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Re: A Question of Simultaneity

The previous postings (mine included have answered (1) with a yes. I think
that is all that is necessary to answer the original question. But, to
answer the others.

for (2), assuming the intermediates are not necessary as you state, meaning
there is no time delay as the pulse travels down the length of the train, it
does so at the speed of light. Therefore I conclude that all frames measure
c for the speeds of the pulses in accordance with the postulates of SR.

(3) No, the distance as seen in the other frame of reference are different
& the emission of the two pulses are not observed as being simultaneous,
necessary so that they will arrive at the center at the same time.

Joel Rauber

-----Original Message-----
From: Robert Cohen [mailto:Robert.Cohen@PO-BOX.ESU.EDU]
Sent: Friday, January 25, 2002 2:27 PM
To: PHYS-L@lists.nau.edu
Subject: Re: A Question of Simultaneity


To me, the question seems to be asking something different
than what has
been addressed so far. Consider a situation in which we have
a series of
light sources along the length of the train.

S S S S S S S O S S S S S S S S

An observer on the train is at point O with two light sources. The
right-most source emits a flash, which then sets off a
chain-reaction of
flashes to its left as each source simultaneously receives and emits a
flash. Eventually, the light source at O flashes.

The same is true when the left-most source emits a flash.
Each source to
its right simultaneously receives and emits a flash.
Eventually, the light
source at O flashes.

(The series of sources is not necessary but helps to visualize the
propogation of the original flash on each side)

1. If the flashes end up simultaneously at O in the train
reference frame,
do they end up simultaneously at O in all reference frames?

2. If the speed of the flash pulse along the train is c in the train
reference frame, is the speed also c in a reference frame
moving at speed v
relative to the train?

3. If the distance from O to the left-most point is the same
as the distance
from O to the right-most point, is the ratio of the distances
also 1 in a
reference frame moving at speed v relative to the train?

Can all three be true?

Perhaps Thomas McCarthy can correct me if I have misinterpreted his
question.

____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ, E. Stroudsburg, PA 18301

-----Original Message-----
From: Bob Sciamanda [mailto:trebor@VELOCITY.NET]
Sent: Friday, January 25, 2002 2:57 PM
To: PHYS-L@lists.nau.edu
Subject: Re: A Question of Simultaneity


Set up two detectors on a railroad car (spaced along the
direction of
travel). Wire the detector outputs into a coincidence counter whose
output blows the train whistle when coincident events occur.
All of this
apparatus is on the moving train.
Now add, on the train, an isotropic light source midway between the
detectors. When this light source fires a pulse, the train
whistle will
blow.
A second observer standing on the ground sees that the whistle was
triggered by light arrivals which were not simultaneous in
the ground
frame, but he realizes that the apparatus is rigged to fire
only for light
arrivals which are simultaneous in the TRAIN frame.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor
----- Original Message -----
From: "Thomas McCarthy" <tmccarthy@SPS.EDU>
To: <PHYS-L@lists.nau.edu>

If two flashes of light appear simultaneous and
consequently trigger
a response, how does the non-silultaneous nature as viewed
from another
frame explain the occur of the same response, yet the light
is not seen
to impinge upon the trigger at the same time? Thanks.
Tom McCarthy