# What’s it like falling into a black hole? What will you see?

The universe is different destroys anything. If you try to hold your breath in space your lungs would explode; if, instead, you inhale every molecule of air, you lose consciousness. In some places, you’ll freeze to death, having lost the last heat of his body; in others it will be so hot that the atoms of your body will turn into plasma. But of all the ways the universe gets rid of objects that are the most fun to send it into a black hole.

## What is beyond the event horizon?

According to our theory of gravity — the General theory of relativity — properties of the black hole are determined by three things. Namely:

1. Mass, or total amount of matter and the equivalent amount of energy (according to the formula E = mc2), which are to the formation and growth of black holes to its current state.
2. Chargeor total electric charge, which exists in a black hole from all the positively and negatively charged objects that fell into the black hole in the history of its life.
3. Angular momentum (moment), or spin, which is a measure of the total quantity of rotational motion that a black hole is by nature.

In reality, all the black holesthat physically exist in our Universe must have a large mass, a significant amount of angular momentum and minor charges. This extremely complicates the situation.

When we normally represent a black hole, we imagine a simple version of it, which is described only by its mass. He has an event horizon around a single point, and the area surrounding the point beyond which light can not escape. This area is absolutely spherical and has a boundary that separates the region from which light can escape and where: the event horizon. The event horizon is at a certain distance (the Schwarzschild radius) from the singularity in all directions at the same time.

This is a simplified version of the realistic black hole, but a great place from which to begin to think about the physics occurring in two different places: the event horizon and inside the event horizon.

Outside the event horizon gravity behaves as you would normally expect. Space bends in the presence of mass, which makes every object in the Universe to experience acceleration in the direction of the Central singularity. If you were at a great distance from a black hole at rest, and allowed the subject to fall into it, what would you see?

Assuming that you managed to keep still, you will see how a falling object accelerates slowly from you to that black hole. It will be accelerated towards the event horizon, then there is something strange. You find that it slows down, fades and becomes redder. But it will not disappear completely. He only gets close to this: will become dull, red and more difficult to detect. You can always see if you watch closely enough.

Now imagine the same scenario, but this time imagine that you are the one falling into a black hole object. Experience what is happening is entirely different.

The event horizon is getting bigger much faster than you expected, because the curvature of space becomes stronger. Around the event horizon space is so curved that you will see many images of the universe, which is outside of us, as if it reflected and turned.

And as soon as you cross the event horizon, you still can see the outer universe, but part of the universe inside the event horizon. In the last moments the space will look completely flat.

## What is black hole?

The physics of all this are complex, but the calculations are quite simple and elegant just made Andrew Hamilton of the University of Colorado in a series of works of the late 2000’s-early 2010-ies. Hamilton has also created a series of spectacular visualizations of what you’ll see falling into a black hole based on these calculations.

Based on these results, we can draw a number of conclusions, many of which are illogical. To try to understand them, you need to change the way space. We normally think of it as a fixed tissue, and we believe that the observer is somewhere “down”. But inside the event horizon you are always moving. Space moves — like a treadmill — continuously by moving all in himself to the singularity.

And it moves so fast that even if you accelerate directly from a singularity with infinite power, you will still fall to the center. Objects outside the event horizon, will continue to send you light from all sides, but you can see only part of properties of the event horizon.

The line that defines the boundary between what can be seen by any observer, is mathematically described by the cardioid where the component with the greatest radius for the event horizon, and the component of the smallest radius is at the singularity. This means that the singularity, even as a point, not necessarily bind all gets it, with all the rest. If you and I fall into the event horizon from different sides at the same time, we will never see the light of each other after there will be the intersection of the event horizon.

The reason for this is the constantly moving fabric of the Universe itself. Inside the event horizon space moves faster than light, therefore nothing can escape from a black hole. That’s why, once in a black hole, you begin to see strange things like multiple images of the same object.

We can understand this by asking a question: where is the singularity?

Inside the event horizon of a black hole, in which direction would you move, you will eventually encounter the singularity. So, oddly enough, a singularity appears in all directions. If your feet point in the direction of acceleration, you will see them in front of him but also on yourself. All this is easily calculated, though very illogical. And this is only for simplified cases: non-rotating black hole.

But let us now turn to the physically interesting case when the black hole is rotating. Black holes owe their origin to systems of substance — like stars which always revolve at some level. In our Universe (and in the General theory of relativity), the angular momentum represents the absolute value of the prisoner for any closed system; there is no way to get rid of it. When a collection of matter collapses to a radius that is smaller than the radius of the event horizon, angular momentum is contained inside it, like mass.

The solution we have here, it will be much harder. Einstein introduced General relativity in 1915 and Karl Schwarzschild received a decision on non-rotating black hole a few months later, in early 1916. But the next step in modeling this problem in a more realistic way — when the black hole has angular momentum, not just mass — was made only in 1963 that Roy Kerr found the exact solution in 1963.

There are several fundamental and important differences between the more naive and simple Schwarzschild solution and more realistic and complex Kerr solution. Among them:

• Instead of a single decision about where the event horizon in a rotating black hole there are two mathematical solutions: inner and outer event horizon.
• Beyond even the outer event horizon there is a place known as the ergosphere, where space itself moves at a speed equal to the speed of light, and particles in it have tremendous acceleration.
• There is a maximum permissible ratio of angular momentum to the mass; if the pulse becomes too strong, the black hole will emit this energy (through gravitational radiation) until it drops to the limit.
• And the most interesting: the singularity in the center of a black hole is not a point on a one dimensional ring, the radius of which is determined by the mass and angular momentum of the black hole.

Given all this, what happens when you fall into a black hole? Yes, the same thing that happens if you get into a nonrotating black hole, except that all the space is not behaving as if he is falling towards the Central singularity. Instead, the space also behaves as if it moves along the direction of rotation as the twisting funnel. The larger the ratio of angular momentum to the mass, the faster it rotates.

This means if you see something falls into a black hole, you will see that it becomes more dull and red, but also spread out in a ring or disk in the direction of rotation. If you fall into a black hole, you will spin like a carousel that attracts you to the center. And when you reach the singularity, it will ring; the different parts of your body will meet with the singularity on the inner ergopowertm black hole Kerr — at different spatial coordinates. You will gradually stop seeing the other parts of your own body.

The most important thing you must understand from all this is that the fabric of space itself is in motion, and the event horizon is defined as the place where even if you move at the speed of light, whichever direction you choose, you will inevitably encounter a singularity.

Visualization Andrew Hamilton is the best and most accurate model of what happens when falling into a black hole, and so illogical that they need to review again and again until you start to understand something (actually not starting). It’s creepy and beautiful, and if you are adventurous enough to ever fly to the black hole and cross the event horizon, it’s the last thing you ever saw.

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