Craig Hogan, "The Unlikely Primeval Sky" (American Scientist, November-December)

Summary

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Podcast Summary: "The Unlikely Primeval Sky"

New Books Network – Interview with Craig Hogan
Date: November 13, 2025
Host: Gregory McNeff
Guest: Professor Craig Hogan, Astrophysicist (University of Chicago)

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Episode Overview

This episode features astrophysicist Craig Hogan discussing his article, "The Unlikely Primeval Sky" (American Scientist, Nov-Dec 2025), which probes one of cosmology’s greatest puzzles: why the Cosmic Microwave Background (CMB)—the universe's earliest observable light—is so improbably smooth and uniform on the largest scales. The conversation traverses cosmic origins, models of early universe physics, and the unresolved mysteries that challenge our understanding of the cosmos, including the implications for new physics and the hunt for quantum gravity.

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Key Discussion Points & Insights

1. Why Explore the Universe’s Early Uniformity?

• Motivation for the Article
  • Hogan wanted to take stock of what we know—and don’t—about our cosmic origins, especially regarding the mysterious smoothness of the early universe.
  • “It's two parts of that are, you know, what are the hard, precise facts we know? ...What are the huge mysteries...?” (Craig Hogan, [01:54])

2. What is the Cosmic Microwave Background (CMB)?

• Definition and Discovery
  • CMB is the "afterglow" of the Big Bang, first detected in 1965.
  • It is radiation from about 380,000 years after the Big Bang, now cooled and stretched across the universe.
  • “The sky is dark at night…but it's actually full of microwaves in all directions. And that is light that has been around since the beginning of the universe.” (Craig Hogan, [02:37])
• Analogy
  • Comparable to seeing only the surface of the sun—not the inside. We see the "surface" of the early universe.

3. The Astonishing Smoothness of the CMB

• Scale & Significance
  • Across vast cosmic distances, the temperature varies by less than 1 part in 10,000.
  • Modern models predict much more "messiness" if the universe arose from random processes.
  • “The temperature of this microwave background is almost exactly the same…1 in 10 to the 4th in all directions. And that's…it’s some kind of deep symmetry.” (Craig Hogan, [04:42])

4. Key Cosmological Models & Theories

• General Relativity & Expanding Universe
  • Einstein’s theory laid the groundwork; the FLRW model describes a universe that is homogeneous and isotropic on large scales.
  • Hubble’s 1920s observations confirmed galaxies are retreating from each other, signaling cosmic expansion.
  • “It really started a bit over a hundred years ago…it's really all about gravity…The theory of that gravity is the one that was invented by Einstein in 1915...” (Craig Hogan, [06:18])
• The Hot Big Bang & Blackbody Radiation
  • The early universe’s “blackbody” spectrum—a precise match with predictions from quantum mechanics (Planck’s Law)—was confirmed by satellite observations.
  • “It really confirms that all this light did start in a very hot, dense early phase because that's the way the Planck spectrum forms…” (Craig Hogan, [09:01])

5. Lambda Cold Dark Matter (ΛCDM) Model Success and Limitations

• Successes

  • ΛCDM broadly explains galaxy formation and CMB fluctuations at small scales.
  • The match between simulations and observed maps is “amazing.” (See [12:23])

• Anomaly at the Largest Scales

  • On the biggest angular separations, the CMB is far smoother than predicted—even smoother than what random quantum fluctuations would generate.
  • “If we occupy a random universe that arose from random noise, we should expect to see all kinds of messy patterns…Instead, we observe a neat uniform pattern that seems extremely unlikely statistically speaking.” (Gregory McNeff summarizing, [11:15])
  • “It's as if they're arranged, it's smoother than you expect…The precision of that is remarkable.” (Craig Hogan, [12:23])

6. A Deep Mystery: Luck, Conspiracy, or New Physics?

• The Symmetry Problem
  • Statistically, fewer than 1 in a thousand simulated universes have CMB maps as smooth as ours (see [14:45]).
  • Raises the question: did we just get “lucky,” or is there an undiscovered principle (symmetry or process) at play?
  • “If it is a symmetry and not a conspiracy, then it's telling us something profound.” (Craig Hogan, [15:26])
• Call for New Physics
  • Standard quantum models may be missing a key ingredient; an unknown symmetry or principle may enforce this large-scale uniformity.
  • “There's some ingredient in that model that the current ideas are not including...This is the universe telling us something.” (Craig Hogan, [15:26])

7. Quantum Mechanics vs. Gravity—The Unsolved Union

• Current Theories
  • Quantum mechanics describes the micro (particles); general relativity describes the macro (space-time).
  • Reconciling both—especially in early universe conditions—is a core challenge.
  • “They fundamentally disagree about some important things and they've never really been reconciled.” (Craig Hogan, [18:06])
• CMB as a Window Into Quantum Gravity
  • The universe may be offering rare, tangible data to guide creation of a quantum gravity theory.

8. Data Sources: Satellites & Surveys

• CMB Observatories
  • COBE, WMAP, and Planck satellites provided the crucial CMB maps ("spectacular").
  • Ground-based telescopes and newer satellites (e.g., Euclid) continue to refine the data.
  • “The microwave background was the first hard evidence we had of very precise uniformity on large scale.” (Craig Hogan, [20:59])
• Galaxy Surveys
  • Projects like the Sloan Digital Sky Survey (SDSS) and DESI build 3D maps of the galaxy distribution—a cosmic web mirroring CMB predictions at small scales.

9. Understanding Structure Formation: Anisotropies & Inflation

• Anisotropy Defined
  • "Anisotropy" = deviations from perfect uniformity in the CMB; "isotropy" would be complete sameness in all directions.
  • “Anisotropies are…departures from [isotropy]...the lumpiness in the maps.” (Craig Hogan, [22:52])
• Inflation Theory
  • Proposes a rapid early expansion to explain overall uniformity, but current quantum models of inflation may still fall short on the smoothness anomaly.
  • “Inflation…was a way to understand how the early universe got going, how the expansion started.” (Craig Hogan, [22:59])

10. The Ongoing Expansion, Hubble Tension, Dark Matter & Dark Energy

• Universal Expansion
  • The universe isn’t just expanding but accelerating (“late-time acceleration”), likely due to "dark energy."
  • Dark energy could be Einstein’s cosmological constant or something stranger—a key riddle.
  • “During the last factor to an expansion, it seems to be speeding up…Einstein's theory tells us that if…‘empty space’…has some energy in it, the gravity of that is repulsive.” (Craig Hogan, [24:48])
• Dark Matter
  • Observed only via gravity—still undetected in labs.
  • “All the hard evidence…still comes from the sky, not from the laboratory.” (Craig Hogan, [26:59])

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Notable Quotes & Memorable Moments

• On the CMB’s Uniformity:
  “The temperature of this microwave background is almost exactly the same...1 in 10,000 in all directions. That’s...some kind of deep symmetry.”
  — Craig Hogan, [04:42]

• On the Big Mystery:
  “It's as if they're arranged, it's smoother than you expect. …This large scale regularity, that's not what you expect in the standard set of ideas people use for the earliest universe.”
  — Craig Hogan, [12:23]

• Statistical Rarity:
  “In brief, fewer than about 1 in a thousand random realizations stay as close to zero as the real sky.”
  — Craig Hogan quoted by Gregory McNeff, [14:45]

• On Missing Physics:
  “Apparently it's missing something…if it is a symmetry and not a conspiracy, then it's telling us something profound.”
  — Craig Hogan, [15:26]

• On Quantum Gravity’s Riddle:
  “They fundamentally disagree about some important things and they've never really been reconciled.”
  — Craig Hogan, [18:06]

• Data’s Importance:
  “People invented quantum mechanics…if it hadn't been for the data. I would like to think...we can listen to nature again."
  — Craig Hogan, [18:06]

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Timestamps for Important Segments

• [01:54] – Motivations for writing the article and current state of cosmology
• [02:37] – What is the CMB and what does it tell us?
• [04:42] – The extraordinary smoothness of the universe
• [06:18] – How general relativity and FLRW models shape our understanding
• [09:01] – Blackbody radiation’s role in confirming the hot Big Bang
• [11:15] – Success of current models and introduction of the smoothness anomaly
• [12:23] – Detailed discussion of the large-scale CMB anomaly
• [14:45] – Statistical unlikelihood of our actual universe under current models
• [15:26] – Quantum mechanics, symmetry, and hints of new physics
• [18:06] – Reconciling quantum mechanics and relativity; quantum gravity
• [20:59] – Where does the data come from? Satellites and surveys
• [22:52] – Anisotropies, inflation, and structure formation
• [24:48] – Universal expansion, dark matter, and dark energy

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Conclusion

Craig Hogan’s conversation vividly illustrated both how much cosmology has achieved (mapping the universe’s structure, confirming the hot Big Bang) and how truly profound its outstanding questions remain. The universe’s uncanny smoothness on the largest scales defies simple random chance, hinting urgently at undiscovered physics—perhaps even the first empirical clue to a theory uniting quantum mechanics and gravity.

For cosmology, these cosmic patterns are more than data—they’re clues to the deepest laws of nature.

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Article Referenced:
The Unlikely Primeval Sky by Craig Hogan, American Scientist, November-December 2025.

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Transcript

[A]

Hello, everybody. This is Marshall Po. I'm the founder and editor of the New Books Network. And if you're listening to this, you know that the NBN is the largest academic podcast network in the world. We reach a worldwide audience of 2 million people. You may have a podcast or you may be thinking about starting a podcast. As you probably know, there are challenges basically of two kinds. One is technical. There are things you have to know in order to get your podcast produced and distributed. And the second is, and this is the biggest problem, you need to get an audience. Building an audience in podcasting is the hardest thing to do today. With this in mind, we at the NBM have started a service called NBN Productions. What we do is help you create a podcast, produce your podcast, distribute your podcast, and we host your podcast. Most importantly, what we do is we distribute your podcast to the NBN audience. We've done this many times with many academic podcasts and we would like to help you. If you would be interested in talking to us about how we can help you with your podcast, please contact us. Just go to the front page of the New Books Network and you will see a link to NBN Productions. Click that, fill out the form, and we can talk. Welcome to the New Books Network.

[B]

Welcome to the New Books Network. I'm your host, Gregory McNeff, and today I'm joined by Professor Craig Hogan, astrophysicist at the University of Chicago and former director of the Fermilab center for Particle Astrophysics. Craig's article, the Unlikely Primeval sky, in the November December issue of the American Scientist explores one of the most beautiful and puzzling findings in modern cosmology. That of all the patterns that could have been preserved in the post Big Bang radiation, the one we actually observe, it is astonishing, smooth on the largest scales. We're going to talk about this unique finding now with Craig. Craig, thank you so much for joining us today to discuss your article.

[C]

I'm delighted to be here. Thanks.

[B]

Craig, why did you write this article? And could you talk a little bit about the research that you've been doing to support it?

[C]

Well, yeah, I thought it was a good time to kind of give everybody an update on where we are with understanding our cosmic origin story. You know, it's. It's been an ongoing process of finding, discovering new facts over the last 60 years or so and developing, you know, physical theories to go with that. And so, and it's two parts of that are, you know, what are the hard, precise facts we know? What do we really understand? Well, and then what are the huge mysteries that are still out there that we haven't explained? Obviously, it's an important question. It's where it all. How it all began.

[B]

Absolutely. And getting to that, could you talk about what the cosmic microwave background is and why it's sometimes called the universe afterglow?

[C]

Right. So 1965, some scientists at Bell Labs discovered really accidentally that there's. The sky is a dark at night. I mean, it looks dark when you look at it at the sky, but it's actually full of microwaves in all directions. And that is light that has been around since the beginning of the universe. And, you know, gradually since then, we learn more and more about it, and it's. And as the details continue to astound and afterglow is a good way to describe it, at the beginning, it was a lot hotter. But these properties that we see today, a lot of them really go back to that very early time.

[B]

And just to clarify, Craig, what we're looking at is radiation from roughly 380,000 years after the Big Bang. And for context, we believe the Big bang occurred roughly 13.8 billion years ago. So literally almost, you know, in. In terms of the life cycle of the universe, almost immediately after, quote, coming into existence, being born, however you want to define it. Right.

[C]

That's right. And. And that those. That's the. That's when the light that we just see now, the ones actually hitting the telescopes now, you know, what's filling the dark sky, that's how long they've been traveling without interacting with matter since that very early time. But the actual light started much earlier than that. And some things about it, because it was, you know, the earlier part was sort. It's sort of like looking at the surface of a star, like the sun. The light starts in the middle of the sun, and we just see the surface. And so it's that surface that we're looking at 380,000 years after big Bang, but the light itself, and actually the spectrum was formed even earlier than that. So there's a lot. You can do a lot more digging.

[B]

Yeah. And it sounds like that's what we're really trying to do. You talk about this puzzle about the observed cosmic microwave background. I'll reference it as CMB is, quote, almost ridiculously atypical. It's so improbable relative to what our models would suggest. Could you talk about that?

[C]

Right. So one of the most distinctive and surprising things about the universe is that it's on very large scales. Averages or very large scales. It's very, very uniform. Every place is like every other. Every direction is like every other. So the temperature of this microwave background is almost exactly the same. It's part smaller than 10 to the 4, 1 in 10 to the 4 in all directions. And that's a, you know, that's, it's some kind of deep symmetry. And it, it contrasts with the universe today, which is pretty complicated. You know, every place is different really. I mean, every planet, every, you know, every square inch of the Earth really is different. So how did that happen? What are the, how did it go from one to the other? And it, and it really is, it's a fact about the universe, not, you know, I described it referred to an origin story, but, you know, it's a story where we actually directly observe many of the stages looking with light back in time.

[B]

And I want to go to that, that shift of that transition from almost uniformity to, as you point out, certain, I guess, overall smoothness throughout the universe. But I want to drill down into that a little bit more, Craig. But before we do, you spend some time talking about Einstein's, obviously his space time fields as well as what you label the Friedman lemaitre, Robertson Walker, the FLRW model and Hubble's discovery of the expanding universe. Could you briefly talk about how those three come together to give us sort of our view of the universe today, of how it's expanding and the importance of gravity and space time in that?

[C]

Yeah, the reason that that's a good place to start the story is that both on the theory and the observational side, it really started a bit over a hundred years ago. Like you said, on the large scales, it's really all about gravity. It's all this, the motion of matter, the distribution of everything. The main force that's shaped and large scales is just gravity. And the theory of that gravity is the one that was invented by Einstein in 1915, the general theory of relativity. And shortly after that, people started to write down cosmological models based on that theory of gravity. Basically, the gravity theory tells you how space and time behave and how they interact with matter. And the cosmological model is like it sounds, it's, it's a whole space time. It describes a whole universe. And, and, and back in the 20s, early 20s, people started to figure out that you could, you know, have a whole universe based on the theory of gravity, which is almost perfectly uniform and, and the same in all directions. Like now we know the real universe is at that time. It was just the idea, it was Just the math. And people started to guess about, well, what could the real universe look like? Einstein did that others. But the real data on that actual comparing it with the actual universe started in the mid-20s, about 100 years ago. And Hubble first showed that the universe has made a galaxy. He started seeing other whole galaxies outside our Milky Way. And by the end of the 20s, he discovered that the universe, it is made of galaxies that are flying apart from each other. The farther away they are, the faster they're moving away. So this is now the Hubble expansion, as we would call it. And that is a property of those, those universes that were invented in relativity 10 years earlier. So that was kind of kicked off the idea of having a cosmological model the way that you. A possibility of actually modeling the universe on large scales.

[B]

Yeah, you write the FLRW model offers a useful way to think about how the universe behaves on a large scale. And to your point, you just mentioned Hubble's discovery of the, I guess the Doppler effect in the expanding universe. But you also say in the beginning space was very dense, very nearly uniform, and very rapidly expanding. Interaction with matter gave radiation during this period a nearly perfect uniform black body spectrum. What are black bodies and how do they prove or suggest the universe did begin with a hot Big Bang?

[C]

Yeah, that's a really important point. And so winding back a little bit. So Hubble, you just look at the local galaxies, you can think about them as moving away from us, but the Einsteinian relativistic models, they would describe it a bit differently. They would say that the space between the galaxies is itself expanding. And so the galaxies, there's a whole system of galaxies is stretching apart. And if you use that better theoretical framework, you can extrapolate it back in time. So the galaxies long ago are much closer together. And particularly if you take what we now observe, the microwave background, you can extrapolate that back in time. So of course, like I said, that wasn't discovered until the 1960s. And that's when this modern Euro cosmology really started, you know. So we cosmology went beyond just thinking about galaxies to thinking about the early universe. You take the microwave background we see and extrapolate it far. It gets hotter and hotter. As you go back in time, it's 2.7 degrees above absolute zero. Now. When it stopped talking to matter 380,000 years after the Big Bang, it was about a thousand times hotter than that. So it was like the surface of a star. Things are pretty hot that's like the surface of a star. That's why it's opaque. The matter is ionized beyond that. And the spectrum that we see, the distribution with wavelength, has this very particular form, a pure black body that what we call the Planck spectrum. And that was invented even earlier. That was max Planck in 1900, the beginning of quantum mechanics, from essentially pure thought wrote down a formula, the Planck law, and that it agrees exactly with the spectrum of light that we see coming from the sky. It's one of the most remarkable things and it really, it really confirms that it all this light really did start in a very hot, dense early phase because that's the way the Planck spectrum forms is when radiation interacts with black, with black body matter, it's talking to very dense hot matter. So that was first shown when the cosmic in detail, when the Cosmic Background Explorer satellite launched and the first results were in the early 90s.

[B]

Okay, I'm going to ask you another clarification question because on the one hand you suggest that we have a pretty good idea of how galaxies were formed. You write the success of the Lambda cold dark matter model, especially its precise agreement with CMB maps as well as its broad agreement with the modern day galaxy distribution, shows quote, that we mostly understand how cosmic structure structures on large scales have evolved almost all the way back to the beginning. And yet, and I think we're getting to the real thesis of your argument and it's fascinating, you say compared with standard noise models, the universe seems too uniform on the very largest scale. If we occupy a random universe that arose from random noise, we should expect to see all kinds of messy patterns preserved in the cmb. Instead we observe a neat uniform pattern that seems extremely unlikely statistically speaking. So either we got extraordinarily lucky or there is some process that requires the universe to be this way. How do you reconcile, I guess our understanding of the universe and galaxy formation with this anomaly, this moodness that seems so unlikely that we're still trying to understand?

[C]

Yeah, well, so that is the number, you're right, that's the number of the mystery that I'm highlighting in the article. But so I guess the first thing to say is that if you, as opposed to looking on the very largest scales, if you look at somewhat smaller scales, so on the sky would be scales of about like one degree, like the size of the sun of the Moon, and less than that, the theory works extremely well. And it's a very, it's a simple gravitational theory. The elements are all really very well controlled, very well measured so you have to say the small scale pattern really is understood extremely well. I show some plots in an article from the Planck satellite. It's kind of amazing how well you're basically looking at vibrations of the plasma at that time when the microwave background was separating from the matter. But the mystery is on the very largest scales, that's when you're comparing places in the sky which are like 90 degrees apart. So the right angles, you know, like very widely separate and, and that, and the surprise there is that it's not like those points on the sky would just be, are they're not consistent with just random noise as the models assume. It's as if they know that there's some, that people even use this word, conspiracy or some things like that. It's as if they, they're, they're arranged, it's smoother than you expect. If, if you compare the, you know, the product of temperatures, wide angular separations, it averages very close to zero. And the precision of that is remarkable. So the fractional precision of the smoothness is comparable to having like the lens of a nice telescope or binoculars or something. It's like, it's highly polished on that scale. The roughness on the small scale is what explains the galaxies and the small scale CMB fluctuations. But this large scale regularity, that's not what you expect in the standard set of ideas people use for the earliest universe. And that is also the pattern that's best preserved from the first moments of time. That large scale structure, it's directly strict relic. It directly remembers just how it forms. That symmetry that's in the cosmological model that you assume seems to be more perfect than it has a right to be.

[B]

Yeah. In fact, you say in the article, in brief, fewer than about one in a thousand random realizations stay as close to zero as the real sky. So certainly the reality isn't what the models would predict. And then hitting on your point about the smoothness at the large scale, you write, this remarkable smoothness could point to some underlying uniformity in the universe. Initial conditions that require new physics to explain. And I thought this was fascinating, these new physics. Clearly quantum mechanics, or sometimes quantized gravity seems to play a role. But how do you think about articulating these new physics or even developing them? I mean, it seems like such a mind bending proposal.

[C]

Well, right. And so I mean, I guess the first thing to say is that the standard picture does have quantum mechanics already. That's already an incredible hypothesis that all the structure is from some kind of quantum mechanical thing. But apparently that, apparently it's missing something that is there. There's some ingredient in that model that the, the current ideas are not including. And you know, and precision is. Yeah, it's a one in a thousand that it could be better than that is. That's the limit of the current measurements. It could be exactly zero. There could be an exact symmetry in some regimes, you know, and when you see a symmetry and it's starting to look like symmetry, that triggers a precise set of ideas, way of thinking about things. And the standard way of formulating the initial conditions doesn't have that symmetry. So that's why I say if it is a symmetry and not a conspiracy, then it's telling us something profound. And that's about. I mean, I guess it's interesting to say that it's real data. Right? I mean, this isn't. So as opposed to just thinking about it or talking about. This is the universe telling us something. There's a fact and it's a very interesting fact and it's not even a really new fact. The smallness of this large angle correlation was first noticed when George Smoot and those guys in the 90s measured the anisotropy. The late George Smooth, I would say recently died very sadly. George is very interested in these ideas I'm talking about. We corresponded last year about it. They noticed it back in the 90s and the data since then, the WMAP and Planck satellites have improved the maps. And it keeps getting more and more surprising. As you measure the better and better maps, it gets more. Looks more and more like a symmetry and not just a fluke.

[B]

Yeah. Two very basic questions, Craig. One just for our readers, in terms of a final theory. On the microscopic level, we have quantum mechanics. And the standard model, which works beautifully and articulates the level of precision, has been proven out to multiple decimals. And then obviously on the macroscopic we have the general theory of relativity. Please correct me if I'm here, but I think we're trying to find a theory that would some way unite them, either ideally at the beginning of the Big bang or possibly on the cusp of black holes. I just wanted to clarify that with you. We have two, like a micro and a macroscopic and I guess Newtonian sitting in our everyday life. And then could you talk about where gravity may play a role here?

[C]

Evolve. Right. So I, like I was saying earlier, gravity controls things on large scales. And like I said, the, the standard theory already kind of assumes that the origin of the structure is from quantum mechanics. But there Is this uncertain? Well, it's, it's one of the frontier mysteries of physics. Now how do you recon. Relativity is 100 years old. So is quantum mechanics. They've, they fundamentally disagree about some important things and they've never really been reconciled. And it's some, in several important ways, fundamental way. I mean you've heard about string theory and things attempts to, you know, reconcile them and that solves some of the problems but not all of them. And, and we don't have any data about it. There aren't any except for this cosmology business. There's no direct imprint of a quantum gravitational effect. So that's the other thing that makes it interesting that if it is new then it's kind of a unique observational window. So you measurement. When people invented quantum mechanics, they never would have invented it if it hadn't been for the data. They were forced by nature into these crazy ways of thinking about things. And I would like to think that we can listen to nature again and pay attention and let that lead to thinking. And so maybe this is, that maybe this is. I mean I don't have a theory of quantum gravity. The fundamental nature of the problem. The reason it's hard is that you know, in quantum mechanics, you know, everything is a superposition. There's multiple possibilities. And in relativity, you know, every, everything happens at a definite place in time. There's no uncertainty in that. There are events in space time and it's, they both have a form of relativity but they're different. And the quantum mechanics is not local. That is, you could have examples shorting your cat experiment. There's also Einstein, Midolski rose with these non local quantum effects. You make a measurement in one place and it instantly changes projects the quantum state everywhere in the future light cone of the past that you share with other locations. So that is not compatible with classical general relativity. So something about the way the universe began included both things. It had something that made the large scale symmetry, the uniformity that we observed that's of symmetry. But it looks like the quantum mechanics also that generated the small scale lumpiness was controlled by symmetries. And those are not. Those symmetries are not all included and the current way of formulating it.

[B]

Yeah, and Craig, you talked about the data. I believe most of the data is drawn either from the Hubble telescope or possibly the James Webb. Could you just talk about where we're getting the data from since the 90s here?

[C]

Well, yeah, for this problem, the most important data, first of all, it's Satellites, these the ones I mentioned. COBE W map and pike, the maps of the microwave Cosmic microwave background. Spectacular. Also ground based maps of the microwave background keep getting better. And the other side of that are the ground based surveys like the Sloan Digital Sky Survey. Most recently there's DESI that are making three dimensional maps of now millions of galaxies. So the article has a picture of one of the recent ones that there's this cosmic web of galaxies. So yeah, the microwave background was the first hard evidence we had of very precise uniformity on large scale. And now we're seeing that, approaching that and direct three dimensional maps. Hugely bigger than the little tiny patch that Hubble looked at where again every part of the universe is like every other. But the departures are very profound and interesting. This web like structure shaped by gravity. So and that's going to get better too. There are other satellites now like Euclid is already up there, they're going to get even better maps.

[B]

No, I was going to ask you or just one clarification. It's those little discrepancies, those non smoothness that does result in these galaxy formations, is that correct?

[C]

Yeah, that's right. The small patches in the microwave background in the 1 degree scale, if you extrapolate that to today, that is the cosmic web scale of the galaxies that we observe. And so yeah, so the tiny variations from quantum mechanics in the initial conditions of the universe, that's why the universe is made of galaxies. As far as we can tell, it directly maps onto it.

[B]

Got it. And I do want to ask you, you used a term and please correct my pronunciation. Anisotropies.

[C]

Anisotropies, yes, thank you.

[B]

I define that and just inflation as well. Alan got then inflation. I think just. I probably should have asked that at the beginning.

[C]

Yeah, anisotropies are. That's you know, departure from ISO. Perfect isopropy would be the same in all directions.

[B]

Got it.

[C]

You know, isotropic universe, all directions. That would be a perfectly smooth sky. Anisotropies of the departures from that. So the lumpiness in the maps and you could see the map from the Planck scanlight, you can see what it looks like. And inflation, the set of ideas that was introduced actually before that was measured. But it was a way to understand how the early universe got going, how the expansion started. And you know, it's an early phase. If you posit some things about how matter and vacuum behave in the early at very high temperature, extreme conditions, then the gravity in the early universe can become repulsive and accelerate instead of Decelerating. So that makes a big rapidly expanding universe. It's a way to explain. But that basic framework and that seems, you know, that's compatible with everything we see. But what isn't compatible with this large scale thing is the, is the quantum, the detailed quantum mechanical model of that, that part of it probably, you know, maybe it needs modification or maybe it's just a conspiracy.

[B]

Yeah, it doesn't seem like it. And I should say the article is so well written, has beautiful graphs and charts and everything and I'm not doing it justice. But thank you very much for your time. Just one or two closing questions, one explanatory. We think the universe is 13.8 billion years old, but per Hubble, it is expanding and in fact it may be accelerating. I think there's a debate called the Hubble tension between I think of U of Chicago astronomer Wendy Friedman and maybe Adam Reese at Hopkins. And right now to see the entire universe. It's almost 48 billion years. Please correct me, I know you have the beach ball in the article, but yeah, if you.

[C]

Right, yeah. So. So this is another ingredient in the standard cosmological model. It's not to do with the beginning of the universe, it's to do with the universe today. Late times, during the last factor to an expansion, it seems to be speeding up. There are two galaxies far apart. They're getting. And that's reenacting what happened during inflation, that there's something exotic about the space in between the galaxies. Einstein's theory tells us that if the empty space, quote unquote empty space, if it's not really empty but has some energy in it, the gravity of that is repulsive and will accelerate an expansion that seems to actually be happening. So that was, that was discovered 1998 from supernova. And that's really needed to get everything right in the structure formation and everything else. So in the recipe for the ingredients of the universe, there's that there's the coldark matter, which is the other fascinating thing that's observed only by its gravity. But it's attractive gravity, not repulsive gravity. That's the next biggest part of it. And then there's ordinary matter, which we also know a lot about. And its composition exactly agrees with what you expect from a hot big bang. And it's a relatively small fraction of the total. So those are the kind of the, you know, what goes into the pot and you know. But it gets stirred up by physics. Yeah.

[B]

And that expansion is still happening in that smooth structure on the large scale that we talked about. Right. I mean, as it continues, there's no change there. And then I have to ask you just alluded to it. Where do you think dark matter or dark energy plays a role here?

[C]

Well, so nobody understands either of those things. I mean, so the good thing about them is that their behavior is very simple. So you don't have to know the details to understand how they gravitationally shape the universe. So dark energy, it could just be what Einstein called the cosmological constant. It could be a property of gravity. It could be that empty space just isn't really empty. And it could be a way that the vacuum of matter feels like quarks and gluons interact with gravity.

[B]

That could.

[C]

The quantum mechanics of that could be another aspect of quantum gravity that generated. We don't know. Nobody has a. There are thousands of papers thinking about it, but again, there's no real data about that. And then the dark matter people have had, over the years, fascinating guesses about it, and they haven't found it except by gravity. It's still just all the hard evidence about it and its properties still come from the sky, not from the laboratory. And so, you know, so they've looked for. There are all kinds of limits from laboratory experiments on what it could possibly be. Many intriguing possibilities have been ruled out, and they're still looking. It's a big enterprise now.

[B]

Yeah. Well, thank you, Craig. It's fascinating. It seems like we're still in the early stages of figuring this out, but hopefully there are either better satellites or at some point, the next evolution of technology. I don't know if Vera Rubin or some of the other satellite observatories that are coming online will help, but Rubin.

[C]

Will be spectacular and it's coming online now.

[B]

Oh, perfect. Yeah, hopefully. We look forward to the next paper updating us on that. Thank you very much for your time today. Again, the article is the Unlikely Primeval sky by Craig Pogan, published in the November December 2025 issue of American Science. Craig, thank you for joining me today and for offering such an elegant glimpse into the unit's earliest moments. It really is fascinating.

[C]

Thank you, Greg. It was delightful.

[D]

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