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Our universe is prone to increasing disorder and chaos.
So how did it generate the extreme complexity
we see in life?
Actually, the laws of physics themselves may demand it.
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How did life begin?
We can seek the answer in the chemistry of the early Earth
or in the biology of the first cell.
In fact, our friends at PBS "Eons"
and "It's OK to be Smart" will do just that in companion
videos to this one.
But we all know that chemistry and biology are just
applied physics.
So can we approach the question of the origin
and the very nature of life from the point of view of physics?
We're sure going to try.
To understand life, we need to understand entropy.
The universe tends toward disorder, decay,
and equilibrium.
A hot cup of coffee will tend towards the same temperature
as the room, and the hot, dense of our universe must expand.
Stars always burn out.
Black holes evaporate.
The particles that make up any system
all have some degree of random motion.
That random motion tends to drive the system
towards the most common arrangement of particles.
Such a random disordered, unspecial arrangement
is a high entropy state.
Interesting arrangements, like thermal energy being
concentrated in your cup of coffee or all the matter
in the observable universe being crunched
into an infinitely dense point are low entropy.
They're highly specific configurations that
almost never happen by chance.
So entropy is sort of a measure of the boringness
of a system, the commonness of the arrangement of particles.
The second law of thermodynamics tells us
that a closed system will only increase in entropy.
The universe will only get more boring.
But there's one type of system that
seems to resist the second law of thermodynamics
and maintain low entropy.
That system is life.
Life has a very low internal entropy
because its structure is extremely
specific and non-random.
The molecular machinery of even a single cell defies belief.
You know what?
I'd prefer to let a real biologist convince you.
Hey, Joe, tell them how it is.
Cells are complex.
OK.
That's a massive understatement.
Inside just a single one of your cells,
you have six billion base pairs of DNA,
storing hundreds of megabytes of data.
Intricate molecular machinery made
of RNA and protein unpacks, transcribes, cuts and splices,
and processes that data to build and control
an entire factory of protein molecular machines, which
in turn, power the entire biological process that is you.
Easy, right?
Not only is life stunningly complex,
but that complexity increases over extremely long time
scales, in fact, over eons.
Right, Blake?
When we look at the fossil record,
we see the evidence of evolution carved in stone.
When we trace the development of fossils over the nearly four
billion years of life on Earth, we
see clear as day the study trend toward greater complexity,
from the first single-celled organisms
to simple ocean invertebrates to an explosion of complex animal
life and finally, to us.
Naively, this presentation and increase in order appears
to contradict the second law of thermodynamics--
entropy appears to either stay constant or decrease.
The Earth's biosphere, at least, becomes less boring over time.
But let me be clear, there is no violation of the second law.
The second law tells us that closed systems
must increase in entropy.
So a system's unable to exchange energy
with the outside environment.
But living organisms and indeed the Earth's biosphere
are not closed.
Both receive energy from outside.
Ultimately, that source of energy is the sun.
Its light warms the atmosphere in the oceans
and it powers photosynthesis at the bottom of the food chain,
driving a complex chain of nutrient synthesis
that ends with whatever you had for dinner last night.
On the other hand, the system of the Earth plus the sun
is increasing in entropy.
Life acts to reduce its own internal entropy
by increasing the entropy of its surroundings.
This was first pointed out by Ludwig Boltzmann, who
described life as a struggle for entropy,
well, more accurately, against entropy
or for negative entropy.
Erwin Schrodinger, in his 1944 book, "What is Life,"
describes life as a process feeding on negative entropy.
Life absorbs order and it ejects disorder into its surroundings.
The type of order that life feeds on
can be thought of as free energy.
By free energy, I mean the special out-of-equilibrium
energy sources like a cup of coffee or the sun.
Another way to say this is that life feeds on energy gradients.
When two systems with very different energy densities
come into contact, energy must flow.
Life feeds on that flow.
In fact, the importance of energy gradients to life
can help us understand the actual origin
of life and its precursors.
The origin of life on Earth isn't known.
We think it started with a self-replicating molecule
similar to RNA.
The companion episode, over on "It's OK to Be Smart,"
will get into the nitty-gritty of that.
Following that synthesis, evolution took hold,
and the first protocell and then first true living cell
pulled itself together.
PBS "Eons" will cover that part as they
explore LUCA, the last universal common ancestor.
But where on Earth did this all happen?
There are a few hypotheses.
Perhaps it was in tidal pools or around deep sea hydrothermal
vents or even on the undersurface of Earth's ice
caps.
These environments share a critical property.
They sit at persistent energy gradients.
The water of tidal pools is both cooled
by the earth and the ocean and warmed by the sun.
Around deep sea vents, the searing gases
from Earth's hot interior meet the frigid water
of the ocean depths.
Beneath the thick ice caps, there's
the transition between the solid and liquid phases of water.
These are places struggling to return to equilibrium.
These systems are doing their best
to obey the second law of thermodynamics
by redistributing their energy as evenly and randomly as they
can.
Heat energy flows from hot to cold,
seeking a uniform temperature, but energy
is also dispersed into every form it can take consistent
with the laws of physics.
Some of that energy gets distributed into chemical bonds
as simple molecules form via every chemical reaction that's
possible given the available raw materials.
As those molecules form, new channels
open up for distributing energy into the chemical bonds
of increasingly complex molecules.
Normally, this local rise in complexity
would all cease when the system reaches thermal equilibrium,
energy is perfectly evenly distributed
and new molecules break apart exactly as
often as they're formed.
But when our energy source is flowing
into a much larger reservoir, why, the ocean, for example,
then equilibrium is never reached.
Complexity can increase indefinitely
as a byproduct of the system striving to redistribute
the endless gradient in energy.
And at some point, natural selection takes over.
Molecules self-catalyze.
They help drive the very reactions
that create more of the same.
Molecules better at that process become more abundant,
and at some point, they become true self-replicators
and eventually, they become life.
But even life and self-replication
might be a very natural part of the same thermodynamic drive
to dissipate energy.
I mean think about it.
Living things are incredible heat dissipation
entropy-maximizing machines.
The most random possible form for energy
is thermal radiation, and the lower
the energy of its component photons,
the higher the entropy.
A plant absorbs the concentrated ultraviolet light from the sun
and reprocesses it into a much higher entropy infrared heat
glow.
Animals consume high-energy density packets of matter
called food and convert it to lower energy density waste as
well as that same infrared heat glow.
Life is great at dissipating energy, and more generally,
it may be that self-replicating systems are the best possible
energy dissipators of all.
This is a new idea proposed by MIT biophysicist Jeremy
England, who puts the thermodynamics of life on more
solid theoretical grounds.
He's demonstrated mathematically that self-replicating molecules
and simple single-cell life are extremely good at shedding heat
in the act of reproduction.
Self-replication randomizes the environment,
even if each new replicator is highly ordered.
And it's not just life that does this.
Consider a perfectly streamlined or laminar flow of some fluid.
This organized flow is disrupted by introducing turbulence.
The laminar flow has a lower entropy than the turbulent flow
because there are fewer ways to rearrange
the particles in the former while preserving
its global properties.
But watch the transition from laminar to turbulent.
While the global structure is disrupted,
substructure develops.
Waves and vortices have their own complex
and regular structures, but they ultimately
serve to dissipate the flow.
Any given eddy taken separately has a lower internal entropy
than its chaotic surroundings, but the source
of that local incidence of low entropy
is the streamline flow that it formed in.
And those turbulent eddies ultimately
serve to increase the entropy of the greater flow.
So given a much larger source of order,
the global process of dissipation of that order
results in eddies of low entropy.
Life appears to be just such an eddy.
In the case of life, the original source
of extreme low entropy is the Big Bang itself.
In the process of redistributing energy
into the most random possible state,
little eddies of order, like galaxies, stars, planets,
and life naturally arise.
These blips in order are actually serving the second law
helping the universe disperse its early extreme low entropy
state.
So I guess that makes you a little eddy of order,
a momentary fluctuation of interesting but ultimately,
in service of the spread of disorder and dullness,
an agent in the inexorable trend to maximize
the entropy of space-time.
This episode is part of a collaboration series
with the amazing channels "It's OK to be Smart,"
and PBS "Eons."
For the full story of the origin of life,
be sure to check out the companion videos.
Just follow the links.
Last week, we talked about the mysterious Unruh effect,
in which accelerating observers find themselves
bathed in a sea of particles.
You guys had a lot to say.
Vacuum Diagrams points out that from the point of view
of an inertial observer, an accelerating particle detector
emits particles instead of absorbing them.
Well, that's right, and we depicted that in the animation
but decided it was a bit too far down the rabbit
hole for the episode.
But in short, the inertial observer
sees the accelerating particle detector
click as though it registered a particle,
but the excitation behind that click
is seen to be due to particle emission
by the detector rather than the absorption of an Unruh
particle.
That emission looks like a straightforward quantum
process, analogous to photon emission by an accelerating
electric charge.
Fernando Franco Felix points out something interesting.
The inertial observer sees that there's
a type of friction between the accelerating
observer and the quantum field which
should inhibit that acceleration by creating a type of drag.
But the accelerating observer doesn't directly
see that friction.
So how do they explain the drag, which they must also feel?
The answer is that the accelerating observer perceives
themselves to be plowing through a bath of Unruh particles,
and these produce the drag.
The accelerating observer must expend more energy
to produce the same acceleration.
Ultimately, that's the source of energy for whatever effects
those Unruh particles cause, whether or not you actually
see the Unruh particles.
Moma the Belly Dancer asks whether this
means that the expansion of the universe
also causes an event horizon?
Well, actually, yes.
The cosmic event horizon is that service
from beyond which we can never obtain new information.
We can actually see that horizon today.
It's around 16 billion light years away.
But the accelerating expansion of the universe
will prevent any photons emitted today
from galaxies at that distance or beyond
from ever reaching us.
Before they get to us, they'll find themselves
in a patch of space that is moving away from us faster
than the speed of light.
That horizon should produce a type of Hawking radiation,
but its wavelength would be comparable to the distance
to that horizon, so it's completely undetectable.
On the other hand, during the inflationary epoch
in the extremely early universe, the cosmic event horizon
was very close to every point.
The inflating universe should have been bathed
in intense Hawking radiation.
Alex Karolsonov notes that the Bremsstrahlung radiation
created close to the Schwarzschild
radius of a kugelblitz might create the Zitterbewegung
effect.
Nice.
I'm sure you can better support the [INAUDIBLE]
of your Gedanken experiment by abseiling into that kugelblitz
with a geiger counter.