In 1973, the yet to be famous physicist
Steven Hawking found himself behind the
Iron Curtain. He was attending a
conference on the formation of nature's
most extreme objects, black holes.
It was the height of the Cold War, a
tense time between East and West, and
both sides were bristling with nuclear
weapons that could obliterate each other
in minutes. And yet here in Warsaw,
Poland, there appeared to be a Thor.
Scientists from both blocks aimed to
meet and exchange ideas, talking
cuttingedge science in a fragile oasis
of intellectual freedom. Those from the
West desperately wanted to know what had
been found by those working on the other
side. What had they discovered that they
had not been able to share? Indeed,
Hawking himself had heard whispers of
remarkable Soviet advances. And there
were also rumors of new insights into
cosmology and the big bang itself.
And one name surfaced again and again in
these discussions, like an echo across
disciplines.
Surely, Hawking thought this name
couldn't belong to a single person.
Perhaps it was a collective, a cabal of
geniuses working under a shared
pseudonym. Indeed, how else wondered
Hawking could one name be tied to such a
dizzying array of breakthroughs?
Eventually, Hawking would put a face to
this extraordinary man. A balding face
in his 50s with dark circular glasses
perched on his nose. Hawking quickly
realized that there was no school of
physicists, no hidden brotherhood of
secret geniuses. It was just one
extraordinary man with one extraordinary
mind. The extraordinary mind of Yakov
Berisovvich Zeldovich.
For decades, hidden behind the Iron
Curtain, Zeldovich had been instrumental
in shaping Soviet science and with his
exceptional intellect was both a prized
asset and a captive of that system.
Unfortunately, he did not live to see
the collapse of the Soviet Union, dying
in 1987. And yet, while his name remains
relatively obscure in the west, his
contributions were legion. But for our
story, it is Delvich's work on the
largest things in the universe that is
most important. His first ingenious
insights into super massive, super
ancient cosmic objects that span
hundreds of millions of light years
across. Mega structures so big that they
dwarf the Milky Way 10,000 times over
and so old that they may hold the secret
to how it all began.
download Opera via my link in the description.
In the late 1970s and early 1980s, a
quiet revolution was unfolding in the
way we saw the universe.
Astronomers were no longer content with
counting galaxies as distant smudges of
light on photographic plates. They
wanted to map their positions in three
dimensions to reveal the true
architecture of the cosmos. They wanted
an atlas of the heavens. And among those
leading this charge to become cosmic
ctographers were two American
astronomers, Margaret Geller and John
Huckra.
Their work was audacious in its
simplicity. They set out to measure the
speeds of many thousands of galaxies
across the sky and use the rules that
underscore the expanding universe. The
faster a galaxy receded, the further
away it must be. With the galaxy speeds
measured by some of the world's largest
telescopes, Geller and Hawker began to
assemble a 3D atlas of the universe.
Collecting the sparse photons from
distant sources took many hours at the
telescopes. But as time wore on, an
amazing picture began to emerge.
For what they found was not some random
scattering of points as if galaxies had
simply been thrown across the heavens.
Instead, they saw a distinct pattern, a
vast cosmic web of filaments and voids.
And as the data built up, there came
another shock. In 1989, Geller and Hakra
unveiled a feature so enormous it defied
comprehension. a wall of thousands of
galaxies stretching hundreds of millions
of light years across the cosmos. They
called it the Great Wall.
And that would be just the beginning.
Following the discovery of the Great
Wall, astronomers would continue to find
almost incomprehensibly large structures
across the sky, the filaments within the
cosmic web. And indeed, many that
followed would be even bigger. Dwarfing
the Great Wall is the Sloan Great Wall,
found in 2003 within the Sloan Digital
Sky Survey and spanning approximately a
60th of the entire observable universe.
Roughly equally long is the South Pole
Wall, which is twice as close to us at
only 500 million lightyears away. And
between these great filaments, the gaps
in the web are the voids, massive
regions of under density. The Sloan wall
frills the edges of the famous Bootes
void which is more than 300 million
lightyears wide. And the South Pole wall
winds around the much larger Eidana
supervoid which some studies put it more
than twice the size of Bootees.
However, these discoveries have been
more than just a ctographers's triumph.
For they raised clear questions about
the fundamental nature of our universe.
Just what forces could have sculpted
this grand design across the depths of
time and space?
Long before the Great Wall was revealed,
Zeldovich had been wrestling with the
question of how structure could form and
grow in the universe. and he had
realized that the cosmos of matter that
emerged from the big bang must have been
exceptionally smooth. But it could not
have been completely smooth. If the
universe had been perfectly smooth at
its moment of creation, it would remain
that featureless sea of matter today
with no stars, no galaxies, and no
structure. So instead, Zeldovich
imagined the universe as a vast sea of
matter gently rippled by primordial
fluctuations.
He also realized that the only force
capable of shaping the universe must be
gravity. With its long reach, it would
amplify these tiny irregularities over
time, pulling matter into sheets and
filaments. This was not chaos, but a
slow choreography dictated by the
precise laws of physics.
He saw that the collapse of matter was
unlikely to be neat, symmetrical, or
even spherical. The collapse was more
likely to be irregular and uneven. And
it was from these ideas that came the
notion of the Zeldovich pancake. This is
a striking metaphor for the collapse of
matter. Zeldovich realized that in an
even collapse, one direction should
collapse the fastest in his picture. As
this one dominant axis rapidly shrinks,
gravity squeezes matter into thin
planes. And so this means that the
universe's first structures were not
neat spheres, but immense flattened
slabs.
Continued collapse would then produce
filaments and dense nodes. It was a
vision that foreshadowed the cosmic web
well before astronomers mapped the
cosmos in any detail.
The elegance of Zeldovich's picture lay
in its simplicity. Yet its implications
were profound. It suggested that minute
fluctuations seeded the universe's grand
design while the pancakes were the
scaffolding upon which the cosmic
architecture would rise. And it would be
the advent of computers that would help
prove these ideas. What Zeldovich had
sketched in elegant theory could now be
tested in virtual synthetic universes.
Their work revealed that Zeldovich's
pancakes were just the beginning. The
universe was not a simple grid, but a
sprawling network of interconnected
strands and showed that an unseen cosmic
matter was central to it.
In the decades before the 1980s,
observations had revealed that the stars
we see are not the dominant stuff of the
universe and that another mass known as
dark matter dominated the cosmos.
Indeed, the sheer amount of dark matter
astonished the scientific community with
almost 100 times more unseen mass than
in the trillions of stars we can see.
And it was this dark matter with its
dominant pull of gravity that collapsed
into clusters, sheets, and filaments.
The raw material of stars, mainly
hydrogen and helium, just came along for
the gravitational ride. But unlike the
boring and simple gravitational physics
of dark matter, which can only slowly
gather and not fully collapse, gas can
interact electromagnetically and thus
collide, cool, and eventually collapse,
bursting into light as new stars roar
into being as high density knots in the
collapsing material. Although this
picture did have an unsettling
conclusion. When we look at any galaxy,
including our own Milky Way, what we are
seeing is the proverbial icing on the
cake. All the stars nestled together are
bound by the gravity of dark matter. And
it is this distribution of unseen matter
that stretches far beyond the visible
edge of the galaxy and links it into the
cosmic web that fills the universe.
By the late 20th century, cosmologists
felt that they had a good idea about the
formation and evolution of galaxies. But
once it seemed clear that galaxies had
grown from seeds, drawing in more and
more matter, the question of the origin
of those galactic seeds remained.
Theoretical ideas had bounced around for
a decade or so. But in 1989, a space
telescope was launched, the Cosmic
Microwave Background Explorer, or Kobe
for short, whose mission was to directly
image the earliest epochs of the
universe.
First observed in the 1960s, the cosmic
microwave background radiation is the
afterglow of creation itself. The
intense radiation of the initial moments
now cooled to a feeble glow at a few
degrees above absolute zero that
entirely fills the cosmos today. Kobe
found that the microwave background was
an almost perfect black body spectrum of
light. A spectrum so pure that it could
only have been forged in the furnace of
the big bang. This was not just a clue.
This was confirmation of the universe's
fiery birth and the idea of a searingly
hot initial few moments. But then came
the subtler truth hidden in the tiniest
of ripples.
Kobe revealed fluctuations at the level
of one part in 10,000. Faint wrinkles
over the entire fabric of the sky. And
it was these that were the seeds from
which galaxies would grow. The
fingerprints of structure etched into
the infant cosmos. In those patterns, we
glimpse the universe as it was 380,000
years after its birth. And so what we
are seeing in the CMBB is the first
sketch of the cosmic web drawn in the
language of gravity and time. These
delicate variations would swell into
filaments and clusters shaping the grand
design we inhabit today.
But that wasn't the end. If it was not
only random fluctuations that were found
in this window into the early universe,
there was something else, something
bigger, something more organized.
And so to find out what caused these
patterns, we must look deeper still back
before the cosmic microwave background
was formed to an era when the universe
was a seething plasma. hot, dense, and
waiting for the first light to break
free.
In the early 1980s, a small group of
astronomers known as the seven samurai
set out to tackle one of the biggest
questions in cosmology. Just how fast is
the universe expanding? The seven
samurai were David Burstein, Roger
Davies, Alan Drestler, Sandra Faber,
Donald Lyndon Bell, Roberto Turovich,
and Gary Vegnner. Each bringing their
own expertise, but together forming a
team that would reshape our
understanding of cosmic motion. Their
observational program was ambitious.
They focused their work on measuring the
distances and velocities of hundreds of
elliptical galaxies. But the payoff was
immense. For with their catalog in hand,
the seven samurai could begin to map the
motions of galaxies across the local
universe, where they were going and how
fast. And what they uncovered was
extraordinary.
Their measurements revealed that
galaxies were not simply drifting apart
with the smooth expansion of the
universe. Instead, they saw that there
must be a vast region of space
containing an immense quantity of mass
that was exerting an immense
gravitational pull, drawing galaxies
towards it. This mysterious
concentration of mass was called the
great attractor. Not, as it turned out,
a single object, but a sprawling region
of space dominated by clusters of
galaxies and dark matter. For cosmology,
this was a revelation. The cosmological
principle assumes that on large scales
the universe is homogeneous and
isotropic, the same everywhere and in
every direction. But the great attractor
showed that even on scales of hundreds
of millions of light years, the
distribution of matter is far from
uniform. Gravity creates flows and these
flows can distort our view of the
universe.
And now, 40 years later, that logic has
led to remarkable discoveries.
Discoveries even larger and more
consequential than the greater attractor
itself.
The beautiful campus of the University
of Queensland sits on a big lazy bend of
the Brisbane River. And it is here that
Cullen Howlett, a young upand cominging
cosmologist, is making his mark in
understanding the nature of the
universe.
But of course, modern cosmology is not
confined by geography. And Cullen works
with leading researchers across the
globe. And this includes Brent Tully at
the University of Hawaii, a veteran when
it comes to mapping the universe.
Together, they were exploring the latest
and most detailed map of the cosmos. We
have known as Cosmic Flows 4. This
modern data set, the distant descendant
of the remarkable work of the seven
samurai, is a compilation of decades of
careful measurements of more than 50,000
galaxies, charting their positions and
motions across vast stretches of space,
revealing the hidden architecture of the
universe. And it was in this cuttingedge
three-dimensional map of the cosmos that
they stumbled upon something unexpected.
For beyond the simple clusters and
superclusters of galaxies, they found a
structure unlike anything they'd seen
before.
A vast spherical shell of galaxies so
large it appeared to defy intuition.
They named it Haleilana, a Hawaiian
phrase meaning from deep darkness comes
murmurss of awakening. And it is an
immense bubble, a billion light years
across, written into the very fabric of
the cosmos.
But what could have possibly created
such a vast mega structure? To unravel
this mystery, we must go back to behind
the iron curtain. Back inside the
incredible mind of Yakov Borisov
Zeldovich.
Zeldovich was a dominant figure and
rightly held in the highest regard. It
was not for nothing that he boasted of
having three gold stars to his orders of
Lenin, while BRV only had two. There's a
simple anecdote that sums up the
forceful character of Zeldovich as well
as his pride for the sheer quantity of
things he discovered during his
lifetime. In 1986, the year before his
death, Zeldovich took part in a visit to
Rome as a delegate of the space program
of the Soviet Union. Finally free of the
restrictions put upon him in previous
visits to the west, he thoroughly
enjoyed attending conferences and
engaging in open discussion with as many
people as he could. And it was during
the event in Rome that he was introduced
to Pope John Paul II and upon their
meeting gifted his holiness two large
red volumes of his own papers. The story
goes that the pope thanked him warmly to
which Zeldovich replied, "Not just
thanks, these are 50 years of my work."
Zeldovich had long understood that the
early universe that emerged from the big
bang was a seething cauldron of light
and matter. Indeed, for hundreds of
thousands of years, it was so hot that
matter was a plasma with all electrons
torn from the nuclei of atoms. In this
state, the light and matter were locked
together, slloshing around as a single
cosmic fluid. However, the tiny ripples
that seeded the matter in the universe
were there. And so, gravity immediately
began to draw dark matter together. The
plasma of matter and light followed
along. But unlike dark matter, this
cosmic fluid possessed pressure that
pushed back, resisting gravity's pull.
This meant that the matter plasma would
collapse, but then the pressure from the
electromagnetic radiation would become
too great, pushing it back out again.
This cycle would then repeat, causing
the plasma to bounce back and forth. And
so this struggle would set up
oscillations,
sound waves rippling through the
primordial fluid, the oldest sound in
the universe.
While Zeldovich blazed the trail with
these ideas, it would be Jim Peebles and
JTU in the west who formalized the
complex physics of these oscillations.
They showed how matter in overdense
regions compressed under gravity but
then rebounded as plasma pressure fought
back. The continued compressions and
reflections, initiating a complex series
of peaks and troughs in the plasma
density. The universe resonated like a
vast instrument with these waves moving
at half the speed of light through the
photon barrier sea. This was not a
gentle hum, but a full symphony playing
out over hundreds of thousands of years.
You can think of these waves like
ripples on a pond expanding outwards
after you throw in a stone. But the
universe was not struck by a single
stone. It was more like tossing in a
handful of pebbles, each sending out its
own expanding rings. The result was a
complex pattern of interference, peaks
and troughs overlapping across space.
However, as the cosmos expanded and
cooled, the music began to fade. And
indeed, at about 380,000 years after the
Big Bang, the universe became too cool
to sustain the plasma and electrons and
protons combined into neutral hydrogen.
The first neutral atoms were created in
the universe, and the bond between
matter and light was severed. The fog
lifted and photons of light streamed
freely across space.
This is rather unhelpfully called cosmic
recombination. Named that way because it
was proposed before the big bang theory
was finished. Physicists at the time
believed that the nuclei were reuniting
with their electrons after a period of
separation, not that these were the
first neutral atoms ever and the re in
recombination stuck. This was the moment
the universe finally became transparent.
the creation of the cosmic microwave
background. The sound waves were frozen
in their tracks and so the freed light
carried with it a frozen record of the
oscillations. A snapshot of the cosmic
symphony etched into the microwave sky
we see today. Indeed, faint variations
observed by the Kobe satellite in the
cosmic microwave background are actually
tiny temperature fluctuations,
signatures of both these oscillations
and the gravitational imprints at the
time of recombination. Galaxies would
form preferentially in the peaks where
gravity had a head start and less so in
the troughs as matter was drawn away.
The frozen waves were thus written into
the distribution of galaxies. A record
of this early symphony preserved across
billions of years.
But again, it is not so simple as the
ripples being a single note. Multiple
waves radiated outwards, leaving a more
complex pattern like the overtones of a
musical instrument. Indeed, it is these
harmonics that etched into the cosmic
web, a silent score that cosmologists
can read today in the clustering of
galaxies.
But how can astronomers find this
complex pattern written into the
distribution of galaxies? The answer
lies in something called a correlation
function.
It sounds intimidating but at its heart
it is a very simple idea. We take our
catalog of galaxies and start counting.
How many pairs of galaxies are there
that are separated by 1 million lighty
years? How many by 2 million? and so on,
building up a picture of the typical
separation between galaxies across the
cosmos. If the universe were completely
random, the correlation function would
be smooth with no special distances
standing out. But we know the early
universe was not random. The waves
rippled through the primordial plasma,
spreading out from tiny peaks in
density. When the universe became
transparent, these waves froze in place,
leaving a preferred scale. the distance
between the splash where the pebble was
thrown and the crest of the ripple when
the wave expansion halted. And this
means that the correlation function
should reveal something remarkable. At
certain separations, there should be a
slight excess of galaxy pairs, a bump in
the curve.
There should be a preferred distance
called the sound horizon at
recombination which is the maximum
distance those waves could travel before
the universe cooled and photons streamed
free.
It is the fossil of a soundwave written
into the cosmic web.
But of course if astronomers are to
measure these peaks in the correlation
function they need immense catalogs of
galaxies. Not just a few hundred or a
few thousand but many millions spread
across vast volumes of space. And as
well as this for each galaxy we need
accurate distances not just positions on
the sky. Without this the subtle signal
of the barrier acoustic oscillations
will be lost in the noise.
And so in the United States, plans were
laid for a survey unlike any attempted
before.
The Sloan Digital Sky Survey, known
colloquially as SDSS, would use a
dedicated 2 1/2 m telescope at Apache
Point Observatory in New Mexico to chart
millions of galaxies across a quarter of
the sky. It was a bold vision for this
survey would measure not just positions
but also obtain spectra giving precise
red shifts and therefore distances. The
Sloan digital sky survey would become
the gold standard for mapping the cosmos
a resource that transformed cosmology.
And yet on the other side of the world a
complimentary effort was also taking
shape. The twoderee field galaxy
redshift survey was initiated on the
Anglo Australian telescope. A 3.9 m
telescope perched on siding spring
mountain in New South Wales. A special
instrument was constructed to ease the
mapping. An electronic hydra with many
eyes with a revolutionary fiber optic
system able to collect the light from up
to 400 individual galaxies at a time.
This leap in efficiency made mapping
across the southern sky possible. And so
the friendly race between the North and
South was on, night after night,
collecting data that was distributed to
the collaborative teams around the
world. Positions were confirmed,
velocities measured, and patch by patch
by patch across the sky. The most
detailed three-dimensional maps ever
made of the cosmos began to take shape.
By the early 2000s, results began to
flow in. The immense cataloges from SDSS
and 2DF were steadily growing larger,
and so astronomers began to measure the
correlation functions of galaxies. This
was the moment of truth. Would the
frozen echoes of the early universe
reveal themselves in the cosmic web?
Teams on both sides of the globe worked
feverishly, crunching through millions
of galaxy positions and red shifts. And
then almost together, the announcements
came. It was SDSS that reported the
first detection, but 2DF was hot on its
heels. The result was almost a dead
heat, a triumph for both hemispheres. In
the northern sky and the southern sky
alike, the same feature appeared, an
unambiguous peak in the correlation
function.
That peak was not random. It sat
precisely at the scale predicted from
the physics of the early universe. The
distance sound waves should have been
able to travel in the primordial plasma
before the cosmos became transparent.
They had found the fossil of a wave
frozen into place for billions of years
and written into the distribution of
galaxies. This was a profound moment.
The baron acoustic oscillations, once a
theoretical curiosity, were now an
observational reality. The music of the
early universe had been heard again, not
in sound, but in the silent arrangement
of galaxies across the sky.
And 20 years later, our first individual
barrier acoustic oscillation was found
and named Halalana,
a vast silent witness to the music of
creation. To quote discoverer Brent
Tully, "We were not looking for BAO."
However, visual examination of maps from
the cosmic flows four compilation of
galaxy distances revealed a structure
that invited further inspection.
The sheer size of Halana is hard to
grasp. It rests roughly 800 million
lightyears away from the Milky Way and
is so large that it contains not only
Hakar and Gella's great wall but the
Sloan great wall as well amongst various
other superclusters. The Boote void
rests near its center encased within its
namesake supercluster the Boote
supercluster from a width of roughly
half a million lighty years when it was
frozen into the cosmic microwave
background 13.8 billion years ago.
Halana now stands stretched to over a
billion lighty years in diameter.
And yet even with all this understanding
of the early structure of the universe,
one mystery remained. We could describe
the oscillations, the sloshing of plasma
and light, but this still did not answer
why the universe had the initial
imperfections.
The origin of these first ripples was
hidden in an even earlier epoch far
beyond the reach of the cosmic microwave
background, waiting for a deeper theory
to explain.
Science can be a strange beast. When you
sit down with your paper and pen or your
keyboard, or when you're adjusting the
setting of your experiment, you don't
know if the results you'll find will
have any impact, or indeed whether
anyone will really care. Black holes
were first proposed by English clergyman
John Mitchell in the 1780s,
only to be forgotten about for nearly
200 years. George Gamoff came up with
quantum tunneling in the late 1920s,
long before later work would highlight
its importance in areas as wide-ranging
as superconductors and nuclear fusion in
the hearts of stars. Even the idea of
dark matter took many years to have an
impact. Its first observations in 1933,
going largely ignored until the thread
was picked back up again in the 1970s.
Indeed, this is why guessing who will
get the next Nobel Prize can be a tricky
prospect because it can be years or even
decades before the importance of a piece
of work and its reach are clear. And
this was the situation in the 1970s when
two physicists Timothy Bunch and Paul
Davies were exploring the quantum nature
of fields in curved spacetime.
Their work was guided by simple
theoretical curiosity. They weren't
thinking about galaxies or the cosmic
microwave background. Yet, what they
found would fundamentally shape our
understanding of both.
And so to truly understand what they
discovered, we must first understand
what a quantum fluctuation is.
To begin with, think of an electron.
Perhaps the picture that pops into your
head is something like a little ball
bearing, a solid particle that carries
an electric charge and whizzes around
the outside of the nucleus of an atom.
However, they're not quite so simple.
Instead, an electron is quantum, a
quantum wave of probability that tells
you the chance of finding the electron
here or there or moving at this speed or
that. But just what is this electron
wave wiggling in? This is where the
notion of the quantum field comes in.
You can think of a quantum field like a
body of water. And just like water can
carry ripples and waves, so can the
quantum field. But unlike a pool of
water, however, the electron quantum
field pervades all of space and carries
the uncountable ripples that represent
all of the electrons in all parts of the
cosmos. And indeed it's not just
electrons but all pieces of reality.
Quarks, photons, neutrinos, all the
particles are ultimately ripples in
their own quantum fields. At a
fundamental level, the universe is
nothing but multiple seas of quantum
waves rippling with quantum particles
and interacting through quantum forces.
And even that is not the end of it.
Imagine a region of space where
electrons are completely absent. The
electron quantum field is still there,
but with no electrons, surely there
should be no electron ripples. And with
no electron ripples, the electron
quantum field should sit still like an
unbroken pond.
And yet, we need to remember that
quantum waves are waves of probability.
And it is these probabilities that
introduce uncertainty into the quantum
picture. This means that the quantum
field can never ever be totally calm.
Instead, it bubbles and boils as ripples
come and go with no seeming origin. This
quantum field frothing is shaped by the
inherent uncertainty of quantum
mechanics. And the ripples also aren't
totally ephemeral. They of course
represent electrons or quarks or
whatever the nature of the field is. And
so the bubbling and boiling of particles
popping in and out of existence. To
physicists, this seething is known as
quantum fluctuations, a fundamental and
statistical property of quantum fields.
And this means that there is a quantum
energy that exists in what we might
think of as the emptiest of spaces.
though being at the truly minuscule
quantum scale means that these
fluctuations are tiny barely detectable
unless of course that is something blows
them up and this brings us back to
Timothy Bunch and Paul Davies.
Their focus was on the mathematics of
quantum theory in an expanding universe
and how the world of the quantum that
ruled the smallcaled universe would
evolve in the dynamic space-time
background of the cosmos. And out of
this work came the bunch davy's vacuum a
particular quantum state that behaves in
a well understood way in a universe that
is stretching. It was elegant and
rigorous, a natural choice for
describing how quantum fields evolve in
a rapidly evolving universe. And yet,
when they published their work, it
barely caused a ripple. Cosmology at the
time was dominated by classical ideas,
and quantum subtleties seemed far
removed from anything observable. The
bunch Davy state was filed away as a
theoretical curiosity interesting to
specialists, but irrelevant to the big
questions of the cosmos. Indeed, few
could imagine that this quiet piece of
theory would one day underpin our entire
understanding of the origin of structure
in the universe. But that all changed
with the arrival of the theory of
inflation.
By the close of the 1970s, cosmologists
were wrestling with numerous deep
puzzles. Why is the universe so smooth
on the largest scales, yet sprinkled
with just the right amount of structure?
Why does space itself appear so flat
when gravity should have curved it long
ago? And why do we see no relics of
exotic particles predicted by high
energy physics? These were cracks in the
standard big bang model and they
demanded an explanation. And so Alan
Guth, a young particle physicist, was
drawn to these problems and his
calculations led him to a radical idea.
What if in its earliest moments the
universe underwent a brief but dramatic
burst of expansion? A period where space
itself inflated exponentially,
flattening it out and diluting the
relics far across the cosmic horizon.
And indeed, that wasn't all that
inflation would do. It would also
provide a mechanism for seeding
structure.
The epoch of inflation was terrifyingly
short, lasting only 10 to the^ of minus
32 seconds, a duration far far smaller
than we could ever measure in a
laboratory. And yet, in this briefest of
epochs, the universe expanded by almost
10 to the power of 30, smoothing out
irregularities in spaceime and
stretching the quantum ripples locked
into the bunch Davy states. These
microscopic quantum fields were
stretched to cosmic scales. Tiny quantum
fluctuations described by states like
the Bunch Davies vacuum were blown up by
the dramatic expansion. And so when
inflation ended much less than a second
after the universe began, these patterns
were imprinted into the matter field,
frozen as real variations in density.
Their uncertainty gone.
And it would be these blown up fossils
of the quantum world that would become
the initial scaffolding for galaxies,
clusters, and the entire cosmic web.
Every structure we see today, from the
smallest dwarf galaxy to the Milky Way
itself, can trace its origin to these
quantum whispers. Inflation turned the
microscopic into the macroscopic,
transforming quantum uncertainty into
architecture. In the ripples of the
cosmic microwave background, we see the
fingerprints of quantum physics written
across the sky. And as well as this,
physicists could chart the mathematical
properties of these matter fluctuations.
Not the precise pattern across the
universe, but their statistical
properties. When they compared their
mathematical predictions to the patterns
observed in the cosmic microwave
background as observed by Kobe, they
found an almost exact agreement. An
agreement that is only improved as more
sensitive telescopes were dispatched
into orbit to stare at the early
universe.
One example of these mathematical
predictions is what is called the scalar
spectral index. A spectrum showing how
many large, medium, and small
fluctuations there are in the CMB. Using
later measurements from the plank
telescope, a descendant of Kobe,
physicists have been able to match the
CMBB spectrum to the spectrum predicted
by inflation to remarkable accuracy.
Inflation models generally predicted a
scalar index slightly less than one. And
the plank missions measured this number
to be 0.96
to an accuracy of five sigma.
And so from these seeds, stars and
galaxies formed. Clusters gathered along
filaments, leaving great voids between
them. Even our own galaxy traces its
origin to one of these quantum ripples.
A faint whisper from the earliest
moments of time. Inflation, therefore,
didn't just solve existing cosmological
puzzles. It connected the smallest
scales of physics to the largest
structures in the universe.
But our story is not over. For all of
these discoveries are not just
intellectual curiosities, satisfying
answers to ancient questions. For we can
use them as tools. For these patterns in
the sky allow us to chart the very
fundamental properties of our expanding
universe.
His
name is among the most famed
astronomers. But before he embarked on
his stellar career, Edwin Hubble had
already lived a remarkable life.
He had studied law at the University of
Oxford, had served in the First World
War, and even dabbled in boxing. But his
true passion lay in the stars. And in
the 1920s, he turned to astronomy with a
bold ambition. He would use the world's
largest telescope, the 100-in Hooker
telescope on Mount Wilson to answer one
of the biggest questions imaginable.
Just how big is the universe?
At the time, many believed the Milky Way
was everything, a potentially endless
sea of stars that it existed forever.
Faint smudges of light had been spotted
in the night sky, but many argued that
they were little more than clouds of
gas. Some, however, began to suspect
that these were island universes, vast
congregations of suns, each a distant
reflection of our own Milky Way, a drift
in the depths of space. And so, it was
Hubble's observations that settled the
debate, resolving the smudges and
identifying them as individual galaxies
in their own right. But it was his
observations of a particular kind of
star, the seafared variable, that truly
shattered the notion of distances over
the cosmos.
This was possible because the speed at
which seed variables pulsed was related
to their brightness and their intrinsic
brightness was always the same. And so
by measuring their timing and thus their
brightness, Hubble could calculate how
far away they were, thus revealing that
those clouds of gas were in fact
separate galaxies far beyond our own.
And through the rest of the 20th century
and into the 21st, astronomers have
further refined their observations in an
effort to refine Hubble's initial
observations to great detail and to
reach out more distantly into the
cosmos. But to see even further,
astronomers have had to use other
galactic features to chart the distant
cosmos. As even the brightest seafiids
are invisible at cosmic distances.
Luckily, to begin with, exploding stars,
supernovi, have proved to be valuable
replacements. Now known as standard
candles, illuminating cosmic distances
over billions of light years.
And yet, despite this, measuring
distances in astronomy is still not
easy. Every method carries
uncertainties, and as careful as
astronomers are, there's always worries
that errors have snuck in as they piece
together the true scale of our universe.
Indeed, as in all good science,
repetition in measurements amongst
different groups and using different
techniques is hugely important. And this
is where Barryon acoustic oscillations
have found their greatest use. In
reading the frozen ripples in the cosmic
microwave background, we have found a
new cosmic ruler on the dwarfs. All the
rest.
To begin with, we have to remember that
these waves had only 380,000 years to
expand before they were frozen when the
universe became transparent.
And so from knowing the physics and thus
the speed of these plasma waves,
cosmologists can calculate precisely
their physical scale. These measurements
give cosmologists a new way to chart the
life and times of the universe. By
comparing the physical scale of the
sound horizon, the extent to which the
waves in the plasma could spread to its
apparent size in the cosmic microwave
background, they've been able to
calculate the expansion rate of the
universe with exquisite precision.
And yet, despite this seemingly clear
success, this is also where the story
takes a twist.
for the number they have found does not
match the value measured from nearby
galaxies and supernova.
Two methods, two answers, and a growing
tension that has become one of the
biggest puzzles in modern cosmology.
It is called the Hubble tension and it's
a problem that has covered countless
pages of academic journals. Local
measurements using seafood and supernovi
suggest the universe is expanding faster
than the rate inferred from the early
cosmos as determined from the cosmic
microwave background. And indeed, the
discrepancy is not trivial, with the
significance of the gap between the two
sets of measurements only getting larger
as observations have become more
refined. It is now so large as to make
astronomers wonder if something
fundamental is missing from our picture
of the universe. And so, what could
explain this discrepancy? Some suggest
that the tension doesn't really exist as
the local measurements are possibly
biased, perhaps by unrecognized
systematics in the calibration of
distances. Indeed, it's important to
remember measuring distances in
astronomy is always hard. Others argue
that the early universe calculations
might be incomplete, hinting at new
physics beyond the standard model of
cosmology. Could dark energy be
evolving? Is there an extra species of
particle or a subtle twist in gravity
itself? These possibilities are
tantalizing and have resulted in a kind
of wild west of theoretical speculation.
But none has yet provided a definitive
answer. For now, it seems we have to
accept that the Hubble tension remains a
tantalizing mystery.
And that is not the end of the uses for
Barryon acoustic oscillations. As
astronomers now use these frozen ripples
in new ways to reveal the fundamental
properties of the universe,
the secret is to combine two sets of
data. The cosmic microwave background
which reveals the scale of the physical
waves at recombination with the vast
cataloges of galaxies obtained from
modern surveys. These galaxy surveys
reveal the same imprint of waves written
into the cosmic web but at a time
billions of years after recombination.
So by comparing these two epochs,
astronomers can trace how the universe
has expanded over deep time. This is at
heart a very elegant method. The cosmic
microwave background provides the
starting point, a ruler calibrated by
the physics of the early universe. And
galaxy surveys can measure how that
ruler appears at different red shifts.
Our standard cosmological model with a
universe containing matter and an
unchanging form of dark energy predicts
a smooth expansion. And so the apparent
size of the baron acoustic oscillations
seen in galaxy surveys should follow a
precise predictable pattern. Any
deviation from that pattern possibly
signaling new physics.
And this brings us to Desessie, the dark
energy spectroscopic instrument.
Conceived in the early 2010s and coming
online in 2021, Desi represents the
culmination of decades of effort to
understand the accelerating universe.
spurred on as it was by the unexpected
discovery in the late '9s of the
acceleration of expansion and the
presence of dark energy.
However, Desi is not a single device,
but a sophisticated assembly of
cuttingedge technologies. At its heart
lies a robotic fiber positioning system
capable of placing 5,000 optical fibers
with exquisite precision across the
telescope's focal plane. Each fiber
feeds light from a distant galaxy or
quazar into one of 10 spectrographs,
allowing Desi to capture the
fingerprints of cosmic expansion on an
industrial scale. This engineering
marvel enables Desi to undertake the
most ambitious galaxy survey ever
attempted. Over 5 years, it will chart
tens of millions of galaxies and
quazars, constructing a
three-dimensional atlas, not just of
space, but of time as well, spanning 11
billion years of history. With this map,
Desi can measure the barrier acoustic
oscillation scale at multiple epochs,
turning those frozen ripples in the
primordial plasma into a detailed
chronicle of how the universe has grown
and stretched under the influence of
dark energy.
Multi-year programs such as DESIE often
release their data in chunks. Data
releases that build up to a final
catalog of everything they observe. And
so in 2025, Desi released its second
chunk with more than 14 million galaxies
and more than a million and a half
quazars mapped across the cosmos. In the
time since its release, astronomers have
dug into the data, teasing out the
signal of the Barryon acoustic
oscillations, and the results have been
surprising to say the least.
Over the multiple epochs, the signal of
the oscillations rises clearly above the
noise with no doubt that this relic of
the early universe is still imprinted on
the cosmos today. But in reconstructing
the expansion history from these
signals, astronomers have found that it
doesn't match the predictions of our
simplest picture of dark energy.
Instead, the data hints at quite strange
behavior, as if dark energy were not
constant, but has been changing and
evolving over billions of years. Of
course, it's not quite yet definitive.
And as more data flows in, this signal
of strange dark energy could become more
significant. Or like so many other
interesting signals in physics, it could
melt back into statistical noise. But it
is already enough to make cosmologists
pause. Could this be the first sign that
our picture of dark energy is
incomplete? Or is there something
deeper, a new ingredient in the cosmic
recipe?
If dark energy is not constant, but
instead evolves with time, the
implications for cosmic history are
profound.
In our standard picture, a steady dark
energy acts like a gentle but relentless
push, causing the universe's expansion
to accelerate ever faster. But if its
strength has changed over billions of
years, the story becomes far more
intricate. Perhaps in the distant past,
dark energy was weaker, allowing gravity
to dominate for longer, thus impacting
the growth of structure. Or perhaps it
was stronger, driving an earlier surge
of expansion that left its mark on the
distribution of galaxies we see today.
And ultimately looking ahead, an
evolving dark energy could rewrite the
ultimate fate of the entire universe.
For if its influence continues to grow,
the universe may race towards a big rip
where galaxies, stars, and even atoms
are torn apart by runaway expansion. And
if it fades, the acceleration could
stall and gravity might one day halt the
expansion, leading to a slow collapse.
Because between these extremes lies a
spectrum of possibilities. Each
demanding new physics to explain why the
vacuum of space is not the simple
immutable backdrop we once imagined.
And finally, it's tempting to wonder
whether these two puzzles, the hints of
evolving dark energy from Desi and the
stubborn Hubble tension are not separate
mysteries at all, but threads of the
same tapestry. If the strength of dark
energy has shifted over cosmic time,
then our extrapolations from the early
universe to the present day may be
subtly flawed, introducing the discord
we see between local and primordial
measurements of expansion. A single
coherent picture could emerge, one that
reshapes our understanding of cosmic
acceleration and the physics driving it.
As Desessie's map grows and new
observations sharpen the view, we may
find that these anomalies are not
accidents, but signposts pointing
towards a deeper truth.
And so, in that Warsaw Conference on
Cosmology and Black Holes of 1973,
Steven Hawking could scarcely have
imagined the universe we now see. Back
then, cosmology was still a fledgling
science, its foundations resting on a
handful of observations and a great deal
of speculation. Yet, among those
whispers of Soviet breakthroughs,
Zeldovich was already sketching a vision
of how structure might emerge.
Fast forward half a century, and the
cosmos has yielded its secrets in ways
that would have astonished even
Zeldovich. We now map the universe not
in hundreds or thousands of galaxies but
in tens of millions tracing its
architecture across billions of years.
Those delicate ripples in the early
plasma. The barriion acoustic
oscillations have become tools rulers
stretching across the cosmic web. We see
hints the dark energy may not be
constant. We puzzle over the Hubble
tension. And in these mysteries the
spirit of Zeldovich lingers. The
audacity to imagine beyond the obvious,
to seek unity in complexity.
From the fragile oasis of Warsaw to the
robotic precision of Desi, the journey
has been long, but the quest remains the
same. To understand where it all came
from and where it is going.
Thanks for watching and we'll see you
next time.