On May 6, 12:55*pm, PD wrote:
On May 6, 11:00*am, rbwinn wrote:





On May 6, 7:58*am, jem wrote:

kenseto wrote:
On May 5, 10:46 am, " wrote:
This is what Einstein exactly said in "Albert Einstein (1879-1955).
Relativity: The Special and General Theory. *1920.", chapter 9.
"Up to now our considerations have been referred to a particular body
of reference, which we have styled a "railway embankment." We suppose
a very long train travelling along the rails with the constant
velocity v and in the direction indicated in Fig. 1. People travelling
in this train will with advantage use the train as a rigid reference-
body (co-ordinate system); they regard all events in reference to the
train. Then every event which takes place along the line also takes
place at a particular point of the train. Also the definition of
simultaneity can be given relative to the train in exactly the same
way as with respect to the embankment. As a natural consequence,
however, the following question arises:
Are two events (e.g. the two strokes of lightning A and B) which are
simultaneous with reference to the railway embankment also
simultaneous relatively to the train? We shall show directly that the
answer must be in the negative.

V - * * ‡ * * * M' * * *‡ * */ Train
----==========================---------
* * * * *A * * * M * * * B * * *Embankment

When we say that the lightning strokes A and B are simultaneous with
respect to the embankment, we mean: the rays of light emitted at the
places A and B, where the lightning occurs, meet each other at the mid-
point M of the length A -- B of the embankment.

Right that's because Einstein stipulated that M is at equal distance
from the strikes and that the speed of light is isotropic in the track
frame. These stipulations automatically specfied that the strikes were
simultaneous to begin with. Otherewise the track observer will not be
able to sees the strikes to be simultaneous.

But the events A and B
also correspond to positions A and B on the train. Let M' be the mid-
point of the distance A -- B on the travelling train. Just when the
flashes of lightning occur, this point M' naturally coincides with the
point M, but it moves towards the right in the diagram with the
velocity v of the train. If an observer sitting in the position M' in
the train did not possess this velocity, then he would remain
permanently at M, and the light rays emitted by the flashes of
lightning A and B would reach him simultaneously, i.e. they would meet
just where he is situated. Now in reality (considered with reference
to the railway embankment) he is hastening towards the beam of light
coming from B, whilst he is riding on ahead of the beam of light
coming from A. Hence the observer will see the beam of light emitted
from B earlier than he will see that emitted from A.

This point of view of the track observer by Einstein is wrong and
bogus.....it appears that Einstein didn't fully understand his own
theory and postulates. What he said above violates the isotropy of the
speed of light in the train and it violates the PoR. The track
observer must use the postulates to predict what the train observer
will see. According to SR the speed of light in the train is isotropic
and the laws of physics in the train is the same as in the track. From
these two postulates the track observer predicts what the train
observer will see as follows:
1/2 the length of the train = L
Therefore at the time of the strikes both M and M' are at equal
distance fron the strikes.
The light path length for the each light front to reach the M'
observer = gamma*L
The transit time for the light fronts to reach M'= gamma*l/c
Therefore the train observer will sees the strikes to be simultaneous
at time = gamma*L/c according to the track clock.

The track observer will see that he sees the strikes to be
simultaneous at time L/c according to the track clock.

What this means is that the strikes in the track frame occur
simultaneously at an earlier time of L/c and the strikes occur
simultaneously at a later time of (gamma*L/c) in the train.

This arguement preserve the isotropy of the speed of light and the PoR
in the train.

The argument, Seto, preserves the general consensus that you have the
mind of a 4-year old. *Here's another opportunity to confirm it.

Here's a picture showing 2 lightning strikes L1 and L2, with light
fronts from the strikes traveling toward 2 observers, one of whom (O2)
is moving to the right relative to the other (O1).

L1...).........O1...O2.....(...L2

Here's a later picture showing the light fronts just reaching O1
simultaneously.

L1............)O1(.....O2......L2

Challenging questions for 4-year olds:

In the second picture, has the light from either lightning strike
reached O2? *Has the light from either lightning strike not reached O2?

Bonus question:

Does the light from both lightning strikes reach O2 simultaneously?- Hide quoted text -

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Ken Seto is right about this. *A photon in S is traveling at 186,000
miles per second as measured by a cesium clock in that frame of
reference. *A photon in S' is traveling at 186,000 miles per second as
measured by a cesium clock in that frame of reference. *What is
occuring is called relativity of time.
With regard to your little diagrams, suppose that the bolts of
lightning strike the front and rear of a train, leaving marks on the
train and on the railroad track. *In the frame of reference of the
track, photons are emitted at the two marks on the track and proceed
to the observer midway between them, reaching him in a time of .5L/c,
where L is the length of the train. *In the frame of reference of the
train photons are emitted at the points where lightning struck in that
frame of reference, the two marks left on the train. *The photons
proceed to the observer in the middle of the train, reaching him in a
time of .5L/c as measured by the cesium clock on the train.

Everything you've said up until this point is fine.
So let's call the time the rear strike hits (and leaves marks on track
and train) Tr (in the track frame) and Tr' (in the train frame). The
time the front strike hits (and leaves marks on track and train) Tf
(in the track frame) and Tf' (in the train frame). We don't know
anything about those times just yet; we've just given them labels.

And given your prescription, then, the track observer can expect to
see flashes from the two strikes at times
(Tr + 0.5L/c) and (Tf + 0.5L/c)
and the train observer can expect to see flashes from the two strikes
at the times
(Tr' + 0.5L/c) and (Tf' + 0.5L/c).
Now, these times in parentheses are what the observers actually see,
and so we can then *deduce* something from those *observed* times
about the nature of the *unobserved* times Tr, Tf, Tr', Tf'.

Interestingly, what happens (in real life, as measured in experiment)
is that the times of the flashes the track observer sees are the same:
(Tr + 0.5L/c) = (Tf + 0.5L/c)
and that the times of the flashes the train observer sees are not the
same:
(Tr' + 0.5L/c) =/= (Tf' + 0.5L/c).

Now, what one naturally concludes from this observation is that
Tr = Tf, that is, the strikes themselves were simultaneous in the
track frame,
and
Tr' =/= Tf', that is, the strikes themselves were not simultaneous in
the train frame.

On the other hand, Seto is of the opinions that
a) Einstein wrote his example with the explicit set-up (he calls it a
stipulation) that Tr=Tf AND Tr' = Tf'. Of course, when shown what
Einstein really wrote, there is no such explicit set-up at all, and
this flummoxes Seto.
b) Even if Einstein didn't write down his example this way, if Tr =
Tf, then it MUST be that Tr' = Tf' (for whatever reason Seto thinks
this is so), and that to hell what the train observer *actually* sees,
one would *logically* demand that (Tr' + 0.5L/c) = (Tf' + 0.5L/c).
c) The truth, according to Seto, is determined by argument and not by
experiment, and so what the train observer *actually* sees is
irrelevant. Seto thinks that he can *logically conclude* what the
train observer MUST see, based on what he thinks is a superior
assumption (that Tr' = Tf' because Tr = Tf), and he further thinks
that the *conclusion* that the train observer sees (Tr' + 0.5L/c) =/=
(Tf' + 0.5L/c) is based on a circular assumption that Tr' =/= Tf' and
doesn't see why one would assume that to begin with. He doesn't get
that what the train observer sees is not a *conclusion* but an
observational *fact* from which we *start*, not where we end up.

What you wrote above is a bunch of bull you made up. I did not say any
of the thing you said above.

Ken Seto



* * *Now you want us to consider what photons emitted at the two
points on the track are doing, and how one reaches the observer on the
train before the other. *It does not happen. *In the frame of
reference of the train, the first photons emitted are emitted at the
points where the lightning left marks on the train. *Any marks left on
the track where made afterward. *Consequently, any photons emitted
from the two marks on the track will reach the observer at the middle
of the train after the photons emitted at the points where the
lightning struck the train. *What about the track moving relative to
the train?
* * Any photons emitted after the marks on the track move away from
the front and rear of the train will reach the observer at the middle
of the train after the photons emitted where- Hide quoted text -

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