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You have obj1 and obj2. As something approaches c speeds it begins to compress. How do we determine which obj is compressed since the movement is relative to the other obj?
Neither object is compressed. Both objects measure the other as length contracted (i.e. shortened), but this is an effect of the relativity of simultaneity and the choice of coordinate systems. Neither will measure any stress in themselves or in the other object (assuming they are both moving inertially) which they would if one or other was compressed.
But how can that be entirely true? If you do a detailed twin paradox calculation the fact that distance for the traveling twin according to Earth is shorter plays a role in the calculations that show differential aging, as discussed in this link here. Take note how crucial the length contraction calculation is. Without that calculation the distance the twins measure will not be what was shown, and that was crucial in showing the difference in their age at the end.Okay I see, so it's basically just an illusion created by the different length of the light's path.
It's not an illusion, precisely. Any measurement you make, using light or not, will get you the same contracted length. You could use calipers, as long as you were quick enough to do it while the object passes at 0.99c or whatever, and you'd have a physical record of the object being only 14% as long as when measured at rest.Okay I see, so it's basically just an illusion created by the different length of the light's path.
Length contraction is a real effect in some senses. However it doesn't impose any stresses on the contracted bodies, and the exact value you measure for it is dependent on your choice of simultaneity convention. As are the Lorentz transforms.That seems pretty straight forward, and it tells me that length contraction is as real as the Lorentz transformation equations themselves are. Is this a fair conclusion?
Okay I see, so it's basically just an illusion created by the different length of the light's path.
You have obj1 and obj2. As something approaches c speeds it begins to compress. How do we determine which obj is compressed since the movement is relative to the other obj?
You have obj1 and obj2. As something approaches c speeds it begins to compress. How do we determine which obj is compressed since the movement is relative to the other obj?
Yeah that's what I thought but this thread combined with the weird way distance is defined in GR as I read about it threw me off a bit. Just trusting the math it's pretty clear that if time dilation is 100% real than so is length contraction... in flat spacetime anyway...Length contraction is a real effect in some senses. However it doesn't impose any stresses on the contracted bodies, and the exact value you measure for it is dependent on your choice of simultaneity convention. As are the Lorentz transforms.
I think @pervect put it better than I did. "Real" isn't a helpful term here since it doesn't have a good definition.Yeah that's what I thought but this thread combined with the weird way distance is defined in GR as I read about it threw me off a bit. Just trusting the math it's pretty clear that if time dilation is 100% real than so is length contraction... in flat spacetime anyway...
And so is the notion of "who is contracted". If it was not, you could determine who is "really moving", which is against the principle of relativity (= all inertial frames are equivalent).You have obj1 and obj2. As something approaches c speeds it begins to compress. How do we determine which obj is compressed since the movement is relative to the other obj?