This apple is at the center of the
universe.
There are roughly 100 million cells
inside an apple and 10 the^ of 25
individual atoms. Each one stretching
for no more than a nanometer across. The
highest number of things that you could
fit inside an apple would be roughly 10
the^ of 102 measured in the smallest
possible cubic unit, a plank volume.
Looking upwards, you could fit roughly
100 apples inside the volume of the
average person and about 10 the^ of 25
inside the volume of the Earth. Roughly
10 the^ of 66 could fit inside the Milky
Way and around 10 to the^ of 84 could
fill the entire extent of the known
cosmos.
And so the apple and you sit at a nexus,
a confluence of competing forces,
interactions, and laws. A place where
all the competing powers of the universe
reach an uneasy truce. The apple is at
the balance point of sizes in the
universe.
The apple at about 10 cm across is
roughly 35 orders of magnitude larger
than the plank length, the smallest
conceivable measure of distance. And
it's about 27 orders of magnitude
smaller than the observable horizon of
the cosmos.
And so 62
62 orders of magnitude separate the
smallest to the largest scales within
the universe. A random number that
describes the entire cosmos and all its
components.
At least it may seem random at first.
For halfway to the bottom, halfway to
the top, the apple is at the center of
the universe. And why it sits precisely
at that balance point may explain why
the cosmos exists at all.
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As I began my university studies, I
asked my venerable teacher for advice
regarding the conditions and prospects
of my chosen field of study. He
described physics to me as a highly
developed nearly fully matured science
and that theoretical physics is
noticeably approaching its completion to
the same degree as geometry did
centuries ago.
So said Max Plank of his teacher Philip
von Jolly under whom he studied in 1875.
And 25 years later, Max Plank would, to
the constonation of his former mentor,
almost entirely revolutionized the
supposedly fully matured science of
physics, and he didn't even mean to.
Plank had been hungry for a physics
education, but he'd found his lectures
to be stuffy and old-fashioned. Besides
the demonstrations of von Jolly, he also
considered his professors Herman von
Helmholtz disorganized and slow, and
Gustaf Kirchoff dry and monotonous. So
he largely taught himself the perfect
recipe for a revolutionary.
At the close of the 18th century, Plank
was attempting to mop up what Von Jolly
would have considered one of the final
long-standing puzzles in physics.
Mathematically describing the spectrum
of radiation emitted by hot glowing
things, like a metal poker taken out of
a fire. Genius after genius had tried
their luck to no avail. But the joke
goes that there are two kinds of
physicists. Those who play by the rules
and those who get physical constants
named after them. And so Plank persisted
and after exhausting all other
possibilities, he introduced what he
called a mathematical trick. Instead of
pouring out light in all possible
quantities, Plank assumed that these hot
objects could only emit discrete chunks
or quanta of radiation. He then
introduced a special number to describe
the smallest possible chunk of light,
a constant. And so the unstoppable fires
of revolution were lit.
By plank's time, physicists had already
grown accustomed to physical constants.
Of course, there are artificial ones
created by scientists, standardized
measurements of space, time, and weight
like the ounce and the meter. But more
importantly, and more fundamentally,
there were some that seem to pop out of
theories of nature, like Newton's
constant that described how strong
gravity was or the speed of light.
Values that seem to have no explanation.
They just were. But despite centuries of
consideration, no constant had ever
described something so tiny as that
which plank used to describe quantum of
light. Indeed, the most precise
measurements at the time were around a
thousandth of an inch or a few microns.
With this kind of equipment, scientists
could study bacteria and the internal
structures of cells. But plank's
constant went far, far beyond that.
This number tells us where and when and
how quantum effects become overwhelming.
Where the certainties of the world we
know melt away into probabilities and
uncertainties.
At roughly equal to 6.626 * 10 ^ of - 34
JW seconds, plank was able to combine
this constant with three other
constants. the speed of light, Newton's
gravitational constant, and Boltzman's
constant to create a system of reference
points for the quantum world. And these
are the plank units. A plank time of
around 10 ^ of - 44 seconds, a plank
energy of around 10 ^ of 9, and a plank
length of around 10 ^ of - 35 m.
These units tell us that any object,
system, event or occurrence that
approaches these limits will be affected
by the world of the quantum. And as to
what happens when systems reach the
plank limits, nobody knows.
These seem to be the limits of the
universe. Beyond these numbers, quantum
chaos rules and our mathematics does not
allow us to go.
However, we shouldn't worry too much
because we're unlikely to run up against
these limits anytime soon.
The world's most powerful particle
accelerator is the Large Hadron Collider
with a peak design collision energy of
14 terra electron volts, which is 14 *
10 ^ of 12 electron volts. If they
collided a tennis ball with that energy,
it would burn as bright as 100,000
Hiroshimas.
And the most energetic particle we have
ever detected anywhere was the so-called
oh my god particle. A cosmic ray with a
whopping 3.2 * 10 ^ of 20 electron
volts. Over 40 million times more
powerful than the particles in the LHC.
The plank energy is almost 40 million
times again more energetic than that. In
2020 a team of German scientists shot
X-rays into a hydrogen molecule. The
X-ray photon bounced off one electron,
sending it scattering away, then
ricocheted off another, sending the
second one free. The two electrons then
interfered with each other. The
scientists were able to measure the
interference pattern and deduce exactly
how long it took for the photon to
bounce from one electron to the other.
247 zepptocs, the shortest duration of
time ever measured. A zepptosecond is
roughly a trillionth of a billionth of a
second. The plank time is another 23
orders of magnitude shorter than that.
And finally, attempts to measure the
size of the electron by trapping it in
an electric chamber show that it must be
no bigger than 10 ^ of minus22 m, the
smallest measurement ever made. The
plank length is a thousand billion times
smaller than that.
The world of the plank scale is unknown
to modern science, hidden from view with
even our most advanced instruments.
Although, thanks to quantum field
theory, we do have some insights as to
what might happen at those impossibly
small scales.
In 1941, Verer Heisenberg made a trip
that would change his entire career. He
visited his longtime friend and mentor
Neils Boore in Nazi occupied Copenhagen.
During a conversation, Heisenberg
brought up nuclear weapons, although his
intentions and motivations were unclear.
Bore understandably assumed that
Heisenberg was trying to encourage him
to join the Nazi atomic weapon effort,
which horrified him. The two parted ways
on uncertain terms, never to speak
directly again. However, the details of
the story remain uncertain. Heisenberg
insisted that his goal was not
recruitment and that bore misunderstood
him. And indeed, Heisenberg's work in
general in World War II remains
ambiguous to this day. We know that he
worked for the Nazis in their attempts
to develop a nuclear bomb. Although he
always maintained that he intentionally
slowed down and delayed the Nazi bomb
project, a suitably uncertain fate for
the man who brought uncertainty into the
quantum world.
Decades earlier, at the height of the
quantum revolution of the 1920s,
Heisenberg had proposed something about
the quantum world completely unlike
anything experienced at macroscopic
scales.
His uncertainty principle stated that it
was impossible to measure both the
position and momentum of a particle to
infinite precision. You measure both to
some degree of uncertainty, but the only
way to pinpoint one property exactly was
to give up knowledge of the other.
While Heisenberg imagined this roadblock
in terms of light hitting matter, a high
precision beam would knock a particle
away while a lower power beam would
remain imprecise. Later work would
reveal that it was a simple fact.
This is just the way nature is. The same
way that gravity exists and light moves
at a constant speed. and the number that
describes the seessaw relationship
between the two properties none other
than Planck's constant, the ultimate
arbiter of the quantum world.
Heisenberg's uncertainty principle tells
us that the quantum fields that soak
spaceime are never quite still. Even
with no particles buzzing around, the
fields have a fixed amount of unknown
energy, a certain amount of ground state
vibration that refuses to leave. And at
the plank scale, these vibrations cause
space and time themselves to distort
beyond all recognition.
At macroscopic scales, well and safe
above the plank length, spaceime is as
smooth as a thin rubber sheet. There are
divots and hills and valleys and
ripples, too, but it's all unbroken.
There are no jagged edges, no loops or
twists or folds. But the uncertainty
baked into the quantum fields causes
energies to rise and fall. Particles to
appear and disappear. Their existence
allowed by uncertainty as long as they
are brief enough not to be noticed.
Because of that energized chaos,
spacetime itself bends and flexes in
response. This is the quantum foam at
the plank scale, roughly 10 ^ of minus
35 m. The fundamental substrate of
reality at the smallest possible
distances. A region where tiny twists
and whirls of spaceime compete for
dominance before vanishing without a
trace. Tiny wormholes connecting one
pocket of space to another before
blinking out of existence.
We have no way of describing the nature
of reality at these scales. Einstein's
general theory of relativity demands
that spacetime must be smooth. Quantum
field theory says that it is not.
Indeed, the plank scale is so small that
many scientists doubt if physics or even
reality as we currently understand it
could ever make sense of it.
And so to try our best to unravel this,
let's go to the cinema.
Films are not really continuous. They're
a series of individual pictures played
back at a speed of 24 frames pers. Our
perception blends the pictures together
into a smooth, seamless hole, giving the
illusion of fluid movement and
continuity, when in reality, no such
continuity exists. But if you could
perceive the movie at a quantum rate,
giving yourself enough time to observe
each individual frame, the illusion
would shatter and you would see the
succession of staccato images for what
they really are. And so is time
quantized at the plank scales. Does our
sense of continuous movement through
time break down? What about space? We
perceive motion to be fluid, not a
series of staggered snapshots. But are
our perceptions fooling us?
We've been able to measure minute
intervals of time displacement in space,
but even with our most advanced
instruments, we can't even come within a
fraction of the plank scales. So, just
what is going on down there? Do time and
space even exist in any meaningful way?
And if they don't, then how does the
structure of the universe arise?
The apple may give us a clue.
The smallest known force interaction is
the weak nuclear force. One of the four
fundamental forces of nature. It has a
range of only 10 ^ of -8 m. So of course
an apple existing at the plank scale
would be far smaller than this. It would
feel the weak nuclear force along with
the strong nuclear force, the
electromagnetic force and gravity all
combined and all strong. Indeed, only in
the first few moments of the Big Bang,
when the universe was but a second old,
did the rest of macroscopic nature
experience these kinds of unknown
physics. And at plank scales, physicists
even believe that all the forces of
nature meld into a single unified hole.
Although what properties that unified
force takes, nobody has been able to
discern. So what becomes of our apple?
Unsurprisingly,
nothing good. According to our best
guesses, the apple collapses to form a
singularity, a point of infinite
density. Pretty final, or so it may
seem.
In the speculative theory of loop
quantum gravity, spacetime is discrete
and quantized at the plank scale. In
this theory, there would be no such
thing as singularities. In loop quantum
gravity, there is a smallest possible
size, a pixelation to spaceime that
prevents objects from getting any
smaller than that. So maybe our apple
would become stuck at the plank scale,
the smallest possible unit of measure in
the universe, unable to compress
further. There it would experience
forces and energies unknown to modern
science. It would have a direct view of
the quantum foam that permeates the
cosmos.
Thankfully, however, both for the apple
and our prospect of a nice midm
morninging snack, our apple is much
larger than the plank scale. At 10 cm in
diameter, over a trillion trillion
trillion plank lengths could fit side by
side across the apple. Indeed, it's so
large compared to the plank scale that
it might as well live in an entirely
different universe. It is so far removed
from the chaotic foam of quantum
uncertainty that permeates spaceime.
But that is not quite the case. But
there is a step between plank and the
apple. To build macroscopic objects, you
need a bridge. To make an apple, you
first need atoms.
We must be clear that when it comes to
atoms, language can be used only as in
poetry.
The experimenters carefully calibrated
their laser. Their target, a single
hydrogen atom in the center of the
chamber chilled to almost absolute zero.
Their goal to take its picture. First
proposed in 1981 by Russian theorists,
it would take until 2025 for someone to
finally make it work. The idea was to
hit the electrons and let them scatter
away. Then carefully measure their
velocities in a way that experimenters
could reconstruct their original
positions. Repeated again and again,
each experiment could build up one shot
at a time a portrait of the atom. And
what they saw was bizarre.
A series of overlapping rings, clusters,
and gaps. What they were mapping was not
the electrons themselves, but the waves
of probability describing where the
electrons might be. Each fire of the
laser encountered the electron in one
particular position. Then another found
it on the other side of the atom, for
example, then again and again. Where the
waves crested showed where the electron
was found most often. The gaps where it
was never found. The atom itself is
roughly 100,000 times larger than the
electron and roughly 10 ^ of 25 times
larger than the plank length. And so
already at even these subatomic scales,
we are unfathomably far from the deepest
structures in the universe.
But why is the atom this big and no
bigger or smaller? Indeed, why are all
the atoms of the same element identical
throughout the cosmos? It's as if every
skyscraper in a city was exactly the
same, made of the same materials and
roughly the same size. There must be
something universal and fundamental
about them.
Of course, the image taken in 2025 of a
real atom differs greatly from our
popular conceptions of it. A central
core surrounded by electrons circling in
their orbits. The atomic symbol is
everywhere. Indeed, it's become so
commonplace that it even stands in as
the generic symbol for all of science.
It is inaccurate and outdated, but it
did represent the first modern attempt
to understand what an atom looked like.
And the man who created that image and
started our journey to a true
understanding of why an atom is the size
and the way it is didn't get off to a
particularly promising start himself.
The young Neils Boore, who someday would
become Heisenberg's mentor and estranged
friend, was not an apt pupil in the
chemistry lab. He had a fondness for
mixing together chemicals that shouldn't
strictly be mixed, leading to explosion
after explosion. Indeed, he was an
expert at breaking glassware. And when
students would hear a muffled boom
coming from the lab down the hall, the
saying was, "Oh, that's a boar." And so,
without a doubt, it was better for
everyone that Bore turned his attention
to theoretical physics.
At the beginning of the quantum
revolution, Boore had quickly become
interested in atomic physics. He was
especially drawn in two directions. One
was the quantum ideas of Max Planck that
certain quantities in the universe could
only act in discrete lumps. The other
was the work of his mentor Ernest
Rutherford who had discovered that
whatever the atom was made of, it had a
small, dense, positively charged core, a
nucleus.
Bore wo these two strands together to
paint a first portrait of the atom. At
the center of B's atom sits the nucleus,
a tight, compact ball of positive
electric charge, agreeing with
Rutherford's experiments. But what about
the electrons? The points of negative
electric charge that exist around the
nucleus. Other scientists thought that
they might form a plum pudding, a thick
soup spread out over space. Instead, B
replaced this with mostly nothing.
B conceived of the electrons as
particles with their relationship to the
core governed by electrostatic
attraction. Their negative charge pulled
as close to the positive nucleus as
possible. But this situation should lead
to collapse with each atom unable to
hold itself together. So bore turned to
the quantum world to solve this problem.
Electrons could not get any closer to
the nucleus because their orbits were
quantized.
Unlike planets around the sun, which can
have any orbit they please, the
electrons had to choose from discrete
specific orbits. For a simple hydrogen
atom with only a single proton in its
nucleus, the nearest an electron can
approach is called the bore radius,
equal to roughly 10 ^ of 24 plank
lengths. Of course that is far far
larger than the nucleus itself which is
typically no wider than a few phentom
about 10 to the^ of 20 plank lengths.
That makes even the smallest atoms over
99.99999999%
empty space with their extent governed
by the competing relationships of
electrostatic repulsion and the
quantization of angular momentum.
And so B's model was a first step into a
quantum view of the atom. It would not
be the last.
Eventually, Irwin Schrodinger would
discover why the electrons were confined
to these orbits and not others. He was
motivated by a bold suggestion made by
the French physicist Louie De Bruy. De
Bruyne had pointed out that light had
both wave and particle-like properties.
And perhaps the same was true for
matter.
When you pluck a guitar string, the
string vibrates, but the string can't
just have any vibration. The ends of the
string are locked in place. And so the
waves must also terminate at either end.
In other words, the waves on a guitar
become quantized. Waves can have a
single peak at the middle of the string
or two peaks or four, but they can never
have half a peak or 2/3 of one.
Schrodinger envisioned the matter wave
of an electron spreading around its
orbit, like wrapping a guitar's neck in
a circle. The electron's orbit was
quantized and confined to certain
distances because its wave had to fit.
And this is the picture that was finally
revealed in the 2025 experiment. Not the
electrons themselves, but the waves that
describe them.
And indeed, this is something key when
we explore the atomic and subatomic
world.
These waves are not real in the same
sense as a wave on the ocean or the
sound waves that ripple through the air.
Schrodinger thought they were physical,
that matter smeared itself out across
space. But he was wrong. Quantum waves
are merely waves of probability.
They describe where the particle might
be located the next time we go looking
for it. Where the waves crest, we have a
good chance of finding the associated
particle. And where they shrink, the
chances are low.
And so it is therefore clear that the
subatomic world is very different to the
macroscopic one. The closer you get to
plank scales, either in terms of size or
time or energy, the more the wave nature
of reality manifests. And the farther
away you are like in the large scale
world, the more the waves are
suppressed.
Although the more we explore, the more
we are finding the line is drawn much
larger than we thought. Indeed, the
largest object that has been shown to
demonstrate a measurable wave nature is
a molecule containing around 2,000
atoms.
While the world of quantum mechanics
would eventually move on from Bor's
initial crude model of the atom, he was
right about one important thing. They
exist and have the properties they do
because of the intersection of different
fundamental forces.
If we were to imagine flying a tiny
spaceship around inside an atom, we
wouldn't see much. The vast majority of
it would be completely empty space
filled with nothing but vibrating
quantum fields. The nucleus would be a
tiny point, a dense ball of positive
charge sitting far away at the center.
The electrons wouldn't be electrons.
There would be invisible quantum waves
that should we decide to observe an
electron would snap out of existence and
give us a measurement of its location.
And so it is the electromagnetic force
competing with quantum mechanics that
gives rise to the ball radius and the
orbits of the electron. And yet, deep
inside the core of the atom, another
series of forces compete with each other
to create the nucleus.
Atoms are not as simple as their
diagrams may suggest. Their nuclei are
bundles of even smaller particles, bags
of protons and neutrons.
Neutrons, as their name might suggest,
are electrically neutral. Protons are
positively charged and the two are
exceptionally close together, less than
a few phentores apart. At that distance,
the electrostatic repulsion is roughly
50 ntons. Barely the amount of force
needed to lift a watermelon. But that
amount of force applied to something as
tiny as a proton. Clearly, the atomic
nucleus should simply blow itself apart.
And yet, it doesn't.
Why?
The year is 1934 in Osaka Imperial
University, Japan.
26-year-old Hideki Yukawa has been up
late, fixated on the mystery of why the
atom does not simply explode, just as he
has been most nights of the past few
years. He has tried dozens of attempts
to resolve the problem, but nothing
seems to work. Unfortunately, he
couldn't turn to experiments for
guidance. Like Boore, he wasn't much of
an experimentalist.
But one late night, long after everyone
else has gone to bed, he is struck with
a moment of clarity.
The thought suddenly flashed into my
mind, he said afterwards. Unbidden like
daylight clearing out the morning fog. A
new force of nature could be carried by
a massive particle which resisted the
electric repulsion and kept the atomic
nucleus stable.
Whatawa started that night would change
our entire understanding of atoms. But
the significance of the moment didn't
strike him. Once I published my paper,
he later said, I felt like a traveler
who rests himself at a small tea shop at
the top of a mountain slope.
At that time, I was not thinking about
whether there were any more mountains
ahead.
We now call this new force of nature,
Yukawa proposed, the strong nuclear
force. To pull a proton or neutron out
of a nucleus requires working against
this force, like resisting gravity to
pull an object from the surface of the
Earth. And this means that there is an
energy associated with each atomic
nucleus. All of nuclear power, from the
atomic bombs that can level cities to
the reactors that light your homes, is
based on extracting this energy. Indeed,
if we could harness the nuclear binding
energy of all the atoms in a sandwich,
it would create an explosion comparable
to several megatons of TNT or a powerful
nuclear warhead. And yet, in the full
modern picture, the binding of the
atomic nucleus isn't fundamental.
It is an accident. And that's because
the protons and neutrons aren't
fundamental either. They themselves are
small bags of even smaller particles
called quarks. And to understand these,
it is time for us to enter a place of
worship.
The central twin spires rise up
gracefully as if it were a modern-day
Tower of Babel. It is a spectacular
edifice designed to emulate a French
Gothic cathedral. Surrounding the main
structure are sculptures, a 21 ton arch
depicting broken symmetry, a moia strip,
a hyperbolic obelisk.
This is Fermy Lab, a particle
accelerator outside of Chicago. And in
1995, it was here where the last
building block of the subatomic universe
finally clicked into place.
Two teams working with the Tevatron,
which at the time was the world's most
powerful particle collider, finally
found what they had been looking for
after two decades of effort, the Top
Quark.
The Top Quark had eluded detection for
so long because of its gargantuan mass.
Indeed, it weighs over 170 million
electron volts. That's 180 times more
massive even than a proton. This huge
mass means that it takes a lot of energy
to create it in the first place and
means that it is incredibly unstable,
blinking out of existence almost as soon
as it's formed. This particle is the
king of the quarks, dwarfing the other
five. The bottom quark, the strange and
charm quarks, and the up and down
quarks.
Quarks are ruled primarily by the strong
force which binds them together through
the exchange of gluons. In fact, the
strong force is so strong that quarks
can never be seen individually. If you
take two quarks and try to separate
them, you have to pour so much energy
into the effort that new particles pop
into existence between them, including
other quarks that immediately bind to
the ones you're trying to pull apart.
And so the discovery of the top cork
locked in place our understanding of the
hierarchy of the atom and why it has the
properties that it does.
Imagine an apple the size of an atom.
Why does its core shrink to a
phentometer and why does the nearest
electron sit a nanometer away? Nature
likes to build things out of stable
foundations, out of entities that can
persist for long periods of time. And
so, atoms exist at the confluence of the
strong and electromagnetic forces and
the ironclad rules of the quantum realm,
where the balance point is reached
between all three. To begin with, there
are six quarks to choose from, but the
most massive ones destroy themselves
long before they have the chance to
build anything larger. That leaves the
lightest ones with a job to create
matter. The up and down quarks which
bind together with the strong nuclear
force to make the protons and neutrons.
The gluons that carry the strong force
have mass giving them a limited range, a
little less than a phento. But some of
the strong force leaks out of the
protons and neutrons. This residual
strong force easily overwhelms the
electrostatic repulsion between protons,
but only for a while up to a few
phentores before the gluons give out and
the electric force takes over. And it is
this that determines the size and shape
of the nucleus, the crossover point
between these two forces. Indeed, the
largest and heaviest element,
oggonesson, contains a whopping 118
protons stretching across over a
thousand phentores. It sits right at the
limit of how big a nucleus can be before
electrostatic repulsion drives protons
away. Of course, like the up and down
quarks, there are many cousins to the
electrons, but they are all heavy and
unstable. Again, only the lightest ones
survive long enough to participate in
something bigger than themselves. And so
the electron feels the attraction of the
nucleus but is prevented from reaching
it because it can only squeeze its wave
function down to a certain limit. And
that is how an atom is formed.
Out of the quantum chaos of the plank
scales comes the zoo of particles and
forces. Certain particles have certain
properties that allow them to build
things much larger than a plank length.
And in this way, an atom is built like a
bustling city of quantum activity.
But of course, the question still
remains. Why did the subatomic
particles, the quarks and electrons have
these specific masses and sizes?
This we truly do not know. It is one of
the great mysteries of modern physics.
Like explorers in an unknown jungle.
Sometimes physicists are here just to
observe and record and save true
understanding for future generations.
But of course that is not the end of the
story and far from the end of the
structures that come together at larger
scales. There are more forces of nature
and more places of convergence that make
much much bigger objects possible.
Out of the cradle onto dry land here it
is standing. Atoms with consciousness,
matter with curiosity stands at the sea
wandering. I, a universe of atoms, an
atom in the universe.
The Tribut River flows through a desert,
cutting a green swath set against the
flattop meases that make up northern
Patagonia. And in 2010, a ranch hand,
Aurelia Hernandez, was out for a walk
when he stumbled across a strange
looking outcropping. Thinking it was a
rock, he brushed away the soil to try to
clear it and kept brushing.
Eventually, he unearthed a fossilized
bone almost 8 ft long. Over the next few
years, paleontologists uncovered more
than 200 fossils at the site and one of
the largest creatures to ever have
lived.
They are called titanosaurs, and you can
see one for yourself at the Field Museum
in Chicago. Its name is Maximo, and it
stretches 122 ft long from tip to tail
and stands 28 ft tall at the head. It
lived over a 100 million years ago. And
when it walked the earth, the ground
quaked under its 70 tons of weight.
Maximo is one of the largest creatures
there has ever been, but it doesn't even
come close to claiming the crown.
The largest living fungus is found in
Malor National Forest in the Blue
Mountains of Eastern Oregon. There, a
single fungal colony spans 3.4 square
miles in area and is over 2,000 years
old. In its time here on the Earth, it
has amassed an estimated weight of over
35,000 tons. That is the biggest. But
what about the smallest? While
biologists debate if viruses count as
living creatures, there is no such
question surrounding bacteria. The
smallest known free-living bacteria is
palagibacta ubiquated as ubiquitous
oceanic bacteria with a length of only a
few hundred nanome. But despite its
minuscule size, the species is so
numerous that the total mass of all
these bacteria outweighs all the fish in
the world's oceans combined. And so life
stretches across quite a large size
range. Indeed, the leap in size between
a bacterium and the Mala National Forest
fungal colony is much greater than that
of an atom to a bacterium. And yet, when
we arrive at this scale, the scale of
life, some truly bizarre physics starts
to occur.
We know that at the smallest scales
between the plank scale and the simplest
living creatures, the universe obeys
relatively simple and straightforward
physical laws. Forces of nature do their
work over certain distances and
particles respond in turn. But there is
no equation in physics that can predict
how a bacterium might consume food or
how a blue whale might sing its song.
Standing between the laws of nature and
biological systems aren't just many
orders of magnitude. There is also an
unimaginable jump in complexity.
And this is the concept of emergence.
How simple rules can lead to
surprisingly complex behaviors. And the
best way to illustrate this is through a
game.
To begin with, imagine a series of cells
forming a grid.
Choose whichever cells you want to be
alive. They are activated. Then proceed
as follows. Any live cell with fewer
than two live neighbors dies as if by
underpopulation. Any live cell with two
or three live neighbors lives on to the
next generation. But any live cell with
more than three live neighbors also dies
as if by overpopulation. And finally,
any dead cell with exactly three live
neighbors becomes a live cell as if by
reproduction.
This is the game of life created by
mathematician John Conway.
First appearing in an issue of
Scientific American in 1970, it shows
how complexity can arise from a set of
simple rules. Indeed, two games of life
with only slightly differing starting
arrangements can lead to wildly
different outcomes with different
patterns, arrangements, and structures
appearing and disappearing and sometimes
even coming back unexpectedly dozens of
iterations later.
Conway's game of life is so complex that
it's what's called Turing complete,
meaning that it can, with sufficient
preparation, act as a fully programmable
generalpurpose computer. This means that
anything you do with the chips and
software in your smartphone can be done
with a suitably large game of life.
And emergence is a property not just of
computer games. It is found everywhere
in the real world. Just because the
world is governed by fundamental laws
and rules doesn't mean that we can use
those laws and rules to describe
everything about the world. For example,
each individual bird in a flock only
follows a simple set of rules, but the
entire flock moves in unpredictable
ways. No single ant knows how to build a
colony. And yet, a colony emerges when
enough ants get together. And it's not
just living creatures. Individual
molecules of hydrogen and oxygen are not
wet. Wetness emerges from countless
interactions among trillions of
molecules. And of course, scientists
believe that our conscious experience of
the world is rooted in the fundamental
forces of nature. And yet, we have no
way of explaining our consciousness.
And so, at some point, billions of years
in the Earth's past, molecules made the
leap from inorganic to organic. An
emergent leap that still today defies
easy explanation.
A single living organism, even a single
bacterium, is perhaps the most complex
structure to be found in the entire
universe with information, energy, and
interactions zipping up and down 10
orders of magnitude in scale. And of
course this is the scale of us of
humanity. An interplay of interactions
largely dominated by the electromagnetic
force. Electromagnetic repulsion and
attraction. The sharing of electrons as
wave functions overlap and so on. This
force binds electrons to nuclei and
atoms to each other. It pushes, pulls,
repels, draws and mixes. Atoms become
molecules. Molecules become compounds.
Compounds become living tissue. A sodium
ion penetrates a membrane in a neuron.
Electromagnetism. Your heart beats a
little faster. Electromagnetism.
The touch of a lover's skin against
yours. Electromagnetism.
And it is electromagnetism that places
limits both on how small and how large a
living creature can be.
The smallest organisms need to be
complex enough to carry out the basic
functions of life. Reproduction,
gathering of nutrients, and so on. So
there must be a minimal number of atoms
and molecules present. And as for the
largest creatures, electrical and
chemical nerve signals can only transmit
information and instructions so quickly.
Indeed, that's why the great sequoas and
fungal colonies can be so much bigger
than Maximo, the dinosaur, or the
largest blue whales. They don't have to
move or react in real time. But even
amongst these more sedate grades,
electromagnetism sets a limit and that
is through heat.
Each cell within any living creature
captures, stores and releases energy.
Like tiny little motors, each of these
processes releases a small amount of
heat and repeated again and again. There
are 30 to 40 trillion cells in the human
body alone. Every creature ends up
having to solve the problem of heat.
This is why large animals like the
elephant have huge ears and no hair to
radiate heat. The largest land animal
possible is estimated to be around 120
tons, just a little bit bigger than
Maximo for exactly this reason.
And finally, all of life mediated by the
electromagnetic force operates at a
scale so important that we defined it as
the common measure of all things.
Only a few hundred years ago, systems of
measurements were based on everyday
experience. A foot is roughly the length
of well, a foot. It is divided into 12
in because it makes it easy to create a
variety of fractions. An acre was the
amount of land a farmer and a team of
oxen could plow in a single day. But the
French Revolution wanted a better
system. This was to be a new country
based on reason, logic, and science. And
so the French Academy of Sciences
devised a new standard of length, the
meter, equal exactly to 110 millionth of
the distance from the North Pole to the
equator on a line passing through, of
course, the Paris Observatory. And in
1983, this definition was revised. The
meter was now the length of the path
traveled by light in a vacuum in 1
299,792,458
of a second. The meter was now defined
using a fundamental constant, the speed
of light, rather than measured
independently. And with this definition
in hand, we have taken the measure of
the cosmos all the way down to the plank
scale. A single plank length has to be
multiplied almost a billion billion
billion billion times to reach a meter
the standard of the microscopic world.
All of life happens in and around a
meter from the nanometer to the tens of
meters. And when we peer into the apple,
we see just how dazzlingly complex the
machinations of life are. All contained
within those scales.
Within each cell is a bustling city, a
veritable biochemical metropolis. For
defensive walls, they have a cuticle
made of fatty acids. Instead of
government offices, they have a nucleus
home to the DNA. Instead of police
officers and firefighters and engineers,
they have proteins and enzymes that go
around fixing, repairing, breaking down,
rebuilding, and warding off invaders.
And instead of power plants, they have
mitochondria, which converts sugar into
usable energy, or the chloroplasts,
which turns sunlight into sugars. And so
everything within the apple's cell is
governed by the force of
electromagnetism. And at the smallest
scales, the strong and weak nuclear
forces.
But of course, that's only three of the
four. There is still one force left to
go. For at far larger scales, scales
bigger than even the greatest living
creatures, gravity comes into its own.
Thus we come to see that if our bodies
are made of star stuff and there is
nothing else says the spectroscope to
make them of we are made of universal
and divine ingredients and the study of
the stars will not let us escape a
wholesome and final knowledge of the
fact
it is time for a road trip across the
surface of the sun.
Our craft leaves the northern polar
regions going south at a leisurely pace
of 70 m an hour, your average morning
commute. The poles themselves are
regions of intense activity as magnetic
fields twist and wind and plunge their
way down into the surface. And alongside
this magnetic activity come convulsions
of plasma as huge mountains of it half
the size of a planet rise up and
collapse in a matter of hours. Before
long on our journey southwards, we
encounter our first granule, one such
chunk of erupting sun stuff. There's
bound to be some turbulence in this
region, which spans some 1,500 km. It
will take most of a day to make the
crossing. After a few days, we reach our
first sunspot, a massive cavity opened
up in the sun as immense magnetic fields
punch down through the plasma, a yawning
chasm a thousand km deep. This one,
however, is roughly medium-sized, just
over the width of the Earth. At our
sensible speed, we will reach the other
side in a few days if we don't stop for
toilet breaks or sleep. As we crawl
onwards, we are met with prominences and
flares. Great arching structures as
magnetic fields funnel stellar material
out into space. These eruptions are
unpredictable and at their peak they can
stretch for a million kilometers or more
into the darkness before plunging back
down, taking up so much volume that they
could cradle all the planets of the
solar system in their embrace. And yet,
we've barely gotten started. At the
present pace, our craft will reach the
equator of the sun, completing a voyage
of a quarter of its entire circumference
in a little over a year.
Best to bring a snack.
Ancient people believed that the sun and
the moon were the same size. And in a
sense, they are. By sheer cosmic
coincidence, the sun is roughly 400
times wider than the moon while sitting
roughly 400 times further away. And it
is because of this coincidence that
Earth is the only planet that gets to
enjoy perfect total solar eclipses. And
yet, even at the great distance of 150
million km away, the sun is still
powerful enough to melt the ice in your
drink on a warm summer afternoon.
Indeed, it's for the best that the
millions of kilome between us are
nothing but vacuum. If the sound
produced by the sun could reach the
Earth, it would be louder than standing
next to a jet engine during takeoff,
every single second of every single day.
This is because the sun is by far the
largest object in the solar system. In
fact, from a certain perspective, the
sun is the solar system with all the
planets, including Jupiter, nothing more
than rounding errors and extra decimals
added onto the mass and radius of our
parent star. The sun alone contains 99%
of all the material in the system. A
million of our Earths could fit within
its volume. And even mighty Jupiter can
do nothing more than barely nudge and
tweak the position of the sun as it
orbits around it. Indeed, the sun is
roughly 10 to the^ of 44 plank lengths
across. The Earth roughly 10 ^ of 42.
But why is the sun so much bigger than
the Earth? Well, as with all the layers
that came before, the answer lies at the
intersection between two competing
forces.
In Sudbury, Ontario in Canada, over
2,000 m beneath the Earth's surface,
sits an unused minehaft.
No sunlight pierces these depths, just
the warmth of the surrounding miles of
rock, bringing the temperature of the
mineshaft to a sweltering 50° C. And at
the center of an otherwise empty chamber
is a strange piece of technology.
It looks like a sort of cosmic egg left
long dormant. But this was not the work
of aliens. It was built by astronomers.
And yet the instrument had no mirrors,
no lenses, no refractors. Indeed, it
couldn't even see the sky, but it could
peer right into the heart of the sun.
And in May 1999, a team of astronomers
activated it.
The observatory consisted of a geodessic
sphere containing a thousand tons of
heavy water donated to the experiment by
Atomic Energy Limited of Canada at no
cost and a market value at the time of
over $330 million.
Mounted across the surface of the sphere
were 9,600
photo multiplier tubes, each one
designed to amplify any feeble flickers
of light within the water. This was the
Sudbury Neutrino Observatory, which for
7 years watched as tiny ghostly
particles stream through it.
The observatory had been designed to
solve a decades old mystery about the
sun. At the opening of the nuclear age,
physicists had realized that fusion
powered the core of our star. Every
fusion reaction produces a neutrino, the
tiniest of the fundamental particles.
Indeed, every single second, hundreds of
trillions of solar neutrinos pass
through your body. But previous
experiments could only detect roughly
1/3 of the expected amount. Did this
mean that the sun was actually 2/3
smaller than it seemed? No, of course
not. The answer, they were in the
nutrinos.
Nutrinos come in three types known as
flavors. And unlike previous
experiments, the Sudbury Nutrino
Observatory could measure neutrinos in
two ways. It could detect just one
flavor, but it could also simultaneously
measure the total number of neutrinos
passing through. And after years of
analysis, the Sudbury Nutrino
Observatory demonstrated that neutrinos
could change flavor as they travel. This
experiment rocked the physics world and
created a mystery known as nutrino
oscillation that persists to the present
day. But it also confirmed that fusion
and fusion alone makes the sun shine.
Every single minute, the sun consumes
roughly an Earth's worth of hydrogen,
fusing it into helium in the core at a
temperature of roughly 10 million
Kelvin. Each conversion leaves behind a
little bit of mass, which translates to
a little bit of energy. Multiplied again
and again, the sun produces more energy
in a single second than the entirety of
humanity uses in a 100,000 years. And
so, as the massive weight of the sun,
the force of gravity pulls inwards,
resisting that is the energy released
from fusion, which pushes outwards as
the flood of radiation tries to escape
the core. Ever in balance, the two
forces maintain equilibrium with one
never quite winning the battle against
the other.
This balance, however, does mean that
stars can only exist in a certain range
of sizes.
At the small end are the red dwarfs.
stars so small and dim that their feeble
light is mostly in the infrared region
of the electromagnetic spectrum. The
smallest known star is EBLM J0555-57AB.
Sitting about 600 light years away, the
star is only about 88 times the mass of
Jupiter. It's right at the limit. Any
smaller and its own gravitational pole
would be too weak to ignite fusion in
its core. It's less than a tenth of the
mass of the sun. And it's so small that
it only has a radius roughly the same as
the planet Saturn. Smaller than this are
the brown dwarfs, strange hybrid objects
that straddle the ambiguous boundaries
between planets and stars. Shortly after
formation, they briefly fuse utterium in
their cores, but then they sputter out,
spending the rest of their lives merely
cooling off. Red dwarfs are by far the
most common kind of star. Roughly 2/3 of
all the stars in the Milky Way are red
dwarfs. And even the nearest star to the
sun, Proxima Centuri, is a red dwarf.
But it's so dim that it's invisible to
the naked eye.
And at the other end of the spectrum are
the true giants of the galaxy, the
largest stars.
The biggest stars are so big that it's
difficult to ascertain their true
extent. The surfaces are bloated and
extended, constantly in flux as they
swell and contract in violent spasms
that reveal their inner nuclear turmoil.
Along with that, their brightness
changes over the course of days, making
it extremely difficult to measure for
sure. And when it comes to the most
massive, most luminous, hottest star
known, analogy fails.
Sitting 136,000 lighty years away,
R136A1
lives in a satellite of the Milky Way,
the large melanic cloud, it weighs
nearly 300 times the mass of the sun and
emits so much light that it outshines a
million suns. But it's so hot that most
of its output is in the form of
ultraviolet radiation. Indeed, to the
naked eye, R136A1
is only 164,000 times brighter than the
sun. At the distance of Proxima Centuri,
just under four light years away, it
would outshine the full moon.
R136A1
exists right at the limit of the most
massive star possible. This is because
heavier stars have more gravitational
pressure in their cores. More
gravitational pressure means a higher
rate of nuclear fusion. More nuclear
fusion means more radiation. And more
radiation means more energy poured into
the body of the star. At a mass higher
than 300 solar masses, the core of any
star would produce so much radiation
that it would blow itself apart in a
furious burst of energies, something
akin to a supernova explosion at the
moment of its birth. However, that's
just the limit. Today, modernday stars
contain traces of elements heavier than
hydrogen and helium. These elements
absorb light, affecting the delicate
balance between gravity and radiation
and governing stellar sizes. But in the
early universe, the first stars had no
such limits. And astronomers believe
they may have swelled to sizes 10,000
times the mass of our sun or more.
There are only two kinds of objects
larger than stars in any galaxy and they
represent the start and end stages of
the dance between radiation and gravity
that makes them possible.
Stars emerge from giant molecular
clouds, vast complexes of gas and dust
that drift loosely through the galaxy,
barely held together by their own
gravity. When perturbed, a gas cloud
contracts under its own weight,
producing dense pockets that eventually
reach the critical densities needed to
ignite nuclear fusion. Indeed, a single
cloud has enough material to produce
hundreds and even thousands of stars.
The largest known cloud is called
Sagittarius B2, which stretches 150
lightyears across or roughly 10 the^ of
18 m and weighs 3 million solar masses.
Located near the center of the Milky
Way, Sagittarius B2 is also home to the
other largest object in the galaxy,
Sagittarius, a star.
This is a super massive black hole, the
ultimate end result of a star's life
when its nuclear fuel is extinguished
and gravity finally wins. Sagittarius A
star is the largest of the black holes
in the Milky Way, weighing a tremendous
4 1/2 million times the mass of the sun.
And so an apple the size of a star,
roughly a billion m across, would not
last very long as an apple. Almost
immediately, the force of gravity would
take over, compressing the core of the
apple to nuclear densities. Once fusion
ignites, the temperatures of the rest of
the apple would climb to thousands of
degrees, turning it into a plasma. For
millions of years, the competition
between radiation and gravity would keep
the apple at a stable size until the
light would give out and gravity would
finally win. And indeed, when it comes
to even larger scales, gravity almost
always conquers all.
almost always.
I have looked farther into space than
every human being did before me.
William Hershel was born in 1738 to
Isaac and Anna. His father was an
oboist. His brother was an oboist.
William was an oboist. Although to be
fair to William, he was more than an
oboist. He also played the violin,
harps, accord organ. He composed 24
symphonies as well as conertos and
church music. But he was also ambitious,
always scheming and plotting to advance
up the social ladder. And so in addition
to his musical pursuits, he also decided
to engage in the most gentlemanly of
trendy pastimes,
astronomy.
He built his own telescopes, ground his
own mirrors, and proceeded to make his
mark on the stars. Quickly, he racked up
achievement after achievement, including
discovering Uranus, spotting new moons
of Saturn, and recording the seasonal
changes in the Martian polar ice caps.
But this was still not enough. And as a
final crescendo to his astronomical
career, he attempted to create a map of
the entire universe.
To make this map, Hershel assumed that
the stars were all the same brightness,
and by looking in particular directions,
he would measure the total brightness,
giving him an estimate of the distance
to that location in the universe. For
the time, his map was astonishing,
revealing a picture of a flattened,
elongated universe, the precursor of our
present understanding of the disc of the
Milky Way galaxy.
If only that oboist could see the maps
we make now. And in 2022, after several
years of operation, the European Space
Ay's Gaia satellite released the largest
catalog of stars ever produced, standing
at nearly 2 billion. It was an
incredible number, and yet less than 1%
of all the stars in the Milky Way.
spanning over a 100,000 lighty years,
containing over 1 and a half trillion
solar masses of stars, gas, and dark
matter, and roughly 10 ^ of 56 times
bigger than the plank length. The Milky
Way is, as galaxies go, rather average.
Indeed, it is dwarfed by our nearest
neighbor, the Andromeda galaxy, which
hosts an estimated 1 trillion individual
stars, more than double the Milky Way,
220,000 light-years across if you
traveled at the same speed that took our
car many months to make progress across
the face of the sun. You would have to
drive for well over a trillion years to
make it from one end of Andromeda to the
other. And indeed, the largest galaxies
make even these giants seem tiny. At the
centers of galaxy clusters sit their
most massive concentrations of matter,
the brightest central galaxies. These
are the downtown cores of the cities
filled with stellar highrises and super
tall skyscrapers. The largest of these
galaxies is known as ESO 38376,
a galaxy so enormous that it defies
description except by bare numbers. It
spans 1.8 8 million lightyears in
diameter and weighs up to 10 times as
much as Andromeda. A crossing here would
take 20 trillion years, more than a
thousand times the current age of the
universe.
Galaxies are what happens when gravity,
by far the weakest of the forces, has
time enough to play
in a way at large enough scales. No
other fundamental force matters. The
universe is on balance, electrically
neutral, and so the electromagnetic
force holds no influence. And the strong
and weak nuclear forces are limited to
subatomic scales. They can't influence
anything beyond their minuscule borders.
And so in terms of fundamental forces,
gravity, and only gravity shapes the
grandest structures in the cosmos. All
it takes is time. The gravity may be
weak, but it is persistent.
All it takes is the tiniest seed. A
small difference in density. That small
seed will attract its surroundings,
helping it grow. With even more mass,
the pull becomes stronger. More and
more, the rich, growing richer. Over
millions and billions of years, the
universe assembled the galaxies out of
the thin uniform fog of the primordial
cosmos.
And gravity is not yet done. For beyond
the bounds of the Milky Way galaxy sit
structures that seem to embrace the
heavens themselves. Grand walls and
glittered canopies spanning tens of
millions of light years on a side. The
culmination of billions of years of
gravitational effort.
Surrounding the Milky Way is a ring of
12 galaxies, each sitting roughly 12
million lightyears away. These galaxies
are the nearest portion of the local
sheet, the Great Wall in which our
galaxy is embedded. Indeed, they are
simply the nearest edge of that sheet,
but their circular arrangement around
the Milky Way has inspired astronomers
to give them a name of their own, the
Council of Giants. And in July 2020, an
international team of astronomers
discovered something even larger. Using
archival data from the Spitzer Space
Telescope, the team managed to pick out
dim galaxies peeking through the
so-called zone of avoidance, the region
of the wider universe that sits beyond
the dense veil of nebulous gas in the
core of the Milky Way. Through there,
they identified a structure almost
beyond description
called the South Pole Wall. It is a
filament of hundreds of thousands of
galaxies extending for over 1.3 billion
light years from end to end. To get a
sense of its extent, its ends are
anchored behind constellations in two
different hemispheres. Perseus in the
north and telescopium in the south,
which are a full 145° apart, nearly on
opposite sides of the sky. If we were to
drive the full length of the South Pole
wall, it would take a million trillion
years, and it might be bigger. The
astronomers involved in its discovery
admit that they don't know if they've
completed their survey. "We are early
explorers of the cosmos," said lead
astronomer Brent Tully of the University
of Hawaii, extending our maps into
unknown territory.
And so just how big is the entire
universe? So far with our most powerful
galaxy surveys, we've mapped out some 10
million galaxies of the suspected 2
trillion that inhabit the observable
universe. We know that these galaxies
twist and lace their way through
filaments, intersecting at clusters and
tracing a pattern that resembles a
gigantic spid's web. This cosmic web is
the largest pattern found in nature,
filling up the observable universe from
end to end with massive voids left
between the glittering braids. And
pocking the cosmic web at these vast
distances are subtle imprints. They're
invisible to the eye and only reveal
themselves as shells of slightly higher
galactic density. These are the leftover
echoes from when massive sound waves
crashed around the very early universe.
They are called barionic acoustic
oscillations or BAOO. A single BAOO
shell can be up to a billion lightyears
across.
Just like the galaxies and the cosmic
web, the size of the universe is
determined by gravity. Indeed, the
contents of the universe set the
expansion rate and the time since the
Big Bang. The rest is history.
But the true extent of the universe is
unknown.
Indeed, for centuries, astronomers had
believed the universe to be infinite.
But of course, in an infinite universe
that is also infinitely old, no matter
where we look, we should see a star.
Even accounting for the relative
slowness of the speed of light at cosmic
scales, with enough time, the sky should
be ablaze everywhere with infinite
light, even in the depths of night.
And with the revelations of the big bang
theory, we discovered that the universe
we can interact with is not infinite. It
has an age. And because of that age, it
has a limit. The universe is only so
old. The speed of light only so swift.
The sky is not illuminated with the
light of infinite suns because the
universe is not infinitely old. In fact,
the expansion of the cosmos carries
galaxies away from view permanently.
At great distances, the recession of
distant galaxies can exceed the speed of
light. We can still see other galaxies
for now, but that's because their light
left long ago. By the time their light
reaches the Earth billions of years
later, the galaxy is long gone from
view, carried away by the inexurable
cosmic expansion.
And so the entire universe could be
infinite. Perhaps we will never know.
Like a lantern lit in a dark forest, our
entire existence is defined by this
sphere of feeble and flickering
illumination.
That sphere is 93 billion lightyear or
roughly 10 ^ of 62 plank lengths in
diameter.
That is the distance to the edge of the
cosmological horizon, the largest
possible scale that we could ever
measure in the universe.
And all that exists on these largest
scales, from the galaxies and the cosmic
web to the ultimate horizon of the
universe itself, was dictated long ago.
For gravity may control the fate of the
universe and be the invisible hand that
sculpts the great creation, but it was
not the instigator. It was not what set
it all in motion. And this is linked to
the biggest mystery in the universe. For
at roughly 100 mega parex or so, the
universe evens out with no larger
structures or differences from place to
place within the cosmic web. This is
called the scale of homogeneity or
somewhat more dramatically the end of
greatness.
This is the mirror image of the plank
scale. Roughly 10 to the power of 59
times larger than its twin, the other
end of the universe.
At the plank scale, reality is nothing
but chaos. At the homogeneity scale,
everything is the same.
Why?
At the very earliest epochs in the
universe, when the entire observable
universe was compressed to scales even
smaller than the plank length, unknown
forces were in action. They set the
universe in motion and through quantum
creativity wrote a story that would be
told over the coming ages. And we call
this event inflation. This is a
hypothetical period that occurred when
the universe was less than 10 ^ of - 35
seconds old. And it was over and done
with by the time the universe turned 10
the^ of - 34 seconds old. In that
briefest flicker of time, the cosmos
became much, much larger, growing in
size by at least 10 ^ of 50 orders of
magnitude, reaching the comparatively
dizzying proportions of an entire atomic
nucleus. And so inflation made
everything bigger, even the quantum
fluctuations that only exist at the
plank scale. Now made microscopic, those
fluctuations imprinted themselves on the
fabric of spaceime, leading to pockets
of slightly higher density scattered
across the vast expanses of the
universe. And these were the seeds that
started it all. What would follow would
be the weaving of the cosmic web itself,
the smallest possible fluctuations in
the universe, intimately connected
through strands of gravity, to the
largest pattern in nature. And this is
the homogeneity scale. These quantum
fluctuations blown up to countless
trillions their original size and
averaged out across the cosmos.
And so now for the final time we can
return to the apple.
An apple at this scale would completely
change the course of cosmic evolution.
It would take eons to play out as
sections of the apple splintered off and
collapsed in on themselves, slowly
imploding under their own weight to
become galaxies in their own right. But
a cosmic scales, a balance would shift.
The present-day universe is ruled by
dark energy, a mysterious force that is
accelerating cosmic expansion. But even
if we were to eliminate dark energy, or
if it were to fizzle out and disappear,
the expansion would not stop. There's
simply not enough matter with enough
mutual gravity to halt expansion.
Indeed, the universe is achingly thin
with an average density of just one
hydrogen atom per cubic meter. An apple,
however, is far far denser than that. An
apple tens of gigapix across would be
more than enough to slow cosmic
expansion, to halt it, and even reverse
it. The future universe would then be
smaller than the past. The Big Bang
turning into a big crunch with the end
point a singularity of infinite density.
The same mysterious state that gave
birth to the cosmos 13.8 billion years
ago.
We do not know why the universe is the
way it is, why it's filled with so much
matter and so much dark energy. The
present- day universe could have been
much smaller or much larger had anything
been different in those early quantum
forges.
There are only four known forces in the
universe and three generations of each
of the particles. Together they dance
and weave and intersect, sometimes
colliding, sometimes colluding. At the
smallest of scales, all the forces melt
together into an incoherent mess. And at
the largest, only gravity remains.
In between is everything else. The
atoms, life, the stars, the galaxies.
Each one bound by a set of rules that
governs their respective domains.
And so perhaps that is the secret as to
why the apple and us is at the center of
the 62 orders of magnitude that span
reality.
We sit at the confluence of all the
forces of nature. Each one working in
its own way to influence what happens
here on the surface of the earth. At the
smallest quantum scales, gravity holds
no sway. At the largest, the other three
fall silent. But here on the earth, at
scales of roughly a meter, everything
comes together. The strong nuclear force
binds together the atoms. The weak
nuclear force transforms them and
creates the table of elements.
Electromagnetism holds electrons in
their shells and glues the atoms
together to make molecules and the dance
of life. And finally, holding everything
together is gravity, giving us a solid
foundation under our feet and an anchor
for our oceans and air.
All the forces of nature across all 62
orders of magnitude that measure
existence work together right here at
the apple, the center of the universe.
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