What would we see if we fell INSIDE a BLACK HOLE? What's beyond the Event Horizon?

What is inside a Black Hole? A black hole is really not a celestial body like a planet or a star. There is really no substance there other than a severely curved space-time. It’a a region in space where matter is condensed to a theoretical infinitely small point – so small in fact that this point effectively disappears from our universe. This is called the gravitational singularity.

So if there is nothing there, what does it mean when we talk about different size black holes? When we talk about the size of a black hole, we are really talking about the size of its event horizon.

The radius of this event horizon is called the Schwarzschild radius. What happens beyond the event horizon can be ascertained by general relativity, but what happens at the singularity is anyone’s guess. The more massive a black hole is, the less its “density” and the less dangerous it is. Very large black holes like the one at the center of the milky way called Sagittarius A* has about the same density as that of water. You could likely go deep inside Sagittarius A*’s event horizon before tidal forces eventually tore you apart near the singularity.

As Adam gets closer to the event horizon, we notice that he speeds up, then he slows down and his space suit appears to get redder and fainter until he disappears from our view. He is still there, but the light reflecting off of him is so red shifted that it is invisible even to our infrared cameras.

He would appear to be completely stationary. This is because at the event horizon, from the perspective of the ship, time stops completely.
From Adam’s perspective his time is running just fine. Spacetime curves more and more severely as he gets close to the black hole. Looking back, all the light reaching him is being blue shifted. Light that was infra red, not visible to him before, is now in the visible spectrum. And light that was visible before has blue shifted to x-rays, and even gamma rays.

Would he be able to see the entire future history of the universe just before he enters the event horizon? He could view this. But it would only be viewable as a small dot of light directly overhead. How is it possible that the people on the ship see Adam as not moving, but Adam is moving and doing just fine? Both perspectives are correct.

This is because the laws of quantum mechanics requires that Adam remains on the outside of the event horizon because otherwise it would violate the conservation laws – that information can never be lost. Einstein’s theory however requires that relative to Adam, nothing is different. Time for him ticks normally.

Adam is now inside the event horizon. But not much changes for him. But he cannot see the light that fell before him, and he can never actually sees the singularity because all light is headed towards it, no light is headed away from it. He still has a sense of upness and downness inside the black hole, but every direction feels downwards.

Time becomes space inside the black hole. Once Adam reaches the singularity, will be ripped to shreds. Is there any way that Adam can escape this grim fate? There are two theoretical scenarios in which he may actually survive. First, if this black hole is charged, called a Reissner-Nordstrom black hole, the singularity singularity creates such a high centrifugal force, that space near it becomes gravitationally repulsive instead of attractive. And this spinning singularity creates an inner horizon that is a worm hole or an Einstein-Rosen bridge. Then he would be catapulted out through a white hole.

And in the second case, if the theory of Loop Quantum Gravity is correct, then there would be no singularity in a black hole at all. This case would be very similar to the rotating black hole, except there would be no infinitely bright light.

And how long would yours or Adam’s trip inside the black hole last? Well in all scenarios it will take only about 16 seconds. So not much time for sight-seeing. The black hole is where quantum mechanics and Relativity collide. Gravity becomes a dominant force at the quantum scale at the singularity.

The great secret that black holes may reveal to us is that there is no objective reality. Reality depends on whom you ask. It seems to be observer dependent. Ultimately Einstein’s equations may lead us to an understanding that not only is time relative, but reality itself may be relative.

#blackhole #arvinash

Many thanks to Dr. Andrew Hamilton, Professor of Astorphysics, University of Colorado
https://jila.colorado.edu/~ajsh/insidebh/index.html

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