Re: Is the speed of light really constant ?

From: Mich (mich_at_efni.com)
Date: 10/11/04 

Date: Sun, 10 Oct 2004 21:54:38 -0400

Good post!

Eric Baird <eric_baird@compuserve.com> wrote in message
news:f3n6m0t1s243a6f4d8j9dqtfnru1dpl6oq@4ax.com...
> On Tue, 28 Sep 2004 22:45:44 -0400, "Mich" <mich@efni.com> wrote:
>
> >What does relativty say the cause of the doppler shift is?
>
> I suppose that depends on which theory we use, and how lightspeeds and
> distances are defined in that theory.

ok. This is specifically the question that I'm asking for though. At first
glance, I was thinking that after an observer changes velocity relative to
the source, a time dilation would occur, leaving the light's speed as being
c. Now, let f' = blueshifted frequency caused by a c+v velocity relative to
two frames of references as per classical prediction .Since we assume the
observer measures the velocity as being c, and not c+v, then; from c+v/x =
c; x= c+v/c.
We therefore have ( f = f' c/c+t ) ; but this also cancels out the
frequency's doppler shift. Now, in order to reclaim the doppler shift,we
could say the light's wavelength contracted, but then, we no longer have a
frequency/ wavelength ratio having the value of c.
So far, I have no clue as to how it works out.

> Under special relativity, the arrival time of the light-pulse at the
> two destinations is supposed to be wholly unaffected by whether or not
> the source is "moving", and all observers agree as to which other
> things happened at those locations at the same local times.
> Suppose that the two observers A and B synchronise their clocks by
> bouncing light-signals back and forth between them to get the total
> round-trip time, and then divide that time by two to calculate their
> mutual observation delay, and set their own clocks to appear to be
> ahead of the other by exactly that amount (ie they to exactly
> compensate for the calculated, equal, observation timelags).

Let us say that observer A sends a light signal to observer B at time 1:00.
The signal bounce from B and returns to A at 2:00. A concludes a 1/2
light hour distance between himself and B. B having received A's signal of
1:00, does the same and starts with a 1:00 light signal .I cannot see how
the clocks can be synchronized without first choosing one reference frame as
being a proper or absolute frame. Only then, it seems,
can either A choose to advance his clock 1/2 hour in order to be
synchronized with B "or" B chooses to synchronize himself with A. If they do
it both at the same time, they are no longer synchronized...it seems.I
wonder what would happen if they both choose to advance their clocks 15
minutes instead?

> Suppose, also, that we somehow deliberately engineer a situation where
> the light-pulses just happen to arrive at each of those two clocks
> exactly at the moment when the clock in question strikes midnight
> (perhaps the signal is a laserbeam that burns a hole straight through
> the hour, minute and second hand as they all line up, pointing at the
> "12" on each clock).
> Under SR, its then easy to say that for these two clocks, the light
> arrived simultaneously, at "midnight",and th eburnholes will verify
> this.

In this, I question the definition of simultanity( if that's a proper word
to use).
Since there is a 1/2 light hour distance, this need to be taken into
question.
Let us say, that, both tried to adjust their clocks in order to be in synch
with the other,
it seems that they will be 15 minutes out of synch. Therefore if both
received the
signal from the emitter at 12:00, the signals were not simultaneous.

>
> Now let's look at the same SR situation from the point of view of the
> emitter "X" that has relative motion wrt the two clocks. For X to be
> able to say that lightspeed is fixed in /their/ frame, they have to be
> able to say that the lightpulses take /different/ amounts of time to
> reach A and B, and that they should NOT hit their targets
> simultaneously.
> How does X reconcile this with the idea that both clocks get "zapped"
> while their dials show the same time?
> Well, says X, those clocks were synchronised at the beginning of the
> experiment using the "bad" assumption that the observation timelag AB
> is the same as the timelag BA. This, says X, has resulted in the two
> clocks being "wrongly" synchronised so that there is actually a
> mismatch in their displayed times that depends partly on the distance
> between them.

I fully agree..

> Since clock A is now argued to be showing the "wrong" time wrt clock B
> (according to X), the fact that both clocks were hit while they were
> /showing/ midnight means that they must have been hit at /different/
> times!

ok

> This idea of diagreements about perceived distant simultaneity runs
> through SR ... if you and I are passing each other at the moment that
> we both see the light from a supernova, we both agree that the light
> hit us both at a common event, but if we both have different ideas
> about what the speed of light really is, we can both end up
> calculating different nominal dates for when the star "really" blew
> up. So if we both draw up a map in the form of a 4D spacetime block
> containing all the events that we see in the surrounding universe,
> both our maps will contain the same events, with the same basic links
> between them, but if you and I mark sets of events that we believe
> happened at the same time (plane of simultaneity), the "planes" in
> your map that are simultaneous are going to be drawn in at an angle
> compared to the "planes" in mine, and our concepts of the "direction
> of time" in the block (the directuion perpendicular to the "plane")
> are going to be similarly skewed and distorted wrt each other.

ok
>
> So SR ends up saying that all observers agree about the local sequence
> of events at any point in the map, but the disagreements about
> supposed lightpeeds give different observers different definitions of
> the supposed spatial distance and time separation of pairs of
> events,and causes them to attach different time and place "labels" to
> the same events.
> The conditions that all frames are supposed to be equivalent, and that
> no matter how many observers you have each of whom is moving at 0.5c
> more then the previous one, the map can never quite turn through 90
> degrees for any observer ... this pretty much gives us SR's velocity
> addition formula, and the Minkowski geometry.

I think I understand this, a bit...
>
> ----------------------------
>
> If we implement the PoR using "historical" emission theory, then the
> logic is different. we then say that we have two emitters passing each
> other when they both emit light-pulses, those pulses will arrive at A
> and B at /genuinely/ different times. if X1'sa signals hit the clocks
> when they are showing midnight, then light from X2, moving
> differently, might hit clock A when the hands haven't reached 12, and
> B when they have already moved on. Each clock gets hit by two
> successive pulses, rather than one combined pulse.
>
> This sort of "old" emission theory is relativistic and "democratic",
> but its a bit of a mess, we have lightsignals overtaking each other
> along the same paths, and no conventient underlying light-metric to
> refer to. Light is emitted at c wrt every object, but the reception
> speeds are all over the place.

>
> --------------------------
>
> A third description might be to implent a "relativistic"
> light-dragging model -- to say that light is emitted at c wrt every
> mass, and received at c wrt every mass, because relatively-moving
> masses simply "drag lightspeed about" in their immediate vicinities.
> In this third sort of relativistic model the two clockkeepers believe
> that the velocity of light between them is being screwed up by the
> motion of the ermitter's mass between them, and that although the
> velocity of light AB and BA might well have been the same if the
> central emitter wasn't there, the presence of the moving emitter
> produces a localised light-dragging effect that messes up the previous
> geometry. So the clocks can end up being physcally synchronised
> synchronised differently depending on whether an intemediate mass is
> screwing up the light-signals
>
>
> >> It's common to describe this third equation (known as the
> >> "relativistic Doppler" equation) as being composed of two components,
> >> that initial c/(c+v) component due to light being assumed to travel
> >> preferentially in your own frame, and an additional Lorentz redshift
> >> component that only depends on relative speed, and not direction, of
> >>
> >> : freq'/freq = SQRT[ 1- vv/cc ]
> >
> >And according to the particle theory the relationship would have been
> >
> > freq'/freq = (c-v)/c... wouldn't this be close to gamma? SQRT[ (cc/cc) -
> >(vv/cc) ]?
>
> Under emission theory, the Doppler predictions divided by eq [1] leave
> a residual Lorentrz-squared effect,
> : freq'/freq = 1- vv/cc
> ,so yes, its similar in character ot the SR prediction, but redder
> than SR by an additional Lorentz factor.
> So experiments designed to report a Lorentz effect under SR would
> normally be expected to report a "Lorentz-squared" effect with
> emission theory.

But isn't the relativistic red shift due to the disagreement in relative
velocities between two frames , when compared to the emission theory?And are
such velocities defined by the shifts themselves?Can we know for certain
which velocity is the true one? If they are observed through events, then we
still have the problem of Relativity having length contractions whereas the
emission would claim a greater velocity... but not in the same magnetude, I
agree;

> So, for instance, if we aim a narrow viewing tube at 90 degrees to a
> moving emitter's path, where "90 degrees" is calibrated in our own lab
> frame, emission theory predicts that we should see a stronger redshift
> than SR says. Under emission theory, the redshift is explained simply
> as an aberration artifact, we are intercepting a rearward-aimed beray
> that reaches us with a recesson redshift component, but the forward
> tilt fo the ray due to aberratiuo nmeans that it accidentally ends up
> registering on our "transverse-aimed" detector.

   Is not the calculation based on the orbit of the earth relative to the
sun, at 30,000km/sec, implementing the length of the tube within the
equation, giving us the light's velocity as being c? My problem concerning
this would be that relative transverse velocities between the sources(stars)
and the earth are "not" 30,000 km/sec, and must be different for different
stars. If I understand properly( but I doubt that I understand this part
clearly), the abberation constant ought not to be a constant at all, even
for Relativity. Therefore, wouldn't the velocity of light concluded as being
c only when the light was absorbed and re-emitted within a medium
stationnary relative to us?...the atmosphere, the lenses?

> >According to your understanding, what causes the doppler shift? A change
in
> >the wavelength? How is this accomplished?
>
> In the first two "nonrelativistic" examples, we have a frequenct
> difference ocurring due to motion effects where the signal is being
> insetrted in th emetric, and again where the signal is being extracted
> In a simple absolute ether theory, we have a mixture of the two
> effects, depending on how fast the medium is supposed to be moving wrt
> each object ("aether wind")

ok

> In simple emission theory, it's the second explanation, and the same
> "stationary emitter" Doppler relationships, but it now applies
> symmetrically for all observers.

ok
>
> In SR, it's "either/or/both" ... we can use either the first
> explanation (supplemented by an additonal Lorentz time dilation
> redshift), or the second explanation (supplemented by an additonal
> Lorentz blueshift), and the final total Doppler effect that we see
> then has the same value either way.

My problem here is that since there is no ether and the light's velocity is
constant for all observers,
why is there no problem using either or both?

> Or we can pick any other "legal" frame that we like, declare that
> light "really" travels preferentially in that frame, and calculate
> /both/ sets of effects, "emitter-to-medium", and "medium-to-observer",
> and when we've done all this (including all the necessary Lorentz
> effects and bearing in mind that the SR velocity addition law means
> that the two smaller velocities won't add up conventionally to give
> our total velocity), the final observable Doppler shift will again be
> exactly the same as before.
> So SR lets us use any arbitrary mix of the two separate effects, as
> long as we do that associated Lorentz and velocity-addition stuff.

If it's not too complicated, could you write those equations down? Maybe
this could give me a clue.

> In a relativistic light-dragging model the distinction between "moving
> observer" and "moving emitter" seems to dissolve away -- we have a
> variation in the effective llight pathlength between source and
> emitter that varies with velocity, but we no longer have a flat
> lightbeam geometry to tell us exactly what those changed distances
> ought to be.
> When I started looking into this, I initially expected that if we were
> merging the two descriptions together, the logical result would be
> special relativity's "merged", "relativistic Doppler" equations,
> giving the same basic relaitonships as SR but in a curved-spacetime
> context.
> But no matter how hard I tried, I couldn't come up with a totally
> legal way of rederiving SR in curved spacetime, and everything seemed
> to be pointing me away from the SR amth and back to the
> emission-theory relationships. These do seem to work suspiciously well
> in this sort of curved-spacetime context, and do seem to solve all
> sorts of problems with current theory, and also turn out to be the
> unique set of energy relaitonships required for p=mv to be correct, so
> I'm 99% sure that this sort of model can't use the SR math, and maybe
> 85% sure that it has to use the emission-theory set.

I'm not certain I understood clearly the above, but, I believe to agree with
you that the particle theory seems to explain many things, and Relativity,
from the very little I do understand of it, seems still paradoxial...to me.

>
> (I think the first issue is why nobody seems to study this sort of
> relativity theory, I guess as soon as a mainstream researcher finds
> that the theory seems incompatible with SR, they are likely to stop
> investigating.)
>
>
> But I can't provide a nice linear derivation that takes a preexisting
> lightmetric, draws a path through it and reads offf the distances,
> becuase in this sort of model, there's no absolute preexisting
> geometry ... as soon as you hurl a new particle through a region, the
> shape of the lightmetric changes in sympathy.
> :(

  I'm not certain I have the capacity to be able in understanding the work
you've been doing in trying to merge the relativistic doppler with S.R. but
would be very interested in trying to read your material....do you have a
web site I could go to?

Thank you very much for your time Eric.

Andre

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