A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: Ste on 6 Mar 2010 06:58 On 5 Mar, 15:59, PD <thedraperfam...(a)gmail.com> wrote: > On Mar 5, 4:55 am, "Inertial" <relativ...(a)rest.com> wrote: > > > > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > >news:057b5351-82a4-4487-8501-6308451c921a(a)x22g2000yqx.googlegroups.com.... > > > > On 5 Mar, 01:31, "Inertial" <relativ...(a)rest.com> wrote: > > >> "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > >>news:8c0ae071-8d13-491b-92d0-cd2e2727af1a(a)u9g2000yqb.googlegroups.com.... > > > >> > On 4 Mar, 12:19, "Inertial" <relativ...(a)rest.com> wrote: > > >> >> "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > >> >> > Not really, because if the total acceleration is small, then so is > > >> >> > the > > >> >> > speed. > > > >> >> That is a nonsense argument. Acceleration can be small and speeds > > >> >> very > > >> >> large. > > > >> > When I went to school, you could not have a large change of speed with > > >> > only a small amount of total acceleration. > > > >> Then you were badly taught. > > > >> a) if you start at speed 0.8c and acceleration at 0.00001 m/s/s .. then > > >> your > > >> speed is still large. you claimed small acceleration means small speed > > > >> b) if you start at speed 0.0 and acceleration at 0.00001 m/s/s .. then > > >> your > > >> speed after a million years will be quite fast. Yet the acceleration was > > >> small and constant. > > > >> You do realize that you cannot 'total' acceleration. and acceleration of > > >> 1m/s/s followed by an acceleration of 1m/s/s is still an acceleration of > > >> 1m/s/s > > > > In any event, we've resolved the meaning of "total acceleration" - > > > Mark suggests using the concept of "impulse" instead. > > > You certainly are taking the long and painful route (for yourself and us) to > > learn the basics of physics. > > Ste: This is exactly what I was telling you earlier, that people will > be less inclined to teach things on your terms, using your language > and indulging your lack of skills, and will advise you that it is more > efficient in the long run to teach after you've acquired some relevant > skills and vocabulary. You didn't seem to think this was the case, and > here you have others telling you the same thing. Reconsider? As I say Paul, the words "total acceleration" I think should have given people some clue as to the meaning - and indeed the more intelligent amongst us here did recognise the meaning, and suggested an alternative word. That said, in this case I'm happy to use an alternative formulation like "impulse", because I can see that it will add further precision to my meanings in future. It's quite different from the disputes that arose over words like "physical" and "material", where each side seems to battle childishly over whose idiosyncratic understanding of the word will prevail, when the time could be better used getting on with the substantive argument.
From: Peter Webb on 6 Mar 2010 07:26 "Bruce Richmond" <bsr3997(a)my-deja.com> wrote in message news:26e68f86-9827-4534-9390-31137fb9853e(a)q15g2000yqj.googlegroups.com... On Mar 5, 1:04 am, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > > You are reading more into that than what I wrote. I am not choosing > > LET over SR. They use the same math > > ================================================== > > Well, e = mc^2 is maths. It appears in SR, but not LET. > > So I guess you were wrong, and they don't use the same maths. It can be derived using LET. SR wasn't the first place it showed up, so it doesn't own it any more than LET does. Others here say they use the same math, so I guess you are wrong :)~ _________________________________ You said that SR uses the same maths. 1. e=mc^2 is maths 2. It appears in SR 3. It does not appear in LET 4. Therefore the maths in LET is not the same as the maths in SR Which part of this do you disagree with? More generally, you are missing the difference between LET and SR. LET compared to SR is a bit like Kepler's laws of planetary motion compared to Newton's laws of gravity. Mathematically, inverse square laws imply elliptical orbits (and Kepler's equal area formula), and Kepler's laws require inverse square forces for gravity. You could say that Kepler is mathematically identical to Newton for calculating planetary motion, because you could derive the inverse square law purely from Kepler. Just as you can derive time dilation purely from LET. What Newton did, in a sense, is create a model of the solar system which obeys the same physical laws as Kepler, but did so using a completely different starting point and framework. Newton and Kepler predict exactly the same kinds of orbits, but Kepler's laws of planetary movement are not the same as Newton's law of gravity, even though mathematically they produce exactly the same orbits. A very similar relationship exists between SR and LET. SR in a sense "explains" LET, just as Newton "explained" Kepler. Kepler's laws were statements about what is observed, Newton explains why these observations occurred. LET was statements about what was observed, SR explains why these observations occur. When Newton's law of gravity came out, it did not invalidate Kepler, and nor did it even make any new predictions concerning elliptical orbits. It did explain however why Kepler's laws were in a sense correct. Physicists did not say immediately after Newton that Kepler was wrong, or his equations were wrong (and indeed they produce mathematically identical elliptical orbits). Newton just told a whole lot more of the story a lot more clearly, and Newton's laws were immediately taken as more fundamental and useful than Kepler. When SR came out, it did not invalidate LET, and nor did it even make any new predictions concerning time dilation. It did explain however why LET's equations were in a sense correct. Physicists did not say immediately after SR that LET was wrong, or its equations are wrong (and indeed they produce mathematically identical time dilation). SR just told a whole lot more of the story a lot more clearly, and SR was immediately taken as more fundamental and useful than LET. Had Kepler known calculus, he could have worked out that the acceleration of a planet is proportional to the inverse square of the distance, and eventually got Newton's law of gravity, which is implicit in elliptical orbits. He didn't. More to the point, he had no explanation of why his laws held; they were empirical and not theoretical in that they described the results of experiments, but provided no theoretical framework. Similarly, if Lorentz and the others had considered the relationships between energy and momentum in the right way, they would have got e=mc^2. They didn't. More to the point, Lorentz had no explanation of why the various transforms worked, they were empirical and not theoretical in that described the results of experiments, but provided no theoretical framework. You can use LET to calculate time dilation, just as you can use Kepler to calculate orbits. But that doesn't mean that Kepler's theories are the same as Newton's, or that LET is the same as SR. HTH
From: Peter Webb on 6 Mar 2010 07:35 > I think the issue is as I described in "plain English" to Ste. > > Let's take 3 clocks, one (A) which gets left behind, one (B) that > sallies out at speed v for a distance L and returns, and one (C) that > sallies out at speed v for a distance 2L and returns. At speed v, the > clocks sent forth are running slow by, say, 2%. I'm really not going > to worry about the accelerations at all because, as all have said, the > acceleration profiles are all the same. Clock B will arrive back at > home having run slow by 2% for the time of its trip and it is now 2 > hours behind clock A, say. Once B arrives home and comes to rest > alongside A, its rate is no longer slower than A's by 2%, and so while > it sits there and waits for C to come home it will *continue* to be 2 > hours behind A. Finally, C comes home, having run slower than A by 2% > for twice as long as B did, and so it will be 4 hours behind A. Since > B is only 2 hours behind A, clock B and clock C are no longer > synchronized. > > What am I missing? What confuses me is that, if the clocks run slow by 2% for all the time that they are moving, how does one reconcile this with the fact that, if one uses the frame of one of the moving clocks, say clock B, then it seems to be to be your argument that there is no slowdown at all for B, and it is the other clocks, A and C, that slow down (i.e. *disregarding* both acceleration and propagation delays). ________________________________ A, B and C are not equivalent. A stays in one inertial reference frame, B and C do not. You would be well advised to read a standard explanation of the twin's paradox. http://en.wikipedia.org/wiki/Twin_paradox is OK, and if you look at the first few paragraphs of "Resolution of the paradox in Special Relativity" on that page it discusses exactly that point, and explains its significance. http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm is similar.
From: Peter Webb on 6 Mar 2010 07:47 > This should make perfect sense to you. If a clock is running 2% > slower, then it is running 2% slower regardless of distance. But if, > as a result of running 2% slower, it falls behind 6 minutes after > running a certain amount of time, then it will fall behind 12 minutes > after running for twice as long. Agreed. The question now is, if we agree that both clocks suffer time dilation in this way, then when they return to the start point, how do they each reconcile the fact that (after accounting for the effects of acceleration) it ought to be the other clock which is slow, when in fact one clock (the one that went furthest from the start point) will be slower than the other? And a third clock, left at the start point, will be running ahead of both? _________________________ They know that the operations were not symmetric. Only one clock remained in the same inertial reference frame throughout. The other two clocks spent different amounts of time in at least 3 different inertial reference frames. Everybody can see this is true, and so nobody expects that the clocks will remain synchronised. If you really want to understand the twin paradox, read http://en.wikipedia.org/wiki/Twin_paradox and feel free to ask any questions you may have. When you read and understand this, then you will understand what is going on. The question with 3 clocks is not materially different to that for two clocks, and it would be trivial to change their diagrams to also include the third clock. This web page obviously took far more time to put together than you can expect that I or anybody else will provide in newsgroup message, and you are not going to understand the twin paradox until you sit down and go through an explanation similar to this. I note it involves no maths beyond the equations of SR itself (simple algebra). So, why don't you?
From: Peter Webb on 6 Mar 2010 07:56
> > Ste: This is exactly what I was telling you earlier, that people will > be less inclined to teach things on your terms, using your language > and indulging your lack of skills, and will advise you that it is more > efficient in the long run to teach after you've acquired some relevant > skills and vocabulary. You didn't seem to think this was the case, and > here you have others telling you the same thing. Reconsider? As I say Paul, the words "total acceleration" I think should have given people some clue as to the meaning - and indeed the more intelligent amongst us here did recognise the meaning, and suggested an alternative word. That said, in this case I'm happy to use an alternative formulation like "impulse", because I can see that it will add further precision to my meanings in future. ____________________________ http://physics.about.com/od/glossary/g/Impulse.htm It's quite different from the disputes that arose over words like "physical" and "material", where each side seems to battle childishly over whose idiosyncratic understanding of the word will prevail, when the time could be better used getting on with the substantive argument. ________________________________ "Physical" and "material" are words that you introduced that have no real meaning in physics. Impulse, on the other hand, has a very specific meaning in this context; it is integral of Force over time (=Momentum, cf Force over distance which is Energy). Use words like that correctly and you might start understanding SR, because instead of discussing the interpretation of English words you are actually discussing physics. |