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Speed of Gravity Experiment Challenged

Posted by michael on from the dueling-banjos dept.

An anonymous reader writes "The previous hoopla over the discovery of the speed of gravity has an opponent from the Lawrence Berkeley National Laboratory. Read about the latest calculations."

8 of 63 comments (clear)

  1. Re:I, too by Kiriwas · · Score: 5, Informative

    That is not what they are trying to prove. The speed of gravity they are referring to is the speed of propigation of a change in gravity. If I am a giant mass which you are being influenced by gravitationally, and I move to a different location, does the force you feel change instantaneously? Or does it change after some set amount of time? Is that amount of time dependent on the distance you are from me? If so, then there is a speed of gravity that is not infinite. These scientists think that is is c, others do not. THAT is the controversy.

  2. Gravity by ArmorFiend · · Score: 4, Funny

    Gravity: we all know it sucks, we just don't know how fast.

  3. Repurcussions by geek42 · · Score: 4, Interesting

    What do you suppose the repurcussions would be if it could be shown that gravity was instantaneous, rather than propagating at the speed of light? Could we use that to transmit information instantaneously? Would that violate causality?

    1. Re:Repurcussions by shadowbearer · · Score: 3, Interesting

      It's been shown (reference, help! :-) that no matter how fast the propogation medium, information propogation is still limited to c. I believe the latest was in the quantum experiments with electrons which were simultaneously created yet still "knew" what the others' state was.

      God, it's late, and I'm tired, someone help me out on this one? I know I've read it over and over :-( just don't remember the specifics.

      SB

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  4. Re:Which one does general relativity predict? by harrkev · · Score: 5, Informative
    'Spose I were rooting for Einstein, then do I want an instantaneous gravity or one that takes time to propagate?


    You would want gravity that moves at the speed of light. This is what most reasonable scientists expect, and probably what they assume.

    All sorts of strange things can happen if it is instantaneous. According to Einstein, two people can disagree about what happens first if they are moving. A person at rest can see that event A happens at the same time as B. A person moving one direction will argue that A happens before B, while a person moving the opposite direction will argue that B happens before A. The strange thing is that everybody would be right!

    Let's assume that gravity can travel at faster-than-light speed, and can be used for communication. Now, a person who is moving can see A happening, and call the operator at "B" and tell them to stop event "B from happening. The person moving in the opposite direction can see B happening and tell the operator at "A" to stop event A from happening. Who is right? Clearly, they both cannot be right!

    It is possible that I am missing something here. Does anybody with more experience in this stuff have more insight?
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  5. Re:I, too by confused+one · · Score: 4, Interesting
    I hate feeding trolls, but sometimes I have to...

    the question could be more fundamental. Does gravity have a speed? Consider this: light is a particle (wave) traveling along a many dimensional space-time membrane. Now, we've defined (more or less) what a photon is; and, how it behaves. We expect it to travel no faster than c. The problem is, we don't really undertand the space-time thing.

    We have some theories as to how space is constructed. One of the things physics is trying to do is to create a theory that ties together space, time, gravity, energy, mass, quantum mechanics (basically everything). It's proving to be very difficult and gravity is the problem. Would a gravity wave have to obey all of the "laws of physics" as we know them? maybe not. Not if our theories are wrong. A lack of understanding wrt gravity might be why we need to make claims about "dark matter" and "dark energy" in order to explain the accelerating universe.

    You have to remember that our "laws" are based on observation. The rules (like no speed exceeds c) are based on mathematical models created to explain the observations. What if the models are close, but wrong?

    Just something to think about.

  6. Re:I, too by bobbozzo · · Score: 4, Funny
    One of the things physics is trying to do is to create a theory that ties together space, time, gravity, energy, mass, quantum mechanics (basically everything). It's proving to be very difficult and gravity is the problem.

    So what you're trying to say is that the speed of gravity is 42?

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  7. Re:I, too by Ceriel+Nosforit · · Score: 3, Interesting

    Switching off my sense of humor for a bit, what he's saying is that 'speed' as we know it won't be a factor in the final equation, but a result of it. Some theories (heard this at CERN in 2001) say that the graviton is a 4D particle/wave. Therefore it would also 'travel' in the time dimension and to call the graviton a tachyon might not even be a silly idea.

    Getting off the beaten path of time, velocity and momentum is /essential/ in coming up with the ToE (Theory of Everything). It'll require a new kind of thinking in the proportions the ToR was to Classic physics. The ToE will take the form of mutual dependency between variables where interaction is not a process, but a function.

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