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Can Milky Way and Andromeda collision reconcile with an Expanding Universe with galaxies spreading away from each other like "raisins in a loaf"? (lemmy.dbzer0.com)

submitted 4 months ago* (last edited 4 months ago) by Melatonin@lemmy.dbzer0.com to c/asklemmy@lemmy.ml

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I understand that our local galaxy group is considered "gravitationally bound" and therefore exempt from the expansion from each other ((, but we don't seem to have other galaxies collected into their own "local groups" of gravitationally bound clusters, so are we saying we're somehow unique? Is there a trick of perception taking place?)) <---edit:this is wrong

I found this quote in the Wikipedia article on the Expansion of the universe.

While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

It seems to me that if we can perceive at cosmological distance something that cannot exist, perhaps we are falsely observing an expanding universe. Maybe everything IS gravitationally bound and we're just seeing expansion because... Relativity?

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[–] victorz@lemmy.world 1 points 4 months ago* (last edited 4 months ago)

Ah yes, I seem to remember a few things now, which helped me to understand this before:

You have a fixed energy output (not sure what to call it, but let's go with that, "energy output"). Either you output all of your energy in the physical dimensions, or in the time dimension (I can't think of anything that does this though), or some in both. Most things output some energy in both, time and the physical, like us for example!
Light is basically all of its energy in the physical dimension and none in the time dimension. Thus a photon doesn't really experience time at all. To it, it feels like absolutely zero time has passed at all between traveling from one end of the universe until it is absorbed by an object at the other end.
To attain the speed of light takes infinite energy, as it takes more and more energy to accelerate mass the faster you get to c, in a way that you never reach c.

These concepts are really helpful in my opinion, to understanding the fact that you can't reach the speed of light, as well as the whole time dilation concept.

I hope it helps someone else.