- As stated in Postulate 2 of the Theory of Special Relativity, the speed of
light through empty space is always measured to be c, regardless of the motion
of the source (or observer).
2) The Relativity of Time
Let’s go back to me on my spaceship, passing by your planet at a speed of c. Let’s
say, as I’m standing in the ship, I sneeze, and then, 1 second later, I sneeze again. If
you were holding a stopwatch and measured the time between my sneezes, you
would not get 1 second. Time is relative. The time as measured by you would not
agree with the time as measured by me.
To see how these time intervals would be related, imagine the following. In my
reference frame, let me call the time between my sneezes ∆T 1. If my velocity past
you is v, then the time that you’d measure between my sneezes would be
∆T 2 = γ • ∆T 1
where γ is the relativistic factor
Proper Time and
Dilated Time
∆T 1 can be referred to as
the proper time, which
is the time measure in