Is Length Contraction in SR physical??
in [Relativity]
|
Prev: Simultaneous events and Einstein's absolute time
Next: New Theory --- The Theory of Quantum Wave Sources
From: Peter Webb on 7 Feb 2010 17:49 > 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? No I don't necessarily agree on this part, because it is neither experimentally proven, and nor is there a physical explanation for it. While I retain an open mind in respect of a physical explanation, I am not willing to accept that there is currently a shred of evidence for it. _________________________________ Except of course for the experimental evidence I have already posted twice.
From: Peter Webb on 7 Feb 2010 17:51 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:55e684ae-d818-408f-8f9b-edabe36ed71e(a)d27g2000yqn.googlegroups.com... > On 7 Feb, 08:44, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > wrote: >> "Ste" <ste_ro...(a)hotmail.com> wrote in message >> >> 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 > > I'm afraid I do not see any link to research on that site. You don't think SLAC conduct research, and you couldn't find any on their website? The link I gave you above explains exactly what would happen in SLAC if the length of the accelerator was not foreshortened by SR, ie it wouldn't work. It does work, almost every day.
From: Ste on 7 Feb 2010 21:59 On 7 Feb, 09:39, mpalenik <markpale...(a)gmail.com> wrote: > On Feb 7, 4:34 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 7 Feb, 07:29, mpalenik <markpale...(a)gmail.com> wrote: > > > > 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? > > > Yes I'm happy to accept this. > > > > 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? > > > No I don't necessarily agree on this part, because it is neither > > experimentally proven, and nor is there a physical explanation for it. > > I didn't say anything about experiments. I said, can we agree that we > did not invoke optics, light, or propegation delays to create this > picture? I'm willing to go with this assumption for the purposes of letting you make an argument, but I'm quite sceptical that this "touching" is achievable in practice without the mediation of EMR. > Or if you'd rather--pretend that we live in a universe where > this is the correct description of what is going on. Can you then > admit that in this picture, light, propagation delays, and optics have > nothing to do with the differences in length and simultanaity? You should note my scepticism once you start saying "let's pretend SR is not about light", but as I say I will of course hear your argument out. > But as long as we're on the subject, what is the physical explanation > for 3 dimensional space? If 3 dimensional space doesn't need a > physical explanation, why does 4 dimensional space need one? 3 dimensional geometry does need a physical explanation, and it's very easy to provide one that appeals to our most obvious intuitions. It's also easy to consider "time" as an additional mathematical "dimension", but which has a completely different conceptual basis in the physical world. That is, the philosophy of time is a question for the ages, but it embodies an intuitive aspect of the physical world which is 'change'. > > While I retain an open mind in respect of a physical explanation, I am > > not willing to accept that there is currently a shred of evidence for > > it. > > We have given you plenty of experimental evidence, it's just that > every time somebody makes a post describing experimental evidence, you > conveniently skip over it. There was a post a few pages back (I think > in this thread) where somebody linked to a page on the John Baez > physics FAQ that referenced dozens of papers describing experimental > evidence. I haven't skipped over experimental evidence at all. There's no point just vaguely alluding to unspecified experimental evidence, which I am neither familiar with, nor have access to, and which you do not discuss in the context of my arguments. Indeed, the FAQ to which you refer quotes "At this time there are no direct tests of length contraction, as measuring the length of a moving object to the precision required has not been feasible". It then goes on to point out that there has been an indirect proof of length contraction... mediated by EMR! Certainly, if *you're* familiar with all this experimental evidence, then surely you can either point out where the evidence (not theory) contradicts my hypothesis, or on the other hand concede that the evidence would not discern between existing interpretations and mine.
From: mpalenik on 7 Feb 2010 22:03 On Feb 7, 9:59 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > I haven't skipped over experimental evidence at all. There's no point > just vaguely alluding to unspecified experimental evidence, which I am > neither familiar with, nor have access to, and which you do not > discuss in the context of my arguments. Fine, then I'm not going to discuss anything else further until you understand the experiment that I referred to in the other thread. It is up to you to explain how the result could possibly be achieved in the context of your arguments. It is not up to me to "figure that out" for you (especially when that result cannot be achieved in the context of your arguments).
From: Ste on 7 Feb 2010 22:05
On 7 Feb, 16:03, "papar...(a)gmail.com" <papar...(a)gmail.com> wrote: > On 6 feb, 23:30, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > What part of this picture do you think is optical? It's *geometrical* > > > it doesn't have anything to do with what you can visibly see. > > > Don't you realise that SR is about the behaviour of *light* - that is, > > EMR? And SR describes how *observations* made by way of *light* change > > in response to physical circumstances? > > This is obviously wrong. First because EMR includes radio, infrared, > ultraviolet, x-rays and gamma rays BESIDES visible light. Yes. And didn't I include an explicit qualifier to that effect when I said "light - that is, EMR"? > The fact is that what is relevant is what it is called the maximum > speed of propagation of interactions (that is when something happens > here, after what interval of time the event propagates to the > destination). This maximum speed of propagation of interactions is > equal to the speed of light in vacuum. But this "maximum speed of propagation of interactions" is purely speculative! Once again, the *real* experimental basis for this is that 'c' is the speed of propagation of electromagnetic interactions. > > > The differences in measurement are due to > > > the different coordinate systems. It has nothing to do with what you > > > *see* it has to do with how you make your measurements. > > > It has *everything* to do with what you *see*. > > It has to do with what you *measure* Yes, and we measure virtually everything by way of EMR. > > > When one > > > observer measures length, he measures along the x axis. When another > > > observer measures length, he measures along the x' axis. The proper > > > length of the object doesn't change, but the measured length has > > > nothing to do with optics, visibility, or propagation delays. > > > Of course the measured length has *everything* to do with optics. How > > do you think we usually carry out measurements? > > > And why do you think the ladder appears the correct size for an > > observer in the x' frame? > > Once again wrong. Measurements are performed in all frequencies of the > spectrum (remember radiotelescopes?) Och, are you really so foolish as to think I was using the word "light" to mean only "visible light"? |