jrm@wdl1.UUCP (08/07/85)
/***** wdl1:net.astro.expert / jrm / 1:03 pm Aug 6, 1985*/ A common science fiction theme is that of a ship orbiting a black hole under intense gravitational and tidal forces. Another is a ship falling into a black hole (usually with discussion of the relativistic effects). However.... By definition, the gravitational feild of a black hole is so intense that not even light or other wavicles with velocity c can escape. My understanding is that gravity propagates with velocity c. (I believe this has been proven. Correct?) Does this not imply that, at least as far as the outside universe is concerned, the black hole has no gravitational feild? Further, since everything with velocity <=c is kept within the black hole, does this not mean that the black hole is undetectable? Even to the extent that you could pass through one or it could pass through you and neither would know anything had happened? Does quantum mechanics affect this? (In terms of "things" escaping from the black hole.) jrm@ford-wdl1 /* ---------- */
gwyn@BRL.ARPA (08/09/85)
From: Doug Gwyn (VLD/VMB) <gwyn@BRL.ARPA> Two of the three modes of "gravity waves" are purely conventional while the third has been shown to propagate at the speed of light. However, this is a "weak field" (nearly Lorentz metric) approximation and one thing for sure about so-called "black holes" is that they are not weak fields! One cannot legitimately treat them as embedded in a flat background space-time when discussing questions such as this in regions very "near" the black hole. My feeling is that one could "define" terms such that gravitational effects propagated locally at the speed of light, even "inside" a black hole. I don't know what good this would do, though. P.S. I'll believe in black holes the day that I see a solution to the real field equations that looks like one, not just to the old 1916 equations.
MJackson.Wbst@Xerox.ARPA (08/09/85)
"P.S. I'll believe in black holes the day that I see a solution to the real field equations that looks like one, not just to the old 1916 equations." If you don't believe in black holes, what do YOU think is the ground state of cold, catalyzed matter when you pile enough of it up? Mark
mcgeer%ucbkim%Berkeley@sri-unix.ARPA (08/09/85)
From: mcgeer%ucbkim@Berkeley (Rick McGeer) I remember asking this same question a few years ago, and I was told by some graduate physics students at the time that either: (1) Gravitons aren't affected by a gravitic field; or (2) There are no gravitons: gravity is strictly the geometric effect of a mass on spacetime. Which of these is correct? According to my friends (and, by the way, they were solid-state guys, not relativists or field theorists), nobody knows. But one of them must be correct, because black holes are observed... Rick
rimey@ucbvax.ARPA (Ken Rimey) (08/10/85)
In article <625@wdl1.UUCP> jrm@wdl1.UUCP writes: > By definition, the gravitational feild of a black hole is so > intense that not even light or other wavicles with velocity c can escape. Yes. By the way, quantum mechanics is not relevant to black holes unless they are very very tiny. Also, "wavicle" is not a real physics term. Say "particle". > My understanding is that gravity propagates with velocity c. (I believe > this has been proven. Correct?) Gravity waves propagate with velocity c. Yes. > Does this not imply that, at least as > far as the outside universe is concerned, the black hole has no > gravitational feild? No. > Further, since everything with velocity <=c is kept within > the black hole, does this not mean that the black hole is undetectable? > Even to the extent that you could pass through one or it could pass > through you and neither would know anything had happened? > ..... > jrm@ford-wdl1 No. Matter cannot escape, but matter outside is certainly affected by the black hole's gravitational field. Ken Rimey
rimey@ucbvax.ARPA (Ken Rimey) (08/10/85)
>> Further, since everything with velocity <=c is kept within >> the black hole, ... >> jrm@ford-wdl1 > >No. Matter cannot escape, but matter outside is certainly affected by >the black hole's gravitational field. > > Ken Rimey > I should make this more clear. In general relativity, the force of gravity has a special status. Particles follow trajectories that are dependent on the curvature of space-time. We call the effect of the curvature on the trajectories gravity. So, there is space-time, and there are particles moving in it. Gravity is not particles. Now, you may have heard talk of gravitons and such. This is not vanilla general relativity. I know nothing about theories of quantum gravity, but I suspect that it would be difficult to calculate things about black holes from these theories. To understand black holes, forget you every heard of gravitons. Ken Rimey (again)
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (08/11/85)
>> "P.S. I'll believe in black holes the day that I see a solution to >> the real field equations that looks like one, not just to the old >> 1916 equations." > > If you don't believe in black holes, what do YOU think is the ground > state of cold, catalyzed matter when you pile enough of it up? I don't think the experiment has been done.
chas@gtss.UUCP (Charles Cleveland) (08/12/85)
Summary: In article <625@wdl1.UUCP> jrm@wdl1.UUCP writes: > >/***** wdl1:net.astro.expert / jrm / 1:03 pm Aug 6, 1985*/ > > A common science fiction theme is that of a ship orbiting > a black hole under intense gravitational and tidal forces. Another is > a ship falling into a black hole (usually with discussion of the > relativistic effects). > However.... > By definition, the gravitational feild of a black hole is so > intense that not even light or other wavicles with velocity c can escape. > My understanding is that gravity propagates with velocity c. (I believe > this has been proven. Correct?) Does this not imply that, at least as > far as the outside universe is concerned, the black hole has no > gravitational feild? > Further, since everything with velocity <=c is kept within > the black hole, does this not mean that the black hole is undetectable? > Even to the extent that you could pass through one or it could pass > through you and neither would know anything had happened? > Does quantum mechanics affect this? (In terms of "things" > escaping from the black hole.) > jrm@ford-wdl1 > >/* ---------- */ Silly me, I forgot to add "Black Hole" to my kill file for net.physics, and inadvertently read this. I'll add it now. Keep your fingers crossed-- I don't know if it can hold another one. :-) -- Charles Cleveland Georgia Tech Surface Studies Georgia Tech School of Physics Atlanta, GA 30332 ...!{akgua,allegra,amd,hplabs,ihnp4,masscomp,ut-ngp}!gatech!gtss!chas ...!{rlgvax,sb1,uf-cgrl,unmvax,ut-sally}!gatech!gtss!chas
myers@bnl.UUCP (Eric Myers) (08/25/85)
> In article <625@wdl1.UUCP> jrm@wdl1.UUCP writes: > > By definition, the gravitational feild of a black hole is so > > intense that not even light or other wavicles with velocity c can escape. > > Yes. By the way, quantum mechanics is not relevant to black holes unless > they are very very tiny. Also, "wavicle" is not a real physics term. Say > "particle". Actually, quantum mechanics is very important to black holes of any size. Because of quantum mechanics black holes are actually not black, but should give off radiation. A rough description of the process is that vacuum fluctuations near the event horizon cause a particle-antiparticle pair to be created for a brief instant (the uncertainty principle) but one of the particles falls through the event horizon. The other particle becomes "real" and can escape from the black hole. This is how a black hole would evaporate. (The virtual particle falling through the event horizon would actually rob the black hole of mass, because energy has to be conserved on the whole.) As for "wavicles", I quite like the term. Wave/Particle duality means that waves are also particles, and particles are also waves. They are actually neither one or the other exclusively, so they are really something else, which could be called a "wavicle". I like that and will use it, and since I'm a physicist it's now a physics term. Eric Myers, Physics Department, Brookhaven National Laboratory, New York -- Eric Myers, Physics Dept., Brookhaven National Laboratory, Lon Guyland, NY myers@bnl.arpa / myers@bnl.bitnet / philabs!sbcs!bnl!myers