I still remember, so many years ago, when the big telescopes became powerful enough, that they brought us pictures of distant galaxies.
For the first time the images of far away, rapidly escaping galaxies were clear enough, that you could see their relativistic contraction. Not only the big Doppler red shift which proved how fast they travel away from us, but also all the relativistic effects of a high relative speed that Dr. Einstein had correctly predicted so many decades ago.
Another magnificent triumph for Relativity and late Albert Einstein.
Except that this never happened. Yes, we saw those distant galaxies quite clearly, but there was no trace of a contraction whatsoever. Not even when the Hubble Space Telescope caught its famous Deep Field series of pictures. The oldest, the fastest the most distant galaxies from the edge of space, showed no relativistic contraction. Not a single one of them.
The standard explanation goes like this:
They are not that fast. A few thousand kilometers per second at the most. What brings them to such apparent speed is the inflating of space. They are moving away from us with nearly the speed of light, but that’s not a speed, it’s an apparent velocity. Thus justly there is no relativistic contraction here!
Let’s say, that a galaxy had been ejected from our cluster, long ago at near light speed, so that it would be a relativistic contraction clearly visible from the beginning. By now, this galaxy would have already been among those caught by the HST camera. And would be static relative to those from HST pictures. The ejected galaxy is shrunken, when the neighboring ones aren’t, despite all of them moving with an equal, highly relativistic speed.
Embarrassing images, aren’t they?
protokol2020 
But the relativistic motion is directly away from us! How would you expect them to look different, apart from the redshift?
Their motions are not always perfectly 90 degrees away.
And even when they are, there should be a relativistic contraction between the front and the back stars of the away moving galaxies.
And the around galaxy center orbiting should be slowed down as well.
And above all … their galactic metabolism should slowed down. Their stars should burn more slowly from our point of view and those galaxies should be dimmer for us. Not just because of the red shift, but some additional effect of time slowing down.
We don’t see that, do we?
>Their motions are not always perfectly 90 degrees away.
>And even when they are, there should be a relativistic contraction between the front and the back stars of the away moving galaxies.
In our reference frame the galaxy is contracted in its direction of motion, which is close to directly away from us. But, we can’t see extension in the direction away from us – our telescopes show a 2-D picture. The small component of the motion that isn’t directly away from us shouldn’t be causing much distortion. So, we see a normal-looking galaxy, with redshift.
>And the around galaxy center orbiting should be slowed down as well.
>And above all … their galactic metabolism should slowed down. Their stars should burn more slowly from our point of view and those galaxies should be dimmer for us. Not just because of the red shift, but some additional effect of time slowing down.
>We don’t see that, do we?
Actually I don’t know if we can’t see that. It’s not something you can see from a photograph. Light levels in galaxy photographs are always increased relative to what you would see if you looked through a telescope with your eye, because otherwise they’d be really dim.
Orbit speed can be measured by using redshifts of the different sides of a galaxy (as long as it’s close enough that you can see both sides), and galaxy light levels are also measured. If you look up these things and find they’re different than expected that would be interesting data. I doubt you’d find that though!
> I doubt you’d find that though!
I doubt you (or anyone else) can show me even not that distant galaxy which has its metabolism slowed down, because it moves away with let say 1/3 of the speed of light.
That should be clearly visible, but there is nothing like that to be seen.
Do you say that it’s invisible due to a small effect and our limited quality pics?
Or do you say: “Yes, well, the space is inflating you know, so we don’t see no relativistic effects!”
The second option is much more popular and once I believed that too. Now, I am quite sceptic. The real picture must be different. I have no idea how things actually work, but that is beside the point.
I just don’t like what I see. Too many a posteriori inventions like space inflation, dark matter, dark energy …
But I can understand that. Even If I don’t like it, I can understand that. But still, don’t like it at all.
I suggested how you could see that (z of stars moving away v stars moving towards us). Check if the speeds are appropriate for the relativistic velocity addition formula. Otherwise you I don’t see how you could see it in a photo. We could also take different photos at different times and see how much changed, but I don’t know how far apart they’d have to be. A thousand years maybe? A million? Actually maybe you could look for gravitational lensing producing two images on different length paths.
There seems to have been a paper not so long ago about high-redshift rotation curves:
https://arxiv.org/abs/1703.04310
This blog post comments on it and says the data is consistent with flat curves despite the paper saying they decrease with radius:
https://tritonstation.wordpress.com/2017/03/19/declining-rotation-curves-at-high-redshift/
Anyway, I don’t see their analysis in enough detail in the paper, but if you did get it, you could check if they properly used relativistic velocity addition and if the rotation curves were appropriate for the galaxy brightness.
>Or do you say: “Yes, well, the space is inflating you know, so we don’t see no relativistic effects!”
No I think you’re right that you get relativistic effects even if the relative motion is because of the space inflating, it’s just that I don’t see how that would result in any observation different from what we actually see.
Let me tell you this.
If a (type I supernova or any other supernova) is exploding before our eyes, in a fast (away moving galaxy, then due to the relativistic time dilatation, is a kind of slow motion explosion, for any observer in our home galaxy.
So it should be dimmer than a (type I supernova) normally is.
Yes or No?
Yes. But I imagine they already account for this when measuring supernova brightness for dark energy measurements and so on.
Regardless of how you choose to view it (relativistic motion or universe expansion)
EDIT BY Thomas:
> you must get an apparent slowdown proportional to the ratio of frequencies, because the frequency is itself a measurement of time.
That is NOT true AT ALL! Time dilatation IS NOT linear. NOT AT ALL.
And what about blue shift galaxies? Do you think they speed up their internal clock?
I will not approve such comments anymore. You have to know the basic stuff.