The first sign would be small.
Through a telescope, a single star would
appear to split in two. Perhaps it would
be dismissed as a mistake, an oddity
caused by a problem with the lens. But
then a few nights later, telescopes
across the globe would spy the same
thing. Detectors around the world would
notice increased levels of cosmic, UV,
and gamma rays. Something energetic
would be detected happening in the
nearby universe.
Then would come the rumbling. To begin
with, it would be subtle, noticed only
by gravitational wave detectors. Strange
ripples in space fitting no known
template. An invisible approaching
threat.
But in time, we would see it stretching
from one horizon to the other. As if it
cut the universe in two, it would pulse
with exotic energies. When it whipsled
onto itself, it would create an
explosion brighter than a supernova. And
indeed, by the time it became visible to
the naked eye, it would already be too
late.
The universe holds close its dark
secrets. Beyond the boundaries of the
known and familiar, past the protection
of the sun, and the circling embrace of
the Milky Way, lie relics of its ancient
past, remnants of the Big Bang itself.
There are defects in the cosmos, and
they have been here a long, long time.
They were there in epochs of fire and
unification at the beginning of
everything. The long eras of splintering
and fracturing, the chaos and violence
before the universe as we know it took
its final shape. They appear in our
theories. We give them names. We assign
them properties. We ask how they might
survive to the present day. How we might
detect them through a subtle signature
in this or that survey. We tell
ourselves we are safe.
But perhaps we are wrong.
anyes.com to try this premium remote access tool free of charge.
We live in a broken universe and in 1983
physicists revealed a more perfect one.
The laboratory was called Underground
Area 1. It sat outside the main
detection chambers of CERN, the
collection of massive particle colliders
situated at the border of France and
Switzerland. The main detector consisted
of a series of cylinders almost 6 m long
and over 2 m wide filled with ultra pure
neutral argon and ethane gases. A
complex zigzagging of 17,000 wires and
over 6,000 sensors tracked the
three-dimensional movement of any
charged particles as they raced through
the chamber. After years of development,
the team at UA1 had hacked together a
new kind of collider, one that combined
protons and anti-rotons together at
nearly the speed of light. With the
machine in operation, the particles
raced around kilometers of circular
track, accelerating to higher energies
with each pass, coming within
centimeters of each other. Finally, at
the last moment, right at the very
limits that the accelerators could
achieve before their beams of particles
drifted off course, the engineers
initiated a carefully orchestrated
sequence of events that brought the twin
beams into collision precisely within
the UA1 chamber.
And for the barest fraction of a second,
when the energies peaked and the
collision ignited to its maximum
intensity, a pure infant universe was
born.
This new universe was unbroken,
symmetric. Strange particles sprung into
existence. the wires and detectors of
the chamber briefly registering their
exotic presence before they flashed
away.
But this was no portal into another
dimension.
It was a window into our past.
Few people anticipated what would happen
on that fateful day in 1983.
Some of them, like Peter Higgs, are well
known today with their names attached to
Nobel prizes and international
recognition. But some stayed out of the
limelight, content to do their work
regardless of the promise of fame.
By all accounts, Sir Thomas Kibble was
the gentleman's gentleman and the
scientist's scientist. He was kind,
gregarious, and dignified. He delighted
in his work, in the camaraderie of his
peers, and his ventures into the
frontiers of physics. Indeed, in 2013,
when Peter Higgs was awarded the Nobel
Prize, he expressed regret that Kibble
was not joining him. And yet, when asked
his own opinion, Kibble simply shrugged.
He was happy with what he had
accomplished, he didn't need a gold
medal to reap his rewards.
But what was it that he had found? What
was it that was confirmed in the fires
of CERN in 1983?
The theory of the Big Bang tells us that
the universe was smaller, hotter, and
denser in the past. Billions of years
ago, the entire observable universe had
a temperature of over a quadrillion
degrees and was compressed into a volume
no bigger than a peach. And Peter Higgs,
Tom Kibble, and others discovered that
at those insane energies, what we call
the forces of nature take on an entirely
different form.
There are four fundamental forces that
control everything within the universe.
Gravity, electromagnetism, and the
strong and weak nuclear forces which
operate at atomic scales. At least there
are usually four. For at high enough
energies, we know that two of these
disperate forces merge together into a
single unified hole. At extreme enough
energy scales, there are no longer four
forces of nature. There are only three.
gravity, the strong force, and the
electroeak force.
This is a symmetry of nature exposed
only at incredibly high energies. The
electromagnetic and weak forces become
two sides of the same coin. The same way
we view electricity and magnetism as two
sides of electromagnetism.
But this symmetry is broken in the
everyday cosmos with some mechanism
driving a wedge between them, making
them appear and act as completely
different forces.
And it was Higs, Kibble, and others who
figured out how to create that wedge
through the introduction of a new
particle field, now named after Higs,
the Higs Bzon.
At high enough energies, the Higs Bzon
is in an unstable but symmetric state,
like a pencil balanced on its tip. But
at low energies, the Higs Bzon devolves,
collapsing into a more stable
equilibrium. However, like a pencil
falling over, that equilibrium is no
longer symmetric. It is the broken
symmetry of the Higs that separates the
weak from the electromagnetic force,
enabling their wildly different
properties. And there only two places
where the more perfect union of the
forces is restored. One is in the heart
of our most powerful particle colliders,
just as scientists at CERN achieved in
1983. And the second is in the earliest
moments of the Big Bang.
But for Kibble, that was just the
beginning. What if this process of
symmetry breaking was not perfect?
And this is when he became interested in
something called phase transitions.
Phase transitions occur when a substance
transforms itself due to changes in
temperature or pressure or density.
freezing, melting, evaporating. The
cycles of water on our planet, from the
dew glistening in the morning sun to the
ice clinking in your glass, are all
examples of phase transitions of water
from one form to another. But it's not
only gases, liquids, and solids. As
another example, within an extremely
dense kind of star called a neutron
star, some atoms are crushed so tightly
together that they transition into a
whole new form of matter dubbed nuclear
pasta by physicists.
Gibble, however, wasn't interested in
your run-of-the-mill phase transition.
He was interested in the kind where
symmetries break.
If you let a pencil fall from its tip a
thousand times, you'll end up with a
thousand different results. Each one is
equally in equilibrium, yet utterly
unique. And yet, at the same time, even
though the unique pencil directions are
all different, it doesn't really matter.
The pencil is lying on the table. The
physics of the situation remains
unchanged.
And so when we turn on a particle
collider and achieve the unification of
the forces, the symmetries between the
weak and electromagnetic forces
manifest. The two forces become one. But
when we turn it off, the hig boson falls
back into a low energy state, one of an
infinite number that it could choose.
Yet it doesn't matter which one. Like
the pencil on the table, what matters is
the asymmetry that breaks the
unification of forces, not the actual
choice of low energy state. And so when
the universe cooled from the hot big
bang within the first nancond of
existence, the Higs Bzon chose a
particular low energy state across the
entire universe.
Or maybe it didn't.
For Kibble worked his way through the
maths of the phase transitions of the
early universe, he realized that the
breaking of the fundamental symmetries
didn't necessarily have to proceed in a
smooth orderly fashion with the entire
cosmos acting in synchronicity as it
cooled off. Some regions may have stayed
hotter a little longer than others. Some
may have experienced random quantum
fluctuations in one direction or
another. No matter what, the Higs Bzon
collapsed. That was certain, but it
could have collapsed in different ways
and at different times as the universe
evolved.
And so Kibble dug a little bit more.
When you freeze a bit of liquid water,
its molecules fall out of a symmetrical
state into an asymmetrical one. A drop
of liquid water looks the same
microscopically at least, no matter how
you look at it. But an ice cube is
different. The water molecules lock up
with each other in regular geometric
patterns. A crystal latice that
transforms the liquid into a solid. But
different parts of the water will freeze
out at different times. The geometric
patterns the molecules form may line up
in different directions. Like one
regiment of soldiers coming to attention
facing one direction and another
regiment facing somewhere else.
Within each region, everything is as it
should be. The water is in its lowest
energy state. The symmetries of liquid
have been broken. And your interaction
with the ice cube, say for example,
putting it in your drink stays the same.
But where these differing regions meet,
a fault line appears. A defect. Kibble
couldn't help himself. He knew of the
analogy of water crystallizing into ice
and applied the same mathematical
techniques to explore what happened in
the early universe.
What he found was a monster. One more
ancient than the galaxies and stars. One
born in the very fires of creation.
When the universe cooled from its
pristine symmetric state, the Higs Bzon
fell from grace. But perhaps in one
region of the universe it fell to one
particular low energy state and in
another region another low energy state
and in yet another yet another low
energy state and on and on and on
repeated again and again throughout the
cosmos.
No matter what the Higs Bzon did its
job. The weak and electromagnetic forces
would never be twinned again. The rest
of physics would proceed regardless of
where in the universe that physics
occurred. But where those regions met,
cracks appeared in spaceime itself.
Topological defects, flaws in the
foundation of the universe.
These would be places where the cosmos
could not reconcile with itself with the
Higs Bzon reaching different states on
opposite sides of the fault line. Kibble
named them cosmic strings, and they were
perhaps the most exotic object that the
universe has ever produced before or
since.
They would have finite width, no more
than a proton, probably less, but
definite spatial extent. They would be
objects of intense trapped energies,
energies that manifested as a mass. And
they would also be incredibly long,
stretching from one end of the universe
to the other, growing along with the
expansion of the cosmos.
And finally, Kibble realized that they
would not be mere features that would
simply appear in space. Unlike the
cracks inside an ice cube or the
boundaries between domains of a magnet,
these cosmic strings were alive.
They would vibrate, curl, loop, and
dramatically interact with the rest of
the universe in curious, powerful, and
violent ways.
Kibble had unleashed something new. A
lost ancient creature, one from distant
days of eras long past, one that could
only be fashioned in the exotic cauldron
of a newborn universe. One that had the
power to create and to destroy.
A cosmic string is unlike anything in
the entire universe because the modern
universe is not capable of producing
them. They could only be made once when
the universe was less than a second old.
Indeed, Kibble found that most of them
probably died dissolving in flashes of
furious energies,
but some of them may have survived
even to the present day. And to
encounter one would be to come face to
face with the oldest creature in the
universe.
The Balrog is a survivor from the
legends of the first age. primeval
spirits of destroying fire, chief
servants of the primeval dark power.
They were supposed to have all been
destroyed, but it is here found that one
had escaped.
In JRR Tolken's hugely popular The Lord
of the Rings, published in 1954, the
heroes of the book encounter a monstrous
creature deep underground. a creature
that has survived from before the world.
This creature is known as a balrog. And
within the mythology of the series, they
are monstrous relics from an age long
before, with some surviving to the
modern day, buried away in the depths,
hidden from view. Yet within the
narrative of the book, the greed of the
dwarves leads them to dig deep into the
earth in search of gold. And they
reawaken this ancient threat.
And so, as with Tolken's cautionary
tale, perhaps we too have dug too deep
in search of answers, unearthing our own
cosmic balrogs.
13.8 billion years ago, in the fires of
the Big Bang, atoms formed out of the
mist. From the primordial blast of
energy, quarks appeared and then shaped
themselves into protons and neutrons.
After roughly a minute of existence,
these protons and neutrons found each
other and formed the first atomic
nuclei. And roughly 380,000 years later,
electrons were freed to join. But of
course, there were also other particles,
too. A whole zoo of them. Different
types of quarks not included in the
atoms. Three types of neutrino, the muon
and ta leptton, and dark matter. And all
of that went on to form all of what we
see. the stars, planets, galaxies, and
nebula that dot the heavens. But that
was not the only zoo that was formed in
the fires of creation. For there was a
second one, an even older one that ruled
in the first instances of reality, less
numerous, but no less powerful, formed
from the very architecture of the
universe.
And so let us begin to understand this
managerie of monsters by exploring
cosmic strings.
A single cosmic string would be no wider
than a proton and probably orders of
magnitude thinner. And yet it would
stretch longer than a galaxy. Indeed, in
some cases, the strings may reach from
one end of the observable universe to
the other. a single unbroken strand of
pure energy reaching tens of billions of
light years in length. And this is
possible because a cosmic string isn't
really made of anything. The same way
that a fold in a piece of paper isn't
made of anything. They are just both
objects of topology, defects. Their
interior regions may be pure vacuum. Or
they may contain the state of the
universe as it was before the weak and
electromagnetic forces split apart. In
other words, cosmic strings may contain
the conditions of reality that we can
recreate with our most powerful
colliders, but stuck in their ancient
state as if frozen in place.
A perfectly straight length of cosmic
string will exert no gravitational
influence on its surroundings. You will
never be pushed from a cosmic string nor
pulled towards it. But you will see it.
We do not yet know exactly how a cosmic
string might interact with the rest of
the particles and forces of the
universe. It might glow brightly, a
constant outpour of X-ray and gamma
radiation. It might create a shower of
exotic particles on its outer surface.
Exotic particles that then quickly decay
into cascades of fastmoving electrons
and neutrinos.
But even if the string itself is silent,
if this defect from another age is
content to lay dormant and not reveal
its secrets to the wider universe, it
can't help but move.
This is because a cosmic string has no
matter to call its own. It's not made of
particles or concentrated radiation.
It's not built from anything. It only
exists as a floor. But still it holds
together as the rest of the universe is
always trying to repair that defect and
restore the normal functioning of the
cosmos throughout space and time. This
gives cosmic strings tension, enormous
tension. And since tension is a form of
energy and energy is a form of mass,
then the strings have incredible weight.
The exact number depends on the type of
theoretical physics you use to build a
cosmic string. But in typical models, a
single cm of string weighs more than 10
to the power of 16 tons. That means 1
kilm of cosmic string outweighs the
entire earth. A cosmic string a billion
lightyears long would weigh a thousand
trillion solar masses, dwarfing even the
heaviest galaxy cluster.
and all that mass without any
gravitational influence at all. It
wouldn't draw anything towards it. In
fact, if the string doesn't otherwise
glow or emit particles, then you'll have
little evidence for its existence
except for one trick.
If you happen to travel around a cosmic
string returning to the precise position
of where you started, you will find that
you have not traveled a complete circle.
Because strings are defects in spaceime,
they act as a wrinkle, distorting the
topology of their surroundings. And so
circles around them do not add all the
way up to 360°.
Although, if the string is in motion,
then it has other ways of making its
presence known. Ripples and vibrations
travel up and down the length of the
strings at the speed of light. Sometimes
kinks will appear which flash away in a
storm of energies. Sometimes the strings
tangle themselves up in loops and knots.
And when they cross, the strings pinch
off, dividing into two. Closed loops of
strings vibrate with resonant
frequencies. And with nowhere else to
go, they emit enormously strong
gravitational waves. Indeed, if the
conditions are right, they may also
explode as powerfully as a supernova
blast, releasing this energy in the form
of familiar high energy particles and
radiation. However, we do not yet know
if this process of tangling and
vibrating itself to death leads to a
cascade that infects the entire cosmic
string. Such back reaction calculations
are too difficult to lead to solid
conclusions. We don't even know how
destructive they might be, although we
do know that due to their density and
tension, they could easily slice through
the earth like a hot knife through
butter.
But most importantly of all, we just
don't know if cosmic strings produced in
the chaotic fires of the primordial
universe could have survived to the
present day. Yet, even if they have not
lasted to our time, they are not
predicted to be the only children of the
phase transitions that rocked the early
universe. There might be a small zoo of
bizarre space-time defects out there for
us to encounter.
Cosmic strings are essentially
one-dimensional. They have finite width,
less than a proton or so, that stretch
for up to tens of billions of light
years. They're caused when multiple
domains of phase transitions meet
together and cannot reconcile their low
energy states. But that's not the only
way for these domains to meet. Alongside
the cosmic strings, there were other
even more exotic creations.
two-dimensional walls that stretched and
vibrated with their enormous tensions.
Thankfully though, most of these
disappeared quickly as they couldn't
hold themselves together in the face of
cosmic expansion. Although some
proposals have surfaced that cosmic
inflation could have stretched these
brains to become big enough to span the
universe and remain stable.
And then there were the zerodimensional
defects. The punctures, the holes, the
places where tension wrapped itself up
into a singular point.
These were the monopoles.
In 1931, Paul Drack, one of the founding
fathers of quantum mechanics, made a
simple and unexpected realization. He
saw that just like anything else in the
universe, electric charge must be
quantized.
This meant that all charges in the
universe were some multiple of a single
fundamental quantity. Meaning that at
least one magnetic monopole must inhabit
the universe. We know that electricity
and magnetism are really two sides of
the same coin. They are mirrors of each
other. But there is one way that this
mirror is not perfect. Electric charge
comes in two varieties, positive and
negative. And magnetic poles also come
in two flavors, north and south. But
positive and negative charges can exist
independently of each other. You can
separate them, isolate them, and combine
them as you please. But if you take a
magnet with north and south poles and
chop it in half, you don't get separated
north and south poles. Instead, you get
two mini magnets, each with their own
pair of poles. But the early universe
did not follow the rules of the modern
one. The exotic physics and chaotic
phase transitions may have generated
enormous numbers of particles that could
carry singular magnetic poles. Particles
with isolated north or south.
Monoples became such a generic
prediction of theories of the early
universe that they actually became a
problem. There were none to be found.
And so in 1980, it was Alan Guth who
figured out a way to slay these ancient
beasts.
He came up with the entire concept of
inflation of the very early universe.
undergoing a process of rapid
uncontrolled exponential expansion with
the express purpose of making the cosmor
so large that the monopoles once
prolific would be so diluted so as to
render them essentially undetectable.
But were we to find one, a monopole
would cause chaos. They predicted to be
huge, up to hundreds of times more
massive than any of the familiar
particles of the standard model. and
their strong magnetic charge would
disrupt normal matter by ripping
electrons out of atoms as they passed.
Although they wouldn't stick around for
long, they could be easily accelerated
by even weak magnetic fields, quickly
reaching velocities approaching the
speed of light.
And finally, there was one more gremlin
born in the flames of the naent cosmos.
In 1976, at the same time that Tom
Kibble was digging too deep into our
cosmic past, Steven Hawing took his own
glimpse into the fires of the Big Bang.
But his objects of interest were much
smaller than cosmic strings, though they
were far more numerous. We know of only
one way to make black holes in the
modern universe. And that's through the
death of a massive star. That's the only
way to reach the pressures, densities,
and gravitational might needed to
compress a lump of matter below its
spart shield limit. But that's just the
modern universe with its relatively calm
rules and laws. The early universe might
have been so chaotic, so turbulent and
so energetic that black holes may have
spontaneously appeared as local energies
reached a catastrophic crescendo,
collapsing entire regions of spaceime
into singularities.
The modern universe cannot make a black
hole smaller than a few solar masses,
but these primordial black holes could
have had masses as small as an asteroid.
And as with cosmic strings, they would
not be content with sitting in the
background.
They emit radiation ever so slightly due
to complex interaction between their
event horizons and the quantum fields
that soak through spaceime. This
radiation causes them to shrink and
eventually disappear altogether.
And the smaller the black hole, the more
it radiates. That means that these
primordial black holes would have been
small enough that their lifetimes may be
equivalent to the present age of the
universe. In other words, they should be
exploding right now.
Hawking proposed this idea as a new
avenue to discovering black holes as
their evaporation should register as
explosions dotting the sky. And so we
watch and wait to see if we can catch a
glimpse of the deaths of these ancient
creatures.
cosmic strings, domain walls, magnetic
monopoles, and primeval black holes.
Ancient monsters that push the limits of
our understanding of physics. And yet,
physical proof has been practically
non-existent for all four. For now, the
space-time zoo is firmly theoretical.
Although, arguably, most of all, cosmic
strings have the highest probability of
being found. And indeed, were they to be
found in the way that we hope, their
discovery would have huge ramifications
for our understanding of how the
universe works.
A theory of everything.
Sometimes space time creates phantom
clones.
First predicted by Einstein in 1912 and
even hinted at by Isaac Newton 250 years
before. Gravitational lensing is what
happens when light bends around the
gravity well of a particularly massive
object on its way to our telescopes.
This distortion can lead to beautiful
oddities in the sky. Galaxies bent like
liquid around other galaxies. Distant
objects seemingly quadrupled.
Collections of stars stretched thin like
spaghetti. And in 1979, a team of
astronomers at Kit Peak National
Observatory in Arizona found one of the
first gravitationally lensed objects,
the distant quazar QSO0967561.
The quazar consisted of two nearby
components with extremely similar
features. Immediately it was clear the
two components were really two images of
the same quazar with its light getting
split into different paths by an
intervening massive object. Indeed, the
difference was substantial. Light from
one of the components arrived at the
Earth about 14 months later than the
other. And yet there was a problem for
there was no nearby galaxy massive
enough to explain that large of a
separation. So what else could it be?
Speculation began. Was this the sign of
a cosmic string wandering between us and
the quazar? A single floating cosmic
string could make its presence known
through its gravitational distortion.
While it has no gravitational push or
pull, it still bends spaceime around it.
And so if you were to look at a distant
star or galaxy and a cosmic string was
sitting between you and the target, the
light from the distant object would get
split. two paths of photons wrapping
around either side of the string. And so
some physicists speculate that this is
what is happening with QSO 0967561,
but to date have failed to turn up any
additional evidence.
Though that is not the only method
experimentalists have explored that uses
Einstein as a guide.
In 1916, Einstein also proposed the idea
of gravitational waves, ripples in
spaceime that would be caused by massive
gravitational events. As with their
cosmic cousin, gravitational lensing,
gravitational waves would not be
detected experimentally until many
decades later, coming from a black hole
merger spotted by the hypers sensitive
lasers of the LIGO telescope. And yet,
we don't always need to create super
sensitive machines to detect these
ripples in spaceime. Sometimes the
universe offers its own measurement
devices.
Pulsars are the husks of dead stars and
they produce beams of radiation from
their north and south poles. They also
spin at a remarkably consistent rate. We
detect them on Earth like a pulsing
lighthouse as their beams wash over us.
And in 2023, the International Nanog
experiment released its 15-year data set
of the timing of 67 pulsars across the
sky, revealing variation in the
regularity of their spins. And using
this, the astronomers were able to
provide strong evidence of a
gravitational wave background across the
universe, ripples in spaceime itself
that it affected very slightly the speed
of the rhythm of the pulsars when they
arrived to Earth. Like a ship taking
longer to arrive in rough seas, the
speed of the light received from the
pulsars had been very slightly altered
by the gravitational peaks and troughs.
There are many proposed sources of this
sloshing background of gravitational
waves and cosmic strings are one
possibility, although arguably not the
forerunner. Indeed, either are papers
speculating it could be domain walls or
simply more black hole mergers. And so,
the hunt for a definitive signal goes
on. To quote cosmologist Eugene Lim, "If
we discover cosmic strings, it'll be the
result of the century." But to quote
Carl Sean, "Extraordinary claims require
extraordinary evidence. And right now,
the evidence is a bit thin." Indeed, it
is true that no cosmic strings have ever
been found conclusively despite decades
of tantalizing evidence. They certainly
don't exist in abundance. Otherwise,
they would have shown up in the cosmic
microwave background and in the cosmic
web. But we also still haven't been able
to rule them out. And so, how else could
we search for them?
Perhaps some believe the greatest living
physicist may hold the answer.
In 1990, chit chatting between sessions
at a physics conference, I asked
attendees who is the smartest physicist
of them all. Several names kept coming
up, but mentioned most was Witten. He's
often likened to Einstein, but one
admirer reached even further back for a
comparison, suggesting that Witten
possesses the greatest mathematical mind
since Newton.
Ask any physicist about Ed Witten, and
you'll immediately see the cult-like
devotion he has earned. Stories about
him echo through the halls of academia
and quotes a tenner penny even from
legends themselves. Roger Penrose says
of him in his book where Witten goes it
does not take long for the others to
follow. He picked up mathematics at an
early age like many scientists but
unlike many scientists he became so
bored with it that he pursued other
endeavors. In the end he became a
history major and dabbled in politics.
And so it was only in 1973 that he
entered graduate school at Princeton in
their applied mathematics program. And
then somehow, nobody's exactly sure how,
this history major ended up working with
David Gross, a giant in his own right,
who would go on to win a Nobel Prize in
physics. From there, Witten began to
work. Indeed, his genius, even amongst
fellow geniuses, was unparalleled. It
said that Gross would give him an
assignment, expecting it to take months
only to have a solution returned to him
the next day. His colleagues would spend
years becoming experts in their domain
only to become second place in less than
a week when Witten learned of the idea.
We know a lot of things, he once said,
but what we don't know is a lot more.
And so naturally, when Witten first
encountered the concept of cosmic
strings in the 1980s, he saw nothing to
fear. Instead, he saw opportunity.
For when Witten first learned about
strings, he didn't think of them as
cosmos defying forces of ancient
physics. Instead, for him, they were
much, much smaller. It was in the 1980s
that physicists realized that string
theory was a candidate for a theory of
everything. that there was a slim
possibility that all forces of nature
and the entire zoo of fundamental
particles could be explained by tiny
vibrating strings. These strings were
small, no bigger than the plank length,
but they vibrated at different
frequencies with each frequency
corresponding to a different kind of
particle or force. But the strings of
string theory were hopelessly out of
reach of both theory and experiment. No
mathematical tool could make firm
predictions as to how the strings
manifested into the multitude of
particles in the universe. And no
particle collider, no matter how
powerful, could ever reach the energies
necessary to directly probe the scale at
which the strings exist. Bar one that
spanned the entire length of the solar
system and beyond. So, how could we
study something that was too small to
ever be seen? Witten realized that the
universe may be able to do it for us.
He was the first to realize that there
might be a surprising connection between
the cosmic strings of phase transitions
in the early universe and the super
strings of his beloved string theory.
And that connection was inflation. The
splitting of the forces just after the
big bang didn't only usher in a phase
transition. It may have also led to an
explosion in expansion. Indeed, if the
theory of inflation is true, in less
than a nancond, the entire universe
expanded to over 10 to the power of 62
times its original size. And in that
inflating universe, everything got
bigger. The subatomic became
macroscopic.
Extremely minute variations in spaceime
would stretch to become the seeds of
gravity that would allow structure to
grow. And in this chaos, Whitten
realized that planklength superstrings
might be able to become cosmic
superstrings blown up countless
trillions of times in size. And so, if
we were able to find a cosmic
superstring, a macroscopic manifestation
of the theoretical underpinnings of
reality written across the sky, it would
provide an unprecedented view into our
most difficult physical theories. We do
not know how to proceed in string theory
as the calculations have proven to be
too complex. But if we had direct
experimental access to one, we could
train our observatories on it and learn
its secrets.
Cosmic superstrings would still be flaws
in spaceime, but of a slightly different
character to regular cosmic strings.
Although Witten's calculations showed
that most of them would evaporate away
shortly after inflation, but he also
found that some might get stuck.
String theory predicts that there is
more to the universe than our usual four
dimensions of spaceime. For the theories
math to work, it requires additional
spatial dimensions. But the universe we
experience is obviously not
extradimensional. So these extra
dimensions have to be tiny, curled up on
themselves all the way down to the plank
scale. And this means that when
inflation stretches out superstrings,
some of them may get caught in those
extra dimensions,
wrapped around and around at microscopic
scales like tangles in a fishing line,
thus preventing them from collapsing in
on themselves in a burst of radiation.
This would allow them to persist and
survive as macroscopic and cosmological
objects where they might go on to wreak
havoc. And so Edwitton was not afraid of
these ancient monsters from the deep
past of the universe. He hoped that we
could see one in real life and transform
his theoretical mathematics into
practical physics.
But how exactly does one go about
hunting cosmic strings or cosmic
superstrings?
Well, for decades, cosmologists thought
their influence might be written on the
stars themselves.
In the chaos and turbulence of the
infant universe, the phase transitions
that split the forces didn't just create
one cosmic string. They would have
created thousands of them. As the cosmos
split and fractured into domains of
distinct low energy states with these
strings separating each one, this should
have formed a colossal string network
that would have spanned the entire
volume of the observable universe which
at the time was no larger than a few
centimeters across. And from there, the
expansion of the universe would have
done its work. Since strings are
entities of spacetime, they would
stretch along with expansion. And so as
the universe got bigger, so would the
strings and its network. And some
physicists speculate that that string
network may have provided the backbone
to the universe.
In the 1980s, cosmologists were
struggling with two seemingly
contradictory observations of the
large-scale universe. For years, they
had recognized that galaxies were not
scattered around randomly, but traced
out dense clumps and thin filaments,
leaving vast empty regions behind. Some
observations suggested that the universe
was made of meatballs, large clumps of
superclusters of galaxies with nothing
in between. Other models hinted at the
existence of vast broad walls of
galaxies, giving the universe a
honeycomb-l like structure. But the
cosmologist J. Richard got offered a
compromise. Why not both? He proposed a
cosmic sponge which featured both dense
clumps, the meatballs and the broad
walls, the honeycomb. But this insight
introduced its own troubling question.
The universe of today is large and
largely homogeneous. It is relatively
the same from place to place. And so,
how do you build a cosmic sponge today
known as the cosmic web? How can you
convince galaxies to group together to
form gigantic universe spanning patterns
on top of a homogeneous background? The
string network was an intriguing
suggestion. In this idea, the cosmic
strings would have twisted and braided
together, tying themselves into knots as
they spanned the breadth of the cosmos.
It seemed the perfect solution to the
cosmic web, providing a gravitational
anchor for matter to accumulate and
build larger structures. And as well as
this, if the cosmic strings were
responsible for building the greatest
structures in the universe, then they
would also leave behind another trace of
their existence. Even if they did
eventually vanish from the cosmic scene,
they should have influenced the
appearance of the cosmic microwave
background, the oldest light in the
universe, left over from when it was
only 380,000 years old.
And so on November the 18th, 1989, John
Mata and George Smoot watched as a Delta
rocket launched their brainchild into
orbit. It was supposed to launch aboard
a space shuttle, but the Challenger
disaster of 1986 forced them to change
plans. The satellite was Kobe, the
cosmic background explorer, and its
purpose was to create the most detailed
map of the cosmic microwave background
ever made.
Mathan Smoot would go on to win the
Nobel Prize for their efforts because
Kobe was indeed able to paint an
exquisite portrait of the young
universe, providing cosmologists with
their first high-res image of that era.
That image is of some of the earliest
seeds of structure to appear in the
cosmos with tiny one part in a 100,000
differences in temperature representing
what would someday grow to become
galaxies and clusters. And the pattern
of those temperature differences, their
sizes and scales tells us what the early
cosmos was doing to plant those seeds.
Cosmic strings should have a very unique
fingerprint that would show up in these
splotches in the sky.
Not a single hint of them was found.
To quote Brian Green, "Nothing to me
would be more poetic. No outcome would
be more graceful than for us to confirm
our theories of the ultra microscopic
makeup of spaceime and matter by turning
our giant telescopes skyward and gazing
at the stars.
For cosmic strings, that day has yet to
come.
But that is not the end of the secrets
they hold. For at the same time the Kobe
rocket was soaring into the sky in 1989,
a rebellious physicist was making his
own calculations.
J. Richard got liked to gamble, but not
at the poker table or the roulette
wheel. He liked to wager about the
future.
In 1989, God was standing at the Berlin
Wall, the infamous dividing line that
biseected the city. He wondered how much
longer it might last. And so, to solve
this riddle, he applied not a theory of
geopolitics to the question, but a
cosmological one. One of the most
important foundational assumptions in
cosmology is known as the Capernac
principle. It states that humanity does
not occupy a privileged or special
position in the universe. Got was
standing at the wall in 1989. He assumed
that he didn't occupy a special position
in space or time. That the fact of the
wall's existence when he happened to be
visiting it was not unique. At the time,
the wall had stood for 28 years. And
using this as a guiding principle, he
calculated the bounds of the probability
of the wall remaining standing into the
future, arriving at a 95% probability
that the wall would last between 139th
and 39 times its present age. In other
words, it would last somewhere between 8
months and 1,092 years. It fell just a
few months later.
Years later, God even applied the same
formulation to estimate the future
longevity of human civilization. Based
on the Capernac principle, he calculated
that humanity would exist for somewhere
between another 100 years and 400,000
years.
But just a short while after his visit
to the Berlin Wall, Got made a different
kind of wager. This one had nothing to
do with political boundaries or even the
fate of the universe. It was about time
travel. In 1991, Got made a claim that
he could travel back in time and all he
would need a pair of cosmic strings.
Time machines have always caused
problems in physics. Our modern language
of space and time comes from Einstein's
general theory of relativity. Matter and
energy tell spacetime how to bend, and
the bending of spaceime tells matter and
energy how to behave. But relativity
itself doesn't care about which
direction in time objects travel in. The
future is the same as the past when it
comes to matters of gravity. And so all
it takes, at least according to general
relativity, is to find special
structures, patterns, or movements that
allow one to travel back in time. In the
parlance of relativity, these are known
as closed timelike curves. paths that
never exceed the speed of light, always
putting one step in front of the other,
but manage to loop back on themselves
and return to their own past.
One of the first people to find a closed
timelike curve in Einstein's maths was
Kirk Godel, who used it to taunt
Einstein. If relativity admitted time
travel into the past, then perhaps it
wasn't as great and powerful as
everybody thought.
Einstein had no response.
But God's time travel required a
universe that was rotating. And the
universe did not seem to be rotating.
And so in 1991, it was God who found
another time travel machine in
Einstein's theory, one that did not
require a rotating universe.
God found that if you take two cosmic
strings of infinite length, bring them
close enough together, then separate
them at nearly the speed of light, a
sort of tunnel in spaceime would open
between them. Since cosmic strings are
topological defects that manifest as
flaws in spaceime, the two separating
strings would work to essentially tear
spaceime apart between them. And if you
were to fly a spaceship down the length
of the string, again traveling at nearly
the speed of light, if you followed a
particular path, you would wind up in
your own past.
But of course, time travel into the past
is supposed to be forbidden. If we found
a cosmic string, therefore, this might
open up a crack in theoretical physics
we could not repair.
And so luckily to this day, no cosmic
strings have ever been found or the
domain walls or the monopoles.
We have no signals, no fragments, no
artifacts from the earliest moments of
the Big Bang. We have searched the
cosmos in vain.
But they should exist. Indeed, the
fractured state of the early universe
presents us one of the greatest unsolved
puzzles in modern physics. The hot big
bang should have made monsters in
abundance, and yet there are none. The
cosmic strings should have built the
cosmic web. The monopoles should have
darted here and there. The primordial
black holes should have wre havoc. And
yet, it's quiet out there. Too quiet. Of
course, this may come as a relief. God's
time machine requires the existence of
the cosmic strings. And time travel into
the past opens up innumerable headaches,
paradoxes, and violations of basic
assumptions of reality like causality.
No cosmic strings means that this chaos
can stay contained as nothing more than
a provocative thought experiment. And so
all we can do is wait and wonder. And if
we're lucky, or perhaps unlucky, then
one of these creatures forged in the
fire of the Big Bang itself may arrive
on our cosmic doorstep.