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Universal gravity

  1. Aug 5, 2015 #1

    Gaz

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    Well we have been talking about the size of the universe and em waves all day and it's lead me to ask this.

    EM waves can no longer effect us from passed the CEH line right . And if gravity also travels at the speed of light a does this mean that once these galaxies are gone passed the CEH they no longer have any gravitational effect on Earth?
     
    Last edited: Aug 5, 2015
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  3. Aug 5, 2015 #2

    marcus

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    Galaxies beyond CEH are ones we cannot send a signal to today, and have it eventually reach them. But signals we sent out in the past might still reach them.

    Likewise signals THEY already sent out in the past might eventually reach us and affect us.

    That goes both for EM and for gravity.

    BTW you know that two neutron stars in tight orbit around each other are sending out ripples in the geometry (according to GR).
    So when you think of sending a signal it could be pushing some electrons up and down along an antenna, or it could be waving a neutron star around and sending ripples in the geometry.

    There is no "action at a distance". What we have done in the past affected the geometry around us, and that effect propagates outward and continues to do so.

    So our gravity would continue to be FELT by a galaxy that is now outside CEH range. But it would not be the geometric effect of what we do today. It would be the geometric effect of our mass and motion as it was in the past---that has propagated out and eventually reached them.
     
  4. Aug 5, 2015 #3

    marcus

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    It is interesting that we never stop seeing galaxies that have passed out of CEH range, their images just pile up at the horizon and slowly redshift into undetectability.

    We never actually see them pass thru the horizon. We see them in slow motion as they were right before---with time slowing down more and more.

    It is like how we see stuff that has fallen thru the event horizon of a BH. We don't see the stuff pass thru and suddenly wink out. It has passed thru but we see it as it was just about to pass thru, but with its time slowed down more and more. piling up like dead leaves on the horizon and redshifting into undetectability
     
  5. Aug 5, 2015 #4

    Gaz

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    That is pretty cool(the neutron star). And I see what you mean thanks =)
     
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