Name: Mike S.
Date: Around 1993
Has the speed of light slowed down over the centuries?
Earthbound measurements of the speed of light show no tendency of
this quantity to change over time. But reliable measurements have been made
for less than two centuries; perhaps this is too short a time span over which
to detect a change. However, looking out at various objects in the universe,
we can observe light from many past times, even billions of years ago. This
has in fact been done. According to the theory, light from remote objects
such as quasars, some of which recede from Earth at a speed nearly equal to
the speed of light, will travel at the same speed as light from other sources.
The "nearly constant" is a bit of hedging. It is risky to make absolute
statements based on measurement; there is always some uncertainty in a
Click here to return to the Physics Archives
Update: June 2012