*Europhys. Lett.*,

**43**(6), pp. 611-616 (1998)

## From the triangle Sagnac experiment to a practical, crucial experiment of the constancy of the speed of light using atomic clocks on moving objects

St. Cloud State University - St. Cloud, Minnesota 56301, USA

Received:
15
April
1998

Accepted:
23
July
1998

According to the triangle Sagnac experiment, between point A and point
B that are moving in a circular motion, the travel times for light or
radio signals from A to B and from B to A are different. The
difference , *i.e.* the Sagnac effect, equals , where D is the foot of the altitude to AB, *V*_{D} is
the speed of point D and *L* is the distance from A to B. The Sagnac
effect exists whether the radius of the circle is as small as only few
centimeters, *e.g.*, in fiber-optic gyroscopes, or as big as
twenty thousand kilometers, *e.g.*, in GPS. Therefore, if we mount
an atomic clock and signal transmitter and receiver on each of two
objects moving at the same speed in a circular motion (it is not
necessary to synchronize the two clocks beforehand), we will find such
a time difference. Practically, using sufficiently large *L* and
*V*_{D}, this time difference can reach around 1 ns, which is
relatively easy to detect with current technology. This experiment
would yield both practical applications and theoretical
implications. First, it can be used as a verification of Sagnac
corrections in GPS. Second, a theoretical problem arises when these
two objects change their paths to a straight line. Would the time
difference still exist (then it contradicts the principle of the
constancy of the speed of light) or does the time difference "jump”
to zero? The result of the experiment will be of great interest.

PACS: 03.30.+p – Special relativity / 06.30.Ft – Time and frequency

*© EDP Sciences, 1998*