# By Caitlin French

### Introduction to Special Relativity

Special relativity, developed by Albert Einstein in 1905, completely transformed our ideas about space and time. Although Newtonian mechanics provides good approximations at low speeds, Einstein corrected mechanics in order to handle situations involving motion near the speed of light. Einstein replaced the Galilean transformations of Newtonian mechanics with the Lorentz transformations in his theory of Special Relativity.

Einstein’s theory is based on two main postulates, from
which many interesting things follow. But the main idea of Special Relativity
is that, if you move fast enough through space, the observations you make about
space and time differ from the observations of other people who are moving at
different speeds.

### The Two Postulates of Special Relativity

Special Relativity is based on two postulates:

1. The laws of physics are invariant (identical) in all
inertial systems (non-accelerating frames of reference moving at a constant
speed).

2. The speed of light (c) in a vacuum is the same in all
frames of reference, regardless of motion relative to the light source. This is
required for the laws of electrodynamics to apply equally for all frames.