Despite being “black” and a “hole”, a black hole is not a dark, empty space.In his theory of relativity, Einstein predicted how black holes are formed. When a massive star dies, it leaves a smaller, remnant core behind. If the core’s mass is at least three times bigger than the mass of our Sun, gravity overwhelms all other forces and turns the core into a black hole.A black hole’s gravity is so strong, that even light can’t get out. That’s why you’ll never see one. But you can detect it from the gamma-ray bursts that the hole emits. These bursts,discovered by Stephen Hawking, now carry his name – Hawking radiation.Stephen Hawking himself believed that black holes can be passages to another universe.Every black hole has an event horizon – the point at which the gravitational pull becomes so strong that you can’t escape from it. The point of no return. If you found yourself outside of that point, you would see that stars are twisted around a perfect circle of darkness.As you start being pulled toward a black hole, you’d be moving faster and faster, accelerated by the force of gravity.The gravitational force of a black hole is very, very strong. If your fell feet-first, your legs would be feeling a stronger gravitational pull than your head. Your body would be stretched apart.The most common black holes are called “stellar”. They can stretch to about 9 miles (15 km) across and be as heavy as 20 suns. If you happened to be pulled towards a stellar black hole, you’d be completely torn apart before you even reach the event horizon.So make sure to choose a supermassive one. The one that is a million times heavier than our Sun. In this case, your body would remain unharmed as you cross the event horizon, as the gravity would be pulling both your feet and your head with almost the same strength.There’s a gravitational singularity at the center of the black hole, where density becomes infinite.You would be squashed into that center and become one with the black hole. You wouldn’t be able to tell anyone about your experience.However, a person observing you outside of the event horizon would see a very different picture. As you were falling into a black hole, for them, you’d be slowing down, get dimmer and redder. In the end, you would just freeze, never crossing the event horizon.This is because space and time in a black hole swap their roles. At the event horizon, time comes to a standstill, while space, on the other hand, moves forward. You wouldn’t be able to turn around and escape the black hole, any more than you can travel back in time.Stephen Hawking, however, found a way, in which the information about your body wouldn’t be lost.He theorized that there are alternate universes with different histories. This means, in one reality you fell into a black hole. In the second one, there was no black hole.It’s impossible to be certain from outside of the event horizon whether there’s a black hole or not until you fall in there.If you crossed the event horizon and there was a black hole… But if you happened to be in a reality where the black hole didn’t exist, you’d still be alive. Just in a different universe.There would be no way for you to get back to ours.