This question can be potentially be interpreted in two ways:
1) “are” the galaxies “really” deformed due to relativistic effects?
2) do the galaxies appear deformed when viewed in a telescope?
The answer to the first question depends on how you extend our reference frame out to them.
If you do it in the standard way then they aren’t “really” length contracted (or actually in a sense they’re expanded, since in the past the same size of galaxy would occupy a larger portion of the universe). If you do it in a way that views the redshift as due to motion (e.g. you go back in time along the light beam reaching us from the galaxy, at each point laying down a space and time coordinate system such that a “stationary” observer according to that coordinate system sees the light beam as having the same redshift that we see) then it is “really” length contracted.
(Edit: as good burning plastic pointed out in a response below, it’s better not to think of it as a real effect. Rather I think it’s better to regard this as definitional—is the galaxy deformed according to the coordinate system we are using.)
The answer to the second question is readily observable. So we should calculate the same answer no matter how you extend the reference frame to the other galaxy, if it’s correct that they are both valid pictures.
Now, since our telescopes see a 2-d picture, the easy answer, that I gave in response to the post on your blog, is that since the motion is almost directly away from us any distortion is along our line of sight and thus is not visible as a deformation in the telescope.
Now I also wanted to do a calculation for 3d telescopes, but I found it difficult to do the calculation for the motion-only-no-expansion picture so am dropping that part of this comment. For a brightness-based distance measure, I think it’s actually an increase, not contraction, of apparent size of a galaxy in the depth direction that you get (as calculated in the standard picture at least).
(edit: I may have messed that up. I imagined an expanding shell of light starting from the far end of a galaxy, then as that shell reaches the near end a new shell expands from the near end. When both shells reach us the shell from the far end the difference in shell sizes is more than the diameter of the galaxy due to universe expansion. So I figured that this would result in some extra dimming of the far and of the galaxy. But I forgot to account for the fact that the ends of the galaxy aren’t stationary in the standard expanding-universe picture—one is moving slightly towards us, the other slightly away if the galaxy as a whole is stationary—which result in the light energy not being evenly distributed across these shells considered in the standard picture. I don’t know which effect will dominate.)
2) do the galaxies appear deformed when viewed in a telescope?
Even in flat Minkowski space-time and even with stereo vision, no they wouldn’t, because the fact that the light from the far side of an object left it earlier than the light from the near side compensates the length “contraction”. If anything, if the object is moving perpendicularly to the line of sight you would see it rotated.
(And I find “length contraction” a pretty misleading name. It’s a purely kinematic effect due to the geometry of spacetime, and no more of a “contraction” than the fact that the height of a pencil is less if it’s askew than if it’s upright.)
No, if an object is moving away from you in Minkowski space time, the time difference of light coming from the far side and from the near side doesn’t compensate the “contraction”—it actually increases the apparent contraction (assuming 3-d perception). For an object moving toward you, it counteracts as you say (and in fact makes the object appear (with our 3-d, but still light-based, camera) longer, just as it also appears to be sped up).
Also what you see when observing a perpendicular motion isn’t actually a rotation. Imagine a cube with opaque edges but otherwise transparent, running at high speed along tracks that are touching and aligned with the edges. The edges must remain touching and aligned with the tracks from any observer’s point of view. So it’s not a rotation but some kind of skew. A sphere will still look circular from a moving observer’s point of view though.
And I find “length contraction” a pretty misleading name. It’s a purely kinematic effect due to the geometry of spacetime, and no more of a “contraction” than the fact that the height of a pencil is less if it’s askew than if it’s upright.
Agreed. I would in fact go further, in that it’s not so much the effect of the geometry of spacetime, as an effect of how we choose to define a coordinate system on that geometry.
No, there is a relativistic mass increase in the galaxies-moving-away picture, and I expect deformation along our line of sight (so not visible in our photographs).
No superluminal galaxies. In the galaxies-moving-away picture, you get the speed by applying the relativistic redshift formula to get the speed from the redshift, which will always come out less than the speed of light while they’re still visible to us. In the conventional picture the galaxies are almost stationary wrt the coordinate system used; you can come up with a superluminal speed by asking “how quickly is the distance between us and that galaxy increasing” where distance is referring to the distance the standard picture would say they are apart from us currently. But that isn’t motion but a change of a distance due to expansion of the universe.
They are “defining ” in a way, that no galaxy is bound to any visible relativistic effect. Everybody does that, albeit on at least two different ways.
How convenient!
We have superluminal galaxies, not bound to relativity. We have nearly light speed galaxies, free of any observable relativistic effect. Our hypothetical ancient space ship sent there (to a nearly light speed away moving galaxy), would slow down all its clocks, the surrounding galaxy wouldn’t.
Unimportant answer: No, it will appear to have slowed down clocks (as was explained to you at the beginning of this thread) and the ancient ship, if it is now at the same distance and stationary with respect to that galaxy, will appear to have the same slowdown.
The more important answer: at this point, this discussion as it is going now is looking pointless.
You have intuitions, backed up by some argumentation, but without a complete mathematical picture, that general relativity produces predictions that don’t match observations.
I have intuitions, backed up by other argumentation, also without a complete mathematical picture, that general relativity produces predictions compatible with observations.
I think my intuitions are better supported, but that’s not what it important.
What is important: general relativity is a physical theory, published long ago and available to anyone, such that this argument can be resolved once and for all by actually doing the math. I am too lazy to do it for the purposes of a comment debate (I might possibly do a blog post though, if it turns out not to be too much work). You come across as probably smart enough to learn how to do the math, so get a general relativity textbook and work it out. You should subjectively estimate a much bigger gain than I do from doing the math, given your subjective assessment that GR gives false predictions and my subjective assessment that it gives true predictions: whoever disproves general relativity will probably get a Nobel prize.
I don’t think, that my intuition should be backed by, or crushed by (doesn’t matter which, really) - more mathematics.
I think my intuition should be backed or crushed by some experimental evidence. Which we probably have.
It seems to me, that no relativistic time slowdown is observed in distant galaxies. What are implications for the GR I really don’t care very much. Theories in Physics are downstream of how the reality is.
It seems to me, that no relativistic time slowdown is observed in distant galaxies.
If you are correct then cosmologists either (1) are very stupid or (2) are knowingly in possession of strong evidence against a pretty much universally accepted, and central, part of physics but haven’t said anything about it.
I am extremely confident that #1 and #2 are both false.
Of course this isn’t scientific evidence that you’re wrong, and if for some reason anything of substance hung on this then it would be appropriate to look more carefully at the evidence and the theory and the mathematics and see what’s going on. And if you really think you’ve got good evidence that relativity is wrong then you should do the work and collect your Nobel prize. For my part, simply on the basis of #1 and #2 (plus the absence of any reason to think you’re so astoundingly smart that it would be unsurprising for all the world’s cosmologists to have simply missed something that you see intuitively) I am confident enough that you’re wrong that I feel no inclination to go to that effort to confirm that the received wisdom hasn’t just yet been overthrown.
I am not very eager to fight against, or for the GR. I don’t care that much about this. It’s a low priority suitable maybe for my occasional blog post and a crosslink to here, where debates are quite long.
Still, no apparent time slowdown in those fast moving galaxies, or some apparent time slowdown—is a bit interesting topic.
As I mentioned earlier, you could count the number of cycles of a laser light beam between two events. For this reason, the apparent slowdown has to be proportional to the redshift. This is a fairly general argument that should work for more theories than just general relativity.
In order for there not to be an apparent slowdown, something really wierd would have to be going on.
At one moment, nothing can be faster than light, the next moment there is a billion of faster than light galaxies.
The next moment, it’s okay, they are not faster than light, only the space is replicating itself between us an them.
Exactly. If you have two ants on a rubber band and you stretch the rubber band, the time derivative of the distance between the ants may be larger than twice the maximum speed at which an ant can walk, but that’s not due to the ants walking so there’s no paradox.
I am not that sure, that there is no paradox. As I see, it can easily be. There is a smaller chance that there isn’t any paradox, after all. Still possible.
I wish, I could find an internet site, which would address those problems. I can’t.
I don’t understand you.
Are those galaxies relativistically “deformed” or not?
This question can be potentially be interpreted in two ways:
1) “are” the galaxies “really” deformed due to relativistic effects?
2) do the galaxies appear deformed when viewed in a telescope?
The answer to the first question depends on how you extend our reference frame out to them. If you do it in the standard way then they aren’t “really” length contracted (or actually in a sense they’re expanded, since in the past the same size of galaxy would occupy a larger portion of the universe). If you do it in a way that views the redshift as due to motion (e.g. you go back in time along the light beam reaching us from the galaxy, at each point laying down a space and time coordinate system such that a “stationary” observer according to that coordinate system sees the light beam as having the same redshift that we see) then it is “really” length contracted.
(Edit: as good burning plastic pointed out in a response below, it’s better not to think of it as a real effect. Rather I think it’s better to regard this as definitional—is the galaxy deformed according to the coordinate system we are using.)
The answer to the second question is readily observable. So we should calculate the same answer no matter how you extend the reference frame to the other galaxy, if it’s correct that they are both valid pictures.
Now, since our telescopes see a 2-d picture, the easy answer, that I gave in response to the post on your blog, is that since the motion is almost directly away from us any distortion is along our line of sight and thus is not visible as a deformation in the telescope.
Now I also wanted to do a calculation for 3d telescopes, but I found it difficult to do the calculation for the motion-only-no-expansion picture so am dropping that part of this comment. For a brightness-based distance measure, I think it’s actually an increase, not contraction, of apparent size of a galaxy in the depth direction that you get (as calculated in the standard picture at least).
(edit: I may have messed that up. I imagined an expanding shell of light starting from the far end of a galaxy, then as that shell reaches the near end a new shell expands from the near end. When both shells reach us the shell from the far end the difference in shell sizes is more than the diameter of the galaxy due to universe expansion. So I figured that this would result in some extra dimming of the far and of the galaxy. But I forgot to account for the fact that the ends of the galaxy aren’t stationary in the standard expanding-universe picture—one is moving slightly towards us, the other slightly away if the galaxy as a whole is stationary—which result in the light energy not being evenly distributed across these shells considered in the standard picture. I don’t know which effect will dominate.)
Even in flat Minkowski space-time and even with stereo vision, no they wouldn’t, because the fact that the light from the far side of an object left it earlier than the light from the near side compensates the length “contraction”. If anything, if the object is moving perpendicularly to the line of sight you would see it rotated.
(And I find “length contraction” a pretty misleading name. It’s a purely kinematic effect due to the geometry of spacetime, and no more of a “contraction” than the fact that the height of a pencil is less if it’s askew than if it’s upright.)
No, if an object is moving away from you in Minkowski space time, the time difference of light coming from the far side and from the near side doesn’t compensate the “contraction”—it actually increases the apparent contraction (assuming 3-d perception). For an object moving toward you, it counteracts as you say (and in fact makes the object appear (with our 3-d, but still light-based, camera) longer, just as it also appears to be sped up).
Also what you see when observing a perpendicular motion isn’t actually a rotation. Imagine a cube with opaque edges but otherwise transparent, running at high speed along tracks that are touching and aligned with the edges. The edges must remain touching and aligned with the tracks from any observer’s point of view. So it’s not a rotation but some kind of skew. A sphere will still look circular from a moving observer’s point of view though.
Agreed. I would in fact go further, in that it’s not so much the effect of the geometry of spacetime, as an effect of how we choose to define a coordinate system on that geometry.
Can you just answer either:
A—Yes, they are deformed and this is visible on our pictures.
B—No, there is no deformation to be seen on our pictures.
B—No deformation to be seen in our pictures.
Okay. Thank you for this straight answer.
No deformations. No relativistic mass increase. Which should also be visible via orbital velocities inside those galaxies.
But that wouldn’t be a problem at all, we have the dark matter for such cases. Even here at home.
In any case, some galaxies are superluminal, what’s the use of relativistic effects for them? No use.
No, there is a relativistic mass increase in the galaxies-moving-away picture, and I expect deformation along our line of sight (so not visible in our photographs).
No superluminal galaxies. In the galaxies-moving-away picture, you get the speed by applying the relativistic redshift formula to get the speed from the redshift, which will always come out less than the speed of light while they’re still visible to us. In the conventional picture the galaxies are almost stationary wrt the coordinate system used; you can come up with a superluminal speed by asking “how quickly is the distance between us and that galaxy increasing” where distance is referring to the distance the standard picture would say they are apart from us currently. But that isn’t motion but a change of a distance due to expansion of the universe.
You are mistaken.
https://arxiv.org/abs/astro-ph/0011070
There are superluminal galaxies. Quote:
They are defining distance based on the conventional picture, then asking how fast it is increasing with time, as I mentioned in my above comment.
They are “defining ” in a way, that no galaxy is bound to any visible relativistic effect. Everybody does that, albeit on at least two different ways.
How convenient!
We have superluminal galaxies, not bound to relativity. We have nearly light speed galaxies, free of any observable relativistic effect. Our hypothetical ancient space ship sent there (to a nearly light speed away moving galaxy), would slow down all its clocks, the surrounding galaxy wouldn’t.
Funny.
Unimportant answer: No, it will appear to have slowed down clocks (as was explained to you at the beginning of this thread) and the ancient ship, if it is now at the same distance and stationary with respect to that galaxy, will appear to have the same slowdown.
The more important answer: at this point, this discussion as it is going now is looking pointless.
You have intuitions, backed up by some argumentation, but without a complete mathematical picture, that general relativity produces predictions that don’t match observations.
I have intuitions, backed up by other argumentation, also without a complete mathematical picture, that general relativity produces predictions compatible with observations.
I think my intuitions are better supported, but that’s not what it important.
What is important: general relativity is a physical theory, published long ago and available to anyone, such that this argument can be resolved once and for all by actually doing the math. I am too lazy to do it for the purposes of a comment debate (I might possibly do a blog post though, if it turns out not to be too much work). You come across as probably smart enough to learn how to do the math, so get a general relativity textbook and work it out. You should subjectively estimate a much bigger gain than I do from doing the math, given your subjective assessment that GR gives false predictions and my subjective assessment that it gives true predictions: whoever disproves general relativity will probably get a Nobel prize.
I don’t think, that my intuition should be backed by, or crushed by (doesn’t matter which, really) - more mathematics.
I think my intuition should be backed or crushed by some experimental evidence. Which we probably have.
It seems to me, that no relativistic time slowdown is observed in distant galaxies. What are implications for the GR I really don’t care very much. Theories in Physics are downstream of how the reality is.
If you are correct then cosmologists either (1) are very stupid or (2) are knowingly in possession of strong evidence against a pretty much universally accepted, and central, part of physics but haven’t said anything about it.
I am extremely confident that #1 and #2 are both false.
Of course this isn’t scientific evidence that you’re wrong, and if for some reason anything of substance hung on this then it would be appropriate to look more carefully at the evidence and the theory and the mathematics and see what’s going on. And if you really think you’ve got good evidence that relativity is wrong then you should do the work and collect your Nobel prize. For my part, simply on the basis of #1 and #2 (plus the absence of any reason to think you’re so astoundingly smart that it would be unsurprising for all the world’s cosmologists to have simply missed something that you see intuitively) I am confident enough that you’re wrong that I feel no inclination to go to that effort to confirm that the received wisdom hasn’t just yet been overthrown.
I am not very eager to fight against, or for the GR. I don’t care that much about this. It’s a low priority suitable maybe for my occasional blog post and a crosslink to here, where debates are quite long.
Still, no apparent time slowdown in those fast moving galaxies, or some apparent time slowdown—is a bit interesting topic.
Isn’t it?
As I mentioned earlier, you could count the number of cycles of a laser light beam between two events. For this reason, the apparent slowdown has to be proportional to the redshift. This is a fairly general argument that should work for more theories than just general relativity.
In order for there not to be an apparent slowdown, something really wierd would have to be going on.
We have seen weirder things going on. A superluminal galaxy is quite weird, isn’t it?
At one moment, nothing can be faster than light, the next moment there is a billion of faster than light galaxies.
The next moment, it’s okay, they are not faster than light, only the space is replicating itself between us an them.
The next moment the space is growing exponentially. What is not that weird, we are accustomed to exponentials when replicating is involved.
Nothing is really weird, except the logic must not be violated. Everything else can be weird as it wants to.
Exactly. If you have two ants on a rubber band and you stretch the rubber band, the time derivative of the distance between the ants may be larger than twice the maximum speed at which an ant can walk, but that’s not due to the ants walking so there’s no paradox.
I am not that sure, that there is no paradox. As I see, it can easily be. There is a smaller chance that there isn’t any paradox, after all. Still possible.
I wish, I could find an internet site, which would address those problems. I can’t.
Can you?