Einstein’s Special Theory

of Relativity

Relative Motion

• ALL motion is relative• Speeds are only measured in relation to other objects• No way to determine in an inertial frame which objects are

moving and which are at rest• No universal reference point to which all motion is

measured

2nd Postulate – The speed of light is constant.

Time

Space=

Time

Space= C

1st Postulate – All the laws of nature are the same in all uniformly moving frames or reference.

The Light Clock

Time

Space=

Time

Space= C

The Light Clock• Einstein proposed time depends on motion

between the observer and the event being observed

• The clock has slowed down to our observation, but has not changed for the spaceship

• All physical processes, including heartbeat, slow down relative to a stationary clock when they occur in a moving frame.

Time Dilation

0

2

21

tt

vc

t0 – Proper time (time measured by an observer at rest with the clock).t – Relativistic time (time measured in the moving system relative to the clock).

Mass Dilation

0

2

21

mm

vc

m0 – Proper mass (mass measured by an observer at rest with the clock).m – Relativistic mass (mass measured in the moving system relative to the clock).

2

02

1v

L Lc

Length Contraction

Lo – Proper length (length measured by the observer at rest with respect to the object).L – Relative length (length measured by the observer moving with respect to the object).

Animation of Length Contraction

Spaceship Moving at the 10 % the Speed of Light   

Spaceship Moving at the 86.5 % the Speed of Light

             Spaceship Moving at the 99 % the

Speed of Light

Spaceship Moving at the 99.99 % the Speed of Light

                                       

Implications of the Postulates

• A rule of relativity is that changes due to alterations of space-time are always seen in the frame of reference of the the “other guy”.

• They see no change in their own frame.

Special Theory of Relativity

• The purpose behind the theory was to address inconsistencies in Maxwell’s electromagnetic theory.