I recently watched a video describing that the expansion of space is a "stretch". Everywhere in the universe expanding together. My question is, does conservation of momentum hold true in this situation?

If everything is expanding then doesn't everything start to move slightly faster away from the center increasing or decreasing the total momentum in the universe?

I recognize that momentum is a vector, so I suppose it is possible that moving objects away from each other faster could just cancel out any change in momentum of the whole system, but it seems strange that everything would cancel out perfectly.

If my understanding of how space expands is incorrect, please tell me. And if all change in the total momentum of the universe does truly cancel out then please explain to me why matter is positioned around us in a way that this is so.

(If you do not understand exactly what I am asking, please let me know how I can clarify my question because I found this concept very difficult to put into words)


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    $\begingroup$ I would have to ask in return: "Conservation of momentum relative to what? What are we measuring the total momentum of the universe against?" $\endgroup$
    – CuriousOne
    Apr 27, 2015 at 1:33
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    $\begingroup$ Closely related: physics.stackexchange.com/questions/62939, see also physics.stackexchange.com/questions/136860 $\endgroup$
    – Kyle Kanos
    Apr 27, 2015 at 1:38
  • $\begingroup$ To answer CuriousOne, relative to anything. Shouldn't it be true regales of the point we choose? $\endgroup$
    – Me2
    Apr 27, 2015 at 1:43
  • $\begingroup$ @Me2: I can't point a telescope towards "anything". I could point it towards e.g. the CMB, then I can measure the motion of my telescope against the CMB. It's something like 370km/s. $\endgroup$
    – CuriousOne
    Apr 27, 2015 at 2:08


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