From: Tom Roberts on
Da Do Ron Ron wrote:
> PD confusingly stated:
>> Isotropy is not a OWLS measurement.

Right. Experiments have shown one-way isotropy, without actually measuring OWLS.
But Da Do Ron Ron does not seem to understand that:

> One-way isotropy was the subject at hand. We all know that experiment
> has shown round-trip isotropy, so your ref. is useless. Specifically,
> the subject
> at hand is one-way light speed invariance. But no experiment has shown
> this.

If you mean that no experiment has DIRECTLY shown one-way light speed
invariance, that is correct. But it has been solidly established, indirectly,
within the context of SR.

In particular, "light speed invariance" is an empty phrase without a complete
theory to test. For non-gravitational measurements, the appropriate theory is
SR. SR has been solidly established within its domain of applicability, and it
includes light speed invariance.

[In a context in which gravitation is important, there is no
light-speed invariance, one-way or round-trip. Indeed, in
general there is not even isotropy (of either type).]


> It cannot simply be assumed at the start because this means nothing.

Well yes, one cannot assume what one is trying to establish. And yes, attempting
to discuss "light speed invariance" divorced from a theory means nothing.


> PD incorrectly stated:
>> Synchronization is a condition that is only satisfied in one frame
>> anyway.

That is not incorrect. Your follow-on claim is so ambiguous that your statement
is tantamount to being incorrect.


> You cannot have one-way light speed invariance unless observers in
> _all_ frames obtain the same speed for light's one-way speed, and
> this
> means that clocks in _all_ frames must be set per Einstein's
> definition.

Your English usage is excessively ambiguous. Your "in all" can mean "in every
one separately", or it could mean "in every one simultaneously" -- the former is
correct the latter is not.

Say, rather, that one-way light speed invariance means that in each inertial
frame a measurement of OWLS will obtain c, independent of the inertial frame
used. In particular, it simply is not possible for a GIVEN pair of clocks to be
synchronized in _all_ frames, though that is one possible interpretation of your
words.

We have three "pieces" that when put together establish one-way light speed
invariance:
A) round-trip invariance of light speed, for all inertial frames occupied
by an earthbound laboratory. Those frames differ by ~60 km/s, and the
experimental accuracy of the invariance is a bit less than 1 m/s.
B) one-way isotropy of light speed, for all inertial frames occupied
by an earthbound laboratory. Again the experimental accuracy is
less than 1 m/s.
C) SR is a comprehensive theory in which one-way light speed invariance
holds precisely, and is consistent with all experiments within its
domain, including A and B.

So while no experiment has directly established one-way light speed invariance,
the indirect evidence is quite solid. In particular, no known theory that does
not have one-way light speed invariance is consistent with these experiments.

I mean MEASURED invariance. There are theories in which the
coordinates have both anisotropy and lack of invariance, but
which are experimentally indistinguishable from SR. In short,
for these theories their anisotropy and non-invariance
precisely cancel out whenever real clocks and real rulers
are used to measure the speed of light.


> And by refusing to complete the given task, you have blocked yourself
> from understanding Einstein's definition of clock synchronization.

I have no idea what you mean by this.


> Here, again, are the rules: [...]

Science is not about arbitrary "rules", but rather is about formulating and
testing theories experimentally. SR has been extensively tested, and has not
been refuted by any experiment within its domain of applicability. That's as
good as it gets.


Tom Roberts
From: Da Do Ron Ron on


T. Roberts stated:
>Say, rather, that one-way light speed invariance means that
>in each inertial frame a measurement of OWLS will obtain c,
>independent of the inertial frame used.

We are now back to square one, but that's better than nothing.

I assume that your above is saying that light's one-way speed can
be measured, and that it can be measured in many inertial frames.

Elsewhere, you have stated that two clocks (in each
inertial frame) are needed to measure the one-way
speed of light.

Also, you have stated that Einstein somehow synchronized
these two clocks (in each inertial frame) in order to
somehow guarantee c invariance.

How are the clocks in special relativity synchronized?
(How is c invariance guaranteed?)
(What is the physical process involved?)

If you cannot tell us, then why did you make that claim
about Einstein's guarantee?

~~RA~~

From: PD on
On Jan 21, 2:21 pm, Da Do Ron Ron <ron_ai...(a)hotmail.com> wrote:
> T. Roberts stated:
>
> >Say, rather, that one-way light speed invariance means that
> >in each inertial frame a measurement of OWLS will obtain c,
> >independent of the inertial frame used.
>
> We are now back to square one, but that's better than nothing.
>
> I assume that your above is saying that light's one-way speed can
> be measured, and that it can be measured in many inertial frames.
>
> Elsewhere, you have stated that two clocks (in each
> inertial frame) are needed to measure the one-way
> speed of light.
>
> Also, you have stated that Einstein somehow synchronized
> these two clocks (in each inertial frame) in order to
> somehow guarantee c invariance.
>
> How are the clocks in special relativity synchronized?

I answered this.

> (How is c invariance guaranteed?)
> (What is the physical process involved?)
>
> If you cannot tell us, then why did you make that claim
> about Einstein's guarantee?
>
> ~~RA~~

From: Tom Roberts on
Da Do Ron Ron wrote:
> T. Roberts stated:
>> Say, rather, that one-way light speed invariance means that
>> in each inertial frame a measurement of OWLS will obtain c,
>> independent of the inertial frame used.
>
> We are now back to square one, but that's better than nothing.

YOU may be at square one, but anybody who has actually studied SR is not.


> I assume that your above is saying that light's one-way speed can
> be measured, and that it can be measured in many inertial frames.

Yes. Of course. By simply using an earthbound laboratory one's measurement is
performed in many different inertial frames as the earth rotates and orbits the
sun. Those frames differ from each other by 60 km/s as the earth orbits the sun;
the accuracy of such measurements is about 60,000 times better than that variation.


> Elsewhere, you have stated that two clocks (in each
> inertial frame) are needed to measure the one-way
> speed of light.
> Also, you have stated that Einstein somehow synchronized
> these two clocks (in each inertial frame) in order to
> somehow guarantee c invariance.

Yes. All you need to do is STUDY in order to learn how "somehow" is achieved.


> How are the clocks in special relativity synchronized?

Einstein described two basic methods to synchronize two clocks A and B at rest
in a given inertial frame:

A) place a light source exactly midway between them. Arrange so the
source simultaneously sends a light pulse (propagating in vacuum)
direct to each clock, and make the clocks start ticking at the
same indicated value when they receive the light pulse.

B) Send a light pulse from A to B, and have B immediately return it
to A (e.g. with a mirror). Adjust the clocks so the reflection
at B occurs at an indicated time midway between the two times at A.

Exercise for the reader: show that method B yields identical
results if A and B are interchanged.

Exercise for the reader: show that methods A and B give
identical results.

Exercise for knowledgeable readers: Einstein discussed two
additional methods. What are they?

Given one-way isotropy in the speed of light (guaranteed in SR by the second
postulate), these two methods are equivalent, and always yield clocks that
measure the speed of light to be isotropic. As no mention of which inertial
frame was used, this applies in any inertial frame, thus ensuring invariance of
the one-way speed of light.


> (How is c invariance guaranteed?)

See above.


> (What is the physical process involved?)

I have no idea what you mean. The propagation of light just occurs however it
happens, and clocks are simply synchronized according to some prescribed method.
What "physical process" do you mean?


> If you cannot tell us, then why did you make that claim
> about Einstein's guarantee?

Don't project your personal inability to discuss such things on to other people.


Tom Roberts
From: Da Do Ron Ron on
T Roberts asked:
>I have no idea what you mean. The propagation of light just occurs
>however it happens, and clocks are simply synchronized according to
>some prescribed method.
>What "physical process" do you mean?

It is the process that you mentioned just prior to your query, namely,
the
"prescribed method" of clock synchronization; however, since you have
not yet properly applied this method to more than one frame, you
cannot
fully understand it.

Yes, I know that you believe that you have done this, because you
said
the following:

>As no mention of which inertial frame was used, this applies in any
>inertial frame, thus ensuring invariance of the one-way speed of light.

But this is wrong, as my prior (simple) diagram should have shown.
As I have tried to get you to see, merely repeating the same frame
over and over (as you just did, and as the Einsteinian version of his
method does) does _not_ convey the full story.

There is only one way to properly show Einstein's convention of
synchronization in more than one frame, and that, as I have tried
to get across, is by letting the frames share the light source.

Giving each frame its own source is to merely and uselessly repeat
the same frame over and over and over.

Here, _again_, is a picture of the start of the physical process
about
which you asked above:

Frame A
[0]---------x----------[?]
Source S~~>light
[0]---------x----------[?] -->v
Frame B

Notice the very careful and very necessary usage of a single light
source.

Notice the equally necessary usage of at least two frames.

Since this is NOT done in any relativity text, no one has yet seen
the
full version of Einstein's definition of clock synchronization.

Therefore, no one has yet seen the full truth re Einstein's
definition.

To repeat, the _ONLY_ way to see the full truth of the definition
is by carrying the above picture to completion.

You, or PD, or Android, or Dirk, or Seto, or Gisse, or _some_ person
MUST fill in the blanks to complete the diagram. Only then will the
full physical process of which we are speaking be made perfectly
clear.

Have I made myself perfectly clear?

I will even bend over backward to carry the picture one step further:

Frame A
[0]---------x----------[?]
Source S---------------->light
----------[0]---------x----------[?] -->v
Frame B

WHAT, pray tell, is the reading NOW on A's right-hand clock per
Einstein's definition of clock synchronization?

Can anyone tell us?

~~RA~~
(as was given, x is the ruler-measured distance
given a ruler at rest wrt the frame in which the
measurement is made)