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Re: SR examination question "survey"



On Fri, 18 May 2001, Michael Edmiston wrote:

...
(difference 2) the revision removes the word "observe" from two places.
This would appear to be an attempt to remove the idea of observations and
switch the context to what the clocks are actually doing. This doesn't make
any sense to me. Each clock is doing what it's supposed to do. Peter's
clock is keeping accurate time in his frame and Jane's clock is keeping
accurate time in her frame. There isn't any "relativity effect" until we
start making observations and comparing them. To make these observations
and comparisons we have to observe and record the positions and times of
events. In the original question the events are poorly described. In the
revised question the events are even more poorly described. "When Peters
clock has made one revolution." What does that mean?

Not that I disagree, of course; I have thought from the beginning
that there is no sense to be made of the phrase "when something
happens" (even if the "something" is a perfectly well-defined
event) unless one specifies *who* is determining when the event
happens. The problem with the question is *not* that the events
are poorly defined, it is that the frame in which the time of
those events is to be determined is not specified.

So I don't understand why you think that changing "when Peter
observes the second hand on his watch to have made..." to "when
the second hand on Peter's watch has made..." makes a difference.

To be concrete, allow me to propose a fourth question for my
survey.

Q4: Consider the following descriptions of two events:

The place and time where/when Peter *observes* the second hand on
his watch to have made one complete revolution.

The place and time where/when the second hand on Peter's watch
*has* made one complete revolution.

Are these descriptions of the same event (within a trivial
uncertainty of about 3 feet and/or 3 microseconds) or not?

John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm