Daniel and Kelly’s Extraordinary Universe - What is quantum spacetime foam?

Episode Date: December 17, 2019

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Hey, Daniel, I've noticed that people just add quantum, the word quantum, to things to make them sound cool. Oh, man, I hate when they do that. Yeah, like quantum combs, quantum cereal. It's like they put it on everything just to make it sound awesome. Yep, I was seeing quantum dog food recently, and I'm pretty sure that's not a real thing. Your dog both loves it and hates it at the same time. But does that mean that just all of quantum mechanics is like a scam? Not all of it.

Like there really is some physics in quantum mechanics, but I'd say most things that are called quantum are probably baloney. Hi, I'm Jorge. I'm a cartoonist and the creator of Ph.D. Comics. Hi, I'm Daniel. I'm a quantum physicist, and that is not baloney. Oh, well, just so happens, I'm a cartoon, uh, baloney cartoonist. So this all brings it together. And welcome to our podcast, Daniel and Jorge, explain the universe, a production of IHeart Radio. In which we explore everything that's crazy and amazing about the universe, from classical physics to quantum mechanics and explain it to you in a way that you can explain to your friends and sound super smart. Yeah, in ways that we do explain it and don't explain it at the same time. We're sort of like a quantum podcast in a way.

We download individual discretized units of explanation into your brain. We spin it up and spin it down for you guys. But quantum mechanics is one of my favorite topics because it is so hard for people to understand usually. But there are ways to look at quantum mechanics and get a new sense of the world to reveal the reality that underlies everything. Yeah, it's your favorite because people don't understand it? It's my favorite because it's a great example of how in physics we can learn that the world is really quite different from the world we expected it to be. that the world we grew up in is not the way the world works. To really understand the universe, we have to remove our blinders.

And quantum mechanics is a great example of that because it requires basically tossing out your entire intuition for how the world works and accepting something very different. Yeah, I feel like that every day that I wake up and read the news. I'm like, what is this universe we're living in? What? Quantum politics, is that you talking about? It's just the quantum news, we'll say.

It makes sense and doesn't make sense. at the same time. It's about a dead cat and in a life cat all at the same time. I feel like quantum mechanics is something a lot of people are fascinated by.

They've heard about it. They hear people use words to explain it that don't quite make sense to them. And so people are thirsty for a real, honest to God, understandable explanation for some of this bizarre quantum phenomena.

Yeah. And it sort of seems like you said, it almost seems like two different universes, you know? There's like the universe that you grew up in as a kid and feel you understand where you take a ball and you balance it and comes back and you can throw a baseball and it lands where you think

it's going to land. And then there's the kind of the quantum universe you learn later on in life where like none of those things you learn as a kid seem to apply. Yeah, precisely because your brain develops all these ideas for how things move based on what you've experienced. Things seem to move through the universe. It seems like they have a smooth path. And so later to grow up and learn that Things don't actually move. They just have these snapshots and then those later snapshots and your brain is filling in the in-between slices to make like a movie of the universe is quite shocking. I wonder if we had evolved to be much, much smaller, if we would have sort of a quantum intuition, if we like had everyday experiences of quantum objects. You mean like if it's taught at the preschool level, if we try to teach kids quantum physics?

No, I don't think we should be doing shortening your equation for babies. You know, coloring, one plus one, spin up, spin down, you know, just the basics that you need to deal with this crazy world we're living in. That's one approach, but I think that people would still struggle because they don't have any actual experience with it. I'm talking about really experiencing quantum mechanics. Like, what if they were quantum effects that were macroscopic? You know, things that were the sides of baseballs operated under quantum rules. It's pretty hard to reveal that the universe is quantum mechanical. It took us thousands of years before we figured that out.

What if it wasn't so subtle? What if it was more obvious? And so people actually had an intuition for this. They're like, oh, electrons, yeah. Those move just like these other quantum basketballs or whatever. That I was playing with in my kindergarten playground. Yeah, maybe that's the next wave of physics education is we need to develop some sort of technology that operates like quantum objects. kids can play with, like, quantum balls.

Yeah. Well, it does seem like it's kind of a separate and new universe, and it feels like there's a quantum version of almost anything. Like, for anything that we have in our world, there seems to be, like, a quantum version of it. Like, you know, I know I can spin here in my chair. And there's also something called quantum spin. And, you know, my battery has charge in it, but there's also something called quantum charge and so on and so on. Yeah, there's even quantum flavor. Yeah, you think in kindergarten that there's only sweet and salty and sour, but there's also quantum flavor. And we have quantum color.

We had a whole podcast episodes about all these weird quantum and chemical properties. Yeah. So you could go to quantum kindergarten too and learn quantum sharing and quantum. And in some cases, these things are metaphors like quantum flavor. These particles don't actually taste like anything. But we're trying to make an analogy. We're trying to extrapolate from something we know, which is flavor, and give you a sense for this weird new quantum thing.

But in other cases, it really does make sense, like quantum spin. Those particles are not spinning in the same way, but they really do have angular momentum. So spin really makes sense. So in some cases, the words are really a stretch. In some cases, they really are applicable. Right. Yeah, that was a pretty good way you spun it there.

That's quantum spin right there. All just so obvious and clear. But yeah, but sometimes, you know, I wonder, sometimes I wonder if physicists are pushing it a little bit too much. And so today on the podcast, we have a great question from a listener that we're going to try to answer. And this is a question from Dale from Dublin. We had a very interesting question about another strange-sounding quantum thing. Here's Dale. Dale from Dublin, Ireland here.

I heard about a thing called quantum foam or spacetime foam. Could you talk about that for a bit and let us know what it is? Cheers, thanks a minute. Well, I love so many things about this. First of all, I love Dale's accent, awesome. And I love that Dale wrote in.

This was just an email he sent me saying, hey, could you explain this? And I asked him to send us a recording so we could talk about it on air because I thought a lot of people might be interested in the answer to this question. So thank you, Dale, for writing in and thank you to everybody who writes in with their questions.

Right. And just as a reminder, we are on Instagram and Twitter at Daniel and Jorge. And if you want Daniel to answer back, try Twitter or the email because Instagram will not answer your question. I don't do quantum social media. Yeah. So if you have a question, send it on into questions at Daniel and Jorge.com or engage with us on Twitter at Daniel and Jorge. Yeah. So this is an interesting question.

Quantum foam, it sort of sounds like one of these products that you say. sell in late night television that will totally clean your bathroom at the molecular level. I think a lot of times in marketing, quantum is just used to describe something to make a sound more modern or technological.

You know, like quantum dog food, that really is a thing. I mean, it's not actually quantum mechanical. No, no. Google Quantum dog food. There is a product. They really do sell dog food and call it quantum. Wow. I think what they mean by that is new, fancy, you know,

savvy to the quantum mechanical world somehow. New fancy, yeah. Well, that's kind of what you guys do in physics as well, isn't it? Oh, this is a charge, but it's kind of new and fancy. We'll call it quantum. Quantum charge. But wait, no, but it actually is new and fancy. Sometimes we do discover stuff in physics that's new and fancy.

All of quantum mechanics is new and fancy. It really does happen. It's not just marketing. Sometimes dog food is new and fancy. Why not? And companies discretized little chunks. That's true. All right, so I should order that product and I should evaluate it before I give my opinion on it.

You're totally right. And quantum dot food, please give us a call. We are opening for a sponsorship in this podcast. I was wondering if Dale from Dublin was the only person thinking about space-time foam. And so I walked around and I asked people what they thought about space-time foam. Had they heard of it? Did they know what Dale was talking about? Did they have any idea what it was?

And these questions, again, didn't happen at UC Irvine. And this happened at a local coffee shop because I was trying to get a sense for the broader public in their understanding of this topic. Yeah, so before you listen to these answers, think about it for a second. If a physicist approached you at a coffee shop, would you be able to answer the question, what is space-time foam? Here's what people had to say. Upper layer to space-time that kind of bubbles up or something, if that makes sense. I have no idea. I have no idea. I have no idea of space-time foam. No, I've not.

Nope. Space time phone, no. Space time phone, no. For space time, Fred, I guess. But I'm down. I'm down. Outer space. I'm not, yeah.

All right. I feel like people were answering, and they were just about to call the police on these. Yeah. You can sort of hear that in these responses. They're like, I am so regretting answering these questions. What are you talking about? I think, yeah.

I mean, people go to a coffee shop to wake up and you're asking them physics questions over their cappuccino foam. Well, you know, I specifically tried to choose people that looked like they were studying, like they had a book open or they were reading something because I was hoping to find people who were, you know, like had their brains on or intellectually engaged in something, were maybe curious about this kind of thing. I didn't interrupt like couples that were smooching. Or if they looked like they were listening to a podcast, you're like, that person probably

knows everything already, right? I try to avoid people who already have their earbuds in because I feel like in public, earbuds mean don't talk to me. Well, this is kind of an interesting question, quantum foam. And I had never heard of it. If you had approached me at a coffee shop, I would have just said, no, please go. Please ask me an easier question. You would have been like, you look like this other physicist I know, and I definitely ignore him in public, so I'm not talking to you. Yeah, as a blanket policy, that's my position on physicists.

All right, so this is an interesting question because it's like you're marrying two words that are very common, space, time, and foam, but that together really don't make any sense. Yes, and that happens so much in quantum mechanics. People say things, they use words together, and you understand the individual words, but you don't really know what it means when you put it together. So we'll get into what space time foam is and what we know about it and how we might be able to find it in this frothy little universe we live in. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport.

The holiday rush. Parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the. The explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay.

Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers.

I'm Gretchen Whitmer, Jody Sweeten. Monica Patton. Elaine Welteroff. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes and gives you the inspiration and maybe the push to make your next pivot. Listen to these women and more on She Pivots, now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history. The predictions will we see a first time winner and the pressure. Billy Jean King says pressure is a privilege, you know.

Plus, the stories and events off the court and, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late. Have you heard about Icon Venus Williams' recent wildcard bids or the young Canadian, Victoria Mboko, making a name for herself? How about Naomi Osaka getting back to form? To hear this and more, listen to Good Game with Sarah Spain, an Iheart women's sports production in partnership with deep blue sports and entertainment on the IHart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports.

All right, Dana, we're talking about space-time foam, and it's not a weird product that you sell on late-night television. It's an actual physical theory in science. And so let's get into that a little bit, and I guess let's start with the first two words. to set us up for the foamy part. So let's talk a little bit about space time because in this case, I think Dale from Dublin used the word as one word, like space time. Not space, comma, time.

He called it space time. So let's maybe refresh for our listeners what it means to say space time. Yeah, it's like you take two words, you put them together, they mean something special. Like green and house. You know, a greenhouse is not just a greenhouse, right? It has its own meaning.

So in the same way, space time is sort of a special word in physics. And of course, you know it's spaces. Space is just the three dimensions of movement. You know, you have X, Y, and Z. And we have a whole other episode about, like, what makes up space. Is it a thing? Because it can wiggle and dance and jiggle and expand and all this stuff. But for our purposes today, let's just think about it as sort of as the directions you can move in, X, Y, and Z. So that's what space means. Yeah, like the space we're in, like where we move around in. Yeah, precisely. Nothing special there. And time is just time, right? Time flows forwards. And you can think of time. In analogy to space, you can think of us as moving through

time, the way you can move through space. And we have a whole podcast episode digging into how time is connected to space and how time is different from space. But Einstein is the guy who put these two things together. He's the first one to construct this idea of space time by taking three dimensions of space so you can move in, and adding the time dimension to it is sort of a fourth dimension. So together, space time is this four-dimensional idea, XYZ, and then time. Right.

I feel like you just said something profound, though. You just said, time is time. Man, time is so fascinating. I could talk endlessly about time. We could spend all of our time talking about time, but maybe it's not time to do that. That one phrase just made me think about my whole life and where I'm going with it,

Well, can I sell you my new product? It's called Quantum Time. Oh, no, there you go. All right, a quantum watch to keep track of the inevitability of time. It's new and fancy and has to be charged every 15 minutes. There you go. All right, so space time is this idea that space and time are not separate. Like maybe if you think about them all together in one package, one four-dimensional bundle,

then it's more appropriate somehow. Like they're related. Like one of them affects the other, so therefore you should keep track of them all at the same time. Precisely. And it was Einstein's theory of special relativity that showed us exactly how space and time are affected by each other.

Specifically how time flows depends on where you are and how fast you are going relative to something else. And so in order to understand time, you can't just have time by itself. Time is not universal. time is local. Time depends on where you are in space. And so it makes much more sense to combine these two things together. It's like having the weather, right? The weather's not the same everywhere. So you want to talk about the weather where you are in Buffalo or in New Delhi or in

Barcelona. And so you pair the weather with the location because that makes more sense. It's called the space time weather continuum, which I hear. Listen to my new quantum weather reports. It's a new Doppler, Quantum 3,000. That probably is a real thing. I mean, you're joking, but there's probably some local station out there with a quantum weather doppler. Some local weatherman in the middle of Barcelona. And Einstein was not crazy, right? Like, he didn't just make this up and it didn't work. It actually works. Like bundling space and time together does tell you something about the universe and there's been theories and experiments done to prove that this is all For reals.

Oh, yes, Einstein was right about this. That doesn't mean Einstein wasn't crazy. I mean, you dig into that guy's personal life. He was more than a little bit crazy. What do you mean? But he was also right about spacetime. All right, so that's space time. And now the question from Dale was, what is space time foam?

And I have to say, I had never heard of this before. Is this a new thing? Is this something that's only been around for a couple of years? Or is this like a French theory or a French theory? I don't know, either one. What is going on with Space Time? foam. Well, I can't endorse your casual slander of an entire culture there, but it is a bit of a fringe theory. It's one of these things that's like, it's an idea that took hold in some

people's minds, but then not a lot of progress was made. So it's sort of just been hanging out there, bubbling up in people's brains without really turning into anything concrete. So it's been around for a while, but it's not really part of the mainstream physics. It's just been foaming up in people's research dockets. And so I know that you keep a brain. rest of all the latest topics in physics and you read all the physics journals and that's probably why you haven't heard about this recently right well at first i thought it was maybe an acronym like maybe f o a m stands for something it's the first of a multiverse which is a new theory by horace ham about how we're the most awesome of all the multiverses and somehow dale from dublin

knew about your theory before you even thought about it and thought to ask in advance wow good job Yeah. Well, in other multiverses, he didn't. But this one, because it's the best, he did. All right. So let's talk about this. So there is something called space-time foam that physicists think might be real and might actually kind of describe what the universe is like. So take us through it, Daniel. What does it mean to put the word space-time and foam together? The idea here is to try to resolve the conflict between our two great theories of physics. We talked about space time in terms of relativity, and that all makes sense. And relativity has been tested out the wazoo and up the wazoo and in the wazoo in every way around the wazoo because it's a great theory. Is that another physics experiment acronym, the wazoo? The wazoo. I'm not sure what it means.

It's a collider in Italy, apparently. It's a collider in Kalamazoo. But special relativity has been extensively tested, and so has general relativity. but we don't know if it really holds universally, that we have suspicions that it probably doesn't work on really, really tiny distances. So general relativity says that space is sort of smooth, that you can chop it up into tinier and tinier bits

and you'll never sort of run out of ways to cut it in half. That like in Zeno's paradox, you could take smaller and smaller steps forever. That's what general relativity says. It predicts it or it assumes it? It assumes it. It uses that as it's a, essential description of what space is, that you could have a particle or an object located

at any point. You know, if you have an infinite number of locations between me and you, that a particle could be at any of those locations. Oh, I see. It's kind of like Newtonian physics, right, almost in a way. Like, it assumes that space is smooth, and it doesn't assume anything that anything is quantized. That's right. And you look at the universe around you, and the universe seems smooth, right? It seems like you could sit anywhere. It seems like if you took a ruler, you could cut it in an infinite number of ways, you know, 50-50, 75, 25, whatever, that there's an infinite number of ways. But just like the screen on your iPhone, it looks really crisp and smooth, but if you zoom in, you discover that there are pixels there. And so general relativity

tells us that the universe is smooth, that space is infinitely sliceable. But that's in conflict with quantum mechanics. Quantum mechanics says that you can't have infinitely sliceable space. Yeah, that at the fundamental level, it's pixelated, kind of like my iPhone screen. Although my iPhone screen these days looks kind of blurry, because as I've said before, I need reading glasses now. I'm not sure that's a problem with your iPhone screen. Well, it's a problem for my new quantum reading glasses. Yeah, and so quantum mechanics has this impact on lots of things that we measure, Things that at large scales seem smooth turn out to be discretized, turned out to be sliced up into chunks. Like a flashlight beam is not a smooth, continuous beam of light.

It's a stream of tiny little packets called photons. The same way your bowl of ice cream is not infinitely choppable into smaller and smaller spoonfuls. There are atoms in there. It's made out of these tiny little Lego pieces. So the same concept can be applied to lots of things. And quantum mechanics says that probably it also applies. to space. So we have this conflict between these two great theories of physics, relativity and quantum mechanics. And the conflict lies in a place that's really hard to spot where things are

super duper small. So meaning the general relativity doesn't know that there is something called quantum physics and quantum mechanics, quantum physics, sort of we don't, do we know that quantum mechanics takes into account general relativity? Or is there such a thing? as bending of space in quantum mechanics? So that's a great question. People have tried to say, let's take Einstein's theory of general relativity and let's make a quantum version of it.

Can we make a version of general relativity where space is pixelated or quantum mechanics comes into account? And currently we have no great functioning theory. Like these theories, you can make a theory of general relativity that is quantized, but it doesn't work when space is really intense, like inside a black hole,

the gravity gets really, really strong, then the theory breaks down and predicts things that don't make sense. It gives you like infinities and all sorts of crazy numbers. So we don't currently have a working theory of what's called quantum gravity that tries to marry all the best things from general relativity and quantum mechanics. So does that mean that quantum mechanics operates kind of in a Newtonian or like perfect kind of pre-Einstein universe? Quantum mechanics operates often in what we call a flat space, you know, space that's not bent by mass.

You can do quantum mechanics in curved space where if you're like near the sun or near a black hole and space is curved. You can do that quantum mechanics. But if you try to do it when space is too curved, when gravity gets really, really strong, then it just doesn't work. We just don't even have a theory.

We can't like even come up with a theory that makes sensible predictions, not to mention check those predictions against actual experiments. All right. So it sounds like general relativity is good for kind of big distances and tells us how the universe works at large scales. And quantum mechanics tells us how it works in really, really tiny scales. But there are situations where the two theories just don't, neither of them work. Yeah. And what we need to do is get inside a black hole and see what happens when you have both small distances. So quantum mechanics is relevant and really intense gravity. So general relativity is relevant. Unfortunately, all the people we've sent into black holes have not yet come back. Yeah, I was going to say that you're using the word we there pretty broadly there.

Any volunteers out there to go visit a black hole? Who wants to be the first person to die at a black hole? And this is where the idea of space-time foam comes from. It comes from an attempt to try to reconcile these two theories. I see. It's another one of these unifying theories, like theories of everything. precisely. There's one theory that says maybe the universe is made out of tiny little loops. That's called loop quantum gravity. Another one says maybe everything is just a tiny vibrating string. That's string

theory. There's even one called spin foam, where everything is like this weird spinning kind of foam. But space time foam is a particular theory that tries to unify quantum mechanics and general relativity. And it imagines space is being made of these tiny little pixels. But these pixels would be quantum mechanical. And so like bubbles in a frothing foam, they might like pop in and out of existence. All right. Let's get people in the loop of this and get a little bit more into what quantum foam or space time foam is and how we know about it and what we might discover if we poke around in the universe. But first, let's take another quick break.

December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. is just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay.

Terrorism. Law and Order Criminal Justice System is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your point. podcast. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the

inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten. Monica Patton. Elaine Welterah. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make. Of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes and gives you the inspiration and maybe the push to make your next pivot. Listen to these women and more on She Pivots. Now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here. And on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing

history, the predictions, well, we see a first-time winner and the pressure. Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court and, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late.

Have you heard about Icon Venus Williams' recent wildcard bids? Or the young Canadian, Victoria Mboko, making a name for herself? How about Naomi Osaka getting back to form? To hear this and more, listen to Good Game with Sarah Spain, an Iheart women's sports production in partnership with deep blue sports and entertainment on the Iheart radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. All right, Daniel, so quantum foam is kind of like quantum dog food in that, you know,

you're trying to make something that your dog will both eat and enjoy at the same time. We're trying to make something that explains both general relativity and quantum mechanics and that your dog will like, I guess, also at the same time. And that's hard because, as you said, they're sort of based on two very different views of the universe. That's right. And, you know, for relativity to work, what we need is a new imagining of it. We need to start from a different conception of what space is. Einstein assumed that space was smooth and continuous and he built his theory upon that assumption. So we need to start from a different assumption and say, actually space has made of these tiny grains or these little

bubbles and understand the nature of those and then build a theory on top of that. And we don't know this is true. It's not clear that spacetime foam is a real description of. space you know it might be that pixels are a better description or loops or little strings or we really just don't know but we need a new idea and so theorists are just sort of being creative and smoking banana peels and saying well maybe it's more like this and you know you look around the macroscopic universe to get inspiration you know and maybe some physicist was smoking a banana peel and looking at soap bubbles and thinking huh maybe space is just like that well it's it's interesting because I feel like there's these two theories

and it's not like you're saying like oh maybe quantum mechanics is wrong and really we just need to extend general relativity or you're not saying oh general relativity is wrong we just need to extend quantum mechanics I feel like you're saying that we we need to throw both of these into the garbage

and kind of come up with one theory start over re-imagined the universe and come up with one theory that you know it sort of looks like one and looks like the other, but actually kind of works continuously across the whole universe.

Yeah, well, we don't know what the necessary process will be. It might be that we can take what we have from general relativity and from quantum mechanics and marry them. Or it might be that, yeah,

we have to toss it out and start all over again. The process of science is iterative, right? It's like a writer writing a draft of a screenplay or something. You just keep trying to make it better and better until it fits. And then at some point you realize, you know what,

this is hot mess of garbage and you've got to toss it out and start all over again. So we don't know. We don't know if, you know, we're one more draft away from something we can publish or if we've got to toss it all out and start on the next book. Right. Or maybe the studio head goes, well, it's too late. Let's just make this bad movie.

Can you make it 25% funnier? We live in that universe that should never have been made. Oh, no. Or the plot twist don't make any sense. And the acting is stiff at best. That's even better than do we live in a simulation. It's do we live in a poorly written simulation. I like that.

I got notes for you, simulation authors, okay? Here's how you should have done the simulation. Here's what Rotten Tomato says about your universe. That's right. Businesses ratings on universe simulations. I like it. There you go. Quantum Rotten Tomatoes is the name of my new website.

Check it out. All right, so step us through. What is quantum foam then? Is it, what does it foam mean? Why is it foam? Does it have bubbles in it? Is it like a froth? Why is it called quantum foam?

Yeah, the idea is that quantum mechanical things fluctuate. They come in and out of existence. If you zoom into particles at the smallest scale, you can't follow them along the way you would follow a baseball. They sort of pop into existence and pop out of existence. They turn into other particles. It's like a constant mess, right? And so lots of things are happening. Like it's bubbling at the surface, kind of like foam.

Those are the things in space and time. This is saying that space time itself is like a foam. Right. And so if space itself is quantized, it's made out of these pixels. And these pixels are quantum mechanical. Then it's possible that the pixels themselves are sort of bubbling in and out of existence. It's one step to go from space is smooth to space is discrete. It's made of pixels.

It's another to say maybe those pixels themselves are not like permanent. They're like temporary. You know, they're ephemeral. They're coming in and out of existence. because in the end, a lot of quantum mechanical things are. Space itself is coming into and out of existence? Like this bit of space right in front of my eyes here. Yeah, precisely.

You know, the object in front of you, for example, whatever is it's in front of you right now. It's a banana or it's an apple or whatever. That's made of quantum mechanical particles. Now, it seems solid. It seems like it's really there. But if you zoomed in on the little particles, the particles that make it up are popping in and out of existence.

They're turning into energy. They're turning back into particles. They're changing into other particles and then coming back. you don't even notice, right? So that phone or whatever in front of you is a frothing mess, but you just don't notice it frothing because the frothing is so tiny. So if it's hard for you to imagine that space itself could also be frothing, remember everything around you is kind of frothing.

Oh, wait, so this would be like under the quantum particles. Like you could have a quantum particle and it's really tiny, but the space it is sitting on could be bubbling underneath it. Is that what you're saying? Precisely. And remember that in modern quantum, mechanics we don't even really think of particles as like the basic element of stuff in the universe particles are just excited states of quantum fields and quantum fields that we had a whole episode on

are a property of space itself so you can't really separate the matter and the space because matter is just an excited state of quantum fields which are a part of space oh but is the space time foam on the same scale as the particles like um you know what i mean like whatever there's a particle that just happens to be sitting on a space-time bubble and that bubble pops, does that particle just disappear? Or is it like riding on top of a whole bunch of little space-time bubbles? Yeah, I think you have to think of particles as part of space because particles are, again, excited states of these fields and the fields themselves are part of space. And so I think it takes a whole new way of thinking about like the nature of the universe at the smallest scale. It's not like particles are sort of filling in slots in

space they're like excited space oh and you're saying that this space is actually more like foam meaning that it's just a whole bunch of little pockets of it kind of pressed together and each one of these pockets is a quantum of space time that's right and we don't know the size of these bubbles if these bubbles exist and we don't know that they do the question is how big would they be and we suspect if they do exist, they'd be super duper, duper, duper tiny. But yeah, the idea is that, you know, you have a localization of energy, that energy is an excited state of all the quantum fields in that space. And that localization of energy could extend across multiple bubbles of quantum space, perhaps, for example, like a photon. And that, you know, can be made of these little frothing bubbles that are

smaller than that packet of energy. And so what am I doing when I'm moving through space? Am I moving from bubble to bubble? Or do I take, like, each one of my particles might be in this bubble or that bubble? Well, you are those bubbles. You're not in those bubbles. You are those bubbles. I am the space-time foam. You are the space-time foam.

And so am I. We are all one with the space-time foam. Remember, you are just an excited state of the space that you are occupying. And when you move, that information, then that energy then moves, you know, it excites another part of the quantum space. It's like you are the wave on the string, right? If I'm holding a string and I wiggle it, you can say like, where does that wiggle go? Well, it moves along the string. The same way, you are wiggling the quantum fields where you are now. And then when you travel somewhere for Thanksgiving, you're going to wiggle those quantum fields.

So don't think about it as you are particles in space somewhere, but you are excited wiggling of space. Oh, I see. I'm just an excitation from one bubble to the next bubble. precisely. And the idea of space-time foam is that maybe space is discretized and those little discreet blobs are popping in and out of existence. They're like not long-lasting. They're not eternal or permanent. They're sort of frothing. Oh, coming in and out. But what if I get stuck in one that pops? I wouldn't recommend that. Does that mean I'm no longer in existence? Then you don't have to buy quantum pet food for your quantum dog because it's quantum out of existence. Now, these things are at a very, very small scale. So unless you're a particle on the

size of quantum foam, you don't have to worry about it. But also, energy is conserved. So if space is frothing somewhere and energetic, if there's an excitation of space here, that energy is going to go somewhere, maybe into the next bubble with the next bubble. So the bubble itself might pop out of existence, but the energy that is represented by that excitation is not going to go away. Oh, it's just going to move on to another bubble? Yeah. That's what you do when you move from place to place. You are exciting those fields and now you're exciting these fields over here. All right. And so there's a theory that says that the universe at the very core level is like a foam, but that's just one competing theory about what it looks like down there. How are we going to find out

which one it is? How do we know if the universe is foamy or if it's not foamy? Well, we need lots of money to build a huge particle collider. That's my answer to everything, right? Right. Money just solves everything for you, doesn't it then? It sort of does. You know, if you want to answer questions about high energy or heavy particles or tiny distances, what you need is a microscope to look at the really, really small.

And the only thing that prevents us from looking at really, really small spaces is having enough money to build a big enough microscope. We know how to do it. It's just really expensive. So we could probe these distances. We think the distances involved are something like 10 to the minus 35 meters,

which is redonculative. tiny. Like if you had a microscope with not just like a 10x, 100x, but like 10 to the 35x, we might be able to see these foam bubbles of space and time. Yeah, we had a whole episode about how you see tiny things and microscopes and electron microscopes and particle colliders. So people should dig into that if they want more information. But basically we can see down to 10 to the minus 20 right now, which is pretty impressive. We think these bubbles are 10 to the minus 35. So 15 orders of magnitude is actually still a lot. You know, we're far away from being

able to see these pixels. So that's one way is to build a really big collider. Another is to try to use like really long distances in space. Oh. To use a space itself like a microscope. The idea is, if space is bubbling and frothing,

then, you know, it's sort of constantly changing. That means that, like, the distance that light has to travel from point A to point B is not necessarily fixed. So they do these crazy experiments where they look at something really, really far away and they try to see it in two different ways. They try to understand like,

you know, let's look at two photons that left that really bright source of light, maybe a quasar, at the same moment, and see if they arrived here on Earth at the same time. If there's a difference, then maybe that's because there was more quantum foam bubbling up for one photon than for the other. Oh, I see.

Because it's foamy. That means the path you take through this foam is sort of random. And so, like, one photon could have hit a really foamy patch, I guess, and gone through a little bit of extra space more than the other particle who just happened to go through a part of space that wasn't as foamy. And so that would tell you, like, oh, space is not consistent. It's kind of frothy. That's the idea. I have to say that I'm skeptical because, you know, on long-distance scales, you would think that these things would average out.

Like, you're going for a billion years than the number of random tosses of. a coin are going to be pretty close to 50-50. So two photons flying through incredible distances in the universe, you know, are going to have pretty even odds to go roughly the same distance. Anyway, they look at these photons. They don't see anything, no surprise. And so they haven't discovered quantum foam. All right.

Well, do you think we'll ever discover whether the universe is made out of quantum foam or or not? I think we will. I think it'll require some really clever mathematics to come up with, like, how these theories might actually work. Because remember, we don't have a functioning theory. We don't have a theory we can actually go test. The theory, if we ask a question, it gives us gibberish.

And so we need to come up with a good theory. And then we need to be really clever about how to test it. And I think maybe some time far in the future where we can get closer to black holes, we'll be able to test some of these theories in environments with really intense gravity. But it's pretty far off in the future. So we need clever ideas and we need awesome new experiments. Right. I guess all of that is just to say,

send Daniel more money is the entire takeaway. Who needs sponsorship from Quantum Dog Food when you can just have a whole podcast to ask people for money? That's right. Email me your quantum dollars to contributions at Danielahorpe.com. Oh, yeah. That does feel like my bank account. It's both there and not there at the same time.

It's constantly fluctuated. Yeah, it's foamy. I have foamy money. Not phony money, foamy money. All right. Well, thank you, Dale, from doubling. We hope that answered your question about what quantum foam or space-time foam is. And I guess the answer is stay tuned. Yeah, it's a really fun idea. It's fun to speculate about what the universe might be like at the smallest scales. It's fun to take ideas from our everyday world and see if they apply at the quantum scale. But today, we don't really know if quantum foam is a thing or just an idea bubbling up in the mind of physicists. So keep on looking and keep us sending us your questions. We're happy to answer them.

All right, we hope you enjoyed that. Thank you for joining us. See you next time. If you still have a question after listening to all these explanations, please drop us a line we'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word, or email us at Feedback at Danielandhorpe.com. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio.

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