bang, this initial huge expansion.
Speaker 2: Seventeen pointy eight billion years ago roughly right.
Speaker 3: And then gravity, you know, the poll of all the matter,
Speaker 3: should have been putting the brakes on, slowing the expansion down.
Speaker 2: And for billions of years that seemed to be the case.
Speaker 3: It was gravity was in charge. The universe was sort
Speaker 3: of coasting, decelerating gradually.
Speaker 2: But then something changed exactly.
Speaker 3: Two independent teams of astronomers, the Supernova Cosmology Project and
Speaker 3: the Heisy Supernova Search Team. They were using distance measurements
Speaker 3: looking way back in time, billions of light years away.
Speaker 2: Seeing the universe as it was long.
Speaker 3: Ago, precisely, and their results were shocking. Around nine billion
Speaker 3: years after the Big Bang, something flipped. The slowdown stopped,
Speaker 3: and the expansion actually started to speed up again.
Speaker 2: Whoa Okay, yeah, whoa.
Speaker 3: Was about right. That accelerating push needed an explanation, you know.
Speaker 3: To overcome gravity's constant pull, you needed something pushing back,
Speaker 3: a repulsive force, some kind of inherent energy of space itself.
Speaker 2: And that's what God called dark energy.
Speaker 3: That's it. It acts like this anti gravity, pushing distant
Speaker 3: galaxies away faster and faster. And this discovery, based on
Speaker 3: using these distant supernovae as cosmic mile markers, was so revolutionary. Well,
Speaker 3: it deservedly won the twenty eleven Nobel Prize.
Speaker 2: And really cement to the idea that the universe was
Speaker 2: accelerating and would just keep doing so forever.
Speaker 3: Maybe that became the standard picture and the.
Speaker 2: Key measuring tool for all of this was the Type
Speaker 2: EA supernova. Why were they considered so reliable? Why the
Speaker 2: standard cand well.
Speaker 3: They were thought to be Anyway, there, your idea is
Speaker 3: pretty neat. Type A supernovae happen in binary star systems.
Speaker 3: You have a white dwarf, which is a dense remnant
Speaker 3: of a star like our Sun, and it's pulling material
Speaker 3: off its companion star. It accretes mass bit by bit
Speaker 3: until it hits a very specific limit, the Chanda Sakar limit.
Speaker 3: It's called about one point four times the mass of
Speaker 3: our Sun. When the white dwarf reaches that exact mass,
Speaker 3: it becomes unstable and just boom, catastrophically detonates.
Speaker 2: Uh Okay, So the trigger is always the same mass.
Speaker 3: That was the crucial assumption. Because the explosion mechanism was
Speaker 3: thought to be identical every time hitting that specific critical mass,
Speaker 3: astronomers assume these explosions would have a highly uniform intrinsic brightness,
Speaker 3: their absolute magnitude would always be the same, right.
Speaker 2: Like, no, you have a perfect one hundred white light.
Speaker 3: Bulb exactly if you know it's true wattage, it's intrinsic brightness.
Speaker 3: You can figure out how far away it is just
Speaker 3: by seeing how dim it looks from Earth.
Speaker 2: The dimmer it appears the farther away. It must be
Speaker 2: simple physics, That was the prince.
Speaker 3: So when astronomers looked at these really distant type Ia supernovae,
Speaker 3: the ones with high redshift that exploded billions of years ago,
Speaker 3: they found they were significantly dimmer than you'd expect if
Speaker 3: the universe was just decelerating or even.
Speaker 2: Coasting, dimmer than they should have been, right.
Speaker 3: And the interpretation of that unexpected dimness was purely cosmological,
Speaker 3: meaning The thinking went like this, They looked dimmer mostly
Speaker 3: because space itself is expanding faster, carrying these distant galaxies
Speaker 3: away from us more quickly.
Speaker 2: So the light gets stretched out more diluted by the
Speaker 2: accelerating expansion between us and them.
Speaker 3: Precisely, more distance, more acceleration meant more dimness, and that
Speaker 3: required some kind of constant, pervasive repulsive force pushing everything apart.
Speaker 2: Dark energy the cosmological.
Speaker 3: Constant exactly, and that's how we landed on the consensus
Speaker 3: view the MLCDM model. The universe is still accelerating today
Speaker 3: and dark energy is constant. Its strength doesn't change.
Speaker 2: If we get technical for a second.
Speaker 3: In technical term, yeah, the equation of state parameter for
Speaker 3: dark energy, often written as W is a seam to
Speaker 3: be exactly minus one.
Speaker 2: W eagles minus one, right.
Speaker 3: And W reals one means the dark energy density is constant.
Speaker 3: It behaves exactly like Einstein's cosmological constant Lambda. And that
Speaker 3: constancy that W egles one is the core pillar that's
Speaker 3: now being seriously challenged.
Speaker 2: Okay, that brings us right to the new evidence, and
Speaker 2: this is where the science seems to be finding cracks
Speaker 2: in that seemingly perfect standard candle. This work comes from
Speaker 2: Professor Young Wook Lee and his team at yonse University, published.
Speaker 3: Recently yes in Monthly Notices of the Royal Astronomical Society, and.
Speaker 2: Their core idea is well, it sounds simple, but the
Speaker 2: implications are huge. Type IA supernovae are not perfect standard candles.
Speaker 2: Their brightness is strongly systematically affected by the age and crucially,
Speaker 2: the chemical makeup the metallicity of the stars that blew up,
Speaker 2: and that has nothing to do with how far away
Speaker 2: they are.
Speaker 3: This is the subtle point that potential changes the whole
Speaker 3: cosmic calculation. See Astronomers already knew supernova weren't perfectly identical.
Speaker 3: They applied corrections luminosity standardizations based on how quickly the
Speaker 3: light curve faded, the stretch and its color.
Speaker 2: Right, trying to iron out the small differences exactly.
Speaker 3: But the Yonce team showed that even after you apply
Speaker 3: those standard corrections, something else still matters a lot, the
Speaker 3: underlying stellar population, the age and the metallicity, the amount
Speaker 3: of heavy elements in the stars that eventually became that
Speaker 3: white dwarf.
Speaker 2: Okay, so explain the systematic bias. How does age or
Speaker 2: metallicity mess with the brightness.
Speaker 3: Well, let's break it down. Think about the early universe.
Speaker 3: Stars formed back then, and stars in younger star forming
Speaker 3: regions today tend to be metal poor. They have fewer
Speaker 3: elements heavier than hydrogen and helium. Okay, The finding is this,
Speaker 3: When a type EA supernova comes from one of these
Speaker 3: younger metal poor stellar populations, that supernova appears systematically fainter,
Speaker 3: intrinsically dimmer than its cousins from older populations. And conversely, conversely,
Speaker 3: supernovae that come from older, more metal rich populations like
Speaker 3: you'd find in more evolve galaxies appear systematically brighter.
Speaker 2: Hang on, why why would the amount of metal or
Speaker 2: the age of the system change the brightness of an
Speaker 2: explosion that's supposed to be triggered at exactly the same
Speaker 2: mass that one point four solar mass limit.
Speaker 3: That's the key stellar astrophysics question they seem to have answered.
Speaker 3: The leading theory relates to how metallicity affects the progenitor system.
Speaker 3: In environments with fewer heavy elements, the winds from the
Speaker 3: companion star might be different. Maybe the structure of the
Speaker 3: white dwarf itself just before it explodes is subtly altered.
Speaker 2: How does that change the boom?
Speaker 3: It seems to affect the thermonuclear runaway, the explosion physics itself. Basically,
Speaker 3: a lower metallicity environment seems to lead to a lower
Speaker 3: yield of radioactive nickel fifty six during the explosion.
Speaker 2: Nickel fifty six that's.
Speaker 3: Important, critically important. Nickel fifty six decays into cobalt fifty six,
Speaker 3: and that radioactive decay chain is what primarily powers the
Speaker 3: peak brightness of the supernova's visible light. So less nickel
Speaker 3: means less fuel for the light.
Speaker 2: Show, meaning less intrinsic brightness.
Speaker 3: Exactly, a metal poor younger system produces a less bright explosion,
Speaker 3: even if it started from the same mass trigger.
Speaker 2: Wow. Okay, So the implication for cosmology is if you're
Speaker 2: looking way back in time at the most distant supernovae.
Speaker 3: The ones used to prove acceleration, right.
Speaker 2: You were inherently looking at younger stellar populations from a
Speaker 2: time when the universe was less chemically.
Speaker 3: Enriched, correct, less metal rich overall.
Speaker 2: So those distant supernovae were already intrinsically functor to begin with,
Speaker 2: just because of when and where they were born.
Speaker 3: That's the core argument. They look dimmer for two reasons. Yes,
Speaker 3: they're far away and subject to cosmological redshift and expansion effects,
Speaker 3: but also they were just less bright from the get
Speaker 3: go due to this stellar age metallicity.
Speaker 2: Bias, which means the amount of dimness we blamed entirely
Speaker 2: on acceleration might.
Speaker 3: Be significantly overestimated. Part of that dimness is just astrophysics,
Speaker 3: not cosmology. It weakens the case that acceleration alone caused
Speaker 3: all the dimming we observed.
Speaker 2: That makes a lot of sense. But hang on, if
Speaker 2: this effect is real, how did the original Nobel winning
Speaker 2: studies miss it? Was there data not good.
Speaker 3: Enough for That's a fair question. It wasn't necessarily a
Speaker 3: flaw in their methods at the time, but more a
Speaker 3: limitation of the data samples they had and the instruments
Speaker 3: available back then.
Speaker 2: Ah okay.
Speaker 3: To really nail down this bias, you need to accurately
Speaker 3: measure the age and metallicity of the host galaxies. For
Speaker 3: hundreds of supernovae covering a huge range of cosmic time.
Speaker 2: Or red shift, you need to know the neighborhood the
Speaker 2: star lived in precisely.
Speaker 3: The Yonse team used a much larger, more modern sample
Speaker 3: three hundred host galaxies, and crucially, they used detailed spectroscopy
Speaker 3: and color magnitude diagrams. They looked at the precise colors
Speaker 3: and spectral fingerprints of the other stars in the host
Speaker 3: galaxy to really pin down the age of the stellar
Speaker 3: population that likely spawned the supernova.
Speaker 2: So they did detailed demographic studies of three hundred different
Speaker 2: galactic homes for these explosions.
Speaker 3: That's a good way to put it. And this much larger,
Speaker 3: more detailed analysis gave them the statistical muscle they needed
Speaker 3: to isolate this subtle effect, this systematic.
Speaker 2: Trend, and the confidence level that's the kicker.
Speaker 3: They confirm this age bias exists at an extremely high
Speaker 3: significance level ninety nine point nine nine nine percent confidence.
Speaker 2: Wow, ninety nine point nine nine nine percent. That's basically certain.
Speaker 3: In statistical terms. Yeah, it means the chance of this
Speaker 3: correlation being just a random flup in the data is
Speaker 3: incredibly tiny, vanishingly small. It strongly suggests this bias is
Speaker 3: real and must be accounted for when using supernovae to
Speaker 3: measure cosmic distances.
Speaker 2: Okay, here's where it gets really interesting. Then this finding
Speaker 2: means that the dimming of those distant supernovae, which we
Speaker 2: previously chalked up entirely to faster and faster cosmic expansion huh,
Speaker 2: actually arises in a significant way from stellar astrophysics from
Speaker 2: a flaw in our standard candle.
Speaker 3: Itself, and that connects the dots directly back to the
Speaker 3: acceleration problem. If those distant supernovae looked dimmer partly because
Speaker 3: they're intrinsically fainter due to their age and metallicity, not
Speaker 3: just because space stretched faster.
Speaker 2: Than our calculation of how much faster space was stretching
Speaker 2: must be wrong. It must be inflated exactly.
Speaker 3: We had changed all the extra dimness to acceleration, but
Speaker 3: if a chunk of that dimness was just the star
Speaker 3: being young and metal poor, then the actual cosmological acceleration
Speaker 3: effect must have been smaller than we calculated.
Speaker 2: Okay, so when you apply this correction, this ninety nine
Speaker 2: point nine nine nine percent certain correction, you have to
Speaker 2: go back to the drawing board with the data, right,
Speaker 2: see what the universe actually looks like according to these
Speaker 2: refined measurements.
Speaker 3: Absolutely, you have to revisit the historical data and see
Speaker 3: what the new numbers tell you.
Speaker 2: And what do they tell them. Did the corrected data
Speaker 2: still fit the standard model?
Speaker 3: No, that's the crucial point. The researchers took the raw
Speaker 3: supernova data, specifically using large data sets like the Dark
Speaker 3: Energy Survey, they applied their systematic age bias correction, and
Speaker 3: then and they tested it against the standard CDM.
Speaker 2: Model, the one with constant dark energy W equals one.
Speaker 3: Right, and unsurprisingly, the corrected supernova data no longer matched
Speaker 3: that model. There is a clear discrepancy.
Speaker 2: How did they show that visually? Yeah?
Speaker 3: They use something called the Hubble residual diagram. It's a
Speaker 3: really important tool. It basically plots how much the observed
Speaker 3: brightness of the supernovae deviates from what a specific cosmological
Speaker 3: model predicts at different distances or red shifts. If the
Speaker 3: universe behaved exactly like the standard constant dark energy model says,
Speaker 3: then the data points on this plot after the standard
Speaker 3: corrections should basically follow along a flat horizontal line, meaning
Speaker 3: no systematic deviation.
Speaker 2: And did they before this new correction?
Speaker 3: Loosely yes, The uncorrected data after standard stretch and color
Speaker 3: fixes kind of scattered around that flat line, which supported
Speaker 3: the ACDM model more or less.
Speaker 2: But after the Yon say Age bias correction.
Speaker 3: Big difference. Corrected data points showed a clear significant systematic
Speaker 3: shift away from that flat line. Instead of staying flat.
Speaker 3: The corrected data traces a curve that deviates significantly from
Speaker 3: the constant dark energy prediction.
Speaker 2: A curve meaning that deviation isn't random, It changes with distance.
Speaker 3: Or time exactly, and that deviation immediately tells you that
Speaker 3: the cosmological constant model Lambda is probably wrong. It doesn't
Speaker 3: fit the refined data.
Speaker 2: So if the standard model is out, what does fit
Speaker 2: the corrected data better?
Speaker 3: The corrected data aligns much much better with models where
Speaker 3: dark energy is not constant. Instead, the data supports models
Speaker 3: where the density and therefore the repulsive force of dark
Speaker 3: energy actually weakens and evolves significantly over cosmic time.
Speaker 2: So WOM isn't stuck at minus one exactly.
Speaker 3: It suggests w is dynamic. Maybe it was more negative
Speaker 3: in the past, driving acceleration, but perhaps today it's slightly
Speaker 3: greater than minus one, indicating a force that's decaying, losing
Speaker 3: its punch.
Speaker 2: You know this sounds familiar, haven't There been other hints
Speaker 2: recently that dark energy might not be constant.
Speaker 3: You're absolutely right. This fits with growing evidence from other
Speaker 3: corners of cosmology.
Speaker 2: Like the DCESI project.
Speaker 3: Exactly. Just last year, results from the Dark Energy Spectroscopic
Speaker 3: Instrument DSi, based in Arizona, which looks at how galaxies
Speaker 3: cluster together, already hinted that the strength of dark energy
Speaker 3: might have changed over time.
Speaker 2: So DCII was seen potential evolution in W two.
Speaker 3: Yes, their data derived from these large scale structure patterns
Speaker 3: pointed towards a dynamic w So the idea of evolving
Speaker 3: dark energy wasn't completely out of the blue. But this
Speaker 3: corrected supernova data provides really strong independent confirmation. It brings
Speaker 3: the supernova measurements into alignment with those other hints.
Speaker 2: Okay, so bringing it all together, the correct and supernova
Speaker 2: may be combined with other data. What's the bottom line
Speaker 2: on the standard CDM model.
Speaker 3: The bottom line, according to this analysis is that the
Speaker 3: combined data rules out the standard CDM model with overwhelming significance.
Speaker 2: Overwhelming significance, not just a maybe.
Speaker 3: No, this isn't a small statistical wabble they're reporting. It's
Speaker 3: presented as a definitive rejection of the current consensus model
Speaker 3: based on this corrected evidence.
Speaker 2: And if you reject the constant dark energy model, you
Speaker 2: have to accept the alternative scenario that does fit the
Speaker 2: corrected data. What does that imply for the expansion of
Speaker 2: the universe right now today?
Speaker 3: It implies something truly profound. It means the universe is
Speaker 3: not accelerating today as we've thought for the last twenty
Speaker 3: five years.
Speaker 2: Wait say that again.
Speaker 3: The analysis suggests that universe has already passed peak acceleration.
Speaker 3: It has transitioned into a state of decelerated expansion. It's
Speaker 3: still expanding, but the rate of expansion is now decreasing.
Speaker 2: So we are currently living in a slowing universe.
Speaker 3: According to these findings. Yes, Professor Lee stated it very clearly.
Speaker 3: He said the universe has already entered a phase of
Speaker 3: decelerated expansion at the present epic, and that dark energy
Speaker 3: evolves much faster than previously thought.
Speaker 2: That is a spleet reversal of the picture that won
Speaker 2: the Nobel Prize.
Speaker 3: It's a massive shift in perspective. The expansion is ongoing,
Speaker 3: but gravity seems to be slowly winning the tug of
Speaker 3: war again, causing the rate of expansion to slow down.
Speaker 2: It's incredible to think about these cosmic transition points. You
Speaker 2: had the first nine billion years or so, gravity slowing
Speaker 2: things down the iteration right then dark energy kicks in,
Speaker 2: It becomes dominant and speeds things up for a few
Speaker 2: billion years.
Speaker 3: Acceleration the arrow we thought we were still in.
Speaker 2: And now if this is right, because dark energy appears
Speaker 2: to be weakening, gravity is starting to reassert its influence
Speaker 2: on the largest scales, causing the expansion rate to slow
Speaker 2: down again.
Speaker 3: The dominance of forces seems to have flipped once more.
Speaker 3: It's a much more dynamic cosmic history than the standard
Speaker 3: model suggested.
Speaker 2: What really gives this study punch, though, isn't just the
Speaker 2: statistics on the age bias, right. It's how it clicks
Speaker 2: with other measurements.
Speaker 3: Absolutely, that's perhaps the most compelling part. It's not just
Speaker 3: the ninety nine point nine nine nine percent confidence the
Speaker 3: correction itself, but the fact that when you apply this correction,
Speaker 3: the supernova data suddenly aligns beautifully with independent ways of
Speaker 3: measuring the universe.
Speaker 2: Methods that previously didn't quite line up with the supernova.
Speaker 3: Result exactly, measurements that had been kind of quietly problematic
Speaker 3: because they just didn't agree with the gold standard results
Speaker 3: from the potentially flawed supernova method.
Speaker 2: Okay, let's talk about those independent data sets. Yeah, you
Speaker 2: mentioned DSi before. The corrected supernova data now aligns with
Speaker 2: models favored by projects like DSi, which used buryonic acoustic
Speaker 2: oscillations BAO and the cosmic microwave background CMB, right.
Speaker 3: Two pillars of modern cosmology completely independent of supernova.
Speaker 2: We hear BAO and CMB mentioned a lot. Maybe, let's
Speaker 2: quickly recap what they actually are, why they're reliable cosmic
Speaker 2: rulers in their own right.
Speaker 3: Good idea. So the CMB the cosmic microwave background. That's
Speaker 3: literally the oldest light in the universe.
Speaker 2: We can see the afterglow of the Big Bang pretty much.
Speaker 3: It's the residual heat and light left over from about
Speaker 3: three hundred and eighty thousand years after the Big Bang.
Speaker 3: That was when the universe cooled down enough for electrons
Speaker 3: and protons to finally combine and form.
Speaker 2: Neutral atoms called recombination, right.
Speaker 3: And that event essentially made the universe transparent to light
Speaker 3: for the first time. So the CME gives us this
Speaker 3: incredible snapshot of the universe when it was extremely young
Speaker 3: and incredibly smooth, but with tiny temperature fluctuations. These fluctuations
Speaker 3: were the seeds of all future structure.
Speaker 2: Okay, that's the CNB a picture of the early universe.
Speaker 2: What about BAO baryonic acoustic oscillations. Sounds complicated.
Speaker 3: It sounds complicated, but the concept is actually based on
Speaker 3: sound waves. Think of the very early universe before recombination,
Speaker 3: as this incredibly hot, dense soup a plasma of particles
Speaker 3: in light got it. In the soup, you had gravity
Speaker 3: trying to pull matter together into clumps, but you also
Speaker 3: had intense radiation pressure from the light pushing outwards. These
Speaker 3: two competing forces created ripples, actual sound waves or pressure
Speaker 3: waves sloshing through the plasma, like.
Speaker 2: Sound waves in air, but in the primordial soup.
Speaker 3: Exactly now, when recombination happened and the universe became transparent,
Speaker 3: the light decoupled from the matter, and those sound waves
Speaker 3: basically frozen place. They left behind a subtle imprint, slightly
Speaker 3: denser shells of matter at a very specific, predictable distance
Speaker 3: from the original clumps.
Speaker 2: Ah a characteristic distance scale imprinted on the matter distribution.
Speaker 3: Precisely, the size of these frozen spheres corresponds to how
Speaker 3: far a sound wave could travel in the plasma before
Speaker 3: recombination happened. We can calculate that distance called the sound
Speaker 3: horizon from fundamental physics. It's a known quantity.
Speaker 2: So it acts like a standard ruler.
Speaker 3: A standard ruler exactly so today, when astronomers map the
Speaker 3: distribution of millions of galaxies across the sky, they look
Speaker 3: for a slight statistical preference for galaxies to be separated
Speaker 3: by that characteristic BAO distance.
Speaker 2: They look for that bump and the correlation function at
Speaker 2: that specific separation.
Speaker 3: That's the one. And because we know the actual physical
Speaker 3: size of that ruler sound horizon by observing its apparent
Speaker 3: size on the sky at different distances, we can measure
Speaker 3: the expansion history of the universe completely independently of supernovae.
Speaker 2: Okay, so BAO and CMB are powerful independent tools. How
Speaker 2: does the corrected supernova data line up with them?
Speaker 3: Now that's the key convergence. The conclusion from the corrected
Speaker 3: supernova data that the universe is decelerating today agrees remarkably
Speaker 3: well with what was independently predicted by analyzes using only
Speaker 3: BAO data or BAO combined with CMB data.
Speaker 2: So those other methods were already hinting at deceleration.
Speaker 3: They were hinting at models that preferred deceleration today, or
Speaker 3: at least were inconsistent with strong ongoing acceleration. But as
Speaker 3: Professor Lee pointed out, this alignment had previously received little attention,
Speaker 3: primarily because the uncorrected supernova data, which everyone trusted as
Speaker 3: the gold standard, pointed so strongly in the other direction
Speaker 3: towards continued acceleration. The discrepancy was usually blamed on potential
Speaker 3: issues with the BAOCMB analysis, not the supernova.
Speaker 2: But now the tables have turned.
Speaker 3: Exactly Now that the supernova data itself has been refined
Speaker 3: and corrected for this well motivated stellar age bias, all
Speaker 3: three major lines of evidence corrected supernova, BAO, and CMB
Speaker 3: seem to converge. They all point towards the same picture,
Speaker 3: a universe slowing down today driven by a dark energy
Speaker 3: that is weakening over time.
Speaker 2: That kind of conversience from independent methods is incredibly powerful
Speaker 2: in science, is it.
Speaker 3: It's the strongest validation you can hope for. It suggests
Speaker 3: the age bias correction isn't just some statistical fluke, but
Speaker 3: reflects a real physical effect that brings different cosmic probes
Speaker 3: into agreement.
Speaker 2: And this convergence also helps with another big headache and cosmology,
Speaker 2: the Hubble tension.
Speaker 3: Yes, it potentially offers a significant step towards resolving the
Speaker 3: Hubble tension.
Speaker 2: Remind us what that is again?
Speaker 3: The Hubble tension is this persistent and statistically significant disagreement
Speaker 3: about a ten percent difference between measurements of the universe's
Speaker 3: current expansion rate. The Hubble constant age air.
Speaker 2: A disagreement between which measurements.
Speaker 3: Between measurements derived from the early universe, primarily the CMB
Speaker 3: data analyzed within the standard CDM model and measurements made
Speaker 3: in the local or late time universe, which heavily rely
Speaker 3: on things like Type IA supernovae to build the cosmic
Speaker 3: distance ladder.
Speaker 2: So early universe measurements give one value for age, late
Speaker 2: universe measurements give a higher value.
Speaker 3: Correct, and the discrepancy is statistically significant, meaning it's unlikely
Speaker 3: to be just random error. Now, think about it. If
Speaker 3: the foundation of that late time measurement, the Type EA
Speaker 3: supernova distance scale, was systematically flawed.
Speaker 2: Because we thought they were brighter than they actually were,
Speaker 2: especially the distant ones due to the age bias.
Speaker 3: Exactly if they were intrinsically fainter, then our distance calculations
Speaker 3: based on their apparent dimness were systematically underestimating their true.
Speaker 2: Distances, making them seem closer, which inflates the calculated expansion
Speaker 2: rate decily.
Speaker 3: If the distances were wrong, the local h heros derive
Speaker 3: using them would appear artificially high. By recalibrating the supernova
Speaker 3: distances using this age bias correction, their inferred distances should increase,
Speaker 3: bringing the late time AHRO measurement down, potentially closing the
Speaker 3: gap with the early universe value derived from the CMB.
Speaker 2: So, fixing the standard candle doesn't just change the future
Speaker 2: fate of the universe. It helps reconcile its past and
Speaker 2: present expansion rates.
Speaker 3: It has the potential to do both. Yes, it addresses
Speaker 3: a fundamental calibration issue that ripples through cosmology.
Speaker 2: Now, to be absolutely sure about this, the Yonce team
Speaker 2: isn't just resting on this correction, right, They're planning more tests.
Speaker 3: That's right. They're already working on what they call an
Speaker 3: evolution free test.
Speaker 2: Evolution free how does that work?
Speaker 3: It's actually a really clever way to directly test their hypothesis.
Speaker 3: Instead of trying to mathematically correct for the age bias,
Speaker 3: they're trying to eliminate it from the sample selection itself. Oh,
Speaker 3: they are selecting supernovae by only comparing explosions that happen
Speaker 3: in host galaxies of the same relative age coeval galaxies,
Speaker 3: but across the full range of cosmic distances.
Speaker 2: Redshifts ah So comparing apples to apples young stellar populations
Speaker 2: only with other young stellar populations old with old exactly.
Speaker 3: By comparing like with like across cosmic time, they aim
Speaker 3: to remove the age menallicity evolution as a confounding variable
Speaker 3: in the distance measurement entirely. If their hypothesis is right,
Speaker 3: this evolution free sample should still show the deceleration trend
Speaker 3: even without applying the correction factor.
Speaker 2: And are they getting results from that yet?
Speaker 3: The paper mentions that early results from this evolution free
Speaker 3: test already seem to support their main conclusion, reinforcing the
Speaker 3: deceleration picture. But to really put the nail in the
Speaker 3: coffin methodologically speaking, they need much much more data, an
Speaker 3: explosion of new data, you might say, yeah, quite literally
Speaker 3: in this case. And that's where the next generation of
Speaker 3: astronomical observatories comes in. Specifically, the Verice Ruben Observator me.
Speaker 2: The new big telescope in Chili exactly.
Speaker 3: It's locating in the Chile, and Andes just recently began
Speaker 3: at scientific operations, and it houses the world's most powerful
Speaker 3: digital camera. Its main job, the Legacy Survey of Space
Speaker 3: and Time LSST, is to repeatedly map the entire southern
Speaker 3: sky over ten years.
Speaker 2: And it's going to find a lot of supernovae.
Speaker 3: An unprecedented number. Crucially for this topic, the Ruben Observatory
Speaker 3: is expected to discover and characterize Type IA supernovae with
Speaker 3: incredible speed and precision. We're talking potentially tens of thousands of.
Speaker 2: Them, tens of thousands compared to the hundreds used in
Speaker 2: current studies.
Speaker 3: Yes, the estimates are that within the next five years
Speaker 3: or so, Ruben could discover and provide detailed host galaxy
Speaker 3: information for more than twenty thousand new supernova host galaxies.
Speaker 2: Wow.
Speaker 3: This enormous data set, combined with Ruben's ability to get
Speaker 3: really precise measurements of the host galaxy properties, their ages,
Speaker 3: their metallicities, will allow for what the Yance researchers themselves
Speaker 3: call a far more robust and definitive test of supernova cosmology.
Speaker 2: So this is really the moment of truth coming up
Speaker 2: in the next few years.
Speaker 3: It really is. We will finally have the statistical power
Speaker 3: and the detailed data needed to either absolutely confirm this
Speaker 3: age bias correction and the resulting deceleration, or perhaps find
Speaker 3: nuances or flaws in the theory. The data will decide.
Speaker 2: Well, let's assume for a moment it is confirmed. What
Speaker 2: are the biggest, broadest implications for how we understand the universe.
Speaker 3: Well. If confirmed, it's arguably the most significant paradigm shift
Speaker 3: in cosmology since dark energy itself was discovered nearly three
Speaker 3: decades ago.
Speaker 2: That's a huge statement it is.
Speaker 3: Firstly, as we discussed, it potentially resolves the nagging Hubble
Speaker 3: tension by fixing the fundamental distant scale calibration.
Speaker 2: That's big, okay.
Speaker 3: Secondly, and perhaps more profoundly, for the ultimate fate of
Speaker 3: the universe, it gives us crucial clues about the physical
Speaker 3: nature of dark energy itself. How so, because if the
Speaker 3: universe is decelerating today, dark energy simply cannot be the
Speaker 3: simple unchanging cosmological constant described by ACDM, where W is
Speaker 3: forever fixed at mextion one. It must be something dynamic,
Speaker 3: something transient, something that weakens over cosmic time.
Speaker 2: So it's not a constant property of space, but more
Speaker 2: like a field or force that's fading away.
Speaker 3: That's the implication. It shifts our focus dramatically. Instead of
Speaker 3: thinking about a static constant energy density filling space, we
Speaker 3: have to consider a dynamic, evolving component of the cosmos,
Speaker 3: one whose influence peaked in the past and is now waning.
Speaker 3: Allowing gravity to gradually regain dominance on cosmic scales.
Speaker 2: Okay, let's try and pull this all together. Then recap
Speaker 2: the core argument that's challenging well thirty years of cosmological thinking.
Speaker 2: We started with the assumption the bedrock really that type
Speaker 2: I is supernovae were perfect standard candles, uniform brightness everywhere
Speaker 2: every time, the.
Speaker 3: One hundred wah bulbs of the cosmos exactly.
Speaker 2: And that is ssumption. Let us, via observations of their
Speaker 2: unexpected dimness at great distances, to conclude the universe was accelerating,
Speaker 2: driven by a constant dark energy CDM. That was the picture. Now,
Speaker 2: new research, backed by this incredibly high ninety nine point
Speaker 2: nine nine nine percent confidence level, shows those candles are
Speaker 2: actually flawed. There's a systematic bias linked to the age
Speaker 2: and metallicity of the stars that explode.
Speaker 3: Younger metal poor systems produce intrinsically fainter supernovae.
Speaker 2: Right, and when you correct for that bias, the picture flips.
Speaker 2: The corrected data suggests the universes no longer accelerating, but
Speaker 2: has actually transitioned to a state of deceleration right now.
Speaker 3: Today, improving or strongly suggesting that dark energy isn't constant.
Speaker 3: It weakens, It evolves over time.
Speaker 2: So this isn't just some academic debate about cosmic speed limits,
Speaker 2: is it. It fundamentally changes the story of our universe's
Speaker 2: ultimate destiny.
Speaker 3: Absolutely, It's about the end game for all matter and energy.
Speaker 3: If dark energy's nature is changing, if it's weakening, then
Speaker 3: the end might not be the endless, cold, accelerating expansion,
Speaker 3: the so called big rip or eternal heat death that
Speaker 3: the standard model predicted.
Speaker 2: So the universe doesn't necessarily rip itself apart or fade
Speaker 2: into cold.
Speaker 3: Darkness, that scenario becomes much less certain. Knowing how dark
Speaker 3: energy evolves, how quickly its weakening, becomes absolutely essential for
Speaker 3: predicting the future, especially if gravity is indeed starting to
Speaker 3: win the cosmic tug of war.
Speaker 2: Again, If dark energy is weakening and the universe is
Speaker 2: already slowing down, where does that road lead? Does expansion
Speaker 2: just stop?
Speaker 3: It could the focus shifts completely away from runaway expansion.
Speaker 3: If the density of this evolving dark energy continues to drop,
Speaker 3: Theoretically it could eventually fall below the average density of
Speaker 3: regular matter and dark.
Speaker 2: Matter, and then gravity really takes over.
Speaker 3: Then gravity would be the undisputed dominant force on cosmic scales.
Speaker 3: Deceleration would continue potentially until the expansion halts entirely and then.
Speaker 2: Reverses reversus meaning contraction.
Speaker 3: Meaning the universe could start collapsing back in on itself,
Speaker 3: heading to towards an eventual recollapse.
Speaker 2: So we go from worrying about big rip to potentially
Speaker 2: facing a big crunch like the old cyclical universe ideas.
Speaker 3: That's the dramatic alternative that re enters the realm of possibility.
Speaker 3: If this evolving dark energy model is correct. You mentioned
Speaker 3: the source material hinted at related research suggesting the universe
Speaker 3: might end in a big crunch around thirty three billion
Speaker 3: years from now. Yeah, well, that kind of scenario suddenly
Speaker 3: moves from speculative fiction back into the arena of scientifically
Speaker 3: plausible futures depending on exactly how dark energy behaves.
Speaker 2: Which leads to a final thought for people to chew on.
Speaker 3: If deceleration continues, if contraction eventually begins, what does that
Speaker 3: mean for our fundamental understanding of gravity and vacuum, energy
Speaker 3: and space itself? What allows the universe to put on
Speaker 3: the brakes and actually reverse course.
Speaker 2: That's a deep one. What fundamental assumptions have to change exactly.
Speaker 3: It's a profound question toom all over.
Speaker 2: And thankfully it's a question we might get a much
Speaker 2: clearer answer to you soon thanks to that flood of
Speaker 2: incredibly precise data we're expecting from the Verisa Reuben Observatory
Speaker 2: over the next few years.
Speaker 3: That's where the next chapter of this story will be written.
Speaker 3: Waiting to see if the light from thousands of new
Speaker 3: supernovae confirms this cosmic shift, potentially from eternal expansion towards
Speaker 3: an ultimate collapse.
Speaker 2: An absolutely fascinating turn in our understanding of the cosmos.
Speaker 2: Thank you for walking us.
Speaker 3: Through that, my pleasure. It's a truly exciting time in cosmology.
Speaker 2: And thank you for joining us on this deep dive
Speaker 2: into the very fabric of space and time. Most stations
Speaker 2: ch