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Doppler Effect Question

  1. May 6, 2007 #1
    So the Red shift of extragalactic bodies means that they are moving away from us. And this effect is seen for all extra galactic objects minus the local group of galaxies. How then is it known that our local group is not the center of the universe? Wouldn't the fact that everything is moving away from us point to us being the center? What evidence disproves us being the center? Thanks
  2. jcsd
  3. May 6, 2007 #2


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    Dearly Missed

    there is no evidence that suggests we are at the center, for two reasons:

    if all distances are expanding the same percentage per unit time (one percent in 140 million years) then it looks to everybody as if they are central to the expansion. Beings in distant galaxies (if there are lifeforms out there) see the same evidence we do---everything surrounding them except for their local group is receding from them exactly the way it is from us. So there is no evidence that we are special.

    there is no clear meaning of the word CENTER in this context.
    an infinite line has no center, if space is infinite there is no center.
    if space is finite then it might be boundaryless, like the surface of a balloon (except 3D) and the surface of a balloon has no location in it that you can call the "center". As far as I know there is no point in space, at the present moment, that it would make sense to call the "center" of space.

    so what you suggest does not work.
  4. May 23, 2007 #3
    i agree with marcus, but i have another way of describing his first point (my uni lecturer likes this one haha)

    if uv got some bread dough, with raisins in it or nuts or whateva, and u put it in the oven, the bread expandes, rite? but the raisins expand away from each other at the same rate

    but if u were sitting on one of those raisins it would seem as if u were still and the other raisins were moving away from u, except those that have no dough between you and them... this also falls into the expansion theory of the universe, where the dough in the bread is thought of as the empty space between galaxies...

    and of course, its red shifted coz the wavelenght of the light gets longer the further away the galaxy is coz its moving away the fastest... like the raisins =P

    hope that helped
  5. May 23, 2007 #4


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    There are a lot of mathmatical reasons why it doesn't work, already discussed, but how about an egocentric reason: if there were a center, we'd have to have hit some sort of cosmic lottery to be at it and there is no reason to believe (evidence to suggest) we are that special.
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