# Black Holes and time

G

#### Guest

How can people say that light is the absolute speed in the universe when light cannot escape a black hole
Light and gravity and all things cannot escape it so how can we say that light is the absolute speed?
if it was light would be free to navigate around a hole as if it was nothing.

And while im on the topic i have heard if we were to send a space craft thru a black hole 1km by 1km our only safepoint of access would be a space 1cm by 1cm without the blackhole crushing the craft...

anyone heard of this?

The speed of light applies to when it is moving, not when it blocked by something (like when it hits an object and a shadow results). If a black hole prevents light from escaping, it can't travel at any speed. Maybe in a black hole, no light is created to begin with.

Light as the fastest comes from Einsteinâ€™s special relativity equations for mass, length and time dilation. Which are:

L = L0<1-(v/c)^2>1/2 Length

t = t0<1-(v/c)^2>1/2 time

m = m0<1-(v/c)^2>1/2 mass

In all three of these equations any number substituted for velocity (v) would result in an error.

Light canâ€™t escape a black hole because gravity bends light and the force of gravity within a black holes event horizon is strong enough to bend light enough that it canâ€™t escape.

<This message has been edited by kentheee (edited 18 September 2000).>

Those equations looked much better in Word when I wrote them.

kentheee, you should use ^ to mean "to the power of", it always comes out in ASCII.

Dr Light, the thing is, nothing ever actually falls into a black hole. At the event horizon, time actually stops. So light never goes slower or faster than c, since the time in the frame it's in slows down. The gravity time dilation stuff is pretty deep math; I've only seen it once or twice. But I know it works out, everywhere except (of course), inside the event horizon, which we can't see anyway.

Yeah, you right. I edited them.

I don't know the equation for time dialation due to gravity. Do you? I would be very intrested in seeing them. The equations above are based on velocity. I guess the time dialation ones would be based general relativity and gravity warping space and time.

Couldn't this be used to travel forward in time? The event horizon is the point at which light can't escape. Wouldn't that mean an object with mass would have an "event horizon" based on its mass and velocity outside of which it could still escape. You could "orbit" the black hole for a period of time and when you left you would be in the future. It wouldn't be very useful since it is a one way ticket, but it may have its uses. The question is though, would that orbit be close enough to the black hole to feel the effects of the time dialation. There would be some dialation based on your velocity itself but would that be enough. Maybe that is how it could be controlled.

Yeah, just a note: General relativity is about how motion effects time, special relativity deals with spacetime warping like gravity and such.

You could use any mass as a forward time machine - even time on the surface of the Earth is flowing slower than in orbit or beyond. It's just more noticeable near a black hole. But, near a black hole the tidal gravitational forces become huge and hard to survive.

Oh, and I'll look up the special relativity equations when I get home.

Raz,

I think you have gotten them backwards, but please let me know if I'm wrong. The equations I posted earlier were from Special Relativity. I alway though General Relativity was the mass warping space-time thing.

Here is an excerpt from this web site( http://www.ncsa.uiuc.edu/Cyberia/NumRel/GenRelativity.html ):

Gravitational Time Dilation
Einstein's Special Theory of Relativity predicted that time does not flow at a fixed rate: moving clocks appear to tick more slowly relative to their stationary counterparts. But this effect only becomes really significant at very high velocities that app roach the speed of light.
When "generalized" to include gravitation, the equations of relativity predict that gravity, or the curvature of spacetime by matter, not only stretches or shrinks distances (depending on their direction with respect to the gravitational field) but also w ill appear to slow down or "dilate" the flow of time.

In most circumstances in the universe, such time dilation is miniscule, but it can become very significant when spacetime is curved by a massive object such as a black hole. For example, an observer far from a black hole would observe time passing extremely slowly for an astronaut falling through the hole's boundary. In fact, the distant observer would never see the hapless victim actually fall in. His or her time, as measured by the observer, would appear to stand still. The slowing of time near a very simple black hole has been simulated on supercomputers at NCSA and visualized in a computer-generated animation.

Maybe a Black Hole is exactly what it's named: a hole (the absence of anything) as opposed to a giant mass like a galaxy. If so, then light, or anything else, would be unobstructed when it flows through it and would be able to travel faster as a result.

If it flowed in one direction into the Black Hole, then we wouldn't see it unless we were on the backside of a Black Hole. And, if light traveled faster, is it still visible light or someting else in the spectrum?

Yeah, sorry. I did get them wrong. How silly to name them both relativity. The names are so easily confused. I'll try to get them straight now...

And NoTime, isn't the whole point of a 'black hole' that it's a huge mass from which nothing can escape? If it wasn't, wouldn't you have to call it something different?

Raz: If a Black Hole is a large mass, then it might properly be called a Black, or Dark, Mass. It could very well be a large mass.

On the other hand, a Black Hole might be a giant void, like the eye of a storm or a funnel, that light and other matter are rushing in to fill. In that case, light would not be generated and we would not see it.

Raz,

Yeah, I get them confused once and a while. I had to look it up to make sure I was right. They are relatively confusing.

After reading up a bit on General I think I understand how gravity causes time dilation. Gen Rel says the gravity and acceleration are the same. I guess if the gravity is strong enough it would be equivalent to a velocity approaching the speed of light and that would account for the time dilation.

No Time,

A black hole is a result of a Red Giant star going supernova. If the star is massive enough it will collapse in on itself becoming extremely dense. It was called a "Black Hole" since in theory of the time there would be no way to observe one. Now it is know that black holes radiate x-rays. These are not actually escaping from in side the event horizon, but rather just outside of it. I think Stephan Hawking theorized this. I'm not sure, but he did write about it.

Basically what happens throughout the universe is partials and anti-partials are created and reunite all the time through out space. When this happens near the edge of the event horizon of a black hole however one partial may be caught within the event horizon and not escape. The other partial will escape and is observed as x-rays.

At the center of a black hole is a very dense and massive object. It is the mass of the object that causes the extreme gravity or curvature of space-time.

There are theories about large black holes caused by many stars in close proximity of each other. They are thought to possibly exist in the center of the galaxy. I donâ€™t know too much about this, but these would be different from the ordinary type of black hole.

Hey guys just want to say thanks for your info.

I just finished reading it all. HEAVY STUFF!
You guys cleared up a lot of stuff for me.

Thanks again