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Newton Vs Einstein.

  1. Apr 9, 2013 #1
    in the special theory of relativity. nothing can move faster than photon
    but in netwon, if mass changed
    it effect right away though how far the two mass
    how can i understand??
     
  2. jcsd
  3. Apr 9, 2013 #2

    mfb

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    No matter can move quicker than the universal speed limit. Photons in vacuum travel at this universal speed limit.
    ???
     
  4. Apr 9, 2013 #3

    phinds

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    mfb answered the first part and I think for the second part you are referring to the fact that in Newtonian mechanics, gravity acted instantaneously over any distance. Newtonian mechanics is WRONG and has been replaced by General Relativity. Gravity does NOT act instantaneously, it acts at the universal speed limit, which light also travels at.
     
  5. Apr 9, 2013 #4
    there has graviton but in newton it can go faster than c. i'm curious about this how can graviton go faster than c
     
  6. Apr 9, 2013 #5

    Doc Al

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    The graviton is part of quantum field theory, not Newtonian gravity.
     
  7. Apr 9, 2013 #6

    phinds

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    Which part of post #3 did you not understand?
     
  8. Apr 9, 2013 #7

    Vanadium 50

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    I just got a PM from huhjinsoo saying that he doesn't understand these messages because of his English. I am not entirely sure how to address this, other than to recommend people try and write as clearly and straightforwardly as possible.
     
  9. Apr 9, 2013 #8

    Drakkith

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    Newton is wrong. Special Relativity is right. Nothing can move faster than a photon.
    If mass changes, it is not felt instantly.
     
  10. Apr 9, 2013 #9

    phinds

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    Newton THOUGHT that gravity was immediate. He was wrong. Gravity travels at the speed of light. Gravitons do NOT travel faster than c, they travel AT c.
     
  11. Apr 10, 2013 #10

    sophiecentaur

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    That could be construed in the wrong way. Newton is right (enough) to deal with a sub-set of problems, SR is right (enough) to deal with a larger sub-set. It really isn't a matter of "Newton vs Einstein". Einstein was all too happy to use Newton when applicable and Science attempts to do without 'competition' where possible (despite the fact that everyone's human and naturally the egos can take over).
     
  12. Apr 10, 2013 #11

    phinds

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    No argument with what you are saying but I think you are expressing subtleties that will be totally lost on the OP, possibly even just confusing to him, and are somewhat irrelevant to his questions anyway.
     
  13. Apr 10, 2013 #12

    sophiecentaur

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    I just want people to avoid getting the notion that early, good Science was 'Wrong' and that the latest accepted Science is necessarily 'Right'. It's a journey and not an absolute business. Newton is fine for most of our life's 'mechanical' experiences.
     
  14. Apr 12, 2013 #13
    Why do you want to avoid that? The fact that science has been wrong before and then replaced old ideas with new and improved ideas in the light of new evidence, is a tribute to the inherent self-correcting nature of science. Being rational isn't, and never was, about being 'right'—it's about drawing a conclusion (or not) from the available evidence (whatever that may be).
     
  15. Apr 12, 2013 #14

    sophiecentaur

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    What are you arguing about? The term 'wrong' is far too loaded to be applied to Newtonian (and a load of other ancient) Physics. Our modern Physics is just as likely to be proved 'wrong' in the future. The conclusions of Newtonian Physics are just as right as they ever were, within the limits of their valid application.
    Right and wrong are naive terms in the context of much of Science and turn the business into a Ya Boo Sucks conversation. Kids / students like nothing better than to think their Scientific 'Parents' are quarreling together and to try to play off one against the other. That sort of attitude is just fruitless and doesn't help them at all. What would be the point of research if it is virtually guaranteed to be proved 'Wrong' in a few years' time? (And is most likely will be - if that's the way you want to look at it)
     
  16. Apr 13, 2013 #15
    To word it different, don't call Newton mechanics wrong; it's offensive.

    It's is more right (accurate) than we can perceive without using very accurate measurements.

    Newton was not as precise as Einstein. Fancy that given the tools available to Newton.
     
  17. Apr 13, 2013 #16
    This brings up something I've wondered about- while we may say the gravity "travels" at the speed of light, what practical significance does this have?

    All the matter that produces gravity alreadt exists. Thus all the gravitaional forces in the Univers are already in place.

    What is the change in gravity that has to "Travel" to effect the rest of the mass in the Universe?
     
  18. Apr 13, 2013 #17

    sophiecentaur

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    The masses out there may all be constant but they are continually changing their positions so their effect on us (and everything else) will be subject to the same sort of delay as the light takes to get there. Orbits and their observed times will all be subject to the delay. Mars would be able to detect the effect of the Moon orbiting the Earth (with the appropriate equipment) and the 28 day variation would be in sync with the Moon's observed orbit.
    But. if that doesn't appeal to you too much, here's a contrived but more dramatic example. The gravitational potential of a dumbell shaped mass can be made to change by bringing the two halves together or moving them apart. If you were orbiting round a massive dumbell shaped star and observed the two pieces moving together or apart, you would observe your orbit changing at the same time as you see them move because the delay would be the same for the light and the g field.
     
  19. Apr 13, 2013 #18

    jedishrfu

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    I never heard that example before, that's pretty cool, Sophiecentaur thanks.
     
  20. Apr 13, 2013 #19

    sophiecentaur

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    That story was presented to me by Herman Bondi, in 1965, when he visited our Uni to talk about Cosmology. His Steady State theory has since been discredited but he was a great lecturer and that story really took my fancy.
     
  21. Apr 13, 2013 #20
    Thanks, that's WAY cool!
     
  22. Apr 13, 2013 #21

    sophiecentaur

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    That's HISTORY sunshine. It's just gobsmacking when I realise just how things in Science have changed since I was young. CMBR, Plate tektonics, DNA structure, Transistors, .,.,., it just goes on. That's one of the few consolations about being a sad old geyser!
     
  23. Apr 13, 2013 #22

    WannabeNewton

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    You are thinking in Newtonian terms of instantaneous action at a distance. Changes in the gravitational field in some neighborhood of space-time won't immediately have effect on some other neighborhood of space-time that the field extends over, the changes take time to propagate across the field.

    Much like in the dipole approximation of electromagnetism, dominant gravitational radiation in the linearized approximation to GR is generated by changing quadrupole moments of massive systems.
     
  24. Apr 14, 2013 #23

    phinds

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    So you support Newton's contention that the action of gravity is instantaneous? You don't think that's wrong?
     
  25. Apr 14, 2013 #24

    sophiecentaur

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    If you are restricted to measuring events on the Earth, I defy to to prove it's wrong - even today.
    But this is just silly Schoolboy stuff. A mature view is based on a culture of improvement and not just saying things are 'wrong' or 'temporarily right'.
    What point are you actually trying to make?
     
  26. Apr 14, 2013 #25

    pervect

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    One thing to be careful of is that the quantum mechanical idea of a force carrying particle.

    Specifically, electromagnetic attraction between unlike charges is not done by the exchange of real particles (photons). It can be understood by the exchange of virtual particles (photons), but some effort is needed to do this correctly.

    Similarly, in a quantum theory of gravity, "gravitational force" would be due to the exchange of virtual gravitons, not real ones.

    Trying to measure the "speed" of a virtual particle is an exercise in confusion. I suspect this confusion is what's motivating the OP, though.
     
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