Part 2 of 2! What are the modern constants of nature? Is the universe fine-tuned for life? Does the multiverse or string theory explain the origins of the constants? I discuss these questions and more in today’s Ask a Spaceman!

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EPISODE TRANSCRIPTION (AUTO GENERATED)

Welcome back everyone to part two of a two part series on the constants of nature. Why are there just two parts? Why not three? No no why not four? Why not just one?

Well, we'll just have to add that number to the list of constants that we can't explain. Last time, I talked about how physics works and how we create models to explain the behavior of objects in the world like the simple example of me throwing a ball to you. In these models, certain numbers appear that we can't explain. Or another way of saying that, sometimes numbers appear that don't come from the laws of physics that must be measured in the real world and then inserted into the equations to get the right predictions. Sometimes, those numbers are bland and just capture a bunch of details that we don't wanna calculate again and again.

But sometimes, those numbers are constant. And they crop up again and again and again in model after model after model. These numbers, the second category, are what are known as fundamental constants. They strike us as carrying significance, much like the Pythagorean Theorem carried significance to the, well, to the Pythagoreans. So, what are those numbers?

Of course, physicist debate about which of the constants are the important ones because physicist debate everything. Some list have 19 numbers, some have more, some have fewer, some tried to build categories of numbers, like, there are the really, really fundamental constants, the less fundamental but still important constants, and then others, you know some say that the only real constants are the ones that don't have any units, the ones that are just bare numbers, like the fine structure constant, like the ratio of the electron to proton mass. Because, you know, if you change your measurement system, you change the value of, say, the speed of light, others disagree about that in general. And this is my very own Paul Sutter classification scheme. There are a few groupings of numbers that seem to be important.

Some of them have units, some of them don't. Some of them maybe considered derived in the sense that you can maybe combine other constants to form them. But honestly, to me, the precise number of constants and the categorization scheme of trying to rank them is, to me, it's just more like Eddington style numerology or or Pythagorean style cultism here. To me, it's losing the force for the trees. There are constants that appear in nature.

The number of constants is going to change with time as our theories evolve and as we gain new knowledge. Okay. The actual listing of the constants isn't so important. What is important is the acknowledgement of what the constants represent. Because what they represent are gaps in our knowledge.

They are places in our very complicated, very sophisticated models that we must fill in from raw measurement. These are places that we cannot derive or explain purely through our theories or laws of physics. And to me, that is the essence of a truly fundamental concept. Who cares if it has units or not? Who cares whether there are four in this category or or five in the other?

You know, that doesn't matter. To me, what matters is this setting and I've categorized them into four different chunks. And to me, these are the four areas of our universe that we cannot explain through physics. And so, to make progress, the thing is, well, if you wanna poke at just one of these, you can push in one of these directions and try to make progress. Because this is not like the stiffness or bounciness of a basketball here.

These are numbers that we don't know where they come from. We can only measure them and then stick them into our equations to get the right answers. But we don't know. One of those areas, one of the categories is the strengths of the forces. Newton's g.

That's the strength of gravity. Why is gravity this strong? I don't know. It just is. The fine structure constant tells us how strong the electromagnetic force is.

Why does it have that value? I don't know. The weak and strong nuclear forces? There are many many numbers that we need to describe how those forces work. Why?

Uh-uh. I don't know. Why is the strong nuclear force the strongest force? I don't know. Why does it have that strength?

Why isn't it in half or twice that? I don't know. So one category is the strength of the forces. Another category is the masses of the fundamental particles. An electron is yay heavy.

A neutrino is lighter than that. Some quarks are really light. Some quarks are really heavy. Gluon weighs this much. Why?

We don't know. There's nothing in our theory of physics to tell us why these particles have the masses that they do. There's another category that does not flow from any knowledge of physics and that's properties of the quantum. Like Planck's constant. Planck's constant describes the scale at which quantum mechanics takes over.

Why does it have the value that it does? I don't know. There's properties of the Higgs field. Why does the Higgs have the interaction strengths that it does? We don't know.

There are various properties of the vacuum structure of space time folded into quantum field theory. Why does it have these properties? We don't know. Go ahead and put in, the strength of dark energy here, that cosmological constant. That appears to be a quantum thing manifesting a very cosmological scales.

That's kinda weird in and of itself. Why? Why those values? Why does the quantum world have these properties instead of other properties? We don't know.

So we can't explain the strengths of the forces. We can't explain the rest masses of the particles. We can't explain the boundaries and properties of the quantum world. And then the last category I call structure of the universe. Just basic facts about the universe.

There are some familiar friends in this category like the speed of light. Speed of light is the speed of causality. It's the connection between space and time. We don't know why the speed of light is the way it is. Why it's not half its speed or twice its speed.

I'm also going to add in here some numbers that you don't often see in tables of fundamental physical constants. Like, the number of forces. There are four forces of nature. Why four? Why not two?

Why not eight? Why not three and a half? I don't know what that would mean, but why not? Why do we have the number of particles that we do? We don't know.

There are three generations of particles. Every particle has two other siblings. Like the electron has the muon and the tau. Same properties except higher mass. Why three generations?

We don't know. So four and three seem important. Pi seems important. Pi tells us how circles are drawn. Heck.

Let's throw in the Pythagorean Theorem, the fact that it's a squared plus b squared equals c squared. Why squared? Why not cubed? Why not? This seems to be telling us about the structure of flat space time.

And, yeah. The universe can be curved and all that, but when it's flat, in the absence of matter and energy, space time is flat and it has these properties. Where triangles look like this. Where right triangles have this kind of proportion. Where pi works.

Why why not others? Why not other relationships? Now, here's another number for the dimensions in the universe. Space time. Three of space, one of time.

Why four? Why three of space? Why just one of time? Negative one is an important number. It's the relation between time and space.

There's a Pythagorean like relationship between space and time, but instead of a squared plus b squared, it's space squared minus time squared. That's weird, But that's how you get special relativity to work. Four categories. The to me, the details don't really matter. But in general, we do not understand why the forces have the strength they do.

We do not understand why the particles have the masses that they do. We do not understand why quantum mechanics is doing its all weird funky quantum thing. And we don't know why the universe has the fundamental structure in relations that it does. However you divide it up, whatever categorization scheme you use, these numbers share some things in common. Besides the fact that they're important and fundamental, they all contribute to Patreon.

That's right. Fundamental Constance contribute to patreon.com/pmsutter. Why don't you pause the episode right now? Sign up to donate. I truly do appreciate it.

And, come on back. No. The the actual thing is that they're unexplained. They cannot be derived from some deeper theory. They have no origin.

They the electron weighs this much because the electron doesn't weigh anything else. The electromagnetic force is this strong because it has no other strength. The universe has four dimensions because it it has four dimensions. This is totally unlike the vast majority of constants that appear in our models in physics. This is not like the acceleration near the earth surface or the bounciness of a basketball.

Those are convenience numbers. So we don't have to grind through the the arduous calculations every single time. We know where those constants come from. But the speed of light, the mass of the electron, Planck's constant, the number of dimensions of the universe, we have no idea. In our quest to understand where these numbers might come from, we can ask another question which is are they really constant?

Can they change? Because if we're able to answer that question, if the constants aren't so constant, then that can help us understand where they came from. I gave an example the last time about throwing a ball. And if I only cared about acceleration due to gravity and had no idea what the force of gravity was, I just measured that acceleration, But then I discovered that the acceleration changes as I move around the earth or change elevation. That would tell me that, oh, this number that I'm plugging into my equations isn't so fundamental.

It's not so constant. It's not so important. There's a deeper theory here. The deeper theory here being Newton's universal law of gravity. And then Einstein's relativity.

By finding out if the constants aren't so constant, we might be able to find something deeper or more fundamental about the universe. Imagine if we found that, I don't know, the mass of the electron can change with time. Then that would tell us that what we call the mass of that particle, what appears to be constant and fundamental is nothing but. Instead, it's just a reflection of our ignorance of deeper physics. Imagine we do find that one of the constants changes with time or is different in different parts of the universe.

We would have a a a hawk, a pathway, a route to uncovering what that new physics is. This is why, as an aside, in my own field of cosmology, we're so fascinated by potential changes in dark energy, in the evolution of the cosmological constant. Because if it's not so constant, we could build a theory around that. We could say, This isn't so fundamental. I can explain where this number comes from.

That deserves its own episode, so so feel free to ask. Anyway, so are the constants of nature, this this list that we make, categorization forces, strength of the forces, masses of the particles, properties of the quantum, basic structure of space time, are they really constant through all of space and time? Well, seems that way. We can't say for 100% totally case closure. We can't do that because there are always limits, always uncertainties, always error bars to our measurements.

But every test we've ever concocted always comes to the same conclusion. Testing the constants isn't easy. Checking to see that they're actually constant is not easy. So measuring the any potential variation in the constants, some non constant features of the constant, involves some of the most high powered and clever experiments we've ever developed. It takes volume.

Absolute volumes of data. Streams of data. Rivers. Oceans of information. At this point, in our exploration of the constants of nature, we're looking at parts per billion shifts in their values.

And there are two general approaches that we take to getting the volumes of data that we need. One is getting hyper precise on measuring something that changes often, like atomic energy transition. So atomic clocks are really useful laboratories. Where you look at, say, a cesium atom, and it and it's vibrating or or the electrons are shifting energy levels constantly. And it's happening, I don't know, like, a trillion times a second, if not more.

And if you just stare at that one system a lot, it's providing a lot of data. And if you watch it for months or years, you have an enormous volume of data on how that system is behaving, and you're staring at it, seeing if any of the constants of nature associated with the models that we use to describe that are changing. You can get away with less precision if you let the universe do the work for you. Like, if you study something from an extreme distance, like a quasar or the cosmic microwave background, something that was generated in the early universe, and then it's had billions of years to reach us, then we can see if anything has changed in those billions of years. If the physics back then was different than the physics now.

So in you can either get hyper precise and see if physics is changing, constants are changing before our very eyes, or you can go out in the universe and say, hey, ten billion years ago, was were the constants of nature any different? And to investigate these changes, we use the models themselves. Yeah. We use models. We take our laws of physics.

We incorporate the constants of nature. The things we can't derive from the models themselves. The things we have to measure and then get into our equations to see if they're right. What we do is relax the assumption that the constants are constant. Like, if we say, okay, Newton's gravitational constant, let's say it it it changes with time.

Let's say it's not constant. Maybe it goes up with time. Maybe it goes down with time. Then we can use our models to see what the follow on effects might be. So if we look at something from the very early universe like the cosmic microwave background or we look at quasars and we say, okay, maybe back then.

What if back then gravity was weaker? Then we can predict. We can fold that assumption into our models or this new assumption into our models and say, okay, if gravity was weaker back then, then quasars should look like this. Then the cosmic microwave background should look like that. And if gravity was stronger way back then, then the the CMB should look like that, and quasars should look like this.

And then we compare to what we actually see in every single time. Everything we measure about the cosmic microwave background, about quasars, about cesium atoms, about a million test we've ever performed. When we compare version a, which is the constants are always constant, constant, to version b, which is the constants aren't so constant after all. Every single time, the story lines up with version a. The constants are just constant.

The constants sure do act like constants. The speed of light, the strength of gravity, the fine structure constant, the electron mass, all of them. We're talking about we have not seen any variations to one part in a billion per year, which is pretty dang constant. Again, it's not ruled out. We can never rule it out.

We can only crank down our precision. The constants of nature may vary with time or throughout space at some tiny subtle level that we can never be able to measure. So we can't ever prove that the constants are constant. We can only say that they are with a high degree of confidence. And for now, we have to act like the constants are constant and grapple with it because the constants being constant opens up two very difficult questions.

Where did they come from? And why do they have the values that they do? I understand that the basketball's stiffness or bounciness, it has that value because of the way the basketball is made of, what it's made of, its materials, the air pressure inside of it. I know that's what's causing its certain value of ability to bounce off the floor. I know that.

That doesn't keep me up at night. I'm also not a basketball player, so, you know, there's that. But the speed of light, the electron mass, Planck's constant. Why do these have the values that they do? We don't know.

And this creates a really sticky, really nasty, really ugly problem for us. Because it looks like the constants of nature are fine tuned. As in, if they had any other value, we'd be dead. Actually less than dead which is probably worse, nonexistent, impossible to be here. Check this out.

Let's say we change, I don't know, the electron mass. Just a tiny bit. A few percent. Okay. Electrons are now, 2% heavier.

No big deal. Right? Well, wrong. This changes atomic energy transition levels. It changes how light is emitted and absorbed.

It changes nuclear fusion rates. In a universe with higher electron mass, stars stop working. In fact, stars don't even form. Nuclear fusion never takes off. The pressures you need never never work.

No stars, no planets, no planets, no life, no life, no us. Change the strength of gravity, big bang doesn't even get started. Change the dimensions of the universe? Light can't propagate. Change anything.

You make quantum effects, macroscopic? Good luck with that. Change anything. Any of the constants, even a teensy bit and it all just goes poof. The history of the universe is completely different.

Let alone chemistry or biology. It's all just gone. We're gone. There's no us in a universe with different constants. That's a real whopper of a realization here.

It feels like we're living on the knife's edge. And if any of these numbers were to change, then our universe would disappear in an instant. That's a rather uncomfortable feeling so I won't blame you if you need to actually sleep tonight and you just pause the episode right here. There are some potential answers, of course, none of which are satisfying. The first response is called the anthropic argument.

The universe is the way it is because if it wasn't the way it is, we wouldn't be here to observe it. Why is the speed of light this way? Oh, because if it had any other value, then consciousness could could not arise, and we would not be able to to measure a speed of light. Why is the strength of gravity the strength of gravity? Same reason.

Why are there four dimensions, instead of five or six? Oh, same reason because consciousness can arise. And so we wouldn't be able to measure. So the only way we can measure the universe is because this universe is compatible with us observing it. Okay.

Maybe that's like eating a whole row of cookies at once. It feels good while you're doing it, but not so great after. It's a strong statement. It's a bold statement. Audacious statement.

Then an hour later, you start to question your life choices. Like, really that's it? That's our answer? That this is the end result of our quest in fundamental physics to get deeper into the inner workings of nature? At some point we just say, well it's the way it is because it's the way it is And if it weren't, we wouldn't be here.

So, let's grab lunch. That doesn't feel right. And I know we can't base theories of physics on vibes. I know. But also, we kinda can because we're making up the rules as we go.

And we've and if we decide it doesn't feel right, that's that's fine. It's not a super solid argument because it doesn't answer anything. It just restates it in more complicated language. Another possibility is that there's more than one universe. That we live in a multiverse with each universe sampling different values of the constants.

There are a few extremely hypothetical ideas in physics that can lead to the multiverse. One is through the concept of the eternal inflation where the very early universe never ended, its period of rapid expansion, and the different portions of the overall multiverse pinched off, so to speak, to create their own bubble universes. Another path to the multiverse comes from string theory, where extra spatial dimensions can twist up on themselves in, like, 10 to five 10 to the 500 different ways or something ridiculous like that. Each possible arrangement leads to a new values of the physical constants and even entirely new laws of physics. The range of possible combinations is known as the landscape with our universe consisting of one point in that landscape, one particular combination.

In these multiverse inspired ideas, there are multitude of universes out there that don't support light. But this one does. Like, you can throw together any old combination of flour and butter and sugar and baking soda and salt, you're not necessarily gonna get a decent cookie out of it. It's only by certain combinations do you get something edible. And so, you can throw all the combinations of constants out there against the wall in this multiverse.

They all get different realizations, but then, you know, most of them don't support life and this one does. So here we are. At the end of the day, it's still the anthropic argument. Still saying the constants are the way they are because here we are to see them. But at least it explains how the different values of the constants can be realized.

The anthropic argument doesn't even do that. It just says it just stops. It says that, well, they they're the way they are because they're the way they are. Otherwise, we wouldn't be able to see them. But it doesn't say, oh, what what what made it?

Maybe I'm a little biased towards against the anthropic argument. You feel free to believe it if you want. It just it it drives me up a wall. I don't like it. That's just me.

The multiverse ideas, okay. They're maybe a little more satisfying but not by much because there are issues with both approaches to the multiverse either through eternal inflation or the landscape. They're both hypothetical and not supported by any available evidence. So that's kind of a bummer. We don't know how regular inflation works, whether eternal inflation is even possible.

String theories can't even make the connection between a particular arrangement of extra dimensions and the physics that it generates, meaning that we can't even make testable predictions in string theory. It's not that string theory is an untested theory of physics, as in it's currently an untestable theory of physics, which is not that great as a physical theory as things go. What's more eternal inflation in string theory contain constants of their own that are not explored by different iterations of the multiverse. For example, string theory assumes a certain number of extra dimensions, a number that is not predicted by the theory itself. Eternal inflation requires any number of extra unknown parameters to make it work.

And so, yeah. Well, inflation itself or eternal inflation can generate different universes that give rise to different, like, speeds of light over here and electron masses over there. It it's still locked in to the process of inflation itself, which carries its own parameters. No matter what, you can't stop inflation or or you must have inflation existing and it must proceed in a certain way for internal inflation to even work. So it both string theory and eternal inflation come with their own constants that we cannot explain.

So these don't seem like satisfying conclusions. No matter what, you still end up with some numbers that you can't explain from pure theory. Maybe we make some progress. Okay. I'll give you that.

Maybe we figure out the multiverse and we're able to make some progress, but we're going to get hit another wall. Maybe, no matter what, values of the constants there are that life will always arise. Yeah. Sure. You know, if you change gravity or the electron mass or whatever, then, certainly our kind of life and our kind of consciousness doesn't arise.

But maybe there's some sort of life. Maybe it's possible to build a universe with different constants that end up with different kinds of life, different kinds of intelligence, and they end up asking the same kind of questions because they can't as we are, because they can't possibly fathom our kind of universe. They're like, oh, we ran the numbers and there's this thing that we discovered that we're calling nuclear fusion. Could you imagine how destructive that would be to life in a universe? There'd be electromagnetic radiation everywhere flooding things.

Oh my god. Like, maybe they're having these kinds of conversations. Maybe it doesn't matter. Maybe you can throw any random constant against the wall, whether it's generated in the multiverse or not. Maybe you can just have any combination of constants and you end up with consciousness through some process that we can't possibly understand And that consciousness ends up asking, why?

Man, maybe their speed of light is like a tenth of our speed of light. And they're like, man, could you imagine if the speed of light was faster than ours? Life would be impossible. This is this is speculation. I'm making things up here.

We don't understand the nature of our own consciousness in our own universe. So, you know, it's a bit of a stretch to talk about other consciousnesses and other kinds of universes. I get that. But that's where we are when it comes to the fundamental constants. We we don't have a lot to hang on here.

Some people argue that this is a fool's errand. That will never be able to truly uncover all the constants of nature, that there are limitations to physics. That we'll never be able to explain certain aspects of our universe from pure theory alone, that they'll just be that they'll just exist. That's I mean, there's a point there because even if you imagine, like a universe from nothing, like real nothing, not just vacuum, but like actual nothing in the universe springing into existence in in with with a certain form and with certain properties, even say like string theory. Let's say string theory is right.

And it's able to explain why the speed of light is the speed of light. It's able to explain why Planck's constant is Planck's constant. Let's say we develop some ultimate theory that is able to explain where all the constants of nature come from and what their origins are, guess what we can explain? Why there's a theory of physics in the first place? Let's say we have an ultimate string theory that is able to explain everything in the universe it can't explain itself.

It can't explain why there is a law of physics when there didn't have to be. And maybe the constants are just representations of that basic fact. That no theory of the universe will be able to explain the reality of existence, of why there's something rather than nothing. And that, yeah, in the future, we can push forward in all four of these categories. We might be able to figure out why the strength of gravity is the strength of gravity.

We might be able to explain why there are four dimensions instead of others, but there will always be some set of numbers that we can't explain. But I like to think that we could figure stuff out even if it's really far away. I mean, this is the, you know, not just the dream of Pythagoras here. This is the dream of Aristotle and Galileo. Like, we've been hacking at this problem for thousands of years.

Don't cut us off now. Don't say we can't do that. I don't like living in a limited future. I like my futures to be full of boundless opportunities. So that doesn't quite sit, right?

You know, of course, there's the opportunity here for divine intervention. That there is some supernatural cause even in its most limited and strictest sense. Like, there is some cause outside of nature that is supernatural to explain why the universe is the way it is, why the constants have the values that they do. That's not exactly physics, which is the whole point of the program of physics. But I'm not gonna hold you back if you want to believe that because honestly, all of our other ideas are, let me see here.

Yeah. Absolutely terrible. So, you know, go for it. Nothing sits right. We don't know why the constants are the way they are.

We don't know why some numbers appear to be so fundamental and so critical and so important and cut across so many different areas of physics and crop up again and again and again without explanation with the values that we do. We have to go out into the universe and measure them and stick them into our models to get the right answer at the end of the day. We don't know if they're telling us something deeper about physics. We don't know if pushing forward in any of these categories of ignorance that I outlined, whether it's the strength of the forces, the masses of the particles, the nature of the quantum, or the structure of space and time itself. We don't know if pushing forward in any of those four directions will lead anywhere useful, will yield any useful fruit.

We don't know if there's a deeper level of physics out there. We don't know if we can explain these constants. So here we are. Just like Pythagoras and his study group slash cult twenty five hundred years ago, there are certain special numbers that appear to rule the universe, and we're not sure why. Maybe we should start worshiping them after all.

Thank you for all the wonderful questions that led to today's episode. Thank you to Chris d, Phil b, Kevin o, Michael c, David m, at h l u boketa, Anthony c, Andres t, Jonty, Renee s, and Alan e. And thank you, of course, for all of your contributions to Patreon. That's patreon.com/pmsutter. I'd like to thank my top contributors this month.

They're Justin g, Chris l, Alberto m, Duncan m, Corey d, Michael p, Nyla, Sam r, John s, Joshua, Scott m, Rob h, Scott m, Louis m, John w, Alexis Gilbert m, Rob w, Jessica m, Jules r, Jim l, David s, Scott r, Heather, Mike s, Pete h, Steve s, Wattwatbird, Lisa r Koozie, Kevin b, Michael b, Eileen g, Dante, Steven w, Brian O, and Michael j. Please keep those reviews coming. That really helps the show visibility, but nothing is more important than more questions. Please keep sending them along, and I will see you next time for more complete knowledge of time and space.

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