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I write code in C++, Python, Java and now Haskell.


Nov
26
comment “Reality” of length contraction in SR
It might be useful to understand where this post goes wrong.
Nov
26
comment “Reality” of length contraction in SR
Any hint as to why this was downvoted?
Nov
26
accepted “Reality” of length contraction in SR
Nov
24
revised “Reality” of length contraction in SR
added 293 characters in body
Nov
24
comment What kind of invariants are proper time and proper length?
@Lubos - thanks. The Wikipedia entry on "proper length" seems to contrast "proper length" and "proper distance". In the end, it is pretty clear that there is $L = L_0/\gamma$ and $d\sigma = \sqrt{dx_\mu dx^\mu}$, with $d\sigma$ invariant, but it looks like the terminology used by some can be a bit confusing :-)
Nov
24
answered “Reality” of length contraction in SR
Nov
23
comment What kind of invariants are proper time and proper length?
Further - that's a different line of reasoning - I thought that identifying "invariants" (exact same before and after Lorentz transformations) was important, because those "invariants" are what really describe the object completely, which sounds like what you are saying about "complete information".
Nov
23
comment What kind of invariants are proper time and proper length?
Actually, the length of the rod becomes $1/\gamma$ right? To me, I thought that because it doesn't keep its value of $1$, it cannot be called "invariant". That's probably just me?
Nov
23
comment What kind of invariants are proper time and proper length?
I am a bit confused - it I take a rod sitting from (0,0) to (0,1) in (t,x), its proper length is its length in that frame where it is at rest, and if and I pass it trough the Lorentz transformation, will I get a "length" of 1? I am confused by the "the value of the proper length is not affected by the transformations". I thought the spacetime interval was the only real invariant for the Lorentz transformation (i.e. if you know its value in one frame, it is the same value in all reference frames, without further adjustment or calculation). Can you explain?
Nov
23
comment “Reality” of length contraction in SR
Moonraker - but also the effects are real, meaning that in the case of the muon, what you are going to be able to measure is influenced by SR. So the question of whether the object "changes" or not is slippery and maybe meaningless. The object has one "real" behavior for an observer and another, equally "real" behavior for another observer.
Nov
22
comment “Reality” of length contraction in SR
Yes - about perspective indeed, but IMHO in a profound way: each observer is "isolated" in his perspective and his perspective is reality to him, because of relativity of simultaneity, which was not the case in the pre-relativity world. It's fascinating :-)
Nov
22
comment “Reality” of length contraction in SR
Makes sense. This was very interesting and the explanations very good. I don't think I have any problem with any of it :-)
Nov
22
comment “Reality” of length contraction in SR
dmckee - I see you are a physicist - so to physicists, the effects of SR on the lifespan of the muon are "real" right? (sounds like a silly question...)
Nov
22
comment “Reality” of length contraction in SR
dmckee - yes, and it is hard to appreciate, because there are 4 dimensions to spacetime, which situation we are not familiar with at all - I think it's best to let go of some of the intuitions we built for ordinary Euclidean space.
Nov
22
awarded  Citizen Patrol
Nov
22
comment “Reality” of length contraction in SR
... continuing the preceding comment: it seems that time dilation and length contraction becomes less important than invariants that you would want to attach to the "real" object. It seems there is natural intellectual progression, asking "what doesn't change?". I think this is one reason invariants are so important/useful in physics.
Nov
22
comment “Reality” of length contraction in SR
Cristoph - 2 comments on that one. First, it appeals to our ordinary Euclidean 3D space intuition, which we should probably not rely on to explore 4D spacetime. Second, I have personally no problem with considering that there are multiple "realities" depending on the state of relative motion of the observers, those "realities" meaning that there are measurable effects (such as in the case of the muon). Also, I think it becomes a good starting point for thinking about invariants: what "really" doesn't change and is the same for all observers (spacetime interval...).
Nov
22
comment “Reality” of length contraction in SR
I found this quote from Einstein, 1911, that is in the Wikipedia under "Length contraction": "The author unjustifiably stated a difference of Lorentz's view and that of mine concerning the physical facts. The question as to whether length contraction really exists or not is misleading. It doesn't "really" exist, in so far as it doesn't exist for a comoving observer; though it "really" exists, i.e. in such a way that it could be demonstrated in principle by physical means by a non-comoving observer."
Nov
22
comment “Reality” of length contraction in SR
Cristoph - that is interesting - I had assumed that in the twin paradox, the fast moving twin would come back younger than the other one, and had also assumed that something "symmetric" would happen for length, assuming that there was "no difference" between $t$ and $x$ - but I was probably wrong in doing that. In other words, I was seeing time dilation and length contraction to be "symmetric" in their effects, when they might not be.
Nov
22
comment “Reality” of length contraction in SR
Also, in the case of the twin paradox, the effect of time dilation seems "real" enough that when the 2 twins re-join, one is older than the other. I've always understood that to mean that depending on the actual path you take through spacetime, your internal clock would run differently. Is it the same for the length of a rod? If I take a rod through 2 different paths in spacetime that meet at some point, will one be shorter than the other?