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: If you look up at the Little Dipper tonight, you
Speaker 2: aren't just seeing a familiar pattern of stars, right.
Speaker 3: It's so easy to just see it as this static,
Speaker 3: you know, beautiful canopy.
Speaker 2: Yeah exactly, But you are actually looking at the very
Speaker 2: edge of the largest and honestly the most impossible map
Speaker 2: ever constructed by human beings.
Speaker 3: It really does shatter your entire sense of scale.
Speaker 2: It does, because we're talking about a three dimensional model
Speaker 2: of the universe that is so vast and like so
Speaker 2: detailed that the data pouring out of it right now
Speaker 2: might actually prove that the fundamental laws of physics are
Speaker 2: actively changing right over our heads.
Speaker 3: And that specific patch of the cosmos near the Little
Speaker 3: Dipper that actually served as the final observation target for
Speaker 3: this monumental.
Speaker 2: Project, which is just wild. We are talking about mapping
Speaker 2: structures that stretch across eleven billion years of history.
Speaker 3: Eleven billion. Yes, it's a number that is almost impossible
Speaker 3: for the human brain to truly internalize.
Speaker 2: And to put that into context for you listening. We
Speaker 2: aren't talking about a map that helps us, you know,
Speaker 2: find nearby planets or plot a Corset alfasentory.
Speaker 3: No, the scale is entirely different, right.
Speaker 2: The Dark Energy Spectroscopic Instrument, or DAI as it's called,
Speaker 2: has just wrapped up its primary run and it delivered
Speaker 2: the highest resolution, most comprehensive three D map of the
Speaker 2: universe in existence.
Speaker 3: So the map itself, interestingly enough, is almost a byproduct.
Speaker 2: Yeah, the map wasn't the actual goal.
Speaker 3: Was it not at all. It's a tool built for
Speaker 3: a very specific, incredibly high stakes. The goal was never
Speaker 3: just cartography for the sake of having a nice atlas
Speaker 3: of the cosmos.
Speaker 2: So they didn't just want to hang a shiny map.
Speaker 3: On the wall exactly. The purpose of mapping millions upon
Speaker 3: millions of distant galaxies is to track down and understand
Speaker 3: a phantom.
Speaker 2: A phantom I love that description.
Speaker 3: Well, we're dealing with dark energy, the invisible repulsive force
Speaker 3: that currently makes up roughly seventy percent of everything in
Speaker 3: the universe.
Speaker 2: Seventy percent that is, I mean everything we can see, touch,
Speaker 2: or interact with is basically a rounding error compared to
Speaker 2: this force.
Speaker 3: It's all just a tiny fraction of.
Speaker 2: Reality, which sets the stakes at an existential level. If
Speaker 2: seventy percent of reality is driven by something we can't see,
Speaker 2: and this new map is suddenly suggesting that our basic
Speaker 2: assumptions about how that force operates are wrong.
Speaker 3: Then we're looking at a paradigm.
Speaker 2: Shift, a total paradigm shift that rewrites the fate of
Speaker 2: the universe. Okay, let's unpack this because before we get
Speaker 2: to the physics breaking anomaly they found, I want to
Speaker 2: ground this in the far physical reality of how you
Speaker 2: even build a.
Speaker 3: Map like this. The sheer engineering is staggering, it really is.
Speaker 2: This entire operation is based in Arizona, right, Yeah.
Speaker 3: At the kit Peak National Observatory, which is managed by
Speaker 3: the US Department of Energies Lawrence Berkeley National Laboratory. Okay,
Speaker 3: And it is vital to understand that DSi is not
Speaker 3: a space telescope.
Speaker 2: Oh right, because we always hear about James Web or
Speaker 2: Hubble exactly.
Speaker 3: It is not floating out in the vacuum, free from interference.
Speaker 3: It is a ground based instrument retrofitted onto an existing
Speaker 3: telescope structure on a mountain.
Speaker 2: Peak, which makes it sound almost I don't know, quoint,
Speaker 2: but the instrumentation is anything but quaint.
Speaker 3: It's a marvel of modern engineering.
Speaker 2: Because when I think of a telescope, I think of
Speaker 2: like a giant mirror or a massive glass lens pointed
Speaker 2: at a patch of sky.
Speaker 3: Right, the traditional galileo setup.
Speaker 2: Yeah, but the DSi instrument operates on a completely different
Speaker 2: mechanical level. The focal plane is packed with five thousand
Speaker 2: individual fiber optic sensors.
Speaker 3: Let's examine the mechanics of that, because it is an
Speaker 3: astonishing feat of miniaturization and robotics.
Speaker 2: Please, because I can barely visualize it.
Speaker 3: So you have a circular plane, and embedded into it
Speaker 3: are these five thousand robotic positioners, Okay, and each one
Speaker 3: holds a tiny fiber optic cable. In the space of
Speaker 3: just a few seconds, all five thousand robots can simultaneously
Speaker 3: pivot and adjust their positions.
Speaker 2: Wait all at the same time.
Speaker 3: All at the same time, they align perfectly with the
Speaker 3: incoming light from five thousand completely different, highly specific distant galaxies.
Speaker 2: That's insant. Wait, how do they move that fast without colliding?
Speaker 2: That is a big question, because if you have five
Speaker 2: thousand robotic arms packed onto a single plate, all swarming
Speaker 2: to find new targets for the next exposure, I mean
Speaker 2: the collision algorithms alone must be a nightmare.
Speaker 3: The choreography is entirely automated and highly highly complex. They
Speaker 3: operate in this tightly packed honeycomb structure.
Speaker 2: Oh, a honeycomb, that makes sense.
Speaker 3: Yeah, And the targeting software calculates the optimal orientation for
Speaker 3: every single positioner. It maximizes the number of galaxies captured
Speaker 3: in a single exposure without any fibers, crossing paths or jamming.
Speaker 2: Oh.
Speaker 3: Once they lock into place, they captured the light, feed
Speaker 3: it down into the spectrographs, and then instantly realign for
Speaker 3: the next patch of sky.
Speaker 2: So it is just an absolute observing machine, completely relentless,
Speaker 2: and the numbers back that up. When the projects spun
Speaker 2: up in May of twenty twenty one, I read that
Speaker 2: the stated goal was to capture light from about thirty
Speaker 2: four million galaxies and quasars.
Speaker 3: Which alone would have been historic.
Speaker 2: Right, thirty four million is a massive number.
Speaker 3: It would have completely redefined the field of cosmology, but.
Speaker 2: The efficiency of the instrument and the clarity of those
Speaker 2: targeting protocols allowed them to vastly outpace their own projection
Speaker 2: by a huge market. Yeah, by the time they took
Speaker 2: that final scheduled shot near the Little Dipper, they hadn't
Speaker 2: just hit thirty four million.
Speaker 3: Not even close.
Speaker 2: They captured over forty seven million galaxies and quasars.
Speaker 3: Plus another twenty million stars just for the sake of completeness, just.
Speaker 2: Threw them in there. That is data set containing information
Speaker 2: from six times as many galaxies and quasars as every
Speaker 2: single previous cosmic survey ever conducted combined.
Speaker 3: The jumpin scale is it's honestly difficult to process.
Speaker 2: It's like we spent decades trying to map a continent
Speaker 2: by looking through a foggy keyhole, and suddenly someone handed
Speaker 2: us a four k drone flying overhead.
Speaker 3: That's a great way to put it. It's the difference
Speaker 3: between mapping a coastline by walking along it with a
Speaker 3: yardstick versus deploying a fleet of light our equipped satellites.
Speaker 2: Yeah, the density of the data is just unprecedented.
Speaker 3: Exactly we are no longer looking at broad, blurry estimates
Speaker 3: of where galaxies tend to gather. We're seeing the intricate,
Speaker 3: thread like structures of the costic web in high definition.
Speaker 2: So let's talk about the visual reality of that three
Speaker 2: D map, because if you sit down and look at
Speaker 2: the rendering of this data, it doesn't look like a
Speaker 2: solid sphere of stars.
Speaker 3: No, it has a very specific geometry.
Speaker 2: Right. It looks like a massive series of wedges, or
Speaker 2: like slices of a pie, radiating out from a central point,
Speaker 2: and Earth is sitting right at the very tip of
Speaker 2: those wedges.
Speaker 3: The wedge shape is an artifact of our vantage point.
Speaker 3: We are observing from a fixed location inside a spiral galaxy,
Speaker 3: the Milky Way. Exactly. We cannot just peel away our
Speaker 3: own galactic environment to get a perfect, unobstructed three hundred
Speaker 3: and sixty degree view of the deeper universe.
Speaker 2: Which explains the most glaring feature of the visual map.
Speaker 2: When you look at it, there is this massive, empty
Speaker 2: black gap cutting right through the middle of the wedges.
Speaker 3: It looks like a blind spot.
Speaker 2: Yeah, it is exactly a blind spot. Why is that there?
Speaker 3: We refer to it as the zone of avoidance because
Speaker 3: our solar system is embedded within the disc of the
Speaker 3: Milky Way. When we aim our telescopes along the plane
Speaker 3: of that disk, we are attempting to look through tens
Speaker 3: of thousands of light years of our own galactic material.
Speaker 2: Oh so it's just blocked gas dust nearby stars. All
Speaker 2: of it is in the way. It's like trying to
Speaker 2: spot a firefly a mile away while someone is shining
Speaker 2: a high beam flashlight directly into your eyes through a
Speaker 2: cloud of smoke.
Speaker 3: That's exactly it. The extinction of light is severe in
Speaker 3: that direction. The interstellar dust absorbs and scatters the faint
Speaker 3: optical light from ancient galaxies, rendering them virtually invisible to
Speaker 3: dii's sensors.
Speaker 2: Wow.
Speaker 3: So the mapping naturally carves out these sweeping wedges above
Speaker 3: and below the galactic plane, where the view out into
Speaker 3: the deep cosmos is relatively clear.
Speaker 2: Okay, so that covers horizontal and vertical spread of the map.
Speaker 2: But a map of the universe is useless if it's flat. True,
Speaker 2: The true triumph here is the third dimension depth. How
Speaker 2: do five thousand robotic fibers in Arizona actually plot the
Speaker 2: depth of a galaxy that is billions of light years away.
Speaker 2: I mean they aren't bouncing radar off these things.
Speaker 3: No, no radar. The third dimension is derived through spectroscopy,
Speaker 3: which is where the true power of the instrument lies.
Speaker 2: Okay, break that down for me.
Speaker 3: So the instrument isn't just taking a picture of a galaxy.
Speaker 3: It is taking the light from that galaxy and breaking
Speaker 3: it apart into its constituent colors, its spectrums, exactly like
Speaker 3: a prism. And this is where we have to talk
Speaker 3: about redshift. Because the universe is expanding, everything is moving
Speaker 3: away from us, right.
Speaker 2: I always hear this compared to the Doppler effect with
Speaker 2: sound like a police siren dropping in pitch as its
Speaker 2: speeds past you.
Speaker 3: It is the optical equivalent of that exact effect. As
Speaker 3: a distant galaxy is carried away from us by the
Speaker 3: expansion of space, the light waves it emitted are physically
Speaker 3: stretched out.
Speaker 2: Over their journey, and longer waves mean red light.
Speaker 3: Correct. Longer light waves shift toward the red end of
Speaker 3: the electromagnetic spectrum.
Speaker 2: So the faster it's moving away from us, the redder
Speaker 2: the light appears by the time it hits the sensor at.
Speaker 3: Kitpeak precisely mm hm. And because we know the expansion
Speaker 3: rate of the universe. That red shift acts as a
Speaker 3: direct proxy for distance. The more the light is shifted
Speaker 3: to the red, the further way the galaxy is.
Speaker 2: That is so elegant.
Speaker 3: What's fascinating here is the crucial realization about time. The
Speaker 3: thing that elevates this from just a map of space
Speaker 3: to a map of time is the finite speed of light.
Speaker 2: Right. I want to clarify how this translates to time
Speaker 2: travel for our listeners, because if DSi locks onto a
Speaker 2: galaxy and measures a red shift that tells us it
Speaker 2: is five billion light years away.
Speaker 3: We aren't seeing where that galaxy.
Speaker 2: Is right now exactly. We are seeing the light that
Speaker 2: left that galaxy five billion years ago.
Speaker 3: You are observing the universe exactly as it existed at
Speaker 3: that precise moment in cosmic history.
Speaker 2: Which just blows my mind every time I think about it.
Speaker 3: It's incredible. When DISI pushes its sensors to the absolute limit,
Speaker 3: capturing the faintest targets, it is looking at light that
Speaker 3: has been traveling for eleven billion years.
Speaker 2: Which means those wedges radiating out from Earth are literal timelines,
Speaker 2: little timelines. Yes, the tip of the wedge is us
Speaker 2: right now, and as you travel outward along the wedge,
Speaker 2: you are moving backward through the epochs of the universe,
Speaker 2: slice by slice, tracing the history of reality back eleven
Speaker 2: billion years.
Speaker 3: A point underscored by d side director doctor Michael Levi,
Speaker 3: who noted how the instrument performed beyond the wildest to
Speaker 3: expectations of the team that built it. I can imagine
Speaker 3: pushing the boundaries of spectroscopy to capture these incredibly faint
Speaker 3: ancient signals requires a level of precision that is honestly
Speaker 3: difficult to overstate.
Speaker 2: And they needed that precision because, as we established earlier,
Speaker 2: they were hunting.
Speaker 3: A ghost, the biggest ghost of all.
Speaker 2: Yeah. They didn't build a time traveling three D map
Speaker 2: just to account galaxies. They built it to watch how seventy
Speaker 2: percent of the universe behaves over time. Let's pivot to
Speaker 2: dark energy.
Speaker 3: Let's do it.
Speaker 2: What exactly was the prevailing assumption about this force before
Speaker 2: DSi started churning out data.
Speaker 3: Well, to frame dark energy correctly, you have to look
Speaker 3: at the fundamental conflict governing the universe. It is a
Speaker 3: cosmic tug of war. Okay, on one side, you have matter,
Speaker 3: This includes stars, planets, gas clouds, and dark matter. All
Speaker 3: of this matter possesses mass, and therefore it exerts gravity.
Speaker 2: And gravity pulls things together.
Speaker 3: Right, Gravity is an attractive force. Its inherent tendency is
Speaker 3: to pull things together, to cause the universe to contract
Speaker 3: and clump.
Speaker 2: So logically, if gravity is the only player on the field,
Speaker 2: the universe should be pulling itself back inward after the
Speaker 2: initial explosion of the Big Bang, like the expansion should
Speaker 2: be slowing down.
Speaker 3: That was the widely held cosmological consensus for decades. Really, yes,
Speaker 3: everyone assumed the expansion must be decelerating due to the
Speaker 3: collective gravitational drag of all the matter in existence.
Speaker 2: But then something changed.
Speaker 3: Observations in the late nineteen nineties absolutely shattered that model.
Speaker 3: Oh wow, instead of slowing down, astronomers realize the expansion
Speaker 3: of the universe is accelerating. Distant galaxies are flying apart
Speaker 3: at an ever increasing velocity.
Speaker 2: Which just defies common sense. I mean, if you throw
Speaker 2: a ball straight up into the air, gravity slows it down,
Speaker 2: it doesn't suddenly accelerate upward into the stratosphere.
Speaker 3: Exactly. For the universe to accelerate its expansion, there must
Speaker 3: be a repulsive force overpowering the attractive force of gravity
Speaker 3: on a macroscopic.
Speaker 2: Scale, and that's the ghost.
Speaker 3: That's the ghost. This invisible pressure driving the fabric of
Speaker 3: space apart is what we term dark energy.
Speaker 2: And because it is responsible for the accelerating expansion of
Speaker 2: the entirety of space, mathematical models dictate that it must
Speaker 2: account for roughly seventy percent of the total energy density
Speaker 2: of the universe. That's right, Okay, so we knew dark
Speaker 2: energy existed, or at least we knew something was pushing
Speaker 2: the universe apart. But how did physicists define it mathematically?
Speaker 2: Because this is where the D sign map throws a
Speaker 2: massive wrench into the machine.
Speaker 3: Right, So the most elegant and widely accepted mathematical explanation
Speaker 3: was to treat dark energy as a cosmological.
Speaker 2: Constant, the operative word being constant.
Speaker 3: Exactly constant. The assumption was that this repulsive energy is
Speaker 3: an intrinsic property of the vacuum of space itself. It's
Speaker 3: uniform everywhere, okay, and crucially, its density never changes.
Speaker 2: Over time, so it's always the same.
Speaker 3: Yes. As the universe expands, it creates more empty space
Speaker 3: and therefore more total dark energy. But the inherent strength
Speaker 3: of that repulsive push per cubic meter remains absolutely rigid
Speaker 3: and unchanging across eternity.
Speaker 2: It's a static rule of the game, a fixed value
Speaker 2: that you just plug into your equations exactly. But the
Speaker 2: bombshell from DSI's early data, and this is just the
Speaker 2: initial three year data set, is that this foundational assumption
Speaker 2: might be entirely wrong.
Speaker 3: It's a massive shock to the community because.
Speaker 2: The data is heavily implying that dark energy is not
Speaker 2: a constant. It suggests that this repulsive force is actually evolving.
Speaker 3: The implications of that word evolving are monumental in the
Speaker 3: field of cosmology.
Speaker 2: I mean, it sounds like it breaks everything.
Speaker 3: It really does. If dark energy is dynamic, if its
Speaker 3: strength fluctuates or changes character as the universe ages, then
Speaker 3: the cosmological constant is a flawed model.
Speaker 2: So what does that mean? It actually is?
Speaker 3: It suggests dark energy might not be a simple property
Speaker 3: of empty space, but rather some kind of dynamic shifting field,
Speaker 3: or even more radically, perhaps an indication that our underlying
Speaker 3: theory of gravity is fundamentally incomplete on cosmic scales.
Speaker 2: Let me stop you there, because here's where it gets
Speaker 2: really interesting. If we throw out the constant part of
Speaker 2: the cosmological constant, what does that.
Speaker 3: Actually leave us with a lot of uncertainty?
Speaker 2: Doesn't a dynamic shifting dark energy completely obliterate our ability
Speaker 2: to predict how the universe ends? Because the ultimate fate
Speaker 2: of reality relies entirely on who wins that cosmic tug
Speaker 2: of war between gravity and dark energy.
Speaker 3: You hit the nail on the head. It entirely rewrites
Speaker 3: the predictive models. Wow. Under the assumption of a cosmological constant,
Speaker 3: the fate of the universe is a slow, relentless expansion.
Speaker 3: It is a scenario often called the Big Freeze or
Speaker 3: heat death.
Speaker 2: The Big Freeze sounds cozy.
Speaker 3: Not quite. The acceleration continues steadily forever, pushing galaxies so
Speaker 3: far apart that they become isolated islands, Stars burn out,
Speaker 3: matter decays, and the universe drifts into a cold, dark,
Speaker 3: infinite emptiness.
Speaker 2: Bleak.
Speaker 3: But you know, predictable, very predictable. But if the strength
Speaker 3: of dark energy is actively changing, then what if the
Speaker 3: force is dynamic? The future becomes wildly uncertain. If dark
Speaker 3: energy is gradually weakening over time, gravity could eventually reclaim dominance.
Speaker 2: Oh, so it could pull everything back together exactly.
Speaker 3: The expansion could halt, reverse and pull all matter back
Speaker 3: together in a catastrophic collapse, A big crunch, A big crunch.
Speaker 2: Okay, And what if it goes the other way? What
Speaker 2: if the push gets stronger?
Speaker 3: Conversely, if the repulsive strength of dark energy is increasing,
Speaker 3: the acceleration could become so violently intense that it eventually
Speaker 3: overpowers the gravitational forces holding galaxy clusters together. Oh no,
Speaker 3: then stellar systems, then planets, and ultimately the atomic bonds
Speaker 3: of matter.
Speaker 2: Itself, literally tearing the actual fabric of reality to shreds.
Speaker 3: Yes, that scenario is known as the big rip.
Speaker 2: The big rip. Okay, I need a minute. That's terrifying.
Speaker 3: It's traumatic, certainly. Doctor Suhadri Natzer, who is an associate
Speaker 3: professor at the University of Portsmouth and co chair of
Speaker 3: the Clustering Working Group for DE and I frame this perfectly.
Speaker 2: What did he say?
Speaker 3: He pointed out that the mere possibility of dark energy
Speaker 3: evolving with time is revolutionary on its own. It demands
Speaker 3: a foundational reassessment of the math we use to describe
Speaker 3: the cosmos.
Speaker 2: But that creates a massive logical problem. In my head.
Speaker 2: We've established that dark energy is totally invisible. We can't
Speaker 2: put it in a jar, we can't directly measure its
Speaker 2: temperature or its mass. So how on earth are these
Speaker 2: researchers using a map of visible tangible galaxies to prove
Speaker 2: that an invisible phantom force is changing its behavior over
Speaker 2: billions of years.
Speaker 3: It's a great question. They do it by tracking the
Speaker 3: physical consequences of that cosmic tug of war over eleven
Speaker 3: billion years.
Speaker 2: Okay, go on.
Speaker 3: Dark energy is invisible, but gravity is not, and the
Speaker 3: way gravity pulls visible matter together leads a structural footprint
Speaker 3: that we can actually measure.
Speaker 2: You're talking about cosmic clustering, specifically.
Speaker 3: Buryon acoustic oscillations, but the broader concept is clustering.
Speaker 2: Right.
Speaker 3: To trace dark energy DSi isn't just looking at individual galaxies.
Speaker 3: It is analyzing the spatial relationships between them. It is
Speaker 3: measuring exactly how galaxies group together at different points in
Speaker 3: cosmic history.
Speaker 2: I need a physical analogy for this, because measuring the
Speaker 2: distance between dots on a map to track an invisible
Speaker 2: force is a leap for me.
Speaker 3: Let's hear it.
Speaker 2: Okay, imagine looking at a crowd of people dispersing after
Speaker 2: a concert from a helicopter. By tracking how the clusters
Speaker 2: of people spread out over an hour, you could deduce
Speaker 2: if there was like a sudden rainstorm pushing them to
Speaker 2: run faster.
Speaker 3: That's a good start. Let's make it a bit more
Speaker 3: physical though. Imagine a giant rubber band stretched across a table.
Speaker 2: Okay, a rubber band.
Speaker 3: You have two heavy iron weights resting on it, pulling
Speaker 3: the rubber band slightly toward each other. The tension of
Speaker 3: the weights pulling together represents gravity.
Speaker 2: Got it.
Speaker 3: Now, the rubber band itself being slowly pulled from the
Speaker 3: edges of the table. That is dark energy.
Speaker 2: Oh, that is a highly functional analogy. So the weights
Speaker 2: naturally want to slide toward each other and clump together,
Speaker 2: but the surface they are resting on is actively being
Speaker 2: stretched in the oposite direction.
Speaker 3: Precisely so, if you want to know if the stretching
Speaker 3: force the dark energy is constant or changing, you don't
Speaker 3: look at the rubber band because you can't see it, right.
Speaker 3: You just measure the distance between the two iron weights
Speaker 3: at different times.
Speaker 2: Oh, if the weights are pulling together fast, gravity is winning.
Speaker 2: If they are suddenly being pulled apart, faster than before,
Speaker 2: the stretching force must be ramping up.
Speaker 3: Exactly, and in the context of the universe, those weights
Speaker 3: are the massive clusters of galaxies. Right in the early
Speaker 3: epochs of the universe, matter was much denser, Galaxies were
Speaker 3: closer together, which meant the gravitational pull between them was
Speaker 3: incredibly strong. Gravity was effectively dominating the tug of war,
Speaker 3: actively pulling material together into these massive, intricate cosmic webs.
Speaker 2: So the weights were tightly grouped.
Speaker 3: But as the universe expanded, driven by dark energy, the
Speaker 3: overall dense.
Speaker 2: Matter dropped, the stretching continued.
Speaker 3: Yes, galaxies were pushed further apart, which inevitably weakened the
Speaker 3: gravitational attraction between them. As gravity's grip loosened on massive scales,
Speaker 3: dark energy began to dictate the structural evolution.
Speaker 2: So the map DSi built allows researchers to literally look
Speaker 2: back at the tightly clumped weights eleven billion years ago
Speaker 2: and then measure how that clumping pattern changes epoch by
Speaker 2: epoch as you move closer to the present day.
Speaker 3: They are essentially reading the historical record of the expansion
Speaker 3: by taking incredibly precise measurements of ancient galaxy clusters and
Speaker 3: comparing their distribution to clusters closer to us. In time,
Speaker 3: they map the exact influence of dark energy at every
Speaker 3: stage of the universe's life, but wait.
Speaker 2: To get those measurements from eleven billion years ago. They
Speaker 2: can't just look at regular galaxies, right, because the light
Speaker 2: from a standard galaxy that far away would be way
Speaker 2: too faint for even the five thousand fiber optic robots
Speaker 2: to pick up.
Speaker 3: You're absolutely right, which is why as significant portion of
Speaker 3: dii's targeting relies on quasars quasars. To map the deepest
Speaker 3: edges of the visible universe, you need a beacon. Quasars
Speaker 3: serve as those distant lighthouses.
Speaker 2: For those who might not be familiar with the sheer
Speaker 2: violence of a quasar, we are talking about an active
Speaker 2: galactic nucleus. It's a supermassive black hole at the center
Speaker 2: of a distant galaxy that is actively feeding on astronomical
Speaker 2: amounts of gas and dust.
Speaker 3: The gravitational friction of that material spiraling into the black
Speaker 3: hole heats to such extreme temperatures that it in miss
Speaker 3: radiation across the entire electromagnetic spectrum. It's so bright unbelievably bright.
Speaker 3: A single quasar can easily outshine the combined light of
Speaker 3: every single star in its host galaxy.
Speaker 2: They are practically screaming across the universe.
Speaker 3: Their extreme luminosity allows disized spectrographs to capture their light
Speaker 3: even from eleven billion light years away. Amazing, But the
Speaker 3: quasars are doing more than just marking a point on
Speaker 3: a map their light. It actually illuminates the invisible material
Speaker 3: lying between them and Earth.
Speaker 2: Like shining a flashlight through a foggy forest. You might
Speaker 2: not see the individual trees in the dark, but the
Speaker 2: beam of the flashlight catches the mist and the branches
Speaker 2: between you and the light source.
Speaker 3: That is an incredibly accurate description of what we call
Speaker 3: the Liman alpha forest technique.
Speaker 2: Oh Lyman alpha forest cool name.
Speaker 3: It is as the brilliant light from a distant quasar
Speaker 3: travels eleven billion light years to reach DSi, it passes
Speaker 3: through massive invisible clouds of intergalactic hydrogen gas. Those gas
Speaker 3: clouds absorb specific tiny slivers of the quasar's light spectrum.
Speaker 2: Leaving dark bands, or like fingerprints, in the light wave
Speaker 2: that DISI eventually captures an Arizona.
Speaker 3: Exactly by analyzing those absorption bands, researchers can map the
Speaker 3: density and distribution of invisible hydrogen gas spanning billions of
Speaker 3: light years.
Speaker 2: That is genius.
Speaker 3: So they aren't just mapping the bright points of light.
Speaker 3: They are mapping the invisible structure of the cosmic web itself.
Speaker 3: And it is this comprehensive, multi layered mapping of visible galaxies,
Speaker 3: brilliant quasars, and invisible gas clouds that provided the clustering data.
Speaker 2: And when they finally ran the math on all of
Speaker 2: that data, tracing the tug of war across eleven billion years,
Speaker 2: the results pointed to an evolving dark energy.
Speaker 3: The strength of the push varied.
Speaker 2: It is an astonishing realization. And you know what strikes
Speaker 2: me is the sheer human capital required to even process
Speaker 2: a thought on this scale. I mean, the instrument is
Speaker 2: a marvel, but the human machinery behind it is just
Speaker 2: as vast.
Speaker 3: The scale of collaboration is a defining characteristic of modern astrophysics.
Speaker 3: You simply cannot process forty seven million spectroscopic measurements with a.
Speaker 2: Small team in the basement, right, It takes an army.
Speaker 3: The DTI collaboration involves over nine hundred researchers spanning more
Speaker 3: than seventy institutions across the globe.
Speaker 2: Nine hundred and I saw that a third of those researchers,
Speaker 2: about three hundred of them, are PhD students. The next
Speaker 2: generation of cosmologists are basically cutting their teeth on a
Speaker 2: day data set that is actively dismantling the models their
Speaker 2: textbooks were based on.
Speaker 3: It represents a massive transfer of institutional knowledge. The project
Speaker 3: is managed by the US Department of Energy at Berkeley Lab,
Speaker 3: but the intellectual lifting is heavily distributed.
Speaker 2: It's a global village, very much so.
Speaker 3: You have major hubs of analysis in the UK, for example,
Speaker 3: with deep involvement from the University of Portsmouth, University College London,
Speaker 3: and Durham University.
Speaker 2: And these teams are currently locked in what they describe
Speaker 2: as churning through the data because the five year survey
Speaker 2: is complete, right, the physical observations for this massive map
Speaker 2: are done and in the camp.
Speaker 3: Yes, the tantalizing evidence for evolving dark energy came from
Speaker 3: the initial three year data release.
Speaker 2: Okay, so what about the rest of it.
Speaker 3: The definitive, highly rigorous cosmological constraints that will emerge from
Speaker 3: the complete five year data set are expected in twenty twenty.
Speaker 2: Seven twenty twenty seven, so the entire physics community is
Speaker 2: essentially holding its breath for the next few years to
Speaker 2: see if the cosmological constant officially died.
Speaker 3: Pretty much.
Speaker 2: But wait, while they are churning through the data for
Speaker 2: dark energy, they've realized this map is so dense and
Speaker 2: so precise that they can use it for completely different
Speaker 2: scientific inquiries.
Speaker 3: The bonus science.
Speaker 2: The side quests. They are using the macrostructure of the
Speaker 2: universe to study the most elusive subatomic particles in existence.
Speaker 3: Yes, they're using the clustering data to calculate the mass
Speaker 3: of neutrinos.
Speaker 2: Okay, I genuinely struggle to wrap my head around this.
Speaker 2: So what does this all mean? Neutrinos are the lightest,
Speaker 2: most ghostlike fundamental particles we know of, right correct, Trillions
Speaker 2: of them are passing through my body right now without
Speaker 2: interacting with anything. How on earth does a giant map
Speaker 2: of massive galaxies help us weigh the tiniest, lightest particles
Speaker 2: in existence.
Speaker 3: If we connect this to the bigger picture, it requires
Speaker 3: linking the microscopic world of quantum mechanics to the macroscopic
Speaker 3: evolution of the cosmos.
Speaker 2: Okay, I'm with you.
Speaker 3: Neutrinos are indeed incredibly elusive. They have virtually zero mass,
Speaker 3: and they travel near the speed of light because they
Speaker 3: interact so weakly with normal matter. Building a laboratory instrument
Speaker 3: to waveh them directly is incredibly difficult.
Speaker 2: That they do have a mass, it's not zero.
Speaker 3: It is not zero, And while an individual neutrino's mass
Speaker 3: is infinitesimally small, they are among the most abundant particles
Speaker 3: in the universe. Right when you aggregate the mass of
Speaker 3: every neutrino in existence, it constitutes a substantial amount of material,
Speaker 3: and anything with mass exerts a gravitational influence.
Speaker 2: Okay, so how does that influence show up on a
Speaker 2: map of galaxies.
Speaker 3: You have to look back at the early universe when
Speaker 3: those massive galaxy clusters were just beginning to form.
Speaker 2: Back to the weights on the rubber band.
Speaker 3: Exactly, gravity was trying to pull dark matter in standard
Speaker 3: matter together into dense structures. But because neutrinos are so hot,
Speaker 3: meaning they move at velocities incredibly close to the speed
Speaker 3: of light, they refuse to be bound by those early
Speaker 3: relatively weak gravitational wells.
Speaker 2: Oh they are moving too fast to be trapped by
Speaker 2: the clumping matter.
Speaker 3: Exactly right through these forming structures, and because they carry
Speaker 3: mass with them as they stream outward, they effectively drag
Speaker 3: a tiny amount of gravitational influence with them. Wow. This process,
Speaker 3: known as free streaming, has a subtle but undeniable effect
Speaker 3: on the formation of the cosmic web. It physically smears
Speaker 3: out the distribution of matter.
Speaker 2: It blurs the sharp edges of the galaxy clusters.
Speaker 3: It suppresses the clumping of matter on certain specific scales.
Speaker 3: Because Dehi's map of where galaxies are positioned is so
Speaker 3: outrageously precise, researchers can scan the data looking for that
Speaker 3: exact statistical smearing effect.
Speaker 2: That is incredible.
Speaker 3: The degree to which the cosmic web has been smoothed
Speaker 3: out serves as a direct measurement of how much mass
Speaker 3: the neutrinos were carrying.
Speaker 2: That is profound. You are using the gravitational architecture of
Speaker 2: the entire observable universe as a scale to weigh a
Speaker 2: subatomic particle.
Speaker 3: It highlights how deeply interconnected the physics of the vacuum
Speaker 3: are with the physics of the very large It really does.
Speaker 2: Doctor Natither mentioned that we have barely scratch the surface
Speaker 2: of what this data set can do, and this neutrino
Speaker 2: weighing is the perfect example, and it is.
Speaker 3: Exactly that multidisciplinary utility that justifies extending the instrument's operational life.
Speaker 2: Wait, they're keeping it going.
Speaker 3: Oh, yes, the initial five year parameters have been fulfilled.
Speaker 3: The primary map is complete, but the hardware is functioning flawlessly.
Speaker 2: So they aren't turning the robots off. They are pushing
Speaker 2: directly into the unknown.
Speaker 3: From twenty twenty four through twenty twenty eight, DSi is
Speaker 3: officially expanding its mission.
Speaker 2: I love that they hit forty seven million targets blue
Speaker 2: past their goals and immediately decided to map the absolute hardest,
Speaker 2: most frustrating parts of the sky just to see what
Speaker 2: they can extract.
Speaker 3: The expansion of the survey area is significant. They are
Speaker 3: increasing the maps coverage by roughly twenty percent, growing the
Speaker 3: observed footprint from fourteen thousand square degrees to seventeen thousand
Speaker 3: square degrees.
Speaker 2: Let's contextualize a square degree because it's not a metric
Speaker 2: you use at the grocery store. It's not if you
Speaker 2: go outside and look at a full moon. The surface
Speaker 2: area that the moon occupies in your field of vision
Speaker 2: is about zero point two square degrees.
Speaker 3: Right.
Speaker 2: The entire sphere of the sky surrounding the Earth is
Speaker 2: a bit over forty one thousand square degrees, So an
Speaker 2: expansion of three thousand square degrees is the equivalent of
Speaker 2: adding a swathe of the sky roughly the size of
Speaker 2: fifteen thousand full moons.
Speaker 3: It is a massive undertaking, particularly because they are actively
Speaker 3: targeting regions that were previously deemed too difficult or inefficient.
Speaker 2: To map, which brings us back to that massive black
Speaker 2: blind spot we discussed earlier, the plane of the Milky Way.
Speaker 3: They are attempting to thread the needle through the zone
Speaker 3: of avoidance.
Speaker 2: But how we talked about how the dust and stellar
Speaker 2: crowding of our own galaxy obscure the faint light from
Speaker 2: the distant universe.
Speaker 3: We did, But the instrumentation on DSi is sensitive enough
Speaker 3: and the background algorithms have become sophisticated enough that they
Speaker 3: believe they can extract viable spectroscopic data from some of
Speaker 3: those highly obscured regions.
Speaker 2: They are literally staring straight into the high beam headlights
Speaker 2: to find the fireflies.
Speaker 3: They really are. But that's only one of the challenging regions.
Speaker 3: What's the other The second area they are expanding into
Speaker 3: pushes further to the south, and the obstacle there isn't
Speaker 3: interstellar dust. It's our own planet's atmosphere.
Speaker 2: Oh, because kit Peak is in Arizona exactly.
Speaker 3: Operating a ground based telescope involves constantly fighting the Earth's atmosphere.
Speaker 3: To observe targets further south, the telescope must angle lower
Speaker 3: toward the horizon, so you.
Speaker 2: Are no longer looking straight up through the thinnest part
Speaker 2: of the atmosphere. You are looking at a sharp angle
Speaker 2: through a massive cross section of air.
Speaker 3: The term is air mass. When you look toward the horizon,
Speaker 3: the light from a distant galaxy has to travel through
Speaker 3: a much thicker layer of turbulent, shifting atmospheric gases before
Speaker 3: it hits the primary.
Speaker 2: Mirror, which causes distortion.
Speaker 3: Massive distortion. It causes atmospheric refraction and significant scattering of
Speaker 3: the optical light.
Speaker 2: It's why stars twinkle violently when they're low on the horizon,
Speaker 2: but look steady when they are straight overhead.
Speaker 3: Exactly, And for an instrument relying on the precise separation
Speaker 3: of light frequencies to measure microscopic ridshifts. That atmosphere twinkling
Speaker 3: is incredibly destructive. The data becomes noisy.
Speaker 2: But they're going for it anyway.
Speaker 3: But again, the analytical pipelines have improved to the point
Speaker 3: where researchers are confident they can clean that noisy data
Speaker 3: and push the map further south than initially thought possible.
Speaker 2: And it's not just about pushing the borders outward, is it.
Speaker 2: They are also turning the instrument back inward, revisiting patches
Speaker 2: of the sky they've already mapped.
Speaker 3: Because the initial sweep naturally prioritized the most prominent, easily
Speaker 3: identifiable targets to build the structural foundation of the map.
Speaker 3: Now they are hunting for a specific class of object
Speaker 3: to increase the density of the data.
Speaker 2: They are looking for luminous red galaxies.
Speaker 3: They're massive, incredibly ancient elliptical galaxies. They have exhausted their
Speaker 3: star forming gas, meaning they are populated by older.
Speaker 2: Redders, which makes them hard to see.
Speaker 3: It very faint and difficult to isolate, but they serve
Speaker 3: as excellent tracers for the mass of dark matter halos
Speaker 3: that dictate the structure of the cosmic web by layering
Speaker 3: the locations of these elusive red galaxies into the existing data.
Speaker 3: They are essentially upgrading the resolution of the map, taking.
Speaker 2: A four K map and cramming even more pixels into it. Exactly,
Speaker 2: but practically speaking, how do you manage that you have
Speaker 2: a telescope that needs to execute its primary tracking, but
Speaker 2: now you are asking it to fight the milky ways,
Speaker 2: glare peer through miles of turbulent atmosphere on the horizon,
Speaker 2: and go hunting for faint red ghosts and previously mapped areas.
Speaker 3: This raises an important question about efficiency. How do we
Speaker 3: ensure it all works? It requires seamless logistical integration.
Speaker 2: The software must be working overtime.
Speaker 3: The expanded mission doesn't operate in a vacuum. These new,
Speaker 3: incredibly challenging observations are being interwoven directly into the ongoing
Speaker 3: observational program. The scheduling software constantly calculates the optimal sequence
Speaker 3: of targets to ensure that the five thousand Rouws body
Speaker 3: positioners are never idle. It is relentless optimization of telescope time.
Speaker 2: It really stands as a monument to human curiosity. We
Speaker 2: built a machine of unprecedented power, finished the largest cartography
Speaker 2: project in history early and the immediate reaction wasn't to
Speaker 2: celebrate and go home.
Speaker 3: No, the reaction was to dig deeper.
Speaker 2: It was to push the machine harder into the darkest,
Speaker 2: dirtiest parts of the sky, just to see what the
Speaker 2: ghost is doing in the shadows.
Speaker 3: It reflects the urgency of the questions being asked. When
Speaker 3: the foundational rules of your field are suddenly called into question,
Speaker 3: you don't turn off the instrument. You collect more data.
Speaker 2: Which brings this entire journey full circle. We started this
Speaker 2: discussion standing on a dark night looking up at the
Speaker 2: Little Dipper, but intellectually we've traveled from a mountain peak
Speaker 2: in Arizona to the edge of the observable universe. Tracing
Speaker 2: the ancient light of forty seven million galaxies across eleven billion.
Speaker 3: Years, we have watched the most comprehensive measurement of the
Speaker 3: cosmic dug of war ever recorded. We've seen how tracking
Speaker 3: the structural evolution of the universe from the tightly bound
Speaker 3: early Epex to the vastly expanded modern era has revealed
Speaker 3: a fundamental anomaly.
Speaker 2: An anomaly suggesting that dark energy, the dominant force of reality,
Speaker 2: might not be an unwavering mathematical constant, but an actively
Speaker 2: evolving pressure. And that is where I want to leave you.
Speaker 2: That's a lot to process, it really is. When we
Speaker 2: think about the laws of physics, we tend to conceptualize
Speaker 2: them as a rigid rule book, a set of mathematical
Speaker 2: constants that were etched into stone at the exact moment
Speaker 2: of the Big Bang, governing everything from the speed of
Speaker 2: light to the pull of gravity. Our job, as we
Speaker 2: understood it, was simply to build better machines to read
Speaker 2: those static rules. But if seventy percent of the universe
Speaker 2: is driven by a force that shifts and changes as
Speaker 2: time passes, it forces a deeply provocative question. If the
Speaker 2: constants of the universe are capable of evolving along with
Speaker 2: the universe itself, perhaps we aren't trying to decipher a
Speaker 2: finished static rulebook at all. Perhaps the universe is still
Speaker 2: actively writing it. Keep that flexibility of reality in mind
Speaker 2: the next time you look up at the night sky.