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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 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. 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
  3. Speed of anti-gravity by GuyMannDude · · Score: 5, Funny

    I'm not sure about the speed of gravity (the force reponsible for attraction between two bodies) but I've noticed that the speed of anti-gravity (the force responsible for repulsion between two bodies) is roughly the speed of light. Everytime I see some hot babe in a bar and start walking towards her, she turns and runs away in the opposite direction when she sees me coming.

    If independent verifcation of this experimental result is needed, I can get my buddies (who always guffaw when this happens) to pledge that these results are repeatble!

    GMD

    --
    watch this
  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.

    --
    -- Two men say they're Jesus. One of them must be wrong. - Dire Straits
    1. Re:gravity doesn't exist, per se by Theaetetus · · Score: 5, Informative
      Superstring or Membrane-theory attempt to join Newtonian and Quantum physics together, and so far seems to be doing so, at least to our admittedly weak understanding (we are just now creating the math to solve the equations).

      In Superstring theory, gravity is not a force, but more is due to a fundamental warping of the multi-dimensional space our universe exists in due to concentrations of matter/energy (yes, according to string theory, and as an outgrowth of relativity, concentrations of energy also create gravity). Thus, if the warping is instantaneous, so would the apparent effect of gravity... but if the warp takes time to propagate, then 'gravity' would travel at a slower speed.

      Interesting result of this, though, is that if gravity is instantaneous, we get an easy FTL communication method... But if gravity isn't instantaneous, then there are all sorts of conservation of energy questions (for example: take the sun away... if gravity is not instantaneous, then the Earth continues to orbit empty space for another 8 minutes... where does that energy come from?)

      Check out The Universe In A Nutshell by Hawking. There's also a _really_ in depth book called Supersymmetry, but I forget the author.

      -T

  5. A copy of the actual paper by MarkusH · · Score: 5, Informative

    This is Mr. Kopeikin's actual paper in PDF format. You can go to this site for other formats.

    Warning: The paper contains some very seriously heavy math. It uses things like the Euler Gamma function, Lorentz factors and stuff like that. You have been warned.

  6. USENET sci.physic FAQ by g4dget · · Score: 5, Informative

    The USENET sci.physics FAQ has a pretty readable explanation of some of the speculation surrounding the speed of gravity.