06 Aug 07
Originally posted by sonhouseIf you're alive then it's not a black hole.
That brings to mind a test, assuming you found yourself inside something with a huge gravitation, how do you know if you are in a black hole? If that idea is right, if the speed of sound = the speed of light, you are in a black hole, then whacking something and producing a sound then measuring its velocity would give you an independent test of what medium you were in, wouldn't it?
06 Aug 07
Originally posted by sonhouseUm, no. The speed of sound only approaches the speed of light as a neutron star gets heavier. It makes no sense to talk about the speed of sound in a black hole, because there is no sound in a singularity. If you whack a singularity it is not going to vibrate.
That brings to mind a test, assuming you found yourself inside something with a huge gravitation, how do you know if you are in a black hole? If that idea is right, if the speed of sound = the speed of light, you are in a black hole, then whacking something and producing a sound then measuring its velocity would give you an independent test of what medium you were in, wouldn't it?
Note that while a black hole appears to be a sphere, it is actually a point; the sphere is merely the volume from which light cannot escape. Nothing particularly special happens if you pass the event horizon and enter the sphere. The speed of sound in the metal of your xylophone is still the same.
07 Aug 07
Originally posted by GregMThe idea of the singularity being a point is in contention by a lot of scientists, it is a bit pedantic to just repeat the dogma of the last century, there are newer theories that say the density does not go infinite but instead is the conduit to a white hole, that is to say, a big bang forming another universe so the point idea is not universally held.
Um, no. The speed of sound only approaches the speed of light as a neutron star gets heavier. It makes no sense to talk about the speed of sound in a black hole, because there is no sound in a singularity. If you whack a singularity it is not going to vibrate.
Note that while a black hole appears to be a sphere, it is actually a point; the sphere is merely ...[text shortened]... rizon and enter the sphere. The speed of sound in the metal of your xylophone is still the same.
07 Aug 07
Originally posted by sonhouseI was reading about this and it's not clear that what you've described is stable, no-one has ever observed a white hole. The singularity is a mathematical nicety, it doesn't ever actually occur - at or before the Planck scale we expect new physics to take over and it's not clear what happens then. With spinning black holes it's all rather complicated but I don't think it changes what I'm about to say.
The idea of the singularity being a point is in contention by a lot of scientists, it is a bit pedantic to just repeat the dogma of the last century, there are newer theories that say the density does not go infinite but instead is the conduit to a white hole, that is to say, a big bang forming another universe so the point idea is not universally held.
Suppose you travel through space and find a non-rotating star which is heavy enough that when the core collapses it goes straight to a black hole - you are sufficiently far away to be reasonably close to being an asymptotic observer but close enough to see what is going on (ie a couple of light hours) - and all the material of the star is gravitationally bound, there is no supernova. As the density increases material cannot escape and everything falls towards the event horizon. But because the rate at which clocks run is slower for observers in a gravitational well the material falling into the black hole appears to take an infinite amount of time to do so. So for an asymptotic observer (you) the black hole is always forming - but never quite getting there.
Let's say you send in a probe to see things close up. As it gets closer to the black hole it's signals to you get more and more stretched out in time as time dilation effects take over. Eventually it will fail due to gravitational tidal forces and be torn into it's constituent particles and thermalized - but let's pretend that we have some engineering solution to that problem and the probe can get messages out via a wormhole (or other convenient science fiction device). The probe then shows the material being compressed, heated and thermalized (as you can see from the ship), but because it's clock is running slower to see anything different to what's on the ship these messages have to go back in time... It sends out pictures of the material falling through the event horizon and then - because the space in the black hole is moving faster than light (*) it cannot show the singularity - or anything in front of it - or even anything behind it since it is moving away faster than light from the in-falling material behind it can go.
For an asymptotic observer sound waves would exist in the material falling in, their speed of propagation would depend on their direction and the wave-forms would be unusual due to the particularly powerful doppler effect. Inside the event horizon waves in the in-falling material cannot propagate as points at different radii have become causally disconnected so there is no way to compress the material at the wave front. So the only waves could be compression waves moving around on points at equal radius from the black hole, they'd be limited by the speed of light.
Since from the point of view of an asymptotic observer the material of the star almost but never quite falls inside it's event horizon it is possible that black holes never happen as Hawking evaporation destroys them before they have time to form.
(*) Looking at the space-time dimensions from the "point of view" of the asymptotic observer, for the probe inside the black hole space-time is so distorted that the radial direction and time have kind of swapped round so that for it the future is the singularity.
09 Aug 07
Originally posted by sonhouseowkay, so it is a hard question to anwer. And there are many well worked out replies.
Talked with a player here, Joe Shmo, we got to talking about physics and stuff, and the speed of sound, he was suprised the speed of sound underwater was faster than in air. I told him it was some 15 times faster than in air because the speed of sound is greater when the density of the material is greater, so the speed of sound in an iron rail is greater ye ...[text shortened]... e speed of light? I assume there is no reason why sound could not propagate inside a black hole.
But......
Please remind me,...
Why do we care?
10 Aug 07
1 edit
I know surprisingly little about everything previously mentioned, I have not yet taken physics so I have little understanding of the concepts, however, I find this very interesting and will probably go down to the library or wait till school starts and talk to my physics teacher in an attempt to gain a slight understanding of the ideas addressed above.
Why do I care; I dunno, I find it interesting.
Why do you care to play chess?
Edit - grammar
- Joined
- 10 Dec 06
- Moves
- 8528
10 Aug 07
Originally posted by Drew Lamd you have every right to find it interesting, as it is
I know surprisingly little about everything previously mentioned, I have not yet taken physics so I have little understanding of the concepts, however, I find this very interesting and will probably go down to the library or wait till school starts and talk to my physics teacher in an attempt to gain a slight understanding of the ideas addressed above.
Wh ...[text shortened]... do I care; I dunno, I find it interesting.
Why do you care to play chess?
Edit - grammar
10 Aug 07
2 edits
Originally posted by Drew LI like to play chess because it is both competitive and relaxing to me.
I know surprisingly little about everything previously mentioned, I have not yet taken physics so I have little understanding of the concepts, however, I find this very interesting and will probably go down to the library or wait till school starts and talk to my physics teacher in an attempt to gain a slight understanding of the ideas addressed above.
Wh ...[text shortened]... do I care; I dunno, I find it interesting.
Why do you care to play chess?
Edit - grammar
And offcourse so can be this discussion to anyone else.
No offence ment.
-Edit-
threadid=74737
12 Aug 07
Originally posted by sonhouseInteresting question. I suppose the real question would be: is a black hole a medium? Can it transmit sound?
Talked with a player here, Joe Shmo, we got to talking about physics and stuff, and the speed of sound, he was suprised the speed of sound underwater was faster than in air. I told him it was some 15 times faster than in air because the speed of sound is greater when the density of the material is greater, so the speed of sound in an iron rail is greater ye ...[text shortened]... e speed of light? I assume there is no reason why sound could not propagate inside a black hole.
16 Aug 07
Originally posted by sonhousehttp://universalfacts.blogspot.com/2005/07/can-you-hear-sound-in-space.html
Talked with a player here, Joe Shmo, we got to talking about physics and stuff, and the speed of sound, he was suprised the speed of sound underwater was faster than in air. I told him it was some 15 times faster than in air because the speed of sound is greater when the density of the material is greater, so the speed of sound in an iron rail is greater ye ...[text shortened]... e speed of light? I assume there is no reason why sound could not propagate inside a black hole.
16 Aug 07
Originally posted by kenanThis blog is wrong. Sound is not only a earthly phenomenon. How can astronauts communicate with earth?
http://universalfacts.blogspot.com/2005/07/can-you-hear-sound-in-space.html
And remember:
(1) Planets are in space.
(2) Earth is a planet.
...therefore...
(3) Earth is in space.
(4) You can hear sound on Earth.
Ergo - you can hear sounds in space.
16 Aug 07
3 edits
Originally posted by FabianFnasThe blog is wrong because the entire universe is not consisted of a big vacuum.
This blog is wrong. Sound is not only a earthly phenomenon. How can astronauts communicate with earth?
And remember:
(1) Planets are in space.
(2) Earth is a planet.
...therefore...
(3) Earth is in space.
(4) You can hear sound on Earth.
Ergo - you can hear sounds in space.
edit: Astronauts communicate using radio vawes.
16 Aug 07
2 edits
Originally posted by FabianFnashttp://www.bu.edu/phpbin/news-cms/news/?dept=1127&id=41655
This blog is wrong. Sound is not only a earthly phenomenon. How can astronauts communicate with earth?
And remember:
(1) Planets are in space.
(2) Earth is a planet.
...therefore...
(3) Earth is in space.
(4) You can hear sound on Earth.
Ergo - you can hear sounds in space.