Wang / Sagnac Devices [Relativity]

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From: Androcles on 21 Oct 2009 12:54

"Tom Roberts" <tjrob137(a)sbcglobal.net> wrote in message
news:R8mdnR97dpkepkLXRVn_vwA(a)giganews.com...
> 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.
>
>
>> 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.
>
> 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.
>

Real bottom line: you are only looking at the beamsplitter, not the
detector,
you incompetent fuckwit.
http://www.androcles01.pwp.blueyonder.co.uk/Sagnac/SagnacRing.JPG
SR is refuted by Sagnac's observations, as I said.

From: Inertial on 21 Oct 2009 20:13

"Henry Wilson DSc." <HW@..> wrote in message
news:k06vd5h2c2qttk2s41ql3oi11pcdls1ov8(a)4ax.com...
> On Thu, 22 Oct 2009 09:32:25 +1100, "Inertial" <relatively(a)rest.com>
> wrote:
>
>>
>><tominlaguna(a)yahoo.com> wrote in message
>>news:cg5ud5hgti6c77jl2gj9d8o55gpi356qr8(a)4ax.com...
>>> On Wed, 21 Oct 2009 19:51:48 +1100, "Inertial" <relatively(a)rest.com>
>>> wrote:
>
>>>>> Look at the Mathpages diagram. It is quite accurate in its
>>>>> representation of what constitutes a change in optical path length.
>>>>
>>>>I know that page well.
>>>>
>>>>The length in the non-rotating frame is different
>>>
>>> No kidding? What length? The physical path length? Is it different
>>> between the stationary and rotating mode? Please explain?
>>
>>Yes .. clearly the distance travelled depends on the frame of reference.
>>
>>Can you not see that in the non-rotating frame the path length is from the
>>start to end one clockwise and one anit-clockwise, but the path does not
>>terminate at the original start point, because the end point has moved ..
>>so
>>one is longer than the other. In the rotating frame, the distance around
>>the device from start to end is identical for both beams .. just as it was
>>when the device was not rotating.
>
> That's why you cannot use the rotating frame. It leads to massive errors.
> Roberts makes the same ones as you do.

I did not make any. One can (and I have several times for you before) do
the emission theory analysis in the non-rotating frame. Its quite simple
(though you get it wrong). You still get (not surprisingly), that the two
beam arrive at the same time at the detector. In the non-rotating frame
they have travelled different distances at different speeds for the same
time. When they arrive at the detector, they arrive at the same time, they
have the same speed wrt the detector, they have the same frequency wrt the
detector .. so they MUST be in phase. So no sagnac effect, hence refuting
the theory.

If you can come up with a plausible consistent non-contradictory explanation
of how two beams with the same frequency and speed arriving at a given
location at the same time after travelling for the same duration can be out
of phase .. go ahead. So far you've not delivered the goods.

> Do you really think the path lengths can change just by changing observer
> frames? How ridiculous.

Of course they do. My my but you do look silly when you make such comments.

Imagine a person walking on the roof of a train.

He walks from one end of the carriage to the other. His path length
according to someone sitting in the train is the length of the carriage

But according to someone on the ground, his path is much longer, because the
train is moving.

No relativity involved for that.

Now .. the length of the carriage doesn't change, of course (ignoring
relativity for now, that is clearly beyond your abilities)

But the distance the person moves (his path length) over time DOES change,
because his speed is different depending on who observes him.

> The truth is, the inertial start point of a particular ray element moves
> backwards in the rotating frame....

Of course it does. If you mark where the ray was emitted in both the
inertial and rotating frames, those marks will move apart over time. The
mark in the inertial frame will rotate backwards in the rotating frame, and
the mark in the rotating frame will rotate forwards in the inertial frame.
Why you think the bleeding obvious is such a mystery that others can't
comprehend is the only mystery there.

> but that's far to hard for you and
> Roberts...

We understand it all perfectly well thanks .. you on the other-hand are so
determined that relativity must be wrong, that it blinds you to your
mistakes

From: Inertial on 21 Oct 2009 20:14

"Henry Wilson DSc." <HW@..> wrote in message
news:ju7vd5di02f43boqk14g92st0dtjkrluq8(a)4ax.com...
> On Thu, 22 Oct 2009 00:37:02 +0100, "Androcles"
> <Headmaster(a)Hogwarts.physics_p>
> wrote:
>>Yep. The idiots don't understand Galilean relativity.
> I'm glad we agree.

I'm glad you two are mutually deluded. Though its much more fun watching
crackpots argue. Maybe you should take on Porat again?

From: Androcles on 21 Oct 2009 20:15

"Henry Wilson DSc ." <HW@..> wrote in message
news:ju7vd5di02f43boqk14g92st0dtjkrluq8(a)4ax.com...
> On Thu, 22 Oct 2009 00:37:02 +0100, "Androcles"
> <Headmaster(a)Hogwarts.physics_p>
> wrote:
>
>>
>>"Henry Wilson DSc ." <HW@..> wrote in message
>>news:k06vd5h2c2qttk2s41ql3oi11pcdls1ov8(a)4ax.com...
>>> On Thu, 22 Oct 2009 09:32:25 +1100, "Inertial" <relatively(a)rest.com>
>>> wrote:
>
>>>>
>>>>Can you not see that in the non-rotating frame the path length is from
>>>>the
>>>>start to end one clockwise and one anit-clockwise, but the path does not
>>>>terminate at the original start point, because the end point has moved
>>>>..
>>>>so
>>>>one is longer than the other. In the rotating frame, the distance
>>>>around
>>>>the device from start to end is identical for both beams .. just as it
>>>>was
>>>>when the device was not rotating.
>>>
>>> That's why you cannot use the rotating frame. It leads to massive
>>> errors.
>>> Roberts makes the same ones as you do.
>>
>>I can use the rotating frame, although I agree with you that the inert
>>idiot
>>can't and hypocrite Humpty Roberts can't.
>>
>>
>>
>>> Do you really think the path lengths can change just by changing
>>> observer
>>> frames? How ridiculous.
>>>
>>> The truth is, the inertial start point of a particular ray element moves
>>> backwards in the rotating frame....but that's far to hard for you and
>>> Roberts...
>>
>>Yep. The idiots don't understand Galilean relativity.
>
> I'm glad we agree.
>
> <unplonk A the A>

That's one of your silliest posts, but it doesn't quite beat
your headless crocodiles.

From: Jonah Thomas on 22 Oct 2009 02:53

Darwin123 <drosen0000(a)yahoo.com> wrote:
> Jonah Thomas <jethom...(a)gmail.com> wrote:
> > Darwin123 <drosen0...(a)yahoo.com> wrote:

> > > Charles Ives described a thought experiment to show why the
> > > Sagnac effect contradicted relativity. He never actually performed
> > > this experiment, but simply guessed what the results would be
> > > based on symmetry. However, the symmetry that he hypothesized did
> > > not exist in the equivalent real-world systme.
> > > He proposed a Sagnac interferometer consisting of a highly
> > > reflective ring of material. There would not be separate mirror,
> > > but a continuous curve of reflective material. He proposed that
> > > the ring was completely circular, so that the optical system had
> > > complete radial symmetry. A rotation by any angle would not change
> > > the system, in his model, by any amount. Suppose two traveling
> > > waves are propagating in opposite directions in this circular
> > > cavity. His argument was that since the cavity is radially
> > > symmetric, there is no way the light waves can "know" that the
> > > cavity was rotating. The surface of this smooth cavity is smooth
> > > and featureless. Motion can not show itself on a featureless
> > > surface. Thus there could be no beats between the two waves, and
> > > thus no Sagnac effect. Since the Saganc effect is predicted by
> > > relativity, the fact there is no Sagnac effect for such a cavity
> > > means relativity is wrong. Note he didn't make the main error
> > > provided by members of the group. He did not claim the Saganc
> > > effect contradicts relativity. His arguement was that the Sagnac
> > > effect couldn't exist under certain conditions that were
> > > consistent with relativity. First, let me point out that
> > > such a system has been made. Sagnac cavities have been constructed
> > > using fibers connected in a circle. There are no separate mirrors
> > > in such a cavity. The reflective surface is a continuous curve.
> > > The Sagnac effect has been observed with such continuously curved
> > > surfaces. So what went wrong with Ives' analysis?
> >
> > If the emitter and the detector move with the mirror, which they had
> > probably better do, then you get a Sagnac effect because they are
> > moving. I believe you could get a sagnac effect with the source and
> > detector moving even if they were bouncing light off mirrors that
> > did not move. But like Ives I have not done the experiment.

> This is probably true (I am not sure). However, in this case the
> source and detector are also under the influence of centripetal
> forces. Therefore, they are "accelerating" in the special relativity
> sense. The detector can't be part of the inertial frame because it is
> accelerating.

Usually when you do engineering-type calculations you can do various
checks by common sense that show whether you have made a whopper of a
mistake. If you are constructing a building of reasonable size and you
calculate that you will need ten thousand truckloads of concrete, there
is probably an error somewhere. If you are estimating the time required
to move a thousand tons of military supplies across the ocean and you
notice that you are estimating each plane will be in the air for two
weeks before it lands, likewise.

With relativity we lose many of the usual checks. It's perfectly
plausible that time travels at different speeds for different observers,
that distances are measured differently by different observers, that two
events will seem simultaneous to one oserver but not to another, etc.
There is one certain check -- if you calculate that something travels
faster than lightspeed then you know you have an error.

Because most of the checks are missing, to make relativistic
calculations you must be very very careful that you are doing it
correctly. It's easy to make a mistake and then rationalise it. Like, if
you make a mistake and calculate that you are two different ages, and
somebody points out "Hey, you have a contradiction here", it's all too
easy to decide that there is no contradiction after all. "No, it's
relativisticly correct. It all depends on which frame I'm in when I
calculate my age. According to the first me frame I'm 117, and in the
second me frame I'm -4, and those are the correct answers."

Recently I saw someone argue that relativisticly it's fine for two
observers to disagree about whether two events happen at the same time
and place or not. By my limited understanding of SR, when two things
happen apart then different observers might reasonably disagree about
which happened first. "Simulataneity" is uncertain for things outside
your lightcone, and even later it's OK for different observers to see it
different. But to disagree whether things happen at the *same* time and
place? It seems to me they probably were making a mistake. Easy to do
when you're a guy on a newsgroup thinking about thought experiments
without actually being very careful about the details. But I didn't want
to argue with him. Just as I don't want to argue with talmudic scholars
about what the Talmud really says, or with fundamentalist christians
about what the Bible really says. I've read them, and I have opinions,
but I get nothing of value from trying to explain the truth to them even
if it happens that I am absolutely correct. Maybe by this time next year
I will be a relativity scholar myself arguing about which
interpretations are relativisticly correct, but right now I just don't
want to bother. People can make whatever claim they want about what
relativity really says, and I will listen and then draw whatever
conclusions make sense to me.

So without arguing about it, I don't understand why you can't consider
the detector from an inertial point of view because it's rotating. When
the question is whether two parts of a split light beam arrive at the
detector at the same time or not, if it's the same time in one frame it
ought to be the same time in all other frames, shouldn't it? If it was a
question when they arrived at two different places then observers might
disagree which was first. But how can they disagree about whether or not
they arrive at the same place and the same time? Don't answer that. I'm
sure there are explanations how it can happen with SR. I really don't
want to know.

> My argument was that the cavity itself is accelerating in the
> sense of special relativity. The atoms and electrons of the reflective
> cavity are accelerating. So even if the source and detector are not
> accelerating (the usual case), the Sagnac effect will still occur (the
> always case).

I don't think so. (Though I could be wrong, and if the experiments have
been done I'll be very interested.) I think the Sagnac effect is due to
the source and detector moving and not the medium. If it's the medium
that moves then you might get some sort of Fizeau effect.

Ives's thought experiment could be done. You make a cylindrical mirror
with carefully-spaced holes. You arrange that light shining into the
cylinder through one hole will bounce repeatedly across the inner
surface of the mirror until it leaves by another hole. Position your
stationary source and detector just so, and then spin the mirror. The
spinning mirror will alternately block the emitter (and detector) and
let the light through. You should see no Sagnac effect when the light
gets through. If you do get an effect I think it will deserve some other
name, and there will be a reason that it is not observed during the
usual Sagnac experiment.

The reason I predict that will have no effect is that the traditional
Sagnac explanation (the one that says the detector moves so that the
light paths are in proportion c+v:c-v) gives the right answer. It does
not depend in any way on the movement of the mirrors along the path, but
only on the movement of the detector. If you get the same effect by
moving the mirrors and leaving the detector alone, then this explanation
gives the correct result entirely by accident. It could be true that
this explanation is not only wrong but has no relation whatsoever to the
correct explanation, but I'm betting the other side, that it does have
some relationship to a correct explanation.

> > > 1) The cavity, though "continuously curved," is made of atoms.
> > > 2) The free electrons on the surface, that cause the reflection of
> > > light, are also discrete up to the limits of quantum mechanics. 3)
> > > The light itself consists of nodes and antinodes. >

> > I doubt all that matters.
>
> > Get your detector and emitter moving along the
> > mirror cylinder and you'll get a Sagnac effect with the mirror not
> > moving at all. If it doesn't matter whether the mirror moves then it
> > does not matter abouut the astoms and the free electrons and the
> > antinodes.
> >
> > But I could be wrong.
>
> It doesn't matter if you decide to ignore the atomic scale details
> of the experiment. Relativity is not a "complete" theory in the sense
> that the equations of relativity uniquely determine the path of the
> particles or light. There is no unique equation of motion, or equation
> of state, that describes all systems with Lorentz invariance (or
> covariant invariance).

Also, the mathpages guy claims that the relativistic explanation and the
classical explanation are the same in this case. All the things that
relativity does different, cancel out for Sagnac while v is not a large
relativistic speed.

> Relativity on a macroscopic scale provides a good short cut
> through all the electrodynamic and quantum mechanical details that
> would completely describe the system. The kinematic parts of
> relativity precisely describe what happens on a macroscopic scale, and
> give no clue as to what happens on the scale of atoms and electrons.
> The nice thing about the kinematics of relativity is that they are
> scale invariant.
> That is part of the reason that relativity is anti-intuitive. As
> has often been said, relativity doesn't tell you why it happens. You
> could read that as meaning that relativity is scale invariant.

In accounting, there is something called GAAP, Generally Accepted
Accounting Principles. There is some argument about the fine details of
how GAAP should go, and it changes slowly, but for the most part it's
more important that all the accountants do it the same way than that
they get the fine details right. At this point relativity looks like
that to me. It's a way to do the accounting so that you can match up the
different observations. it isn't as much about what happens as it is
about how to balance the books when you measure what happens. And it
works for that purpose.

> If you really wanted to describe the Sagnac effect in atomic scale
> detail, you would have to model the motion of electrons in
> the mirrors. You have to model the mtion of the atoms in the mirrors.
> For consistency, you would have to use relativistic equations for the
> motions of electrons. Of course, this is a level of detail unnecessary
> for understand the Sagnac cavity on a macroscopic level.

Yes. Unless the explanations fail on a macroscopic level. Then maybe we
can duck down to the electrons and make it work on that level.

> The relativistic explanation usually given is an end run around
> the atomic scale explanation. Its is a macroscopic explanation.
> Embedded in this derivation is the microscopic details. Like, how do
> the electrons in the mirror move to create reflection?
> I think Herbert Ives didn't understand this. He treated relativity
> like it was an equation of motion which it is not. He ignored the
> question of why the material reflects light. He decided that if there
> is no feature obvious to the naked eye, then there is no microscopic
> properties that are important. He was wrong.