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For a lack of better word, I used growing and shrinking in the question, but what I really mean is: Are objects that are now in the observable universe passing getting out of range in the future, or are objects that are now outside of the observable universe ever come close enough to pass over into the observable universe? Or both?

Is the number of objects in the observable universe growing or shrinking due to "migration"?

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  • $\begingroup$ By Hubble's law, I must say it is growing. $\endgroup$
    – Sensebe
    Commented Nov 18, 2014 at 16:43
  • $\begingroup$ Sometimes you can expect magic in the answer (if anyone posts), like Jupiter's apparent backward motion as seen from the earth. $\endgroup$
    – Sensebe
    Commented Nov 18, 2014 at 16:50
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    $\begingroup$ In a matter-dominated universe, more objects are always coming inside the horizon, but in a universe dominated by dark energy it's the other way around. Our universe is transitioning from matter-dominated to dark-energy-dominated, so at some point things will stop coming in and start going out, but I think that hasn't happened yet. $\endgroup$
    – user4552
    Commented Nov 18, 2014 at 17:00
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    $\begingroup$ @BenCrowell Objects will move out and the comoving hubble horizon will shrink, but the proper hubble radius will remain constant for a cosmological constant dark energy domination in a flat universe and will keep increasing if the equation of state of dark energy is greater than -1. Of course, the minuscule matter contribution to the energy density will add some growth term to the proper hubble radius. So in terms of proper distance, the size of the observable universe will likely keep growing $\endgroup$
    – Jim
    Commented Nov 18, 2014 at 19:30
  • $\begingroup$ @Jim The question was about comoving distance, though, - not proper distance. $\endgroup$
    – Max
    Commented Nov 21, 2019 at 14:04

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