I think of there being one Big Bang.

Right.

Now, is it just you or—Just me.

Just you.

Okay, you think there's 10.

That's right, there's 10 bangs.

There's 10 bangs.

That's right.

Tell me about your 10 bangs.

Yeah, our observations of the cosmic microwave background radiation and other observations have hinted strongly that our universe began in an event known as cosmic inflation.

And it turns out that that requires energy and space to exist prior to the existence of our universe.

Hakeem, there's no other way to start other than by saying, welcome to Particles of Thought.

Thank you so much, Caitlin.

I've been here before.

Yeah, I feel a little bit like an imposter in this seat.

Oh my God, that's not how I see you.

But it's for, it's for good reason.

Yes.

So today we're flipping the interview.

I am interviewing you.

And the occasion is you just came out with this book.

Yes.

Why Do We Exist?

The 9 Realms of the Universe That Make You Possible.

Yes.

Nothing ambitious there.

Nothing, nothing, yeah.

No, just everything in the universe, existence.

Let's dig into why do we exist.

Yes.

First, I just wanna start with what kind of inspired you to write this book?

I mean, this is not a small topic.

I've read the whole book.

I actually listened to the whole book.

I listened to the audiobook, which again, I'll recommend the audiobook for our podcast listeners.

I hope your publisher doesn't mind.

Is that okay if I say that?

The audiobook is good?

Yeah, that is good because they don't actually have to print a book, so the profit margin is bigger.

Oh, you make more.

Oh yeah, okay.

So download the audiobook twice.

So this is basically all of physics.

Essentially, yes, it is.

This is everything.

I don't know what there's left to write about.

What motivated this book?

Why'd you decide to write it?

So think about this.

This is my first real science book.

So I wanted to come out with something, you know, I might not ever get another chance, you know?

So I wanted to get out there what my crazy thoughts are.

And my crazy thought, the craziest one is, you know, we physicists have been kinda stuck for about a quarter century now in terms of coming up with anything new fundamental insights into the universe.

And I think that the way, 2 things have happened, is that with everything we have done, we're at a point where we can actually ask crazy questions like why do we exist seriously, right?

That's typically left for the mystics and faith and that sort of thing.

And the second thing that's kinda wild here is that I think that we need more imagination than we have.

We have a lot of calculation, we have a lot of experimentation, and the imaginers are, you know, you got your armchair quarterbacks that watch shows like you make with NOVA, and they're like, I've solved the problem of dark matter, right?

I get those emails.

And then you have those people— I usually forward them to you.

Right?

Then you have the people that do it professionally, and we tend to converge into particular camps, right?

So how can I allow just everybody to participate in this endeavor to help humanity move forward?

Well, if I'm gonna do that, I have to give you a cognitive map of reality for you to understand everything so that you can make that contribution.

And I feel like the narratives that we've had, they're pretty disjointed.

You know, you got the Big Bang over here, you got the Drake Equation over there, but there is no cohesive story that brings all of existence together.

Mm-hmm.

And that's what I wanted to do.

I wanted it to be an introduction to the rigor and world of everythingness, but also a provocation and invitation to participate.

So let's talk about that map.

The way you divide this book up is into 9 realms.

I think you call them 9 cosmic realms?

What, 9 realms of existence?

9 realms of existence?

Yes, yes.

So just, we're gonna dig into a bunch of them, but just as the overview, what are these realms?

Tell us a little bit about it.

So there are 3 realms that are kinda human-specific, right?

Those are the The middle realm, the realm of life, and the realm of imagination.

Mm-hmm.

Then there are 3 realms that are somewhat cosmic, right?

There's the cosmological realm, there's the dark realm of dark matter, dark energy, then there are the realms beyond horizons, like within black holes, beyond the cosmic event horizon.

And then there are the 3 foundational realms.

There is the quantum realm, there is the temporal realm, and there is the multiverse realm.

I think you got them all.

I did?

The producers are checking them off as I— It's almost like I wrote the book, huh?

Yeah, you did.

You did write this book, didn't you?

Because I was wondering, you know, maybe it was really— Written by Nils?

Yeah, yeah, yeah.

So I was listening to this book as I was actually on my morning walk.

I was walking through the Boston Public Garden.

And this is around the part where you're talking about Newton and the apple falling from the tree and really understanding what spacetime is.

Right.

And the whole spacetime concept for me basically makes sense when you're thinking about the moon going around the Earth, the Earth going around the sun, it's following the curve of spacetime.

And where it starts to fall apart for me is when that apple hits the ground.

Yes.

Splat, right?

Right, yeah.

'Cause then it's like, well, what's happening to spacetime?

Yeah.

And so, Professor, I want you to check my understanding here.

What I kind of realized in listening to your book is that when that apple hits the ground, or when I'm sitting on the ground looking at a tree in that park, spacetime is still moving through me, but we are here.

Yeah.

Because that interface where spacetime hits dense matter, and the apple crashes to the ground, or we humans walk around, is kind of like the substrate.

Right?

Your middle realm is like that substrate of where things can, life can grow.

Yes, it is like that.

And it is the middle in terms of scale between the largest and smallest physical entities of the universe in logarithmic scale.

And it also is the middle of our intuition.

It is where, you know, remember, this book is to help other people understand and think about the universe.

But you understand and think about the universe in a context of the middle realm, this middle realm context.

And it doesn't translate to the quantum realm, or to the cosmological realm, or to the realms beyond horizons.

So one of the things you learn really early in a career as a physicist is that your intuition leads you wrong to understand the deeper nature of the universe, right?

And that's why a lot of, I consider, Ibn al-Haytham as the first modern scientist in 1021, who wrote the Book of Optics.

But a lot of people consider it to be Galileo, right?

600 years later.

Because he did something that was different, right?

So Ibn al-Haytham was the guy who installed the idea that we only accept as true what we observe to be true, right?

Forget speculative philosophy.

If you don't observe it to be true, you can't accept it as true.

But Galileo said, yeah, that may be true, but to understand the deepest truths, we have to think thoughts that we could never observe, right?

We have to think of experiments that we could never actually do in real life.

For example, in his case it was, what if I remove all friction, right?

Mm-hmm.

Can't do that, right?

But when you have that thought, once you let your mind consider that, you get very quickly to, an object at rest or in motion remains at rest or in motion unless acted upon by an outside force, which we all take for granted today, right?

But it was revolutionary when Galileo thought that.

So the middle realm is sort of like where everything we're used to is, essentially.

Everything we're used to.

And does that include all matter?

Because I think star formation was in your middle realm.

That's right, star formation's in the middle realm.

But what happens is when you get to a large enough scale, you start to see spacetime's dynamics begin to dominate.

the curvature of spacetime, the flow of spacetime begins to dominate.

And then when you get sufficiently small, the certainty of our universe begins to break apart into probabilistic descriptions.

That reminds me of what you had to say about Pluto.

So speaking of things— You're gonna make people mad at me.

I know, well yeah, well yeah.

Or not.

I mean, but you don't seem to care about that.

Yeah, that's true, I don't.

That is my impression.

Yeah, I do not, yeah.

Well, because I'll tell you another insight.

You know, we talked about the temporal realm.

So the thing about this is that I realize that it's already 100 million years from now and I'm already dead.

So I'm not really worried about that kind of stuff.

Yeah, we're gonna get to that.

Yeah, yeah, you're jumping ahead, but not really, because we're already there.

We're already there.

That's right.

You did read my book!

We're gonna get there.

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So most— I'd say about 20 years ago.

Yeah.

Pluto was reclassified as a dwarf planet.

Right.

And you say it ain't so.

No, yeah, yeah, call it whatever kind of planet you want, but it's a planet.

Like, to me, anybody that is sufficiently massive to be spherically rounded by gravity, right, or gravitationally rounded, and it depends, right?

Bodies are made of rock or ice generally, so icy ones can be rounded at a smaller mass than rocky ones.

But yeah, I call that a planet.

So whether it's a major planet or a minor planet, it doesn't really matter because in those environments, is where the stuff that interests us humans can take place.

Hmm, so okay.

I had thought you were trying to say that Pluto actually should be called a planet, as should a whole bunch of other bodies.

Yeah, absolutely.

The Moon is a planet.

Yeah, it's just a planet orbiting another planet.

So what makes a planet major, right?

If I were to take Earth and put it in orbit around Jupiter, does it cease to be a planet?

According to, was it the International— Astronomical Union?

Yes.

Exactly, but that's ridiculous, right?

And planetary bodies move around all the time.

They get ejected from their orbits.

Yeah, yeah, yeah.

So I take a broader view of it.

And so if you look at it, where do we find the water worlds?

They're mostly in the moons, not in the major planets, right?

That's where the oceans are located, on the moons.

So that's where the action is.

And if you look at the geology and the chemistry and the biology, it's gonna be on these gravitationally rounded worlds.

Generally.

Major, minor, dwarf.

What's the opposite of dwarf?

Giant?

Giant.

Yeah.

I love that you call, you have a different name for brown dwarfs and white dwarfs.

Yeah.

Instead of brown dwarfs, brown dwarfs are often called failed planets.

I call them starlets.

They were stars that were in the process of forming, didn't quite make it.

So now you're just a starlet.

And what about white dwarfs?

That's a dead— I don't have a name for white dwarfs.

Did I come up with a name for white dwarfs?

Well, I mean, if you're gonna rename brown dwarfs.

Yeah, well, there's also red dwarfs.

Yeah.

And then our sun is a yellow dwarf.

Is it really?

Yeah.

Yeah, our sun's considered a yellow dwarf.

So let's talk a little bit about Star formation.

Yes.

You spend a lot of time in your book talking a little bit about that.

Yeah.

Why?

Why is that so important?

Well, if you're gonna have an understanding of your existence, you gotta understand how things originate, right?

And so there are basic, a small list of how does this originate?

The universe, galaxies, stars, planets, life, right?

So I have to go through each one of those for you to have an understanding.

But the other thing is, is that in telling that story, you get some general principles that you get to understand about how things work in the universe.

So an undercurrent in the book is how energy moves through the universe and how important that is.

And so I think star formation gives you a good idea of that, but it also places you in the right mind state because we are the residue of the residue of the residue, right?

So, you know, if you look at the origin of the universe, you start off with equal amounts of matter and antimatter, and only 1 part in a billion, which is a residue, is left over to be normal matter, right?

And then when you form a star, at the end there's a residual amount of stuff that doesn't get incorporated into the star, that becomes planets.

So that's like a residue, right?

Planets are made from the residue.

Hmm.

And even the matter is, you know, the star is residue.

And then, here you come with life, right?

This chemical, that reaction that's just like a slime on the surface of a planet.

We're not like, we are this thin layer.

I'm not slime.

You're not?

All right, some humans are definitely slimy.

Sometimes I'm slimy.

All right, well, there's, bacterial films were the first slime.

And we haven't, although we've moved beyond that, if I was Galactus coming to Earth, it's this very thin layer, thinner than the atmosphere, right, which is a super thin layer.

Life is a super thin layer that goes subsurface and a bit above the surface, but it's a super thin layer of, it's like a bacterial slime, that's what life is.

Like for example, what about my beach, right?

You know, the universe is so big, right?

There's hundreds of billions of stars in our galaxy.

So we think of the sun as massive, 100 times bigger than the Earth.

But if someone were to reach into our galaxy and throw away a handful of stars, the galaxy wouldn't notice.

And then there are so many damn galaxies, which, you know, our galaxy is 87,000 light years across.

If some giant grabbed a handful of galaxies and threw them out in the universe, no one would notice, right?

So we humans thinking we're the center of everything, I gotta let you know.

Think of the universe like you're not a member of it.

Don't make it about you.

Make it general so that you can better understand it and study it.

One of the interesting things that your book said is that, I think something like half of the stars in the galaxy are binary?

Half the stars in the night sky.

In the night sky.

Yeah, so it turns out that once you get to small stars, which are most stars, binaries don't occur as often, right?

But once you get to a certain star size, like around the Sun or whatever, they occur about 50% of the time.

So like half of them are like Tatooine solar systems?

Exactly.

I mean, this is the norm.

That's so crazy.

Why aren't we a binary?

Some people say we were, right?

And some people say, oh, maybe Jupiter was our binary partner.

Then there's the whole like, what was that Nemesis star that created the periodicity in extinction record, which they now think doesn't exist.

And, but we also know that the sun was part of a cluster that it was born in that kinda dissipated.

And we also have evidence of nearby supernovae.

So it looks like there was a lot of dynamics in our environment that could have potentially broken apart a binary system.

But, you know, this binary breaking apart is one of the almost necessary steps for forming new stars, right?

Because they spin so fast as they shrink, that they couldn't be able to shrink any further, 'cause they're just spinning so darn fast, right?

So the only way they can shrink further is if they break into 2 parts, and then instead of that orbital motion, that spinning going into individual stars spinning, it goes to them orbiting each other.

So it's like a relatively stable configuration.

It makes the thing more stable.

So about half of them end up just being binaries.

Exactly.

That's so cool.

So you go through in the book, Sort of the different— well, how life was created on Earth, what a kind of gigantic cosmic coincidence that feels like it was.

Right, but not.

But, well, but not because of— You see, it's inevitable but coincidental at the same time.

And that has to— this has to do something with large numbers.

Tell us about that.

That's right.

That's right.

You have a rule about— Oh yeah, yeah.

The thing about large numbers is the unlikely becomes the certain, right?

You know, something that is incredibly unlikely, say for example, it's sort of like—But not impossible.

But not, oh yeah, not impossible.

If the probability is non-zero, if you get enough numbers, you can raise it up to certainty.

So anything that has a, the smallest probability that you can imagine, if you give it infinity, it is going to occur.

So anyway, I asked 2 questions.

One question is, how likely is life to be in our galaxy and how widely distributed should it be?

And how widely distributed should multicellular life be, right?

'Cause that is a threshold.

So if you look at our galaxy, if you look at our planet, life started very early in the planet's existence.

And there's a lot of scientists that feel that the environment of newly formed planets is preferentially favorable to forming life.

Not the old cold worlds, the ones that have a lot of energy and a lot of chemistry going on, right?

If there are liquids available.

So the thing is, is that the universe is trying to kill you.

Life can't show up anywhere.

So the first thing you need to know is, is my star a just right star for life?

So what's the bottom line?

Is there life in the universe?

Sorry, is there life in the galaxy?

Okay, I calculate that there should be 1 in a billion stars should have, 1 in a billion star systems should have multicellular life.

But, so that's 100,000 in our galaxy.

But then, the other thing is, is that most planets don't orbit stars.

They're free-floating, they're those starlets and those rogue planets, so-called rogue planets.

I call them free planets.

Free planets, right.

Yeah, those are like, if I take Jupiter and its little set of moons, Io, Europa, Ganymede, and Callisto, and have it leave our solar system, the idea of geological energy powering life at the bottom of the ocean on Europa doesn't change because it's no longer near the sun.

So Jupiters with orbiting moons, but in that case it would be, I don't know what to call it.

That's a likely place for life.

So I calculate that there should be billions of single, small life, simple life forms, billions of bodies with simple life forms in our galaxy.

Really?

Yeah.

Wow, wait wait—But never beyond simple.

So you think our galaxy has 100,000 systems that might have multicellular life?

Exactly.

Now how many of those— And then a lot more free-floating planets that could have it.

No, no, no, free-floating planets are unlikely to have multicellular life.

To get multicellular life— No, no, single-celled life.

Single cellular life, yeah.

Bacteria, archaea, and viruses, there's probably billions of worlds throughout the galaxy.

Wow.

Yeah, that's my guess.

And when you look at multicellular life, you know, there are, you know, that oxygen chemistry is what's necessary to power multicellular life.

That's still pretty optimistic, it seems.

Hundreds of thousands of other places within our galaxy.

Yeah, but then how many of them become technological, right?

Okay, so let's move to the cosmological realm.

Oh yeah.

I feel like this might be everybody's favorite realm.

Oh really?

Yeah, well maybe the dark realm has some— I was thinking of realm beyond horizons myself, 'cause it's so unexpected, but yeah.

Well, I mean, okay, so for folks who don't necessarily know all of your realm definitions, I think a lot of folks are super excited about the cosmological realm.

What really surprised me was, like, sense of size and scales of the realm.

So, like, tell us a little bit about, like, how many stars are in a galaxy, galaxies in the universe, how far apart they are.

How can you wrap your head around this scale of this realm?

That's what I try to imagine.

So there's 2 elements of it, right?

I wanna give you a picture that's relatable.

So I like to play this game with my students.

This is something that every physicist is gonna tell you in their class, how we're mostly empty space, which isn't technically true, but kinda, right?

And why do we say that?

Because the mass, all of your heft, is in the nuclei of your atoms.

And those nuclei are 100,000 times smaller than the atom itself.

So they occupy a tiny, tiny fraction of its volume.

So that means that the nuclei in atoms are separated from each other by hundreds of thousands of times their own size, right?

So if I'm a human being, say, call me 1 meter to be easy, right?

The next human would be 100,000 meters away, which is 100 kilometers away, right?

50, 60 miles, right?

If they were atoms.

Yeah, if they were atoms, spread like atoms, the next human to you would be 50, 60 miles away, right?

Then I say, let's take it up a level to stars.

So a star like the sun is about 2 light seconds across, but stars are light years apart.

And how many seconds are there in a year?

Pi times 10 to the 7, around 31 million, right?

And so that means that, what that translates to is stars are tens of millions of times their own size apart from each other, right?

So again, if I'm 1 meter, the next star would be 10, the next human would be 10,000 kilometers away from me.

Which is not even on Earth anymore, right?

You're somewhere in space.

Right, so stars are very, very far apart from each other.

Very, very far apart.

So now after telling you about atoms and stars, I've set you up.

So now galaxies, how far apart do you think they are?

Super far.

Super far!

No, try like 10, right?

So the Andromeda Galaxy is only 13 Milky Ways away.

So now, how many galaxies are in the observable universe?

You hear some people say 2 trillion, that was on an observation that was corrected.

It's right now, the best guess is hundreds of billions.

So if I was to take what the old number they gave us, 400 billion, and now I wanna make a real-world analog.

Where can I find something that is tens to hundreds of times their own size apart from each other, and there's about 400 billion of them?

Oh, I know, air molecules.

They're about 10 to 100 times their own size apart from each other.

And what volume of air constitutes about 400 billion?

About a cubic millimeter.

So the best way to visualize the universe of galaxies is to visualize a cubic millimeter of air.

That's the observable universe.

So the next realms, the Dark Realm, the Quantum Realm, I wanna go there.

These are the really mind-warping realms, so I think we're gonna need to take a breath.

These are the ones, this is where it starts to really feel like, science fiction.

Yes.

But we're gonna get to that.

All right.

In the next episode of— In the next episode.

All right, Hakeem, it's time to talk about time.

Oh.

The temporal realm.

Yes.

We're starting to, we're moving, we're easing into the trippy realms.

That's right, yeah.

So this is another one of those realms where you present some information, some wisdom that kind of goes against what I've been trained to understand.

Yeah, yeah.

They're wrong, by the way.

Yes, this is what you will say.

I always learned you can't go faster than the speed of light.

You say it ain't so.

I say it ain't so.

How do I go faster than light?

You just get on space-time and ride.

That's how you do it, right?

Well, because the nature of space is that it is expanding.

So when something is expanding, points further away from you, right, if I take a point, okay, this point is 10 light years away, all right?

In a true expanding situation, a point twice as far away as say, did I say 100 light years or 10?

I don't know.

All right, let's say 100 light years away.

A point 200 light years away will necessarily be moving away twice as fast, right?

And they don't have to be moving through space, it's just that space is expanding.

The example I came up with many years ago is a rubber band.

If I have a rubber band and I hold it on each end, right?

And let's say it's 1 meter long.

In 1 second, I stretch it so it's 2 meters long.

Now let's look at how different entities, life forms on that rubber band would understand it.

One on this end would see the opposite end move away at 1 meter per second.

Someone in the middle, right?

The middle would move from being the middle that's half a meter away from this hand to be in the middle now 1 meter away from this hand.

So this observer will see the opposite end move away at 1 meter per second.

They see the center move away at half a meter per second, right?

And then the point right near where I'm holding it doesn't move away hardly at all, right?

So things farther away move away faster, and it's directly proportional.

Something 3 times farther away moves away 3 times as fast.

4 times farther away, 4 times as fast.

So if you go far enough away, it's moving away from you at the speed of light.

But that doesn't necessarily mean you're moving that fast, right?

You're not, yeah.

It's— or it's moving.

Neither of you are moving.

No, you're both moving.

Space is just being created between you, but you're not actually moving.

See, no, no, no, no, no.

Space created and space expanding.

Stretching a rubber band and creating new rubber band are 2 different statements, right?

So space is expanding, stretching.

Lengths are getting longer.

And so you're not moving through space, but you're definitely moving farther away.

You're moving farther away.

Yeah, at a rate.

And that rate can— there is no limit on how fast you can go.

So basically, from a certain frame of reference compared to someplace far away, you could say you're moving faster than the speed of light.

That's right, relative to that.

But that doesn't help you get anywhere faster.

No, it doesn't help you get anywhere faster.

It's not useful.

I didn't say it was useful.

Okay, well, this is a bit of a disappointment.

All right, we were playing games talking about that right now was really in the future and the future is now.

What the hell were we talking about?

We were talking about the temporal realm and the fact that— So how can all that be?

Well, there are these 2 philosophies of time.

One philosophy is that time is an unfolding, right?

This state is needed in order to produce the next state.

And there's a lot of physicists that— that is our intuition, right?

And a lot of physicists believe that.

But when you look closely at the laws of physics, it seems to suggest otherwise, right?

And the most famous example, which I didn't describe very well on StarTalk, is this thing called the Andromeda Paradox.

I'll give you another chance.

Thank you, thank you.

So basically, there's that classic example of Einstein where you have someone in a train with a lantern that emits a light, right?

You put the lantern in the center of the train car.

The light goes out in all directions equally at the same speed, the speed of light, and when it reaches the 2 doors at the ends of the train, it hits sensors that cause the doors to open.

So if you're sitting in a train, you see both doors open at the same time, right?

But if you're sitting outside of the train, you see the back door move toward the light and the front door move away.

So you will see the back door open first and the front door will open after.

Because the speed of light is constant.

Because the speed of light is a constant, right?

So Einstein called this the relativity of simultaneity.

Events that appear to be simultaneous to one observer are not to other observers.

But the speed of light is the same to all observers.

But the speed of light is the same to all observers.

Now let's add distance to that.

So let's assume that the time between door number 1 opening and door number 2 opening is a second.

That would be a very big train car, but that's the example we're going with.

And let's say instead of having one train car, there's an infinite string of train cars.

What would happen is, as the light travels to the next train car, you add that difference again.

So the first doors open 1 second apart, the next one will open 2 seconds apart, the next one will open 3 seconds apart, 4 seconds apart.

And so if you go far enough, they can be opening a year apart, or 10 years apart, or a century apart, right?

But for people in the train, they're all opening simultaneously.

Right?

So the question becomes, how do you define now?

Well, now is a set of events that are all occurring simultaneously.

But there is no such thing.

Simultaneously is not a universal thing.

It's a relative thing.

So if now is defined by a set of simultaneous events, everybody that's moving differently and everybody that is in a different energetic state, like different, different gravitational state, they have their own now, right?

Their planes of now are tilted relative to one another.

There is no universal now.

So, but can you say like everybody on Earth has the same now?

Or at least everybody in my time zone?

Well, because the effects of relativity don't really show up till you're moving near the speed of light, that's true, right?

That's approximately true.

So you can't use this as an excuse to show up late to your flight and be like— No!

—the plane left early.

That's not gonna work.

That's not gonna work.

That's not gonna work.

But I have found a phrase that works.

The queen is never late.

Ah, because she sets what the time is.

Exactly.

So I'm always on time, unless it's for the plane or the train, right?

They're not gonna wait for me.

But you telling me I'm showing up late for work?

No, I'm not.

I'm early.

I wanna talk a little bit about the Big Bang.

What realm does that live in?

That lives in the temporal realm.

Temporal realm.

Yeah, that's right.

Okay, so let's travel back to the temporal realm for a second.

Another one of the pieces of conventional wisdom that you're like, nope, sorry.

Yes.

Not the way I talk, not the way I think about it.

Right, yeah.

I think of there being one Big Bang.

Right.

Now, is it just you or?

Just me.

Just you, okay.

You think there's 10.

That's right, there's 10 bangs.

There's 10 bangs.

That's right.

Tell me about your 10 bangs.

Yeah, so— And why, like why?

I'll tell you why, because the idea that we have of the Big Bang is kind of, that is in general understanding, it's kinda antiquated, right?

So among physicists, we no longer think of the Big Bang as the beginning of the universe, right?

And we realize that there was a time before time, right?

Yeah.

So our observations of the cosmic microwave background radiation and other observations have hinted strongly that our universe began in an event known as cosmic inflation.

And it turns out that that requires energy and space to exist prior to the existence of our universe.

And that space is a rapidly expanding space.

And there's an actual observational signature called super horizon fluctuations in the cosmic microwave background radiation, which have been measured to high precision by the Planck satellite, right?

So the signal is real.

And so if you look at what that inflaton, that inflation event, what could have triggered it?

What's the physical mechanism?

You come to the idea of a fundamental quantum field known as the inflaton field.

And what it does is— So this is before the Big Bang?

Before the Big Bang, right?

It's there rapidly expanding.

So this is time before time?

Time before time.

But you're not saying this is before the universe began?

Yes, before allness began.

There's not a universe of nothingness.

There's this rapidly inflating inflaton field.

And then one part of it stops— it comes down out of that inflation scenario, all right?

And in the process of doing it, energy gets put into our real spacetime and it rapidly expands, right?

So first, so essentially the other thing that I talk about in the quantum realm— This kinda sounds like chemistry to me.

Like you have this substance and then you like take a little bit out or add it and then boom.

Then boom, right?

You get this phase change.

That's kinda what it is, it's a sudden phase change.

But now in the quantum realm, I talk about the fact that there are certain things that we're taught as physicists, but we don't get that deep into it.

They're super consequential, and we talk about the consequences.

One, for example, is that every electron, for example, is identical.

You can't tell one from the other.

So what is that telling you?

That's telling you that it is not the real physical entity.

So the example I give is a musical note.

A D sharp is a D sharp.

Right?

But a D sharp really isn't a thing.

Vibrating air is a thing.

The instrument that made it is a thing.

The D sharp is that energy of that instrument being inserted into the air.

So what we call an electron, physicists call an excitation of the quantum field of the electron.

And what we mean by excitation is shorthand for energy has been added, energy has been injected, right?

Mm-hmm.

So every particle is like a musical note.

So when you look at the evolution of the universe, I think that a better way of looking at it than the standard way that we look at it with these weird names, baryogenesis, hadronization, nucleosynthesis, is energy moving from one quantum field to another.

So you have energy going from the inflaton field into spacetime, bang one.

Then you have an event that we call reheating, which is energy going from the inflaton field into the quantum fields of the particles.

And that is the event that gives rise to a universe of stuff, right?

Because that first bang that expanded space rapidly, no matter what you had in space before that, space evolves to emptiness.

So you're basically saying that for the Big Bang, you're taking stuff from another field.

Yeah.

It's taking that stuff from that other field that creates our universe.

Exactly.

So the first thing is that we have these fundamental forces.

the strong force, the weak force, the electromagnetic force, the gravitational force.

And what each of— what happens as the universe evolves is that energy, in order to minimize the potential energy associated with these other fields, with specific fields, it goes through phases of moving energy from one set of quantum fields into another set of quantum fields.

So the overall trend in our universe, for the most part, is energy going from the matter fields into the electromagnetic field where it then gets stretched out by the expansion of spacetime, right?

Mm-hmm.

When photons get redshifted, they lose energy by getting stretched.

So the universe, we often speak in terms of a heat death, right?

So what that heat death is, the evolution of the universe is taking away matter, energy from matter all the time.

First, you had these strong force reactions, right?

When you formed protons and neutrons, and you form nuclei.

Then you have the electromagnetic interactions.

First helium nuclei capture one electron, then they capture a second electron, then hydrogen captures an electron.

And then the universe goes from being a plasma to a gas.

And then the reverse happens.

Gravity starts squeezing energy out of matter, right?

Through nuclear fusion, it's packing matter together, and that matter shines, and we call that a star.

And that high-energy light went into that gas and started ionizing it.

So that meant that that matter took some of its electro— converted some of that energy into electromagnetic energy, and then some of that electromagnetic energy went back into matter to make the universe a universe of plasma rather than a universe of gas, right?

But if you look at all those steps of energy moving from one quantum field to another, 9 have occurred and completed, and we are in the 10th one right now, where gravity is squeezing the energy out of matter.

It's heady stuff.

It's heady stuff.

And I mean, you go into a lot more depth in the book, and you explain it so clearly.

I don't think we can possibly do justice in even a kind of long, in-depth podcast to what's in the book.

So folks listening who wanna learn more about this, definitely go to the book.

I do wanna talk about this last realm, which is the realm of the imagination.

Love it.

What's that doing in a physics book?

Well, how the hell you think you got that physics book?

Right?

The realm of beyond horizons didn't give you a book, the human imagination gave you a book.

'Cause I think it's a game changer, right?

The thing about realms is that the rules change in each realm.

And the rules of one realm don't apply to the other.

And the human imagination is, man, wow, what a thing we have.

Like, other animals have imaginations to some degree, but what we have been able to do is, you know, and, and that's why I still believe in peace on Earth, because we can imagine it, right?

We haven't yet accomplished it, but if you can imagine it, you can aspire to it, you can create it.

Uh, and just like we created the James Webb Space Telescope, the Event Horizon Telescope, gravitational wave detectors, we can create peace on Earth.

Because ultimately as a life form, we want to survive into the future.

And the universe is set up not just to destroy all life, but to destroy all matter.

But by having the imagination that we have, we can outlive the expiration date that the universe has in store for us.

So, well, the universe or like the solar system has in store for us?

The universe!

All right, so walk us through that.

You have a pretty optimistic view of what humanity might be able to accomplish.

Yes, yeah.

But it's also rooted in science.

Absolutely, yeah.

So like, it is spring 2026 when we're recording this.

Yeah.

What's the future look like?

Here's the thing with species, right?

Very few species last beyond 10 million years, okay?

And, you know, it depends on how you define human.

So Homo erectus lasted 2 million years.

Homo sapiens, we've been around for about 300,000.

Can we make it 10 million?

Can we make it 100 million?

Can we make it a billion?

Well, if we're gonna make it those great distances, there's a lot of change that's gonna happen on Earth during that time period.

We're gonna have to adjust to a lot of things.

But no matter how you look at it, there's one thing that is super important that you can't do anything without, and that is energy, right?

Even if you look at economies, there is this plot of the amount of energy a society has and the size of its economy.

Energy is the key.

And what has happened in recent years?

We have finally gotten more energy out of a fusion reaction than we got in.

So that means that in the future, we're gonna have fusion reactors, almost unlimited clean energy.

So what does that mean?

That means that, you know, we have the Artemis missions that are happening right now.

They're going to the moon.

We're planning a permanent moon base.

If you're able to survive on the moon, surviving on Mars is easy.

It's just not as fast to get back and forth.

But Mars has an atmosphere, right?

Moon has no atmospheric pressure.

It has dust from hell that destroys everything.

It has jagged edges.

It electromagnetically sticks to everything.

And for the Apollo astronauts, it destroyed their equipment, their spacesuits.

It's awful stuff.

So if you learn to, it's like New York City.

If you can make it there, you can make it anywhere, right?

The only way we're gonna survive any type of massive event that's going to occur, asteroid collisions, cometary collisions, things like global warming, nuclear winter, climate change, I argue that they're not gonna destroy, we're not gonna go extinct from those, right?

It could be massive suffering, massive loss of life, massive change, in how we live, but not necessarily extinction-level events, okay?

But we will face extinction-level events, and our response to those is gonna require abundant energy to survive.

Now the next thing is, is that the sun is evolving.

So if we do make it a billion years, right, the sun is gonna be bigger, Earth is gonna warm up, and we might have to move outward in the solar system.

So the old thinking was, "we're gonna have to go to another star system."

If you have the ability to go to another star system, you have the ability to stay in your own solar system.

Build your fusion reactions and move to Titan, right?

All right, so we just scratched, I'd say scratched the surface of the 9 Realms.

You cover a lot in this book, like essentially all of existence and physics and also the future of humanity.

So very ambitious.

Folks can read the book, download the audiobook.

Also find your— this is very different from your first book, A Quantum Life.

It is.

What would you say was the hardest part of writing this book?

Wow.

So I'm not gonna say dealing with my agent who kept rejecting my ideas one after the other, even after I'd written a couple of chapters.

Wow, what was the hardest part?

Well, I'll tell you what was different.

This included a lot fewer tears than writing A Quantum Life.

But the thing that happened is that, you know, books don't write themselves.

So in order for me to write a realm.

I literally had to go in there in my mind.

You know, I isolate myself and I really had to go in.

And what would happen is I'd be in there all day.

You know, I might start working, I might work, write for 10 hours, 12 hours at a time, and I'm in that zone.

And so when I stop writing and come out and look at the world, the world looks strange because I've been in the quantum realm, right?

And for after a while, I started thinking to myself like, wow, now I get it how people say people study some topic so intently that they end up going— so intensely, they end up going mad.

I began to feel that way.

Yeah, I began to feel that way.

Like A Beautiful Mind.

Like, I was losing my touch with our actual reality because I was living in these realms that we never get to explore in real life.

Oh, that's crazy.

Yeah, yeah.

So, like, when then you went back to real life, did you start— did you, like, start speaking in physics?

Like— That happened years and years ago.

Your wife asks you something, you're like, I don't know, that's beyond my horizon.

No, I did not.

Thanks, Hakeem.

Thank you for this, Caitlin.

For taking a chance, taking a moment to swap seats and share your perspective on everything.

Yeah, thank you for letting me see how my interviewees feel, right?

It was very nerve-wracking starting out, but I— Well, now I know how you feel.

Powerful.

No, sweaty palms.

I mean, I feel like a kid in a candy store asking people about their work.

It's fun.

Yeah, it is so fun.

I love it.

And, you know, I got to see you interview people on NOVA, and now I get to be interviewed by you.

Yeah, see, it wasn't so bad.

Thank you guys so much.

I love NOVA, and you guys have been so good to me, and this is another example of that.

We love you.

Thank you.

Thank you.