What would happen if you fell inside a black hole?
It could happen to anyone.
Maybe you're out trying to find a new habitable planet for the human race, or maybe you're just on a long walk and you slip. Whatever the circumstances, at some point we all find ourselves confronted with the age-old question: what happens when you fall into a black hole?
For smaller black holes, like those formed from collapsed stars, the gradient in the gravitational pull is so steep (i.e. the force of gravity changes rapidly as you move closer) that you would not get anywhere close to the perimeter of the black hole. The gravitational pull on your feet would be so much stronger than that on your head that you would be pulled apart like string cheese pretty quickly. This is called spaghettification.
However, around a larger black hole (around the size of our solar system), the reality is stranger than that. You would have more time to approach before being torn in two. In fact, given a large enough black hole, you’d have all the time in the universe.
The instant you would enter the black hole, reality would split in two. In one, you would be instantly burned, and in the other, you would plunge on into the black hole completely unharmed.
Einstein taught us that gravity warps space itself, causing it to curve. So given a dense enough object, space-time can become so warped that it twists in on itself, burrowing a hole through the very fabric of reality. A massive star that has run out of fuel can produce this kind of extreme density. As it buckles under its own weight and collapses inward, space-time caves in with it. The gravitational field becomes so strong that not even light can escape, rendering the region where the star used to be profoundly dark: a black hole.
As you keep falling inside the black hole, space becomes more and more curvy until it becomes infinitely curved at the center . As you fall, you will approach the speed of light. The FASTER you move through space, the SLOWER you will move through time.
Furthermore, as you fall, there are things that have been falling in front of you that have experienced an even greater 'time dilation' than you have.
So if you're able to look forward toward the black hole, you see every object that has fallen into it in the past. And then if you look backwards, you'll be able to see everything that will ever fall into the black hole behind you. So basically, you will able to witness it all: from the Big Bang to the Big Crunch (a hypothetical scenario for the ultimate fate of the universe).
Then you’ll soon encounter an event horizon. It is that point on the boundary of the black hole where the gravitational force is so strong that light cannot escape it. Once you get closer than the event horizon, there is no coming back. This horizon is ablaze with energy. Quantum effects at the edge create streams of hot particles that radiate back out into the universe. This is called Hawking radiation, after the physicist Stephen Hawking, who predicted it.
After falling more and more, ultimately you will reach a point called the singularity. Space and time cease to be meaningful ideas, and the laws of physics as we know them — all of which require space and time — no longer apply.
BUT THIS IS ONE SIDE OF THE STORY.
If your friend (let’s say Anne) is witnessing your journey who watches in horror as you plunge toward the black hole, while she remains safely outside. From where she's floating, things are about to get weird. Her reality is a lot different than yours.
As you are accelerating towards the event horizon, Anne sees you stretch and twist, as if she were viewing you through a giant magnifying glass. What's more, the closer you get to the horizon the more you appear to move in SLOW MOTION.
When you reach the event horizon, from Anne’s point of view you will appear to get frozen. It looks like you would have hit the pause button. According to Anne, you’ll get destroyed by the stretching of space, the stopping of time, and the fires of Hawking radiation. Before you ever cross over into the black hole's darkness, you're reduced to ash.
Not just that, Anne would even be able to collect your ash and return to Earth. But how is it possible?
I mean, you are alive. You are chilling inside the black hole. Then why is she insisting that you've been burned to a crisp by radiation outside the horizon? Is she hallucinating?
Well, Anne is being perfectly reasonable. In fact, the laws of nature require that you remain outside the black hole as seen from Anne's perspective. That's because quantum physics demands that information can NEVER be lost. Every bit of information that accounts for your existence has to stay on the outside of the horizon, so Anne is only obeying the laws of physics.
On the other hand, the laws of physics also require that you sail through the horizon without encountering hot particles or anything out of the ordinary. Otherwise, you'd be in violation of Einstein's theory of general relativity.
So the laws of physics require that you be both outside the black hole in a pile of ashes and inside the black hole alive and well. Last but not least, there's the third law of physics that says information can't be cloned. You have to be in two places, but there can only be one copy of you.
Somehow, the laws of physics point us towards a conclusion that seems rather nonsensical. Physicists call this infuriating problem - the black hole information paradox. Luckily, in the 1990s they found a way to resolve it.
Leonard Susskind realized that there is no paradox, because no one person ever sees your clone. Anne only sees one copy of you. You only see one copy of you. You and Anne can never compare notes. And there's no third observer who can see both inside and outside a black hole simultaneously. So, no laws of physics are broken.
Unless that is, you demand to know which story is really true. Are you really dead or are you really alive?
The great secret that black holes have revealed to us is - that there is none, really. Reality depends on whom you ask. There is Anne's reality and there is your reality. End of story.
No one knows the answer. Maybe Anne will someday solve the most contentious questions in fundamental physics.