Special Relativity: What Time is it?

Michael Fowler, Physics Department, UVa.

Special Relativity in a Nutshell

Einstein’s Theory of Special Relativity, discussed in the last lecture, may be summarized as follows:

The Laws of Physics are the same in any Inertial Frame of Reference.  (Such frames move at steady velocities with respect to each other.)  

These Laws include in particular Maxwell’s Equations describing electric and magnetic fields, which predict that light always travels at a particular speed c, equal to about 3×108 meters per second, that is,186,300 miles per second.  

It follows that any measurement of the speed of any flash of light by any observer in any inertial frame will give the same answer c.

We have already noted one counter-intuitive consequence of this, that two different observers moving relative to each other, each measuring the speed of the same blob of light relative to himself, will both get c, even if their relative motion is in the same direction as the motion of the blob of light.

We shall now explore how this simple assumption changes everything we thought we understood about time and space.