Well, from the excerpts you posted. Allowing for the possibility that I have bong-water for brains, it seems to me that one or another of the Cited Ones rather contradict each other, don’t your think? In the interests of avoiding bloating post syndrome, I wont quote.
As for the experiment, I guess I have to further assume for the stated masses A and B to be at relative rest AND accelerating towards each other is that they didn’t exist until that very instant. That would do it, I guess. Other than that, I must confess, I can’t. At rest,AND accelerating. Perhaps I’m too dim to digest the paradox, but there it is.
One of those quotes set me off, though:
If a mass propogates gravity waves, which behave in a similar fashion to light waves, i.e, thier relative speed
THEN
if Godawfulhuge Mass A is acclerating in my direction, might I get blue-shifted gravity waves? And vice-versa?
If we could in fact make two massess suddenly exist, if I follow you, then the amount of time that must pass before any mutual gravitational exists is directly tied to the speed of light, hence the speed of gravitational propagation.
In that case, would the waves meet at the mid-point between the two masses? Would their mutual gravity begin at that point, or does it take long enough for both waves to reach thier opposite number? And if gravity is waves, does it have wavelength? Interference phenomena?
No paradox. Throw a ball straight up. At its maximum height, the ball’s velocity is zero. Gravity is the only force acting upon it, so the acceleration is 9.8 m/s^2 down.
Yes, gravity waves behave like other waves: they can interfere, they’ll be Doppler shifted if the source is moving (not necessarily accelerating) relative to the receiver, etc. Note that not all gravity is gravity waves; if a mass is just sitting there, it’ll be gravitating, but not waving. Something (position, distribution, amount, etc.) about the mass has to change to produce waves. The wavelength is just the propagation speed (c, in this case) divided by the frequency with which the system is changing.
As to an object at rest, acceleration just means that it’s not going to stay at rest. If you’re stopped at a light, and step on the gas, then at the moment you step on it, you’re still at rest, but you’re accelerating, but at any later moment, you’re not at rest anymore.
No. They do indeed explain things somewhat differently, but I do not see any contradictions. They all agree that gravitational effects propagate at “c”.
Incidentally, I slightly resent your implication that I am employing an “Appeal to Authority” fallacy. I suspect that you do not understand the fallacy. I do not claim that those authorities are correct because they are authorities. Rather, their writings are a sample of current physical thinking that seem to me to be reasonably clear to the non-expert reader.
I hope this has already been adequately addressed by other posters. I suggest that you expend some though towards the difference between velocity and acceleration; if you don’t understand the difference, you’re going to have great difficulty holding your own in any discussion of physics.
Yes, but I think that the only effect would be interference between the waves.
It takes long enough for both waves to reach their opposite number. Gravitational waves travel at the speed of light in vacuum. No information may be transmitted faster than the speed of light in vacuum. If the mutual gravity began at the point where the waves meet, then information could be transmitted at twice the speed of light in vacuum.
Earlier on you showed that you are aware that the gravitational “force” between bodies is “really” (in general relativity) just bodies reacting to the local curvature of space-time. A gravitational wave is a change in the local curvature of space-time. A body cannot react to a change in the local curvature of space time until that change arrives at the locality of the body.
Of course I understand! It similir to Ad Homonym, like when an arguments sounds just like a reasonable one…but it ain’t. This thread on gravity speed has been dandy mental gymnastics, good for brain fiber! However, it has set one hook that still annoys me. A mass can be at rest and accelerating at the same instance? No way, Joseph. That sort of says that “going to move” is the same as “is moving”. No, no, (1.0 times ten to third)times no! Of course, I recognize that your arguments don’t necessarily depend on that being true.
Please e-mail a serving of crow when the first gravity wave is definitively detected. I can wait.
Apparently you made it to graduate school without taking (and learning something from) basic calculas and a basic physiscs course that included Newtonian mechanics.
It appears that teaching you about your error is too large a task to take on here; several other posters have pointed out your error and offered simple explanations and scenarios from everyday experience. II suggest that you ask an undrgraduate who has taken calculas and basic physics.
Pardon? I have never claimed that gravity waves do not exist. Detecting a gravity wave and measuring the speed of a gravity wae are two different propositions (though possible to do in the same appropriate experiment).
Not to take FF’s side, but wouldn’t any experiment which observes the speed of gravity necessarily be measuring gravity waves? A wave would be the propagation of some change in the local gravity field.
Well, measuring the speed of gravity waves would (probably) require detecting the durn things, but it would be possible to detect them without measuring the speed, so yes, they are two separate problems. And yes, any propagation of information using gravity could be considered a wave, although it wouldn’t necessarily be sinusoidal with a nice, well-defined wavelength, etc. It could be just a pulse.
On another note, although gravity waves have not been detected, evidence for their existance has been. Pulsars are spinning down, loosing both kinetic energy and angular momentum, and gravity waves are the only method proposed consistent with the observations. Further, there have been some observations of the effects of gravity waves on galactic dust distributions; some would even go so far as to call this a detection (so they’re using a whole galaxy as a detector. You have a problem with that? ) The fact that we’ve never detected them with man-made apparatus just means that we aren’t trying hard enough.
As indirect evidence, from the LIGO Home Page Fact Sheet:
"More specifically, LIGO has the possibility to:
Verify directly general relativity’s prediction that gravitational waves exist.
Test general relativity’s prediction that these waves propagate at the same speed as light, and that the graviton (the fundamental particle that accompanies these waves) has zero rest mass.
Test general relativity’s prediction that the forces the waves exert on matter are perpendicular to the waves’ direction of travel, and stretch matter along one perpendicular direction while squeezing it along the other; and also, thereby, test general relativity’s prediction that the graviton has twice the rate of spin as the photon.
Firmly verify that black holes exist, and test general relativity’s predictions for the violently pulsating space-time curvature accompanying the collision of two black holes. This will be the most stringent test ever of Einstein’s general relativity theory."
Note that they list existence and propagation speed as two items …
being a bit of a physics dunce, i am really pleased with what i have learned from the debate. ta all. i think i still believe that info cannot travel faster than c. ta einstein. the implications of this being otherwise seem too horrible to contemplate. i still struggle with how gravity/distortions in space time is transmitted. i am sure i ma not alone. this board is great though. ta again
) The fact that we’ve never detected them with man-made apparatus just means that we aren’t trying hard enough.