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 [music] 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
Astron. 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
[music] and the constellations turned
overhead. By the second century,
astronomers such as Claudius Tommy had
envisioned a geocentric [music]
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 Herschel
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 [music] galaxies
in a much larger cosmos. That is until
1923 when Edwin Hubble resolved the
question once and for all. Peering
through the 100 inch 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 [music] 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 lighty years 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 par. However, that number
was not quite accurate and even Hubble
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 [music] 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/ second per mega parc
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 Penzius 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 anosoproy 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 CMBB 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 Maer 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. [music]
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 [music] in late 2024,
another investigation by Daniel Skolnik,
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 far away 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, Skolnik, a
professor of physics at Duke University,
said, "Our model of cosmology might be
broken [music] 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
[music] 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 Ferron Bana
and Gurgi Gabbor Vanifoldi. 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 [music] brink of
understanding the missing piece. And
even if we can keep our cosmological
model, [music] 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 [music] 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.
Is the universe inescapable?
If we were to conquer the limitations of
light speed and were to travel to
space's furthest edge, what might we
find? Just more space, infinite planets,
and planetary systems? Or would we
somehow come back to where we started?
Amazingly, according to scientists, all
of these are possible. But which one is
correct comes down to the nature of that
unseen world all around us.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we continue
our series exploring the unseen world of
4D space and discuss possible answers to
the question, what is the shape of the
universe itself?
But first, let's begin by talking about
infinity.
You are likely already familiar with
infinity. In maths, it is the concept of
a number so large it cannot possibly be
beaten. Of course, no such number
exists. For any number you can name, I
could come up with a number that is at
least one larger than it. But in a way,
that's sort of the point. In infinity,
there is always another number. And when
it comes to our universe, [music] we
have so far discovered no edges. There
may always be another star or planet.
An infinite universe is a little
mind-boggling for us. We live in a very
finite world with edges and endings. So,
the idea that there might be literally
infinite more planets out there is a
little bewildering. [music] However, as
we develop more and more powerful
telescopes and pushed back the darkness
further and further at the edges of what
we can observe in our universe, all we
are finding is that even the darkest
patches of the night sky are turning out
to be brimming with stars. So,
increasingly, an infinite universe might
be something we are forced to
contemplate.
But that is not to say that just because
the universe is infinite, there are not
a finite number of things in it. That
may sound a little counterintuitive, but
let me show you what I mean. Believe it
or not, there are different kinds of
infinity when it comes to our universe.
Three possible scenarios could be true.
A flat universe, a spherical one, or a
hyperbolic universe. Allow me to
explain. In a flat universe, if we were
to form a grid to broadly represent
reality, everything would seem fairly
standard. All the lines would either be
parallel to each other or perpendicular.
An infinite universe of this variety
would simply extend outwards in all
directions forever and ever. This is a
little boring, so I won't spend too much
time on it. However, this is a lot like
we perceive the universe to be. For the
most part, all lines of direction appear
straight to us. We can distinctly see
the planets and stars around us and we
notice no real curving or warping.
However, this is not the only way that
the lines can be drawn. Consider for a
moment a black hole. You may immediately
notice the strange rings that appear to
run around its equator as well as across
the top of it and along the bottom. This
is something of an illusion. There are
no rings across the top or bottom of
this black hole. What you are seeing is
the equatorial ring that's on the other
side of the black hole. However, due to
the powerful gravity of the black hole,
the light that is hitting it is not
bouncing off upwards or downwards into
space. Instead, the rays are curving
towards us as the black hole's gravity
pulls them in. You are seeing the top
and bottom of the ring at the same time.
Light being bent by gravity. What do I
mean by that? Actually, this is an
excellent example of our second kind of
universe. In a flat universe, all the
lines that make up reality are fairly
straight. But what if we were to come up
with a rule? All the lines must instead
curve towards each other. There is only
one way such a universe could be drawn,
and that is in a sphere. Consider trying
to draw two parallel lines on a sphere.
You might start off well, but will
quickly realize that your task is
impossible. All lines would converge
towards each other, intersecting at
least twice as they returned back to
where they started. What would a
universe that was based on these kind of
lines look like? Essentially, rather
than going in the straight line you
thought you were going in, you actually
would be traveling in a massive curve.
It's a bit like those computer games
where you travel off one end of the
screen only to reappear from the other
side. In a spherical universe, you could
travel infinitely, but ultimately you
would only end up arriving back where
you started with a powerful enough
telescope. And if light were to travel a
whole lot faster all of a sudden, it
would be possible to look at the back of
your own head. This kind of universe
contains a [music] finite amount of
things, but it appears infinite because
you just keep bumping into the same
things infinite times.
Thanks to objects like black holes and
powerful stars, we do indeed have
evidence that our reality sometimes is a
curved spherical one, at least near
large bodies of mass. The inside of a
black hole's event horizon is this kind
of infinite space. No matter what path
you take, you can never get out of it.
However, let's consider our last
example, the hyperbolic universe. This
one is the hardest to visualize, but the
idea is simple. Instead of having all
lines remain parallel or move towards
each other, every line must move away
from everything.
Drawing this is inherently tricky
because everything keeps getting wider
exponentially. The only way you can do
that is to either buckle your nice flat
disc until it becomes something like
this or warp what you are seeing like
this. All of the objects in this image
are squares. However, they are squares
that are obeying our rule that all their
lines must be diverging away from each
other. This leads to the very strange
situation where you can have five
squares all meeting up at a corner
instead of the usual three that is
possible in normal 2D space. All right,
this seems a little confusing. What does
it mean if space is hyperbolic?
Well, let's consider what it is we are
curving around. You might have noticed
when we talked about our spherical shape
that there must be something we are
curving around. That direction of
curvature is in regards to time.
Imagine, if you will, a series of
timelines.
We go a little more in depth with the
interplay between space and time in my
last video, which I would really
recommend you check out. But for now,
just remember for this model that
objects in time move forward along their
timelines in the direction of up or the
future. If they move left or right, they
are moving through space, getting closer
to each other. If we introduce a large
mass into this model, it warps the
timelines.
Now, if you were a small object
traveling along one of those arrows that
[music] got too close to the mass,
suddenly your path of travel no longer
goes directly up towards the future. It
pulls you left or right towards the
mass. There are several reasons for
this, but the essential thing to
recognize here is that now your straight
path [music] towards the future pulls
you in towards the planet. So, you'll
have to accelerate away from it just to
stay on a straight path. In a nutshell,
you are experiencing gravitational pull.
Even the planet is affected by this. The
atoms on either side of it are squeezed
[music] towards the center of mass as if
it were being forced down a narrow tube
by giant invisible hands. Let's get back
to hyperbolic space. In this model,
[music] the opposite thing is happening.
All lines are moving away from each
other. We could represent this by
curving space and letting our timelines
be straight, which is nice because
[music] it captures the idea that from
your perspective, your time is always
ticking forward normally. But let's warp
this slightly so that space is flat.
It's all a matter of perspective after
all. Here, parallel lines are also
impossible. But this time, rather than
converging, all parallel lines diverge
more and more. Everything moves further
and further apart. H why does that sound
familiar? It is because that is what the
universe is doing. This is not
noticeable within a galaxy where there
is enough mass and gravity to keep
everything together. However, from what
we can see of the universe as a whole,
every [music] galaxy is moving away from
every other galaxy. Scientists try to
explain that with dark energy. But maybe
all that is happening is that the
universe is just naturally hyperbolic in
its shape.
So what would that mean if the universe
really was hyperbolic?
It would mean that the universe was
really infinite. The flat space we
looked at was infinite. For each
lightyear you traveled out, you discover
another light years worth of space.
However, with hyperbolic space, you
discover more than another light years
worth of space. It's like opening
infinite doors, except inside each door
are two new ones.
The possibilities would be far more
endless, far more infinite than in just
regular flat space models. But also, it
means that given enough time, the rest
of the universe would drift away from us
until our galaxy was all that was left.
Scientists have looked across the
universe, however, have not noticed this
hyperbolic space in action. In fact,
things all look pretty flat. So [music]
perhaps flat space is the correct
answer. Yet this still leaves room to me
for hyperbolic space to be the default.
After all, if matter is curving space
towards it and the universe appears
flat, it would make [music] sense that
the universe was curved in the inverse
at least to some degree. Perhaps all
three models are true. Perhaps the
universe is by default hyperbolic, but
mass brings it together in such a way
that it perfectly offsets the inverse
curves of the universe to the point
where everything appears flat. There
certainly seems to be some evidence that
this is the case, but it's very
difficult to know for sure. Which model
do you think is correct? Or maybe you
feel that we do not live in an infinite
universe at all. Please leave a comment
down below to tell me what you think.
But for now, just remember the unseen
world might be a lot more influential on
our universe than we are currently aware
of.
When the James Web Space Telescope
finally saw the edges of the universe,
we knew we had a problem.
Web was able to resolve light emitted
from stars 13 billion years ago, helping
us to peer back in time to some of the
universe's earliest moments.
But what we saw was not a sparssely
populated proto universe where matter
was only just starting to coalesce into
the first tiny intermittent galaxies
here and there. The early universe was a
bustling place. It had galaxies,
too many of them. They were too bright.
and the black holes we started to spot
in their hearts had grown too big too
quickly.
Some began to proclaim that our models
were wrong and cosmology was in crisis.
And while some of these problems have
begun to alleviate as better data came
in, other problems simply became more
prominent. But in a strange twist, one
of the most resilient mysteries in all
of this might be about to unravel thanks
to a small black hole with an impossibly
big appetite. Its name is LID 568,
and we've just seen it breaking the
Edington limit, consuming matter faster
than it should be able to. And it might
just be the key to everything.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we explore LID
568, the Edington limit, and its
groundbreaking implications on
cosmology,
a black hole breaking physics. By now, I
really shouldn't be surprised.
It takes time to cook up a galaxy.
Interstellar gas and dust [music] need
time to subtly come together under
gravity until a critical mass is reached
and stars begin to ignite. These stars
[music] live and die and from their
deaths, new stars are formed. This too
takes time. Cosmologists have observed
our universe and [music] based on what
they saw created models for how old our
universe is and how quickly galaxies
form. which is why a James [music] Web
Space Telescope data caused such a
crisis. Things were not as the models
predicted. [music]
Fortunately, some of those problems
proved solvable in the months [music]
after the data was released. For
example, the brightness of the galaxies
we could see through web. This
brightness implied that there were far
too many stars present in those
galaxies. So many stars should have
taken much longer to form. And yet there
they were, fuzzy red dots at the [music]
edge of Web's resolution. However,
scientists at the University of Texas
studying Web's cosmic evolution early
release survey realized there could be
another explanation for all that excess
light. And [music] counterintuitively,
that explanation was black holes.
If we work under the assumption that
there were massive black holes in these
galaxies rapidly consuming cosmic gas,
then the intense friction given off by
these hungry leviathans as they ate
created an excess of light in their
accretion discs. This explains why
galaxies overall seemed brighter and
were throwing off our estimates. Once
you add these shining black holes, you
don't need so many stars. The mass of
each problematic galaxy dropped and
everything fell back into line with the
cosmological model. Problem solved.
This reinforced how important black
holes are to our understanding of the
early universe, which was in and of
itself a problem because the black holes
themselves broke our models, too. In
particular, cosmologists struggled with
the thorny question of how they'd come
to be.
For small black holes known as stellar
black holes, there was no issue. Stella
black holes have masses a few to 100
times that of our sun. And we understand
very well how they are formed.
They are the collapsed remnants of a
sufficiently massive star and there
would have been time for such black
holes to form in the early universe. But
scientists were struggling with the
super massive black holes with masses
tens of thousands to billions of times
that of our sun which tend to lurk at
the central point of galaxies and due to
something called the Edington limit.
There just shouldn't have been time for
these kinds of black holes to have
formed where and when webb saw them. And
yet there they were and they were
numerous.
Stella black holes can grow as time goes
on, provided [music] you funnel more
mass into them. But how quickly?
In 1920, an English astronomer and
physicist called Arthur Edington
formulated the idea that there was a
limit to how quickly either a star or a
black hole could grow. This was because
photons carry momentum. A tiny amount,
true, but enough to exert a push. This
is what pushes solar sails on certain
hypothetical spaceship designs. That
tiny amount of momentum imparted by
photons. For mass to enter into a star,
it has to push against a constant stream
of photons that are radiating outward.
And at a certain level of brightness,
not even gravity is strong enough to
pull against the flow. This is called
the Edington limit. And stars that brush
against its boundaries, such as Volria
stars, bright stars at least 20 times
more massive than the sun, emanating
powerful stellar winds, are just the
slightest nudge away from blowing
themselves apart. For black holes, you
might think this would be less of a
problem. isn't the whole point of black
holes that they don't radiate any light.
But their accretion discs are a
different story. As we discussed
earlier, accretion discs around super
massive black holes can be incredibly
bright, particularly around super
massive black holes, sometimes dwarfing
the brightness of the stars in the
galaxy they reside in. With brightness
comes resistance to gravity, and black
holes have to obey the Edington limit,
too.
So even though given enough time and
mass, stellar black holes could
theoretically [music] grow into super
massive black holes, it doesn't seem
plausible that this actually explains
all the super massive black holes we see
in the early universe. simulations have
been run and although it is technically
possible to grow a stellar black hole
into a super massive black hole in that
time frame, it would require those black
holes to be feeding at near the Edington
limit nonstop since their birth, which
just doesn't [music] happen. Black holes
in real life often run out of mass
nearby and need to wait to run into more
or for more to come to them. To further
complicate the matter, we're not
completely sure that super massive black
holes are the grown-up version of
stellar black holes in the first place.
Although it seems like common sense to
assume so, scientists have been confused
at the lack of the intermediate stage of
black holes observable in our universe.
To be frank, they've not cited any, at
least none for sure.
Super massive black holes are common at
the center of galaxies. And there are
thought to be 100 million stellar black
holes in our Milky Way alone based on
the number we've seen. But intermediate
black holes are suspiciously lacking
with only a handful of potential
candidates. You would think we'd see a
lot more.
Struggling for certainty, scientists
began to hypothesize that super massive
black holes were instead born in some
other way. Many cosmologists have been
exploring the idea that because
everything was much closer together in
an early universe, things might have
been dense enough that interstellar dust
itself could conceivably have collapsed
to form a black hole directly, skipping
the star step altogether. If this is
true, and there is some evidence to
support the theory, then perhaps super
massive black holes were once capable of
simply being born that size or near it
right from the offset, even if such a
thing is no longer possible in our more
spread out universe today. But this is
by no means certain. But then lid 568
came onto the scene and the pendulum
swung the other way again.
Lid 568 is a very distant black hole
between 12.1 and 12.3 billion lightyears
away. It's so far away [music] from us
that we can't see it at all using
visible light. The expansion of the
universe has redshifted it all into
infrared ranges. But even its infrared
emissions were too dim to be picked up
by heavy hitters like Hubble alone. It
took the Chandra Cosmos Legacy Surveys
combined telescopes and the incredible
resolution of the James Web Space
Telescope to see it at all. Even then,
LID 568's whole galaxy is a little more
than a faint red and compact dot. But
the light emissions from this red dot
are [music] revealing.
X-rays given off by lid 568's accretion
disc reveal that it was actively
consuming matter in its galaxy's heart
in a way that no one expected.
You see, LID 568 crucially breaks the
Edington limit. And not just by a
little, it's 40 times over the accretion
speed limit. It's well on its way to
having its license revoked. How is this
possible?
It turns out that breaking the Edington
limit is in fact possible, but only for
short bursts or in sneaky ways. For
example, jets can help you get around
the Edington limit. If all your photons
are being blasted off in a single
concentrated direction, all the other
directions can eat to their heart's
content with no photon feedback getting
in the way of a good meal. There are
other possibilities. While Edington's
limit says that once the brightness of
the accretion disc becomes too high, all
the black holes food will be blown away.
There is a period of time before this
happens where a greedy black hole can
snatch at the escaping matter and
potentially enter super Edington
territory. like an overeager diner, it
might pay for it later, but for a short
burst, that level of accretion can
occur.
If this is true, it might just explain
how super massive black holes in the
early universe came to exist. And
certainly, lid 568 exists and is the
clearest example to date of a black hole
accreting this quickly. that demands our
consideration. Much like the impossible
super massive black holes themselves,
they are there. It's now our job to
attempt to understand how that's
possible.
So, mysteries [music] remain. If lid 568
is increasing matter past the Edington
limit, it proves such a thing is
possible. But what of the other strange
things [music] Web saw? Where are the
intermediate black holes that stellar
black holes ought to grow into on their
way to becoming super massive? Why are
there so many galaxies in the early
universe more than our model should
allow? Do direct collapse black holes,
ones formed from the cosmic dust itself
with no stellar intervening step, really
exist?
Our models might be on the right track,
but something is missing or incomplete.
Black holes exert a phenomenal influence
on our universe, and there are secrets
surrounding them that they guard
jealously.
But as powerful as the James Web Space
Telescope is, it has not [music] allowed
us to crack this mystery. Not yet. But
then perhaps we ought to be pacing
ourselves. Thanks to our telescopes, we
have seen billions of trillions of stars
and that's a lot of data. Accrete too
much information all at once and it
might prove difficult to absorb it all.
So says Edington and his rule is never
to be broken except of course when it
is.
We often think of black holes as
destroyers. They suck everything within
their reach into them and give nothing
back. They are the end, the final
destruction of the universe. And yet,
what if I said to you that they might
actually prove to be our salvation?
Black holes might provide the answer to
traveling faster than the speed of light
and solving the energy crisis in ways we
couldn't have even imagined until
recently.
And as by now I have come to expect,
they do so by messing with the fabric of
reality itself and by completely
countering my expectations of physics.
Perhaps we have been thinking about
black holes all wrong.
I'm Alex Mccoan and you're watching
Astramm. Join me again for the fifth
video in my series about black holes,
where once again my mind has been blown
by the incredible potential and
implications of these very real objects
in our universe.
I've talked before about the formation
of black holes in this series, including
aspects about their event horizons,
how they are created,
and how they might possibly end.
But to understand how a black hole
ignores the usual limitations on faster
than light travel and does so in a way
that you can benefit from it without
having to go inside a black hole's event
horizon and how it produces near
limitless energy at the same time then
we are going to have to understand more
about the features of black holes than
we've covered so far. So, a quick recap.
What is a black hole? In its simplest
form, a black hole is an object in space
that is so massive and so dense that the
gravity it creates is too powerful for
anything to escape it. We are familiar
with the iconic black spherical zone
that surrounds a black hole. This is the
black hole's event horizon. This sphere
is the demarcation point between
escapable gravity and inescapable
gravity.
Because the gravitational pull increases
the closer you get to a black hole. Once
you go beyond the event horizon,
nothing, not even light, can travel fast
enough to get away again. Beyond that,
though, it's actually quite difficult to
say much about the black hole's features
at all. Precisely because of the event
horizon, we cannot see what the inside
of a black hole looks like. In fact,
there are only three things we can say
about black holes with any degree of
certainty. They have mass, they have
charge, and they have angular momentum.
You might wonder how we know these
things about black holes given that no
light can leave them to tell us about
them. The key to these three
characteristics is that all three of
them represent aspects of the black hole
that can be felt outside the black holes
event horizon. Charge, for instance,
works the same way around a black hole
as it does around any other charged
object. That is to say, if a black hole
is charged, then it will attract objects
that have different charge to it and
repel objects that share its charge.
Think of it like a giant magnet pushing
and pulling on the universe around it.
Scientists can track objects that
approach a black hole and by seeing how
quickly certain objects known to have a
charge move towards it, scientists can
predict the charge of the black hole
itself.
Interplaying with this is mass.
The mass of a black hole can also be
felt outside the sphere of the event
horizon. In fact, it is the main creator
of the event horizon in the first place.
This is because mass creates gravity and
does so in a linear fashion in
accordance with the same principles you
might find in Gor's law, a theorem about
electromagnetism,
albeit with a gravitational analog.
So, it's possible too to calculate the
mass of an object by seeing how far away
objects are before they start to
accelerate towards it and how quickly
they accelerate. Although obviously you
need to factor in charge at the same
time or your results might get skewed.
Finally, angular momentum or spin. It is
possible to detect the spin of a large
mass object and we are going to dive
into the how in just a bit. For now,
let's just accept it as a given and
recognize that black holes are certainly
very high mass objects.
There are varying sizes of black holes
in existence. The smallest known as
micro black holes have a mass that's
comparable to that of our moon or 7.35 *
10 ^ 22 kg.
They fit all this into a space that's
just 0.2 2 mm in diameter, which is
incredible. It really gives you a sense
of how dense a black hole can be.
Something thinner in size than a human
hair, packing the mass of the moon. And
that's just the smallest ones. Stellar
black holes have a mass equal to 10
times our sun and have a diameter equal
to 60 km.
Intermediate black holes are the mass of
1,000 suns and fit all of that into a
diameter of 2,000 km, which is still
much smaller than the Earth. It is the
largest black holes that really dwarf us
with masses between 100,000 to 10
billion times the mass of the sun and
sizes ranging from 0.001
to 400 astronomical units. an
astronomical unit being the distance
from the Earth to the Sun.
But other than those three features,
there are in theory no other differences
between them. If you put two black holes
in the same room and made sure they had
the same mass, charge, and spin, it
would be impossible to tell them apart.
However, these three features are enough
to have some interesting effects on the
area of space outside a black hole.
Traveling inside a black hole is
impossible. Space and time break down
past the event horizon. But we think we
know a few things that must exist inside
one. Beating in the heart of a black
hole, there is thought to lie the
singularity.
In truth, this actually is the black
hole. When we were discussing diameters
earlier, that is just the diameter of
the event horizon. Again, we are not
certain what a black hole actually looks
like because light can never escape it.
In a space that is infinitely small,
there is a point where all the mass of
the black hole is packed so that it is
infinitely dense. For the simplest
models of black holes, the ones that do
not spin, this is a single point. In a
rotating black hole, this is more like a
little spinning ring. Otherwise, it
would be difficult to define spin for a
point that has no volume. Our
current physics get very strange around
such a black hole. If ideal paths are
traveled around this point, it becomes
mathematically possible to do some very
strange things like meet up with your
own past. This has some disturbing
implications for causality and gets into
time travel paradoxes like the
grandfather paradox. So that probably
only shows for certain that our ideas
about singularities are not quite right
yet. Because the singularity is so
small, it'll take the successful merging
of quantum theory and general relativity
theory to properly explain what is going
on inside a black hole. And we have not
yet managed to do this. It may one day
turn out that singularities do not exist
in the hearts of black holes at all. But
this is the extent of our knowledge so
far.
Well, whatever it is that lies inside a
black hole, it powers our faster than
light engine because like most objects
in the universe, it spins. And oh, does
it spin.
As we travel out from the center of the
black hole, we pass through the event
horizon with little fanfare. The event
horizon actually cannot be detected
locally, although a person outside the
black hole might watch you slow down to
a complete stop as you travel through
it. From your perspective, it actually
might seem like time is flowing
normally. Normally, that is until the
universe outside the black hole [music]
runs its course in an instant because
time outside the black hole is traveling
so fast compared to you. This is the
essence of relativity and we talk about
it in another of my videos which you can
look at here.
In fact, the only evidence you might
have that you've passed the event
horizon at all is because of something
that exists just outside it, the photon
sphere.
In a zone just outside the event
horizon, there exists a point in space
where if a photon enters it at just the
right angle, it will enter a perfect
orbit around the black hole in much the
same way the moon perfectly orbits the
Earth. This infiniteesimally thin zone
is known as the photon sphere. And given
the number of photons that have flown
past black holes in all the millions of
years they have existed, it is probably
filled with photons. It is quite
possible that you would be instantly
fried as you pass through this point.
However, it is just outside here that we
find the zone that interests us, the
ergosphere.
This is the zone around a black hole
where we can most easily detect its
spin. And this is because in this zone
it is impossible for us not to move. You
see, mass affects space. We see this in
the curving effect of gravity on the
travel of objects through that region of
space. However, it might be more
accurate to say that mass drags on the
space around it. As it moves through
space, it brings a little bit of that
space along with it for the ride. And
when an object as massive as a black
hole spins, there is an effect known as
frame dragging. To put it simply,
reality around the black hole begins to
spin in a whirlpool that cannot be
fought against. Much like a real
whirlpool, anything caught within the
ergosphere is spun around the black hole
because the frame of reference it sits
in is being pulled.
Sort of like how a person moves because
they are standing on a moving walkway.
The greater the spin of the massive
object, the faster this happens. And in
the ergosphere, this can occur at a
speed so fast that by the event horizon,
space is moving faster than the speed of
light. You would need to travel faster
than the speed of light in the opposite
direction just to stay at a relative
standstill from the point of view of the
outside observer, which of course you
cannot do.
But isn't this against the laws of
physics? Doesn't Einstein say that
nothing can travel faster than the speed
of light? The answer to that is yes. But
black holes have found an interesting
loophole. You see, this rule only
applies locally. Right where you are in
your frame of reference, nothing can go
faster than the speed of light. But
thanks to relativity, it is possible for
frames of reference to move away from
each other so fast that objects in them
appear to be breaking this light barrier
from your point of view.
But if you move next to them and entered
their frame of reference, they would
seem to slow down and would start
obeying the laws of physics again. It's
a really weird effect, but frame
dragging is an actual thing. It is by
measuring frame dragging that scientists
can learn the spin of a black hole.
However, according to a man called Roger
Penrose, there may even be a way of
exploiting it. If you were to send a
rocket into this section of the
ergosphere, the rocket would speed up
due to being caught in the whirlpool of
reality. Once it had gained enough
speed, it could then fire a propellant
in such a direction that it pushed
itself out of the whirlpool again, but
now traveling at a much faster speed.
This method, named the Penrose process,
could hypothetically net you energy
equal to about 20% of the mass of your
rocket. Now that might not sound like
much, but remember according to
Einstein's E= MC², your 20% mass would
produce energy equal to itself times by
299,792,458
squared. That's a lot of energy.
So to harness this colossal kinetic
energy, all you would need to do is
travel to the nearest black hole, which
is roughly 3,000 lighty years from us,
and enter its ergosphere with a rocket
capable of surviving the intense
gravitational forces there. Ideally, you
would need to find one that was not
surrounded by an accretion disc because
those get up to temperatures of millions
of degrees as they are swung around at
near light speeds and melt from solids
down to gas and plasma. But you get the
idea. Easy.
Okay, maybe this is a little impractical
for us, but the implications for faster
than light travel that black holes
demonstrate through frame dragging might
just offer us the key to one day beat
the light barrier for real. Not by going
faster than light ourselves, but by
somehow convincing the frame of
reference we are in to travel at those
faster speeds, just like they do around
a black hole.
Of course, if this requires the energy
of a black hole to accomplish, we might
be out of luck for now. But it's an
incredible glimpse into what is
possible, and scientists [music] are
already looking into the power of frame
dragging for future travel. But maybe
that's a topic for another video.
Either way, this all just highlights
once again how our universe really is
very different from what we might have
ever imagined.
Movement through space is inevitable.
You might not feel it, but right now
you're sitting on a planet that is
spinning on its axis, moving you at up
to 1,600 [music]
km hour, depending on your latitude. The
Earth circles the sun. The sun moves
through the Milky Way. The Milky Way
moves through the [music] local group of
galaxies.
And the local group moves through our
local supercluster.
And even that supercluster of galaxies
is in motion heading towards the
Shappley supercluster where scientists
believe that there is a particularly
large concentration of galaxies. I hope
all this motion isn't making you too
dizzy. But on the grandest scales of our
universe, something strange is
happening. Scientists have begun to
realize that there is not enough mass in
the Shappley supercluster to pull us
towards it at the rate that we see.
About 50% of the cause of that motion is
unaccounted for. In 2017, researchers
discovered a possible source for the
rest of that motion. But it's not
something pulling us, it's something
pushing.
I'm Alex Mccoan and you're watching
Astramm. Join with me today as we
explore the evidence for the region of
space known as the dipole repeller and
try to understand how in a universe
filled with gravity, something can push
us instead of pull.
Let's start with a little context. It's
taken a long time for astronomers to
recognize that this motion was taking
place. To understand that we were
moving, scientists first had to make a
map of the regions of space around us.
And although we as a species have been
mapping the stars since the beginnings
of civilization, it was only thanks to
Mr. Hubble [music] in 1924 that we
proved there are actually stars in other
galaxies outside the Milky Way. Before
then, although astronomers had seen
fuzzy little clusters of light in the
night sky that we now know to be
galaxies, the common wisdom was that
these were gas cloud spiral nebula
within the Milky Way, not something that
existed [music] beyond it.
Hubble noticed several sephiid stars, a
type of variable star with a cycle of
variation closely linked their
luminosity within one such spiral nebula
and used the fact that this luminosity
was very predictable based [music] on
distance to calculate very precisely how
far away they were. Surprising many, he
proved that they do exist beyond the
Milky Way. Since then, astronomers have
been scrambling to catch up with the new
reality of galaxies and superclusters
and set about mapping the locations and
distances to every galaxy they could
find. Hubble had been studying
Andromeda, our closest neighboring major
galaxy, but there were others. By the
1970s, Steven Gregory, Lar Thompson, and
William Tiff definitively proved that
[music] galaxies didn't just float
randomly in space, but converged into
superclusters, large filamentary or
sheetlike structures that exist between
large bubbles of void. They mapped the
first supercluster, the Koma
supercluster, which covered a region of
space 100 million lighty years across. A
whopping 95%
of all galaxies are found in these
superructures.
It wasn't until 2014 that our own
supercluster, the Lanakius supercluster,
was fully mapped. You might be surprised
to hear it happened in that order. After
all, wouldn't common sense say it's
easier to map regions of space closer to
us rather than ones further away? Why
was it only nearly a century [music]
after the discovery of other galaxies
existing and 40 years after mapping the
first supercluster that we finally
[music] turned to our own?
The answer is that mapping the local
regions of space [music] around us is
surprisingly challenging. And it's all
because of the Milky Way getting in the
Milky Way.
The Milky Way is full of gas and dust.
And these regions are so difficult to
penetrate that we can't really see
beyond them. Towards the center of the
Milky Way, this effect gets so bad that
scientists [music] have dubbed the whole
area the zone of avoidance. Very little
light gets through it. Not being able to
see in this area is particularly
relevant to our current discussion for
reasons we'll get to later.
In contrast to our local area, distant
galaxies are easier to study as all you
have to do is point your telescope at a
single point in the night sky and let it
drink in the light. Mapping the area
around us requires looking at every
point in the night sky. It's proved
quite difficult, although astronomers
are now getting a better handle on it.
Thanks to their efforts in looking at
thousands of galaxies in our galactic
neighborhood and by studying galaxy's
peculiar motion, or their motion
relative to the cosmic background
radiation that ignores [music] the
expansion of the universe, scientists
have been able to group gravitationally
bound galaxies into superclusters. At
the center of our Lanaya supercluster
lies a point known as the [music] great
attractor. An area 150 to 250 million
lighty years away from us that we in the
Milky Way are slowly drifting towards.
Sadly, the great attractor lies within
the zone of avoidance. So, it's tricky
to see clearly what lies there. To
confound things further, the Lania Kia
supercluster was also found to be
moving. It travels towards another
supercluster known as the Shappley
supercluster taking us along with it. At
the center of this supercluster lies the
Shappley attractor which also is
believed to be incredibly dense in terms
of mass. But frustratingly, this second
attractor also lies in the zone of
avoidance, making it difficult to see
exactly what's going on over there, too.
Thankfully, as X-ray and infrared
telescopes improved, it became possible
to take a better look at these two
attractors.
But this is where the mystery begins.
What mass is there is not quite massive
enough to account for our apparent
motion in that direction. Which is why a
team of researchers from the University
of Hawaii published an article in Nature
to attempt to explain this discrepancy.
The team was made up of Yehuda Hoffman,
Daniel Homed
R. Brent Tully, and Helen [music]
M. Corttois. Together, they created a
new kind of map of the local universe
around us. This time, instead of simply
noting galaxy's positions, they
highlighted their motions instead. This
allowed them to create a map of flow
lines which after mathematical analysis
allowed them to make assumptions about
the locations of masses in our nearby
superclusters.
Their results were surprising. A lot of
our local mass is moving towards the
Shappley supercluster which is [music]
what you would expect. But they also
found a lot of mass is moving away from
another specific region in space. They
call this mystery patch of space the
dipole repeller.
Together the dipole repeller and the
chapplier attractor both contribute
about 50% to our motion working together
in tandem. Hence the name dipole. But
how?
Gravity is a force that so far as we
have observed only pulls. [music]
What lies in this region of space that
allows a push to happen? Could it be a
strange collection of white holes? The
theoretical opposite of black holes that
we've talked about in videos before? Or
perhaps some source of anti-gravity?
Not quite. The answer is nothing.
The dipole repeller is a void, a bubble
about 100 [music] million lightyears
across that does not contain many, if
any, major galaxies. It's one of the
bubbles that exists between the
filaments of the universe's structures.
But interestingly, our galaxy's current
motion lines up much more satisfyingly
with the push from this region than it
does from the pull of the Shappley
attractor, which is a compelling
argument in this theory's favor. So, how
does nothing push?
The answer is actually that this could
be a pseudo force more than it is a real
one. Imagine a universe where all the
galaxies were spaced equally. While the
gravity of galaxies above would pull
you, the gravity of galaxies below you
would do the same. So would the pole of
galaxies to your left and to your right.
In this way, the varying forces of all
these gravities would balance each
other, leaving you to not really travel
in any direction. You'd be in a perfect
equilibrium. But what would happen if we
removed the galaxies from one of these
[music] directions? What would happen if
we added a void? Well, then the scales
would tip. [music] There would be one
direction that no longer pulled you,
leaving the opposite direction pull to
act on you unimpeded. As a [music]
result, you would move away from the
void as if it were pushing you.
Everything near a void [music] will thus
move away from it, making it seem to
have a repelling gravitational force. It
is something of an optical illusion.
There is another explanation for why a
void space might push you, which might
work in tandem with the pseudo force.
The universe is expanding, and that
expansion [music] shows no sign of
slowing down. In fact, it seems to be
speeding up. However, this expansion is
counteracted [music] by gravity. And in
areas where there is more gravity, less
expansion seems to take place. Stars
aren't just being pushed away from each
other, they're also being pulled
together. Conversely, in a void, there
is nothing to contain this rampant
expansion. As a result, void spaces
literally will swell compared to their
supercluster counterparts. It might be
done by warping the fabric of reality,
but this also achieves a sort of push.
Since 2017, not much more has come to
light about the existence of the dipole
repeller, as this is still an expanding
field of research. There's some debate
about whether it's really there or how
influential it might be on our galaxy's
current motion. It is difficult to
observe due to the Milky [music] Way's
obscuring effect and there is always a
challenge inherent in trying to spot the
[music] absence of a thing rather than
its presence. However, Tali and his
fellow researchers hope [music] that
with the aid of future ultra sensitive
surveys in multiple spectrums of light,
it will be possible to map out the few
[music] galaxies that lie in this void
and generally confirm its existence in
the region they hypothesize.
We are constantly moving through space.
But even the science of space [music] is
always in motion. Each new galaxy along
with data regarding its red shift and
travel speed helps us develop a broader
understanding of the movement of the
galaxy. It's fascinating to think that
not all of that motion is caused by the
pole of gravity. It might turn out that
sometimes the universe just needs a
little push to get going.
Can information travel backwards in
time? It's the sort of thing that would
be really useful if it were true. You
could tell your past self not to eat
that burrito that didn't agree with you,
or you could reveal to yourself they're
winning lottery numbers. But it just
doesn't happen. The resulting paradoxes
alone would make the whole thing
laughable. In our universe, time always
seems to flow in one direction, forward.
The idea of traveling backwards in time,
or even simply communicating with your
past self seems so outlandish, it can't
possibly be true. So why is it that on
the quantum level, information seems to
be doing just this?
What? You haven't noticed particles
communicating backwards in time? Well,
perhaps we need to talk about the
strangeness that is quantum mechanics.
It is an effect that if understood could
one day bring us technologies like
faster than light communication or
faster than light travel. At least if we
could somehow harness it. But even if we
can't, it's an undeniably strange
insight into the unseen world around us.
I'm Alex Mccoan and you're watching
Astramm. You're about to see some
realworld experiments that are
mindbendingly weird. And if by the end
of this video you enjoyed what you
learned, feel free to give this video a
like and subscribe to the channel. Just
please don't break causality when you
do.
So, what do I mean by particles
traveling backwards in time? By all
accounts, it doesn't seem possible. In
previous videos, I mentioned that
objects would require infinite energy to
even go fast enough to reach the speed
of light. So, how could something go so
fast as to reverse the usual direction
of time and arrive at a destination?
Just not instantly, but before they
left. Not even light can do that. And
it's the fastest thing we know of. Well,
this rule about nothing traveling faster
than light is mostly true for the macros
scale universe that we live in. And by
macros scale, I mean everything
significantly larger than an atom. But
physicist John Stewart Bell noticed an
exception to this rule when it comes to
quantum entangled particles.
Okay, so let's start there. What is a
quantum tangled particle? In quantum
physics, it's possible to hit two
particles together in such a way as to
link them together so that by measuring
the one particle, you learn things about
the other. For instance, if you know
that the particles originally had a
total of zero momentum and you learn the
momentum of one of the newly quantumly
tangled particles, you know the momentum
of the other particle will be the exact
reverse, making sure the total remains
zero. Effectively, by measuring the one
particle, you can learn things about the
other. This works for other particle
properties, too, such as position,
polarization, or spin.
On the surface, there's nothing too
weird about this. It's no different from
me meeting up with a friend and
discussing our plans for the evening. We
agree to go out and we agree that I will
pay for the evening and my friend won't.
Then no matter how far we go on our
night out or even if at some point
separate, I know I will be paying and my
friend will know that he won't. This is
how Einstein thought it worked. Only it
turned out that Einstein was wrong.
Because as it happens, me and my friend
did not discuss in advance who would be
paying. And the strangest of all, we
still both agree with each other anyway,
100% of the time, no matter how far
apart we are. This is the strange thing
about quantum entanglement and quantum
physics in general. We like to think of
particles as having fixed properties.
However, our first mindbending
experiment shows that particles only
have properties when you detect those
properties. Until then, they're kind of
vague about the whole properties thing.
Instead, only relying on probabilities
as defined by a quantum wave equation.
This doesn't make sense intuitively.
Looking at a thing shouldn't be what
gives it properties, right? Well, how
would you know? If a tree falls in the
woods, does it make a sound? According
to quantum physics, not necessarily.
Let's talk about the first mindbending
experiment, the Bell experiment. The
maths for this is pretty complicated,
but bear with me. It's worth the ride.
The experiment was first conceptualized
by John Stewart Bell, who wanted to know
if particles really did have secret
properties that they carried around with
them, known as hidden variables, or
whether they really were making some of
it up on the spot. He noticed an
interesting mathematical fact about the
spin of particles. Before we go any
further, I should probably mention that
quantum spin isn't the same as normal
spin. Misleadingly, quantum spin
actually defines whether a particle is
influenced, pushed, or pulled by a
magnetic field. The name isn't
important, but it is important to note
that these particles aren't actually
spinning and so can have different spin
values in almost any given direction.
Now, let's take two quantum entangled
particles and let's say that we've
arranged it so that their spin adds up
to a total of zero between them. This
means that if one particle would be
pulled by a field, the other will be
pushed by it an equal amount along that
direction. with the understanding that
this doesn't tell you anything about
their spin in other directions.
One of the features of quantum spin is
that if we measure an entangled particle
spin in any given direction, let's say
up and down, it will have a 50% chance
to be spinning up and an equal 50%
chance to be spinning down. But
remember, once you measure the other
entangled particle, it will have a 100%
chance to be spinning in the opposite
direction to the first particle.
On this fact alone, there is no way to
tell if the two particles already knew
their spin or are somehow deciding it on
the spot and conferring it with each
other now that they've been asked. But
Belle noticed a clever thing by asking a
clever question.
If you measured two quantum entangled
particles from two randomly selected
directions, what are the odds that their
spin for different directions would
match? Now let's define that at any time
a particle is spinning towards a
detector, its spin is up and anytime it
is spinning away from a detector, it
spin is down. What are the odds that
both particles would be spinning up up
or down down when tested? and what are
the odds that they would contrast?
Let's formalize this with a little
experiment.
Here we have two entangled particles
with three detectors reading their spin
in different directions.
If particle A and B are both read with
the top detector, then one of their
spins will be up and the other will be
down. They are entangled. This is what
we looked at previously. However, if
particle A is read using the top
detector, while particle B is read with
one of the other two, these two
directions of spin aren't opposites. So,
particle B has flexibility in which way
it goes.
Quantum physics claims the particles are
making up their attributes on the spot.
So once you'd measured the spin of
particle A using the top detector, it
was a 50/50 whether the spin on the
other particle using one of the other
detectors would match or contrast.
But this is not what classical physics
predicted. Let me show you what I mean.
Classical physics claims that particles
each carry around secret information
defining their spin in any given
direction. So for our three tested
directions, each particle would have a
value already. They aren't making it up
on the spot.
Let's say hypothetically our particles
hidden information states up down for
particle A and down up for particle B.
As B must be opposite to A for each of
the directions 1 2 and three.
Let's pick out a random detector for A.
We select detector one. Detector one
tells us that A is spinning up.
Now let's select a random detector for
particle B. We select one there too.
This detector gives us a reading of
down.
One one up down.
We can actually map out all the possible
outcomes of this process of random
selection in the graph. There are nine
possible outcomes if you were to only
measure from two detectors at a given
time. 1 one two 1 3 2 1 2 2 and so on.
For each of these possible selections,
we have fixed hidden variable results
that we know already because we
hypothetically defined them earlier.
Let's fill them in. Now,
of course, if you detect particles using
the same detector on both particles,
you'll get a contrasting result because
they're entangled. But we're not
interested in these results. Classical
physics and quantum physics both agree
on this, so let's remove them.
What are the odds that two different
detectors for particle A and B will see
the same result? And what are the odds
they'll differ? Remember,
quantum physics expected it to be 50/50.
Particles are making up their values on
the spot, and so it's perfectly random
which they'll choose, as they aren't
confined by the opposite rule here. But
in this table, classical physics says
that contrasting results only happen a
third of the time. The other times,
they're either both up or both down.
If we do this many times, assigning
different directions each time and
ignore exceptions, for instance, where
the spins of the particles are all up,
up or down, down, down, once you crunch
the numbers, the important thing to take
from all of this is that according to
the maths, classical physics predicts a
matching outcome 55% of the time, while
quantum physics continues to simply
predict 50%. Pretty table be damned.
This percentage difference was the key.
By quantumly entangling particles and
running this test over and over again,
you could now see which percentage was
correct. And it turned out the winner
was quantum physics. particles were just
apparently making up their spin results
on the spot. Which is spooky because not
only does that call into question our
perceptions of reality itself, but that
also means that the moment one particle
decided on its spin result, its quantum
entangled partner instantly knew that
that decision had happened. You could
test both particles at once, no matter
the distance, and this same result would
come back.
Somehow, information had traveled from
the one particle to the other in no time
at all, far faster than light itself.
So already something strange was going
on here. This result disproved
Einstein's predictions and showed that
some information does seem to go faster
than light. But we can take this one
step further and have information going
back in time. There is another
experiment known as the delayed choice
test. Its primary purpose was to explore
the fundamental nature of light, whether
it was a wave or a particle, and to
figure out when it decided to be one or
the other. Experiments like the double
slit experiment had done this in the
past to mixed results. Sometimes light
behaved in a wavelike manner, creating
interference patterns on detectors that
could only happen if a wave was
interfering with itself. But sometimes
it behaved like a particle, hitting only
a single point on a detector.
But most baffling of all, it seemed to
change which it behaved like depending
on whether you were observing its path
through space or not.
If it could go through multiple paths
and no one was watching to see which it
did go through, light simply went
through both like a wave. But observed
it went through just the one like a
particle.
This result was baffling enough and
deserves a video on its own. But in
2006, a number of scientists took it one
step further by asking an interesting
question. What would happen if you tried
to observe the light after it had to
pick a path? Consider this experiment.
A single photon is sent into a beam
splitter with a 50/50 chance of either
being allowed to carry on its way along
path one or getting reflected up along
path two. Once on either path, the
photon is bounced off mirrors with both
paths reconverging here where the other
beam splitter is inserted. Once again,
the photon has a 50/50 chance to go
either way with an even chance of
arriving at one of the two detectors.
If light were just a particle, sending a
single photon into this experiment would
give you an even chance of it arriving
at one detector or the other.
You'd not be able to tell which way it
went as the two beam splitters make that
impossible to know, but you could see
where it ended up. However, this does
not occur. When the second beam splitter
is present, the light produces an
interference pattern, indicating that
the single photon went down both paths,
ultimately bumping into itself before
moving on to both detectors. This seems
like strong evidence that light is a
wave. It certainly behaves like one
here.
But what happens if you remove the
second beam splitter? Suddenly you know
which path the light traveled down. If
light arrives at the top detector, it
must have arrived from path one. If it
arrives at the side detector, it must
have come along path two. And something
about this knowledge spooks the light.
It stops going down both paths. And
suddenly each photon only arrives at one
detector. Here's the question. What
happens if you insert the beam splitter
after the photon has already started
down either one or both routes? This is
why the test is called delayed choice.
If you delay choosing how exactly you
intend to detect the photon, whether by
knowing which path it came down or
making that ambiguous to you, what
happens to the light? What happens is a
very strange thing. When this experiment
was performed, it was done multiple
times with the beam splitter randomly
being inserted or not, but always being
inserted after the photon had entered
one or both paths.
And yet, the results came back
unequivocal.
If the beam splitter was present, the
photon suddenly and seemingly
retroactively stopped picking a path. If
the beam splitter was removed, the
photon seemingly knew it would later be
detected and picked a specific path to
accommodate.
Somehow the beam splitter being added or
removed in the future changed what the
photon did in the past.
So what is happening here? Is it really
true that particles somehow saw the
future? Did the experiment cause
information to be sent back into the
past? Or is there some other principle
at play here that explains this whole
thing that accounts for the instant
transmission of information between
quantum particles and allows it to be
perfectly rational that light could
travel down one path or both at the same
time?
Personally, I'm inclined to think that
this is more likely. We clearly don't
understand what is happening here. But
it must be admitted. If we don't
understand what is happening, there's
nothing to say that causality isn't
being ignored. In some way, maybe on the
quantum level, time really is more fluid
than it is up here in the larger
universe. Maybe space and time simply do
not apply down there.
And maybe one day someone will be able
to come up with a theory that allows all
these strange phenomena to finally make
some sense. Until then, we'll just have
to keep asking the same question. Can
information travel backwards in time?
Until then, we'll just have to all agree
on one thing. Quantum physics is
strange.
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