Slashdot Mirror

← Back to Stories (view on slashdot.org)

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."

7 of 63 comments (clear)

  1. 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

      --
      It's old. The more humans I meet, the more I like my cats. At least they are honest.
    2. Re:Repurcussions by KDan · · Score: 2, Interesting

      I'm sorry, but your post shows remarkable lack of understanding for what relativity means when it says "nothing can move faster than light". The movement of anything faster than light is mathematically equivalent to it moving backwards in time. That holds true for information as well.

      Do not try to understand this by imagining a universe with an absolute time frame. That is the very understandable mistake that led you to the above post in the first place. The point of relativity is that there is no such frame of reference (it is one of the two postulates of special relativity, the other being that the speed of light is constant in all inertial frames of reference).

      I'll add that quantum entanglement has yet to produce any information transmission faster than light - and most likely it will be prevented, like one of the ancestor posts mentioned, by either some noise or some inherent randomness of the process so that you won't be able to transmit any actual information through the process (it will be a bit like having two dice that always produce the same completely random result. You might know what the person with the other die got, but that won't help you transmit information).

      Daniel

      --
      Carpe Diem
  2. 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.

  3. Re:I, too by Rares+Marian · · Score: 2, Interesting

    If there is a difference, the error was already recorded as a specific force constant. Obviously if a body is moving away the average force over a second is going to be less than if it sits still.

    So we already recorded the difference without taking the speed of gravity into account. Our values are good to an extent, they fail where our theory is wrong.

    --
    The message on the other side of this sig is false.
  4. 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.

    --
    All rites reversed 2010
  5. Re:Faster than light doesn't mean backwards in tim by Anonymous Coward · · Score: 1, Interesting

    Wouldn't basic calculus seem to indicate that there should be a speed between "delay, slower than instantaneous" and "time travel, faster than instantaneous"? If at some message speed X that may be greater than C, communication between two points can be not only instantaneous, but as you say can allow the sender to receive a response before they send, then shouldn't there be a speed between X and C where communication between two points is "merely" instantaneous? Clearly, this is not true of C, where there is a time delay.