gwyn@brl-vgr.ARPA (Doug Gwyn ) (04/26/84)
To the extent that gravitation is correctly described by the general theory of relativity, gravitational effects cannot be "instantaneous". General relativity does not contradict the special theory, it extends it. Causality arguments are the same (speed-of-light limit on propagating influence).
jbf@ccieng5.UUCP (Jens Bernhard Fiederer) (04/27/84)
I didn't even know photons had a gravitational field. I thought they were affected by the sun's gravity simply because they follow the curvature of space, which is affected by gravity. Jens -- "Some people are eccentric, but I am just plain odd" Reachable as ....allegra![rayssd,rlgvax]!ccieng5!jbf
palmer@uw-june.UUCP (04/27/84)
fnord
The experiment described by Charles Poirier (two very-high-energy
lasers fire photons of gravitationally significant mass so that they
pass near to each other and are deflected) is very interesting, and
rather hard to solve.
In the first place, the gravitational field due to the photon guns
will change when their mass-energy is put into the photon.
A second, more major complication, is the effect of
gravitomagnetics. Just as a moving charged particle produces a
magnetic field, a moving, massive particle produces a gravito-magnetic
field. (Electric and magnetic fields are each the other as seen in a
different frame of reference. Ditto for gravity and gravito-magnetism.)
In the case of electromagnetics, for charged particles moving at a few
percent of the speed of light, the effect of magnetic fields is to make
the force on particle B (stationary in its frame of reference) due to
particle A (moving in B's frame) the same as if particle A were
stationary at the point it WOULD be if it continued on its straight-
line path while the electromagnetic signal was travelling from A to B.
I do not know whether this result holds for the gravity of an
object moving at lightspeed, but the qualitative effect is the same.
An additional wierdness may be due to the fact that the photon is
in its own gravitational well. This may mean that it travels slower
than the speed of (low-energy) light due to time dilation. Are there
any general relativists on the net who know anything at all about that
about which I know next to nothing? (whew, all that to avoid havingf a
preposition at the end :-))
David Palmerels@pur-phy.UUCP (Eric Strobel) (05/08/84)
Such an experiment has been done!! I don't recall the reference, but an experiment was done in which two laser beams were passed close by one another and a deflection in accordance with General Relativity was measured. Anyone out there know more specific info?? ------------------------------------------------------------------------ | "Things always look | A message from the mental maze that darkest just before | calls itself: they go totally black!!" | | -- Col. Hannibal Smith | ERIC STROBEL | --------------------------------| UUCP: {decvax,ucbvax,harpo,allegra,inuxc,seismo,teklabs}!pur-ee!Physics:els INTERNET: els @ pur-phy.UUCP