User:Lethe/blackhole

Black Holes are scary.

every black hole has a boundary called the event horizon. It's the point beyond which nothing can return. Not even light. If you were hanging out in your space ship just above the event horizon, swinging you legs out of the airlock, getting a good view of the galactic arm, and you accidentally let one foot swing into the event horizon, your leg would come back with a foot missing. You wouldn't even feel it go, because the pain signal can't escape the black hole.

There is a supermassive black hole at the center of every galaxy. These are typically millions of times more massive than our sun. Although the gravitational tidal forces from a regular sized black hole would crush you long before you approached the event horizon, so the above scenario with your foot would be unlikely, with supermassive black holes, the gravitational tidal forces are quite weak at the event horizon; your spaceship could cross the event horizon and you'd never even notice it. An interstellar Bermuda Triangle so to speak. You'd never notice it, but once you crossed the event horizon, you'd never be heard from again by the outside universe.

Once you cross the event horizon, all your particles approach the center of the black hole. the coordinate that describes the distance to the center becomes "time-like" so that your descent towards the center is as inevitable as the fact that tomorrow will follow today. The descent towards the center is the flow of time.

As you approach the center, the gravitational forces tend to stretch you out lengthwise (radial direction) and squeeze you in the horizontal directions. This force can be quite weak near the event horizon if the black hole is massive enough, but as you approach the center, this force gets stronger, and eventually approaches infinity. This is called the singularity.

No one is quite sure what happens at the singularity. If you've ever taken a physics class, perhaps you've seen Coulomb's Law? It looks like this: F=kqQ/r^2. That equation also has a singularity, at r=0. It's just a division by zero error. The singularity in Coulomb's law isn't real. When r gets small enough, you have to replace Coulomb's law by quantum mechanics, which replaces the singularity by something more well-behaved than division by zero (which can get the Math police knocking down your door)

At the moment, theories which can deal with quantum gravity are very speculative, so it's not clear what happens to the singularity from the more simple models of gravity once quantum effects are taken into account. Is it still there? Some of them can be taken care of. Other's it's not clear.

Once you've reached the singularity, every particle in your body will be separated (even your quarks, which are otherwise not allowed to be separate. A separate quark has never been seen on earth, they can only be found in black holes, quark stars, and at the Big Bang). Your constituent properties may go through a wormhole after that. The topology of the black hole allows it to connect through the singularity to another Universe.

What if two distant galaxies collided, and the power of the collision sent a couple of black holes scattering, and one passed by the Earth, just close enough to let the Earth get caught in its event horizon? I would say we should all panic and have "End of the World"-sex, but might not even know it were happening until it were too late.

Scary, right?

OK, any questions?