My understanding was that in a gravitationally bound system like that, the orbits would be slightly larger (or slower for the same distance) based on the rate of expansion and the distance, but not grow any unless the rate of expansion increases. Like maybe the earth is a few angstroms farther from the sun than in a not expanding universe, but that number doesn’t change as long as the expansion keeps going the same. Same for galaxies and clusters.
At the planetary scale, such a change would be completely overpowered by other orbit defining effects, like resonance, mass flow/loss, and even drag.
At the cluster scale, I can absolutely see spacetime expansion overpowering gravity.
At the galaxy level, I can’t tell. Does spacetime expansion limit the size of galaxies? Is that limit shrinking due to the acceleration of expansion? Are galaxies under that limit larger than otherwise expected? Is this effect large enough to effect the speed of galaxy rotation and does it need to be taken into accout when measuring the effects of dark matter?
At the cluster level it will depend on the velocities and distances. For example, using very rough numbers the current expansion rate means that space between us and the Andromeda galaxy is expanding at 55 km/s. Seems fast until you realize the distance needed to see the effect build to this level. For perspective I found someone’s calculation to reduce it to solar system level to end up with ~10 meters/AU/year. But of course at this distance gravity dominates so we can’t measure that directly and it may not even be large enough to consider.
A larger and slower moving galactic cluster would be more affected than a tighter one. I don’t know what our Local Group would be considered to be, but there are a hundred or so galaxies around us that appear blue shifted, so they are moving towards us even with the expansion.
That wouldn’t significantly affect most galaxies though, would it? The rasin bread model might insinuate that the space in a galaxy isn’t expanding (which is wrong), but it is accurate in thst gslaxies themselves are not growing larger.
I see where this is diverging a little bit.
But everything is expanding. Including matter. But the mass isn’t chaning.
But this also includes the space in between the objects.
So objects are getting further apart, but so are the objects getting bigger at the same rate.
The mind bend for me was realsing it’s not space that expanding really, it’s distance.
This is why distant light is red shifted. Because what started out as white, has had the wavelength expand with the universe, making it appear more red.
Yes, all distances are expanding, but not everything in space is expanding. Atoms aren’t expanding because atomic forces are far stronger than expansion is, for example.
Yet the distance between galaxies is increasing, so there must be a crossover point where one structure can stay structured but a slightly bigger structure is torn apart.
My question was if this size is larger or smaller than galaxies, and it seems to be quite a bit larger than galaxies at the moment.
The interesting thing is that the expansion is increasing, so this size limit is shrinking. Unless some change in forses happens (like inflation or some kind of false vacuum collapse) the limit will eventually be smaller than galaxies and they’ll get ripped apart. Eventually star systems will be ripped apart too, then stars (if any remain at that point) then planets, molecules, atoms, and bosons; and if if that continues to quarks funny things start happening that kind of look like the big bang.
That last part is still speculation of course, but I do still wonder if the expansion of the universe affects galaxy formation and dynamics, and if ancient galaxies were different in part because of this.
