Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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