Sometimes physics can make you feel a little insignificant.

You know, the Earth isn't the center of the universe.

It's just one of many tiny rocks orbiting countless suns and zillions of galaxies.

And the universe has existed for billions of years before we came along, happily doing its thing without us.

But sometimes physics can also make us feel quite special.

When we look at the laws of nature and the values of its constants, life seems to depend very strongly on these little details.

A tiny tweak here or a change there in life as we know it would be impossible.

Stephen Hawkings said, quote the laws of science as we know them at present contained many fundamental numbers, like the size of the electric charge of the electron, or the ratio of the masses of the proton and the electron.

The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life.

End quote?

Is Hawking right?

Can it physics tell us if we're special?

Can it reveal if the universe seems to have been set up so that life can exist?

Welcome to Daniel and Kelly's extraordinarily important universe.

Hello.

I'm Kelly Winer Smith.

I study parasites and space, and I'm so glad that the universe is fine tuned for life, including parasitically.

Hi, I'm Daniel.

I'm a particle physicist.

I want to unravel the nature of the universe so we know who to blame for, including parasites.

Again, you know, we should blame someone for human and livestock and pet parasites.

If I could selectively remove those, I would, right, yeah.

Right, mosquitoes?

Whose idea was that?

A bad idea?

Whoever's idea, it's a bad one.

I got some notes on the universe.

Yeah, I need to figure out how to give those notes too.

So here's my question for you.

So we're talking about life in the universe, and often when you see depictions of aliens in movies or like comics or whatever, they have tentacles.

Daniel, do you think aliens are likely to have tentacles?

I wonder what the origin of that is.

Wow, Yeah, it must be some early science fiction depiction attempting to describe like life differently.

I mean, one thing I love in science fiction is you can see people doing this thing.

They are trying they're aware that life should be different on other planets.

We shouldn't just expect humans everywhere, and they're adding little tweaks like Starchek is the most hilarious version of this, right, They're like, how about humans but wrinkly foreheads?

Or humans but pointy ears?

You know.

It's like the smallest nudge in that direction.

It's pretty hilarious.

But the idea is right, you know, And so I bet tentacles are just another move in that direction.

Do I expect life to have tentacles on other planets?

Wow, there's not a less qualified person to answer that question.

I mean, I don't know anyone else who thinks about aliens as much as you do, Daniel, So I'm sure there's some less qualified that's pro Jude.

Well, you know, there's a whole chapter in my new book Do Aliens Speak Physics available now at Aliens Speak Physics dot Com, where we talk about how aliens might perceive the universe, what they might see, how they might explore it, how they might sense the universe, and if that might lead them to learn different things about the universe and think about it differently.

I don't think it matters so much if they're using tentacles or fingers or weird slimy protrubances.

But I do think it's interesting how they might see the universe and sense it and think about it differently.

Well, but like they're going to need a way to pick up their iPhones to watch cat videos.

Surely that's universal, you know, I.

Think there was a lot lot of time on Earth where life survived without cat videos.

Kelly, what, Yeah, it's possible.

I know, seems inconceivable.

If I, you know, try to work my way back through the haze of time, It's possible.

I didn't have an iPhone at some point.

So today we're talking about whether or not the universe is fine tuned for life with or without cat videos and.

So, and this is a really fun topic because it touches on physics.

Of course, it forces us to think about the structure of the universe, how is it organized?

But then my favorite bit, it asks us to wonder what that means?

All right, what does it tell us about the nature of the universe.

So today we're going to be walking a fine line between physics and philosophy, not just the ideas but their consequences.

Oh amazing, all right, So at physics conferences.

Do you all get philosophical or are you talking about like how to fix the particle collider?

No?

No, no, Philosophy is a bad word of physics conferences.

No.

No.

Physicists are not interested in these questions, and a lot of them really look down there, knows that anybody who is oh what a bum I mean.

Fiman, for example, said that physicists need philosophers as much as like birds need ornithologists.

What yeah, well someone's got to study the birds.

I do see the point.

I mean, it's true that philosophy is not the central concern of psists, like let's try to figure out how the universe works, but which questions are interesting definitely comes from philosophy.

Why these questions are interesting, what their answers mean, That's all philosophy.

And the reason the whole field is fascinating, in my opinion, is because the philosophical implications.

Figuring out what the universe has made out of tells you how it works at the most basic level, reveals the true nature of reality.

That's all interesting because of philosophy.

And I think physicists are all doing philosophy, they just don't realize it.

Like a lot of them hold very strong philosophical opinions, like, yes, these particles are real even if we weren't looking at them.

It feels like a very naturalist, scientific view of the universe.

But it's also a strong philosophical opinion about what truth means that goes well beyond science.

So yeah, I think the physics community should be more open to philosophy.

You gave a much deeper answer that I was expecting.

I just wanted to say, these things are really fun to think about and to talk about.

But yes, I agree with all the stuff that you just said.

Also, you accidentally accessed a Daniel rant, so.

Well you kept it concise.

I'm impressed.

My Kelly rants can go on for hours.

But all right, all right, Well, I was wondering what people out there thought about this question whether the universe is fine tuned for life, So I reached out to our group of volunteers and asked them to chime in.

If you would like to join this group, please write to us to questions at Danielankelly dot org.

Life in our universe is inevitable, and I believe that it is also probably plentiful.

Yeah, I think that life has evolved within the laws of physics that we have.

I say no, because the laws of physics were operating long before or life existed on our planet.

The laws of physics aren't as fine tuned as they could be, because I want to have a world where life is even crazier and there's way more connections that atom can make than what carbon does.

That's a good question.

Maybe, as in all biology, it depends what does that mean?

Well, I don't believe so, I'm feel little bit of anything.

It's the other way around.

If you changed almost any parameter in physics, life couldn't exist.

Life evolved according to the laws of physics.

I think that while we might not exist if the laws of physics were different, other people might, and those people would be inclined to look at their laws of physics and think they were fine tuned for them.

A constance of physics that if they were off just by a small margin, there wouldn't be galaxies, elements, or life as we know it.

You have all of these knobs with very specific numbers associated with many.

Of which would destroy all life if altered.

So you got me if by fine tuned for life you mean the ability to consume other forms of life and often shocking and horrifying ways.

Then yes, I do think that the perception of our lives fine tunes our laws of physics.

There were so many great answers here, and so many answers that made me think these people are really listening.

You know, it's biology.

So it depends.

Bravo, bravo.

Love the in joke responses that's nice.

Yeah, but yeah, in general, great answers here.

So let's go ahead and jump in.

So you you wanted to know, is the universe fine tuned for life?

What does fine tuned mean in particular?

Yeah, this is a really interesting question philosophically, and I love you got to start with like, well, what do you even mean by the words in the question?

You know, you're really digging into philosophy.

So here this is inspired by the fact the physics has laws, you know, like F equals MA, or you know, the laws of general relativity or special relativity.

But there are also numbers.

You know, there's things like the speed of light, or there's the gravitational constant.

There are numbers there.

Sometimes we don't know why those numbers have their values.

There are things that we just went and measured about the universe.

The speed of light is a great example, like, we don't know why the speed of light is what it is.

It could have been bigger, it could have been smaller, or could it is there some constraint there, And these numbers are important.

You know.

If you change these numbers, you change the conditions of the universe, the nature of our experience in the universe, and of course therefore the conditions for life.

Take the speed of life.

For example, if the speed of light was much much bigger, then we could see a much larger range of the universe, which sounds great, right, But also more of the universe could see us, and an alien death ray could travel to Earth much more rapidly if the speed of light light was higher.

So you know, if the speed of light was instantaneous, for example, then anywhere in the universe an alien could point a death ray at us and just obliterate us with no warning.

So you know, it changes the context of life.

And people wonder, like, if these values are different and that changes the way life works, then why do they have these values, the ones that seem so well suited for life as we know it?

Okay, so that's the essay answer to what does fine tunes me?

What would the one sentence answer be, because I think I lost track a little bit at one point.

Okay, the one sentence answer is like, there are numbers in the universe, and if you change them a little bit, life doesn't work the way we know that it does.

So why do they have these values?

Amazing?

This is why you're such a great professor.

Which are the numbers that we care about?

Which are the ones that determine if there's life or not?

Yes, So the example that I gave the speed of light is a very intuitive one, very concrete, but it's not actually the right way to think about these numbers.

The numbers we should think about are not the nu numbers that have units in them.

We should think about the dimensionless numbers, the ones that are pure numbers.

Because if you think about it, like the speed of light, it's three times ten to the eight meters per second meters per second.

It depends on these human things meters and seconds.

And if you changed meters and seconds at the same time, you could keep the speed of light the same, Or if you just change the length of the definition of a meter, you could change the speed of light.

So you know, you get on fuzzy philosophical grounds if you rest everything on the definition of human units.

You've yet again convinced me that we need philosophy alongside physics.

Okay, I think I see where you're coming from.

You know, like meters and things, they come in units of ten, probably because we have ten fingers and time probably, Yeah, why why do we have sixty seconds in a minute?

Daniel?

Let's probably there's got to be a human explanation there too, right, the universe didn't tell us there are sixty seconds in a minute.

Yeah.

I don't think there's any astronomical connection to the length of a minute or one of a second.

You know.

The only things determined by astronomy are like the length of a year, how long it takes the Earth to go around the sun, and the length of a day, how long it takes the Earth to spin.

But even those are local quantities right other places in the universe they won't have the same year or the same day length.

So all of these are just human derived constants.

And the way to think about this and to wonder like why is this important?

Is to imagine whether you could notice if these numbers are changed, you know.

Imagine, for example, I changed what a meter is, but I also spread out the universe more right, Or I changed the speed of light and I expanded the universe.

You couldn't tell, right, there's no difference.

There's no experiment you could do to determine whether I had transformed the universe, made it bigger, but then also increased the length of a meter and the speed of light or shrunk it.

So these numbers, if it's possible to change them and not have any impact on the physics or the nature of our experience, then they're not good choices for like the basic measurements of the universe.

So not only do we want to be free of human bias because that feels weird and local and colloquial and we can't talk to aliens about it.

Also we want to make sure that if we do change these numbers, it really does change the universe in a way that we can measure.

That's why we focus on dimensionless numbers, things that have no units in them.

This is why the meaning of life is forty two.

It doesn't have any dimensions.

So it's true anywhere you.

Go exactly exactly, so bad examples of things that you might think control the universe but don't actually are.

Like the example I gave earlier, this speed of light for the reasons I just described, right, the speed of light.

It is a constant, but it has units, and so you can change it as long as you also change those arbitrary units and have no impact on the nature of the universe.

Another example is like the force of gravity on Earth.

Right, Yes, the force of gravity affects the way life has evolved, but it actually comes from other constants like the big gravitational constant and the mass of Earth and all sorts of stuff, and of course it has dimensions or the things like Avagadro's number.

Right, this is a dimensionless quantity, but it's totally arbitrary.

It's just a number we made up to feel useful.

But we have figured out a bunch of constants of the universe that are dimensionless and that if you changed any of them would significantly impact the nature of the universe and life on Earth.

Okay, so it's not just that the number needs to be dimensionless.

It also needs to not have been arbitrarily picked by people, and it needs to Why can't Why does geometrical not work because wouldn't circles be the same anywhere.

Yeah, so you're thinking about like pi, right, is pi a fundamental nature of the universe.

It's a fascinating question, Like pie is dimensionless?

You're right, and it's not arbitrary.

Right, we didn't make up pie.

Pi is the ratio of the circumference of a circle to its diameter, and that feels really deep.

But I don't know that it's physical.

You know, it's geometrical.

It tells you about the nature of space, and so if, for example, space is curved, pie has a different value.

So in that sense it tells you about the nature of curvature of the universe.

But that's already encapsulated in some of the other quantities.

I think.

So you could argue about pie.

I think that's on the edge philosophically.

It'd be really cool, though, to talk to aliens about pie.

It see if like they have an understanding of it that's deeper than we do.

But it's sort of a function of three D space.

What I'm hearing you say is that if we meet aliens, I can't start dissecting them until after you've asked them about pie, because may I mean maybe they can tell me about their parasites and we can skip the dissection.

Yeah, that's right.

I'm sure they'd be very grateful for you to pull whatever those bits are out of their whatever holes.

Okay, all right, we're not going to get on the topic of transient anuses again.

So tell me about what kind of dimensionless numbers are we looking for?

All right?

So it's time to dive into the dimensionless numbers that define the current human understanding of the universe.

And there are twenty six of them, right and six?

I know it sounds like a lot, right, It feels like, boy, we have a lot of work to do because I think the goal is a theory with zero numbers or one number.

Maybe I'm not sure you could actually get to zero numbers.

But the simpler the theory the better.

Right, But we have twenty six numbers.

So we have twenty six numbers in what is there like an equation that determines if life is fine tuned?

What are these twenty six numbers all about?

These are twenty six numbers in our current laws of physics.

Ok.

We don't have all the physics in one equation.

We have a bunch of equations and some of those equations have numbers in them that we can't remove or derive or predict.

We just measure them.

We don't know why they have those values.

So two of them relate to the strength of forces.

So, for example, the fine structure constant is a number that's all over the place in physics, and you can express it in terms of other physical constants.

It's the charge of an electron squared divided by h Bar times the speed of light.

That's what I was going to guess.

Everybody just talks about that, right, yes, right back of the hand.

Yeah, yeah, Well it's a funny number because you have to sort of put these other physical constants together to get something that has no units.

It's a pure number.

But this number controls the strength of electromagnetism.

Like if you increase the fine structure constant, electromagnetism gets more powerful, meaning that like the force between two electrons at a fixed distance would grow as you increase the fine structure constant.

Okay, And this also controls the weak force, because you remember, the weak force is connected to electromagnetism.

The Higgs mechanism unifies these things.

It's called electroweak symmetry and tells us that the weak force and electromagnetism are actually connected.

So this one number determines the strength of electromagnetism and also with another number we're going to talk about in a minute of the strength of the weak force.

So that's three of the four forces already just from this one number.

And so that sounds to me like if we tinkered with any of those things, are day to day's experiences would be very different.

But have we already hit on things that like we would die I or we would not be here if they were different.

Yeah, this number is why we have chemistry.

So like if you have notes for the universe, we could already start there because you know this controls like electron orbitals, right, this controls how far they are away from the nucleus because electrons in quantum states around the nucleus are there in some sort of balance.

They're balancing their energy with the attraction from the nucleus.

It's similar in spirit to like an orbit.

Right, we have a force between them, but you still have velocity.

Of course electrons are not actually orbiting, but it's similar in spirit.

And anyway, if you increase the fine structure constant.

Electron orbitals would shrink, right, their distance on average of electrons from the nucleus would shrink.

It would make atoms harder for them to bond.

And if you released it, if you decreased the affine structure constant, then the atoms would grow larger and they would have a looser hold.

And so all of chemistry would be different.

Because remember all of chemistry, the whole periodic table, and how atoms interact and their properties.

Are they bitter, are they solid, are they metallic?

Do they conduct?

Depend on the behavior of electrons around these nuclei and how they like to touch each other or not, And this constant directly affects them.

So you tweak this thing even a little bit, all of chemistry is different.

Do you still get water, we don't know.

Do you still get all sorts of things that allow life to form, you know, DNA and RNA and all the complicated machinery of life all depends on this number being what it is.

All right, So my existential dread is starting to creep up as I think about all of these factors, where if they change at all, life falls apart.

And when we get back from the break, we'll talk about more of these things upon which our lives depend.

Okay, So, Daniel, we just finished talking about the fine structure constant.

Yeah, and you talked about how if it changed at all, probably chemistry would change, which would mean life as we know it would change.

Before we get onto the next one, I'm going to slow us down even farther, okay, and say, how do we know for sure that there's not some third or fourth thing out there that we haven't measured that would like accommodate if we made some changes, or like maybe we don't really understand what's important, Like how I guess how sure are we that there's not something we're missing here?

Well, there's lots of things we could be missing.

It could be, for example, that this number has to be what it is.

You know, we have a theory in which this number is a parameter that's not predicted and we have to go out and measure it, and so in our theory, this number could have other values, like if you're at the control panel of the universe, this is just a knob, and according to our theory, you could crank that number up or down, or you could even be changing right, it's not guaranteed that this thing is fixed.

All of our measurements suggest that it's fixed, and when we look back into the history of the universe, we see physics playing out the same way with the same find structure constant.

So it appears to be constant.

But that's just a measurement.

But it could be that our theory is just incomplete, that there's a better theory out there that's more clever, and it requires the fine structure constant to be this value.

It predicts it.

I mean, that would be Nobel Prize winning stuff.

You come up with another theory for electroname inmics that predicts this thing and shows why it has to have this particular value.

We can't have any other value.

Boom.

You have left us forward one thousand years or whatever in physics, and you've shown us why this number is what it is.

So in that sense we could be missing something for sure.

Okay, great, that's what I was asking.

But there's lots of other numbers out there.

And the second one also relates to a force.

So the other quantum force that's out there is the strong nuclear force.

So that's four fundamental quantum forces and electricity magnetism, and the weak force, which all bundle together into a single electra week.

And then the fourth fundamental force is the strong nuclear force, which holds protons and neutrons together and also holds the nucleus together and all that good stuff.

And this one we have not yet unified with the other three quantum forces into a grand unified force.

People are working on that, but we don't have that figured out yet.

So we have a whole separate system of equations.

They're inspired by the same machinery.

It's all quantum field theory, but it's a different quantum field, and the numbers are all different, and it uses weird color charges whatever.

So we got another number there, the strong coupling constant, and that's just a number, and it tells us how strong is the strong force.

And it's a much bigger number than the fine structure constant, which is why the strong force is called the strong force, because it's so dang strong.

And because you physicists aren't super clever with your naming structures.

What would you have called the strong coupling constant killing.

The hulk force or something.

We hold nucleus together, that's right.

Right, already we've made improvements here.

I'm available whenever you guys need suggestions.

I'd love to zoom in on the nucleus and see tiny little hulks in there.

That would be better than gluons, right, little hulcons or something.

Yeah, I'm going to copyright that little hulky nose.

Anyway.

This also has a big impact on the nature of life.

We were talking a minute ago about the electron and how that determines a lot of the properties of the atom and chemistry, but of course the nucleus is important too, and in the nucleus it's the strong force that dominates.

You have neutrons which have no charge, and you have protons which have positive charge, and those protons don't like to be near each other.

But the strong force is strong enough to overcome that and keep all those positive charge protons bound together into a nucleus and to create those protons and neutrons in the first place.

And that's really the building block of all of matter and everything in the universe.

So if the strong force constant was different, you wouldn't get nuclei the same way.

You wouldn't get the same isotopes.

You might not even be able to manufacture these things in the hearts of stars.

Okay, yeah, that sounds pretty fundamental.

Why can't we make these things in the hearts of stars?

Yeah, So the strong force determines not just how protons and neutrons come together, like how you build them, but how they like to stick together well a nuclei that they can form.

And so you know what happens in a nucleus is you have protons and neutrons and those things are all neutral from a color charge point of view.

So you might wonder, like, how does the nucleus stick together?

Anyway, There's all these positive charges from protons and neutral charges from neutrons, and everything is also neutral from a strong forest point of view, So how does this stick together?

And the answer is residual strong charge because what's happening is that the quarks in one proton are talking to the quarks inside another neutron, and so those charges are talking to each other.

And that only happens if a strong is strong enough.

If you change the nature of the strong force, then you might not get fusion.

For example, like what happens when you try to stick two protons together inside the heart of a star to go from hydrogen, which is what the big mag made to things like helium and lithium and carbon and oxygen and all the stuff that we need for life.

Is you rely on the strong force to be able to grab those protons when they get close enough and stick them together.

So you start changing with the strong force, you're going to change fundamentally the chemistry, the fusion that's happening inside the hearts of stars, and some of these steps in nucleosynthesis are pretty tricky.

So to get carbon, for example, requires like a complicated combination of three helium simultaneously, and like this is very dependent on the strong force.

So if you have your hand on that knob and you like accidentally tweak it a little bit, you could change fundamentally what's happening inside all the stars in the universe.

All right, So I'm feeling a little bit uncomfortable that you keep talking about chemistry, but we should push on.

So this is the strong coupling.

So for the fine structure constant, you gave us an equation to let us know what values are going in there.

What values go into the strong coupling constant?

Yeah, great question.

The strong coupling constant is just a number, and it's one that we derived sort of later on, So we just measured it directly because we didn't even know about the strong force until, you know, a few decades or almost a century ago, Whereas the fine structure constant comes from electromagnetism, and there were earlier experiments, you know, things to like measure the speed of light and things to measure each bar, and then we derived most of the theory of electromagnetism in terms of those existing constants, and then later realized, oh, we should put these together in terms of a dimensionless one.

So short answer is, we can't express the strong coupling constant in terms of other constants because we realized later on, oh, we should just define the dimensionless thing first.

So the fine structure constant is a bit of a historical anomaly, and we sort of came to this way of thinking about things later on.

Your initial explanation convinced me that this is important.

But the explanation you just gave me for how we determined the value does not convince me that this is a that we have figured out the right way to measure this.

Well, we don't know that we figured it out.

The right way.

But we have a theory, and that theory has a number in it.

We can't predict that number.

Okay, like our theory of the strong force would work with different values of this knob.

You know, you make it more powerful, you could make it less powerful.

Our theory essentially describes a huge range of possible strong forces, and then we have to go out in the universe and figure out which one do we have.

Oh, we have the one where the knob is set to this value.

And then of course the question why what does it mean?

And that's the philosophical joy of physics, right You discover the universe is set up in a certain way, and then you wonder why this way and not some other way?

Does it have to be this way?

What does it mean that it is this way?

But what we know is that this is a number we have no explanation for.

It's independent as far as we know of the other constant find structure constant.

You could change strong cupling constant separately from the fine structure constant and you would definitely notice and any change you would observe.

So we can't explain it.

And it seems very sensitive to the value that it's set to.

So yeah, I think it's pretty good example of something that's fine tuned.

No, biology is so complicated, you guys are always like, it defends but right anyway, So if I had to guess some other values that should show up in the constant, I would guess that it would have something to do with like the mass of the mass particles in the force particles, but those would have dimensions because they'd be mass and so yes, so I'm wrong.

You're mostly right.

I mean you're on the right track.

Oh good.

Definitely, the masses of the particles influence the way things happen.

You know, if the electron were heavier, if the electron were lighter, you would get different chemistry.

If the heavy versions of the upquirk were lighter, then they might exist more often and play a role in life for example.

So you definitely need to capture that somehow.

But you're right.

You also want to avoid dimension full numbers things that are related in terms of mass.

So we have twelve particle masses for the matter particles, there are twelve fermions.

There's six quarks up down charm strange bottom top, and six leptons electron muon tau and then the three neutrinos.

So that's twelve numbers, and we can make them dimensionless just by expressing them relative to g which is the gravitational constant, And so we can't sort of cook up a dimensionless number which reflects these masses.

Think about it, like, what we're doing here is expressing the mass ratios.

More like, so, why is it correct to be looking at the mass relative to gravity as opposed to relative to the average mass of an elephant.

Why is gravity the right the right thing to use to make your mass dimensionless?

Yeah, yeah, because the nature of the universe depends on this ratio.

So if you cranked down the gravitational constant and made everything weaker, and then you cranked up the mass to compensate, everything would behave the same gravitationally, And the opposite is true too.

If you made gravity stronger and then you just weakened all the masses, you wouldn't notice.

And so it's really this ratio that determines the behavior of these things, whether they decay in to each other, all the masses, all this kind of stuff, and so boom, that's twelve numbers right there, And that's kind of a mess.

You know, like these other things, like, okay, they're fundamental forces and determined chemistry, you could begrudge a couple of them.

It feels like icky to me that we have twelve numbers here.

I mean it's divisible by two.

That feels like a thing that physicists like.

It would be icky er to me if there was like something that had three instead of something divisible by two.

Yeah, that's true.

I mean I think it feels icky for a couple of reasons.

One is I want this number to be small.

I mean the number of numbers.

I wish the humanity had a theory with like one, two, three numbers.

It would feel like we were on the verb of figuring it all out.

So boom, adding twelve and one fell swoop.

Ugh.

That's like an admission that were newer clo to the answer.

And I think it also reflects the fact that we haven't solved another mystery, which is where this twelve comes from, which is why are there twelve particles?

Right?

It feels like this is just wrapping up one piece of ignorance into another.

That's what I say.

There should be an explanation for like why do we have three copies?

Of every particle.

What it's the relationship between the quarks and leftons.

Anyway, those are deeper mysteries, and I feel like if those were solved, then we could reduce the number of numbers, but we aren't there yet, so we've got to pay the price and add twelve numbers to our list.

And you know, in terms of sensitivity, like obviously the masses of the up, down, and electron are very important because those are the things the building blocks of life as we know it, and atomic matter and you know, me and you and bananas and kittens and all that stuff.

The other particles, like the top court it's super heavy and so it rarely appears in the universe outside of like high energy collisions at the LHC or alien facilities or cosmic rays.

So probably life is less sensitive to that.

Like if you cranked up the top quark mass or cranked it down, probably you would still get life pretty much as we know it.

Particle physicists might discover it earlier or later, so the Nobel Prize trajectory would be different, like the specific scientific history.

But you could make a pretty good argument that we're not that sensitive to the mass of the top quark for example.

Well, and I think giving out of Nobel prizes is not like a fundamental feature of the universe.

I don't know that we need to account for that necessarily.

But the other side of this, the strength of gravity is really important.

You know, if gravity were a lot weaker, then we wouldn't get it clumping things together.

You know, the whole history of the universe is that we start with very dense plasma, which has some slight over densities and slight under densities due to quantum fluctuations, and it's dense enough, and gravity is strong enough, despite its overwhelming weakness to start gathering this stuff together to form structure.

So structure in the universe only comes because of gravity, and because gravity is powerful enough to pull this stuff together.

If gravity were a little weaker, then you wouldn't get galaxies.

You wouldn't get stars and planets.

As it is, the gravity of atomic matter of the protons and neutrons and electrons wasn't enough to form galaxies and stars and planets.

We needed help from the dark matter.

Like if you had a universe without dark matter, just with the normal matter atoms and whatever, you wouldn't get galaxies and stars and planets fourteen billion years into the universe.

It would take a lot lot longer if it ever happened at all.

So it takes not just gravity, but the right amount of gravity and the right density of dark matter to construct this structure that we live on.

The whole framework of the universe depends on gravity having its strength, all.

Right, So now you've convinced me that it's important to have gravity in here instead of the average mass of.

A big element.

But it also goes the other direction, like if gravity was too strong, then we wouldn't have the universe that we know and love.

We would have a lot more black holes.

It would like pull stuff together more rapidly.

We'd have smaller stars because you get more seeding of individual bits.

Like remember the way stars forms.

You have a huge cloud of gas and there are little seeds there, little places where gravity is slightly more powerful.

But if gravity was everywhere more powerful, you get more seeds and you had with smaller stars.

And smaller stars are colder, like our sun is unusually big and hot for the universe.

So in a universe with stronger gravity, you get more black holes and a bunch of small cold stars, and that would be a very different kind of universe to grow up in.

And so is the fact that our sun is unusually big and hot.

Does that kind of explain why life is so rare in the universe that you kind of need a big, hot sun.

It's a hypothesis I've heard, you know, because most of the stars in the galaxy are red dwarfs.

So why didn't we evolve around a red dwarf?

Does that mean that the sun is the only kind of place that life can evolve or does it just mean we got lucky and got a bigger, hotter sun.

And it's just you know, in most universes we would have evolved around red dwarfs.

Red dwarfs seem a little bit more chaotic there may be not as stable as our star is.

But this is the problem with an equals one philosophizing, Right, we have one example and we're trying to draw conclusions from it.

You know how dangerous that is.

Like you have two kids, they're very different.

I have two kids, they're very different.

Imagine you only had one kid and you're like, well, every kid that I have is like this kid.

Obviously that's not true, you know, And so it's very dangerous to generalize from one example to assume that this example tells you something inherent about the process you're studying.

So it's pretty dangerous.

Yeah, let's take a break and then we'll talk about the last few constants that determine whether or not you get to stay alive.

All right, Daniel, we're talking about constants that are necessary for life as we know it.

Which constants have we not talked about yet?

So there's a few more messy particle physics constants that indicate that particle physicists really haven't figured it out yet.

There's three more particle masses we have to account for.

This is the Higgs Boson mass, the W mass, and the Z mass.

And the W and Z mass are the reason that the weak force is weaker than electromagnetism.

So the fine structure constant sets the strength of electroweak force.

But part of that electroweak force is the weak force, and that's weaker because the W and Z masses have the values that they have.

We don't know why they are, you know, according to our theory, there could have been different values there.

They tend to be very large, which makes the weak force very weak.

In other universes, maybe the weak force is stronger, and they didn't call it the weak force, you know, called the mini hulk force or something like that.

That's the universe I want to live in.

Yeah, the Higgs Boson is a special mystery.

Why it has the value that it does.

We suspect the Higgs Boson mass should be much much bigger.

Our calculations for the Higgs Boson mass involve calculating a ten digit number and then subtracting from it another ten digit independent number and getting this three digit mass.

The Higgs Boson masses one hundred and twenty five GeV.

But like, what are the odds having these two ten digit numbers exactly balanced or almost exactly balanced.

So the Higgs mass itself, people think, is fine tuned and it controls the masses of everything else.

And so this whole thing feels like very arbitrary and not well understood.

So that's three more masses.

And so here too, we've got masses, and so what are they relative to?

Yeah, good point, they're relative again to the gravitational constant to big G.

So we can keep them dimensionless.

Okay, the fact that there's three feels wrong, but we'll move on.

I guess you're not Catholic.

You don't find the universe to be three ish fundamentally.

Huh.

I was raised Catholic, but I don't go to mess anymore.

My apologies.

Well, that's probably just because of the fine tuning of the constants.

It's not your fault.

Oh yeah, okay.

So then we have eight more parameters that mean particle physicists haven't figured it out yet, and these are how the fermions talk to each other.

We have these complicated mixing parameters that tell us like how different neutrinos turn from one into another, or how quarks can turn from one flavor into another flavor.

And so there's eight numbers there that we just measure in the universe.

We can't predict.

We don't know why they have their values.

I hope alien physicists have figured it out.

But again, these things determine the nature of the universe, That determine how often particles change from one kind to the other.

Probably life is not super sensitive to these because it mostly involves the heavier, rarer particles that we don't see mostly in terms of life.

But you know, we don't understand these things super well.

These things could also determine things like the matter anti matter asymmetry in the universe.

I think a lot of this is why we have matter and not antimatter in the universe.

So in a universe where these numbers are different, you might have a perfect balance between matter and antimatter.

And then in the beginning of the universe, you get no electrons, you get no protons, you just get light.

It's all the matter and antimatter annihilates into photons and that's it.

And so it could be that these numbers determine the matter antimatter asymmetry, which is why we're made of matter, or you know, other sets of these values, you could end up with the universe made of antimatter that they of course would call matter.

And so it's not well understood, but it could certainly influence the nature of the universe.

I'll note that as you're talking about these conditions under which we might all be annihilated, you have this weird like sparkle in your eye.

But anyway, so just to try to bottom line where we are so far, there is at least twenty six dimensionless values in the equations that govern how the universe works, and they vary in the extent to which we think that they are critical for the universe to work as we know it.

So some of these you can tinker with a little bit, maybe you'd still get life.

And some of these, if you tinkered with them even a teeny tiny bit, it's hard to imagine that you could ever get life, yes, exactly.

And the last one is the cosmological constant.

This is a big one.

This is the one that determines how fast the universe is accelerating.

It's our best explanation for dark matter.

You know, we think that space has some inherent potential energy, and according to general relativity, if space has potential energy in it, then you get this repulsive, accelerating expansion in the universe.

And so this is very important for the formation of the universe as we know it.

If the expansion rate is too large, then the universe starts to tear itself apart before gravity can do its work and form stars and planets.

If this number is too small, the universe collapses due to gravity very early on into one mega black hole.

And so you can't tweak the cosmos constant very much, which is the source of all the recent consternation.

You know, people have been trying to measure this number and finding that, oh, actually, it doesn't make sense to happen be a single number, and it needs to change over time because the structure of the universe is very sensitive to this number.

And the more we measure about the evolution of the structure, the more we have questions about whether this number actually is a constant or whatever.

But the point is this is a big one.

It controls the structure of the universe as we know it.

And so, yeah, a lot of these the universe is very sensitive to Some of them.

You might be able to fudge a little bit, but we're still faced with these questions like does this mean the universe is fine tuned?

We have all these numbers that we don't have predictions for if we change them a little bit, life would be different.

What does that really mean?

And that's where we get into the philosophy.

Yeah, I feel like quite clearly this is where physicists should start talking about the existence of God and stuff.

But I don't see that in the outline.

And so what what are the philosophical explanations that physicists tackle?

So my favorite explot is, Look, we're just not done.

There is a theory out there that does explain these things, that tells us why it has to be this way that connects these masses.

And maybe that theory has zero or maybe has one parameter.

But if we had a deeper insight, or we could crib on alien physics textbooks, you know, or even future humanity that maybe we just have a deeper understanding and the universe has to be this way.

We just don't get it yet.

That's my favorite explanation because it also inspires more research, you know, it tells us to keep digging, that there are more answers there and if we keep going, we'll figure it out.

So that's why I like that explanation, not because I know that it's true or I can argue for it like scientifically, but it's the one that inspires us to keep going, because that's the whole motivation of science.

Right, Let's keep trying to understand, let's keep looking for those explanations.

We have no reason to believe those explanations exist or that the universe is sensible at some fundamental level.

Anyway, I have some sort of operating just on the assumption that it is, and so it's worth well, so far, let's keep going.

But I like that explanation because it's actionable.

It's like, Okay, we don't know, but let's not give up, let's keep trying.

And so all right, so we've got that's explanation one.

What's explanation two.

Explanation two is that there is no explanation.

These are just random, right, and they could have any value, and we happen to live in a universe where these values are the ones that we need for life, and so life evolves according to the laws of physics to fit into it.

It sort of shapes life.

You know, some other weird form of life couldn't have evolved in these universe because our form of life is very sensitive to the chemistry and the structure of universe and all this kind of stuff.

And you know, there's an explanation here that's called the anthropic principle that says that we wouldn't be here if those fine tuned constants weren't fine tuned to the numbers needed for life to be as we know it.

So in most of those universes where you change those numbers, you don't get Daniel and Kelly having a podcast conversation about it.

You don't get people writing philosophy papers about it.

Not a question because we're not there to ask it.

And so this sort of says, well, look, this is a big coincidence, but there's no deeper explanation.

But so doesn't that kind of depend heavily on what we know?

Like how how we understand how things worked out?

Like if you tinkered with these values, maybe you wouldn't end up with galaxies, you would end up with like one big flat disc that we all live on or something.

And maybe we'd all have tentacles.

And how much are we biased by tentacles.

A bad outcome or a good outcome?

I'm trying to figure that out.

Oh, I don't know.

I could see it going either way.

It's hard to watch cat videos when you only have tentacles.

You know.

Can you use your suckers to control the phone?

I don't know how that works.

I mean you can get attachments for your suckers maybe, and that could help you with your phone.

But we're getting off topic here.

But yeah, but so how I mean, how do we know that the universe couldn't just look so different that it's like beyond our ability to comprehend.

Yeah, you're exactly right, and that's another explanation, right, So, wrapping up the anthropic explanation, I agree with you.

And the thing I don't like about it is that it tells us to stop looking.

It says, look, there are no answers, so don't waste your time, and it can hide real explanations, like there are sometimes real explanations.

And if you just say, look, I don't know and just the way it is, and we wouldn't be here to ask these questions otherwise, then it stops you from finding true answers.

So I'm not a big fan of the anthropic explanation.

And another answer to this question is that we don't know what life would be like in these other scenarios.

It's true that if you tweak the fine structure constant, you get very different chemistry, and therefore you would have to have different life, but we don't know what that life would be like, and if that life would also ask this question, and it presumes the structure.

This question presumes that like we are some sort of outlier, we're unusual in our complexity and intelligence.

It might be that we're kind of simple and boring, and that if you changed one of these fine structured constants or one of the other constants, get a much more interesting universe filled with life.

And they're all super intelligent and they figured it out fast and light travel and like we're a bad outcome.

We're like, oh boy, you know, I hope we don't get that universe right.

And so call comes down to the question you asked earlier, basically, like do aliens have tentacles?

We can't imagine life as we don't know it.

It's very hard for us to think outside the box.

We don't know where the box edges are, what assumptions we're making.

The bee don't even realize, and it's very almost impossible to calculate.

You might say, well, Daniel, you're a physicist, change the numbers, run the simulations, tell us what those universes are like, right, that involves so much complexity.

We can't even tell you, like how stars form.

We don't understand the nature of the universe.

We have to just go out and look, right.

We can't start from these principles and tell you how our universe should look because we can't do the calculations.

It's too complicated.

You know, we can't like predict what chicken soup taste like from particle physics, right, that's too many numbers.

We can't predict the weather, we don't understand turbulence, and so I can't then change these numbers and tell you what the universe would look like.

It's too complicated.

We're not capable of doing that.

So we don't know, right, And you're right that it could be that in most settings of these numbers we get interesting stuff life and intelligence and happiness and parasites and tentacles, good or bad.

So yeah, we don't know, and I think that's what you were asking, and so then let's just wrap up.

The last possible answer is like, well, maybe they are fine tuned, you know, maybe we're living in a simulation, or God exists and they have set these numbers to be the way they are, and discovering these things means that we're special.

And I don't like that answer because it makes us sound special.

And anything that makes us sound special is too tempting and too seductive and makes me very skeptical.

I'm with you there, all right, So thanks everyone for coming along on this ride between physics and philosophy exploring the nature of the universe, what it all means, what we've learned, and what we have yet to figure out.

See y'all next time.

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