Why does our universe work the way it does? What are its laws? How did it start with the Big Bang‚ and how will it end?
Scientists like Prof. Dan Hooper from the University of Chicago use something called the Standard Model of Physics to explain our universe, but there’s one big problem: The model has black hole-sized gaps in it. What is dark matter? What is dark energy and why does it make up 70 percent of our universe? Where is all the anti-matter?
Hooper says it will probably take a paradigm-shifting discovery to answer these questions, and that those are a once-in-a-lifetime event. But, this year, something called the muon G-2 experiment at UChicago-affiliated Fermilab may have been just that discovery. It threatens to break the “standard model” and open a whole new kind of physics. Hooper explains it all, and responds to our previous episode with Harvard’s Avi Loeb about aliens.
(Episode published June 3, 2021)
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Paul Rand: Why is our universe the way it is? How does it work? What makes it tick? Why this universe?
Paul Rand: Not only is this question fascinating on its own, but considering that this is the only universe we’re going to get, we better try piecing it together.
Dan Hooper: So just picture a puzzle laying out in your table.
Paul Rand: This is Dan Hooper, professor of astronomy and astrophysics at the University of Chicago and host of another UChicago podcast, Why This Universe?
Dan Hooper: You don’t even know what kind of picture you’re trying to make yet. You’ve got eight pieces out there and you just see some colors and stuff. And then you put two or three more pieces down and you say, ‘‘Oh, that’s a face. And oh, that’s an arm. And that’s a building.’’
Paul Rand: Over the course of human history, we’ve completed a lot of this puzzle, but there are still plenty of missing pieces to keep people like Dan busy.
Dan Hooper: We’re asking questions about why does the universe work that way it does. What laws does it obey? How did those laws come to be in place? How did the universe began? How will it end?
Paul Rand: When we talk about the formation of our universe, we’re often talking in terms of billions, even tens of billions of years. But Hooper thinks that all the most important stuff actually happened in the first few seconds, right after the big bang.
Dan Hooper: Well, they’re definitely the most interesting seconds of our universe’s history. The whole stage was set for the rest of cosmic history in that tiny window of time. And there are at least four things we can’t explain about our universe’s first fraction of a second.
Paul Rand: One...
Dan Hooper: The nature of matter, and anti-matter.
Paul Rand: Two...
Dan Hooper: Dark matter.
Paul Rand: Three...
Dan Hooper: Dark energy.
Paul Rand: And four, why the universe is...
Dan Hooper: Remarkably uniform.
Paul Rand: From the University of Chicago Podcast Network, this is Big Brains, a show about the pioneering research and pivotal breakthroughs that are reshaping our world. Today on the show, the missing puzzle pieces of the universe. I’m your host, Paul Rand.
Paul Rand: Dan Hooper wasn’t always going to be a physicist. As an undergrad, he thought he’d be a music major. He dabbled in economics and then history.
Dan Hooper: I wound up taking an intro to modern physics class. And in that quarter, I learned about the theory of relativity and I learned a little bit about the theory of quantum physics. Those two things were the most exciting things I’ve ever learned about in my life. I almost instantly like turned on a dime and said, ‘‘This is what I want to do. I’m going to read and learn as much as I can about this stuff.’’ I became a good student all of a sudden. I’ve never been a good student before. I’ve never turned around. I’ve never looked back. That was definitely what I wanted to do.
Paul Rand: One of the things that Hooper learned about in that physics class is something called the Standard Model of Particle Physics. It’s currently scientists’ best theory to describe the most basic building blocks of the universe.
Dan Hooper: I think it’s fair to say every experiment we can do in a laboratory of the deep down laws of physics that dictate how the universe works, the Standard Model predicts all of that. It’s remarkable this success of this theory. On the other hand...
Paul Rand: The Standard Model has some major holes. And like anyone who’s ever tried to put together a puzzle with missing pieces, it can drive scientists a bit crazy.
Dan Hooper: So most of the energy in the universe is in the stuff we call dark matter and dark energy, there’s no space for that in the Standard Model. That is not explain by the Standard Model. We think shortly after the big bang, there was this explosive era of growth we call inflation. That’s not explained by the Standard Model. In fact, even the laws of gravity, even the force of gravity doesn’t have a place in the Standard Model.
Paul Rand: Hooper spends most of his time searching for answers to four of the most glaring gaps in the Standard Model. And they each bring us back to the first seconds of the universe. Let’s start with the problem of anti-matter.
Dan Hooper: So probably your audience has heard about anti-matter before, but basically the idea is for every kind of matter that exists in the universe, the laws of physics say there has to exist kind of an equal and opposite version of that. And it turns out that you can only create matter when you create a long with it an equal amount of anti-matter. And you can only destroy matter when you destroy along with it in equal amount of anti-matter. And then that two cosmologists raises a big question.
Dan Hooper: Why do we find ourselves living in a universe with a bunch of matter in it in very little anti-matter? How did that come to be? We had every reason to think that the big bang should have started with equal amounts of both of these things. And somehow we wound up in a universe where all the anti-matters disappeared, or at least almost all of it. And a lot of matters stayed behind. We don’t have a good answer to this. We have a lot of guesses. We had a lot of speculations, but something happened in that first fraction of a second that we don’t currently know about, that explains how this came to be set up.
Paul Rand: Okay. So you mentioned dark matter a little bit ago, and that’s the second missing piece of the standard model, right?
Dan Hooper: Yeah. When astronomers, astrophysicists, cosmologists look around at the universe, they reached the conclusion pretty quickly that most of the matter out there is not made of atoms. It’s not any kind of matter that we’re familiar with. It’s not on the periodic table or anything like that. Instead, it’s something else that doesn’t appreciably radiate, reflect or absorb light. And for a lack of a better name, we call this stuff dark matter. You don’t know what it is, but we have a placeholder in the word or phrase, dark matter.
Dan Hooper: We do know it was almost certainly formed in the first fraction of a second after the big bang. We have lots of ideas for what it might be. And we have a lot of experiments ongoing to test some of those ideas. But so far it just remains an entirely open question what this stuff is or how it maybe came to be formed in that formative era shortly after the big bang.
Paul Rand: So what makes dark matter important or worth studying?
Dan Hooper: Well, if it weren’t for the dark matter our universe would be a very different place. As the universe expanded and cooled, it started out in a pretty uniform or homogeneous distribution of matter. There’s pretty much the same amount of stuff everywhere. And if it weren’t for the dark matter, it would have more or less stayed that way. We wouldn’t have very many galaxies or planets or stars. It would just be kind of a big old soup of atoms.
Dan Hooper: But the dark matter was able to collapse into structures under the influence of gravity, forming what I like to think of as the scaffolding of our universe. So the dark matter formed the scaffolding first, then the gravity of that dark matter pulled in the atoms allowing for the formation of things like galaxies, and eventually stars, planets, and us.
Paul Rand: All right. So the third gap that you talk about is dark energy. What’s the difference between dark matter and dark energy?
Dan Hooper: So they’re actually very different things. So whereas dark matter is a form of matter, even if it’s very hard to detect or otherwise interact with, dark energy is something else entirely. You can think of dark energy as being the energy that’s built into the vacuum of space itself. So if I took, I don’t know, say take a random cubic meter of space out there in the universe somewhere, and I take all the atoms out of that space, I’ll take all the photons of light, all the neutrinos, all the particles, all the energy you can and make it totally empty. It turns out that meter of space still contains a fixed amount of energy built into it.
Dan Hooper: And furthermore, unlike other forms of matter and energy, this dark energy doesn’t get diluted as the universe gets bigger. So as that cubic meter of space expands, say it becomes two cubic meters of space, the density of matter will go down by a factor of two. But the density of the dark energy doesn’t change. So in a sense as the universe expands, it creates more dark energy. And that means that as universe has gotten bigger, dark energy has played a bigger and more important role in its evolution. And in fact, these days, our universe is dominated by dark energy and that’s causing the universe to grow at a faster and faster rate.
Paul Rand: So we don’t know what dark energy is, even though it makes up about 70% of the universe. And that’s kind of scary to think about. Even though Hooper says, it will be a long time before a dark energy radically changes life on earth, it will be the main player in the very distant future.
Dan Hooper: So what I have in mind is that as the universe gets expanding faster and faster, and it gets bigger and bigger as a result of dark energy, there will be more parts of our universe that we become disconnected from. What I mean by that is if I go back far enough to some distant part of our universe and imagine I try to send to the earth a signal, maybe I send a beam of light or a radio beam or something that beam travels at the speed of light.
Dan Hooper: If I’m far enough away from the earth and the space is expanding fast enough, that will actually be growing at a speed faster than the speed of light. So that beam will never reach us. So in this sense, we get cut off from distant parts of the universe. We have a horizon around us that we can never experience anything beyond, and dark energy makes that horizon shrink as time goes on.
Dan Hooper: So in the very, very, very distant future, trillions of trillions of years from now, we’re going to be in a situation where the whole night sky will be empty of other galaxies. We’ll basically have one big super galaxy that we live in and everything beyond that will be gone forever. We will never be able to study those parts of the universe. They’ll simply be causally disconnected from us for all time.
Paul Rand: Let’s come up too, again, your fourth puzzle. You talk about why our universe is so homogeneous. I wonder if you can talk about what you mean by that and as such, why is it so puzzling?
Dan Hooper: Yeah. Here’s the thing. If you just said, ‘‘Here’s the big bang theory, here’s how it works, you would have no reason to think that if I pointed a telescope in one direction of the sky and looked back as far as I could, and then I took that telescope and I point it into some other direction, the sky, some very different direction of the sky and looked back as far as I could. There’s no reason to think those places should look the same.
Dan Hooper: But that’s not what we see. When we look at the light that’s as far back as we can, what we call the cosmic microwave background, this light looks the same no matter where we point our telescopes. At least to like one part in 100,000. So remarkably uniform. And this raises a bunch of questions. It’s kind of like if I told you that the temperature in New York City and in Beijing right now was the same to one part in 100,000. That would be pretty weird. It would require some sort of explanation or maybe just an incredibly bizarre coincidence.
Dan Hooper: But now let’s say I told you not just those two cities, but all the others, thousands and thousands and thousands of other cities that you can think of. They all have the same temperature to one part in 100,000. This would require something to have made them all sync up in this way. You’d have to have an explanation. So similarly, we look at the early universe, and we say some mechanism must have been in place to explain how all of these parts of the universe, which were totally disconnected from each other at the time could have come to have been in essentially identical state.
Paul Rand: So there’s no complete consensus on what the answer is to this, but the most popular idea among cosmologists is that maybe our universe underwent another burst of expansion shortly after the big bang, something called cosmic inflation.
Dan Hooper: The working theories we have now of inflation describe a picture in which something like 10 to the minus 32 seconds pass. And in that period of time, the universe doesn’t just get bigger, but it gets wildly bigger, exploding in volume by unimaginably large, large degree. It means that if any two particles were next to each other at the beginning of inflation a tiny, tiny fraction of a second later, they were effectively different universes, totally causally disconnected from each other, never could be in contact again.
Dan Hooper: But now we have a way of figuring out how they could have been synchronized because once they were in contact and then they were torn apart by inflation, leaving our universe in a smooth and homogeneous configuration like we see in today.
Paul Rand: All four of these mysteries remain unanswered, and we don’t know if we’ll find the answers in our lifetime.
Dan Hooper: 100 years ago, we knew nothing about cosmology yet.
Paul Rand: Right.
Dan Hooper: We were still arguing about whether the Milky Way was the whole universe or one of many galaxies out in the universe. We didn’t even know that 100 years ago.
Paul Rand: So do you think we’ll be in a similar spot assuming you make it another a hundred years that we’ll look back and say, ‘‘We knew nothing back in 2020, ‘21’’? Or do you think we’ve actually like with the standard model, we’ve got 90% of this downer. We’re figuring out the other remaining 10%.
Dan Hooper: Yeah. I could guess, but the fact is I just don’t know because there are some branches of human inquiry that don’t make great progress in any given 100 years. I don’t think we know a lot more about, I don’t know, metallurgy than we did a century ago. We’ve learned things, but there haven’t been total transformations of our way of understanding things or our understanding of the zoology is kind of qualitatively similar to what it was 100 years ago or something. Maybe the metallurgists and zoologists would take offense to that, but I’m not trying to do that.
Paul Rand: Don’t want to upset the metallurgists.
Dan Hooper: But every once in a while, there is a kind of paradigm shift that opens an entirely new landscape of possibilities for a field.
Paul Rand: It’s a little early to tell, but a very recent discovery could be the paradigm shift that physicists have been waiting for.
Tape: Now, an international team of scientists working on a project in the United States say that they have discovered strong evidence for the existence of a new force of nature. They say that some subatomic particles called muons don’t behave in a way predicted by current theories of physics.
Paul Rand: The experiment happened at Fermilab near Chicago, which is managed by the university where Dan Hooper is a senior scientist. And the breakthrough could have been the known laws of physics. It’s called the Muon-G2 experiments.
Dan Hooper: Let me kind of paint the picture here. So there’s this elementary particle called a Muon, basically a heavy unstable version of an electron. And you can use that theory, we talked about in the beginning of the podcast, a standard model to predict how this particle should react to a magnetic field. So you put a particle like this in a magnetic field, and it spins kind of like a top. Exactly the rate that it spins at, depends on something we call the magnetic moment of the Muon.
Dan Hooper: You can use the standard model to very, very precisely calculate what this number should be, what the nuance magnetic moment should be. And then you can go and you can measure it in an experiment like we’ve just done at Fermilab. And it turns out the best we can tell the number that is being measured is not compatible with the number of predicted by the theory. If this is true and there’s still a lot of I’s to dot and T’s to cross, but if it turns out to be true and robust, that means the standard model is breaking.
Dan Hooper: This is evidence of, for the first time that there’s a law of physics that’s interacting with the particles that we’re studying in these laboratories, that we don’t currently know about, and it’s changing the way this particle interacts in a magnetic field. That could be that there are new forms of matter or new forces at play. It could be any number of things. But the really exciting thing is that we’ve been waiting for decades for the standard model to break so we can build something bigger and new. And this looks like it could be that moment in time where we’re finally seeing the standard model break for the first time in history.
Paul Rand: So how revolutionary could the Muon results be?
Dan Hooper: So the short answer is we don’t know. There are lots of different ways you could resolve this. I’ve worked on a couple of ways to do this myself. One very popular theory among a particle physicist is something called super symmetry. Basically would double the known number of particles. And it would solve a lot of theoretical problems that we’ve been struggling with for decades. These new particles would interact in all sorts of complicated ways. Some of them might be dark matter candidates and in the sense that they might be the particles that make up the dark matter of our universe.
Dan Hooper: There could be entirely new forces. So right now we know of four forces in nature. There’s gravity. There’s a force of electromagnetism and then there are two forces that we call the strong and weak nuclear forces. This might be evidence of a fifth force, which could have a lot of important implications for early universe, and for the larger structure of the laws of physics of our universe.
Dan Hooper: Also, every time you get another piece like this, it helps you see the bigger picture. So maybe this is a one step towards a grand unified theory of nature or a theory of everything as we like to call them. Maybe that’s being optimistic, but this is the sort of advance that could get you closer to having that sort of a true remarkable achievement.
Paul Rand: After the break, the philosophy of physics, and Dan Hooper responds to our recent episode with Avi Loeb.
Paul Rand: Thank you for listening to Big Brains. If you’re enjoying our podcast, please take a minute to give us a review and a rating. And tell a friend about the show too. We hope to share these conversations about pioneering research with as many people as possible. Again, thanks for listening. The size of these mysteries of physics is well as large as our universe. And yet it’s also as small as the atoms that make us up.
Paul Rand: At both of those scales, it’s hard to keep philosophical questions from creeping in. In fact, one of the classes that Dan Hooper teaches is called philosophical problems in cosmology.
Dan Hooper: I’m not a philosopher in any professional sense. I’m certainly an enthusiast of philosophy and especially philosophy of science.
Paul Rand: And one of the philosophical questions of the field is whether physics allows for free will.
Dan Hooper: Yeah, that’s one of my favorite topics. Well, I still remember when I started to think about this for the first time when I was in my undergraduate classical physics course, and the professor was talking about some stuff that Pierre-Simon Laplace said more than 200 years ago. Basically what he pointed out is if you knew perfectly the location and velocity of every particle in the whole universe at any moment in time, just one particular moment in time, and you had a big enough computer.
Dan Hooper: I think he didn’t use the word computer, but he had in mind, some sort of calculating machine, you could put the laws of physics and that configuration into that computer, and it could be used to sort out not only what the universe was like at every point in time prior to that, but also at every point in time after that.
Dan Hooper: It would be hard to reconcile that reality with any kind of system in which you look at somebody and say, ‘‘They are truly responsible for what they do.’’ After all, we’re just made of atoms and those atoms follow the laws of physics. And if you can, without asking for my input, tell me exactly what I’m going to do in every moment in the future, then I can hardly be said to have any kind of freedom and having made any kinds of choices.
Dan Hooper: Now, of course, this is complicated in 20th century physics for a couple of different reasons. Quantum physics isn’t deterministic, it’s more of a random sort of procedure, at least in what we call the Copenhagen view of quantum mechanics. But I don’t think that gives you freedom in the same sense that if every time I were to make a decision, I had to roll a dice and do whatever the die told me to do. That wouldn’t be free. It would just be haphazard. And the same goes for things having to do a chaos and other sorts of random facets or things that you can’t control, but at least aren’t deterministic in a strict sense.
Dan Hooper: When I look at the universe and its laws of physics as we understand it, there’s no reason to think that anybody has something that I would call a freedom, at least in the way that might make somebody morally culpable for their actions or praiseworthy for their actions as well.
Paul Rand: That’s a big thought. [inaudible 00:22:35] you get back and you said the understanding of physics is really in the scientific realm, but as you talk like that, it almost feels like it’s starting to veer into the territory, not of necessarily philosophy, but even religion. And how does that process for you?
Dan Hooper: Yeah. I happen to not be a particularly religious person. I’m an atheist and I don’t think there is any space for divine judgment or something. But if you do believe in a deity that judges or rewards, or punishes based on one’s actions, it’s pretty hard to reconcile that with what we know about physics and how the laws of physics in our universe work. And the longer I did physics, the more random and unintentional the universe seemed.
Dan Hooper: It didn’t seem like it if somebody were planning a universe for some grand purpose, this does not look like that universe. This looks like a universe that fell into place through a bunch of circumstance or happenstance or something. But on the other hand, I know many physicists, including very talented and knowledgeable physicists who do great work, who aren’t atheist. So I don’t think, at least it just on a sociological or psychological vantage point, being a theist is not incompatible with being a physicist or a scientist. That is just objectively the case.
Paul Rand: When it comes to thinking about the questions of our universe, our recent episode with another cosmologist Avi Loeb of Harvard certainly comes to mind.
Dan Hooper: Yeah, I listened to that one.
Paul Rand: Loeb claims that an alien space artifact entered our solar system in 2017.
Tape: Astronomers were excited to discover the interstellar object last year. It was named Oumuamua. that’s Hawaiian for messenger or scout.
Avi Loeb: We have a wager similar to the wager that Pascal posed, he talked about God and said, ‘‘Either God exists or God doesn’t exist.’’ If God exists, the implications are huge. Therefore, we have to consider that possibility. And I do the same for Oumuamua being a technological relic. I say, if it is a technological relic, the implications are huge for society.
Paul Rand: And it turned out that we pick the right time to have Loeb on the podcast. Just a few weeks later, everyone is talking about aliens.
Tape: We have tackled many strange stories on 60 Minutes, but perhaps none like this. It’s the story of the U.S. government’s grudging acknowledgement of unidentified aerial phenomena.
Tape: Well, it’s true. And I’m actually being serious here is that there’s footage and records of objects in the skies that we don’t know exactly what they are.
Tape: The US government knows something unexplained is out there. And next month we may get answers. The Pentagon has until late June to tell Congress in an unclassified report what it knows about unidentified flying objects.
Paul Rand: Loeb’s assertion that we likely witnessed an alien artifact in 2017, isn’t incredibly controversial among his peers. So we wanted to get Hooper’s take.
Dan Hooper: I personally think that’s an idea worth exploring and talking about, and I’m perfectly fine with that. I’m even fine with him writing his book about it and going on podcasts and talking about it. I probably share a different view than Avi in the sense that he actually thinks this is very likely to be true if I’m understanding correctly. And I probably would conclude that it is a long shot that it’s true, but an interesting long shot and one worth devoting some intellectual resources to toward. I had a kind of similar response from some of my colleagues, something like 10 years ago when I was on an episode of a TV program called Ancient Aliens.
Tape: Are holy sites around the world the product of man’s reverence for God? Or are they the result of contact with ancient space travelers?
Dan Hooper: It’s kind of a silly show. I don’t know if you’re aware of it, but this particular episode, they wanted somebody to come on and talk about Einstein and relativity. And I agreed to do that.
Dan Hooper: Einstein like to think about what it would be like from a first person perspective sitting on a beam of light moving through space. And what would you see from that perspective? He had all sorts of different visual ways of thinking about physics.
Dan Hooper: I never mentioned the word aliens or anything about aliens, but then after my little six-minute introduction on Einstein, then the plot twisted.
Tape: Is it possible as ancient astronauts theorists contend that Einstein’s ability to enter altered states of consciousness connected him to an extra terrestrial world.
Dan Hooper: And people criticized me for participating in that kind of ecosystem. But I actually am of the view that even if some of it is a little bit goofy, if you get people who were going to watch some random show on cable TV or whatever, maybe it’s better to have them watching a show where they learn a little bit about Einstein than some show about the Kardashians.
Paul Rand: It’s not many times you get to really have Einstein and the Kardashians in the same sentence. So I want to give you credit for that.
Dan Hooper: I’m pretty flexible about what scientists shouldn’t... What their obligations are about talking about this stuff with the public. I think exciting the public has real value and whatever you think about Avi Loeb, he’s definitely capable of doing that. I think I’ll take my hat off to him any day.
Paul Rand: Yeah. A fascinating guy and he’s a wonderful talker. But he is not shy about criticizing theoretical physics. I wonder as you listen to that, what kind of reactions was that pulling out of you?
Dan Hooper: Yeah. I have some mixed feelings about it. So first of all, Avi, I mean, I don’t agree with everything he says, but he’s just clearly brilliant. So I don’t think you should discard anything he has to say without pondering it pretty deeply. But I probably don’t share his view about theoretical physics being a particularly myopic in its vision or something. It is the case. They can be a conservative community, small 'C' conservative, in the sense that they don’t want to look at circumstantial or inconclusive evidence and consider the most grandiose interpretations of that data. At least that they’re more reluctant to do that.
Paul Rand: Hooper, may be just as careful in his interpretations, but he’s definitely interested in grandiose conversations. And if you wanted to hear him go even deeper into the mysteries of the universe, black holes, quantum mechanics, multiple dimensions, you can find him on his University of Chicago Podcast Network show, Why This Universe?
Dan Hooper: So since last summer, I’ve been making a podcast with my co-host, Shalma Wegsman. Shalma was an undergrad here at the University of Chicago, and we did research together before starting the podcast. But she’s a grad student at NYU now. We do these roughly 30-minute explainers on what we think are some of the most exciting things in physics. So we dig a little deeper into the topics that we talked about here today where we spend a whole half an hour on one idea or sometimes two or three half an hours on one idea. It’s been a great experience making the podcast, and a lot of people seem to like it. So check it out.
Matt Hodapp: Big Brains is a production of the U Chicago Podcast Network. If you liked what you heard, please leave us a review and a rating. The shows is hosted by Paul M. Rand and produced by me, Matt Hodapp with assistance from Alyssa Eads. Thanks for listening.
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