When the idea of black holes first emerged out of the equations of Einstein’s theory
of general relativity, physicists weren’t exactly sure how serious to take these all-consuming
mathematical objects. Today, scientists have undeniable evidence for the existence of black
holes, and it is common knowledge that these mathematical objects really do exist in our
universe! But the equations that predicted the existence of black holes also predicted
the existence of opposite twins of black holes known as white holes! So, what are white holes,
and do they also exist in our universe? Today, we will be analyzing white holes and some
of their defining characteristics!
In the late 1960s when scientists were exploring Einstein’s field equations that gave rise
to black holes, they discovered that there is another solution to these same equations
that give rise to white holes. Although the exact mathematics of this can be a bit complex,
a simple analogy can be made to better understand how white holes also popped up in the solution.
Suppose we want to find the square root of 4. One simple solution to this would be 2
since 2x2 is 4. But that is not the only solution since -2x-2 is also 4 giving another solution
in the form of -2 this time. So, the question ‘what is the square root of 4’ does not
have just 1 solution, but 2 equally valid and legitimate solution. Similarly, the equations
that describe black holes, also have a second solution to them that describes the mathematical
opposites of black holes referred to as white holes.
White holes are created when astrophysicists mathematically explore the environment around
black holes, but with the condition that there is no mass within the event horizon. A white
hole would look exactly like a black hole if we were to observe it from afar. Similar
to a black hole, a white hole may vary in size, have a spin or be stationary, and have
a ring of dust and gas cloud gather around its event horizon. However, there would be
one key difference in the behavior of a white hole as compared to its counterpart. While
a black hole is defined as a region of inward-flowing time with an event horizon from inside of
which nothing can ever escape, including light, a white hole is a complete opposite! It is
a region of outward flowing space-time with an event horizon that prohibits entry. Nothing
outside of a white hole can ever enter it, and everything inside must always be ejected
including light! For this reason, we would expect white holes to be extremely bright
with intense radiation being emitted from within. So far, we have looked, but have not
detected any such entities in our universe. But that doesn’t make it any less true,
mathematically speaking.
Some scientists believe that black holes and white holes may be as intertwined as their
names suggest. As a result, some physicists describe white holes as the “time inverse
of black holes”. In other words, reversing the video footage of a black hole will leave
us with a white hole. So, white holes may simply be the opposite end of black holes
which are connected by theoretical tunnels of space-time called wormholes. So the matter
and energy falling into a black hole would eventually beam out of a white hole, somewhere
in this or another universe. In simpler terms, we can think of this entire system as a one-way
street where you can only enter from one point and exit from the other point!
Now, we know that space-time is so warped near black holes that any event occurring
at the event horizon happens infinitely far in the future from the outside perspective.
For this reason, the singularity of a black hole exists in the future. But once something
goes into the singularity, space and time switch their roles according to the Schwarzschild
Metric. This means that events occurring at the event horizon of a white hole must happen
infinitely far in the past with the condition that its singularity must exist in the past!
So, while a black hole's event horizon is a point of no return, a white hole's event
horizon is a point of no admission. The objects inside white holes must leave and interact
with the outside world, but since nothing can get in, including light, the interior
is cut off from the universe's past. This means that no outside event can ever affect
the inside of a white hole. In the words of James Bardeen, a black-hole pioneer and professor
emeritus at the University of Washington, "somehow it's more disturbing to have a singularity
in the past that can affect everything in the outside world."
While general relativity describes both black holes and white holes in theory, no one exactly
knows how white holes form. A black hole can form in space when a massive star’s core
implodes compressing all of the star’s mass in a tiny region of space. But if we tried
to play this backwards where an event horizon explodes into a fully functional star, it
would be violating the second law of thermodynamics which states that entropy in a closed system
must increase over time.
Furthermore, according to Hal Haggard, a theoretical physicist at Bard College in New York, even
if large white holes did form in the universe, they may not be around for too long. This
is because any matter that is being spewed out by the white holes would collide with
the matter in its orbit. This would cause the system to collapse into a black hole.
So, a long-lived white hole is highly unlikely according to him.
Another theory of how white holes could form is the fact that information could never be
destroyed, according to quantum mechanics, even if it is inside a black hole while general
relativity holds that nothing can ever come out of a black hole. So, what happens to that
information when the black holes radiate away through Hawking Radiation? Some scientists
think that similar to the quantization of light and matter, space itself can be quantized.
This would allow black holes to only shrink to a certain limit before rebounding outward
in a “quantum bounce” giving birth to an expanding white hole!
But that is not all! Some scientists believe that we may be a part of the ultimate white
hole. This is because the mathematics behind the Big Bang and white holes is largely similar
in many ways. And since Einstein’s equations say nothing about how white holes are formed,
and we have no clue about what happened before the Big Bang, these similarities are enough
for some scientists to suggest that white holes and Big Bang are one and the same! According
to astrophysicist Ezequiel Treister, “You can think of the Big Bang as the ultimate
white hole, a white hole cannot be created, so the only way to have it is if the universe
‘comes’ with one.”
But such claims remain speculative due to the lack of any real evidence. But this has
not stopped researchers from coming up with interesting theories. Some theories suggest
that white holes might even be necessary to solve some longstanding problems in physics
such as the nature of dark matter or the nature of the universe itself! Unfortunately, no
one knows for sure whether white holes truly exist. Maybe there just isn’t any room for
the existence of white holes in our universe. Perhaps, they are purely theoretical objects
arising from the beauty and complexity of mathematics, the language of the universe!
But we will never know for sure unless we keep searching on!
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