[speedfreek]

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hey btw what's the latest on this? Are stars actually accelerating away from each other (last I heard), Or are stars accelerating towards each other but not enough to collapse?

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This is pretty much the most popular current cosmological theory:

The expansion of space is something that is measurable at the largest scales only, i.e. between us and the more distant galaxies. It is theorised to happen in areas with no gravity, or that the expansion is such a weak force that any gravity overcomes it.

The expansion of space is metric, which means it is the metric that defines distance that changes over time. This means that any unit of distance will change by the same factor as any other unit over a given time - in the time it takes 1 meter to expand to become what used to be 2 meters all distances double, so 1 billion ly becomes 2 billion ly. This is how distant galaxies can recede from us at apparent speeds that are faster than light.

We can only measure the expansion of space using the redshift of objects over around 5 billion light years away. This is when the redshift is dominated by cosmological redshift, where light has been actually stretched by the expansion of the space it has passed through. At closer distances, the effect of the expansion is much less (for the actual rate of expansion is extremely small) and so any redshift of a closer object is dominated by relativistic doppler effect, where the light is apparently changed by our relative speed to the object we are observing.

We think the rate of expansion is accelerating because where we have objects of a known magnitude (type 1a supernovae) that show up over large distances, we can more accurately estimate their distance using both redshift and the difference between their absolute and apparent magnitude. When we measure these supernovae, we built up a picture where the closer ones had moved away from us further than expected when compared to the more distant ones.

But stars aren't accelerating away from each other - distant galaxies are. There is no measurable effect of expansion within galaxies themselves, or between close clusters of galaxies, only in the vast empty areas between the clusters of galaxies.

And in fact, it is misleading to think of the distant galaxies as accelerating away, as that implies inertial motion. It is more accurate to say the distance between us and the distant galaxies is increasing at an accelerating rate, through no movement of ours or their own, but through the space in between us growing.