Comment on Uh oh lol

• deltapi@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

  The expansion is supposed to be happening everywhere at the same time, not just at the edges.
  For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.
  Our present understanding suggests that ‘normal’ universal expansion should not (in and of itself) result in anything moving towards us.

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  • Kolanaki@pawb.social ⁨3⁩ ⁨weeks⁩ ago

    Aren’t the milky way and andromeda on a collision course with each other?

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    • Zink@programming.dev ⁨3⁩ ⁨weeks⁩ ago

      Yep. Space is expanding everywhere at once, but the effect is minuscule at the scales we’re used to. And even at galactic scales the “speed” of expansion might seem like a lot to us, but it still isn’t enough to overcome the motion of objects. I looked up some rough numbers to give you an idea:

      The rate of expansion of space is 73 km/s/Mpc. So for every 3.26 million light-years between you and a distant galaxy, the space between you and that galaxy is expanding by 73 kilometers per second.

      Andromeda’s blue shift indicates it’s headed towards us at 110 km/s. And in my non-expert head I’m thinking that blueshifted light must have already been redshifted by the millions of years traveling through space to reach us. So the galaxy’s speed through space towards us when the light was emitted was considerably higher.

      Andromeda is 2.5 Million light-years away, btw. So the cumulative distance of space between here and there is expanding at something like 73 km/s/Mpc * 2.5 Mly * 1Mpc/3.26Mly = 57 km/s.

      But when talking about relativistic distances and speeds, basic terms regarding time and location don’t always make sense.

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    • Starski@lemmy.zip ⁨3⁩ ⁨weeks⁩ ago

      Yes, but not because of universal expansion really, they’re just headed in a direction that is going to intersect at some point, likely combining the two galaxies together. This’ll be so far in the future we’ll all be long dead though, on top of it being unlikely that anything is going to even come close to our solar system

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      • Kolanaki@pawb.social ⁨3⁩ ⁨weeks⁩ ago

        That’s the other part I find fascinating; these two galaxies are gonna intersect, but our solar system probably won’t hit anything. That’s so gnar.

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  • Davel23@fedia.io ⁨3⁩ ⁨weeks⁩ ago

    For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.

    Galaxies are gravitationally bound, they do not expand in the same way as the universe.

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    • deltapi@lemmy.world ⁨2⁩ ⁨weeks⁩ ago

      Fair enough, I should have been thinking bigger.

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• ProfessorPeregrine@reddthat.com ⁨3⁩ ⁨weeks⁩ ago

  Expansion red-shifts light.

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