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Rationally speaking, is a presentation of New York City skeptics dedicated to promoting critical thinking, skeptical inquiry and science education. For more information, please visit us at NYC Skeptic's Doug. Welcome to, rationally speaking, the podcast, where we explore the borderlands between reason and nonsense, I am your host, Massimo Pelusi, and with me, as always, is my co-host, Julia Gillard. Julia, what are we going to talk about today? Massimo, I am delighted to announce that today's guest is Professor Max Tegmark, who's a physicist, a cosmologist at MIT.

Max has won widespread respect in for his work in mainstream physics on precision cosmology. But he's also embarked on some more speculative investigations into, for example, the nature of reality, which he has written about in his book that is hot off the presses and now on bookstore shelves called Our Mathematical Universe. Max, welcome to the show.

Thank you very much, Julia. And my condolences to you. To be outnumbered by to Max's loss, of course, is just the Swedish version of the name Massimo. That's right.

I hadn't realized how outnumbered I was until you just said that. But now all of a sudden, I feel like an embattled minority.

Yeah, well, try not to beat up on you, Max. Welcome. It's a pleasure to have you here. The very first question I have for you is very basic. So I guess you should give us maybe the capsule version of of these these mathematical universal hypotheses. And I know, however, that that hypothesis includes the concept of the external reality of a mathematical structure.

So I'll ask you to tell us, what do you mean by mathematical structure and in what sense are mathematical structures externally real?

So there you go.

When you first hear about these ideas, they sound kind of nuts, because when you look around ourselves and our surroundings, we don't see anything that looks mathematical, maybe except the page numbers in the book or something else human made. So where is all this math that I'm talking about in the book?

However, we physicists have, of course, realize that all of this stuff around this is made of elementary particles. And even if the properties I would ascribe to say. Do you have attacked any of your guys? For dog, a cat? No, but I'm familiar with them. It was a cat has the property of being cute, then fluffy and a little bit shy.

Those don't sound like mathematical properties. Right. But you know that that cat is made out of elementary particles like quarks and electrons. And what is the properties that the electron has? Well, it has the property minus one, one 1/2 and one. And we physicists have come up with a geeky sounding name for these properties, like the electric charge and the spin and the Lepton number. But they are just mathematical properties, just numbers. And the same can be said about all of the other particles that make the building blocks of all the stuff around us.

And what about the space that that cap is in? What properties of space? Well, it has the property, three dimensionality of space, the largest number of pencils that can hold perpendicular to each other. That's also a number of mathematical property. And then we've discovered since that space also has properties called curvature and topology, which are mathematical, too. And if you remember, once you realize that both the stuff in space and space itself have no properties at all other than mathematical properties, it starts to feel a little bit less nutty, this notion that everything is mathematical.

Can I ask, what is the difference between saying that the physical universe is math or is made of math versus saying that math describes the universe?

Oh, that's an excellent question. The if math if if our physical world had some properties that were mathematical or at least approximately mathematical, we could say math describes or at least approximates the universe. But if it has only mathematical properties, if there's not a single property that external reality has, which is not mathematical, then in that sense it really is purely mathematical.

Now, I think I understand what you're saying. And actually, as it turns out, there is a somewhat long history in philosophy of similar ideas. And when I looked up your hypothesis, it turns out that from a philosophical perspective, it can be followed as a combination of three different philosophical positions. So you may have for a second and I want to know, what do you think? First of all, if you think that's that's a reasonably, reasonably good description of what you're talking about.

And second, what do you think about these these these positions? So, as I said, three philosophical positions. One is mathematical. Pythagorean is more math, sometimes referred to as mathematical Platonism. That's the idea that mathematical structures are real, then also mathematical monism, which is a distinct position. That's the idea that only mathematical structures are real. That is that the world is made of mathematics.

Because you were just saying and then finally of something called UNTEACH Structural Realism, which actually one of our former guests, James Latterman, talked about.

And that is the idea that the ultimate constituents of the universe, as we understand it, are, in fact mathematical structures. So so a combination. It seems to me that what you're proposing is actually a combination of all three of these positions, or am I missing something or is there something that shouldn't belong to that list?

I think that's that's exactly correct what you're saying. I'm I agree with all of those things and combined also.

And on steroids, when you mentioned structural realism, you mentioned plural of mathematical structures. But ultimately, when we look at the physical world and a bunch of equations, there's only a single mathematical structure that we're all part of. And it can in turn have parts just like the mathematical structure known as the dodecahedron has parts that has a lot of different corners. And changes in our mathematical structure can have a lot of parts corresponding to particles or or other more complicated things.

I think it's also really fun that when you bring up these different viewpoints to look at the whole spectrum and see what is it that's controversial about this, because the basic idea that the universe has at least some mathematical properties is, of course, very old. Already the ancient Greeks.

Right, looked at into the middle, which is why you mentioned the Pythagoreans, for example, by the time the Renaissance came around Galileo, it's your so last name was Countryman from Italy, famously explained, famously exclaimed that Our Universe is a book written in the language of mathematics because he was so impressed by all these mathematical patterns and regularities of motion and. Yet as time went on, he just kept discovering even more irregularities.

For example, if you take three discoveries of the planet, Neptune of the radiowaves and of the Higgs boson, what tool was it that allowed us to discover these?

What would you say? Well, I'm guessing you're going to say mathematical theorizing. Yeah.

Or if you really wanted to. Well, it would be the pencil with which these equations were written out. It's it's really impressive. I mean, you had some people noticed that Uranus wasn't quite moving. Right. Did a bunch of calculations. A letter was sent to this astronomer saying, point your telescope to such and such a direction in the sky and such and such a time. And you'll see a new planet. He did. And boom, there was Neptune.

Similarly, James Clerk Maxwell was messing with his pencil and managed to unify all the equations of electricity and magnetism and predicted that if you built a certain kind of machine, you could send radio waves with, it was built.

And now we have cell phones. And the Wi-Fi that lets us do this is a Skype interview here. And then finally, very recently, Peter Higgs is guys, of course, no use his pencil and predicted that if you built the biggest machine that scientists had ever built and smash particles together in a certain way, you'd find a new particle there and boom, it was there and the Nobel Prize was handed out. And this is a very powerful tool.

And we have to ask why? What does this mean?

And this is this this is where it really gets controversial, in my opinion, because some of my colleagues will say, well, it doesn't mean anything. For some reason, our universe is approximately as described by math, at least some respects. And that's useful. We should be grateful for it, but not do any philosophizing. And then there are other people. I think it probably means something and they've argued a lot about what it means. Eugene Wigner, for instance, wrote a paper about 50 years ago where he talked about the unreasonable effectiveness of mathematics and the physical sciences and basically argue that they deserved an explanation.

But he didn't offer one. And then and then on the extreme end of the spectrum, you have me there arguing that actually it really does mean something. And what it means is that everything is mathematical. The reason that we keep finding these mathematical regularities that approximately describe stuff is simply because sometimes simpler math can approximate more complicated math. So I'm saying that all of the physical theories we've found so far are simply approximations of the true theory that. Maybe one of you guys or one of the listeners will discover in the future that will unify quantum mechanics with gravity and let us just not going to be me.

So I think I'm still a little hung up on the difference between everything being describable by math and everything, literally being math.

And when I when I imagine a universe where that only consists of mathematical objects, I guess I could imagine that in a much simpler form than the sort of messy matter and energy filled universe that I see around me. I could imagine just, you know, a whole bunch of mathematical equations written down in some form, maybe not an hour, you know, in script, on paper, but, you know, inscribed in some form in the universe. And yet what I see in front of me, around me, even if it can all be described by those equations, seems like a different thing than those equations.

It seems like somehow you need an additional step where somehow you breathe life into those equations or use them to create something to help you understand.

That's a very, very deep question. And and I'm glad that you use Stephen Hawking, his famous phrase. Also, what is it that breathes life into the equations and makes the universe for them to describe that unintentionally?

Well, the best tribute we can pay to poems or nice phrases is to memorize them, of course, and use them. So what is that exactly?

Well, one of the things I talk about at great length in my book is not just this idea that things are mathematical and the evidence for it and so on and what it means, but actually what it implies where it leads you, because that, I think, is actually the most fascinating part. If you if you think about something like the integers in our one, two, three, four or five, etc., you can add and multiply and so on.

That's a famous mathematical structure. Piano proximities. The mathematicians have studied great lengths. There are a lot of ways of describing the integers you learned in school to describe them by referring to them as one, two, three, four or five, I learned to describe them as I thought, to see them and Masimo Doit today, quadrilogy, chinquapin and so on. And it's the same mathematical structure with many descriptions. And also it doesn't matter what symbols to used for them.

For example, in India, they use different symbols for writing than integers from one to 10 than we do here, which caused me a terrible confusion when I was stranded at a small train station trying to figure out what platform my train was on and stuff like that. And the symbols were different. And the key thing is that mathematicians define a mathematical structure as that which is described by all equivalent descriptions. So it sort of strips away all the human baggage that went into naming the objects and naming the relationship and leaves just the pure integers themselves.

And then if you if you take that point of view, you can actually write a computer program that just starts classifying and making a long list of all mathematical structures in principle, starting with simpler and then gradually getting more complicated as a sort of telephone book. Each structure can have a number if they're accountably many. And then you have to ask your question, Julia, because it becomes very personal. OK, there are all these different mathematical structures, but we see only one universe with one set of laws of physics.

What about all the other ones? I don't think that there is anything breathing fire into the equations and making a universe for them to create because in a mathematical structure isn't created the integers one, two, three, etc. and the relations between them to be created, they would have not existed in their existence. There's no time in them. There are some mathematical structures that generally don't exist in space and time. Instead, space and time exist in some of them.

There is a mathematical structure called Minkowski Space that Einstein came along with it and studied it together. It describes space time where time is just the fourth dimension and this mathematical structure. And if these structures that aren't created, if they all exist equally, that must mean that actually. All the other mathematical structures which we think of as just failed physics theories that didn't describe our world actually describe a different world, which is just as real as ours.

We call our one the real one and give the Nobel Prize for discovering that math because. It happens to be the one we live in, but string theory, for instance, if if that were to turn out to be the correct math for describing our universe isn't actually telling you something fundamental about the full reality. And it's just telling us of telling us our address in this space of all the mathematical structures, just like. The number two written on the front of our house here, it doesn't tell us anything fundamental about our universe or even about our street, it just tells me where on the street I am or the number eight, the number of planets in our solar system.

Sorry, Pluto. But it it doesn't tell us anything fundamental about all universe together. This tells us. Where we are in it, so if if you were telling some kind of intergalactic mailman, you know where to deliver a letter, you would say, bring it to this. Solar system, know that one there with eight planets in it, and then you go to that street in the house that says to one atom and it's like, well, which universe are you talking about?

Oh, the one with the scribe. By these equations of string theory, that would be our. So in other words, the answer to your question ultimately of what breathes fire into equations is nothing. And if you take that seriously, it means that the true reality is even bigger than we thought. Not only do we have all of this awesome space, all the galaxies we can see with our telescope and maybe all these parallel universes that we physicists have been talking about of various kinds.

But there's even yet another level, which I call the fourth level of parallel universes, which includes all of the different mathematical structures. What is the biggest reality of all? So I have to ask, how could we test this, is it at all testable and if so, how do we go about that?

This makes a lot of predictions. The first obvious prediction it makes is that the. We're going to find even more mathematical regularity if as we keep looking for them. If this were all a fluke and if there was something fundamentally non mathematical about a universe, if I'm ultimately wrong, then that means physics is ultimately doomed. And one day we're going to bump up against the roadblock beyond which we just cannot proceed. Whereas if I'm right. And it's all math, then there is no roadblock and.

Our ultimate ability to understand our reality is only going to be limited by our imagination, but also other ways you can test all sorts of theories involving parallel universes. It's important to remember that parallel universes are not a theory. They're is simply a prediction of certain theories. So, for example. If you take Einstein's theory of general relativity, it's a bunch of math. It predicts a whole bunch of things. But you can observe like how the sun bends starlight, how Mercury's orbit is kind of weird and all sorts of other things.

And it also predicts stuff that you can never observe, like what exactly happens inside of the monster black hole in the middle of our galaxy. But. For theory to be testable, you don't have to be able to test everything and observe everything first before we take for a theory to be testable. You don't have to be able to observe everything and predict just at least one thing it predicts, because if that's wrong, theory goes in the trash and because we've tested Einstein's gravity theory and so many other ways.

We're forced to also take seriously what predicts what's happening inside a black hole. And in the same way. We have this theory of inflation, for instance, which is predicted very successfully, all sorts of stuff about our Big Bang and is now the best explanation for what? Generated the big bang in the first place. It also predicts that space is huge, vastly larger than what we can see, maybe even infinite, giving us all sorts of parallel universes.

So if we buy that theory, which forced us to buy into those other things and we test those other things by testing. The fundamental theory of inflation, if you can kill inflation, you can kill those parallel universes. On the other hand, you can't just say, oh, you know, I like what Alan Guth and Andre Linda and others did with inflation that explain or we see in the background. But on our economy, they don't like this parallel universe stuff.

I'm going to opt out of it. You can't do that, of course, unless you can come up with a different set of equations which predict also explains everything you can see. And not the rest, and a lot of people have tried and failed so far, so that's the sort of philosophical way I like to think about how to test theories that predict stuff that you can directly observe.

So, Max, in following up with Julia's question a little bit in the past, you suggested that your hypothesis has no free parameters and has not been ruled out observationally. Therefore, it's favored by Occam's razor. Now, I understand the reasoning there, but would you mind explaining, first of all and what do you mean by having no free parameters? And second, what could you comment on the idea that some philosophers and probably some scientist as well would say, well, yeah, about Occam's razor.

It's a little bit of a weak juristic if we're talking about such a broad ranging theory. So what about these free parameters and what about relying on Ockham's Razor? Great, so let's talk about the parameters first, so I when I teach at MIT, a lot of students like to come to school and tee shirts with equations on them and the nerds.

Yeah, but this is some kind of a geek myself. I have to tolerate it. And for example, one student recently came to class with a t shirt saying and Maxwell said. And then there was Maxwell's equations and there was light.

And on that t shirt, if you look closely at the equations, there's actually a parameter. And No. Which is about one divided by one hundred thirty seven, if you unpack it, just sort of built in to. Our universe itself, another parameter like that that we already talked about is three, the number of space dimensions and it turns out that we're with only thirty two parameters like this, plus a few little switches that can be. Small hole numbers, you can actually calculate every number that we've ever measured in science.

At least in principle and. A common measure of how good a theory is, is if it can get more out of it, then you have to put into it if you have a theory that's supposed to explain. Seven numbers that you can measure about the hydrogen atom, but it had. Eight free parameters. That's pretty lame. You can always fit seven parameters with seven. What's much cooler is in fact with only three parameters and quantum mechanics, you can predict about one hundred thousand numbers which have been measured about atoms like what kind of colors come out of different kind of atoms in different circumstances.

And what's generally happened over the over time in science is that as we've discovered more and more mathematical regularities, we've come up with more and more kinds of data compression, more and more ways of doing away with things we previously just had to put in my hand and calculating them from first principles. And what's so cool about? The mathematical universe hypothesis is simply the statement that all mathematical structures exist, it doesn't have any numbers in them at all. If you pick any one structure and you study it, there might be a lot of numbers or parameters that characterize that.

But it's not part of the theory, so the theory is super easy to state, and if it's true, then it means that we basically have to reframe the way we think about physics. We used to think about it as, oh, physics is all about measuring these numbers, which tell us something about reality, like the number three, why are the three dimensions of space and so on. Why is it that. There are eight planets in our solar system, gradually we realized that some of these parameters, like the number eight in our solar system, were not parameters, have told us about reality, but they were just part of our address.

And string theorists now suspect that even the chart, the one hundred thirty seven number that we talked about for electromagnetism might be like that, too. It might be different if you go to very, very different parts of space. So that too might be is part of our address. And maybe even space itself has nine. Maybe space itself even has nine dimensions and six of them are curled up to the tiniest scales and three of them are really big.

And some string theorists think that they go elsewhere. You might have not three, but a different number of dimensions. So even the three might just be part of our address. And if you continue this progression to its logical and ultimate conclusion, you get the mathematical universe hypothesis that says that every single number you ever measure just tells you because we know nothing about reality itself, but just something about your address, something about you, something about where you are.

Max, I have the intuition which may be completely off base, that any universe you could possibly imagine existing could be described by some math, which makes me confused about the prediction that you suggested, the prediction that would test the mathematical universe hypothesis, which is that if we someday get to the point where we can no longer explain our universe with math, then, you know, that's falsified your theory.

That's a really interesting point that you make that Julia. And in fact, this is a way in which what I'm saying differs from what some philosophers have said, like not the principle of fecundity, for example, where he says that everything that logically could exist does exist. If you say that everything that you can imagine exists, that's already pretty vague. And it doesn't seem like a very strong statement, almost an empty statement. True that things exist mathematically, though, it's actually very, very restrictive for things that exist mathematically.

It's so restrictive that mathematicians often prove complicated theorems just to show that something actually exists, which means that it's free from a contradiction. And the. If you take it more down to earth example, Plato, for example, was very fascinated by the question of looking at mathematical objects in three dimensions that are perfectly regular. He platonic solids. Before you've thought very much about this, you might think, oh. There are infinitely many of them, but actually there are only five.

That exist mathematically, there is you can make the tetrahedron out of three triangles and you can make the cube six squares and you can make the octahedron and the icosahedron and then you can make the dodecahedron out of 12 Pentagons and that's it. And that's very typical of mathematical structures in general. And that's why you can write a computer program that just spits out the mathematical structures that exist. It's really hard to find a mathematical structure that matches the random thing that we imagine.

And usually it's impossible. So if we get to the point where it seems like math can no longer explain our universe, that is actually that's actually possible. It's not just the case that, well, we should be using different math. Like I had sort of felt like maybe you were setting up a prediction that could never actually come true and thus far falsify the theory. But it would it could, in fact, be the case that a. I don't know.

The universe could just could not be described by math at a certain point. The it's probably better that I leave the critics of this formula. There are there countless theories. But but it's important to remember that. Even though many people think of math just as a bag of tricks for manipulating numbers or maybe as a sadistic form of torture invented by school teachers to make us feel bad, that's not how modern mathematicians think about it. They think about it in a very broad sense.

They think of a medical structure is just an abstract settlement of entities with relations between them. And the key thing is that these elements in the mathematical structure, they don't have any properties at all other than what's given by the relations between them. And, for example, five is not yellow, even though I'm a little bit of synesthesia that feels that way. But it has the really great minds think alike. And to think like about five.

Well, I think it came from having a set of refrigerator magnets when I was a kid that were of all the letters and numbers and they had various colors. So that I think I have pseudo synesthesia.

Maybe so. But in any case, the number five, it has the property of being the sum of two and three and so on. But the only kind of properties it has or how it's related to the other numbers doesn't have any intrinsic properties at all. And this is really key also. So since we have so much philosophical expertise on this call here because of the so-called infinite regress problem, because if you always the traditional thing to try to do is explain the properties of something in terms of the properties.

Of its constituents, so that might seem like you just doomed to, oh, it's turtles all the way down that you can, but actually. With the mathematical universe hypothesis, you get rescued, you can say, oh, let's look at this, this cat we talked about, it's made of molecules. The molecules are made of atoms. Atoms are made of protons and neutrons and electrons and protons and neutrons are made out of quarks, et cetera.

But ultimately, what are these when you get down to elementary particles that aren't made of anything further, what properties they have? They only have mathematical properties, numbers, as we talked about. And the numbers themselves have no properties at all intrinsically. They're just the relationships between the numbers that matter. And so we live then. So the solution to this problem is that we live in a relational reality where everything we perceive all the properties of a cat and all of our friends and everything comes ultimately not from the properties of what they're made out of, but only from the relations between things.

Well, so, again, a follow up on this issue of mathematical possibility. So, first of all, you mentioned No.6 principle of planted and that one of you actually is somewhat restrict. I mean, it sounds like it just says that anything one can imagine is real, but it actually says anything that is logically consistent is real. Right. Which means that actually the criteria I mean, depending on how you think about the relationship between logic and mathematics and there is quite a bit of debate there, it may amount to a very similar thing to what you're talking about.

Meaning that the laws of logic or and or the laws of mathematics may restrict the number of possible universes or structure out there.

Now, the question, however, is this in terms of of possible limitations and possible criticism of the theory, some of your critics are brought up, of course, the omnipresent, because it pops up everywhere I look these days, Gödel's incompleteness theorems.

Now, what did they have to do with your theory? And do they really actually suggest the sort of possible limitation or a possible problem for your theory? And before you even get there, very briefly, what the hell are Gödel's incompleteness theorems?

Fascinating questions. So he threw a real monkey wrench into the foundations of mathematics. But about a century ago, Hilbert had envisioned that one day you would be able to prove, he said, that mathematical things only exist if they're free from contradiction. And his vision was that you should be able to prove that certain mathematical structures like no theory, was free from contradiction.

And then girls said it impossible if there is a proof. And we're in the painful situation now where. Even the kind of math we learn in school over the years, we cannot actually prove that there is no proof that zero equals one. So it's conceivable possibility that seems problematic would sort of collapse. Now, what do I say about this? I talk a lot about this in our mathematical universe, the book, and I have actually a very radical view on this because I'm a physicist.

So all of the issues with journalists incompleteness theory come from. Infinity, you only have these problems when you deal with mathematical structures, with infinitely many things in them, and it's also it's also interesting to realize that many of the biggest problems we have in physics today also come from infinity, not from the same thing. And we have. Long been plagued by various kinds of infinities like singularities inside of black holes and what to make of them. And if this inflation theory we talked about goes on forever, then you get another terrible kind of infinite problems with infinitely many copies of you.

And it turns out to be a seemingly hopeless to predict anything and actually an infinity skeptic. Why? Because in physics, we have never actually seen anything infinite in nature, neither anything infinitely big or anything infinitely small like the continuum. Now, when I teach physics at MIT. I'm always implicitly assuming the infinite, even to this define the distance between two points in space, I have to write down a real number like seven point eight five five seven two five seven four four with infinitely many decimals.

Right. I have to give an infinite amount of information just to specify that one little silly distance. Yet we've never measured anything in physics to better than 17 decimal places and we've never seen anything bigger than our universe, which has only a tenth the power. Eighty nine particles in it. So everything is actually very finite. And my hunch is that we simply use the infinite in our theories and in our mathematics because it's super convenient. If you look at space, if you drink a glass of water, it looks like a wonderfully continuous fluid.

So you can define the density of the water at infinitely many different points, even though you know that that's actually wrong because the water is made of atoms. Right. But it's much simpler. To make the approximation that it's infinitely smooth, if you do that, you can write down and have your Stokes equations describe everything about how the water moves, everything about how the air moves. You can use that to make the weather forecast for tomorrow predicting tornadoes.

You can use it for explaining why you hear me and how to optimize airplanes and stuff like it is useful. That's why we love it. But it's important not to confuse convenience with truth. So my guess is that there is nothing truly infinite. And this is actually something which a lot of the early, great mathematicians like Gauss and Connock are worried about, too. More recently, we've been so seduced by the Infinity concept that most people don't question it anymore.

And if you banish the infinite, then limit yourself to finite mathematical structures, the kind of things that computers can deal with. Then Geritol goes out the window and you don't have any problems. We go. We know also that finite math is perfectly capable of describing all the physics we've discovered so far for the simple reason that we can make our physics calculations and simulations on computers, which can only store a finite amount of information. Right. Right.

But so let me let me follow up very quickly on this point, because I think it's interesting and I've heard before of sort of infinity sceptics, but does that infinity skepticism sort of extend to also inherently a purely however you want to define mathematical structures like, for instance, do you actually think that there is the largest number of them all or is there an infinite number of numbers? Because if the answer is no, there is no no largest number at all, then aren't you admitted that there is in fact something that is infinite just because we can't measure that?

That may be just our limitations as in terms of exploiting the universe physically. But if you're actually arguing that mathematical structures are real and it turns out that there is there are there is an infinity of mathematical structures of a certain kind, doesn't that create a problem where the data is? Understand your point?

I think as long as you banish mathematical structures that have infinitely many elements in them, they will all be perfectly rigorously defined and consistent. And that's all I think we need for this. You know, I have the feeling that even if we humans get confused when you try to calculate stuff and sometimes get Infinity's for our answers, our universe itself isn't confused at all. It knows exactly what to do to figure out what to do next. And it's perfectly defined.

So I don't. But what about I really don't like the idea that our universe is in some sense undefined. And it won't be if if if it's a finite mathematical universe. But this is a stronger hypothesis. I call it a finite universe hypothesis than the more general one. And the best way to study this, frankly, is, I think, to do some more for us physicists to question infinitely more and see if we can find infinite, finite alternatives to all our seductively elegant, infinite theories, which is which is hard work, but very, very, very fun.

The other thing, the only thing I said which is infinite. Yeah. Is what Einstein once said, that there are only two things that might be infinite. Our universe and human stupidity, and he's not so sure about the universe. So I'm going the challenge. I think our universe is there's nothing really infinite about it. And second, however, humans can be pretty dumb. And and this is another thing I talked a lot about in the book.

And in fact, the whole end of it is about this. What does this mean for us if everything is mathematical? On one hand, there's all the good news. We already talked about that it means there won't be any roadblocks and we can potentially understand it all. But on the other hand, if we think about our future, I can't help as a scientist and as a cosmologist to feel kind of appalled by how how stupidly we manage our planet.

So we are extremely lucky that we live on this spinning little ball in space at a nice, convenient temperature with a convenience store nearby and resources that could, in principle, let us live here for a billion years or more. And they've even spread life off the planet and into vastly larger parts of our universe. But at the same time, we're we're constantly gambling and taking enormous risks entirely wiping ourselves out, putting a very, very small fraction of our resources into actually trying to safeguard our future.

So the name of this podcast is, of course, rationally speaking. And I think if we're going to speak rationally, we have to also when we look at the big picture, ask ourselves a. Do we really want to spend such a tiny fraction of our resources thinking about our future survival as we do, if you go ask just random people in a poll here in the Boston subway? I think people would typically be able to name more. Random facts about celebrities, then they would be able to name.

Events that already came close to annihilating the human race, if you ask, oh, I think that's a sure bet. Yeah, and is that the way we really want it? Is it really good to have sort of have our heads in the sand and just keep hoping for the best? We we tend to be very focused on what's going to happen next week and maybe in the next election cycle. But from a cosmic perspective, you know, we've been in this universe has been around for thirteen point eight billion years.

We have billions of years at our disposal. And yet. We aren't small and insignificant. I feel I feel that the I used to feel more and more insignificant the more I learned about the vastness of it all, but gradually. I've come to change my mind completely and feel that it's quite likely that we are actually the only life and our whole universe advanced enough to have telescopes and even be able to see all these awesome galaxies out there. So if you ask them why are they beautiful, these galaxies, that it's because of you.

If nobody were looking, they would just be a giant waste of space. So I don't think that we should. That is a universe that gives meaning to us, but we are giving meaning to our universe and that makes us a very, very important and more and more urgently this time in which we're living, even though if I take my vitamins and do my workouts and stuff, maybe I can only get one hundred years. It feels like nothing compared to thirteen point eight billion.

But we this is the first century when we really had the power to annihilate ourselves. Since the Big Bang and and this is I think it's in our lifetime that it's going to be decided basically whether we whether we get our act together and do something wonderful in the future or or wipe out. So I hope everybody listens. This joins in and helps make a difference. So I couldn't agree more with that general point, you're definitely preaching to the choir on rationally speaking, but I just.

Even though we're basically out of time, I couldn't help but ask you about a particular kind of test that you've proposed in the past, not to test the mathematical universe hypothesis, but to test, I guess, the many worlds interpretation of quantum physics, which involves essentially playing Russian roulette. Would you mind explaining this briefly? You did a such good, such a good job being brief with Girls and completeness theorem. So I'm hoping you can explain this one briefly to.

So we're talking now about what I like, what I call a Level three multiverse in the book, which is another kind of multiverse that is predicted by the simplest, the mathematical form of quantum mechanics and the. People love arguing about whether this is all nonsense or whether it's whether it's all real. I talk in the book a lot about the so-called quantum suicide experiment that you're exactly referring to here, where you you put yourself into a quantum superposition of being dead or alive.

And then if those parallel universes exist, you should find that you sort of feel immortal. But I'm actually, as I say in the book, changed my mind about this.

I actually think it doesn't work out just because because I don't believe in the infinite and it really, really requires and that things are infinitely subdivided for this to happen. But there's a much easier way to test whether these parallel universes exist, which isn't even very dangerous for your own health, which is just to try to build really, really big quantum computers. There's a huge effort to try to do this now, of course, because if you can build one.

You cannot only have. Your credit card, by breaking the famous prime number based RSA code that they would take, even if you might be able to hack it in one second on a quantum computer, even if it would take longer than the age of the universe to do on a normal computer.

And and the idea behind this is if this works. The reason that the quantum computer can do it is because it's in a way, the ultimate parallel computer. It's taking advantage of doing parallel processing and all these parallel universes and then bringing it all together and giving you an answer very quickly. So if you can do this and it really works, then I think going can be really hard to deny the reality of those things. After all, if something helps you and gives you the answer would be kind of rude and arrogant to say it doesn't exist.

Well, that does sound less dangerous, albeit less sexy than the quantum suicide test of of the multiple universe hypothesis. But so I look forward to reading your book, which technically hasn't come out yet as we're recording this, but we'll have hit the shelves by the time this episode is out. And I encourage all of our listeners to check it out as well. It's already been highly recommended by more prestigious physicists than I can count. But unfortunately, we are all out of time for this section of the podcast.

So I'm going to wrap this up now and move on to the rationally speaking, PEX. Welcome back. Every episode, we pick a suggestion for our listeners that has tickled our irrational fancy. This time we ask our guest, Max Tegmark, for his suggestion. Max. So in those parallel universes where I'm more rude and obnoxious, I would of course recommend my first ever book or mathematical universe. But in this universe, I will instead recommend, I think, the book that made the biggest difference in my own life, which is the book that made me change my mind and switch from economics into into physics.

It's actually not a physics book. It's called Surely You're Joking, Mr. Feynman. And it's a book which, when I read it, had all these fascinating stories about this this great character, how to pick locks and and various other adventures. But I was just so fascinated by reading between the lines that he loved physics, which perplexed me because physics used to be my most boring subject in high school. And I'm like, what on earth have I missed?

It's like if I'm walking down the street and I see this absolutely gorgeous woman walking arm in arm with some guy who looks like a total loser, I would think to myself, I'm missing something.

This guy must have some hidden qualities.

So that happens to me very often, actually.

So I couldn't resist reading Feynman's own physics books after that, that he had written an. It was love at first sight. Then the rest is history. Great. Well, we will put up a link on our site to surely you're joking, Mr. Feynman, which surely will be right at the center of all the Venn diagram of the people who listen to our show. So if they haven't read it yet, I'm sure they'll love it. And we'll also link to our mathematical universe, which I said I as I said, I can highly recommend just based on knowing Max and hearing the recommendations of of other physicists.

Max, it's been a pleasure having you on the show.

Thank you so much for joining us.

Yes. Thank you for coming online. Thank you. Grazie, Miller. Well, this concludes another episode of Rationally Speaking. Join us next time for more explorations on the borderlands between reason and nonsense. The rationally speaking podcast is presented by New York City skeptics for program notes, links, and to get involved in an online conversation about this and other episodes, please visit rationally speaking podcast Dog. This podcast is produced by Benny Pollack and recorded in the heart of Greenwich Village, New York.

Our theme, Truth by Todd Rundgren, is used by permission. Thank you for listening.