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From: mpalenik on 3 Mar 2010 12:25
On Mar 3, 12:21 pm, mpalenik <markpale...(a)gmail.com> wrote:
> On Mar 3, 12:15 pm, PD <thedraperfam...(a)gmail.com> wrote:
>
>
>
> > On Mar 3, 11:04 am, mpalenik <markpale...(a)gmail.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. 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.
> > > > 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.
>
> > > Ste, there is a very easy thought experiment that I posted a few pages
> > > back that proves this wrong.  Get someone to run through it with you.
> > > I don't have the patience or time.  Even if a moving observer receives
> > > two pulses at the same time while half way between the two sources, he
> > > will conclude that they were not emitted at the same time BECAUSE the
> > > speed of light is the same in every frame.  If the speed of light were
> > > different in the moving observer's frame (like it is with sound), you
> > > would be correct.  But since the speed of light is the same in the
> > > moving observer's frame as in the rest frame, he has no choice but to
> > > conclude that the two pulses were emitted at different times, despite
> > > the fact that he receives them at the same time and he is half way
> > > between the two emitters.
>
> > ???
>
> I'll post it again:
>
> ------x-----
>
>       ^
>
> ------x-----
>
> An object, indicated by the "^" is moving vertically along the
> screen.  The two x's send out light pulses simultaneously in the rest
> frame that both reach the moving ^ when it is exactly half way between
> the two x's.
>
> Because of this, the ^ will recieve both pulses simultaneously in
> every frame--however, in the ^ frame, the observer will say that the
> two x's did not emmit the light pulse simultaneously, even though he
> recieved both pulses simultaneously.
>
> This proves that SR has nothing to do with correcting for propagation
> delays.  I don't have the time or patience to explain this to Ste, but
> I'm sure it's easily comprehensible to everyone else.
>
> (PD: note that since it's the x's moving in the ^ frame, and since the
> light is emitted when the lower x is closer to the ^ and the upper x
> is farther, the moving ^ must conclude that the light from the upper x
> was emitted first, even though both pulses hit him at the same time.
> This is because the light is moving at speed c in his frame and not c
> +v and c-v.  This probably isn't clear to Ste, but I think you see
> what I'm going for)

Oops, I realized just now that I wasn't responding to the post that I
thought I was. Hang on a second--that wasn't meant as a reply to your
post.
From: waldofj on 3 Mar 2010 12:25
> > 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.
What are disagreeing with? The LTE's make it clear that if C goes to
infinity RoS vanishes. Look at the equation for time
t' = (t - vx/c^2) * gamma
it is the vx/c^2 term that introduces RoS (i.e. the tilt of the x'
axis on a spacetime diagram)
If c goes to infinity this term vanishes and along with it RoS. Also
gamma goes to 1 and the LT reduces to the GT
It seems to me that any physical scenario one comes up with to
describe this must come to the same conclusion. Don't you think?
btw, I'm just jumping into this thread now, if all this has been said
before
DOH!
From: mpalenik on 3 Mar 2010 12:31
On Mar 3, 12:25 pm, mpalenik <markpale...(a)gmail.com> wrote:
> On Mar 3, 12:21 pm, mpalenik <markpale...(a)gmail.com> wrote:
>
>
>
> > On Mar 3, 12:15 pm, PD <thedraperfam...(a)gmail.com> wrote:
>
> > > On Mar 3, 11:04 am, mpalenik <markpale...(a)gmail.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. 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.
> > > > > 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.
>
> > > > Ste, there is a very easy thought experiment that I posted a few pages
> > > > back that proves this wrong.  Get someone to run through it with you.
> > > > I don't have the patience or time.  Even if a moving observer receives
> > > > two pulses at the same time while half way between the two sources, he
> > > > will conclude that they were not emitted at the same time BECAUSE the
> > > > speed of light is the same in every frame.  If the speed of light were
> > > > different in the moving observer's frame (like it is with sound), you
> > > > would be correct.  But since the speed of light is the same in the
> > > > moving observer's frame as in the rest frame, he has no choice but to
> > > > conclude that the two pulses were emitted at different times, despite
> > > > the fact that he receives them at the same time and he is half way
> > > > between the two emitters.
>
> > > ???
>
> > I'll post it again:
>
> > ------x-----
>
> >       ^
>
> > ------x-----
>
> > An object, indicated by the "^" is moving vertically along the
> > screen.  The two x's send out light pulses simultaneously in the rest
> > frame that both reach the moving ^ when it is exactly half way between
> > the two x's.
>
> > Because of this, the ^ will recieve both pulses simultaneously in
> > every frame--however, in the ^ frame, the observer will say that the
> > two x's did not emmit the light pulse simultaneously, even though he
> > recieved both pulses simultaneously.
>
> > This proves that SR has nothing to do with correcting for propagation
> > delays.  I don't have the time or patience to explain this to Ste, but
> > I'm sure it's easily comprehensible to everyone else.
>
> > (PD: note that since it's the x's moving in the ^ frame, and since the
> > light is emitted when the lower x is closer to the ^ and the upper x
> > is farther, the moving ^ must conclude that the light from the upper x
> > was emitted first, even though both pulses hit him at the same time.
> > This is because the light is moving at speed c in his frame and not c
> > +v and c-v.  This probably isn't clear to Ste, but I think you see
> > what I'm going for)
>
> Oops, I realized just now that I wasn't responding to the post that I
> thought I was.  Hang on a second--that wasn't meant as a reply to your
> post.

I had temporarily switched to tree view when I responded to that
message because I was looking for another message and I thought I
might be able to find it better that way. I had actually meant to
respond to something Ste posted, but I can't find it now. I must have
accidentally clicked on your message before hitting reply. I think it
was just a couple messages up in the same branch of the tree as what
you responded to, PD.
From: Ste on 3 Mar 2010 12:52
On 3 Mar, 12:30, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
wrote:
> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> >> You say you are here to learn about SR.
>
> > I am here to learn more about the *conceptual basis* of SR.
>
> Minkowksi space time?

No.


> >> Do you believe SR is true?
>
> > I accept it's mathematical form has some obvious truth, yes.
>
> Do you believe that it correctly predicts the results of every experiment
> that it claims to? That clocks run slower,

No. In SR, clocks *appear* to run slower as you are increasing your
distance from the clock. The effect is entirely apparent in SR.



> and 80 foot ladders can fit through 40 feet barns,

It remains slightly unclear, but I'm inclined to say no, although it
can certainly be made to appear to happen in certain circumstances.



> and that the speed of light is measured the same in
> every intertial frame of reference and this speed is independent of the
> speed of the emitter, receiver, and underlying medium of transmission?

Yes. I think I've been able to reconcile this partially, but only
vaguely and within a definitely non-standard conceptual framework, and
it is forced to completely dispense with any corpuscular form of
matter, and instead relies wholly on fields. Unfortunately it's
probably the sort of thing that physicists spend their lives thinking
about and never quite put their finger on.



> If you believe all of those things, then you are saying more than "SR has
> some obvious truths in its mathematical form" you are saying it is an
> accurate portrayal of reality - ie, what happens when you conduct those
> experiments, what physically and actually happens, is exactly as predicted
> by Relativity.

I think we all agree that SR portrays reality, but none of us seem to
be able to agree on what kind of reality it portrays.



> If, on the other hand, you do not believe in the twin "paradox" actually
> happening, you don't believe in SR.

We resolved the twins paradox months ago. The astronaut twin undergoes
asymmetrical acceleration, and that is why he returns younger.



> If you do believe the predictions of SR
> that one twin is older, then you believe that time dilation is more than
> some mathematical fiction, its what actually happens in the real world.

On the contrary. The involvement of acceleration, which is the domain
of GR, makes me wonder why this is held to be a paradox in SR at all.
And yes, the acceleration causes real effects for the astronaut twin.



> So, when relativity predicts that one twin will age more than the other, is
> this just some mathematical truth, or is it what really happens as well?

It really happens, due to acceleration.



> So, do you believe that SR is correct in its prediction (for example) that
> if one twin were to be sent off into space at 0.9c for 10 years they would
> have aged less on their return than the twin that stayed at home?

I'm not sure SR does predict this. As I understand it, GR is required
to predict this effect. The problem for SR was, as I understand it,
explaining why SR *doesn't* predict that effect.



> Do you agree its correct when it says that an 80 foot ladder could fit
> inside a 40 foot barn?

No, I'm not confident about that prediction. I think it's more likely
to be an apparent effect.



> You seem to agree they are "mathematical truths". Do you also agree those
> equations correctly predict the outcomes of real world experiments, which
> means they are far more than simply "mathematical truths"?

The question is of interpreting the mathematical predictions. As I say
above, there is a difference between what is real and what is merely
apparent.
From: Ste on 3 Mar 2010 13:23
On 3 Mar, 12:40, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
wrote:
> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> news:899e0123-23bd-47d9-b8d6-d32f3a59e32b(a)g10g2000yqh.googlegroups.com...
>
>
>
>
>
> > On 3 Mar, 02:15, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> > wrote:
> >> Next, what is the fundamental cause (confining ourselves to SR) of
> >> this non-simultaneity? As I say, as far as I can tell, it's a simple
> >> function of the finite speed of propagation. But I'm told that it
> >> isn't, so I need to know on what grounds a simple propagation
> >> explanation does not suffice.
>
> >> ________________________________
> >> Hey! You asked a question about SR ! Far out!
>
> >> The ultimate reason (or, more accurately "an" ultimate reason) is that
> >> the
> >> speed of light is the same in all inertial reference frames, and does not
> >> depend on the speeds of two different observers. This makes the
> >> propagation
> >> delay a function of the frame of reference you pick, and not a function
> >> of
> >> the underlying dynamics.
>
> > I won't pretend to understand how this is supposedly not a function of
> > the speed of propagation.
>
> Try and express your question more clearly.
>
> What is it that you don't understand? You can't understand why what exactly
> is not a function of the speed of propagation of what, exactly?

Because, as far as I can tell, accounting for the relative distance
between sender and receiver (and any changes in that distance) appears
to fully account for the observed effects of SR.
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