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Experiment This Weekend To Measure Speed Of Gravity

Posted by timothy on from the ch-ch-ch-changes dept.

An anonymous reader writes: "Is gravity an instantaneous phenomenon, as we were taught in high school, or is its speed, like all other Einsteinian phenomena, bounded by the speed of light? A radical new experiment, proposed by Sergei Kopeikin, and involving the Very Long Baseline Array, is set to occur this weekend, and results should be known within about two weeks."

8 of 91 comments (clear)

  1. If it's instantaneous... by crow · · Score: 5, Interesting

    If it's instantaneous, then that would provide a means of faster-than-light communication. Of course, it's probably impractical, as the amount of mass we would have to move to be detectable at a significant distance would be prohibitive. ...unless you had some way to implement gravity shielding, and turn it on and off like smoke signals.

    Fun to think about. Probably more practical for a science fiction story than reality.

    1. Re:If it's instantaneous... by melquiades · · Score: 3, Interesting

      the amount of mass we would have to move to be detectable at a significant distance would be prohibitive

      Well, perhaps a very finely-tuned vibration of a specific type could show up in a Fourier spread, even if the power were incredibly low. But even so.....

      Probably more practical for a science fiction story than reality.

      Undoubtedly! But fun to speculate.

    2. Re:If it's instantaneous... by crow · · Score: 4, Interesting

      My understanding was that you don't convert between mass and energy. Mass and energy are one. It all depends on how you observe it. If my understanding here is correct, then energy produces gravity, just like any other mass. However, because of the huge c^2 factor, it would take a huge amount of energy to test this; sounds like another good experiment.

      Or is my understanding whacked?

  2. Re:Bound by Speed of Light by Frank+Grimes · · Score: 2, Interesting
    high school physics is wrong and the gravitational force is bound by the speed of light just like all other force fields.
    Of course, high school physics is wrong. The mark of a good high school physics teacher is that he will tell you when he's making a gross approximation that ignores relativity, friction, air resistance, or quantum mechanics.

    Of course, these type of gross approximations continue well into college physics, where they are refered to as "back of the envelope calculations." And still, a good teacher will let you know what approximations he is making.

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  3. Does it have a speed? by brejc8 · · Score: 4, Interesting

    I was on the impression that gravity was instant.
    Imagine two balls spinning around eachother in space. each ball sees the other one a bit in the past. They will get faster and faster as they see eachother infront of themselves. Sortof surfing eachothers gravitational field.

    Or am I just wrong?

    --
    Mouse powered Chips, Open source Processors and Lego
  4. gravity doesn't exist, per se by medcalf · · Score: 4, Interesting

    OK, that's a bit strong of a statement. My physics prof uncle taught me at a very young age that all of science is a best approximation of how things work, and that we sometimes realize that we were way off in cause, even though our theories do a good job of describing effect. A case in point is Newtonian physics vs. Relativity. Newtonian physics works until you get to very large or very small measurements, and then it breaks down completely.

    As I understand it, Quantum theory describes the very small very well, and Relativity describes the very large very well, and each describes the middle (our normal perception) fairly well (particularly relativity). There has been a search to unify these into a single theory, but it keeps breaking down, and my understanding is that it's gravity that generally gets in the way.

    As a result, I've come to the conclusion that we are very wrong about gravity at a fundamental level, though our understanding is certainly good enough to get from place to place in space. The problem is, I don't know what to replace that underlying understanding with. My cosmology isn't complete there.

    It seems that either way that this experiment turns out, it is going to be one of those events which is looked back on as pivotal in our understanding of the world.

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    -- Two men say they're Jesus. One of them must be wrong. - Dire Straits
    1. Re:gravity doesn't exist, per se by nivedita · · Score: 2, Interesting

      It's true that general relativity raises some thorny issues to do with conservation of energy, but your example isn't actually one of them, since according to GTR, it is impossible for the sun to "suddenly disappear". This was one of the most beautiful things about GTR which distinguishes it from other field theories: the equations of motion follow from the equations of the gravitational field, rather than being tacked on later. In electromagnetism, on the other hand, there are equations describing the field, and then the equation qE+qv\cross B = m dv/dt that follows from Newton's laws and describes the motion of the charges. Thus it's possible to have a consistent EM field with stationary charges, raising questions of what holds the charges stationary, whereas it is not possible to have a consistent gravitational field with stationary masses.

  5. My bad. by Anonymous Coward · · Score: 1, Interesting

    Sorry.

    On a related note, I was just reading a page at the VLBA, and their data collection methods sound rather archaic:

    Astronomical data from the observations are recorded on digital tape at each antenna site. The tapes are then shipped to the Socorro Operations Center where they are correlated and the results sent to the scientists.