question about light and blackholes


by magus
Tags: blackholes, light
Ambitwistor
Ambitwistor is offline
#19
Nov20-03, 10:17 PM
P: 837
Originally posted by Unkaspam
Gravitons escape from black holes all the time, at no loss to their gravitational energy.
Virtual gravitons escape, but since they are not real, they do not carry any real energy, information, or anything else observable out of the black hole.

Does that mean gravity travels faster than light (in order to escape the event horizon of a black hole?)
When people speak of "the speed of gravity", they mean the speed at which observable gravitational influences, i.e., changes in the gravitational field, propagate. According to that definition, the speed of gravity is the same as the speed of light.
Unkaspam
Unkaspam is offline
#20
Nov22-03, 07:29 PM
P: 42
Originally posted by Ambitwistor
When people speak of "the speed of gravity", they mean the speed at which observable gravitational influences, i.e., changes in the gravitational field, propagate. According to that definition, the speed of gravity is the same as the speed of light.
Can a gravitational field be viewed simply as the sphere of influence or effect generated by a mass? Are there actual waves of gravity or simply a sphere of gravitationally influenced events that demonstrate the effects of a gravitational source?

How do we observe and verify something going faster than light?
Ambitwistor
Ambitwistor is offline
#21
Nov22-03, 10:49 PM
P: 837
Are there actual waves of gravity or simply a sphere of gravitationally influenced events that demonstrate the effects of a gravitational source?
I'm not sure what the difference is. Take, say, electromagnetic radiation (light): "Are there actual waves of electromagnetism, or simply a sphere of electromagnetically influenced events that demonstrate the effects of an electromagnetic source?" The answer to this question is the same as the answer to the corresponding gravitational question, but I don't know whether that answer is "yes" or "no" because I don't understand the question.


How do we observe and verify something going faster than light?
Well, here is one way: send a wave past two detectors. See how long it takes between reaching one and reaching the other. Knowing the distance between them, determine its speed.
Unkaspam
Unkaspam is offline
#22
Nov23-03, 02:53 PM
P: 42
Originally posted by Ambitwistor
I'm not sure what the difference is. Take, say, electromagnetic radiation (light): "Are there actual waves of electromagnetism, or simply a sphere of electromagnetically influenced events that demonstrate the effects of an electromagnetic source?" The answer to this question is the same as the answer to the corresponding gravitational question, but I don't know whether that answer is "yes" or "no" because I don't understand the question.
When a wave of water moves a leaf of seaweed we can say the mass of water and its motion are the cause of the event. When an object falls to the ground is this caused by a wave of gravity or a condition created by a source of gravity?

To put it another way, when there is an eclipse and the earth is in shadow, there is no "shadow wave" emanating from the moon, the shadow is simply an effect of the moon blocking the sun, there are no "shadowtons" or shadow waves.

So what I'm asking is does gravity emanate from a source as a wave, in the way that light radiates from a source, or are we simply seeing the tell tale effects of gravity within a defined sphere of an inert source?
Ambitwistor
Ambitwistor is offline
#23
Nov23-03, 03:06 PM
P: 837
When a wave of water moves a leaf of seaweed we can say the mass of water and its motion are the cause of the event. When an object falls to the ground is this caused by a wave of gravity or a condition created by a source of gravity?
A static gravitational field (such as, more or less, the Earth's gravitational field) doesn't have any gravitational waves, but objects still fall. (Likewise, the electric field around a point charge doesn't have any electromagnetic waves, but charges are still attracted or repelled from it.) Gravitational waves are changes in the gravitational field, just like electromagnetic waves (light) are changes in the electromagnetic field.

So what I'm asking is does gravity emanate from a source as a wave, in the way that light radiates from a source,
I think you are confusing some issues.

Gravitational waves can emanate from a source as a wave, analogous to how light (electromagnetic waves) radiates from a source. But electromagnetic waves are not responsible for, say, the electrostatic attraction (or repulsion) between two charges, nor are gravitational waves intrinsically responsible for the attraction of two masses. Nothing has to "emanate" from a mass or charge, in the sense of some effect propagating at some speed through space, in order for one body to influence another. (But if you change the source, then the effects of that change will propagate out in terms of changes in the field at successively more distant points.)

or are we simply seeing the tell tale effects of gravity within a defined sphere of an inert source?
I still don't know what you're talking about.
Unkaspam
Unkaspam is offline
#24
Nov23-03, 04:04 PM
P: 42
Originally posted by Ambitwistor
A static gravitational field (such as, more or less, the Earth's gravitational field) doesn't have any gravitational waves, but objects still fall. (Likewise, the electric field around a point charge doesn't have any electromagnetic waves, but charges are still attracted or repelled from it.) Gravitational waves are changes in the gravitational field, just like electromagnetic waves (light) are changes in the electromagnetic field.



I think you are confusing some issues.

Gravitational waves can emanate from a source as a wave, analogous to how light (electromagnetic waves) radiates from a source. But electromagnetic waves are not responsible for, say, the electrostatic attraction (or repulsion) between two charges, nor are gravitational waves intrinsically responsible for the attraction of two masses. Nothing has to "emanate" from a mass or charge, in the sense of some effect propagating at some speed through space, in order for one body to influence another. (But if you change the source, then the effects of that change will propagate out in terms of changes in the field at successively more distant points.)



I still don't know what you're talking about.
You've managed to answer my question anyways, thanks.
sheldon
sheldon is offline
#25
Dec6-03, 01:10 AM
sheldon's Avatar
P: 156
This is so heavy spicoli! Nothing escapes the black hole period. NOTHING NOTHING. Not even your thought waves:)
jedijesus
jedijesus is offline
#26
Dec8-03, 05:47 AM
P: 15
[QUOTE]Originally posted by magus
[B]i was just wandering..... at the point where gravity is strong enough to be greater than the kinetic energy of which light possesses, do photons of light actually radiate some distance from the collapsed star then slow to rest and fall back to the surface, as a cannonball being shot straight up in Earth's atmosphere would, or at this point are the particles simply not capable of being emitted. or is their some other explanation of which i have not accounted for.
thx,
the point of which you are speaking, is called the event horizon. light particals are not able to withstand the graivty of the sigularity. Thus they are sucked in. They don't go out and then get sucked into a black hole, they just go into the black hole. Now when they are sucked in, they give of a nasty gamma burst that is detectible. They give this off because of the energy that is involved with clashing into a singulary which is like smashing into Earths atmosphere. And that is what can detect it, with other obsevations of course.
jedijesus
jedijesus is offline
#27
Dec8-03, 06:00 AM
P: 15
the event horizon is the edge of a black hole. the gavity there is greater than you can imagine. if light is going into the black hole, you are not going to see it. When light clashes with the event horizon of a black hole, it give off gamma rays. Thats it, that is the only way to see it. If you could optically see a black hole, it wouldn't be a black hole
Ambitwistor
Ambitwistor is offline
#28
Dec8-03, 10:04 AM
P: 837
When light clashes with the event horizon of a black hole, it give off gamma rays.
No, it doesn't. It just falls in. When people say that black holes radiate X-rays and gamma rays and such, that radiation comes from matter which is outside of the black hole.


Register to reply

Related Discussions
Question about physics of light / light travel General Physics 6
Blackholes light gravity Special & General Relativity 1
What happens when you fall into a blackhole? Beyond the Standard Model 0
Some Question About Blackholes Astrophysics 1
what happens when two black holes meet? Astrophysics 4