Good visualization but inaccurate. Space between galaxies in a cluster and even the stars in a galaxy is also growing. The difference is in scale. There’s so much distance between galactic clusters and the largest structures of the universe that added up that expansion amount is so much bigger. The balloon analogy with galaxies as dots on the surface is closer since the dots also do grow some, but the balloon would have to be huge to capture a good scale comparison.
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.
Correct, the differences make the analogy good enough to visualize the concept. It does however suffer from the same problem as the balloon one, in which someone can get the impression the expansion has a center. The wiki for the expansion of the universe goes through the various analogies and where they break down.
I would suggest Dr Becky’s Youtube channel for a number of excellent videos on the expansion as well as the current problem of getting an accurate measurement of the correct Hubble expansion rate. The James Webb telescope was hoped to solve that dilemma, but we still aren’t sure.
Good visualization but inaccurate. Space between galaxies in a cluster and even the stars in a galaxy is also growing. The difference is in scale. There’s so much distance between galactic clusters and the largest structures of the universe that added up that expansion amount is so much bigger. The balloon analogy with galaxies as dots on the surface is closer since the dots also do grow some, but the balloon would have to be huge to capture a good scale comparison.
There’s still a center of the balloon and bread
Am I getting bigger too?
Are you sure that galaxies are growing? They’re gravitationally bound enough to have organized orbits, do those orbits get larger over time?
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.
Correct, the differences make the analogy good enough to visualize the concept. It does however suffer from the same problem as the balloon one, in which someone can get the impression the expansion has a center. The wiki for the expansion of the universe goes through the various analogies and where they break down.
I would suggest Dr Becky’s Youtube channel for a number of excellent videos on the expansion as well as the current problem of getting an accurate measurement of the correct Hubble expansion rate. The James Webb telescope was hoped to solve that dilemma, but we still aren’t sure.
Metaphors are great if you assume they’re mostly wrong