Frequently Asked Questions
know the "Twin Paradox". It shows that, if one of the twins
travels at large velocities, his age appears younger than the
twin, who did not travel. This application of relativity is well
but of course such experiment has never been done and cannot be
verified experimentally. It is more challenging to
that has already been verified experimentally. Let us
Let us use a very accurate method of measuring the size of the
From a location on the equator, let us use the international
standard of length to measure a distance of about 300 meters along
equator. In fact, the exact distance is really 299.792458 meters
that this distance is exactly one microsecond-light.
distance, we draw a line on the ground. Then we repeat the same
measurement along the Earth equator for another similar distance
meters, and we draw another line. This procedure is repeated
of times until the full circle around the Earth is completed and
experimenter arrives again at the point of departure. This
illustrated below on figure 1. We find that the number
on the Earth equator is about 133 425.
In the second part of the experiment, we send a beam of light
the Earth equator. We can anticipate that at each microsecond, the
of light passes each line drawn on the ground, because they have
spaced by one microsecond-light (by definition). When we
eastward, light goes across 133425 lines, and therefore take
microseconds to go around the world, passing each line every
microsecond. Also, when we send the beam westward, the beam
also passes one line every micro-second, so that light takes
complete the trip around the world. Of course, the experiment is
done and light is traveling inside a vacuum pipe in which air has
completely pumped out.
following the Sagnac effect published in 1914 it has been shown
experimentally that light takes a longer time to go around the
Eastward than Westward. The Sagnac effect is well known. It has
added in the Global Positioning System (GPS) to determine time and
coordinates on Earth. The Sagnac effect is also used in optical
gyroscopes. It is very well extablished.
How can the experiment above with light moving across each of the
133425 lines every microsecond be compatible with the observed
effect? How can the time taken, to go around the world be longer
going Eastward then Westward, since there are the same number of
(133425)? Light takes exactly one microsecond to go between
The answer to this problem will be given (and explained) here as
as I have time to write it down, probably during the first part of
2000. Make a bookmark
want to remember the Web address.
Explanation now published at "The GPS and the Constant
course, it is not a real paradox. It is physical reality.
is logical and uses conventional logic (I mean without the magic
Note: Don't tell me that it is because the
is rotating. So what?
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llustration of the
Paradox #1 December, 1999
New Choice of Questions