Despite existing on a small planet in a
tiny corner of the cosmos, astronomers
know exactly how much visible matter the
entire universe should contain. The
problem is that for decades, 40% of it
has been missing. And I'm not just
talking about the ever mysterious dark
matter and dark energy. Galaxy clusters
don't seem to have as much visible mass
as our models say should be there.
Entire galaxies seem to have lost huge
reservoirs of the material they were
born with. Even the space between
galaxies, enormous cosmic deserts are
emptier than our best theories predict.
This missing mass has to be out there.
that or all our models of cosmology are
wrong. But every time we've looked,
we've found nothing. And believe me,
we've tried. We've used our most
powerful telescopes, deepest surveys,
and most sensitive detectors in the
search. The missing mass just remains
invisible, slipping past our instruments
like a ghost. That is until now. For the
first time in history, we may have
finally found where the missing mass of
all the universe has been hiding. And
it's in plain sight. Astronomers have
captured images of vast gaseous
filaments that stretch 23 million
lightyear between galaxy clusters. It
may just be one filament, but finding it
has huge ramifications.
Is this the very first detailed image of
the cosmic web? As scientists now hunt
for more, this discovery has the power
to determine whether our cosmological
models are correct.
I'm Alex Mccoan and you're watching
Astramm. Join me as we reveal how
astronomers have snatched a glimpse of
the near invisible network that
underpins the cosmos. finally revealing
the hiding place for our universe's
missing visible matter. And with it,
let's start unraveling the truth behind
our cosmic evolution.
When we measure all of the gas, dust,
planets, stars, and galaxies, everything
we can see in the whole universe using
everything from infrared to visible
light and beyond to gamma rays, it adds
up to a colossal amount, more than 100
sexilion
kg. That's 10 with 53 zeros after it.
But really, this only accounts for a
small fraction of the total matter that
scientists predict to exist. In fact,
this visible ordinary matter is thought
to make up just 5% of the universe. The
rest is stuff we don't completely
understand. Dark matter is believed to
account for 27%. And dark energy 68%.
Despite their names, dark energy isn't
related to dark matter. What they have
in common is that we can't detect or see
them. Dark energy is thought to be a
seemingly invisible type of energy
causing the universe's expansion to
accelerate over time. And dark matter is
a type of matter that has mass but is
invisible to us as it doesn't absorb,
reflect, or emit any light. I've talked
about dark energy in previous videos,
and that is truly its own mystery. You
can explore those if you're interested
to find out more about the topic, but
for this video, I'll just focus on the
matter at hand. So, 95% of our universe
is likely not made of visible ordinary
matter. And of the 5% that is
technically visible matter, also known
as barionic matter, about 40% has been
missing since the Big Bang 13.8 billion
years ago. Now, I know what you're
thinking. How do we know it's missing if
we've never seen it? We certainly
weren't around back then. Thankfully,
the early universe itself left us the
answer. Measurements of the cosmic
microwave background have allowed
cosmologists to calculate exactly how
much barionic and non-barionic matter
was created as a result of the Big Bang
to an accuracy level of better than a
few%. That gives us a precise budget for
how many atoms should be in the universe
today. But just because it's made of
stuff that's visible to us doesn't mean
it's easy to see. When astronomers go
out and count up all the stars, gas,
dust, and plasma we can see with the
help of models and simulations, we only
find about 60% of what should be there.
The rest has to exist for early universe
physics to make sense. But unless we can
find it, we can't prove that our models
are right. Maybe we've got it all wrong.
Thankfully, scientists haven't been that
quick to give up and instead turned
their attention to working out where the
missing mass may be lurking. And they
came up with an intriguing hypothesis.
Missing barionic matter is not the only
missing mass. And perhaps they're hiding
together.
Nearly a century ago, Swissborn
astronomer Fritz Zviki noticed that
galaxies in the Coma cluster moved too
quickly for the amount of gravity that
would be created by their visible matter
alone. Yes, including the missing stuff.
Instead, he thought another form of mass
must be there. And in 1933,
Siki dubbed this missing substance dunul
materi, the German for dark matter.
In the 1970s, American astronomer Vera
Rubin had a similar experience. She was
observing spiral galaxies and wondered
how stars on the outer edge of the
spiral galaxies were able to move so
quickly without flying off into space
again. Some unknown mass must have been
pulling them back in. And she concluded
the same as there must be dark matter
holding them together. This new type of
stuff interacts with its ordinary
barionic counterpart through gravity,
but it doesn't interact with the
electromagnetic spectrum, meaning that
it doesn't absorb, reflect, or emit any
light. This makes dark matter extremely
difficult to find and seemingly
impossible to observe, at least
directly. Yet, it influences the cosmos
on a galactic scale. It may even be
helping to conceal our missing barionic
matter.
Since the 1980s, early observations of
galaxy distribution have revealed a
cosmic pattern, a web like a backbone
across the universe. This skeletonlike
structure has become known as the cosmic
web. It's thought to have formed as a
result of slight density fluctuations in
the early universe, which can be seen in
the cosmic microwave background, or
CMBB, a fingerprint of our universe's
ancient microwave radiation from about
380,000
years after the Big Bang. These tiny
fluctuations in density laid out a
blueprint for where matter would collect
over space and time. where there were
higher densities, more mass would be
drawn in until this great structure was
formed. We already know that CNB
simulations using supercomputers
estimate that dark matter accounts for
five times more of the universe than
ordinary matter. So, it's perhaps no
surprise that the cosmic web is thought
to contain primarily dark matter.
permeating every corner of our universe.
It's made of filaments stretching tens
to hundreds of millions of light years
across the universe. Where filaments
intersect, the concentration of mass is
so great that high density nodes are
able to form, containing hundreds or
even thousands of galaxies. The cosmic
web is real. We've mapped large swaths
of it. Our galaxy is part of what's
known as the local group, a collection
of a few dozen neighboring galaxies near
to our own. Our local group belongs to a
larger collection called the Lania
supercluster, which contains some
100,000 galaxies and measures 500
million lightyears across. As you might
have guessed, all these galaxies are
strung along the cosmic web like beads
on strings perched along the edge of
great voids.
But even though we've been mapping this
cosmic web for decades, most of what we
can see is the beads, the distribution
of galaxy clusters along the web, not
the strings that hold them together or
the filaments themselves.
Or is it?
Whilst most of the visible matter in the
universe is tied up in galaxies, not all
of it is. The dark matter in the cosmic
web has a pretty strong pole itself.
There, bound up as vast diffused gas in
those long strings or filaments is where
large scale cosmological simulations
have predicted we might not only find
dark matter but our missing invisible
matter too. This low density diffused
gas is known as the warm hot
intergalactic medium.
But simulations are one thing. Detecting
these diffused filaments is another. And
this is where historically we've not had
much luck. Although that started to
change about 20 years ago. In 2005,
NASA's Shandra X-ray Observatory imaged
two huge intergalactic clouds of
diffused gas. We'd seen clouds like this
around our own galaxy and in others
local to us, but not between distant
galaxies.
Could it be gas on the cosmic web? This
was some of the first evidence that the
cosmic web was hiding our missing mass.
But the light was too faint to
completely isolate it. So scientists
couldn't quite be sure. Then in 2012, a
combination of 18 Hubble images was used
to infer the presence of a filament
funneling matter into the galaxy cluster
MAX J0717.
Scientists found it by studying the
distortion of light from background
galaxies due to the gravity of the
filament's dark matter. But again, it
wasn't a direct detection. We still
couldn't say we've actually seen them,
inching ever closer to a discovery. It
was just 2 years later that astronomers
moved beyond indirect detection and
statistical evidence into the realm of
the visible. A team led by Sebastiano
Canalupo from the University of
California observed an enormous filament
of hydrogen gas at nearly 2 million
lighty years across. They spotted it
after it was illuminated by a giant
cosmic flashlight, a bright quazar
shining at it from 10 billion lighty
years away. This was the first time part
of the cosmic web had been seen
directly.
Using the same illumination principle,
in 2019, astronomers revealed whole
networks of hydrogen filaments
surrounding a massive protocluster
directly imaging the web on mega parex
scales. But these detections were only
possible thanks to our cosmic
flashlights. To understand cosmic
filaments as they typically exist in
darkness, we needed a new imaging
technique. And in 2023, scientists made
a breakthrough.
At the WMEK Observatory in Hawaii, a
team of astronomers had designed a
dedicated instrument to search for
filaments of hydrogen, more specifically
dim lyman alpha emission, the spectral
fingerprint of hydrogen as it absorbs
and remits radiation. And it worked. In
fact, they've made entire 3D maps of
these filaments. This was just the start
of the discoveries. In January 2025, the
picture sharpened dramatically.
A team of international astronomers
captured one of the clearest direct
images yet. Using the multi-unit
spectroscopic explorer or MUSE mounted
on the very large telescope at the
European Southern Observatory, they
imaged a pair of quazar host galaxies
with a cosmic filament about 3 million
lightyears long. And using supercomputer
models built on the Muse data,
researchers were able to simulate a
filament that matches the one they
observed in real life. This was a
spectacular achievement. But there was a
catch. These observations were from the
early universe. They traced cooler
hydrogen gas billions of years in the
past, not hot diffused material thought
to contain most of the universe's
missing bionic matter. Today, our models
predict it stretched along thin
filaments of the cosmic web in the local
universe. But here, the signal is far
fainter and harder to isolate. We were
stuck.
In June 2025,
astronomers finally found what they were
looking for. They were able to isolate
and spectroscopically measure the hot
lowdensity gas of an individual cosmic
web filament in the local universe,
marking a breakthrough moment in our
quest to locate the missing barionic
matter.
A team of European researchers headed by
lead author Constantinos Migas at Leiden
University in the Netherlands used Jax's
Suzaku X-ray Space Telescope to map a
single filament in faint X-ray emissions
over a wide area of space. They then
used the XMM Newton to pinpoint sources
of X-ray contamination. In this case,
super massive black holes, which had to
be removed from the data in order to map
the filament. In this image, you can see
what they found. A filament of the
cosmic web connecting four galaxy
clusters, two on each end, each one as a
white spot surrounded by color. The band
of purple stretched between them
resembling a honeycomb or bone
marrow-like texture is the filament of
X-ray emitting hot gas
located in the Sharply supercluster at
supercluster of more than 8,000
galaxies. The filament stretches across
a distance of 23 million lightyear which
is the equivalent of about 230 Milky
Ways end to end. Its mass comes in at
roughly 10 times that of the entire
Milky Way galaxy. And the temperature of
the filament's hot gas is a scorching 10
million° C. It reveals in detail for the
first time how galaxy clusters are
connected over colossal distances and
uncovers the vast cosmic web that
underpins the structure of our entire
universe like the very bones of a cosmic
skeleton upon which everything else
forms. And according to the paper's
co-author, the filament is exactly what
we expected from the best large scale
cosmological simulations of the
universe. We got it right.
The latest breakthroughs in observing
filaments lend important evidence and
support for our current standard model
of cosmic evolution known as the lambda
cold dark matter model. The model is
underpinned by dark matter which has
been too complicated for us to catch a
glimpse of thus far. So observing this
once thought missing visible matter on
the cosmic web is a big step in the
right direction. But to truly know
whether our models match reality, we
need more than one or two filaments. We
need to map the entire skeleton, or at
least much more of it. And that is where
another mission, Uklid, comes in.
Launched in 2023, Issa's Uklid mission
is designed to piece together a more
accurate picture of the cosmic web
structure and history and dig into the
nature of dark matter and dark energy.
Ukalid will help us measure galactic
shapes with precision, revealing how
dark matter distorts space through
gravitational lensing and measure red
shifts, giving us a 3D position for each
galaxy. This combination will allow
Uklid to infer the locations of the dark
matter filaments, not just the galaxies
on them, and give us precise locations
to look for more gas. By 2030, Uklid
will likely be able to confirm if the
cosmic web matches results from the XMM
Newton filament discovery and the
pattern seen in the cosmic microwave
background. If it's a perfect match,
that would be one of the strongest
confirmations of the big bang model in
the history of science.
If not, then something is fundamentally
missing in our standard model. Whether
it's our understanding of dark matter,
gravity, or the early universe. Either
way, with the help of Uklid and the
latest observations of these cosmic
filaments, cosmology is poised to be
changed forever.
One day, the universe, as we know it, at
least is going to end. And nearly 30
years ago, scientists reached a general
consensus on our universe's most likely
fate. It is that over trillions of
years, its galaxies will drift farther
and farther apart. Stars will cool off
and die out. Black holes will slowly
evaporate until all that's left is an
infinite expanse of cold, dark space.
This is the so-called big freeze powered
by dark energy. It's a consequence of
the accelerating expansion of our
universe. By far the most likely outcome
for the end of everything. Or so we
thought.
New groundbreaking findings from the
dark energy spectroscopy instrument or
desi may be uncovering a different
story. It's found that dark energy's
grip on our universe could be in fact
weakening. But what does this mean?
If true, and the cosmic engine that
powers our universe is running out of
steam, then the very fate of the
universe hangs in the balance. I'm Alex
Mccoan, and you're watching Astramm.
Join me as we investigate this profound
shift in our understanding of the
universe and explore why dark energy may
be running out of power. Could it be
that all our cosmological models are
wrong? Or is there another explanation?
Let's travel back to 1998.
At that point, we already knew that the
universe was expanding thanks to Edwin
Hubble's observations almost 70 years
earlier, but scientists were still
attempting to pin down exactly how fast.
In fact, many were wondering if the
expansion would eventually slow down.
Logically, this seemed to make sense.
The tug of gravity should bring
everything closer and closer together
over time. Right now, all of this could
be solved by working out the Hubble
constant, a value that represents the
speed at which the universe is expanding
right now. It can be measured in two
ways. By studying patterns in the cosmic
microwave background or by looking at
distant red shifts.
By the way, scientists have found that
these two methods don't produce the same
results. But I've got another video on
that particular crisis that you can
watch here to find out more. In this
video, however, we're going to
concentrate on the red shift method.
Historically, the red shift of seafared
variable stars has been used for this,
but type 1A supernova also work well.
And without knowing it, the astronomers
studying these immense explosions were
on the brink of a jawdropping discovery.
We know how bright type 1A supernova
should be because they all explode in
pretty much the same way. Thermon
nuclear detonations of white dwarfs in
binary systems by comparing their true
brightness to how dim they look from
here on Earth. We can measure their
distances. Then by using the supernova's
red shift, the amount of light that has
been stretched along its journey, we can
determine how fast they're moving away
from us. and therefore how fast the
universe was expanding when their light
was emitted. Easy enough, right? Well,
when two independent teams of
astronomers observed more than 50 type
1A supernova, they found that the light
appeared fainter than expected, which
although perhaps sounds trivial, turned
out to be a pretty big deal.
Teams led by Sal Pelmuta, Brian Schmidt,
and Adam Ree discovered that distant
supernova were dimmer because they were
farther away than we expected. This was
a huge revelation as it came with a
rather shocking consequence. It meant
that the expansion of the universe was
not slowing but actually speeding up.
some unforeseen force was seemingly
pushing entire galaxies apart.
To visualize this, imagine if you took a
marker pen and drew dots on the outside
of an uninflated balloon. As you blow it
up with air, the dots get farther and
farther away from each other because the
balloon itself, the space the dots
reside in, is expanding in all
directions. This unexpected result
created more questions than it answered.
A big one being what is the force
driving this acceleration?
Unfortunately, the answer is still we
don't know. But it's been given the name
dark energy and most scientists think
it's a property of the vacuum of space
itself, the energy of empty space. Other
scientists think it may be a type of
energy fluid or field that fills space
or even some kind of defect in the
fabric of spaceime like one-dimensional
wrinkles socalled cosmic strings. And
others think it may just be a flaw in
our understanding of general relativity
on the scale of the observable universe
and that the matter could be resolved
without the need for dark energy at all.
But whatever it is or isn't, dark energy
presents a mystery that is intertwined
with the accelerating expansion of the
universe. This was such a monumental
discovery that following the 1998
finding, Ree, Hulm, and Schmidt, the
three astronomers who led the
investigations were awarded the Nobel
Prize in physics for their work.
This discovery of dark energy gave rise
to a new model of cosmology. The lambda
cold dark matter or lambda CDM model.
Lambda is a Greek letter that represents
the cosmological constant. First
postulated by Einstein. Today it
represents the mathematical parameters
of dark energy. The other three letters
CDM stand for cold dark matter. It's
become what we today refer to as the
standard model of cosmology and it gives
mathematical context to everything from
the big bang to the future fate of our
universe and of course all that happens
in between.
For decades, it's been the most widely
accepted and most accurate model we have
for the evolution of our cosmos.
Confusingly, dark matter doesn't have
anything to do with dark energy. We just
use the word dark to describe two
different things that we don't
understand. Well, while dark energy is
the force that's causing the universe to
expand at an accelerating rate, dark
matter is what we call the stuff in our
universe that doesn't interact with the
electromagnetic field. As in, it doesn't
absorb or emit or interact at all with
light. However, we believe it exists
because we can observe its gravitational
interaction within the universe. And the
word cold in the model's name just
refers to this dark matter having very
little energy since temperature can be
thought of as a way to measure the
energy of atoms. But if those two things
make up the entire name of the model,
the lambda cold dark matter model, what
about everything we can see and do know
about? It may not be reflected in the
name but it is captured within the model
itself. Visible matter and radiation
including light all belong to the
category known as barionic matter. Using
independent measurements and
observations, the scientific community
has come to a consensus that under this
standard model, about 68% of our
universe is made up of dark energy, or
this fundamental property of spaceime
that we know very little about. with
visible matter making up only about 5%
and dark matter accounting for 27% of
our universe. Let that sink in. 68% of
our universe is made up of something we
don't understand and can't measure
directly.
However, a crucial aspect of our
standard model is that lambda or dark
energy is assumed to be a constant.
Almost every cosmological calculation
relies on this being fact. It tells us
that our universe has an ever
accelerating rate of expansion and that
it will therefore face a cold lonely
fate. Galaxies will continue to drift
further apart as the space between
everything expands. Stars will burn out,
die, and cool off. All of the heat and
energy in our universe will be spread
impossibly thin over incomprehensible
distances until the universe's final
temperature hovers somewhere barely
above absolute zero, ending in what
astronomers call the big freeze.
But what if we're wrong? For the first
time since the discovery of dark energy,
we may have uncovered one of its key
properties, and it's not what
astronomers expected.
In 2024, the Dark Energy Survey released
the largest ever sample of supernova
results from a single survey, having
studied the deaths of more than 1,500
stars.
Initially, the data seemed in line with
the idea that dark energy is constant.
But when they combined the data with
other results, like measurements from
the cosmic microwave background and
earlier galaxy surveys, something didn't
quite add up. It was starting to look
like dark energy might in fact change
over time. Now, a changing dark energy
is not what scientists expected to find.
and it caused them a big problem.
Although it was a promising result,
there were uncertainties involved. So,
it was nowhere near being decisive
proof. To find out the truth,
astronomers needed a far bigger, more
detailed map of the universe to test
whether this hint was real. And for
that, they turned to Desi.
Installed on the 4meter male telescope
in Arizona, the dark energy
spectroscopic instrument is charting the
optical spectra of tens of millions of
galaxies and quazars across billions of
years of cosmic history with one mission
to test whether or not dark energy is
constant. Able to capture light from
5,000 galaxies simultaneously. Desi is
measuring the position and receding
velocity of some 40 million galaxies in
order to accurately measure the
expansion history of the universe over
the past 11 billion years. This is a
truly international effort involving
more than 900 researchers from more than
70 institutions around the world. And in
2025,
the first major data sets were released.
They included results from the first
three years of the survey with two more
to go. And what they show is nothing
short of extraordinary.
Desi used data from nearly 15 million
galaxies to build the largest
three-dimensional map of the universe
ever created. This 3D map lets us fly
through millions of galaxies, each
containing 200 to 300 billion stars.
Earth is at the center of this
animation, and every dot is an entire
galaxy. The blue represents farther
galaxies from us, while the white shows
closer objects. In other words, this map
is almost unfathomably dense with
galaxies.
Using this data, a team of astronomers
have measured barrier acoustic
oscillations or BAOs from more than 14
million galaxies and quazars. BAOs are
basically the fossilized echoes of sound
waves from the early universe. By
tracking how they change in size across
cosmic time, researchers can work out
exactly how fast the universe was
expanding at any given moment. Here, the
lighter blue color represents sound
waves rippling through the primordial
cosmic sea of our early universe. Over
time, those slight variations froze in
place, carrying with them a slightly
more dense collection of matter. Over
hundreds of millions of years, those
waves would gather more and more
material, eventually becoming stars and
galaxies. These waves are still visible
today in the form of the cosmic web.
The researchers then combined this desi
data with other measurements like the
microwave radiation left over from the
dawn of the universe known as the cosmic
microwave background, supernova red
shifts, and weak gravitational lensing
or how the light from distant galaxies
warps due to gravity. And what they
found added more weight to the 2024
discovery. Not only does it look like
dark energy's influence is changing, but
it's potentially decreasing over time.
In fact, they found that dark energy's
push may have weakened by roughly 10% in
the last 4.5 billion years. You can
think of it kind of like a foot still on
the gas pedal, but gently lifting, which
means that the car is still
accelerating, but at a slower rate than
before.
Likewise, the expansion of our universe
is still accelerating, but not quite as
rapidly as it was a few billion years
ago. And if dark energy is evolving
rather than remaining constant, then our
standard model of cosmology is missing
something and something big.
Assuming this model shattering discovery
is correct, it could mean a very
different future for our cosmos. Instead
of a big freeze where our universe
expands forever, leaving us with a cold,
dark, lonely end, we may end up
experiencing an alternative reality. If
dark energy's influence continues to
weaken over time, decreasing until it
becomes negative, then eventually
expansion of our universe could stop
altogether.
Instead of a big freeze, it would end in
a much more violent cataclysm.
Imagine the raw power of the Big Bang
exploding and expanding out with enough
energy, heat, and matter to form all the
galaxies and stars across our universe.
And now imagine the exact opposite of
that. A reverse big bang where
everything changes direction and rushes
in toward a single point with enough
intensity to undo everything that ever
existed in one cosmically colossal big
crunch.
I've spoken before about the possibility
of a big crunch as well as other
theories about how physics gets weird at
the end of the universe. If you want to
know more, I recommend watching the
video linked here. Now, if dark energy
is an evolving variable, there is one
other perhaps even more important to us.
Impact. It means our current model of
cosmology is incomplete. It could mean
that the theory of general relativity
needs modification, too, and that
there's more to learn about particle
physics, possibly involving new fields
or forces.
But before we rewrite any textbooks, we
have to be sure. And right now, we're
close, but we're not quite there. Sigma,
or standard deviation, is the way
scientists measure confidence. The
higher the sigma, the less likely a
result is due to random chance. And in
the chase for evolving dark energy,
those sigma levels have been climbing.
On its own, desi data lands us just
above two sigma, which is about 95%
confidence. Interesting, but nothing
you'd bet your career on. Combine Desi
with other instruments, and the number
rises past 3 sigma, even brushing the
4.2 two sigma mark in some combinations.
Roughly 99.997%
confidence.
While this is considered to be strong
evidence, meaning that the result was
unlikely due to random chance, it's
still not quite at the level physicists
require for it to be considered a solid
discovery. For example, other evidence
with this confidence level has turned
out to be false before. So physicists
typically wait for even clearer results
before claiming a new discovery. The
gold standard in physics comes when
confidence reaches 99.99994%
which is sigma 5 and even then things
can still be wrong. For example in 2011
physicists at the Grand Saso laboratory
in Italy measured some nutrinos arriving
a few nanconds early. a feat that would
require the particles to have traveled
faster than the speed of light, breaking
the cosmic speed limit. They reported a
confidence level of six sigma, even more
impressive than the gold standard for
new discoveries. To put that into
perspective, barring any unexpected
mistakes in the experiment, 5 sigma
represents about a 1 in 1.7 million
chance of the result being a fluke. and
six sigma is more like a one in 500
million chance of the result being
wrong. So this was quite an astonishing
observation and it made headlines around
the globe. Unfortunately, it was later
revealed that the physics breaking
observation had actually been due to a
faulty fiber optic cable and clock
synchronization error rather than
nutrinos breaking the laws of physics.
Needless to say, there's still a little
way to go with the concept of evolving
dark energy.
Now in its fourth year of the 5-year
survey, Desi is well on its way to
having measured 50 million galaxies and
quazars, continuing to offer valuable
data in the quest to understand dark
energy. But it's not our only tool. Over
the next few years, new experiments will
be conducted. Other missions will
further the exploration of the nature of
dark energy and complimentary data sets
will come out for analysis. European
space ay's Uklid and NASA's Nancy Grace
Roman Space Telescope will extend
measurements across even larger volumes
of space and at higher red shifts. And
the Very Rubin Observatory will scan the
sky for millions of supernova, providing
the enormous data set needed to
hopefully bring us to the five sigma
mark. I personally can't wait to see
what they find. But in the meantime, the
new Desi findings are tantalizing and
bring us to the precipice of a whole new
view of both our standard model of
cosmic evolution and the ultimate fate
of our universe.
Let me know in the comments what you
think. Will the universe end in a big
freeze or is a big crunch on its way?
What ending or rebirth do you imagine
for our universe?
There's a crisis in the cosmos and the
fate of the entire universe depends on
it. We've known that we live in an
expanding universe since 1929 when Edwin
Hubble first proved galaxies are moving
farther and farther apart as time goes
on. This expansion has come to underpin
our entire theory of cosmic evolution
from the big bang to the formation of
galaxies. The key factor is the rate of
the expansion of the universe, a value
that has become known as the Hubble
constant. We thought this value was
pretty set, but now astronomers aren't
so sure. Do we stand on the brink of a
cosmic revolution? Or could it be that
our entire model of the universe is
wrong?
I'm Alex Mccoan and you're watching
Astramm. Join me as we explore the
crisis gripping cosmology, revealing how
Hubble's greatest discovery has become
one of today's most troublesome
questions.
For most of human history, the universe
was small, or at least we thought it
was. Some ancient civilizations imagined
Earth to be flat and covered by a dome
of stars. The sun and moon rose and set
and the constellations turned overhead.
By the second century, astronomers such
as Claudius Tommy had envisioned a
geocentric universe with Earth fixed at
the center and the sun, moon, planets,
and stars all revolving around us. This
would be the reigning model for more
than a thousand years until the 1500s
when Nicolas Capernicus proposed a
heliocentric model where our Earth was
one of several planets circling the sun.
A revolutionary idea. Fast forward to
the 18th century and William Hershel
mapped some of the stars in our galaxy,
the Milky Way, proving that it was a
vast discshaped system. As antiquated as
it may sound now, astronomers debated
for some time whether the Milky Way was
the entire universe or if it was in fact
one of several island galaxies in a much
larger cosmos. That is until 1923
when Edwin Hubble resolved the question
once and for all. Peering through the
100inch Hooker telescope at the Mount
Wilson Observatory in California, the
world's largest telescope at the time,
Hubble was able to resolve individual
stars in Andromeda and within them found
his first sephiid variable using Levit's
law named after Henrieta Levit who found
more than 2,400 variable stars and
discovered that they could be used to
measure distances across the universe.
Hubble determined that Andromeda was
some 900,000 light-years from Earth, an
astonishing distance, too far away to be
part of the Milky Way. This proved that
another galaxy with its own stars
existed outside of our own. Overnight,
Hubble widened our view of the universe
immeasurably.
But he didn't stop there.
He would go on to use Levit's law to
identify 23 other galaxies and measure
their distances, some as far away as 20
million lightyears from our planet.
Ultimately, Hubble concluded that
millions of other galaxies must exist
outside of our own forever changing
astronomy. But Hubble's next
revolutionary discovery also needed the
work of Vesto Slifer, an astronomer born
on a farm in Indiana in 1875.
He joined the Lowel Observatory in
Flagstaff, Arizona in 1901. And between
1912 and 1925, he made systematic
observations of more than 40 spiral
galaxies. At the time it was known that
the light observed from these distant
galaxies could be split into spectral
components and depending on what
elements were present in the light
source different patterns would appear.
If the object being observed was moving
away then those same patterns would be
present only they would be shifted
towards the red end of the spectrum what
we call red shift. Through years of
observation, Sifer found that nearly all
galaxies appear to be moving away from
us. But at the time, he didn't have a
way to measure the distances to these
far away bodies, let alone their
velocity.
In 1927, Belgian scientist George
Lamemetra proposed a theory that the
universe was the same in all directions
and that if Einstein's theory of
relativity was right, it must also be
expanding. But he had no evidence to
support this theory. So it was ignored
for the most part. That is until we
bring Hubble back into the picture. Like
most scientists at the time, Hubble was
unaware of Lmetra's theory or of another
similar one proposed a few years earlier
by Soviet scientist Alexander
Freriedman. Instead, from the
observatory on Mount Wilson, Hubble made
the same observation as Lifer that
galaxies seem to be moving away from us.
But he noticed something that nobody
else had spotted before. The farther
away a galaxy was, the more red shift it
appeared to have, meaning the faster it
was racing away from us. And this was
happening in every direction.
More observations revealed that almost
all galaxies appeared to be moving away
from each other and that the red shift
of a galaxy was directly proportional to
the distance of the galaxy from Earth.
This was a major breakthrough. It meant
that the universe must be expanding.
Hubble announced his finding in 1929 and
following its publication, it became
supporting evidence for Lmetra's
expanding universe theory, which would
become known as the big bang. Hubble's
initial measurement of the rate of the
expansion of the universe, which would
become known as the Hubble constant, was
roughly 160 km/s per million lightyear.
That's about 500 km/s per mega parcel
himself worked to refine it over his
career. Since then, the Hubble constant
has become a fundamental value in
cosmology. We've used it to establish
the age and the size of the universe.
And those numbers are important for
many, if not all, other cosmological
calculations.
To narrow in on the most precise value
for the Hubble constant, astronomers
have used two primary methods. But
something about this value isn't adding
up. One way astronomers measure the
Hubble constant is through additional
observations of red shift. In other
words, the same way Hubble made his
initial discoveries known as the cosmic
distance ladder or late universe method.
It measures the expansion as we see it
now billions of years after the big
bang. The more examples of distant red
shift that we are able to get, the more
accurate the measurement should become.
Over the years, this has refined the
Hubble constant to approximately 73.5
km/s
per mega par. quite a bit less than
Hubble's original value. The other way
to measure the Hubble constant is
through the early universe method, a
newer technique that estimates the
expansion by rewinding the clock back to
the start. This relies on images of the
cosmic microwave background or CMBB, an
ancient microwave radiation, which is
essentially a snapshot of the universe
from about 380,000
years after the Big Bang. This cosmic
microwave remnant had been predicted in
1948 by Ralph Alfa and Robert Herman.
Arno Pensius and Robert Wilson detected
its presence in the 1960s, winning the
Nobel Prize for their work. But it
wasn't until later that we got a
detailed enough image to predict the age
of the universe with precision. In 2003,
the Wilkinson Microwave Anisoptropy
Probe or WAP released an all sky map
that showed the early universe, a time
before there were even any stars. You
can think of it like this. Imagine you
come from the scene of an explosion that
has already happened. You see fragments
strewn all over the place and you can't
make out what the original object used
to look like. But then someone hands you
a snapshot of just after the explosion
began. I bet now you could trace each
piece back where it belonged in the
original image. This is similar to how
astronomers use the cosmic microwave
radiation to trace our present universe
back to just after the Big Bang. Most
recently, in 2013, the European Space
Ay's Plank Cosmology Probe was able to
capture an even more detailed all sky
image of the background radiation,
showing subtle fluctuations in
temperature that would eventually ripple
out to create dark matter webs forming
clusters of galaxies and voids across
the universe.
When astronomers take the image of the
CNB and fast forward it to the present
day, it's like pressing play on the
video of the explosion, they get a
predicted Hubble constant of about 67.4
km/s per mega par. But you might notice
this value is considerably smaller than
the Hubble constant we've observed
through red shift, which is a problem. I
really can't stress enough how the
expansion of the universe has become a
pillar of our standard model of
cosmology. The Hubble constant ties into
our most fundamental physics. From
Einstein's theory of general relativity
to the idea that the universe evolved
from a dense hot early state known as
the big bang, otherwise known as the
lambda cold dark matter model. It
emerged in the late 1990s and has seemed
to work beautifully ever since. An
important feature of this model is that
scientists expected gravity to slow the
expansion over time, but instead they've
actually found it's now speeding up.
Thankfully, this didn't break the model.
Something seems to be pushing space
apart faster and faster. And we believe
that something is dark energy. As the
universe grows, dark energy's effect
becomes stronger, causing galaxies to
move away faster and making the Hubble
constant, the rate of our universe's
expansion, increase over time. Both
methods of calculating the Hubble
constant are meant to give us the
current rate of expansion. So, it's not
this acceleration that's making the
results differ. But how can we have one
unified cosmological model with two
different values for such a fundamental
rate? This discrepancy has become known
as the Hubble tension. Not because it
represents an actual tension force, but
instead probably because of all the
atmosphere it creates at cosmologist
dinner parties. And to be honest, I get
it. It could mean we've got our entire
cosmological model wrong.
It was thought that as more accurate
data was collected, these two values
would converge on one agreed value
Hubble constant. But therein lies the
problem. As we've gotten more recent
independent measurements of the red
shift, the number isn't converging.
Instead, the gap is being reinforced.
One independent measurement came from
Mega Maza hosting galaxies. These have
certain molecules like water vapor that
can amplify microwave radiation near a
black hole at the center of a galaxy.
This can create a maser which is like a
laser but with microwave radiation
instead of visible light. Mega mazes are
extremely powerful and their microwave
emissions can be mapped precisely using
telescopes. That means they can be used
to measure the mass of the black hole
and give a very accurate geometric
distance to their host galaxy, allowing
us to calculate the Hubble constant with
presumably a very accurate distance
measurement.
In 2020, astronomer DW Pes and others
used this method to measure a Hubble
constant of 73.9
km/s per mega paras with 95 to 99%
confidence. In other words, they were
very sure. And in late 2024, another
investigation by Daniel Skolnick, Adam
G. Reese and others resulted in a
similarly shocking value. They used data
from the dark energy spectroscopic
instrument to study 12 different type 1A
supernova that were dotted across the
Koma galaxy cluster around 320 million
lighty years away. What they found was a
Hubble constant of 76.5
km/s per mega parc. Most recently in
2025, researchers from the Interun
University Center for Astronomy and
Astrophysics in India used mirror
variable stars in our galaxy as anchors
to measure the distance of mirror
variables in faraway galaxies. A similar
method to the original way of using
sephiid variables. They found a Hubble
constant value of 73 km/s per mega parc.
All of these measurements roughly agree
but fall far outside of the error range
of the plank measurements based on the
CMBB radiation. So something seems to be
missing from our understanding of the
universe. Astronomers including two who
worked on the desi investigation have
been ringing the alarm bells. The
paper's lead author, Skolnick, a
professor of physics at Duke University,
said, "Our model of cosmology might be
broken and noted that the Hubble tension
is feeling more like a Hubble crisis.
Without resolution, the model we use to
interpret the universe rests on shaky
grounds. Everything from when galaxies
formed to how clusters evolve and even
predictions of the cosmic future hang in
the balance. If the Hubble constant
turns out to be the lower value
calculated from background microwave
radiation, then we live in a 13.8
billion-year-old universe that will
likely go on expanding forever. A
steady, predictable future with constant
dark energy. But if the Hubble constant
is the higher value observed from red
shift, then our universe may be
expanding faster than the current model
predicts, and things may be weirder than
we thought. If that were the case, then
our universe may be younger, something
like 12 to 13 billion years old, and it
may mean that we're missing something
fundamental in our understanding of the
early universe, dark energy, or
relativity.
Some scientists have proposed that
radical adjustments may be needed to
reconcile the Hubble tension. These
proposed adjustments have included
things like decaying dark matter or dark
energy that varies over time. And
scientists have even explored the idea
of modifying the dark energy equation of
state, representing what could be a
change to general relativity itself.
something that may force us to
re-evaluate our entire understanding of
not just the cosmos but also our very
understanding of physics. But another
recent idea has been gaining traction.
One that could save our model of
cosmology without needing to rewrite
physics. And all it needs to work is a
little spin. No, really. The 2025 paper
suggests that perhaps we've missed a
very slow rotation or spin of the
universe published by Balash Andre
Ziggoti Istvan Zapui Imray Ferrrons Bana
and Gurgi Gabbor Vanafaldi. The idea is
that a very slow universal rotation once
every 500 billion years would be slow
enough to go undetected but significant
enough to affect how space has expanded
over time. In fact, their preliminary
calculations showed that this slow spin
could validate both values we have for
the Hubble constant. When spin is
introduced into the model, it predicts
an early universe with a lower rate of
expansion like we get from the CNB
calculations and it also predicts a
present universe with the higher rate of
expansion like we get from red shift
measurements. These are exciting initial
results. Zapui, one of the ideas authors
from the University of Hawaii,
paraphrased the Greek philosopher
Heracitis of Ephesus when explaining the
hypothesis who said panta ray meaning
everything moves.
And indeed with how promising the
initial results are, it may be true
entire universe and all.
Though the authors were clear that this
is just a preliminary calculation
focused only on the Hubble constant, the
next step towards solidifying this idea
will be more complex models and
simulations to check the hypothesis
against other observations.
I believe this idea is a reminder that
there's still a lot to learn about our
universe, but it's far too soon to think
about throwing out our entire model of
cosmic evolution, especially when we may
be just on the brink of understanding
the missing piece. And even if we can
keep our cosmological model, it would
still mean a new rotating variant of it.
one where cosmic parameters and values
shift to accommodate our new reality.
And this idea has one other major perk.
It doesn't violate any known laws of
physics. Besides, I quite like the idea
that not only is our planet spinning and
our solar system rotating, but so too
are the Milky Way galaxy and our entire
universe.
If you've been following the Astramm
Answer series recently, you'll notice
that we've talked a lot about how the
universe is structured.
Filament structures of galaxies being
pulled apart by the universe's expansion
with bubbles or voids forming in the
gaps.
Because of the universe's expansion,
everything is moving away from
everything. But of course, this isn't
totally true in practice due to a
mysterious force called gravity.
Gravity is a pulling force or
technically it is the curvature of
spaceime caused by uneven distribution
of mass.
On very small scales, gravity is hardly
relevant at all. I don't feel any pull
towards objects around me, only towards
the earth because it is so massive.
Celestial objects close enough to the
sun are most influenced by its gravity.
And all stars in the galaxy orbit around
a super massive black hole at the
galaxy's core. But it doesn't stop
there. You've probably heard that the
Andromeda galaxy is hurtling towards us.
How can that be when everything is
moving apart?
Gravity.
Objects that are close enough together
with a large enough mass are pulled
towards each other by gravity faster
than the universe can expand.
This is why we have galaxy
superclusters. And in fact, we are part
of one. Gravity is keeping these galaxy
clusters bound together, meaning over
extremely large time scales, collisions
aren't totally unusual.
In fact, a new theory has recently been
proposed that the Milky Way may have
recently experienced a collision with a
large melanic cloud-sized diffused
galaxy called Antlia 2. Scientists have
discovered that the Milky Way has
ripples consistent with it having had a
collision in the past, but we couldn't
pinpoint what it collided with until Gia
discovered the Antelier 2 galaxy hidden
behind our galactic disc. This makes it
very hard to spot as although it is
massive, it is very spread out due to
the collision and being behind our
galactic disc makes it hard to see due
to the stars and dust in the way. But
that brings us onto the main topic of
this episode, the great attractor.
In an opposite vein from the supervoids
video, where there are regions of space
where there is an almost total absence
of mass for hundreds of millions of
light years in any direction, the great
attractor is the biggest concentration
of mass for hundreds of millions of
light years. It is so massive that even
though our galaxy is between 150 to 250
million lighty years away, we and all
galaxies around it are currently moving
towards it. Estimates put its mass at
roughly 1,000 trillion suns, which is
enough for many thousands of galaxies.
But what could possibly be there that is
that massive?
Well, for the longest time it was a
total mystery because like Andla 2, the
region where the great attractor is
located is hidden behind our galaxy's
disc. However, X-ray telescopes can see
through the disc. And recent
technological improvements and advances
in X-ray telescopes have meant that we
have been able to detect thousands of
galaxies in the region where the great
attractor is supposed to be. But the
mass detected didn't add up. There
wasn't enough present to create such a
pull. Further analysis has revealed
something very interesting that while we
are being pulled towards the great
attractor, there is something even more
massive behind it. Located 650 million
lighty years away called the Shappley
attractor or the Shappley supercluster.
Located there are many thousands of
galaxies densely packed together with a
mass of 10,000 trillion suns and
everything within 1 billion light years
is being pulled towards it. On the other
hand, looking the opposite direction
from the Shappley supercluster, we see
an underd
called the dipole repeller.
It isn't actually repelling mass, but
due to all the mass around it being
pulled towards more dense regions by
gravity, it creates the illusion that it
is repelling that mass. Although there
are some scientists that do claim that
an unknown repelling force is at work
there. Simply put, we are still in very
early days when it comes to
understanding the universe.
We do observe certain things like the
motion of galaxies, dense galaxy groups
and absences of galaxies in large voids
or repelling regions. We observe the
expansion of the universe and observe
the filamentary structures. But the
universe is an impossibly large place.
We can only see so far, only live so
long. Plus, our technology is limited.
We have theories which try and explain
what we see, but I really wouldn't be
surprised to see these theories change
as more data becomes accessible. Some
may ask, what's the point then? However,
I for one am hugely grateful for the
bright minds working on this as
discovering our place in the universe is
so fascinating. I'm glad humans have an
insatiable need to explore and
understand everything around them. This
innate sense of wonder and curiosity is
what drives the evolution of mankind,
and I am excited to witness it.
A massive thank you to our astronauts on
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