What happens if you fall into a black hole?
Surely you believe that if you fall into a black hole, then instant death awaits you. But in reality, physicists believe, your fate will be much stranger. This could happen to anyone in the future. Maybe you are trying to find a new habitable planet for the human race, or you just fell asleep on the long journey. What happens if you fall into a black hole? You would expect to be crushed or torn apart. But it’s not that simple.
The moment you enter the black hole, reality will be split in two. In one you will be immediately destroyed, and in the other you will plunge into a black hole completely unharmed.
A black hole is a place where the laws of physics we know don’t work. Einstein taught us that gravity bends space itself, deforms it. Therefore, if you take a sufficiently dense object, space-time can become so crooked that it wraps itself in itself, making a hole in the very fabric of reality.
A massive star that has run out of fuel could provide the extreme density needed to create this warped patch of space. Bending under its own weight and collapsing, the massive object pulls space-time along with it. The gravitational field becomes so powerful that even light cannot leave it, which dooms the region in which this star is located to a dark fate: a black hole.
The outer edge of a black hole is its event horizon, the point at which the force of gravity opposes the attempts of light to leave it. Get too close and there will be no return.
The event horizon burns with energy. Quantum effects at this boundary create streams of hot particles flowing back into the universe. This is the so-called Hawking radiation, named after the physicist Stephen Hawking, who predicted its existence. After enough time, the black hole will evaporate its mass completely and disappear.
As you plunge into the black hole, you will find that space becomes more and more curved until at the very center it becomes infinitely curved. This is a singularity. Space and time no longer have any meaning, and the laws of physics we know that need space and time no longer work.
What’s going on at the singularity? No one knows. Another universe? Oblivion? Is Matthew McConaughey floating on the other side of the bookshelves? Riddle.
What happens if you accidentally fall into one of these cosmic aberrations? First, ask your space partner – let’s call her Anna – who watches in horror as you float towards the black hole while it remains at a safe distance. She observes strange things.
If you accelerate towards the event horizon, Anna sees you stretch and distort, as if she is looking at you through a giant magnifying glass. Also, the closer you get to the horizon, the more your movements slow down.
You cannot shout because there is no air in space, but you can try to signal Anna a Morse message with the light of your iPhone (there is even an application for this). However, your words will reach it more and more slowly, as the light waves are stretched to lower and redder frequencies: “Okay, good, good, good …”.
When you reach the horizon, Anna will see that you are frozen, as if someone had pressed the pause button. You will be imprinted there, immobilized and elongated across the entire horizon, as the rising heat begins to absorb you.
According to Anna, you are slowly being erased by the stretching of space, the stopping of time and the warmth of Hawking’s radiation. Before plunging into the darkness of a black hole, you will turn to ash.
But before we start planning the funeral, let’s forget about Anna and see this eerie scene from your point of view. And do you know what’s going on here? Nothing.
You float straight into nature’s most sinister manifestation and you don’t get a bump or bruise – and you certainly don’t stretch, slow down, or fry with radiation. Because you are in free fall and do not experience gravity: Einstein called this “the happiest thought.”
After all, the event horizon is not a brick wall floating in space. It is an artifact of perspective. An observer who remains outside the black hole cannot see through it, but that is not your problem. There is no horizon for you.
If the black hole were smaller, you would have problems. The force of gravity would be much stronger at your feet than at your head, and would stretch you like spaghetti. Luckily for you, it’s a big black hole, millions of times more massive than the Sun, so the forces that could spaghettize you are weak enough to be ignored.
Moreover, in a sufficiently large black hole, you could live the rest of your life, and then die in a singularity.
How normal this life will be is a big question, given that you have been sucked against your will into a gap in the space-time continuum and there is no turning back.
But if you think about it, we are all familiar with this feeling, from the experience of communicating not with space, but with time. Time only moves forward, never backward, and sucks us in against our will, leaving no chance of retreat.
This is not just an analogy. Black holes distort space and time to such an extreme state that within the event horizon of a black hole, space and time actually change roles. In fact, it is time that sucks you into the singularity. You cannot turn around and walk out of a black hole in the same way that you cannot turn around and go back into the past.
At this point, you ask yourself: what is wrong with Anna? If you are chilling inside a black hole surrounded by empty space, why does your partner see you burn up in radiation on the event horizon? Hallucinations?
In fact, Anna is in perfect health. From her point of view, you really burned out on the horizon. This is not an illusion. She could even collect your ashes and send them home.
In fact, the laws of nature require you to stay outside the black hole, as seen from Anna’s point of view. This is because quantum physics requires that information not be lost, not lost. Every bit of information that speaks of your existence must remain outside the horizon so that Anna’s laws of physics are not violated.
On the other hand, the laws of physics also require you to float across the horizon without colliding with hot particles or anything out of the ordinary. Otherwise, you will violate Einstein’s “happiest thought” and his theory of general relativity.
So, the laws of physics require that you simultaneously be outside a black hole in the form of a handful of ash and inside a black hole, alive and well. And there is also a third law of physics which says that information cannot be cloned. You must be in two places, but there can only be one copy of you.
One way or another, the laws of physics lead us to a conclusion that seems rather meaningless. Physicists call this puzzle the black hole information paradox. Fortunately, in the 1990s, they found a way to solve it.
Leonard Susskind came to the conclusion that there is no paradox, since no one sees your copy. Anna sees only one copy of you. You only see one copy of yourself. You and Anna will never be able to compare them (and your observations, too). And there is no third observer who can simultaneously observe a black hole from the inside and outside. So no laws of physics are violated.
But you probably would like to know whose story is true. Are you dead or alive? In fact, there is no truth here. The one who looks at the world from the first person is alive. You, who remained on the horizon of the black hole and turned to ash, are dead. There is a splitting of reality, where in one you are no longer there.
There are phenomena where there is no truth; everyone perceives it differently.
For example, you can fly to a parallel world, where you live for only a couple of days, and then return back to Earth. When you return, you will find that all your relatives and friends have long passed away, and the world you are used to has changed to one degree or another. You went to a parallel universe when the year was 2024 on Earth, and you returned in 2088, although it seemed only a few days had passed.
Yes, it really took only a couple of days for you, but on Earth this very period of time proceeded differently, with you it proceeded much more slowly, but this does not change the essence: the time is the same for everyone, but it flows differently everywhere. In your universe, this time was perceived as many years, and in a parallel universe you perceived this time as some three or four days, and unlike your friends of that time, your body has aged for these same three or four days, but not more … Returning back, you can consider that you are in the future, and in part this is true. You will return young and healthy, and these 64 years on Earth were for you several days in a parallel world.
In the summer of 2012, physicists Ahmed Almeiri, Donald Marolph, Joe Polchinski, and James Sully, collectively known as AMPS, conceived a thought experiment that threatened to turn everything we had gathered about black holes. They suggested that Susskind’s decision was based on the fact that any discrepancy between you and Anna is mediated by the event horizon. It doesn’t matter if Anna saw an unfortunate version of you torn apart by Hawking radiation, since the horizon prevents her from seeing another version of you floating in a black hole.
But what if she had a way to find out what was on the other side of the horizon without crossing it?
Ordinary relativity will say no, no, but quantum mechanics blur the rules a little. Anna could look beyond the horizon using a little trick that Einstein called “spooky action at a distance.”This happens when two sets of particles, separated in space, are mysteriously “entangled”. They are part of a single invisible whole, so the information that describes them is mysteriously linked between them.
The idea behind AMPS is based on this phenomenon. Let’s say Anna scoops up some information from the horizon – let’s call her A.
If her story is correct, and you’ve already entered a better world, then A scooped up in Hawking radiation outside the black hole should be entangled with another piece of information B, which is also part of the hot cloud of radiation. On the other hand, if your story is correct and you are alive and well on the other side of the event horizon, then A must be entangled with another piece of information C, which is somewhere inside the black hole. But here’s the point: every bit of information can only be confused once. This implies that A can be entangled with either B or C, but not simultaneously with both.
So Anna takes her particle A and puts it in a manual entanglement decoding machine, which gives her the answer: B or C.
If the answer is C, your story wins, but the laws of quantum mechanics are broken. If A is entangled with C, which is deep inside a black hole, then that piece of information is lost to Anna forever. This violates the quantum law of the impossibility of losing information.
B remains. If Anna’s decoding engine finds that A is entangled with B, Anna wins, and general relativity loses. If A is entangled with B, Anna’s story will be the only true story, which means that you actually burned to the ground. Instead of sailing straight across the horizon, as relativity suggests, you’ll be faced with a blazing wall of fire. So we’re back to where we started: what happens when you fall into a black hole? Do you slip through it and live a normal life, thanks to a reality that is strangely dependent on the observer? Or do you approach the horizon of a black hole only to collide with a deadly wall of fire?
Nobody knows the answer, and therefore this question has become one of the most controversial in the field of fundamental physics.
For more than a century, physicists have been trying to reconcile general relativity with quantum mechanics, believing that one of them will eventually have to yield. Solving the paradox of the aforementioned wall of fire should point to a winner and also lead us to an even deeper theory of the universe.
One of the clues may lie in Anna’s decoding machine. Figuring out which of the other bits of information is confused with A is extremely difficult. So physicists Daniel Harlow of Princeton University in New Jersey and Patrick Hayden of Stanford University in California decided to figure out how long it would take to decode. In 2013, they calculated that even with the fastest computer that can exist, it would take Anna an incredible amount of time to decipher the entanglement. By the time she finds the answer, the black hole has long since evaporated, disappeared from the Universe and takes with it the riddle of the deadly wall of fire.
If so, then the sheer complexity of the problem could prevent Anna from figuring out whose story is true. Both stories will remain equally true, the laws of physics will remain intact, reality will depend on the observer, and no one will be in danger of being consumed by a wall of fire. It also gives physicists new food for thought: the filthy connections between complex calculations (the kind that Anna can’t do) and space-time. Perhaps there is more lurking here somewhere.
These are black holes. They are not only annoying obstacles for space travelers. They are also theoretical laboratories that bring the laws of physics to white heat, and the subtle nuances of our Universe are brought to such a level that they can no longer be ignored.