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One of the biggest puzzles in physics today is one that sounds straight out of science
fiction. Just what would happen if you fell into a black hole?
Make no mistake—the answer to this bizarre question is that you would DIE—that's not
up for debate. But it's HOW you would die that's keeping physicists up at night. There
are currently two major camps fighting over this gruesome scenario, and the outcome this
fight could actually revolutionize the fundamental laws of nature.
To begin to understand this controversy, you first need to know what a black hole is. Black
holes form when stars collapse under their own weight. For most of the past century,
scientists have thought that due to the intense pull of gravity, all the matter that made
up the collapsed star gets squished into a teeny tiny dot. This dot is called a 'singularity,"
and it's incredibly dense. It's basically a pit of gravity in the fabric of spacetime,
and the closer you are to this dense dot of mass, the stronger the pull of gravity is.
Some physicists describe this pull as a river that leads to a waterfall. If you're significantly
upstream of the precipice, you can easily steer you raft to safety. But once you get
far enough downstream, no matter how fast you paddle in the opposite direction, you
can't escape the river's pull and you'll topple over the edge. For black holes, this "point
of no return" is called the "event horizon," and it's the place where nothing, not even
the fastest thing in the universe—light—can escape the singularity's gravitational pull.
So, what would happen if you passed through an event horizon? For years scientists thought
they knew how you would meet your demise. Say you were travelling feet first towards
the singularity. Initially, you wouldn't notice that you'd passed any significant boundary,
but your feet would experience a greater gravitational pull than your head, and would begin moving
faster than the rest of your body. Thus, you would get stretched into a long person-noodle
until your body eventually snapped. Each noodle-y piece of you would stretch and progressively
break into smaller and smaller pieces until you were nothing but a collection of subatomic
particles smushed against the rest of the mass at the singularity. This "stretching"
hypothesis actually has a name. Physicists call it "Spaghettification."
The spaghettificiation theory satisfied most physicists for years. But, then, in 1974,
the physicist Stephen Hawking proposed what is now a widely accepted idea about the nature
of black holes. He said that black holes will eventually evaporate—basically they'll disintegrate.
This is really complicated stuff, but essentially they'll start radiating particles from their
event horizon, and even though these particles don't come from the singularity, the mass
within the black hole will start to shrink.
But there's a problem with this idea. It violates a key principle of quantum physics—information
cannot be destroyed. And, just to clarify, when physicists say "information" they're
referring to quantum mechanical properties of the particles that make up... everything
in universe. So, here's the issue. If by definition, matter
and information that gets sucked inside a black hole can't escape, then when the black
hole evaporates, all that information stored inside of it would just... disappear!
Until recently, many scientists satisfied their frustration with this "information paradox"
by saying that maybe we just need to think about the inside and outside of a black hole
as different realms that can't communicate. We could save any information that fell into
a black hole by allowing it to exist in two places—both stuck inside, and leaking outside
with the Hawking radiation. Usually, physicists would say that you can't have two different
copies of identical information at once. But since the realms can't communicate, the particles
would get a free pass.
But then, in 2012, the physicist Joseph Polchinski and his colleagues realized that the paradox
might be even more complicated than anyone previously thought.
They imagined what would happen if you had two entangled particles—particles that are
quantum mechanically-linked—and you tossed one of them into the black hole and kept an
eye on the other one. This would create a problem. By their very nature, the entangled
particles would need to be able to respond to one another. But if you bought into this
whole "two realms" concept, the particles couldn't do that.
So, they came up with a new, revolutionary idea about how black holes might work that
got rid of the problem of these two realms. They entirely threw out the idea of a black
hole that could spaghettify you, saying that matter doesn't get sucked into a black hole
at all. Instead, matter might hit the event horizon and incinerate. The information about
where that matter came from and where it goes would get conserved. It might go bouncing
off into the universe, but nothing would get sucked past the horizon. And, that's because
there IS nothing beyond the horizon. According to Polchinski and his colleagues, black holes
don't have centers at all!
This is a totally wild, and problematic, idea. It's essentially saying that beyond this event
horizon "firewall," you hit...the END of the universe. And that throws into question Einstein's
theory of general relativity because it is literally a rip in the fabric of spacetime
itself.
This firewall idea really rankled a bunch of physicists, including Stephen Hawking who
released a statement that has left the rest of the physics community perplexed. He's now
said that both concepts of what black holes are are wrong. In a two-page statement, he
wrote that there are no singularities, but that there are also no event horizons! Instead,
there are apparent horizons, which store and scramble all matter and energy that they suck
in. This may solve the entangled particle problem—the two particles are still quantum
mechanically linked—and it may even solve the information loss issue (well, kinda, the
information is scrambled, but theoretically not irretrievable.) But, without a singularity
to create a strong gravitational pull, it still messes with general relativity.
If this leaves you scratching your head, you're in good company. Other physicists are confused
why Hawking proposed this idea—so far, it just seems like a third, equally problematic
solution. So, for now, you decide: if you fell into a black hole, would you rather be
spaghettified, toasted, or scrambled? Frankly, they all sound pretty unappetizing to me.