Can Life Really Be Explained By Physics?

I think that life is the most fascinating,  naturallyoccurring phenomenon in the universe, and I think that's uncontroversial.

I  mean clearly, the human brain is the most complex structure that we know of.

It is a product of the laws of nature, but we are a long way from understanding how that  produces the experience of living right.

And so really, if you wanna ask what's the meaning of  life, then first of all, we need to understand life, and secondly, we understand consciousness  'cause meaning emerges from consciousness.

I think it's a little unfair that everything  sounds so much better with your accent as you explain things about the origin of the universe  and origin of life.

It's a little unfair.

So, are you saying that it's not the inherent poetry in my construction of sentences  or the conveying of ideas, it's just the accent?

60/40, we'll call it 60/40.

We'll go with that.

60/40, I'll take that.

I recently sat down with Science Communicator, Brian Cox.

Now, he's a physicist, but our  conversation didn't focus on the Big Bang, or alien worlds, the strangeness of black holes, or  any of that stuff.

We talked about what it means to be alive.

Now, life is one of those things  where... well, you know it when you see it, right?

But what is it exactly, that  makes me different from a rock?

So maybe by looking to physics and asking some  questions about the fundamental rules of the universe, we can understand the meaning  of life.

Like literally.

Really, really?

Hey smart people, Joe here.

Y'all might know  this already, but I'm a biologist, a doctor of the biological sciences to be exact.

So why would  I need to call up a physicist to talk about life?

Well, next to why are we here?

And where is here?

What is life?

Is one of the biggest questions out there.

And it's one that people have asked  in various ways since people have existed.

But in every era before today, it's typically  involved a supernatural answer.

It's a very new idea, just in the past couple of centuries,  to look only to nature for the answer instead.

And one of the things that inspired this change in  perspective was the dawn of modern physics.

Every living thing that has ever existed is a product of  the universe.

And every process in the universe, from the swirling of the galaxy to the  fusion that makes stars shine, to well, life, they all have one thing in common.

They all  have to follow the laws of physics.

If you look in a textbook, you get to some paragraph that lists  life as like several attributes.

Stuff like, it's organized into cells or that it can grow.

That it  can reproduce, that it uses energy.

So you sort of get this like checklist of what is life.

Then I  noticed the longer that you study, you start to realize that there are exceptions to these things.

I mean a crystal can grow and replicate itself.

Soap bubbles have very particular  cellular order.

The ocean, just the water and the chemicals dissolved  in it can maintain homeostasis and pH and stability.

Just consider a simple flame.

It can reproduce, it uses energy.

It can grow and even form complex structures, but you  probably wouldn't argue that a candle is alive.

As you said, biology, that's what I've  learned when talking to biologists, that is the science of exceptions, isn't it?

And so it makes me think that what we  learn in school about what is life is totally insufficient for really  describing what it actually is.

Yeah, absolutely.

So I'm surprised and curious, why a physicist  would be so interested in questions about life.

I think, ultimately, cosmology, so what I do,  astronomy, you know, those subjects.

They raise profound questions.

The first question I get when  I talk about size and scale of the universe from people, from audiences is, "What does it all  mean?

What am I to take from these things that you are saying?"

And that word, meaning, doesn't  sound like a scientific term.

But clearly that meaning exists in the universe, 'cause it means  something to us.

Our great hero, Carl Sagan said, I remember there was a great  celebration of our civilization on Cosmos.

And he showed that the arts and the music and  the architecture, and at the end of it, he said, These are some of the things that hydrogen atoms  do given 15 billion years of cosmic evolution.

But in any case, that's true, isn't it?

It's true.

Long answer to a short question is that I think that life is absolutely fundamental  to understanding the universe.

So, let's look at life through Carl Sagan's  perspective, as atoms doing interesting things, and see what we can learn.

This view  of life as very interesting physics actually goes back to the physicist, Erwin  Schrödinger.

In 1944 he published this book, "What Is Life?"

Schrodinger asked, if we  look at life down at its most basic units, very small things like atoms, maybe we can use  physics and mathematics to describe how big bunches of those atoms can form complex  things like you and me.

This was a very different approach versus someone like Charles  Darwin, who viewed the world through an animal or ecosystem sized lens.

My conversation with Brian  touched on a few ideas from physics that together, can help us understand what makes life different  from the other, less interesting atoms in the universe.

Energy is the first big thing that is  required for living things to do what they do.

So, what is a useful definition for energy in  terms of how it can help us understand life?

I mean energy is, it's notoriously, I mean  we can define it mathematically and say, kinetic energy is half mv squared, and things  like that.

If you go to relativity, by the way, then you end up saying, it's the component of the  four vector that points in the time direction.

It's a thing that's conserved.

That's why it's  useful in physics.

It's not created or destroyed.

This is a deeply strange truth about the universe.

From the Big Bang to today, all of the energy  that ever was is still out there.

This energy can change from one form to another, but all there  is all there is.

And since the beginning of time, that energy has been getting more  disordered along with the whole universe.

If you imagine a cup of coffee and you delicately  put the cream on top of the cup of coffee, so that's an ordered system.

So, we have created  order.

The cream's on the top and the coffee's underneath.

And then if you sit there and maybe  you give it a little stir just to give it a kick, and it mixes up so it becomes more disordered.

But in the process, you get complex structures,  swells in the cream, swells in the coffee.

So, a pattern emerges spontaneously  on the road from order to disorder.

These patterns can be so complex that no other  coffee and milk in the universe is exactly like this one.

But eventually as time goes on,  we end up in a state of maximum disorder.

A perfectly boring cup of coffee.

And the  universe has been doing basically this.

The universe started off in a highly ordered  way at the Big Bang, and it's on its way to a more disordered and increasingly boring state.

The  heat death at the end of the universe.

This is all described by the second law of thermodynamics.

The universe, as in, the whole entire universe is evolving towards increasing entropy, aka more  disorder.

So what does this have to do with life?

And in the process, there can be swells in  the coffee, and in that sense we're swells in the coffee.

So, we're almost like an inevitable  consequence of the march from order to disorder.

I think maybe the basic understanding that most  people have about complexity in the universe is that it's supposed to run the other direction.

It's supposed to be the things don't get more interesting and complex.

They get more or  disordered.

So is life breaking the rules?

No, you can have local complexity emerge.

So, in  the language of thermodynamics, it's a reduction in entropy, so things can get more ordered, as  long as you pay the price in the environment.

So the environment has to get less ordered.

That's  why your refrigerator works.

A refrigerator, how do you cool the inside?

That's making order  inside.

You can see that, when you put water into it, it turns into ice crystals.

So by cooling  it down, you're allowing this complexity to emerge.

But how you do that?

Well, you've got  a big heater on the back.

So, the key part of the refrigerator is not something to do with the  inside.

It's the big heating element on the back, which is throwing disorder out into your  kitchen.

And where does it get the energy to do that come from?

It comes from a power  station, which might be burning fossil fuel, or it might be nuclear power, whatever it is.

But you can trace it back.

Now you might say, and you're probably gonna say, "Well, okay then,  but where does the original order come from?"

And it's a very good question, it's the Big  Bang.

So ultimately, the profound question is why was the universe born with a reservoir?

You  can think of it as a reservoir of order which can unravel over billions of years and allow complex  structures to exist in the process of unraveling.

Our Sun, like every other star in the universe,  is a tiny pocket of complexity and order in a universe becoming more disordered.

What stars do basically, is take a bit of that original order from the beginning of the  universe, and hold on to it for a while, slowly giving it up over billions of years, in a more  disordered form.

Energy in the form of sunlight.

You probably know that all life on Earth today  gets its energy from the Sun, whether directly through photosynthesis, or indirectly,  by eating things that do photosynthesis, or eating the things that eat the  things that do photosynthesis.

But ultimately it's the Sun, our little clump  of order in an increasingly disordered cosmos, that's basically the furnace powering the  steam engine of life.

So we're still tapping this reservoir from the very first moments of the  universe and using it to do interesting things.

Yeah, so it's a good approximation.

Now, the  Earth radiates as much energy out into space as it receives from the Sun.

'Cause if it didn't, it  just heats up.

But essentially what life is doing is sitting in that cascade of energy.

And it's just siphoning a bit  of order off from the sunlight.

This is a really important and kind of  mind-blowing point.

When it comes to order and entropy, not all energy is created equal.

Earth  absorbs as much sunlight energy as it gives off in the form of infrared radiation energy.

But that  infrared radiation energy has more disorder than the original sunlight.

When a leaf absorbs visible  light from the Sun, it grabs a bit of that order, it uses this order to do interesting things  like split water into hydrogen and oxygen, and to make sugars, then it pays the universe  back for the order that it borrowed by releasing infrared radiation.

The Sun isn't just  a source of energy.

It's a source of order.

When cells borrow that ordered  energy and turn it into things like DNA and ATP, we send back what we owe as  less ordered energy in the form of heat.

But it is true that as you sit there, you're  actually hastening the demise of the universe, you personally.

Because what  you're doing is you're making, you're radiating disorder out into  the universe in a cavalier fashion in order that you can live and process information  and maintain your structure.

But you are actually making the universe more disordered as  a results, and it's getting disordered faster than it would be if you didn't exist.

So it's sort of your fault, the end of time.

So life doesn't just run on energy.

It runs  on order that we borrow and then pay back.

But how can you use order to actually do stuff?

Like move or repair your cells or copy your DNA.

For a minute, let's leave thermodynamics  behind and think about one of humanity's oldest ways of harnessing energy to do work, the water  wheel.

If you put a water wheel in a still pond, not much is gonna happen.

There's no current  moving the water in one direction.

Or more accurately on the molecular level,  water is bouncing around in every direction.

That's disordered energy.

You can't  really do anything with it.

But if we have a situation where all the water is  moving in one direction, then that's useful.

This moving water has more order.

So we can  stick a wheel in it and borrow energy to do work.

Believe it or not, this is essentially what living  things do.

They tap into sources of highly ordered energy to power molecular machines.

Only, instead  of water, that highly ordered source of energy is protons.

The details are complex and definitely  worth their own video.

But basically when we burn food using oxygen, we borrow some of its ordered  energy to pile up protons inside mitochondria.

Or in a chloroplast, ordered energy from the  Sun is used to pile up protons in one place.

And when we let these piled up protons flow out,  that's useful energy, like water moving downhill.

[Brian] Then sticks this little thing in it called  ATP synthase and that spins around and makes ATP, and then you do all this stuff.

It's literally a  water wheel that sits in a waterfall of protons.

We're sort of glorified like  mills on a pond, they're just turning water wheels, they're just very small  and perhaps much more complicated.

Photosynthesis is just a way to use the Sun to rip water apart  and stack up protons.

The mitochondria is the same thing.

It's a little bag that rips things  apart and stacks protons up on one side so that we can wash them through this water wheel  and make fuel to continue doing other interesting things in cells.

Literally why the mitochondria  is the powerhouse of the cell.

Now, you know.

One of the great commonalities in all living  things is the way that they manage energy.

I'm thinking in particular of the fact that all living  things pump protons around across membranes.

And as far as I'm aware, that's common to everything.

I don't think there's an exception to that.

Believe it or not, this universal trait can give  us a huge clue as to how life might have started.

Or at least where it started.

In the rocks  of the deep sea hydrothermal vents, we find pockets with lots of protons on one side  and not many on the other.

These proton rivers are a natural energy source that many  scientists believe billions of years ago, powered the first transition from  regular chemistry to living biochemistry.

I tend to think of it, initially, the origin  of life is a transition from geochemistry to biochemistry, which it must have been.

You have to  have a world, it's geologically active and somehow chemistry gets sufficiently complex  that it can store information and copy.

Information, this is the other key  ingredient that seems to separate living things from nonliving things.

So  what does that mean?

In every living cell, in addition to the energy or molecular machines  that we discussed already, we can find one more example of complexity and order hiding in  this universe that's on the road to disorder.

DNA and the genetic code.

One of the  biggest discoveries in the history of biology is that there is a physical molecule  that carries the instructions for a living, DNA.

The information is in the structure.

It's  an arrangement of atoms into an ordered pattern and that lets us extract some meaning from it  and do the interesting things that life does.

Now, spoiler alert, eventually you and me and  every living thing on Earth will die.

But life itself will go on, thanks to this information  stored in ourselves.

Because I share some of that information with you.

I share some with  other apes, I even share some of the banana.

The instructions for living are a form of information  that's bigger than any one living thing.

My picture is, that really the Earth is a giant  genetic database.

And it happens that that data is stored in little local objects.

So there  are bits of it.

So there's some in me and some in blades of grass and so on.

'Cause what we're  talking about here is that just the ever shifting gradual change in where the information  is stored in this great database of life.

But this brings up one more big problem.

And  it's one that we don't have an answer for.

If we could somehow go back through time, meeting  every ancestor along the way from early animals to single celled microbes, all the way back to  something so simple, it can copy itself using only chemical reactions.

Well, at what point  do you decide that's the first living thing?

It's a label, isn't it?

It's semantics, I think.

It reminds me of the debate in astronomy  about whether Pluto is a planet.

'Cause I first of all, don't care, but that's  because I'm not a professional astronomer.

They spend ages having meetings, and defining what  a planet is.

Actually, it's an interesting world that orbits around a star.

It might not clear its  own way, it might not be big enough to be a planet and so on, but it's just an interesting world.

So, I don't care what it is.

I think we'll only truly understand how life could begin, when we see  a second genesis somewhere.

Which that's why Mars is so interesting and so important, because  it's the most accessible, possible example.

It's interesting to note that if we're interested  in questions about the origin of life, it might be easier to see that on Mars than it is on Earth  'cause on Earth, the evidence has been wiped away.

The only evidence we have is in our genome.

It's  the living things today, which are separated by 3.8 billion years or so from the first living  things.

But on Mars, it's been in deep freeze with little geology and no weathering for well over  three billion years.

So if life began on Mars, we may well have more pristine evidence of how it  began on that planet, than we have on this planet.

Of course not everyone thinks that these  are questions that science can answer.

I had a professor in college, a biochemistry  professor, who once told us that finding a useful definition for life well, science  couldn't help you there.

As he put it, "It was a question for poets."

And I  asked Brian, if he agreed with that.

Our presence in the universe is probably the most, well it's amongst the most interesting  scientific questions.

And arguably the most important and interesting scientific  question.

How did we come to be here?

And that doesn't just mean, how did the universe  begin?

It means literally how did, on this planet, how did atoms get complex enough to start  exploring the universe?

Living things are one of the categories of objects that are created by the  laws of nature, permitted to exist by the laws of nature.

Another one are stars.

So we understand,  we say, well, let's understand the origin of the stars and we know what we're talking about.

So I  think in that sense, it's perfectly reasonable to say, well, let's understand the origin of the  living things.

'Cause the living things are a structure in the way that stars are a structure.

They're just a lot more complicated.

It's the most profound question, how did life emerge in this  universe?

In the live shows, I start with the question, what does it mean to live a finite,  fragile life in an infinite eternal universe?

Then I immediately say that I don't know  because if I knew I'd charge more for tickets At least you're honest.

Or actually, When we look at everything that we know  about being alive and we try to distill it down to protons and the movement  of heat and energy from here to there or that the letters of the genetic code are  just a repeating pattern of information, that can be uncomfortable.

I mean, being  alive certainly feels like more than that.

Nature forces you into  uncomfortable position sometimes.

Often, when you look at it.

And that's good  for you, It's good for you to be confused.

I hope that that idea applies to life.

Because uncertainty can be excitement.

And it's what sets you at the edge of when  you're standing at the cliff of, at the edge of human knowledge.

I mean stepping forward is  exciting.

You're skydiving into the unknown.

I think it's one of the great unanswered questions  and that's what makes it interesting.

And that's what I'm interested in.

I'm interested  in questions that we've not yet answered, but we have a chance of groping towards an answer.