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The Space-Buoy: Revisited

  1. Jun 16, 2004 #1
    in one of my previous threads i outlined an apparatus that i believe could be used to determine a fixed location in space.

    i'd like for some people knowledgable in SR and other great theories to take a look over it and see if it indeed does what its supposed to.

    the machine consists OF:

    1 heavy duty computing device
    4 photon receptors
    4 equal length long ass poles and 4 photon emitters connected to sychronized clocks
    some thrusters for movement.

    now the idea for this consists of detecting the difference in arrival times of the photons from different directions.

    if the photons from any source arrive SOONER than other sources, we can conclude we are moving towards that emitter. we merely perform some calculations, use our thrusters to slow us down, and take another measurement.

    when we finally receive the light from all sources at the same time we will be at complete universal rest, and objects functioning in this relativistic inertial frame will bear true space/time
     
  2. jcsd
  3. Jun 16, 2004 #2

    ram1024 i see a basic flaw: You are going to need more than a few buoys, and there aren't enough SR thoerists (I never thought I would ever say those words) to perfrom all the required analysis. I hope you aren't restricting the project to just one generation, are you?
     
  4. Jun 16, 2004 #3

    LURCH

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    This statement...
    ...appears to have no meaning. We are currently receiving light from all sources at the same time, are we not? The same would hold true no matter where the buoy was located, or what direction it was "moving".
     
  5. Jun 16, 2004 #4

    Alkatran

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    It doesn't matter what your speed is, to you the light will seem to arrive at the same time. (Think of the center emitting the light instead of receiving it, and it makes a bit more sense why it won't work)

    Personnaly, I want to know how kinetic energy is measured. Since it adds mass, wouldn't you be at absolute rest when your mass was minimal? Or is kinetic energy somehow relative as well?
     
  6. Jun 16, 2004 #5
    I agree. It seems as though the concept, in general, is correct, but the choice of using photons for it is not.
    Positional stability or reference would be best considered through the mechanisms which determine it... mass, kinetic energy, etc.
    Instead of photon emitters/detectors, perhaps a more suitable choice would be electron emitters/detectors.
     
  7. Jun 16, 2004 #6

    Alkatran

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    *Starts thinking*

    Alright, if you're moving, you have more kinetic energy. This obviously leads to the finding of absolute zero unless kinetic energy is somehow relative. In fact, if kinetic energy is relative, then a persons mass is relative, their energy is relative.. heat is relative... ugh Do things get colder/hotter the faster you go? :rofl:
     
  8. Jun 16, 2004 #7
    according to current SR postulates...

    [observer](o)------------------------<-)[photon emitter]

    any motion of the observer in the direction of the emitter will cause the photon to be intercepted sooner. you see yourself at rest compared to the rest of the included components of the machine, therefore you would conclude the photons were not emitted simultaneously (gathered this from the other einstein train paradox thread)

    but we KNOW the photons were all emitted simultaneously (synchronized clocks, all moving in the same inertial frame), therefore that cannot be the problem.

    so the only other resolution is, we're moving towards the photon that arrives first. once we perform enough test/adjustments to reach equilibrium, we will establish the universal rest frame
     
  9. Jun 16, 2004 #8

    Alkatran

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    You can't "know" the photons were sent out simultaneously. The reason being that if you are at rest, your simultanity is different than if you are moving. (Think about this, how are you signalling all the emitters at once?)

    I don't know how to explain this because I haven't before... but consider this:

    Let's say the speed of light is 2 m/s. Let's say you're moving at 1m/s. We are observing your movement (you are going 1m/s faster than us) but we are in the same inertial frame (Impossible I know, but for simplicity's sake..). Oh, and the light emitters are 2m away (there are two of them, one on each side).

    You are at position 0, emitters at -2 and 2. They emit.
    One second later: You have travelled one meter. The light on your left has travelled at (2 + 1)m/s=3m/s and the light on your right has travelled at (-2+1)m/s = -1m/s. The light on your left has moved 3 m to position 1, the one on your right has moved 1 m to position 1, and you are position 1. Simultaneous reception.
     
  10. Jun 16, 2004 #9
    i do not signal the emitters, they do their own thing based upon clocks that are calibrated to be running the same as each other. they are all attached to the same apparatus and so any inertial forces felt by one is felt by all, thus they can remain synchronized.

    i think you mixed your emitters up in your example btw :D
     
  11. Jun 16, 2004 #10

    Alkatran

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    Alright, here's a picture so you can understand what I mean.

    [​IMG]

    The red dot is the receptor, the green dot is a photon moving right, and the blue dot is a photon moving left. The speed of light is set to 2 for simplicity.

    *edit* I'd like to point out that the photon at 2 has a speed of -2 (relative to stationary observer) and the one at -2 has a speed of 2. This is probably what made you think I mixed them up.
     
    Last edited: Jun 16, 2004
  12. Jun 17, 2004 #11

    russ_watters

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    I thought the poles were fixed length and not moving with respect to the emitter?

    You are measuring the speed of light in 4 different directions at once, expecting to find a difference. With thrusters, you change your velocity until they equal out, correct?

    This sounds like a 4-way version of the Michelson-Morley eperiment.

    Problem: the MM experiment showed no such variation in the speed of light.
     
  13. Jun 17, 2004 #12
    exactly, there is no relative motion towards the emitters because of the fixed poles. but any true motion will STILL create an interception of photons sooner than expected UNLESS the speed of light is not constant...
     
  14. Jun 17, 2004 #13
    I think Alkatran hit on the real problem with this. He's right when he says that you can't know that the emmiters sent the photons at the same time - not even if they're based on synchronised clocks. The trouble is that the flow of time is variable in SR. Which means the clocks can become unsynchronised.

    They tested this with one of the space programs a while back: Take 2 synchronized high precision (nuclear decay I think) clocks, send one off on a high speed scoot around the earth, bring it back to the starting point, and hey-presto, they're no longer in sync!

    So if you imagine your apparatus sitting in the lab on earth, emmiters winking away in sync, then you take one emmiter with its clock attached and whirl it around your head for a bit (OK, longer than a bit...).... Then reattach the emmiter-clock combo to the apparatus, and the next (and all subsequent) strikes will be out of sync with the emitters you didn't touch.

    That would imply that the entire system (comprising you, all emmiters and all the poles) changed your velocity in some way. Which you didn't. Did you?...
     
  15. Jun 17, 2004 #14
    the clocks are all attached to the same apparatus, so any inertial changes are felt by all of them equally.

    they're not going to become unsynchronized
     
  16. Jun 17, 2004 #15
    Ah.. So there's strictly no spinning or rotating alowed then?
    But what if the absolute reference frame does rotate around a point?

    If there's an absolute inertial frame, then couldn't there be an absolute centre of the universe, around which it would be free to rotate? (Actually, I don't really see why it would have to be spinning around the centre - it could be off-set...)
     
  17. Jun 17, 2004 #16
    well probably there would be, if at any given moment you could calculate the location of EVERYTHING in the universe and take the average. But the "center" would be dynamic, changing as the universe changes, so it wouldn't reveal very much :D
     
  18. Jun 17, 2004 #17
    I'm not sure that the location of items in the universe has much impact on where the centre is. And I'm pretty sure that averaging them wouldn't help - what about empty space? Isn't the current thinking that since no matter where you stand, the edge of the universe is moving away from you at c, then every point is the centre?

    In any case, my point is that you might HAVE to include rotation possibilities if you want to find a universal reference frame. In which case, the only place were all emmiter would sync is at the centre of rotation, isn't it?
     
  19. Jun 17, 2004 #18

    Alkatran

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    Rotation can be felt through the outward force it creates. So rotation can be stopped.

    Why hasn't anyone mentioned the fact that no matter what your speed is, if the clocks emit photons at the same time (for you, and they will if they have gone through all the same changes) they will arrive at the same time?
     
  20. Jun 17, 2004 #19

    LURCH

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    Oh man! I just figured out what are apparatus would look like and how it works. Light from each of the emitters will reach the detector in the center at the same time, no matter what speed or direction he apparatus is traveling. When I say "at the same time", I mean the same time from the detector's frame of reference. To an outside observer, the entire apparatus may appear to be moving in any direction or at any speed, and based on these properties, light from different emitters would appear to reach the center at different times from that outside observer's point of view, but no matter what happens to light pulses will always be simultaneous from the detector's point of view.

    So, rather than finding a state that is "absolutely stationary", this device would produce measurements which will prove that it is stationary relative to itself.
     
  21. Jun 17, 2004 #20

    russ_watters

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    Nope. This really is covered by time/space dilation. Its the MM experiment in 4 directions instead of 2.
    Isn't that what the MM experiment proved too?
     
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