On the 21st of May 2019, we captured a
strange pulse coming from the other side
of the universe. A gravitational wave
the fraction of a diameter of a proton
that had traveled more than 17 billion
lightyear to reach us. Usually signals
of this magnitude are caused by black
hole merges. But there was something a
little off about this wave. It didn't
look like other black hole merges we
were used to. It was too short and
missing half of the waveform. This
signal bamboozled the scientific
community until in 2025, a team proposed
an explanation so wild it sent
theoretical physicists into a frenzy.
What if this signal wasn't produced in
our universe at all? What if it had
traveled through a wormhole from a
parallel universe?
I'm Alex Mccoan and you're watching
Astramm. Join me today as we break down
the physics of wormholes. Untangle the
mindbending relationship between quantum
entanglement and space-time geometry and
examine whether we really eavesdropped
on an echo from another universe.
When the laser interferometer
gravitational wave observatory or LIGO
detected the signal of gravitational
wave GW190521,
researchers realized something
exhilarating.
If their interpretation of the colliding
black hole size and mass was correct,
they just made the first detection of an
intermediate mass black hole in human
history. I've made another video about
these types of black holes before that
you can watch here. You see, until then,
we had only observed stellar mass black
holes. Any black hole under 65 solar
masses and super massive black holes or
black holes measuring hundreds of
thousands to billions of times the mass
of our sun. The math says there should
be a third category, intermediate mass
black holes, measuring about 100 to
100,000 times the mass of our sun. And
computer simulations agree, but we'd
never seen one directly until this
gravitational wave floated across our
radars, hinting that one might be out
there. This signal seemed to be an echo
of two black holes colliding. One
measuring 85 solar masses and the other
66. They emerged to form a black hole
142 times the mass of our sun. And if
you're doing the math here, yes, that
means nine full sun's worth of mass were
instantly converted into pure
gravitational energy. As if this weren't
exciting enough, in 2025, a research
team led by Ki Li at the Hang Cha
Institute for Advanced Study, University
of Chinese Academy of Sciences, took a
closer look at the signal left behind by
gravitational wave GW190521.
And they noticed something unusual. No
matter how they sliced it, this just
didn't look like a typical black hole
merger signal. They started to wonder
what alternative explanation could there
be for what they were seeing.
Normally, when two super massive cosmic
bodies collide, like neutron stars or
black holes, that collision emits tiny
ripples in spaceime that travel outward
in every direction. Sometimes these
gravitational waves eventually reach
Earth where we can detect them with our
groundbased laser interferometers such
as LIGO and Virgo based in the US and
Italy respectively. Depending on what
the signal we receive looks and sounds
like, we can deduce what type of event
occurred, how far away it was, and how
big the objects involved were likely to
be. When two black holes merge, they go
through a threepar process which gives
its signal key characteristics that are
easy to identify. In other words,
scientists know if a gravitational wave
was created by a black hole merger
thanks to its shape. The whole universe
is filled with spectacular patterns,
structures, and signals like this. It's
one of the things I find most
fascinating and not to mention beautiful
about the cosmos. It's this mix of
beauty and intrigue that I really try to
get across in astron videos, but it's
to the gravitational wave signals that black hole merges send out.
The first phase is the inspiral phase.
As the black holes circle each other,
they're constantly radiating energy away
in the form of gravitational waves.
Since they're losing energy, their orbit
gradually shrinks, which makes them move
faster as the gravity they exert on each
other increases. The faster they move,
the more energy they emit, creating a
positive feedback loop. [music] They get
closer and closer and move faster and
faster. So, what does this mean for the
gravitational wave signal? Well, it
increases in amplitude and frequency as
time goes on, like an upward tick. If
you convert that signal into sound, it
creates a rising tone, kind of like a
bird. That's why we say black hole
collisions produce a characteristic
chirp.
The second phase is the merger, the
moment the black holes actually collide.
At this moment, the amplitude of the
signal reaches its absolute maximum,
marking not only the highest peak, but
also the most intense rapid compression
of the wave. It's immediately followed
by the third and final phase, the ring
down. It takes a while for the newly
formed black hole to stabilize.
Initially, [music] it's wobbly and
distorted before finally settling into a
spherical shape. And all the while it
continues to produce gravitational waves
but in a different capacity than before.
In the case of GW190521,
the ringdown occurred simultaneously in
two distinct frequencies. A fundamental
tone at 63 Hz and a second at 98 Hz,
both of which faded out within 26 to 30
milliseconds. [music]
The black hole is similar to a bell that
rings, producing a spectrum of multiple
fading tones that encode information
about the bell, explains Colin Kapano
from the Albert Einstein Institute.
Analyzing the ring down of a black hole
merger can give us insights into the
mass and spin of both the new black hole
and its progenitors. So that's exactly
what you usually see with a black hole
merger. But GW190521
was different somehow. This particular
gravitational wave signal completely
lacked a clearly identifiable inspiral
phase. It just showed the merger and
ringdown phases. And this led KI and his
team to propose an absolutely outlandish
idea. What if this signal was the echo
of a black hole collision not in our
universe but in a parallel one? A signal
that traveled through a wormhole to
reach us.
Wormholes might sound like science
fiction, but they are a mathematical
possibility. In fact, as Einstein worked
on his theory of general relativity, the
concept of bridges arose naturally from
his field equations as hypothetical
geometric and topological features of
the universe. Later, as scientists in
the 1980s speculated about traveling
from one [music] side of the cosmos to
another, this theoretical bridge evolved
into the fan favorite we now call a
wormhole. So, what are they?
Essentially, wormholes act as shortcuts
through spaceime, a tunnel that connects
two very distant parts of the universe,
or potentially even parallel universes.
But we've never observed a wormhole in
reality. But if we did somehow stumble
across one, it wouldn't look like the
tunnels you might think of. Instead of a
flat hole that gets darker and darker, a
wormhole would act as a spherical 3D
window, showing you a warped view of the
final destination on the other side of
the hole. Much like a black hole, it
would be surrounded by gravitational
lensing that distorts the surrounding
starfield.
Now, we're moving deep into hypothetical
territory, so bear in mind some things
we cover will be contested, debatable,
and [music] just downright strange.
There are different kinds of wormholes,
but let's start with the classic one,
the Einstein Rosen Bridge. This is a
geometric structure where you have a
black hole on one side and a white hole
on the other that exits into another
universe. Let me break that down. As you
probably know, matter can only enter but
never exit a black hole. Once an object
crosses the event horizon, it cannot
return. A white hole is the opposite, a
hypothetical structure where information
can only exit into the universe but
never fall into the white hole. The
Einstein field equations that define
black holes are symmetric with respect
to time. This means that the
mathematical solution for a black hole
where everything collapses into a
singularity at some point in the future
can be reversed. In this setup, the
singularity becomes the past and the
matter is ejected from the white hole.
The white hole's event horizon would
effectively act as a line beyond which
nothing can enter. Because of this,
white holes are commonly described as
acting like a black hole running
backward in time. The Einstein Rosen
Bridge is theorized [music] to connect a
black hole with its white hole
counterpart via a one-way street of
sorts. But the problem is the math says
that this structure should be incredibly
unstable. It would collapse so
instantaneously that even light wouldn't
be able to travel through it. So if the
GW190521
signal couldn't have passed through an
Einstein Rosen Bridge, what other kind
of wormhole might it have traveled
through?
In 1988, astrophysicists Michael Morris
and Kip Thorne proposed a way to make
wormholes traversible. Thorne went on to
consult on the film Interstellar and
later won a Nobel Prize in physics for
his contributions to the LIGO detector
and the first direct observation of
gravitational waves. So, let these
credentials lend weight to the bizarre
theory I'm about to share. Morris and
Thorne suggest the choke point or throat
of the wormhole could be held open
against gravity by a kind of scaffolding
which would make it traversible.
However, this would require a
theoretical type of material known as
exotic matter to act as said scaffolding
holding the tunnel open. Exotic matter
is not the same thing as antimatter,
which does have positive mass and is a
real observable material. Instead, it
refers to materials that possess unusual
properties such as negative mass,
negative energy density, or negative
pressure. Meaning, it often acts in
bizarre and counterintuitive ways. For
example, in the normal world, when you
push a glass to the left, it will topple
over to the left. But if the glass has
negative mass, pushing it to the left
would make it fall to the right. it will
accelerate in the opposite direction of
the force applied.
Normal matter attracts other matter
through gravity. Drop a shoe and it
falls to the ground. But exotic matter
with negative energy does the opposite.
Instead of being pulled towards other
matter, it's pushed away from it. And
crucially, it pushes back. That
repulsive force is what could
theoretically prop a wormhole throat
open against the crushing pole of
gravity. Even if this breaks your brain
a little, these kinds of properties
aren't technically forbidden by the
maths, and they don't violate the laws
of conservation of momentum or energy.
In other words, they can't officially be
discarded as impossible, even though
we've never seen them. Thus follows the
question, if a traversible wormhole like
this could exist, could we really hear a
signal ring down through it from the
universe on the other side? Wouldn't the
information get lost or distorted
somehow? Well, turns out wormholes might
connect more than just black and white
holes. They could be the missing link
between general relativity and quantum
mechanics.
General relativity describes the
universe at its largest scales. Gravity,
black holes, the fabric of spaceime
itself. Quantum mechanics describes it
at its smallest. Particles, energy, the
subatomic world. But when you try to use
both at the same time, say at the center
of a black hole, the maths breaks down
completely. However, in 2013,
theoretical physicists Leonard Suskin
and Juan Malda put forth a conjecture
that if true could unify these two rival
fields. And you guessed it, the answer
has to do with wormholes. How exactly?
Well, they propose that wormholes and
quantum entanglement might actually be
the same thing. that when two particles
become entangled, they're linked in such
a way that whatever happens to one
instantly affects the other, even if
they're galaxies apart. For example, if
you measure the spin of one, its
entangled partner will instantly snap
into the opposite spin. At first glance,
it might seem like this would violate
the law that nothing can travel faster
than light. Surely, these particles are
somehow communicating. But there isn't
actually any information passing from
one to the other. The outcome of both
particles are random. Suskind and
Maldisena suggested these entangled
particles might literally be connected
by a geometric structure, a tiny
wormhole that links them through
spaceime. Sound familiar? This is known
as the ER equals EPR conjecture. named
after two famous papers from 1935.
Einstein Rosenbridge equals Einstein
Bodolski Rosen entanglement.
If this idea proves true, it blows black
hole science wide open. Quantum
mechanics states that information cannot
be destroyed ever. Yet everything that
falls into a black hole eventually seems
to evaporate and vanish forever. This is
the information paradox.
In 2012, a group of physicists tried to
resolve it, but ended up creating an
even bigger problem. The Amps team from
UC Santa Barbara, named after the
initials of his authors, showed that if
you insist on both quantum mechanics
being correct and that information can
escape the black hole, then the event
horizon would look like a wall of
incredibly high energy radiation, not
the smooth, unremarkable boundary
predicted by general relativity.
Therefore, these two theories seem to
directly contradict each other, creating
what is known as the firewall paradox.
But this is where things for once slot
together nicely. The ER equals EPR
conjecture offers a way out of this
tangle. See, back in 1974, Steven
Hawking postulated that black holes have
quantum effects near the event horizon
that cause them to slowly emit what has
become known as Hawking radiation,
evaporating over incomprehensibly long
time scales. The question [music] is
whether that radiation carries any
imprint of what originally fell in or
whether it's just random noise. If these
hawking radiation particles escaping the
black hole are entangled with particles
inside it via a wormhole, then
information was never truly trapped in
the way we always assumed. If the inside
and outside of the black hole share a
quantum connection, the information is
recoverable in principle from the
Hawking radiation itself. But the
problem with ER equals EPR is that it
had only been demonstrated for [music]
an extremely idealized scenario. two
black holes in perfect thermal
equilibrium.
Real black holes are certainly not that.
They are chaotic and messy. They're
constantly being bombarded by infalling
matter, radiation, and quantum
fluctuations. If ER equals EPR only
works for perfectly neat black holes
that don't really exist, it's not much
of a solution. So in 2025, a team of
researchers set out to test if the
conjecture would hold up in more
realistic conditions. They created a
model of a theoretical pair of deeply
entangled black holes connected by an
Einstein rose and bridge known as a
complex EPR pair. They started with an
idealized wormhole, one which is smooth
and symmetrical inside, and
progressively scrambled the quantum
entanglement between the black holes,
making them increasingly chaotic. And
they found something no one expected.
Even when quantum entanglement is messy
and random, the wormhole remains a
predictable, stable tunnel. It gets
longer, bumpier, more deformed, and
develops lumpy segments, earning it the
title the Einstein rose and caterpillar.
And crucially, it remains a
geometrically stable, traversible
structure where the classical laws of
gravity still hold. And perhaps most
intriguingly, nowhere in their typical
models, those that started from rest,
did they encounter a firewall at the
event horizon. So coming back to our
gravitational wave, for it to have
actually traveled through a wormhole to
us, two things need to be true. Firstly,
wormholes connecting entangle black
holes need to be real and stable enough
to transmit a signal, which the Einstein
Rosen Caterpillar seems to demonstrate
as at the very least a theoretical
possibility. Secondly, information needs
to be able to travel through it. And in
2022, a Harvard le team managed to do
just that in an experiment that sounds
stranger than fiction. They built a
holographic wormhole on a quantum
computer and successfully sent
information through it.
While we all pick our jaws up off the
floor, let's break down what that insane
sentence actually means. The experiment
[music] traces back to Daniel Jafferis
at Harvard who in 2016 calculated that
if you can take two entangled quantum
systems and couple them together in the
right way, you can perform an operation
on one side that according to ER equals
EPR should physically hold a wormhole
open and push information through it.
But the question was, could you actually
build that system and test it? 6 years
later, a team led by Maria Spyropulu at
Caltech did exactly that. They used
Google's Sycamore, a superconducting
quantum processor to simulate two
entangle quantum systems that by the
rules of ER equals EPR should be
connected by a wormhole. And here's what
happened. A unit of information, a
quantum bit or cubit, was injected via a
single particle into one side of a
two-sided system. That encoded
information diffused from just the one
particle across all the particles on
that side of the system like a drop of
ink dissolving into water. Then the team
performed a specific rotation across all
the cubits, equivalent in the
gravitational picture to sending a pulse
of negative energy through the wormhole
or propping it open with exotic matter.
Eventually, the encoded information
reemerged on the other side of the
system. Not only that, but it had
converged or refocused itself from its
diffused state back onto a single
particle, the entangled partner of the
original particle that carried the cubit
into the system [music] in the first
place. In other words, researchers had
sent information into a quantum tunnel
and successfully retrieved it on the
other side. Spyro Pulu couldn't believe
her eyes, saying the moment felt like
seeing the first data from the Higs Bzon
discovery. However, the physics
community quickly urged caution. [music]
Some analyses argued that the quantum
model was far too simple to capture the
true complex properties of black holes,
meaning the demonstration shouldn't be
thought of as a literal holographic
wormhole. Yet, even if it wasn't a
perfect cosmic replica, her team had
just shown that a quantum system
governed purely by the rules of quantum
mechanics [music] could in principle
behave in a way that is mathematically
identical to a wormhole in a
gravitational theory. The physics of
both the quantum and the gravitational
scales are similar even if the physical
reality looks completely different. So
coming back to the strange gravitational
wave that started it all in May 2019. If
it really did travel through a wormhole
to reach us, this experiment is the
closest thing we have to a proof of
concept that such a journey is both
mathematically and experimentally
demonstrable. But can we conclusively
say one way or the other whether it did?
Well, knowing everything we know about
wormholes, quantum entanglement, and
information, let's reassess the paper
that launched us on this topsyturvy
journey. Key lie and his team put
forward the idea that gravitational wave
signal GW190521
is the echo of a black hole merger in
another universe. In that reality, two
black holes spiraled and merged together
normally. But instead of creating a
larger black hole, they created a
wormhole with one end in that universe
and the other in ours. We didn't hear
the inspiral part of the signal because
it stayed in the parallel universe. But
as the ringown phase radiated outward,
some of those waves traveled down the
wormhole and emerged on our side. We
know it's theoretically possible for the
wormhole to be held open by negative
energy and for information to pass
through it. So, this isn't as outlandish
as it might have initially seemed. The
authors go a step further to explain why
the signal was so short, just 0.1
seconds long. They postulate we only
detected one pulse rather than a series
of progressively weaker echoes as you'd
expect with a ring down because the
wormhole rapidly collapsed into a black
hole or the later echoes were simply too
weak for our detectors to pick up.
Technically, this can't be ruled out as
a theory since there is a nonzero
possibility that this could accurately
describe what we saw. But the authors
admit that even with the missing in
spiral phase, a binary black hole merger
in our own universe fits the
gravitational wave data better than this
explanation. Still, this study brings
more value than a fun theoretical
thought experiment. It's important
because it gives astronomers a concrete
way to test an exotic idea against real
detector data. The Harvard quantum
computer experiment showed that
wormhole-like dynamics could potentially
be mathematically real and testable. The
Einstein Rosen Caterpillar shows that
wormholes connecting entangled black
holes aren't just science fiction. They
can emerge naturally from the maths of
quantum chaos. And these two findings
together along with the ER equals EPR
conjecture build an ever stronger case
for a mathematical connection between
quantum mechanics and general
relativity. By studying real merging
black holes like the ones behind
GW190521,
we get to play with the systems where
this frontier pushing physics might
apply. In the future, our detection of
these events will only get more precise.
Since 2023, LIGO and Virgo have been
operating with a 30% increased
sensitivity, allowing detection of a
merger every 2 to 3 days. Given that
we've only been able to detect
gravitational waves for a decade, this
field is in its infancy. With
improvements to our models and
technology, who knows, maybe one day
we'll not only be able to conclusively
find wormholes, but even be able to send
stuff through them. I, for one, am
hopeful that they won't always remain
elusive and confined to equations and
sci-fi stories. But for now, we'll have
to wait and see.
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