What Caused the “Big Bang”?

SPEAKER 1: All right. Danny, it's all you.

SPEAKER 2: Things out there?

SPEAKER 1: Sure.

SPEAKER 2: Hello. Welcome to a special 0 degree edition of Retired Faculty Association speaker series. Before I introduce our speaker, I'd like to let you all know that our next speaker will be on Wednesday, January 31, at Alumni Hall at 4:00 PM, and it will be Phil Bourne, who is the founding dean of the UVA School of Data Science.

The title of his talk will be the "UVA School of Data Science, A School Without Walls." And this is going to be what we hope will be the first in a series of talks about what is new at UVA. So it's my pleasure to introduce Kelsey Johnson. Kelsey is Professor of Astronomy at the University of Virginia. She has published over 100 research articles, mostly focused on the evolution of galaxies.

KELSEY JOHNSON: Oh, my God you did your homework.

SPEAKER 2: Yes, I did. She is a recipient of numerous research awards including NSF Career Award, NSF Distinguished Lectureship, a Packard Fellowship. She has also written for a broader audience and articles in The New York Times, The Washington Post, and Scientific American.

She is one of the university's recognized best teachers. She's a recipient of a UVA All University Teaching Award, a Z-Society Distinguished Professorship or Professor, and she's been named as one of the Atlantic Coast Conference's distinguished professors.

As she is the current president of the American Astronomical Society, she's a past director of the Echols Scholars Program, and she is the founding director of UVA's Dark Skies Bright Kids Program, which is a program to enhance science education in underserved areas.

And finally, I'd like to mention that she is the author of the 2019 children's book Constellations for Kids, a copy of which will be given to my granddaughter at Christmas after I read it. Please join me in welcoming Kelsey.

KELSEY JOHNSON: Oh, my gosh. Thanks, . Wow, that's a treat. I didn't know you were doing an introduction at all. So once again, folks on Zoom, really, really happy to have you here. If something goes wrong technically on your end, please give a shout out. I don't think anyone in the room can hear you. I think Kelly is monitoring the chat, so go ahead and throw something in the chat if you need to, and she'll let me in the room, but also I've got you in my earpiece.

This is fun. As you may know, you may not know yesterday was the last day of classes. I don't know if you care about that anymore. So this is a great way to celebrate the end of the semester by talking about the beginning of the universe, which for me is fun. This is how I have fun.

And also I'll say it is a treat to have people in the room who are here of their own free will and want to learn, and there are no grades involved and I don't have to grade anyone, and I think that that's great. Sorry, there's a request to allow recording, so I'm to go ahead and allow that.

We are going to go from 0 to 60 in terms of existentialness pretty fast. And so I want to start with a little bit of just grounding us, and I'm going to start by telling you what I think is a kind of embarrassing story about my oldest daughter, who is now a third year here at UVA, majoring in bio chem, by the way, so if anyone wants to help her out.

She was about-- I want to say she was four years old. We live out-- we live down past North, like in North Garden, like down-- like Dr. Hose is our go-to, for example. So we have a pretty long drive into town. And I was driving her to preschool one day. She was about 4. She was siting in the back seat as she's supposed to, and it's raining. The rain is important part of the story.

And she's sitting back there kind of quietly staring out the window, and I think for those of you who have children, I think you know that when children are quiet for a long time, you know it's not quiet inside. Something is going to something is going to surface.

And I was kind of driving with some trepidation, hoping we could make it to preschool and could get to work without something erupting. And out she comes with her little voice from the back seat and she says, mommy, I have a question. And I think right away I know that tone, and I know she's going to come out with some Zinger because the week before she was like, mommy, I have a question. And she's like, where did the first mommy come from? And I was like, Oh, no. I'm not ready for this.

So she says, mommy, I have a question, and I'm like, OK. sweetie, what is it? And she's like, where does water come from? It's like, oh, phew, I've got this. so, I mean, keeping in mind she's 4 and explaining the water cycle to a 4-year-old isn't like totally trivial, but they know what rain is and they know what lakes are and they know what clouds are, evaporation is like the trickiest part of it.

But it was-- I thought it was going OK and I was pretty proud of myself explaining the water cycle to a 4-year-old while driving into town in the rain. She's watching the rain and I'm thinking that's why she's asking about water and maybe it is, and she's getting this-- I'm keeping my eye on her in the rear view mirror and she's getting this-- I call it crumple face when kids are just like, I'm not happy and I don't know how to express it, so my face is showing all of my emotions.

She's getting this crumple face, and I can tell she's unhappy and I'm like, what is wrong with my explanation of the water cycle? I feel like I nailed this. And she's like, no, mommy that's not-- no, no, where does water come from? What do you mean where does the water come from? And she's like, well, like where does it come from before it's in the rain? And I was like, oh, OK, so I'm an astronomer. I've got this.

And it turns out if you don't know this, this is kind of a fun fact, you can share it your next holiday party. Most of the water on Earth came from comets. And so there are these huge dusty-- I call them snowballs, but there's no snow in space. These huge dusty balls of frozen water of some form that crashed-- the early solar system was nasty and stuff was flying around and crashing into Earth, and comets brought a whole lot of water that was then frozen but became liquid to Earth.

So I'm explaining this to her and I'm trying to do it again in terms for a 4-year-old, and also the self-talk in my head is like, oh, no, now she's going to be worried about comets hitting Earth. So I'm prepping myself to try to tell her that comets hitting Earth are really-- could still happen, although I'm not going to tell her that, but it's really unlikely. We don't want it to happen anytime soon, and you're totally safe.

I'm ready for that follow up, and she's getting crumple face again and she's like, no, mommy, no, where's the water come from? And I'm like, what do you mean where does the water come from? I told you where it came from. It comes from comets. And she's like, no, where does it come from before the comets? And I was like, oh, no.

So on our drive to town, we went through the water cycle. We went through comets, we went through molecules and interstellar clouds, we went back through stellar nucleosynthesis, and then all the way back to the Big Bang, at which point, guess what she asks, where does it come from?

And I was like-- well, fortunately, we had pulled into daycare at that point and I parked the car and said, well, sweetie, lots of people have different ideas about this. I don't want to use words like hypotheses or theories because she's 4. Lots of people have different ideas, and we don't really know which one is right, and she's like, well, like what ideas? We're at school. Let's go in.

So I like this story, one, because I get to reminisce about my then 4-year-old who is now 20. I also like it because I think it speaks to-- I saw lots of you nodding. It speaks to this like, I think innate curiosity we have as humans to know where things came from, where we came from, what our origins are.

But the other thing that this story highlights to me that's really important is this concept of infinite regression. For every cause-- we're so used to taking causality for granted. If you drop a cup, it will break, and there's a cause. And we can take causality like x caused y and something caused x and then something caused the thing that caused x, and we just live with causality as part of our everyday life.

But when we hit the Big Bang, when we hit the beginning of the universe, this infinite regression actually becomes a problem. And even if I could tell you, and this is the spoiler alert, I'm not actually going to tell you what caused the Big Bang, just I'm going to give you some options, even if I could tell you what caused the Big Bang, then being educated, intelligent, curious humans, your next question might be, well what caused that thing that caused the Big Bang? And then what caused the thing that caused the thing that caused the Big Bang?

And we end up mired in philosophical infinite regression, and it's not clear what the path out of that is. And so we really hit the intersection here of science and philosophy and theology and think that's what makes it really cool to talk about. So yeah, Kelly.

Oh, that's annoying. I wonder how I can stop that and show what fun would it be if there isn't a technical problem. I wonder how to make that go away. Be well, I mean, we could just do it this way, and that could just make this really big. Not ideal, but it would work. Kind of a hack. Maybe we need duct tape and WD-40, and then everything will be fine. Is this doable enough? Does that work for people online? OK. Thank you for letting me know what that was.

Yeah, that's what I did, and then, I mean, I'll do it again. I'll do it again, and you can see what happens, and folks online can tell me if they're seeing the same thing. Yeah, our folks online seeing the same thing? Oh, all right. I wonder if I can hold on. Maybe I can make those go away. This slideshow.

OK. Let's try this. How about now? OK. Let's go with that, and then we'll see what happens. I can't see what I'm doing, but that's OK. That's overrated anyway. Let me-- I'm trying to move the Zoom window, which is blocking my controls. All right. That's fine. We'll wing it. If anything goes wrong, I'm sure you're a very forgiving audience.

So now what I want to do is take a moment and try to get our heads around the timescales we're talking about. I think even for astronomers who think about this every day, the timescales we're talking about, I think we kind of get desensitized to them. I imagine it's like if you were a surgeon and you do open heart surgery every day, you might get desensitized to blood and Gore and people dying, I don't know.

So for astronomers, we deal with these incredible timescales every day, but I think it's important for what we're talking about that we have kind of a visceral sense of this. So I want to introduce you to-- where did this is go? There we go. Here we go. The cosmic calendar.

All right. Now I've figured out how to turn them off. Let's see. Will this work? There's an off button. OK. If you fall asleep, I'm blaming it on you. I don't know how to keep the-- I've never taught in this room, so this room is like magic to me. I don't know what's going on. Let's try that.

All right. So this is what we're calling the cosmic calendar, and it goes from midnight on January 1 right to 11:59:59:59 on December 31. So it's the arc of a year with the Big Bang on midnight of January 1st and then the whole year January, February, March, April, you've got your months down, all the way down to December.

This is a time scale that we have all experienced many times, which is why I like it. Some of us have experienced this timescale more than others, but it's an arc you have a visceral sense for. So if you imagine this whole year with the Big Bang happening at midnight on January 1, it isn't until sort of May of that year that we even get galaxies like the Milky Way. So spring like the flowers are blooming. We get galaxies like the Milky Way.

It's not until September that we get our solar system. So we're in what I think is the best weather in Virginia in September. So we're September, and it's not until November that we get like eukaryotes, we're starting to get sort of decent kinds of life. We don't get multicellular life at all until December. So that's the arc of the year.

We're going to zoom into December, and on this calendar, the whole first half of December, it doesn't look like much happens at all. Imagine that if you were a critter living at that time, you thought it was very eventful, but from our perspective it's kind of like nothing happens.

So now we're in December. We're the last month of the year. It's not until Christmas Day that dinosaurs are doing their thing, and they go extinct five days later. So their whole arc of dinosaurs like ruling the Earth was like all of five days. And if we zoom in to that very last day, the whole arc of our evolution from primates happens on that last day on December 31. So I want you to get a visceral sense of really how incredibly young we are. And we can zoom in even more.

So here's that last minute of December. The whole year has gone by. Think back to what you were doing a year ago on January, and more than that time has gone by. And basically all of human history, all of recorded human history happens in that last minute. We have sort of prehistoric life here with some artifacts, all the way up to-- we get through written records, we have Christ, we have Muhammad, we have the Chinese dynasties, all of that goes up to here.

So guess what, we're going to zoom in once again to that last second so that very last two of December 31, it's literally about to till midnight where everyone celebrates and clinked champagne or whatever it is you do. I'm usually in bed, but some people celebrate, I'm told. That very last second is everything from the Scientific Revolution, through the Industrial Revolution, through the wars, up until today.

I think this is incredible right think this helps to keep our human hubris a little bit in check in terms of how young we actually are. So just to make this a little bit more personal, on the scale of this cosmic calendar, think for a second about what your lifespan has been and what you have lived through and the experience of the universe, and I won't make anyone share their answers, which I would do if I were teaching a class, but the average human life scale, the average human life span on this cosmic calendar is 0.23 seconds.

So don't know what you've done in the last 0.23 seconds. Apparently, you're wasting your life like listening to me talking. 0.23 seconds is like-- it's not even-- it's practically not even measurable. That's a photo finish and a race. So we really have some look back time here to reckon with.

Now that we've set the stage, we have a better I hope a visceral sense of the times that are involved. We can go all the way back to the beginning. And before we do that, what I want to do is spend a little bit of just a minute talking about the phrase Big Bang Theory to begin with because if you are a cross-section of normal humans and probably you're not because of who you are, but most normal humans have some pretty big misconceptions about what the Big Bang is and isn't. And popular culture really doesn't help with this, but I want to make sure we're all on the same page.

So the first problem with the phrase Big Bang Theory is, of course, the word theory. And part of the problem here with the word theory is that the word theory has been co-opted by popular colloquial language to mean like some idea someone's uncle had that whatever may or may not be true. It might be crazy. But in a scientific sense, theory has a real meaning. Theory means it's not just some random hypothesis, it's actually something that's been tested and is being tested, and can be tested.

And in the case of the Big Bang, what's even worse about using the word theory is that in science, the word theory is supposed to be used when something is being tested, but it hasn't been tested as much as it could be. Once you have tested something in every way you possibly can and you've thrown every test at it with independent data and independent methods and you've tried to break it over and over again and you can't break it, then you call it a law.

Effectively, that's what the Big Bang is. We have a mountain of evidence from all kinds of independent lines of inquiry that tell us that this is what happened, and we've tried to break it, and we can't. This is the only viable scientific answer we have on the table.

I want to be clear about the word scientific because there are things outside of science that could also be answers, but this is the only answer that can be empirically tested for the origin of the universe, and insofar as we can test it, it has passed with flying colors over and over and over again. So it really should be a law. It shouldn't even be a theory. The other so-- I want to back up. So we know that the Big Bang happened, but we don't know why it happened or how it happened, and those are different issues, and that's where we're headed.

The other problem with the phrase the Big Bang Theory is the term Big Bang. So for most people who see the term Big Bang, you might think that means like an explosion. That would make sense. And it turns out that's not actually what we mean, and this goes back to-- I don't know if any of you have heard of a scientist, a physicist named Fred Hoyle.

He was really quite brilliant and very popular in the mid 1900s, had lots of incredible advances scientifically, but he was, I would say, a staunch dyed-in-the-wool atheist. And because of his beliefs about atheism, he thought that the Big Bang meant that there had to be a creator, and if there had to be a creator, he didn't like it. And so he spent his life opposing the Big Bang to his deathbed.

He opposed the Big Bang because he thought-- because it didn't align with what he thought his beliefs were, which is like antithetical to science, so there's some irony built in here. But Hoyle was a very popular figure, and he did lots of radio shows and wrote things, and he was on a BBC Radio show and was making fun of this hypothesis for the creation of the universe as we know it.

And in making fun of it, in jest, he called it the Big Bang and it stuck. And now we're stuck with it because terminology and science has the inertia of-- I don't even know what has the most inertia of anything. Something big. It's a lot of inertia. And so we're stuck with the term Big Bang. It doesn't mean what we mean, though.

When we as astronomers talk about the Big Bang, what we mean is there was this tiny, little, possibly finite nugget of a universe that started out incredibly small, at least the observable universe started out credibly small, and in ridiculously short timescales, expanded a whole lot. If want to put numbers on that, it went from being like this tiny little-- you could think of a tiny little piece of the fabric of spacetime expanded by a factor of 10 to the 26th.

Now I don't know how many of you remember-- I know not all of you are mathematicians or scientists, but 10 to the 26th means you take 10 and you add 26 zeros to it. It's a really big number. I don't even know if it has a name-- a gazillion, bazillion, quadrillion, million, like I don't know what that is. it's a really, really, really, really, really big number.

And so the universe started from some kind of a pocket of the universe, this tiny little nothing, expanded by a factor of 10 to the 26 in 10 to the minus 32 seconds. So that's the opposite. So 10 to the minus 32 means we take a decimal point, and we put 32 zeros. So it expanded extraordinarily fast, much faster than the speed of light in what we call cosmic inflation. That is what we mean by the Big Bang. It's not an explosion in space. Is an explosion of space.

And to put a finer point on this, that means that the Big Bang literally happened everywhere, including where we are now. So 13.7 billion years ago, the Big Bang happened here, like right here, and the universe has been evolving since then, and here we are. So the Big Bang happened everywhere. It wasn't a place in space.

Now what caused that cosmic inflation, what caused it to expand by a factor of 10 to the 26th and 10 to the minus 32 seconds is an open question. We don't know the answer to that. In any case, this word causes lots-- this phrase causes lots of problems, especially the word theory in popular culture.

Back to this cosmic calendar. Now what I want us to think about is how far we can push science. In terms of our trying to understand the origin of the universe, what can we do with empirical inquiry? What can we do-- how far back can we do it? And that's where the rubber hits the road. If we can't test it, it's not science.

So thanks to an amazing new telescope known as the James Webb Space Telescope, we call it JWST, well, one of the things Danny didn't say in my introduction because I don't-- he said everything else he possibly could have.

I was on the advisory committee for the James Webb Space Telescope when it was being-- when it was being commissioned, and so I don't know if you all have been following the news releases from James Webb, but the photos that are coming out are just-- they're just breathtaking and phenomenal. I pulled this one as an example.

This is an image of the universe from-- well, there are galaxies that are-- sorry, let me back up. I realize you all don't stare at these images every single day like I do. So this is an image where the telescope is staring at this tiny little point in the sky and collecting light. And we see everything in that cone of light.

And so some things that we see in this image are actually not terribly far away. So, for example, a couple stars are peeking and you can see one here, you can see one up there because-- you can tell because they have these diffraction spikes which are-- for the record, stars don't actually have spikes. It's from optics, and we don't need to worry about that.

But when you zoom in, and just so you know, this is an image you can find online, and you can zoom in to actually see it with the proper detail to really see what you're looking at. You can zoom in and see teeny tiny little smudges that you can probably barely even see from where you're sitting. We can zoom into those, and we are looking at baby galaxies from when the universe was still like in the middle of January, from when it's less than a billion years old.

Now just to show you a few of these, I wanted to zoom in a little bit. Here are some of those teeny tiny baby galaxies. These are galaxies-- we're literally looking back in time because light has travel time. So we're literally looking back in time from light that has been traveling to us for 13 billion years. And so we are seeing these galaxies from when the universe was ballpark half a billion years old, halfway through January, and I love these. You can see they don't look regular. They don't look like nice spiral galaxies, they're blobby and they're clumpy, and they're super red, which has to do with what they're made of.

But JWST is-- oh, I really should probably plug my computer in, shouldn't I? That didn't occur to me as we were starting up. So JWST is giving us this power to look back to just incredibly early times. Let me pause for-- there we go. The alert went away that my computer is about to lose power. But that's not the farthest back we can see. We can also see back to here, when the universe was only about 300,000, 400,000 years old.

This is the cosmic microwave background. This is relic radiation from when the universe was basically a hot soup. I'm not going to go into the physics of this, but the point is we can get light from when the universe was 300, 400,000 years old. Now I want to show this because this image, the cosmic microwave background, in terms of empirical inquiry, which I care a lot about as a scientist, this is the farthest back we can get light ever.

So we can't probe the universe with telescopes earlier than this time. That is our limit. We can do a lot, like we can learn a lot about the universe back to there, but this is our limit in terms of actually using light. That's not the end of the story, though. It turns out that before this time, the universe was basically a hot soup, and I mean, a really hot soup, to be clear, not like a tepid lukewarm soup. Like a really hot soup.

But the physics of that are really straightforward and really well understood. It sounds like it ought to be complicated because we're talking about the beginning of the universe, but it's not. It's actually really straightforward physics. And to that point, we can in physics laboratories today recreate conditions and study them back to-- I want some kind of suspense music right now. Think how far back we can actually recreate conditions in the universe. 0.00000009 cosmic seconds after the Big Bang.

This to me utterly blows my mind. Now don't want to say these are small scale experiments, it's not like they're recreating the whole universe, but they can recreate in small pockets the conditions that existed in the universe at the time. So this is where empirical inquiry-- this is our limits of empirical inquiry right now, and I think it's actually pretty astounding.

It turns out that in terms of cosmic time though and everything that was happening, the difference between 0 and 0.00000009 cosmic seconds is a lot. A lot happened in the universe and that sort of fraction of a second, but this is one of our limits in terms of empirical inquiry.

So as we look back, so part of what I wanted to do is give you a sense of where we have confidence, where things are speculation, and where we throw up our hands. And so we have lots of confidence. Actually, the modern universe is far more complicated than the early universe.

We have all kinds of weird asymmetries and physics has done stuff, but as we go back in time, we can go back to 10 to the minus to 10 to the minus 4 seconds, and we still have a pretty decent understanding of the physics. I wouldn't say it's complete, but it's decent. We're not blind. When we go before that, physics really starts to lose our ability to test it. We're not quite there, and then now my zoom screen is blocking the bottom. I wonder if I can make this go away. That worked? Yes. OK.

Where we really hit a wall, so I've taken you as far back as astronomy can go with telescopes, I've taken you as far back as we can go in labs, and then we have theoretical physics at all, regardless of whether we can test it. That hits a wall at 10 to the minus 43 seconds. This is known as the Planck time.

When we hit the Planck time, all hell breaks loose in terms of physics, for a couple of reasons. One is that now quantum mechanics is sort of ruling the day because of the time scales, and the spatial scales we're thinking about. What that means-- for those of you who aren't familiar with quantum mechanics and that probably means your normal well-adjusted humans is that spacetime itself is not well defined.

Space and time are not well-defined entities. In fact, it means they're kind of a frothing, foaming, not defined form. So even defining-- talking about spacetime at all when we hit 10 to the minus 43 seconds doesn't even really make physical sense. So that's one problem.

The other problem, when we hit 10 to the minus 43 seconds is that this point, the two major pillars of modern physics that have held up to every test that's been thrown at them, we have general relativity on one hand, which deals with gravity and mass, and on the other hand, we have quantum mechanics, which deals with really, really small things. These are the two pillars of modern physics on which almost everything else is based.

When we get to quantum scales like this, and the two places this really rears its head in the universe are the Big Bang and in black holes, those two pillars of modern physics don't get along. They're not compatible, which means we know that we don't know the physics. We know that. Something's got to give, we just don't know what it is yet. There are some hypotheses out there, but they're not testable yet.

So we know we don't even know the physics, we know-- so literally the laws of physics, as we understand them, break down. That makes it awfully hard to proceed in terms of even empirical inquiry or science or logic or theory. And so this is where I think scientists have to be really careful about being honest about what we know and what we don't know.

After-- I should say before 10 to the minus 43 seconds, the only real leverage we have is to ask whether the hypotheses on the table are consistent with existing physics that seems to work. If they're not consistent with existing physics it seems to work, we tend to rule them out. If they are, they stay on the table. But there's probably a lot of stuff that's not even on the table because we don't know the physics that we don't know.

So we go back to equal zero, maybe one of the problems that now comes out of physics and our understanding of the Big Bang is that one of the conjectures that's on the table is that time itself, as a dimension, came into existence with the Big Bang. So if that's true, that would mean that time is finite. The alternative is that time is not finite, that it's infinite.

And both of these options, that time is infinite or time is finite, have sort of philosophical problems we have to work through, and great thinkers have been thinking about these for a very long time. So, for example, one of-- I happen to have an intellectual crush on Thomas Aquinas. I just-- I don't know where that came from, but I do-- he spent a lot of time thinking about this, and he used this argument thinking through the philosophical problems to actually conclude that this meant that God, a God existed and that God existed outside of time.

So how did he come to that? So one of the problems with time being infinite is-- let's say time is infinite. Let's say it goes back infinitely far before the Big Bang. Well, the question comes up, if time is infinite, of all these points in time, why did the universe began at this one, and not some other one because it should-- and why did it not already begin because there was an infinite amount of time before that? So what was happening then? And, in fact, if time is infinite, why has everything not run down? everything should run down.

So there are these-- all these problems with time being infinite. There's a fun quote, well, supposed quote. There's a little bit of debate on this, and if any of you are experts on this, I would love your take on it.

So many, many centuries before Thomas Aquinas, Saint Augustine was thinking about this, and there's an anecdote that he was asked, well, what was God doing before he made the universe? Which gets to this question of, if there was an infinite amount of time before the universe, what was going on? So what was God doing before he created the universe? And Saint Augustine answered along the lines of he was preparing hell for people who pry into the mysteries of the universe. So I guess I'm in trouble.

But what if time is finite? If time is finite, we also have problems. And a lot of it comes down to our system of linguistics and our inherent exposure and reliance on causality. If there's no time before the Big Bang, it isn't clear how we have causality. How can something cause something if there's no temporal framework in which that can happen?

And so we run into all kinds of problems with words like, we can't talk about before the Big Bang because that doesn't make sense because there's no time before the Big Bang. We can't talk-- we can't even talk about causes. Can't even talk about what caused the Big Bang if there's no time before the Big Bang. And so we end up in another philosophical problem.

So to be clear, I don't know what the way out is. Great people have been thinking about this for a long time. I don't have really anything to add to the thoughts. They've already come up with excerpts that it keeps-- this literally keeps me up at night.

I don't know if any of you ever have insomnia because you're thinking about stuff at work, sometimes it's like sociopolitical stuff, but sometimes, for me, it's like intellectual stuff. I get myself into an intellectual knot about this at night and can't fall asleep and it drives me crazy. So thank you for being here. It's like group therapy to listen to me talk about it.

The next philosophical problem is this-- let's just put the whole time thing aside and say, OK, we don't understand time, we know we don't understand time, let's put that aside. We also have this problem of demonstrably, in terms of empirical inquiry, we have something. We are here in this room. We have something. Why do we have something instead of nothing? It's only like one of the biggest questions of the universe.

And the problem with getting at this question is it turns out you have to define something, and you have to define nothing. So I'm sure this is greatly amusing to people who are paying tuition for my students. When I cover this material in class, we actually spend a whole class period talking about different types of nothing. I'm not kidding you, because we take-- I mean, think about if you were to define nothing, how would you define it?

It's just it's not a well-defined concept even academically. And so we have to think about how we define nothing. So to define nothing, I want to invite you to consider some different types of something. So normally, when we think of things, we think of actual things like tables or people or even light, we can think of as a thing.

So we think of-- I'm going to call it mass energy. Matter energy, we think of as like normal things, and I think normal people, when they think of nothing, just think of not having those things. For sure, not having tables and chairs, maybe if you're being even a little bit more abstract, not having energy, not having light. So not having those things. And that's fine. That's one form of nothing.

But there are other things that sort of exist in their own way. So, for example, space time in astrophysics, spacetime is actually like a malleable fabric. You can't touch it per se. We don't interact with it physically that way, but it's a thing that we think of as real that exists. So that's a thing. So you can imagine there being space, time that doesn't have anything in it but you still have that spacetime. That's not nothing.

Likewise, we have-- even if we didn't have spacetime, we have these rules or these laws of physics. Now they're super abstract and super conceptual, but they're still things that exist, that inform the universe and tell the universe what to do. So the first type of nothing is really pretty straightforward. We just don't have chairs and tables or light.

The second type of nothing means we don't have chairs and tables, but we also don't even have the room for them to be in. We don't have this arena in which things can exist. And that's harder to conceptualize, but it's not, I think, terrible.

And this third type of nothing is more like-- it's a nothing, nothing. We don't have stuff, we don't have the room for the stuff to be in, and we don't even have the rules that the stuff needs to follow. So when we talk about this, when I teach this material in class, we have to be really careful what we mean when we say we're getting something from nothing, and what does that mean.

And when we go through the different options for what could have caused the Big Bang or preceded the Big Bang, one of the things I invite my students to do and I want to invite you to do is think about what, if any kind of nothing they came from. And in many cases, you'll find they didn't come from nothing, and all we've kind of done is kick the can down the road because we just have a different kind of something.

I love this quote, I get hung up on this a lot. This is one of the things that drives me crazy. I think I have a very hard time envisioning a cosmos without laws or rules that tell things how to behave. But why those? And what sort of-- this is a quote from the late Stephen Hawking. "What breathes fire into them, and gives them a universe to describe?" So this is where I get really hung up.

One thing I want to point out before we start working through the options, for what could have caused the Big Bang is this, and this is my only slide with math. If you don't do math, that's fine. You don't need to. I'm going to explain this. This is actually a remarkable feature of the universe that I think is kind of underappreciated. It turns out the universe that we live in, that, we can observe has a net worth of 0.

And so it actually is in some sense nothing. What the universe did was it seems to have taken out a loan from somewhere. So in other words, what I mean by this is that if we look at math like we can look at all the math in the observable universe, all the mass energy that has the positive value, and you could-- if you wanted to fill it in, you don't need to.

So we have positive energy from the mass energy of the universe, and then we have gravity and we have potential energy. And if you think back to whatever physics, you might know potential energy is negative. In the observable universe, the positive mass energy is as near as we can tell. Exactly equal to the negative energy of the Earth.

And so the universe seems to have a net worth of 0, which is fascinating because now it's not-- why do we have something instead of nothing? So in some sense, we still kind of have nothing, but there was some mechanism for a loan. Where did the loan come from? Who is stupid enough to allow this line of credit to the universe? Like, I don't know. So the universe has taken out a loan, and so the question is where did that loan come from? What is it that gave the universe the ability to have these two in balance, the positive and the negative?

OK. Let's go through some options. I'm not going to tell you which is right because I don't know. I'll probably tell you which is my favorite, and I'll tell you why it's my favorite. And being my favorite, of course, doesn't make it right. It just makes it my favorite. So one of the first options on the table for what caused the Big Bang is a cyclic universe. This is a concept and a philosophy that has been popular across many peoples, across time, there's a lot of wisdom in different cultures that brings thing into cycles.

And so it has a lot of appeal, right, a cycle has appeal, it has an aesthetic appeal, it has an appeal in terms of balance. So in this case, we have a Big Bang and the universe goes on and expands, and eventually because-- it's like throwing a ball up in the air. You throw a ball up in the air, and eventually the ball slows down and it falls back.

The universe is kind of doing the same thing in this scenario. So we threw the ball up in the air, it went up as high as it could, and then it starts falling back down and collapsing. So in this scheme called the cyclic universe, right it just keeps going around and around and around the circle, and it may be that the universe we're living in is somewhere over here. We're still expanding.

Turns out, at least in the observable universe, we have effectively ruled this out. And what happened was-- this happened a couple of decades ago actually. This was a huge question. The question was, how fast is the universe expanding, and given how fast it is expanding, how much of that expansion slow-- it's expanding, but is that expansion slowing down? And how fast is it slowing down? Because that will tell us the fate of the universe.

So two really high-powered independent teams went out to measure how fast the universe is decelerating. The ball is going up in the air, but it's slowing down. How fast is it decelerating? They both went out independently like the Nobel Prize is on the line, there's a lot of fighting, intellectual, good-natured fighting, mind you, but like the teams are both literally vying for the Nobel Prize.

They go out to measure how fast the universe is decelerating, and the data start to come in and things are looking really wacky, and more data come in and they look more wacky and the teams talk to each other and they're like what is going on because both teams found independently simultaneously that the universe is not, in fact, decelerating, it's accelerating.

And this is what we call dark energy. It's one of the greatest mysteries in modern physics. We don't know what it is. We have some hypotheses, but none of them are bearing fruit. So for reasons we don't understand, something is injecting into the-- energy into the universe, and its expansion is actually accelerating. It'd be like-- if you threw that ball up into the air, and instead of slowing down and falling back, it actually accelerated away from you and like shot out into space, that's what the universe is doing.

Granted, there's a lot of physics about this we don't know. And we know we don't know and we don't understand, but insofar as we do understand it, there's no way this is going to happen right in fact, the fate of the universe is quite grim, very cold, very dark, everything moves apart from each other, and eventually there's nothing within your horizon.

So there's physics-- like, I said there's physics we don't understand. There are ways that this could turn around if we can come up with some kind of phase transition the universe could go through. But for now, I think this is off the table, which is sad because it would be a lovely explanation.

Next up, this is probably the most conceptually challenging I think of the explanations for the beginning of the universe. This came from Stephen Hawking and his collaborator, Hartle. Their idea was what if the universe didn't have a beginning because time didn't have a beginning?

And the way they thought about this, the analogy I like to use is you think about the globe of the Earth, and how lines of latitude and lines of longitude are orthogonal, and if you were to go-- you're an intrepid explorer and you're going to the South Pole, and those lines of latitude and longitude continue to be orthogonal, let's imagine the lines of longitude as lines of time right so as you go back to the South Pole you're going farther and farther and farther back in time.

When you get to the South Pole, this remarkable thing happens because of the coordinate system we use. There's nothing particularly special about the South Pole, except for that's where the Earth axis happens to have us rotating, but because of the coordinate system we've used and the fact that that's where the Earth's axis goes through, when you get to the South Pole, when you're at the South Pole every direction is North. There's no east, there's no West, it's just North.

And so what effectively happens depending on the coordinate system you choose, if you choose a system like that on the globe is that as you move back in time toward the South Pole, time the lines of latitude actually curve in and sort of act like space. So as you go back to the beginning of time, what would be time equals 0, time actually becomes spacelike.

So in this scenario that Hawken and his collaborators came up with, imagine this is the South Pole. As we go back in time, time curves in and becomes more spacelike. And so if there were before, it would be over here on the left, except there can't be because time sort of just goes to this pole and because of the coordinate system we're using, there's nothing before. It just is what it is.

So I think about this in terms of types of nothing. Now we get out of this causality issue, we get out of the issues of time being finite or infinite, but we still have to explain why this whole sort of situation exists to begin with, like why this? Where did this construct come from? It's still something. It's still not nothing. It just kind of kicks the can a little bit down the road.

OK. Next option, back to quantum mechanics. I love quantum mechanics. In this case, this is meant to be sort of a visualization of how we think about the fabric of spacetime when we get down to quantum mechanical timescales.

So like I said earlier, on these scale, space and time don't exist independently as things it's like a frothing foam, and so maybe out of this sort of quantum foam like a universe kind of bubbled up into existence and maybe this sort of throat here got pinched off and it went and floated off on its own.

I think that if you were to go to a party of physicists and sort of poll the room on what they thought the most likely explanation was for the creation of the universe, this is probably what most physicists would say if I had to guess, in part because there's a quantum loophole. We like that there's a quantum explanation that could get us to how this might happen.

Now there's a big difference between in quantum mechanics sort of particles popping into existence out of, I would say quote nothing, but it's really from quantum fields, and universe is popping into existence, but the loophole is there and there's a scientific path there. It doesn't explain where all this came from to begin with. So again, we're just kicking the can down the road.

Here's just another-- it's a slight variation on this. This gets into what is called eternal inflation. The idea is out of some initial quantum foam that in the cosmos, maybe it wasn't just our universe that came into existence. Maybe other universes are coming into existence too or did come into existence of all different shapes and sizes and properties and parameters.

Many folks like this idea because it helps us explain things like fine tuning, which I'm not planning to talk about today, but if you want to talk about fine tuning we can. This gets us an explanation for how fine tuning might happen.

We have membranes. So in this scheme, what you have to do because we have these puny 3D human brains that aren't so good at thinking about other dimensions, we have to envision that all of our three dimensions in space are actually like a two-dimensional membrane by analogy, and that we can't perceive this extra dimension for whatever reason.

There are viable hypotheses on the table with peer-reviewed papers with lots of citations that our universe could actually be a three-dimensional membrane sort of floating in a higher dimensional space that we call the bulk because we're really creative. And these membranes-- our membrane may not be the only one.

Who's to say like, I know we always default to thinking we're the center of the universe, and I'd like to think that we can move past that. But humans just have this tendency. There could be other membranes too, and maybe they're all floating around in this bulk. And what happens if they collide? Like, oh, OK, stand back. So that is one conjecture that is on the table for what caused the Big Bang.

This is going to sound maybe a little bit shocking this is starting to be empirically testable with what we see from particle properties in the lab. I won't say it's ruled out, but it's not looking promising right now. So but the fact that this is becoming empirically testable, I think is actually also kind of astounding.

This is my favorite explanation, just to be clear. The idea here is that in any universe when you form a black, hole and we form black holes all over our universe, what happens is within that black hole, within the mouth of the black hole, so you can imagine this scenario is a black hole forming in a universe, a baby universe could get spawned off.

This really technically could be like a wormhole, if you've heard of wormholes. Technically, they're called Einstein-Rosen bridges, which in the Thor movies, they actually got right and called by their proper scientific name. So if you want to go back and watch Thor, they call them Einstein-Rosen bridges. It turns out concepts like wormholes, which are allowed in general relativity, although not yet observed empirically, are very, very sensitive.

And if they exist, we think they would probably close off really fast. So in this, case a baby universe would be formed, the umbilical cord to this universe would probably be cut off fairly quickly, and then you would spawn off this whole sort of other baby galaxy. This, like I said, no empirical evidence for it, but it's my favorite probably in part because I have kids, but also I love all the possibilities this opens up.

It means with every black hole or maybe every black hole there's a new baby universe, which is kind of fun to think about. It's fun to think about our universe having come from a parent universe, which, by the way, all of our observations are consistent with. The Big Bang is consistent with this happening, and this would be the equivalent of like a white hole from the other side.

It gives the possibility of natural selection, and so in this case when baby universes are formed they could inherit some of the physical characteristics of their parent universe, kind of like genetics. And some universes would be more prone to make black holes than other universes. And if they're more prone to make black holes, they're going to have more babies. So you can imagine sort of almost evolution in terms of physics. So that is my favorite explanation.

And finally, you can't talk about the Big Bang and not talk about this-- a huge fraction of our population, and I'm not-- I try really to be really careful when I'm teaching this to not show my hand to my students, and I'm also not going to show my hand to you, but a lot of people believe, for reasons like Thomas Aquinas did, that all of this points to their having to be something outside of human our human ability to comprehend, including the possibility of a creator.

Now I want to be careful here because we're not necessarily talking about a conventional god. That's on the table, sure, we can't empirically test it. It could be, for example, a high school experiment. And some metaphysics extra universal concept, some super higher power being is literally doing a lab experiment or a homework assignment, where they're super higher being teacher has said, create a universe that evolves to have intelligent life. That could literally be a homework assignment. We can't rule that out.

And, in fact, it could also be a simulation. I know that is like a batshit-crazy idea that most people have a knee jerk reaction against for good reason, but there are actually deep philosophical papers written on the possibility of the universe being a simulation and what that would mean, and it's not as unlikely as it might sound, especially when we look at what would be needed. So a higher power of some kind is still on the table. It's outside of the realm of empirical inquiry.

And then the final explanation I always leave with, because we have to acknowledge our human brains and their limitations, we like to think that we're super intellectually advanced, and maybe we're the most intellectually advanced creatures on this planet, but that's not-- our DNA is what? Barely more than 1% different than chimps, some biologists in the room will correct me on that if I'm wrong.

What if our DNA were like even 1% more further advanced in terms of intellectual ability? Imagine what we could do? There's no way I could teach my dogs quantum mechanics or general relativity. There's just no way. So who's to say that we're the apex of intellectual achievement, that we've thought of everything that could be thought of, and that we've-- and we're just all that? I would argue that we're probably not as great as we think we are.

So we have to acknowledge-- we have to acknowledge if we don't want to be full of hubris and arrogance and myopic, that there are probably options and solutions we haven't thought of because we maybe don't even have the ability to think of them.

So finally, I just want to remind us one more slide after this. Right now, as of now, maybe this will change in the next generation, the limit of science, the limit of testability empirical inquiry is 10 to the minus 43 seconds. I would argue that any scientist that tells you that we know what happened before 10 to the minus 43 seconds is full of it, because we can't. We don't have the physics to do that.

Before that time, and this is meant to be an analogy to that South Pole as we go to the South Pole because of our coordinate systems. I just love this. I think here be dragons. It's unexplored, and we don't know. And I actually think that's one of the most beautiful things about it. I love talking about things in science that are open to possibilities for which we don't have answers, and we can think about possibilities, and we can be creative, and we can dive into what I think in this case is a really rich interdisciplinary space.

So I will leave that there. I'm right on time, I think. And, Danny, do you want to take questions or maybe Kelly you can tell me if there are any questions online. I'm happy-- I love questions. You all have been teachers. You know what it's like if you finish a lecture and no one asks you questions. It's like really depressing.

Yeah, good question. Let me repeat this for folks who are online. The question is when I showed the slide of-- can't hop to it quickly-- the cosmic microwave background, which is a big oval of blotchiness that you might recall the question is, why can't we see farther back in time than that? Which is a really, really great question.

Yeah. Well done. Yeah. Yeah, there have been three different generations of telescopes that have looked at the cosmic microwave background. In fact, did my senior thesis as an undergraduate using COBE data, which was the very first one. The problem is, and this gets into a little bit of physics. So if you want to turn out for the-- turn out for the physics, that's OK, but if you want to hang on, that's OK too.

Before that time in the universe, atoms were ionized, which means-- I don't mean to be pedantic, but I don't know if everyone has the same background. Like electrons and protons, we're not hanging out together. Every time an electron would try to join a proton and become an atom, it would get re-ionized. And so you have this plasma, you have this soup of protons and electrons.

What happens is the way that interacts with light because light is-- another name for light is electromagnetic radiation. And what that means is that as electromagnetic radiation, when light interacts with charged particles like protons and electrons, its path actually gets bent. And so because the universe-- before that time period, before 300 400,000 years was completely ionized, what that means is that light was doing like a Plinko.

Light would travel like this way a little bit and then go this way a little bit and this way a little bit. It just kept getting bent and bounced around and moved, and so it's kind of like seeing-- the best analogy I have is, what is it? Like translucent glass in a sense where you can see there's light coming from behind it, but you have no information about what's behind it. And because the light just keeps getting processed and moved from those ionized particles, so it's not that there isn't light from before, it's that all that light from before it has just gotten remassaged and moved around.

AUDIENCE: [INAUDIBLE]

KELSEY JOHNSON: Yeah, all of it. Yeah, all of it, even radio wavelengths. Yeah, it would be great because it sounds like a lot about this. So radio light can make it through a lot of stuff. We won't get into the physics of that, but like you know that intuitively. You could turn on a radio and hear and you would get radio reception because radio can make it through stuff walls and clouds of gas and dust, but even radio light in this case can't do it, which is a real pity. So it's a real observational limit for light.

Now one thing you didn't ask but I'm going to answer anyway is there's a new-- I'm a great professor, right? That sounded really bad. I love answering questions people didn't ask. The question that maybe you would ask if I gave you enough time is we have another tool under our belt now that came online in the last decade that doesn't involve light-- gravitational waves.

We now have a way. We have detectors and they're nascent. But we have detectors that can actually measure ripples in the actual fabric of spacetime from massive things doing things in the universe. It's like if you could imagine playing in a lake and you spin around with your hand, your hand in that lake makes a wave, it makes a ripple that goes out. It's the same thing in the universe when massive objects move. They make these ripples in the fabric of spacetime.

Now for us to detect them right now with our nascent detectors, they have to be really big, whomping ripples, like black holes merging kind of ripples, but it's a new tool, and that could allow us to probe farther back in time, not with light, but with gravity. And so that tool I think is really over coming decades is really going to come to the forefront.

AUDIENCE: So you [INAUDIBLE].

[LAUGHTER]

KELSEY JOHNSON: I love talking to you people. Dark matter gets factored in with the mass energy because it does have mass, and so we infer the-- sorry, I should back up and explain dark matter to people. When we look out at the universe, there is something there, we don't know what it is, but it interacts with gravity. Gravity appears to be the only thing it interacts with. It doesn't interact with light, it doesn't appear to interact with any of the other forces. It only interacts with gravity.

Because it doesn't interact with light, that means we can't see it, we can't see it, either an absorption or emission or it's anything that does like that, but we can see its effect on stuff around it. And so we infer actually tremendous amounts of mass in the universe that we can't see. The fraction of mass we can see like tables and chairs and people and atoms and hydrogen and gas is incredibly small.

Most of the mass in the universe is in the form of this dark thing that we call dark matter, again, creativity for astronomers. We don't know what it is, but that is factored in because we can infer how much of it is there, even if we don't know what it is. So that gets factored into the mass energy bucket.

OK. So let me repeat the question for folks online. So the question-- the person has read Larry Krauss, who we could talk about later, have some issues with him-- what is the best book on my favorite baby universes? Probably the easiest to thing to find on the market right now is there's a physicist named Lee Smolin, S-M-O-L-I-N, who is generally credited with coming out with this idea. So he has some popular books on it.

The other thing-- I'll just put on the table in a very self-aggrandizing way, is I have a book that's coming out next fall that we'll talk about this. So if you want to wait nine months, you can get my book too, but the best book on the market right now is probably Lee Smolin's book, S-M-O-L-I-N. Anything else?

AUDIENCE: Could you explain again the mass? Because the [INAUDIBLE].

KELSEY JOHNSON: I can try. So the question is, how the mass energy in the universe is equal to the gravitational potential energy in the universe, and why that equals alone. So I'll start with a caveat that we only know what we can know from the universe that we can observe, and so there is a caveat there. There could be stuff outside of the observable universe, we don't know what it's doing.

But when we look at the observable universe with our Fancy Schmancy telescopes like James Webb or the very large array or any telescope you want, we can basically add up all of the mass energy in the universe by looking at the galaxies, looking at the dark matter, looking at the light. We can add it all up and say, how much is that? And that's all positive energy.

Then those very same telescopes, we can look at all of those things. Look at how much gravitational potential energy they have, look at how fast the universe is expanding, and we can determine how much negative energy things have dynamically. And so we do that and we add up that bucket of how much negative energy things have, and then we add up this bucket over here of how much positive mass energy exists in the universe.

And as near as we can tell, there's a little bit of wiggle room here because we're talking about astronomy. We're happy if we're within a factor of 2. But as near as we can tell, they're the same, which means the net energy of the universe is 0 or as close to 0 as we can get, which is wild.

And so what that means is normally one of-- many conservation principles I think are sort of drilled into students in school, and one of those conservation principles is the conservation of mass, there's conservation of momentum, there's conservation of energy.

So in this case, it's the conservation of energy is what really troubles people about the Big Bang because if we believe in conservation of energy, and then we get to how do you have something instead of nothing because that sort of violates our cherished conservation principles, well, if the net worth of the universe is zero, we haven't actually violated the conservation principle. We still have the same 0 energy we might have had before the Big Bang.

The question is, how did we go-- how do we go from having nothing, like no mass energy, to still having nothing, no mass energy, but also like a fancy house and a car that we owe the bank for? It's not clear how we were allowed to do that. I don't have a better answer for you. I hope that helps.

AUDIENCE: I think given the hour, I'd like to thank you, Kelsey, for [INAUDIBLE].

KELSEY JOHNSON: My pleasure. My pleasure.

AUDIENCE: And there's more.

KELSEY JOHNSON: There's more What the world?

AUDIENCE: So this is our much coveted Retired Faculty Association gift. Let me pull it out. If you can hang your Black holes on [INAUDIBLE].

KELSEY JOHNSON: Wow.

AUDIENCE: The other hanger made by [INAUDIBLE].

KELSEY JOHNSON: This is beautiful. Are we saying that people need more potassium? What is the message here? So I love bananas. This is great.

AUDIENCE: It's a banana thing in the conservation of [INAUDIBLE].

KELSEY JOHNSON: I love it. Thank you. That's great. And thank you for-- wow. I can't even imagine how you would make this. That takes a lot of talent. Well done. Well done. I'm very impressed.

Oh, God, yeah, I don't need another Jefferson cup. I don't think anyone does-- this was really fun for me. I hope it was fun for you, and I hope you learned something.

AUDIENCE: Yes. Thank you.

KELSEY JOHNSON: You're welcome. All right. Folks online, thank you for being there. Thank you for your questions, and I hope the technical part wasn't too annoying.