How can an observer distinguish two objects that are moving from each other in space compared to those that are moving with space due to expansion of the universe?
This is interesting, but kind of vague. This looks to me more like the light wave hadn't changed, but the measure changed. Meaning everything shrunk. Can We interpret this as matter shrinking, and because of that the wave seems to have larger wave length? Is there a shrinking matter theory?
I was thinking about it a lot, and I am not sure how to explain cosmological red shift under conditions that just distance between comoving worldliness changes. How can this produce the effect of red shift? I always assume that the space in which the wave travels gets stretched.
I understand that We can say that what is expanding are worldliness of comoving observers. But something actually has to change for this to happen? This is more of an effect. What is the cause? I can imagine that the space is expanding, or time is expanding, both, or everything is shrinking...
Thank you for the responses. What I assume from most of the responses is that it that this just an interpretation, and We can attribute the expansion to expansion of space, time or both arbitrarily, without any change at all.
For me, it is logical to assume that if We think that all spacial...
I am trying to find some sources about time dimension expansion during spacetime expansion.
Why do We assume that only spacial dimensions expand? I only found a lot of weird arguments.
Btw, temporal dimension expansion does not mean that second was shorter in the past. Similarly to spacial...
Doesn't periphery length contracts? It moves faster. Speed contracts lengths.
Also, this mixes SR and GR. An observer on the edge of a rotating disk would measure distances along the disk to be larger than an observer at the center would predict based on the non-rotating radius and the angle...
What the hell man? I already told you like five times that time unit is not changing with time expansion. No matter how you shrink or expand the time dimension a second is still second. Same as 1 meter is still 1 meter even if space expands. On the contrary, if meter extended with expansion of...
Doesn't rotational symmetry of spacetime include time? At least in SR via Lorentzian transformations? But in GR the rotational symmetry only holds locally, isn't it?
To your suggested experiment, the objects move and light carries angular momentum, it's path is curved by gravity etc., you can't...
I think it would be pretty influential if space expanded only in x, y and not z.
If space expanded 1m/s/km (1m per second per km) in each of the spacial dimension (x, y, z) then after 1s the volume of space of 1km2 becomes cca 1.003 km2 after 1s. If you assumed it expanded only in x and y then...
How do you know that it makes no difference to anything real?
If time is expanding as well, and We assume it is just space, don't We calculate badly the rate of the expansion of space? If time expansion is indeed happening then space is not expanding that fast, because the part of the perceived...
I fully agree with what you wrote, but "how do you tell" is my own question. Why do We assume it is just space expanding? I can very well say that it is both time and space that is expanding. If you can't distinguish if space or time is expanding then until proven otherwise We should assume that...
I am not sure how any of it is relevant. I already specified in the opening post that the measuring unit second is not changing. Furthermore, I am in no way changing the pace of the time, measuring of the time or length of the unit of the time.