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Gravity waves and gravitational radiation

  1. Nov 26, 2015 #1
    My understanding of electromagnetic radiation is this:

    When a charged particle accelerates, there is a change in its associated electric field at all points in space, though not instantaneously. The "electric field wave" is basically the propagation of the disturbance that occurs when the electric field at a given point in space "updates" due to the acceleration of the particle. And of course, this electric field wave is accompanied by a perpendicularly propagating magnetic field wave, and together they travel at speed of light c.

    So analogously, any particle that has a non-zero mass must have a gravitational field, and whenever that particle accelerates, there should be a similar gravitational disturbance that radiates (I'm assuming also at the speed of light), right? In other words, is the existence of a gravitational "wave" not undeniable based on these considerations?

    Therefore I'm wondering what the current debate regarding the "existence" of gravity waves and gravitational radiation is about. They must exist, no? Is it just a question of whether the waves are too weak to be of any significance experimentally?
     
  2. jcsd
  3. Nov 26, 2015 #2

    phyzguy

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    Yes, correct.

    Yes, agreed.

    Assuming General Relativity is correct, it is clear that gravitational waves must exist. The Hulse-Taylor binary work, for which they received the Nobel prize, is also indirect evidence that they do exist. However, until they are directly detected, there will always be some doubt. Maybe GR isn't correct. We should continue work to detect them as a further test of GR. This is how science works. Also,if we do detect them, they will be a further window into the universe, because in principle we can detect gravitational waves from places (like the inner most parts of core collapse supernovae) from which EM waves cannot escape. But, to answer your original question, I think any physicist who has studied GR is quite confident that gravitational waves exist.
     
  4. Nov 27, 2015 #3
    Thank you for the insightful answer. Yes, I realize I have been taking the existence of a gravitational field for granted, without really thinking about the underlying mechanism - i.e. GR and the curvature of space-time according to latest theory. I had thought my simple argument involving the analogy to EM radiation must validate the idea of gravitational radiation, because a field has to change in response to a mass's acceleration; but in fact, the "field" itself is a mathematical construct to explain action at a distance, not a proven fact (at least in the case of gravity, since it has not been observed directly).

    I briefly looked up Hulse-Taylor binary, and was interested to read about the indirect evidence of gravitational radiation. I'm excited for the day when physicists do directly observe gravitational waves. In the meantime, I'll entertain myself by imagining very weak gravitational radiation being emitted from my car whenever I step on the accelerator. : )
     
  5. Nov 27, 2015 #4
    I'm no physicist, but I have a theory of my own: The EM wave does radiate as indicated (at c in a vacuum). Gravity, on the other hand, may not radiate as the mass particle moves, but exists everywhere, however slight. As such, only its magnitude adjusts with position. I'm told Cassini proves that gravity radiates at speed within 1% of c but don't know how this was done. Any clarification would be most welcome as it would appear to prove me dead wrong.
     
  6. Nov 27, 2015 #5

    phyzguy

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    Please read the forum rules at this link. Personal theories are not allowed. The intent of the forum is discussion of mainstream science.
     
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