A constant speed of light in all reference frames? Surely you can't be serious. [Physics]

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From: BURT on 10 Mar 2010 18:34

On Mar 10, 3:30 pm, BURT <macromi...(a)yahoo.com> wrote:
> On Mar 9, 9:01 pm, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> wrote:
>
>
>
>
>
> > > I'm sorry about these questions but, what does privileged mean?
>
> > > _______________________________
> > > Somehow better than the others. Special in some sense. For example, the
> > > reference frame of the ether is privleged because it is the only reference
> > > frame where lengths and times are "correct".
>
> > > There
> > > is certainly physical consequences of the medium (such as field
> > > profile alterations due to motion) but there is certainly nothing
> > > priveleged as in having different properties about it.
>
> > > _____________________________
> > > It is privileged; it is the unique reference frame for which the real
> > > length
> > > is the same as the measured length. Or so I understand it; as I said, I
> > > don't actually believe it exists at all.
>
> > Real length??? What makes length real?
>
> Distances across round atoms reveal atomic size that does not vary.
>
> Mitch Raemsch
>
>
>
>
>
> > ___________________________
> > Ask the people who believe in the ether. It's their concept.
> > BTW, you asked for a definition of a "privileged reference frame". I posted
> > a not very good one. But this is a standard term in physics, not for me to
> > define. Googling it gives 150,000 hits, and the very first onehttp://en..wikipedia.org/wiki/Preferred_frameexplainsit exactly in this
> > context opf SR. Should have done this in the first place.- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

There are 4 electron shells that determine the four fundamental sizes
of the atom. If they are not round there would be different
fundamental sizes by the fact of being lopsided.

Mitch Raemsch

From: Bruce Richmond on 10 Mar 2010 19:45

On Mar 10, 9:36 am, mpc755 <mpc...(a)gmail.com> wrote:
> On Mar 10, 8:05 am, "Inertial" <relativ...(a)rest.com> wrote:
>
>
>
>
>
> > "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in message
>
> >news:4b970c19$0$8039$afc38c87(a)news.optusnet.com.au...
>
> > > I know I still have a long way to go but my goal here is to truely
> > > understand SR, not to just parrot explainations. LET helped me see
> > > that the math of SR is correct, but I also realize it has become a
> > > hiderence in understanding SR.
>
> > > ________________________________
> > > Good. There is one key insight which makes the jump from LET to SR a
> > > little easier (in my opinion).
>
> > > For all the talk of relative motion against the ether in LET, the
> > > equations work out exactly the same whatever you choose as the rest frame
> > > of the ether. So the actual rest frame of the ether cannot be detected
> > > within LET.
>
> > That's right. That's what Dono doesn't get.
>
> > > Its only a small hop, skip and jump from saying that "it cannot be
> > > detected" to "it doesn't exist".
>
> > Or at least 'it doesn't matter'.
>
> > Once you go beyond just the aether frame, and relating frames directly to
> > it, LET becomes more of a hinderance than a help
>
> > LET tells you (for instance) that even though objects at rest in frame A may
> > be more length compressed and time slowed than those in frame B (where A
> > moves faster in the aether frame than B) .. yet A will see objects at rest
> > in B as being more contracted and time dilated than its own. Which really
> > confuses those who use the simple 'motion in the aether shrinks and slows
> > things' idea of LET as a way to 'understand' into a spin. You end up with a
> > strange combination of real compression and apparent contraction, real
> > slowing and apparent time dilaton. Its not really helpful :):)
>
> It is helpful in that it gets 'us' closer to understanding what occurs
> to objects as they move with respect to the aether.
>
> The issue with LET is everything is relative.
>
> For example, "the state of the [ether] is at every place determined by
> connections with the matter and the state of the ether in neighbouring
> places" - Albert Einstein.

You like Einstein quotes about the ether so try this one:

http://www-groups.dcs.st-and.ac.uk/~history/Extras/Einstein_ether.html

"We may assume the existence of an ether; only we must give up
ascribing a definite state of motion to it" - Albert Einstein.

> This means the aether is more at rest with
> respect to the embankment than it is with respect to the train. The
> train is moving relative to the aether so it will be length contracted
> while the embankment will not. The ruler the Observer on the
> embankment uses to measure the length of the train is not length
> contracted. The ruler the Observer on the train uses to measure the
> length of the embankment is length contracted. The Observer on the
> embankment and the Observer on the train conclude the embankment is
> longer than the train.
>
> The same holds true for the clocks on the train and on the embankment.
> Since the train is moving relative to the aether while the embankment
> is more at rest with respect to the aether there will be a greater
> pressure associated with the aether on the clock on the train causing
> it to tick slower. If the Observers on the embankment and on the train
> where able to 'see' each others clocks as the M and M' pass each other
> both the Observer on the train and the Observer on the embankment
> would conclude the clock on the train ticks slower than the clock on
> the embankment.- Hide quoted text -
>
> - Show quoted text -

According to both SR and LET there is no experiment that can reveal
which frame is at rest WRT the ether, so there is no way to know which
frame is more at rest WRT the ether.

From: mpc755 on 10 Mar 2010 20:00

On Mar 10, 7:45 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
> On Mar 10, 9:36 am, mpc755 <mpc...(a)gmail.com> wrote:
>
>
>
> > On Mar 10, 8:05 am, "Inertial" <relativ...(a)rest.com> wrote:
>
> > > "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in message
>
> > >news:4b970c19$0$8039$afc38c87(a)news.optusnet.com.au...
>
> > > > I know I still have a long way to go but my goal here is to truely
> > > > understand SR, not to just parrot explainations. LET helped me see
> > > > that the math of SR is correct, but I also realize it has become a
> > > > hiderence in understanding SR.
>
> > > > ________________________________
> > > > Good. There is one key insight which makes the jump from LET to SR a
> > > > little easier (in my opinion).
>
> > > > For all the talk of relative motion against the ether in LET, the
> > > > equations work out exactly the same whatever you choose as the rest frame
> > > > of the ether. So the actual rest frame of the ether cannot be detected
> > > > within LET.
>
> > > That's right. That's what Dono doesn't get.
>
> > > > Its only a small hop, skip and jump from saying that "it cannot be
> > > > detected" to "it doesn't exist".
>
> > > Or at least 'it doesn't matter'.
>
> > > Once you go beyond just the aether frame, and relating frames directly to
> > > it, LET becomes more of a hinderance than a help
>
> > > LET tells you (for instance) that even though objects at rest in frame A may
> > > be more length compressed and time slowed than those in frame B (where A
> > > moves faster in the aether frame than B) .. yet A will see objects at rest
> > > in B as being more contracted and time dilated than its own. Which really
> > > confuses those who use the simple 'motion in the aether shrinks and slows
> > > things' idea of LET as a way to 'understand' into a spin. You end up with a
> > > strange combination of real compression and apparent contraction, real
> > > slowing and apparent time dilaton. Its not really helpful :):)
>
> > It is helpful in that it gets 'us' closer to understanding what occurs
> > to objects as they move with respect to the aether.
>
> > The issue with LET is everything is relative.
>
> > For example, "the state of the [ether] is at every place determined by
> > connections with the matter and the state of the ether in neighbouring
> > places" - Albert Einstein.
>
> You like Einstein quotes about the ether so try this one:
>
> http://www-groups.dcs.st-and.ac.uk/~history/Extras/Einstein_ether.html
>
> "We may assume the existence of an ether; only we must give up
> ascribing a definite state of motion to it" - Albert Einstein.
>

To make a post such as yours without a definition of what Einstein
means by 'motion' shows how little you know.

"If the existence of such floats for tracking the motion of the
particles of a fluid were a fundamental impossibility in physics - if,
in fact nothing else whatever were observable than the shape of the
space occupied by the water as it varies in time, we should have no
ground for the assumption that water consists of movable particles.
But all the same we could characterise it as a medium."

"[extended physical objects to which the idea of motion cannot be
applied] may not be thought of as consisting of particles which allow
themselves to be separately tracked through time."

"The special theory of relativity forbids us to assume the ether to
consist of particles observable through time, but the hypothesis of
ether in itself is not in conflict with the special theory of
relativity. Only we must be on our guard against ascribing a state of
motion to the ether."

"But this ether may not be thought of as endowed with the quality
characteristic of ponderable media, as consisting of parts which may
be tracked through time. The idea of motion may not be applied to it."

Once you are willing to understand how Einstein defined motion, as
particles which can be separately tracked through time, maybe you can
advance from your state of being an ignoramus.

p.s. You still haven't answered how it is the train is length
contacted because it is moving relative to the aether and the
embankment is more at rest with respect to the embankment but at the
same time LET has everything being relative. The answer is both the
Observer at M and the Observer at M' will determine the train to be
length contracted and for the clocks on the train to be ticking slower
than the clocks on the embankment.

It is one thing having to deal with the QM delusional denial posters
on this forum and it is something entirely different having to deal
with the likes of you.

Once you realize in the earth frame of reference the aether is more at
rest with respect to the embankment than it is to the train you can
respond to my posts, until then, don't waste my time.

>
>
> > This means the aether is more at rest with
> > respect to the embankment than it is with respect to the train. The
> > train is moving relative to the aether so it will be length contracted
> > while the embankment will not. The ruler the Observer on the
> > embankment uses to measure the length of the train is not length
> > contracted. The ruler the Observer on the train uses to measure the
> > length of the embankment is length contracted. The Observer on the
> > embankment and the Observer on the train conclude the embankment is
> > longer than the train.
>
> > The same holds true for the clocks on the train and on the embankment.
> > Since the train is moving relative to the aether while the embankment
> > is more at rest with respect to the aether there will be a greater
> > pressure associated with the aether on the clock on the train causing
> > it to tick slower. If the Observers on the embankment and on the train
> > where able to 'see' each others clocks as the M and M' pass each other
> > both the Observer on the train and the Observer on the embankment
> > would conclude the clock on the train ticks slower than the clock on
> > the embankment.- Hide quoted text -
>
> > - Show quoted text -
>
> According to both SR and LET there is no experiment that can reveal
> which frame is at rest WRT the ether, so there is no way to know which
> frame is more at rest WRT the ether.

From: mpc755 on 10 Mar 2010 20:10

On Mar 10, 7:45 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
> On Mar 10, 9:36 am, mpc755 <mpc...(a)gmail.com> wrote:
>
>
>
> > On Mar 10, 8:05 am, "Inertial" <relativ...(a)rest.com> wrote:
>
> > > "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in message
>
> > >news:4b970c19$0$8039$afc38c87(a)news.optusnet.com.au...
>
> > > > I know I still have a long way to go but my goal here is to truely
> > > > understand SR, not to just parrot explainations. LET helped me see
> > > > that the math of SR is correct, but I also realize it has become a
> > > > hiderence in understanding SR.
>
> > > > ________________________________
> > > > Good. There is one key insight which makes the jump from LET to SR a
> > > > little easier (in my opinion).
>
> > > > For all the talk of relative motion against the ether in LET, the
> > > > equations work out exactly the same whatever you choose as the rest frame
> > > > of the ether. So the actual rest frame of the ether cannot be detected
> > > > within LET.
>
> > > That's right. That's what Dono doesn't get.
>
> > > > Its only a small hop, skip and jump from saying that "it cannot be
> > > > detected" to "it doesn't exist".
>
> > > Or at least 'it doesn't matter'.
>
> > > Once you go beyond just the aether frame, and relating frames directly to
> > > it, LET becomes more of a hinderance than a help
>
> > > LET tells you (for instance) that even though objects at rest in frame A may
> > > be more length compressed and time slowed than those in frame B (where A
> > > moves faster in the aether frame than B) .. yet A will see objects at rest
> > > in B as being more contracted and time dilated than its own. Which really
> > > confuses those who use the simple 'motion in the aether shrinks and slows
> > > things' idea of LET as a way to 'understand' into a spin. You end up with a
> > > strange combination of real compression and apparent contraction, real
> > > slowing and apparent time dilaton. Its not really helpful :):)
>
> > It is helpful in that it gets 'us' closer to understanding what occurs
> > to objects as they move with respect to the aether.
>
> > The issue with LET is everything is relative.
>
> > For example, "the state of the [ether] is at every place determined by
> > connections with the matter and the state of the ether in neighbouring
> > places" - Albert Einstein.
>
> You like Einstein quotes about the ether so try this one:
>
> http://www-groups.dcs.st-and.ac.uk/~history/Extras/Einstein_ether.html
>
> "We may assume the existence of an ether; only we must give up
> ascribing a definite state of motion to it" - Albert Einstein.
>

"If the existence of such floats for tracking the motion of the
particles of a fluid were a fundamental impossibility in physics - if,
in fact nothing else whatever were observable than the shape of the
space occupied by the water as it varies in time, we should have no
ground for the assumption that water consists of movable particles.
But all the same we could characterise it as a medium."

"[extended physical objects to which the idea of motion cannot be
applied] may not be thought of as consisting of particles which allow
themselves to be separately tracked through time."

"The special theory of relativity forbids us to assume the ether to
consist of particles observable through time, but the hypothesis of
ether in itself is not in conflict with the special theory of
relativity. Only we must be on our guard against ascribing a state of
motion to the ether."

"But this ether may not be thought of as endowed with the quality
characteristic of ponderable media, as consisting of parts which may
be tracked through time. The idea of motion may not be applied to it."

Once you are willing to understand how Einstein defined motion, as
particles which can be separately tracked through time, maybe you can
advance from your statement.

p.s. You still haven't answered how it is the train is length
contacted because it is moving relative to the aether and the
embankment is more at rest with respect to the embankment but at the
same time LET has everything being relative. The answer is both the
Observer at M and the Observer at M' will determine the train to be
length contracted and for the clocks on the train to be ticking slower
than the clocks on the embankment.

>
>
> > This means the aether is more at rest with
> > respect to the embankment than it is with respect to the train. The
> > train is moving relative to the aether so it will be length contracted
> > while the embankment will not. The ruler the Observer on the
> > embankment uses to measure the length of the train is not length
> > contracted. The ruler the Observer on the train uses to measure the
> > length of the embankment is length contracted. The Observer on the
> > embankment and the Observer on the train conclude the embankment is
> > longer than the train.
>
> > The same holds true for the clocks on the train and on the embankment.
> > Since the train is moving relative to the aether while the embankment
> > is more at rest with respect to the aether there will be a greater
> > pressure associated with the aether on the clock on the train causing
> > it to tick slower. If the Observers on the embankment and on the train
> > where able to 'see' each others clocks as the M and M' pass each other
> > both the Observer on the train and the Observer on the embankment
> > would conclude the clock on the train ticks slower than the clock on
> > the embankment.- Hide quoted text -
>
> > - Show quoted text -
>
> According to both SR and LET there is no experiment that can reveal
> which frame is at rest WRT the ether, so there is no way to know which
> frame is more at rest WRT the ether.

The clock which ticks the fastest is most at rest with respect to the
aether.

From: Bruce Richmond on 10 Mar 2010 20:12

On Mar 10, 10:50 am, PD <thedraperfam...(a)gmail.com> wrote:
> On Mar 9, 7:58 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
>
> > On Mar 9, 9:31 am, PD <thedraperfam...(a)gmail.com> wrote:
>
> > > On Mar 8, 11:53 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
>
> > > > On Mar 8, 1:58 am, "Inertial" <relativ...(a)rest.com> wrote:
>
> > > > > "Bruce Richmond" <bsr3...(a)my-deja.com> wrote in message
>
> > > > >news:29fd9f7d-c9b4-41e6-b33a-585c3e0e7acf(a)q23g2000yqd.googlegroups..com...
>
> > > > > > On Mar 7, 9:48 pm, "Inertial" <relativ...(a)rest.com> wrote:
> > > > > >> "Bruce Richmond" <bsr3...(a)my-deja.com> wrote in message
>
> > > > > >>news:1c6a2640-39f5-4ea4-9c85-127e71f4e6a2(a)33g2000yqj.googlegroups.com...
>
> > > > > >> > On Mar 7, 6:58 pm, "Inertial" <relativ...(a)rest.com> wrote:
> > > > > >> >> "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in message
>
> > > > > >> >>news:4b943853$0$11336$afc38c87(a)news.optusnet.com.au...
>
> > > > > >> >> > "Inertial" <relativ...(a)rest.com> wrote in message
> > > > > >> >> >news:4b942bcf$0$27789$c3e8da3(a)news.astraweb.com...
> > > > > >> >> >> "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote in
> > > > > >> >> >> message
> > > > > >> >> >>news:4b93bf73$0$28464$afc38c87(a)news.optusnet.com.au...
>
> > > > > >> >> >>>>> 1) your statement: "For clarity, both effects are purely
> > > > > >> >> >>>>> observational - SR presumes (ideal) clock mechanisms are
> > > > > >> >> >>>>> completely
> > > > > >> >> >>>>> unaffected by a clock's motion." -- I agree the physical
> > > > > >> >> >>>>> mechanism
> > > > > >> >> >>>>> of
> > > > > >> >> >>>>> the clock is unaffected, but this is a really misleading
> > > > > >> >> >>>>> statement,
> > > > > >> >> >>>>> since the amount of proper time that the clock consumes is
> > > > > >> >> >>>>> affected
> > > > > >> >> >>>>> by
> > > > > >> >> >>>>> its motion. Are you trying to say
>
> > > > > >> >> >>>> I was "trying to say" exactly what I did say. If you didn't find
> > > > > >> >> >>>> it
> > > > > >> >> >>>> clear enough, try this: relative slow-downs/speed-ups observed in
> > > > > >> >> >>>> the
> > > > > >> >> >>>> readings of SR's ideal clocks aren't due to changes in the tick
> > > > > >> >> >>>> mechanisms of those clocks.
>
> > > > > >> >> >>> I still don't find it clear, as it begs the question - it says
> > > > > >> >> >>> what
> > > > > >> >> >>> doesn't cause the change, not what does cause the change.
>
> > > > > >> >> >>> The standard SR answer is much more direct - the clocks slow down
> > > > > >> >> >>> due
> > > > > >> >> >>> to
> > > > > >> >> >>> relativistic time dilatation from them being in different
> > > > > >> >> >>> reference
> > > > > >> >> >>> frames.
>
> > > > > >> >> >>> Is that standard position of SR also your position? Or is your
> > > > > >> >> >>> somehow
> > > > > >> >> >>> different?
>
> > > > > >> >> >> SR says that the difference in clock sync (clock settings) cause
> > > > > >> >> >> the
> > > > > >> >> >> measurement of length to be contracted and measurement of clock
> > > > > >> >> >> ticking
> > > > > >> >> >> rates to be dilated.
>
> > > > > >> >> > More or less.
>
> > > > > >> >> That's what it is :)
>
> > > > > >> >> > But I asked you about *your* position, not SR's position.
>
> > > > > >> >> My position is SR's position
>
> > > > > >> >> > Do you agree that that the clocks slow down due to relativistic time
> > > > > >> >> > dilation, as predicted by SR, or not?
>
> > > > > >> >> They are measured as slower, just as a rod is measured as shorter.
> > > > > >> >> This
> > > > > >> >> is
> > > > > >> >> due to the difference in simultaneity. They don't slow down because a
> > > > > >> >> moving observer is looking at them any more than a rod shrinks because
> > > > > >> >> a
> > > > > >> >> relatively moving observer is looking at it.
>
> > > > > >> >> Here's a little example you might follow .. with time differences
> > > > > >> >> exagerated
> > > > > >> >> for clarity
>
> > > > > >> >> Here are six clocks, in tow rows (S and S'), all ticking at the
> > > > > >> >> correct
> > > > > >> >> rate, but set with different times...
>
> > > > > >> >> S' 10:30 11:00=A 11:30 <--v
> > > > > >> >> S 11:30=C 11:00=B 10:30 -->v
>
> > > > > >> >> Clocks B sees the A is synchronized with it.
>
> > > > > >> >> Now .. the clocks are moving in opposite directions so after an hour
> > > > > >> >> we
> > > > > >> >> have
>
> > > > > >> >> S' 11:30 12:00=A 12:30
> > > > > >> >> S 12:30=C 12:00=B 11:30
>
> > > > > >> >> Clock A has moved away from clock B .. but another clock (C) in S can
> > > > > >> >> see
> > > > > >> >> the time on it. Clock C sees that clock A is half an hour slow (A
> > > > > >> >> shows
> > > > > >> >> 12:00 when C shows 12:30). So according to the clocks in S, clock A
> > > > > >> >> is
> > > > > >> >> ticking slower. We also note that clock B now sees a *different* S'
> > > > > >> >> clock
> > > > > >> >> next to it as being fast (it shows 12:30 when B shows 12:00)
>
> > > > > >> >> If you look at the same scenario but from the point of view of the
> > > > > >> >> other
> > > > > >> >> row
> > > > > >> >> of clocks, you get symmetric results.
>
> > > > > >> >> This is how clock synch affects measured ticking rates for moving
> > > > > >> >> clocks
> > > > > >> >> in
> > > > > >> >> SR. Even though the clocks themselves do NOT change their intrinsic
> > > > > >> >> ticking
> > > > > >> >> rates.- Hide quoted text -
>
> > > > > >> > Looks good, but let's take it one step further. The observer with
> > > > > >> > clock A jumps to frame S" which is traveling in the same direction as
> > > > > >> > S relative to S' but at twice the velocity.
>
> > > > > >> > S" 1:00 12:00=A 11:00 -->2v
> > > > > >> > S' 11:30 12:00=A 12:30 <--v
> > > > > >> > S 12:30=C 12:00=B 11:30 -->v
>
> > > > > >> > Clocks A and B continue to tick at there same intrinsic ticking rate
> > > > > >> > and an hour later A has overtaken B.
>
> > > > > >> > S" 2:00 1:00=A 12:00 -->2v
> > > > > >> > S' 12:30 1:00=A 1:30 <--v
> > > > > >> > S 1:30=C 1:00=B 12:30 -->v
>
> > > > > >> > The above provides the same situation as the twins paradox. Clock A
> > > > > >> > left clock B and returned. So why doesn't clock A show less time
> > > > > >> > elapsed than B? (Note the clocks in S" are further out of sync than
> > > > > >> > those in S due to the higher velocity.)
>
> > > > > >> The three clock situation cannot be so easily drawn .. bit like trying to
> > > > > >> drawing a three dimensional figure in 2d :) This sort of diagram only
> > > > > >> really works for a single pair of clocks looking from a third frame in
> > > > > >> which
> > > > > >> they move with the same speed. Things are trickier when there is frame
> > > > > >> jumping going on :):)- Hide quoted text -
>
> > > > > >> - Show quoted text -
>
> > > > > > The question still remains, if there is no change in the tick rate of
> > > > > > the clock, how can clock A have fewer ticks recorded when it is
> > > > > > brought back to clock B?
>
> > > > > Look at the Lorentz transforms to see. Its all due to clock synch.- Hide quoted text -
>
> > > > > - Show quoted text -
>
> > > > You are going to give yourself a head cold with all that arm waving..
> > > > You are saying the tick rate doesn't change, yet SR says that the
> > > > returning twin's clock will show less elapsed time. You don't see any
> > > > conflict there?
>
> > > No, there is no conflict. When you say that the tick rate does not
> > > change, this is a LOCAL statement. What it means is that a process
> > > measured locally with this clock will still have the same duration.
>
> > That is not what we were discussing. I agree that the clock continues
> > to tick at a rate of one second per proper second in the rest frame of
> > the clock. The question was whether the slowed tick rate measured in
> > the frame of the stay at home twin is real, or an illusion due to the
> > clock sync proceedure, as length contraction is.
>
> I don't know that length contraction IS an illusion. Length is
> *defined* operationally by relying on simultaneity, and so the REAL
> length according to that definition is of course frame-dependent,
> because simultaneity is frame-dependent.
>
> > If it is an illusion
> > the accumulated time on the two clocks should be the same when they
> > are brought back together. The way Inertial described it, it came
> > across as an illusion caused purely by clock sync.
>
> > I hate discussing what is "real". In a sense length contraction is
> > real because the pole will fit into the barn.
>
> Absolutely. If I have a clear understanding of what "simultaneous"
> means in a given reference frame, and I close the barn doors
> simultaneously with the pole between them, and there are no marks on
> the doors where the pole hit either one of them, then I can't think of
> any sensible meaning of "fit" that would hold these circumstances to
> be true and yet the pole does not fit in the barn in this frame. And
> since the pole fits, I cannot think of any sensible meaning of
> "shorter" where the pole would fit in the barn and yet be not shorter
> than the barn.

Careful here. I don't see how you can claim that the rod really is
shorter but that the clock didn't really slow down. The fact that the
rod has different measured lengths at the same time tells me that the
measured length is a matter of perception, which can be distorted.
But the fact that the returned clock has less elapsed time tells me
that it isn't just how I looked at it. If we are to agree that length
contraction and time dialation are real I'm good with that. But don't
then tell me that the clock didn't slow down. It slowed in our frame
but the traveling twin couldn't detect it because he used the
coordinates of his new frame of reference to measure it.

> > But with length
> > contraction there is no accumulated length to inspect when the pole is
> > brought to rest.
>
> This is true. The twin puzzle is a different animal that the barn-pole
> paradox. In the twin puzzle, there is no symmetry in terms of inertial
> motion. One twin is DEFINITELY not residing wholly in one inertial
> reference frame, and that is a frame-independent observation.
>
> > I can see that the measured slowing of the clock is
> > due to the rotation of the time coordinates when it changed frames,
> > but that doesn't make it any less real.
>
> > > For example, if the half-life of a muon that is slow in frame A and is
> > > measured with a clock at rest in A is 2.2 us, then if you make the
> > > same measurement of the half-life of a muon that is slow in frame B
> > > and is measured with a clock at rest in B, clock B will still show the
> > > half-life to be 2.2 us. In this sense, we say that the clock tick rate
> > > has not changed, because measurements of local phenomena are
> > > unchanged.
>
> > Yes, but again you are measuring locally, more or less in the rest
> > frame of the muon. We know that if we measure the half life of a fast
> > moving muon it is longer, as if its personal clock was ticking slower.
>
> > > However, this does NOT mean that the tick rate of clock B will agree
> > > with the clock rate of all other clocks, nor that it will read the
> > > durations of nonlocal processes to be the same.
>
> > > Do you see the distinction?
>
> > If we set up a light clock with a vertical bouncing beam, and have it
> > send a flash back to the stay at home twin every time the beam hits
> > the top, we can tell just how fast the clock is ticking. The signal
> > will be doppler shifted, but the total count is what it is. None of
> > the flashes drifted off and avoided detection. I am not claiming this
> > slowing is due to motion wrt an ether. It is due to the finite speed
> > of light and how we define/construct the coordinate systems.
>
> The last sentence is right, but how we define/construct the coordinate
> systems is constrained by the structure of spacetime (and this in fact
> produces the finite speed of light). That is, there is no way to
> define/construct a coordinate system in our spacetime such that these
> effects go away. (You are free to try.)
>
> PD
>
> > Bruce