Is Length Contraction in SR physical??
in [Relativity]
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From: Ste on 7 Feb 2010 02:24 On 7 Feb, 04:14, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 6, 9:35 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > You can only measure along the x axis at a given t the parts of the > > > ladder that intersect the x axis at that given t. > > > Of course. Because t=0 represents what you're visually observing in > > the present. > > Right, so if you see a length contraction in my picture, it means that > you're trying to observe parts of the rod that aren't at t=0. Look at > the intersection with the volume the rod sweeps out with t=0. This > intersection is *larger* than the length of the rod (you can see it > extends slightly past the edge of the circle). Ah, I know what you mean. You mean if the rod sweeps out in the direction of the t'-axis. Yes, in that case it does become longer - I was sweeping it out along the t-axis. > > > The two ends of the > > > ladder intersect the x axis at *different* values of t'. This > > > corresponds to different *times* in the ladder's frame. Look at where > > > the t' lines extended from the endpoints of the ladder intersect the x > > > axis. You'll see the line they intersect to make a line that is > > > *longer* than the length of the ladder. This has nothing to do with > > > optical illusions. This has to do with the amount of space the ladder > > > traces out along the x axis as it moves through spacetime. > > > I'm afraid I disagree with this interpretation. I'm reminded of > > Einstein's quip that the "only thing that gets in the way of thinking, > > is education". > > This is not an interpretation. One never seems to be a single step away from interpretation. > This is you using the diagram > incorrectly. Yes, that's fair enough. > We haven't even gotten to the interpretation yet. You > need to look at the diagram the right way first before we can > interpret anything. This is not a subjective description that I'm > talking about. If you look at the intersection of the 2D volume the > ladder traces out with the t=0 line (the x axis) you will see this > intersection has a greater length than the ladder itself. Indeed.
From: mpalenik on 7 Feb 2010 02:29 On Feb 7, 2:24 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 7 Feb, 04:14, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 6, 9:35 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > You can only measure along the x axis at a given t the parts of the > > > > ladder that intersect the x axis at that given t. > > > > Of course. Because t=0 represents what you're visually observing in > > > the present. > > > Right, so if you see a length contraction in my picture, it means that > > you're trying to observe parts of the rod that aren't at t=0. Look at > > the intersection with the volume the rod sweeps out with t=0. This > > intersection is *larger* than the length of the rod (you can see it > > extends slightly past the edge of the circle). > > Ah, I know what you mean. You mean if the rod sweeps out in the > direction of the t'-axis. Yes, in that case it does become longer - I > was sweeping it out along the t-axis. > The rod has to sweep out over the t' axis because it's moving horizontally. If you sweep it out over the t axis, that represents something that is at rest (in the x,t frame). Do we agree on this so far? Can we also agree that we have not talked about light, optics, or propagation delays at all in creating this picture. You could physically touch the rod at all of the points along the x axis at t=0. That is, if you had men standing there with there fingers stretched out at any of those points, the rod would brush up against them, and thus this has nothing to do with optical illusion. Do we agree so far?
From: Peter Webb on 7 Feb 2010 03:44 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:b1df1f82-d222-40bc-9de1-f00e3e043fca(a)q4g2000yqm.googlegroups.com... On 7 Feb, 03:57, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 6, 9:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > Secondly, we can determine whether any part of the pole was > > > > > outside > > > > > the barn when those doors were closed by looking for the marks the > > > > > ends of the pole would have made on the door. In the absence of > > > > > those > > > > > marks, we can safely conclude that the entire pole was inside the > > > > > barn > > > > > at the time the doors were closed. > > > > > Agreed. I would expect this test is definitive, were it possible to > > > > carry out. > > > > And this has been tested in equivalent experiment. Documented. > > > Has it really? Which experiment was that, because my sources say that > > length contraction has *never* been experimentally observed. > > I already told you the answer to that. Please look again. No it hasn't Paul. The experiment you describe, or anything like it, has not been carried out, and the literature makes this clear that physical length contraction has not been observed experimentally. _________________________________ I already gave you a direct link to where the effect is observed experimentally hundreds of times a day: http://www2.slac.stanford.edu/vvc/theory/relativity.html > > > Seto does not read experimental papers, because he finds them > > > confusing. So instead he believes what makes sense to him, rather than > > > letting experimental results tell him something different. > > > You have to concede at least the possibility Paul that the reason Ken > > finds them confusing, and so do I, is because *we* can see that they > > rest on certain assumptions. That is, assumptions that you've > > internalised, and assumptions which me and Ken reject. > > In Seto's case, it has more to do with thinking that SR says something > it does not. I haven't yet figured out whether you are in the same > boat. > The only assumptions I make are those that have testable consequences. > Which ones of those do you think I have that you reject? At least one of the assumptions to which I refer is that observation reflects reality. So if length contraction is observed, it must be "real", but in my view this is as childish as saying you're 12 feet tall simply because you're looking into a curved mirror. As I say, I am quite firmly of the view that SR describes the behaviour of EMR - in other words, it describes what you see with your eyes - and says nothing about physical reality. ____________________________ Well, you are wrong. Perhaps if you studied physics for more than a month ......
From: Ste on 7 Feb 2010 04:05 On 7 Feb, 05:55, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 7, 12:38 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > As I say, I am quite firmly of the view that SR describes the > > behaviour of EMR - in other words, it describes what you see with your > > eyes - and says nothing about physical reality.- Hide quoted text - > > Respond to my post that has the link to my second picture before you > respond to this, but here's something for you to consider. > > Special relativity predicts that an object will undergo length > contraction in its direction of motion. Any observer "at rest" at any > location should observe this length contraction. > > Say that a car drives past you close to the speed of light. You take > a picture exactly at the instant when the center of the car is > directly in front of you. Since the two ends of the car are > equidistant from you, if propagation delay were the only thing going > on, you should not see any sort of length contraction in the > photograph. But SR still predicts that the car should be contracted > in its direction of motion, independant of the location of the > observer. Indeed. I don't totally rule out physical length contraction, but I would require a physical, classical, explanation first. I simply don't accept the argument of "rotation into time".
From: mpalenik on 7 Feb 2010 04:11
On Feb 7, 4:05 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 7 Feb, 05:55, mpalenik <markpale...(a)gmail.com> wrote: > > > > > > > On Feb 7, 12:38 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > As I say, I am quite firmly of the view that SR describes the > > > behaviour of EMR - in other words, it describes what you see with your > > > eyes - and says nothing about physical reality.- Hide quoted text - > > > Respond to my post that has the link to my second picture before you > > respond to this, but here's something for you to consider. > > > Special relativity predicts that an object will undergo length > > contraction in its direction of motion. Any observer "at rest" at any > > location should observe this length contraction. > > > Say that a car drives past you close to the speed of light. You take > > a picture exactly at the instant when the center of the car is > > directly in front of you. Since the two ends of the car are > > equidistant from you, if propagation delay were the only thing going > > on, you should not see any sort of length contraction in the > > photograph. But SR still predicts that the car should be contracted > > in its direction of motion, independant of the location of the > > observer. > > Indeed. I don't totally rule out physical length contraction, but I > would require a physical, classical, explanation first. I simply don't > accept the argument of "rotation into time".- Hide quoted text - > > - Show quoted text - Whether you choose to accept it or not, that is the correct explanation. There is no other physical explanation for what's happening. This is the entire point of the visual exercise that I've posted. It's to get you to see that length contraction is a geometric effect related to rotation. There's no other way to describe it. Can you at least admit that a rotation in time would produce length contraction and the differences in simultanaity described by SR? If so, then the only reason you have to believe that it isn't true is because you don't like it. That's not being scientific at all. |