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Gravity bounce?

  1. Oct 28, 2003 #1


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    i have looked on the net but i can not find a site that
    explains the MECHANICS of gravity wave production, as i understand
    it is an oscilation in space time, if gravity is warped
    space time how can the destruction of a massive body make it
    oscilate, it implies some sort of bounce, but how can
    space time bounce, or is the above total wrong?
  2. jcsd
  3. Oct 28, 2003 #2

    I think that you have understood the concept the Gravitational Waves in a way that u shouldn't have. Imagine water ina bucket. This represents Space-Time without Mass in it. Now when you throw a stone, there are ripples produced or when a boat moves through water, there are ripple produced. Now it is said by GR that mass / energy curves the space-time fabric. So the presence of a mass-energy sorce curves space-time. Whenever there a cosmic event that involves really high levels of energy, then, there are ripples produced in the fabric. These ripples travel through the vastness of space and are called gravitational waves.

  4. Oct 28, 2003 #3


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    thankyou sridhar-n

    i understand your analogy, the part im not sure of is
    what is actualy oscilating .
  5. Oct 28, 2003 #4


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    astute question as yours so often are

    would you accept that two neutron stars circling each other could produce a rippling? I think so. Something going around and around is similar to something bouncing up and down---periodic motion.

    an electric charge going around and around produces a radio wave---the gravity wave equations are not too different from the "bending" in the electric&magnetic fields that propagates as wave

    but suppose the two neutron stars dont circle each other at all but just approach each other along a straight line and simply smash into each other?----kerblam, it's over.

    that is like a one-time spark jumping a gap----no bounce, at least no obvious bounce in any simple sense: you charge two things and bring them close, and a spark jumps, and that's it, over.

    but even the jumping of a spark sends out a radio wavelet, a brief click pulse. any time a charge of electricity ACCELERATES it sheds energy even if only in the form of a brief pulse, you can even pick up the crackles as static on the radio sometimes

    and maybe wolram if you looked very closely at the neutron stars colliding you would actually see a bounce---the momentum of the collision causing a brief over-compression, which produces a rebound and so on----like the vibrations resulting from a traincrash

    Maybe the essential thing is believing in the reality of the gravitational field (pictured as a bunch of arrows in space or as a curvature or however)---the gravitational field associated with two stars-----with two centers of attraction----is a different shape from the field associated with one star only. So when two things crash the field must CHANGE SHAPE. Field equations, whether EM or grav, are such that any time a field changes shape it causes a ripple effect as the information spreads out into the world, the information that at some locale the field has changed---that is all waves are:

    waves dont have to be periodic, they can be one-timers, but what they are above all is the information spreading out that the field has undergone some change in some locale

    just an oversimplification but may help answer yr question
    Last edited: Oct 28, 2003
  6. Oct 29, 2003 #5


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    waves dont have to be periodic, they can be one-timers, but what they are above all is the information spreading out that the field has undergone some change in some locale
    yes now i am convinced, a major event can not occure without
    some sort of reaction in the medium it exists in.
    many thanks.
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