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From: Jerry on 6 Mar 2010 09:21
On Mar 6, 6:26 am, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
wrote:

> 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.

An excellent analogy that I've never seen before!!!
I'll remember it.

Jerry
From: kenseto on 6 Mar 2010 09:29
On Mar 5, 12:12 am, "Inertial" <relativ...(a)rest.com> wrote:
> "Bruce Richmond" <bsr3...(a)my-deja.com> wrote in message
>
> news:7806715d-93d2-49ff-ad67-6dac8ea64d8c(a)e7g2000yqf.googlegroups.com...
>
>
>
>
>
> > On Mar 4, 10:48 am, PD <thedraperfam...(a)gmail.com> wrote:
> >> On Mar 3, 10:59 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
>
> >> > On Mar 3, 11:21 am, PD <thedraperfam...(a)gmail.com> wrote:
>
> >> > > On Mar 2, 8:12 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
>
> >> > > > > It is not a function of finite propagation speeds, this we know,
> >> > > > > because we took into account the finite propagation speeds in our
> >> > > > > procedure for determining simultaneity/nonsimultaneity. Do you
> >> > > > > not
> >> > > > > remember that?
>
> >> > > > I beg to differ.  It is not a "mere" or "simple" function of finite
> >> > > > propagation speed, but it *is* a function of it IMO.  RoS only took
> >> > > > it
> >> > > > into account by allowing us to use different time coordinates in
> >> > > > each
> >> > > > frame.  If the speed of light was infinite there would be no RoS.
>
> >> > > I disagree. All that is needed in relativity of simultaneity is a
> >> > > signal speed that can be VERIFIED to be the same from both events by
> >> > > either observer.
>
> >> > Well you are going to have problems with that.  There is no way to
> >> > *know* that the speed is the same both ways.
>
> >> Yes, there is. That's what isotropy experiments have determined. I'm
> >> surprised you weren't aware of this.
>
> > Do you mean like this one?
>
> >http://mysite.verizon.net/cephalobus_alienus/papers/Gagnon_et_al_1988...
>
> > The author is kind enough to point out problems in some similar
> > experiments, while failing to notice any in his own.
>
> > For example, has he made any assumption about contraction of his
> > equipment in the direction of motion?  Tom Roberts has written posts
> > in this group showing where some of these experiments are in effect
> > two way measurements.
>
> >> > That is why Einstein
> >> > wrote, "But it is not possible without further assumption to compare,
> >> > in respect of time, an event at A with an event at B. We have so far
> >> > defined only an ``A time'' and a ``B time.'' We have not defined a
> >> > common ``time'' for A and B, for the latter cannot be defined at all
> >> > unless we establish by definition that the ``time'' required by light
> >> > to travel from A to B equals the ``time'' it requires to travel from B
> >> > to A."
>
> >> > > Since the distance from the events to the observer is
> >> > > equal, as verifiable at any time by each observer, we learn from this
> >> > > that each observer KNOWS the propagation delays from each event to
> >> > > the
> >> > > observer are equal. This acknowledges the propagation delays
> >> > > completely, but simply allows for verification that they are the
> >> > > same.
>
> >> > Assuming the speed of light is the same in both directions.
>
> >> Which is an experimentally confirmed fact. Done well after Einstein's
> >> comments on the matter, by the way.
>
> > Provide a link to an experiment and I'll take a look.
>
> >> > > Then the determination of simultaneity or nonsimultaneity of the
> >> > > original events is completely unambiguous: If the observer receives
> >> > > both signals at the same time, then (because the propagation delays
> >> > > are the same) the original events were simultaneous; if the observer
> >> > > receives both signals at different times, then (because the
> >> > > propagation delays are the same) the original events were
> >> > > nonsimultaneous.
>
> >> > > Then the frame-dependence of simultaneity follows directly from the
> >> > > experimental *observation* that for the same pair of events, one
> >> > > observer correctly and unambiguously concludes the events were
> >> > > simultaneous, and the other observer correctly and unambiguously
> >> > > concludes the events were nonsimultaneous.
>
> >> > > You've mentioned in the past that you found your disbelief in
> >> > > relativity stems from being unable to find a good, understandable
> >> > > explanation of it. I invite you to read back on this thread where I
> >> > > was trying to explain to Ste (who has a similar complaint) how this
> >> > > comes about.
>
> >> > No need.  Lorentz showed how all frames could measure the speed of
> >> > light to be c.  That in effect confirms the second postulate, which is
> >> > the stumbling block for many.
>
> >> Well then, you are just *choosing* what you would like to believe. In
> >> this case, lodging a complaint against relativity that it is not well
> >> explained, when you are not interested in pursuing a better
> >> explanation, having settled on LET instead, is a bit on the
> >> disingenuous side.
>
> > You are reading more into that than what I wrote.  I am not choosing
> > LET over SR.  They use the same math
>
> Yes
>
> > and I consider them two
> > interpertations of the same thing.
>
> Not at all.  Very different as far as how they explain reality
>
> LET has and required a fixed (theoretically undetectable) aether in a fixed
> absolute frame.
> SR does not specify nor require anything about an aether
>
> LET has objects physically compressed due to absolute motion thru the aether
> SR has no absolute motion, so objects are not affected by such motion
>
> LET has processes physically slowed due to absolute motion thru the aether
> SR has no absolute motion, so processes are not affected by such motion
>
> LET has a side-effect of the speed of light being measured as the same in
> all frames of reference, due to measuring with compressed rulers and slowed
> clocks, even though its only really has that speed relative to the aether,
> SR has no absolute compression and slowing, and the speed of light really is
> c
>
> LET has a side-effect of an appearance of the lorentz transforms holding on
> measured values, due to measuring with compressed rulers and slowed clocks.
> SR has no absolute compression and slowing, so the lorentz transform hold
>
> >  The LET interpertation had the
> > advantage, for me, of showing how c + or - v could end up being
> > measured c in all frames.
>
> In SR there is no c+v or c-v, because there is no fixed absolute aether
> frame in which light really travels at c.

Then why did Einstein say that M' is runshing toward the light front
from the front (c+v) and receding away from the light front from the
rear (c-v)??

Ken Seto

>
> >  Given that was possible I no longer had any
> > problem accepting the second postulate.  Eventually I became aware
> > that the second postulate wasn't so much an assumption as a
> > stipulation.  We will consider the speed of light to be our standard.
>
> No .. it is an observed fact.  Not a stipulation
>
> > Recently I have been going back and re-reading some of the books I
> > have bought over the years to see if I can come to grips with some of
> > the modern interpertations of SR.  After thinking about it for awhile
> > I have realized that my objections about the changing definition of c
> > were petty/anal.
>
> :)  Always a good conclusion to reach .. it shows you really are thinking
> and learning and advancing.
>
> >  An analogy would be that there used to be 24 hours
> > in a day, 60 minutes in an hour, and 60 seconds in a minute.  Now we
> > have defined a second as so many transitions of an atom, and can
> > measure the variation in the length of a day.  The new way is better.
> > That it is not in perfect agreement with the old doesn't change much.
> > There was nothing sacred about the old.  So yes, an old dog can be
> > taught new tricks :)
>
> > Bruce
>
> And several points up my estimation ladder for doing so and admitting it
> :):)- Hide quoted text -
>
> - Show quoted text -

From: waldofj on 6 Mar 2010 09:46
> > In SR there is no c+v or c-v, because there is no fixed absolute aether
> > frame in which light really travels at c.
>
> Then why did Einstein say that M' is runshing toward the light front
> from the front (c+v) and receding away from the light front from the
> rear (c-v)??
>
> Ken Seto
that is from the point of view of the observer on the ground and it's
called closing speed (c + v) and separating speed (c - v).
Why is that so difficult to understand?
From: rotchm on 6 Mar 2010 09:48

>LET was statements about what was observed, SR
> explains why these observations occur.

Hmmm, the opposite is generally said.

SR is a math theory which predicts outcomes of observations.
LET is a physical theory, predicting and dynamically explaining the
outcome.

This is often pointed out in the literature and in some scholarly
books on SR.
From: Peter Webb on 6 Mar 2010 10:03

Then why did Einstein say that M' is runshing toward the light front
from the front (c+v) and receding away from the light front from the
rear (c-v)??

____________________________
If you want to know why the expressions c+v and c-v appear in Einstein's
1905 paper, it is because from the viewpoint of some inertial reference
frame then an object moving at v is moving with a relative velocity of v+c
to a light ray travelling in the opposite direction, and similarly for c-v.

A simpler example: We fire two photons in opposite directions. After 1
second, they are 2 light seconds apart, their relative velocity is 2c,
measured in the frame which fired the photons.

HTH



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