Re: The concept of time contractrion in special relativity

From: Androcles (androc1es_at_nospamblueyonder.co.uk)
Date: 06/10/04 

Date: Thu, 10 Jun 2004 23:37:24 GMT

"sal" <believer@nospam.com> wrote in message
news:50ef9dc74a269d66d8c1082c504ef1bd@news.teranews.com...
| Funny -- ever since Pentcho started this thread I've been getting more
| hits on the revolving twins page...
|
| On Tue, 08 Jun 2004 15:30:42 -0700, Pentcho Valev wrote:
|
| > "Dirk Van de moortel" <dirkvandemoortel@ThankS-NO-SperM.hotmail.com>
wrote
| > in message news:<rMmxc.148794$38.7567485@phobos.telenet-ops.be>...
| >
| >> "Pentcho Valev" <pvalev@yahoo.com> wrote in message
| >> news:bdf02d35.0406080907.13e0d289@posting.google.com...
| >
| >> > Excitingly, apart from time dilation, special relativity deals with
| >> > the concept of time contraction in selected cases:
| >> >
| >> >
http://groups.google.com/groups?as_umsgid=c2893ecb.0110042020.64c70626@posting.google.com
| >> >
| >> > http://physicsinsights.org/revolving_twins.html
| >> >
| >> > I tried to imagine this in different light-clock setups but failed. I
| >> > also asked Dirk Vdm to present a small teaching material entitled
| >> > "Time dilation convertible into time contraction when necessary" but
| >> > he seems to have more important work to do.
| >>
| >> Some of that work consists of waiting for an answer to 4 questions I
| >> asked you on some of the 27 threads you have started.
| >>
| >> > Can someone demonstrate
| >> > time contraction by using the standard light clock setup? Or perhaps
| >> > the concept cannot be explained within special relativity?
| >>
| >> It can be explained,
| >
| >
| > Yes it can. Sal has already explained it. Awful term, he said. He will
be
| > more careful with his language from now on. But you don't believe him do
| > you?
|
| Just to reiterate -- not that it's likely to help -- I said the _term_ was
| bad because it's confusing and its meaning is far from self-evident. Does
| "time contraction" suggest that the observed clock rate speeds up or
| slows down? "Contract" means "shrink", which could be taken to mean
| either go faster or go slower.
|
| But I didn't say the effect didn't exist. I didn't even say the effect
| isn't worth understanding.
|
| Rather, I said the effect was already well understood and making a big
| deal out of it or pretending it implies some sort of contradiction is
| making a tempest in a teapot.
|
|
| > Because he has already written
| >
| > Sal: "Somewhere in the orbit, the clocks on ship B must run faster than
| > the clocks on ship A, as viewed from ship A's frame of reference."
|
| Credit where credit is due: Lots of other people said this before I said
| it. As it happens, I first encountered it when Androcles brought it up as
| a challenge (I think he may have called it a "paradox" or
| "contradiction" or some such word like that rather than a "challenge" but
| I'm sure that's what he really meant).
|
|
| > This is not a terminological mistake.
| > You know and sal knows it isn't.
| > This is a statement contradicting the second postulate
|
| No, it contradicts the "first assertion": You assert, first of all, that
| you understand enough math to follow arguments in the realm of special
| relativity. This contradicts that assertion.
|
| > but which, if
| > carefully introduced, saves special relativity by masking the inherent
| > contradiction
|
| No, if carefully introduced it can be used to cloud the water in an
| attempt to mask your confusion about what any of this means.
|
| Read the math, not just the English introduction, you might actually learn
| something.
|
|
| > in the revolving clocks problem. For that reason textbooks
| > avoid this problem.
|
| No, the ones that avoid the revolving clocks problem (certainly, not all
| do), avoid it because it's a mess. Textbook authors, for good reasons,
| prefer examples which are reasonably concise but still illustrate the
| point they're trying to make. This example is not especially concise.
|
| They don't mention "time contraction" simply because the term isn't in
| common use. I have no idea whether common use of the term would cause
| more confusion than it cleared up, but I rather suspect it might.
|
| > It is too dangerous to introduce, even implicitly,
| > time contraction in a theory where time dilation is a basic concept.
| > Only sal does not understand that and introduces time contraction
| > explicitly.
|
| Really, it was Androcles, not me :-) I just explained it, I didn't
| introduce it.
|
| > But, as he sais, he will be more careful from now on. I am
| > sure he will.
|
| Nah, I've changed my mind about that. This is too entertaining -- I
| finally posted something that got an actual discussion going; usually all
| I elicit with my posts are yawns... ;-)
|
| >
| > Pentcho Valev
|
| --
| To email me directly, take out nospam and put back foobox.

I get yawn's too, or just a s*** from Andersen.
I recently posted this one.
According to theory, the little white ball is hiding behind the big red
ball.

Referring to http://www.manybody.org/cgi-bin/starlab/binary_demo.pl
cited by nTaul Andersen, calculate the orbit of Algol.
Empirical data. Round figures:
Period = 70 hours
Eclipse = 10 hours.
That's 1/7 * 360 degrees = 52 degrees
Letting radius = 1 for the larger star, the secondary can be no further than
2 / sin(26 degrees) = 4.56 radii separation. See diagram at
http://www.androc1es.pwp.blueyonder.co.uk/AlgolEclipse.JPG

The calculation according to Andersen must then be:
0.8 days ~ 20 hours for the period, but it is known to be 70 hours.
This implies the separation is greater than 4.56.
If the separation is greater then 4.56, then the eclipse angle will be less
than 52 degrees.
Andersen would calculate the separation as slightly over 11 radii to get the
70 hour period, but that reduces the observed eclipse angle to less than 1/7
of the period.
asin(1/5.6) ~ 10 degrees.
So the eclipse of Algol should be 20*70 /360 about 4 hours, not 10 hours.
But it isn't. How come?
No matter how we try, we cannot reconcile the 10 hour eclipse with
separation distance.

Seems to me that nobody is actually interested in dealing with real data.
Entertainment is better, I suppose.
Androcles.

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