Postulates of special relativity first postulate all

Postulates of Special
Relativity
•
First Postulate: All laws of nature
are the same in all uniformly
moving frames of reference
–
i.e. The behavior of a coin when
flipped on a plane that is moving at
constant velocity is no different than if
flipped while standing still
•
No experiment confined in the
moving reference frame itself can
determine whether or not there is
uniform motion

Postulates of Special
Relativity
•
Second Postulate: The speed
of light, c , in empty space will
always have the same value
regardless of the motion of
the source or observer.

Time Dilation
•
Light Clock: A
flash of light
bounces back
and forth
between
parallel
mirrors and
“ticks” equal
intervals of
time

Time Dilation
•
Consider a light clock observed from someone
inside a fast-moving space ship
–
This observer would see the light bouncing
vertically up and down
•
Consider a light clock observed from someone
outside a fast-moving space ship
–
This observer would see the light moving along a
diagonal path, which is therefore longer

The Twin Trip
•
Consider identical twins:
–
One twin takes a high speed round-
trip journey
–
The other twin stays on Earth
•
When he returns, the traveling
twin will be younger than his stay-
at-home twin
–
i.e.) Traveling at 50% c , 1.15 years
will elapse on earth
–
i.e.) Traveling at 99.5% c , 10 years
will elapse on earth

The Twin Trip