What Is a White Hole? (Opposite of Black Hole)
A celebrated astrophysicist is intently studying the skies in search of his elusive quarry,
combing through the thousands of images coming to him from the state-of-the-art International
Event Horizon telescope. Finally, after months and months of searching, he thinks he may have
found what he's been looking for all this time - in the images he sees the telltale signs of a
mysterious phenomenon called a black hole. But as he scrutinizes the images captured by the
powerful telescope, something doesn't seem quite right. There, right in front of his very eyes,
the black hole appears to be … burping!? The scientist knows that this should be impossible:
nothing can escape from a black hole, not even light - that's why they're so hard to find - but
here is photographic evidence of matter coming out of a black hole! Could it be that this is
not a black hole at all, but the black hole's neglected twin - a white hole? Could this be his
chance to once and for all answer the questions that have been nagging at him throughout his whole
career - What is a white hole? How do they form? How do they work!? And, do they even exist at all?
In 1915, Einstein's field equations turned the world of physics on its head. His theory
of relativity described the force of gravity and shattered the prevailing paradigm of the
nature of reality - rather than being rigid, space and time can actually bend and fold,
along with the mass of stars and planets. Within a year, scientists had calculated how
space-time curves around a single ball of mass - the seeds of what today is called the singularity.
Physicists were able to describe how a spherical mass shrunken down to infinitely dense point
could wrap space around it so tightly that a region of space is effectively
pinched off from rest of universe, creating a no-mans land beyond the event horizon where
the laws of physics no longer apply and the link between cause and effect is shattered.
A black hole is an incredibly dense area of space where all matter has
been squeezed into an impossibly tiny space, called the singularity. This creates such an
intense gravitational pull that nothing, not even light, can escape from the black hole's clutches.
A tiny black hole might be the size of a single atom, but have a mass equal to a large mountain.
Stellar black holes, formed when a dying star collapses in on itself in a supernova,
can have a mass up to 20 times greater than our sun. The largest black holes are called
supermassive black holes, and they can be found at the center of every galaxy in our universe. The
supermassive black hole at the center of our Milky Way galaxy, named Sagittarius A*, has as much mass
as 4 million of our suns, all condensed into a tiny ball only as big as a few million Earths.
A black hole's event horizon is what we would consider the surface of the black hole, although
it's not a surface in the true sense of the word - it's not a membrane or barrier, but rather, the
threshold beyond which there is no going back. The event horizon is the point of no return - nothing
that crosses the event horizon can ever come back. Even light cannot escape the black hole once it's
passed the event horizon. Once something - or someone - has crossed the event horizon,
they will begin the inevitable process of falling towards the black hole's singularity,
eventually dissolving into the singularity itself. We can only guess what happens after that.
Physicists have been studying black holes for decades and are only just
beginning to understand them. Only recently have
they turned their attention to the black hole's neglected twin - the white hole.
From afar, a white hole would appear identical to its better-known cousin,
a black hole. Like a black hole, a white hole might be big or small,
might spin or remain stationary, and might be electrically charged. A white hole would also
be surrounded by a ring of dust, and a cloud of gas and debris would gather at its event horizon.
The key difference between a black hole and a white hole is that white holes burp.
Yes, burp. Unlike a black hole, from which nothing can escape,
matter actually can cross the event horizon and come out of a white hole. It's only in these
moments, when objects emerge from the white hole, that scientists can definitively say
that what they are looking at is a white hole, and not a black hole.
If a black hole's event horizon is the point of no return, then the event horizon of a white hole
could be described as the point of no admission - nothing can ever cross the event horizon of
a white hole and reach the interior. In a black hole, objects in the space outside can cross the
event horizon and affect the interior of the black hole, but matter inside the black hole can never
again interact with space outside. In a white hole, the reverse holds true - objects from inside
the white hole can cross the event horizon and interact with objects in the space outside of it,
but nothing on the outside can ever enter the white hole or affect the inside.
This is because a white hole is a black hole's time reversal, according to physicists.
A black hole's singularity exists in the future, whereas a white hole's singularity exists in the
past. Since the interior of the white hole is cut off from the universe's past via its event
horizon, no outside object or event will ever affect the inside of a white hole. James Bardeen,
a black hole pioneer and professor emeritus at the University of Washington
explains the magnitude of this difference: “Somehow it's more disturbing to have a
singularity in the past than can affect everything in the outside world”, he says.
Scientists had theorized about the existence of black holes for hundreds of years before
Einstein's theory of relativity paved the way for physicists to prove their
existence - theoretically, at least. Since no light escapes from a black hole, they are
invisible to the naked eye. Until very recently, the only way scientists have been able to find
evidence of black holes has been to look for signs of their impact on the surrounding universe.
Stars, gasses and other space objects behave differently near a black hole than they do
elsewhere in the universe as the black hole's intense gravity pulls on them. Using telescopes
equipped with special tools, scientists can pick up a type of high-energy light emitted
by objects that interact with a black hole's gravitational forces, and reverberation mapping
can measure the radiation given off by the ring of debris that surrounds the black hole, helping
physicists pinpoint the location of a black hole, even if they can't see the black hole itself.
Finally, in 2019, scientists made a stunning breakthrough in the study of black holes
when the International Event Horizon telescope captured the world's first image of a black hole.
Technically, what they captured was the black hole's shadow, since the absence of
light reflecting from a black hole makes the black hole itself impossible to see, but nevertheless,
this was the world's first solid, photographic proof of the existence of black holes.
If black holes have finally been proven to be real, does that mean that white holes are a proven
fact of the universe, too? Well, not exactly. While Einstein's theory of general relativity
does describe the existence of both black and white holes, it doesn't explain how a white
hole might actually form in space. A black hole forms when a dying star implodes in a supernova,
collapsing all of the star's matter into an impossibly tiny area cordoned off from the
rest of space. The reverse doesn't quite make sense - the idea of a white hole exploding into
a fully-functioning star would be a bit like unscrambling an egg: it just wouldn't work.
This idea also violates the statistical law that entropy must increase over time.
Furthermore, if a white hole did form, the matter it releases when it “burps”
would collide with the matter in orbit around the white hole. These collisions
would cause the entire system to collapse into a black hole. Perhaps if white holes do exist,
they don't remain as a white hole for long. Hal Haggard, a theoretical physicist at Bard College
in New York, has said that “a long-lived white hole, I think, is very unlikely.”
Other scientists have different theories about white holes that help
explain some of the inconsistencies. Steven Hawking discovered back in the
1970s that black holes leak energy, which led him to wonder - how do black holes die?
And what happens to everything that's been trapped inside of a black hole when it dies?
The theory of general relativity holds that nothing can get out of a black hole, but quantum
mechanics prevents any information inside a black hole from being deleted. So where does it go?
Some have taken this to mean that a white hole is actually the result of the death of a black hole.
As a black hole dies, it may become so small - as small as one microgram in size,
about the mass of a human hair - that it would no longer obey the laws of physics as we know them.
This infinitesimally tiny object would be so small that it would defy gravity,
but inside it would hide a cavernous interior full of everything it swallowed
in its previous life as a black hole. It's small size and gravity-defying
behaviour could allow it to remain stable enough to eventually spit out information
and matter that had been swallowed by the black hole, becoming a “burping” white hole instead.
If this theory holds true, the universe could one day come to be dominated by white holes.
After all of the stars in the universe have burnt out and imploded into black holes, and then after
all of those black holes themselves have all died, the universe might be nothing but a sea of burping
white holes. Thankfully, this could only happen in a universe countless trillions of times older
than our universe currently is, so it's not a scenario we need to worry about any time soon.
There are many more questions than answers when it comes to white holes, and that leaves room for
plenty of imaginative theories about what a white hole actually is. Some scientists actually think
that we are currently living inside the ultimate white hole. To these black hole physicists,
the behavior of a white hole looks suspiciously similar to a little thing we call the Big Bang.
The explosion of matter and energy resulting from the Big Bang that created our universe
is remarkably similar to the way theorists suspect that white holes release matter.
“The geometry is very similar in the two cases," Hal Haggard, the physicist from Bard College, has
said. "Even to the point of being mathematically identical at times." This theory has attracted
plenty of criticism, but Haggard intends to follow this rabbit hole to the very end,
saying “Why wouldn't you investigate whether white holes have interesting consequences? It may be
that those consequences aren't what you expected, but it would be foolhardy to ignore them.”
We may still be a long way off from being able to look into a telescope and watch with our own
eyes as a white hole burps out matter into the surrounding universe. Although we've only just
gotten our first glimpse of a black hole - and though we have yet to even lay eyes on a white
hole - scientists will undoubtedly discover more about these mysterious phenomena in the future.
If the past has taught us anything, it's that just because we can't see something
doesn't mean it isn't out there. Only time will tell which theory about white holes
will prove to be correct - or if we had it completely wrong all along. One day we may
get an answer to the question “What is a white hole?” but until then, it remains
yet another of the countless as-yet-unsolved mysteries of our vast and unknowable universe.
If you thought this video was fascinating, you'll definitely want to check out “What
Would Happen to Your Body in Space?”, or, you might like this other interesting one!
