[MUSIC PLAYING] 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. [MUSIC PLAYING] 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.
