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Speed of force > speed of light.

  1. Jan 17, 2009 #1
    A very fine almost massless thread about 30 seconds at the speed of light long that can't stretch and can't break is strung out taut in a vacuum in space. It has a loop on one end. Suddenly Voyager 1 's as it passes by catches on the loop with it's antenna and gives it a tug. No part of the string travels faster than the speed of light but... the other end moves instantly.
    I know the thread is fictitious and can't exist but if something like that existed could it happen? Kind of a long Newton's cradle.
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  3. Jan 17, 2009 #2


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    No. Information cannot propagate faster than the speed of light. This includes waves.
  4. Jan 17, 2009 #3


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    It does not move instantly, a signal will propagate at the speed of sound in the thread.
  5. Jan 17, 2009 #4
    What made me think of this was the famous question how fast does the force of gravity propagate if a mass could suddenly appear in space.
  6. Jan 18, 2009 #5
    I suspect instantaneous would be faster than the speed of light.

    According to a news story appearing in the New York Times many years ago the Russians, using an atomic clock at the South Pole were timing the delay between a nuclear detonation in the far north and the south pole and found no lapse of time, as the detonation was instantaneously recorded the instant it occurred.
  7. Jan 18, 2009 #6
    A gravitational wave would propagate at the speed of light.

    I think you mean simultaneous detonations, not instantaneous. According to SR, two events occurring simultaneously in one frame of reference may be seen from another f.o.r. as occurring non-simultaneously. No information/energy can be transmitted/propagated faster than the speed of light, the speed at which particles/waves with zero rest mass move (EM waves/photons, gravitational waves/gravitons).
  8. Jan 18, 2009 #7
    That was the whole point which made it a news story.

    I don't know if you are aware of this but many years ago GE was doing research and development on instantaneous transformation, but how far they got I don't know as that sort of thing is usually classified.

    If you are right about the speed of light we have a bit of a problem with space exploration I would think.

    In fact relativity and light speed are a whole subject, which would make for some very interesting discussion.

    We don't know if light speed is consistent or constant across space as it could be that as space is stretched by expansion light speed decreases with distance.

    This would mean there is no possible way to get there by any means known today.

    You must keep in mind that our perception of light speed is no different than our linear perception of a fast train, which in my mind does seem a bit strange.
  9. Jan 18, 2009 #8
    I apologize for making a mess of this.....let me try again.

    There was only one detonation and it occurred in the north, but the recording station was in Antarctica. They wanted to determine how long it would take for the equipment to detect the detonation in the north. And using atomic clocks that were synchronized they discovered that the delay was zero. The response was instantaneous, which is why it made the news. This supports some of the work by Townsend Brown, as it was his contention that the universe was simultaneous, which means we cannot see the past simply by looking up at the sky. We see the universe in terms of real time events remaining relative to our planet earth.
  10. Jan 18, 2009 #9
    I'm not sure that gravity propagates, as this has not been demonstrated or proven to be a fact.

    If you think about it, it would be a bit inconvenient if it did. Where would that leave us?

    And if it does propagate, where does it propagate from?

    I realize there are hopes of finding gravitons and or gravity waves, but I have never heard of nature changing to accommodate one's hopes.
  11. Jan 18, 2009 #10


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    There is a little too much speculation going on here when you are challenging GR.

    The speed of light in a vacuum is constant. This has been verified time and time again.

    According to GR, gravity propagates at the speed of light. The effect is something akin to ripples resulting in the change in gravity which propagate through the spacetime medium at the speed of light.

    As far as your experiment conducted by the Russians is confirmed, the entire thing stinks of bad data, a hoax, or something in between.
  12. Jan 18, 2009 #11
    You said that gravity propagates at light speed, did you not say that?

    How can gravity itself propagate at light speed?

    Or how can gravity propagate at any speed? Where pray tell is the evidence to support this?

    Gravity results from a space time curve, its an effect of the space/time curve so its not a force unto itself, so what would cause gravity to propagate?

    Is this a physics forum or the small world view of science?

    Speculation? Who is speculating? "The speed of light is constant in a vacuum", which should read...the speed of light is considered to be constant in a vacuum at the present time.

    But there has been much justifiable debate on the subject for many years, due to the fact that those doing the evaluating kept coming up with different answers over many years.

    It seems almost like a game of hide the pea, because we can come up with a static value simply by applying static terms, but if we apply dynamic terms we are going to come up with a dynamic answer, which is going to be different each and every time we perform the exercise.

    Also, is the universe not dynamic? What aspect of universe would remain static in a dynamic state? Only those things we deem to be constant? That is neither logical or rational.

    If the idea is to explore and think then we must consider all the possibilities, but if the idea is to control the available information we must forego thinking and refuse to consider any possibilities other than those given official certification.

    I hope everyone including students are given the opportunity to think for themselves.
  13. Jan 18, 2009 #12

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    Then you should supply evidence. For example, when was this test? How was the blast detected? Surely not radiation - the earth was in the way. Seismically? Then you are arguing that the speed of sound is faster than the speed of light, something trivially falsified during thunderstorms.
  14. Jan 18, 2009 #13


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    Wiki covers this. Predicting and measuring the orbits of planets. Do they orbit based on current position, meaning gravity is instant, or based on previous position at the time it would take light to trave between a planet and sun (speed of gravity based on c)? What I get from this article is that it's too close to be able to measure if gravity travels exactly at c.

  15. Jan 18, 2009 #14

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    Jeff, I'm not 100% happy with the Wikipedia article.

    One reason is that they don't explain why this is hard. The problem is simple - measuring the speed of gravity is the same as measuring how quickly the gravitational force changes at a large distance when the mass configuration is rearranged. Every large mass we have access to is moving slowly with respect to gravity, so these changes happen on a long time scale relative to what we want to measure.

    There are no direct measurements of the speed of gravity. There are two pieces of evidence that it travels close to c. One is the energy loss from binary pulsars, which is related to the speed of gravity, and matches the prediction for cg = c. The other is the Shapiro effect in occultations by Jupiter. The best paper on this is by Carlip, where he points out that both c and cg are intertwined in non-trivial ways, but that this measurement does strongly constrain non-GR theories of gravity (the only kind where c and cg can differ).
  16. Jan 18, 2009 #15
    David Barclay, or anyone else, could you explain/make corrections to these statements if they are wrong or misleading. I apologize for making false assumptions, as I have very little knowledge in these fields (GR/SR). I also believe that I misinterpreted the experiment you described. Thank you.
  17. Jan 18, 2009 #16


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    This is not even close to correct. The speed of seismic waves is between 3 km/s for S waves and 8 km/s for P waves. That is nowhere near the speed of light, let alone instantaneous. Ignoring the violations of SR, if it were instantaneous then seismic monitoring stations would not be able to locate the epicenter.

    Not that I expect you to be interested in evidence (either examining contradictory evidence or providing supporting evidence). You strike me as a fairly typical crackpot.
  18. Jan 18, 2009 #17


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    .. and with that, this thread is done. If the OP is still unclear about this, he/she can look up all the supporting evidence that has been given.

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