Slashdot Mirror

← Back to Stories (view on slashdot.org)

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."

7 of 91 comments (clear)

  1. Press Release by greenhide · · Score: 2, Informative

    The University of Missouri has also released a press release concerning the experiment.

    --
    Karma: Chevy Kavalierma.
  2. 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.

  3. 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

  4. Of course it is understood by Anonymous Coward · · Score: 1, Informative

    According to relativity, gravity propagates at the speed of light. Since the Earth is attracted to where the Sun *was* 499 sec ago, you'd expect wierd orbits that don't follow the experimental data. It so happens that the curvature of space-time caused by the Sun pushes the orbit in the other direction and compensates exactly up to the 4th order.

    In other words, speed-of-light gravity + curved space-time (Einstein) = instantaneous gravity + Euclidean space (Newton) + 4th order error.

    That 4th order term fixes the discrepency in Mercury's orbit, so Einstein's theory wins over Newton's because it explains Mercury's orbit. Speed-of-light gravity it is.

    1. Re:Of course it is understood by Anonymous Coward · · Score: 1, Informative

      Except that because of minor effects due to factors like the Sun being not perfectly spherical, electromagnetic interactions with the Sun's field, and such like, that 4th order error term should not match what Einstein predicts.

      Somebody cooked the books.

  5. 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.

  6. Results timeframe off by VisualStim · · Score: 3, Informative

    "... and results should be known within about two weeks."

    The articles says two months.