Black Holes

[Zorland]

Originally Posted by Genadinee

So, why does light get pulled into a Black hole? I was under the impression that light being an electromagnetic wave would be able to run away but the very thing 'black' hole is or was thinking because light cannot escape from it.

Genuine question btw if you can explain it to me would be cool.

G

It is indeed a good question, and confused many physicists for years. Photons have no mass. How can they possibly experience a force from a black hole then!! Isaac Newton, who came up with the first theory of gravity, explained gravity as a force like any other. Force = Mass of object / (distance from object)^2 . According to this theory of gravity, light could escape no matter how great the mass of a black hole.

However, Einstein (a smart guy) refined the theory of gravity with what is now called the General Theory of Relativity. In his theory, the force of gravity is a geometrical force. (The math here is really complicated so I have to make some bad analogies). You can think of it like this, take a sheet with stripes. The stripes are the paths that a photon would follow (straight lines). Now drop a large weight onto the sheet. It will deform the sheet.

Now if you look at the lines, it appears that they bend toward the mass. This is the geometrical nature of the force. Mass warps "spacetime" and that forces the straight line paths of photons (these are called geodesics for anyone wanting to study more math!) to bend toward the mass.

Now if you drop a bunch of large masses onto the sheet, they will all end up in the same area (if they are close enough together). If they are heavy enough, they will rip through the sheet. The mathematical term for this is called a "singularity" and it is a point of infinite bending of the "spacetime" sheet. That is a blackhole. All the stripes on the sheet entering the "black hole" get stuck there because of the rip in the sheet. They have no path to follow back out.

As I said, it's a bad analogy. You can prove from the math that you need to travel faster than the speed to escape, but I was never good at General Relativity and so I cannot remember how to prove this at the moment :>(

[Zorland]

Originally Posted by qujam

The gravitational field of a black hole (hence the reason its black) is so strong it can capture light waves. Due to wave-particle duality, even electromagnetic waves have, at least a theoretical, mass.

Momentum, not mass!

[Zorland]

Originally Posted by Jolene

I understand it this way.
.....
Correct?

Absolutely correct. I also like the bit about the tomatoes.

[Jolene]

My tomato example ))
The "Raumzeitkrümmung" "Spacetime bending" is like you put many tomatos on a blanket and they make a dent into the blanket, when you imagine billions of billions of billions tomatos on the blanket (universe) you come to the conclusion that the whole universe has to be round.
A wormhole also called the Einstein-Rosen-Brücke is also some kind of spacetime bending.
You could (COULD) travel from one spot to another one that is million of lighttravel years away in no time. It bends the universe, the squeezed tomatoes aka black holes do the same. They bend the spacetime and everything is falling into it towards the middle, so light also will not go straight anymore it will follow the bending towards the squeezed tomatoes (now called ketchup)

Ah yes and what Zorland means is what Hawkins said ?? That the flee space has to be faster than light and since nothing is faster than light nothing can flee also not the light. And the gravity is unmeasuerable big, and my tomatoe isn't existing anymore, there is no mass anymore, it is so small that it doesn't exist. The space is bended towards 0.

[Abadonn]

Originally Posted by Zorland

As I said, it's a bad analogy. You can prove from the math that you need to travel faster than the speed to escape, but I was never good at General Relativity and so I cannot remember how to prove this at the moment :>(

I'll let you know after we get next selo upgrade.

[qujam]

Originally Posted by Zorland

Momentum, not mass!

Surely if they have momentum p = mv implies a theoretical mass

(no symbol font on here so had to use p)

[Zorland]

P=Mv is a large object approximation. The photon momentum is derived from another one of Einstein's equations...

E^2 = (pc)^2 + (mc^2)^2

In the case of a photon (m=0) this reduces to
E=pc

It's pretty crazy, I admit, to think of something with non-zero momentum yet zero mass.

[Jolene]

What I said none existent ketchup p ))

[qujam]

Ah that makes more sense

[Genadine]

How can something exist if it has no mass?

Everything must be made up of something else?

Or is there multiple items that simply 'exist' and we have no clue atm how to prove them?