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From: Jonah Thomas on 22 Oct 2009 23:19
bz <bz+mspep(a)ch100-5.chem.lsu.edu> wrote:
> tominlaguna(a)yahoo.com wrote in
> news:bqs0e5lqmuqtjqft1lvurh8ui21i974qp0@ 4ax.com:
>
> > Almost correct. For example, in the situation where a mirror is
> > moving normally toward a source at velocity v, the mirror will
> > experience the light as arriving at c + v. Upon reflection, the
> > light will be traveling at c + 2v with respect to the source; and,
> > as you state, at c + v with respect to the mirror.
>
> Easily tested by experiment:
> a) Two parallel mirrors, moving toward and away from each other (one
> attached to the voice coil of a loud speaker, or plated onto a surface
> of a quartz crystal).
> b) laser beam bouncing back and forth between the mirrors many times.
> If the bounce is n times, then the final velocity of the light exiting
> from the pair of mirrors should
> be c+n*v and c-n*v
>
> Should be an easy 'high school physics lab' test.
>
> If you demonstrate light is ballistic, you will earn a nobel prize.
>
> From a previous post of mine, several years ago [paraphrased]
> At 10000 cm/s peak rate of motion for the mirror (447 mph), and aiming
> for c+/- 1%, we need 1.5e4 reflections. Keep the mirrors close
> together, lets say 0.1 cm (about 40/1000 th of an inch, the path
> length would be about 15 meters. Over that distance, the beam
> divergence for a good laser should be small enough to allow such an
> experiment, making sure we have the right reflection at the output
> end, if our laser beam is about 0.01 mm in diameter, we need mirrors
> that are about 15 cm long.
>
> I don't see any reason that experiment can not be done.
> [unparaphrased]
>
> So, you just need to send pulses through the pair of mirrors, and
> measure
> the speed of the output pulse by seeing how long it takes to go by two
>
> detectors spaced a known distance apart. A +/- 1% variation in the
> speed of light should be rather noticable.

Neat!

Would you have to do it in vacuum? A mirror traveling at 2000 times the
speed of sound might generate quite a pressure wave across 1 millimeter
or so. Maybe enough to bend the mirror.

Say it oscillates between 0.5 mm and 1.5 mm, that's a frequency around
100000 cycles per second, kind of ultrasonic. It ought to be doable, but
again better in vacuum. You could make it smaller distances with a
higher frequency. Or with a better laser you could use a longer mirror
and a slower speed.
From: Inertial on 23 Oct 2009 00:59

"Jonah Thomas" <jethomas5(a)gmail.com> wrote in message
news:20091022224911.2710b175.jethomas5(a)gmail.com...
> "Inertial" <relatively(a)rest.com> wrote:
>> "Jonah Thomas" <jethomas5(a)gmail.com> wrote
>
>> [snip]
>> >> >> >> >>Doppler shift is a change in observed frequency.
>> > No, the formula gives a definition. The vague descriptions do not.
>>
>> You seem confused by the concept of a definition for a term (ie what
>> the phrase means), and a formula that gives a value for it (ie how to
>> calculate the value for it).
>>
>> You need to have both, of course. You need to know how to calculate
>> the value in specific instance .. and you need to know what the value
>> you just calculated actually means.

Doppler shift is an effect on frequency (ad possible wavelength) caused by
motion of the observer and source. That's what it means. You can give a
value to it be applying the relevant formula. That then menas you know what
the formula is for.

> Sure, but what it means *is* how you measure it.

Not really .. then it is just a number.

> You can come up with
> theories to explain it that are compatible with the measurements,

I didn't say anything about theories that explain it .. I said
(qaulitiatively) what the effect is.

> but
> the actual definition of each term *is* what you do to find it. The
> theoretical explanations are secondary.

And so emission theory would be wrong, as it does not give the same results
for Doppler shift for EMR as we observer? SR gets the answers correct.

>> >> Regardless .. Doppler shift is an effect on the observed wavelength
>> >> and/or frequency due to motion of source and/or observer. For
>> >light> in SR (and as observed) one only needs to consider the
>> >relative motion> of source and observer, and both wavelength and
>> >frequency are> affected.
>> >
>> > If the speed of the wave is constant, then both wavelength and
>> > frequency have to be affected.
>>
>> Maybe .. maybe not. For light, according to SR, yes
>
> By definition, if speed equals wavelength times frequency.

No .. not by definition. It is not always both frequency and wavelength
affected by Doppler. It depends on the situation. But for light it is
always both due to the constant speed of light.

>> > If the wavelength is constant then speed and
>> > frequency have to be affected.
>>
>> All that follows form the relationship between frequency, wavelength
>> and speed, of course.
>
> Yes, exactly.
>
>> > It depends.
>>
>> Exactly .. it does all depend .. which is why I have described it as
>> above.
>>
>> Saying Doppler shift is just an effect on frequency (as you did
>> originally) is misleading. It can also affect wavelength. Which is
>> why is the point I was trying to make.
>
> If it's defined on frequency

Not always. There are formulas for how wavelength is affected and how
frequency is affected.

> and you extend it to wavelength,

Its not me that is extending it.

> you are
> making implicit assumptions.

No .. I am just describing the effect, which in some cases affects
wavelength.

> You'll get correct results as long as those
> assumptions hold up.

I'm not making any assumptions. A Doppler shift can include a shift in
wavelength. Gees.

>> Perhaps rather than "Or wavelength .. Or both" I should have more
>> correctly said "or both frequency and wavelength" .. as Doppler will
>> always affect frequency, but may or may not affect wavelength.
>
> That's how I'm thinking of it right now.

Good. Glad you finally got there

> Given a medium which controls
> the speed of the waves, doppler must affect both.

No .. not always.

> Without a medium all
> bets are off but doppler might easily still affect both.

No .. all best are not off are all. For example, we know from experiment
that Doppler affects both frequency and wavelength for light (despite
Henry's deluded denials), and the effect is as predicted by SR.

From: tominlaguna on 23 Oct 2009 02:11
On Wed, 21 Oct 2009 11:49:07 -0500, Tom Roberts
<tjrob137(a)sbcglobal.net> wrote:

>tominlaguna(a)yahoo.com wrote:
>> I think there is another problem trying to use Snell's Law of
>> Reflection with SRT and that has to do with moving mirrors. In
>> Ditchburn's book "Light" (1976) page 418, he shows the angle of
>> incidence and the angle of reflection to be different for a moving
>> mirror, though the speed of the incoming and reflected waves are
>> identical.
>
>This is not a problem: Snell's law for mirrors applies ONLY in the inertial
>frame of the mirror. When viewed using other frames, the angle of reflection can
>be different from the angle of incidence. This is just basic SR applied to the
>physical situation, and there's no contradiction or problem here.

I can buy that. The same thing occurs when you model reflections in
the Ballistic theory. I think, however, there is still a problem in
identifying the proper equation. In "Insights into Optics" (1991) by
Heavens and Ditchburn, there is a totally different equation with no
explanation as to why the formula changed; I seem to recall the actual
publication data was after Ditchburn's death.

>> In Waldron's book, "The Wave and Ballistic Theories of Light" (1977)
>> page 162, he shows the generalized Snell's law which occurs when there
>> is relative motion between the source and the mirror. It is ONLY when
>> there is RELATIVE motion between source and mirror that a change in
>> the speed of light can occur with the emission theory.
>>
>> Since there is no relative motion between the Sagnac source and the
>> Sagnac mirrors, there is no change in light speed. It is plain and
>> simple classical physics as described by Dufour and Prunier.
>
>I don't have those references, but statements like "there is no relative motion
>between the Sagnac source and the Sagnac mirrors" are FAR TOO AMBIGUOUS -- you
>MUST state in which frame or coordinates this claim is valid. In particular, in
>the inertial frame of the center it is just plain wrong. But in the rotating
>system it is correct.

You make a good point. I will refine my description to incorporate
your suggestion.

>Consider Sagnac interferometer in vacuum using mirrors:
>In such an emission theory, analyzed in the rotating coordinates, the speed of
>light is c for both rays, and the path lengths are equal, so the prediction is
>no fringe shift. In such an emission theory, analyzed in the inertial frame of
>the center, the speed of light varies for each leg, and the two rays have
>different path lengths; a careful computation putting it all together gives the
>same prediction of no fringe shift [reference lost].
>
>Bottom line: such an emission theory is refuted by Sagnac's observations, as I said.

Wrong.
>
>Tom Roberts
From: tominlaguna on 23 Oct 2009 02:25
On Fri, 16 Oct 2009 16:08:07 +0100, tominlaguna(a)yahoo.com wrote:

>
[snip]

Tom Roberts has prompted a refinement to my description of the Sagnac
experiment which I have incorporated below:

Now let's refer to the actual Sagnac diagram which is located at:
http://commons.wikimedia.org/wiki/File:Sagnac-Interferometer.png

Now we'll follow the clockwise beam from start to finish and numerate
each step for later identification:

1. Light is emitted from source O at c with respect to that source.
2. The light arrives at and is reflected off mirror m at speed c since
there is no "line-of-sight" relative motion between m and O.
3. The light arrives at and is refracted though the collimator lens at
C, arriving at speed c and departing at speed c since there is no
"line-of-sight" relative motion between C and m.
4. The light arrives at the half-silvered prism mirror at j at speed c
since there is no "line-of-sight" relative motion between C and j.
5. The light is split at j and departs the prism after refraction at
speed c. (The other half is reflected off j at speed c and begins its
counter-clockwise journey after a second refraction.)
6. The diagram identifies the clockwise beam with label T and the
counter-clockwise beam with label R.
7. Beam T arrives at mirror M1 at c since there is no relative motion
between M1 and J. The angle of incidence is 1/2 angle a1.
8. Beam T reflects off mirror M1 at speed c and at an angle of
reflection of 1/2 angle a1.
9. Beam T arrives at mirror M2 at speed c since there is no
"line-of-sight" relative motion between M1 and M2 and at an angle of
incidence of 1/2 angle a2.
10. Beam T reflects off M2 at speed c and an angle of reflection of
1/2 angle a2.
11. Beam T proceeds to mirror M3 arriving at speed c since there is no
"line-of-sight" relative motion between M2 and M3, arriving at an
angle of incidence of 1/2 angle a3.
12. Beam T reflects off M3 at speed c and angle of reflection of 1/2
angle a3.
13. Beam T proceeds to mirror M4 arriving at speed c since there is no
"line-of-sight" relative motion between M3 and M4, arriving at an
angle of incidence of 1/2 angle a4.
14. Beam T reflects off M4 at speed c and angle of reflection of 1/2
angle a4.
15. Beam T arrives at the half-silvered prism mirror at j at speed c
since there is no"line-of-sight" relative motion between M4 and j.
16. After refraction, Beam T passes through mirror j and after a
second refraction proceeds toward telescope L at speed c.
17. It is at mirror j that Beam T and Beam R are mixed to produce
interference fringes.
18. Beam T arrives at telescope L at c since there is no
"line-of-sight" relative motion between mirror j and telescope L.
19. Beam T proceeds down the telescope and arrives at the photographic
plate PP' at speed c since there is no "line-of-sight" relative motion
between telescope L and the film at PP'.
20. The diagram properly shows that counter-clockwise beam R arrives
before the clockwise beam T since it has traversed a shorter optical
path length; made shorter due to rotation.
21. The reader can reconstruct the path steps in a similar manner for
the counter-clockwise beam.

Summarizing:

A. The Ballistic Theory of Light has 2 Postulates: (1) Light is
emitted at c with respect to its source and (2) light is reflected a c
with respect to the mirror image of the source.
B. With the Ballistic Theory of Light, the beams of light traverse
the optical circuit at speed c in each direction since there is no
"line-of-sight" relative motion element-to-element.
C. The angle of incidence equals the angle of reflection at all
points of reflection.
D. The counter-clockwise beam arrives sooner than the opposing beam
because it has a shorter optical path length to traverse.
E. The Ballistic Theory of Light is compatible with the Sagnac
experiment.
From: tominlaguna on 23 Oct 2009 03:31
On Fri, 23 Oct 2009 02:32:10 +0000 (UTC), bz
<bz+mspep(a)ch100-5.chem.lsu.edu> wrote:

>tominlaguna(a)yahoo.com wrote in news:bqs0e5lqmuqtjqft1lvurh8ui21i974qp0@
>4ax.com:
>
>> Almost correct. For example, in the situation where a mirror is
>> moving normally toward a source at velocity v, the mirror will
>> experience the light as arriving at c + v. Upon reflection, the light
>> will be traveling at c + 2v with respect to the source; and, as you
>> state, at c + v with respect to the mirror.
>
>Easily tested by experiment:
>a) Two parallel mirrors, moving toward and away from each other (one
>attached to the voice coil of a loud speaker, or plated onto a surface of a
>quartz crystal).
>b) laser beam bouncing back and forth between the mirrors many times.
>If the bounce is n times, then the final velocity of the light exiting from
>the pair of mirrors should
>be c+n*v and c-n*v

That is a very interesting concept. I will try to model it and see if
it can be done easily. I am thinking the result might be c+/-2n*v.

>Should be an easy 'high school physics lab' test.
>
>If you demonstrate light is ballistic, you will earn a nobel prize.
>
>From a previous post of mine, several years ago [paraphrased]
>At 10000 cm/s peak rate of motion for the mirror (447 mph), and aiming for
>c+/- 1%, we need 1.5e4 reflections. Keep the mirrors close together, lets
>say 0.1 cm (about 40/1000 th of an inch, the path length would be about 15
>meters. Over that distance, the beam divergence for a good laser should be
>small enough to allow such an experiment, making sure we have the right
>reflection at the output end, if our laser beam is about 0.01 mm in
>diameter, we need mirrors that are about 15 cm long.
>
>I don't see any reason that experiment can not be done.
>[unparaphrased]
>
> So, you just need to send pulses through the pair of mirrors, and measure
>the speed of the output pulse by seeing how long it takes to go by two
>detectors spaced a known distance apart. A +/- 1% variation in the speed of
>light should be rather noticable.
>
>Good luck.
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