Is Length Contraction in SR physical??
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From: Ste on 5 Feb 2010 01:59 On 5 Feb, 05:21, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > "mpalenik" <markpale...(a)gmail.com> wrote in message > > news:354b0737-033a-4c12-a8dc-4e17f4b00974(a)d27g2000yqn.googlegroups.com... > On Feb 4, 10:12 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 5 Feb, 00:27, artful <artful...(a)hotmail.com> wrote: > > > > That you cannot see the analgoy just shows you have NO idea what SR > > > says > > > > Both have a longer length object fitting within a shorter spae > > > > Both have a geometrical rotation and projection > > > > The ladder fits thru the doorway just as 'physically' as a pole fits > > > in the barn. > > > How on Earth do you work that one out? > > > For the analogy to work, the ladder must be constrained lengthwise, > > not widthwise.- Hide quoted text - > > > - Show quoted text - > > This is what we've been trying to get across to you. It has to do > with coordinates and what one observer calls time and space relative > to another. > > The ladder is a little bit too long to fit into the barn but you could > rotate it and still fit it into the barn. Say, for example, you lift > the front end so the ladder is now at a 45 degree angle. You could > now fit it into the barn. You've rotated part of it into "height", > from "length". > > But there's another way you could rotate it, as well. You can rotate > it into "time". If you run with the ladder, you're "rotating" the > front of it a little bit into the future and the back of it a little > bit into the past. > > What a moving observer percieves as "time" is the direction of his > motion through 4 dimensional spacetime. What he percieves as "space" > is the 3 dimensional volume perpendicular to that direction. Thus, > "space" in the moving frame is not the same as "space" in the rest > frame. It extends part way into the future along one direction and > part way into the past along the other (in the rest frame). > > ______________________________________ > > An excellent explanation for somebody familiar with the concept of Minkowski > 4-space. But if Ste was familiar with the concept of Minkowski 4-space, we > wouldn't be having this discussion in the first place. > > But I'm impressed. It's laughable that two people who already claim to understand are patting themselves on the back for coming up with an allegedly "impressive" explantion, and yet the people to whom the concept was to be explained are still not convinced.
From: mpalenik on 5 Feb 2010 02:08 On Feb 5, 1:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 04:31, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 4, 11:22 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > Yes, I'm sure I've employed such a similar wily device when getting a > > > sofa through a doorway before. But we're assuming that the ladder > > > *isn't* rotated. > > > See below. It is rotated not in length and height but in length and > > time. > > It is not "rotated" in any physical sense. > > > > > But there's another way you could rotate it, as well. You can rotate > > > > it into "time". If you run with the ladder, you're "rotating" the > > > > front of it a little bit into the future and the back of it a little > > > > bit into the past. > > > > Haha! I've nearly spat my tea out! I've never heard such a ludicrous > > > statement before I came to sci.physics.relativity! > > > The fact that you find it ridiculous has no bearing on physical > > reality. > > What I do and do not find laughable has *full* bearing on physical > reality. > > > All it demonstrates is that you are not familiar with the > > theory of relativity. > > Then why is it that I seem to be able to understand it so well, even > though I have no idea how to apply it mathematically? > You have repeatedly expressed an incorrect understanding of the theory and refuse to acknowledge it, despite the fact that multiple people, including myself, have explained that your interpretation is flawed. Why you think you understand it "so well" is beyond me. > > > Of course, I understand what you're getting at, although I understand > > > the concept differently. What you're getting at is the effect of > > > propagation delays, > > > No, this has nothing to do with propagation delays. > > What *does* it have to do with then? Bear in mind that a propagation > delay is a *physical* concept. A "rotation in time" is a purely > geometric concept. > > And incidentally, you're not the first person to have said "it has > nothing to do with propagation delay", and yet no one who has said > that has yet described *any* effect (in SR) that is not adequately > explained by propagation delays. If you work through the math, you'll see that the effects I'm describing are *after* propagation delay has been accounted for. It is *not* adequately accounted for by propagation delays. Those must be accounted for *separately*. > > > > whereby both doors can appear to close > > > simultaneously when, in physical reality, the distant door has already > > > started to open before the near door closed. > > > No, the doors close simultaneously in the frame of the barn but NOT in > > the frame of the moving ladder. This is *after* correcting for any > > "propagation delays" in the observation of the two doors. > > I'm afraid I don't accept this. If it is necessary to make the analogy > more complex, then consider this. The ladder has an observer sitting > on each end of the ladder (in addition to the person stood in the > middle of the barn watching the ladder go by). > > The observer at the fore of the ladder naturally sees the front door > close before the back door, and the front door will start to open > again before the back door has even shut. The observer astern of the > ladder sees the back door close before the front. The observer stood > still in the middle of the barn equidistant from each door sees both > doors close simultaneously. No, this is not how special relativity works. You must *first* account for the propagation delays. The observers at the front and rear of the latter, after accounting for propagation delays, will each see the door open and shut at the same time. The relativistic effects have to do with differences measured due to VELOCITY, NOT POSITION. > > Now *of physical necessity*, the observer in the barn who sees the > doors close with the ladder inside, *must* be able to answer our > question. If the ladder is inside the barn, then this observer cannot > *possibly* observe both doors to be shut, unless the ladder is > *wholly* and *physically* inside the barn. > > The question that remains outstanding, is whether the ladder *actually > fits* inside the barn, or whether it crashes before it even gets all > the way into the barn. It fits in the barn in the barn frame, where both ends are in the barn simultaneously. > > > > But that's why Ken wants a simple answer to the *physical reality*, > > > which is why I devised a setup where the doors are equidistant from an > > > observer (and therefore both must truly close simultaneously), > > > This is what you don't understand, in this scenario, they are ONLY > > closing simultaneously in the barn frame. > > Yes, and the observer is *in* the barn frame. > > > To a moving observer (at > > ANY location, even a moving observer located at the center of the > > barn) they do not close simultaneously. *THIS* is what the theory of > > relativity states. > > Bollocks! The doors cannot possibly close simultaneously "for the > barn", unless they also *appear* to close simultaneously for the > stationary observer positioned inside the barn and equidistant from > each door. They DO appear to close simultaneously for the stationary observer at the center of the barn. I have never said otherwise. > > Also, even though this has nothing to do with the analogy as I > presented it, an observer moving along an axis that is always > equidistant from both doors *can* be moving and also observe the doors > to be closing simultaneously. Only if you fail to take into account relativity. Under Newtonian physics, you are correct. Under relativistic physics, you are not. > > > > > > > What a moving observer percieves as "time" is the direction of his > > > > motion through 4 dimensional spacetime. What he percieves as "space" > > > > is the 3 dimensional volume perpendicular to that direction. Thus, > > > > "space" in the moving frame is not the same as "space" in the rest > > > > frame. It extends part way into the future along one direction and > > > > part way into the past along the other (in the rest frame). > > > > Indeed. What's most worrying for me is that I can understand exactly > > > what you're describing, and yet you can't understand what me and Ken > > > are asking. > > > > Incidentally, if you understand the maths of SR (I don't), perhaps you > > > should try testing this one out. Have the observer in the middle of > > > the barn, the doors close simultaneously according to that observer, > > > and the ladder travelling at something just less than the speed of > > > light. Can the observer possibly observe the ladder inside the barn > > > with both doors closed in this situation?- Hide quoted text - > > > This is what the original scenario represents. An observer, at rest > > with respect to the barn, in the center of the barn, sees both doors > > close at the same time with the ladder inside the barn. The person > > running with the ladder does not see them close simultaneously, but > > sees the front and back doors close and open at just the right time > > for him to run through. This is what the math says and is a very > > basic problem that might be given to a student who has just started > > studying relativity. > > Listen, the question isn't what a moving observer would observe. The > question is what the observer stationary inside the barn would > observe. A stationary observer at the center of the barn observes both doors closing simultaneously while the ladder is inside. I have said this before. Despite the fact that your flawed understanding of relativity prohibits this, this is what happens. > > He cannot possibly observe the ladder move into the barn, and then for > the doors to close simultaneously, and the ladder physically fit > inside. If the maths seems to be suggesting this, then you're > misinterpreting the maths. No, you don't understand the math, let alone relativity itself.
From: mpalenik on 5 Feb 2010 02:09 On Feb 5, 1:59 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 05:21, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: > > > > > > > "mpalenik" <markpale...(a)gmail.com> wrote in message > > >news:354b0737-033a-4c12-a8dc-4e17f4b00974(a)d27g2000yqn.googlegroups.com.... > > On Feb 4, 10:12 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 5 Feb, 00:27, artful <artful...(a)hotmail.com> wrote: > > > > > That you cannot see the analgoy just shows you have NO idea what SR > > > > says > > > > > Both have a longer length object fitting within a shorter spae > > > > > Both have a geometrical rotation and projection > > > > > The ladder fits thru the doorway just as 'physically' as a pole fits > > > > in the barn. > > > > How on Earth do you work that one out? > > > > For the analogy to work, the ladder must be constrained lengthwise, > > > not widthwise.- Hide quoted text - > > > > - Show quoted text - > > > This is what we've been trying to get across to you. It has to do > > with coordinates and what one observer calls time and space relative > > to another. > > > The ladder is a little bit too long to fit into the barn but you could > > rotate it and still fit it into the barn. Say, for example, you lift > > the front end so the ladder is now at a 45 degree angle. You could > > now fit it into the barn. You've rotated part of it into "height", > > from "length". > > > But there's another way you could rotate it, as well. You can rotate > > it into "time". If you run with the ladder, you're "rotating" the > > front of it a little bit into the future and the back of it a little > > bit into the past. > > > What a moving observer percieves as "time" is the direction of his > > motion through 4 dimensional spacetime. What he percieves as "space" > > is the 3 dimensional volume perpendicular to that direction. Thus, > > "space" in the moving frame is not the same as "space" in the rest > > frame. It extends part way into the future along one direction and > > part way into the past along the other (in the rest frame). > > > ______________________________________ > > > An excellent explanation for somebody familiar with the concept of Minkowski > > 4-space. But if Ste was familiar with the concept of Minkowski 4-space, we > > wouldn't be having this discussion in the first place. > > > But I'm impressed. > > It's laughable that two people who already claim to understand are > patting themselves on the back for coming up with an allegedly > "impressive" explantion, and yet the people to whom the concept was to > be explained are still not convinced.- Hide quoted text - > > - Show quoted text - Actually, I think his point was that you wouldn't understand my explanation. It looks like he was right.
From: mpalenik on 5 Feb 2010 02:11 On Feb 5, 1:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Feb, 04:31, mpalenik <markpale...(a)gmail.com> wrote: > > > On Feb 4, 11:22 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > Yes, I'm sure I've employed such a similar wily device when getting a > > > sofa through a doorway before. But we're assuming that the ladder > > > *isn't* rotated. > > > See below. It is rotated not in length and height but in length and > > time. > > It is not "rotated" in any physical sense. I missed this in my last reply, but I meant to catch it. Yes, it is rotated in a physical sense, which you would know if you understood Minkowski spacetime. I've tried to explain this to you, but you continually counter with "I don't accept that," as if it were a valid argument.
From: Ste on 5 Feb 2010 02:18
On 5 Feb, 07:11, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 5, 1:55 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 5 Feb, 04:31, mpalenik <markpale...(a)gmail.com> wrote: > > > > On Feb 4, 11:22 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > Yes, I'm sure I've employed such a similar wily device when getting a > > > > sofa through a doorway before. But we're assuming that the ladder > > > > *isn't* rotated. > > > > See below. It is rotated not in length and height but in length and > > > time. > > > It is not "rotated" in any physical sense. > > I missed this in my last reply, but I meant to catch it. Yes, it is > rotated in a physical sense, which you would know if you understood > Minkowski spacetime. I've tried to explain this to you, but you > continually counter with "I don't accept that," as if it were a valid > argument. But, by the same token, all you're saying is "you must accept it". The bottom line is, I don't. As far as I'm concerned, these are geometric effects, not physical effects. But I'm open to any experimental evidence that you may have that you actually understand and can discuss with me. |