# Special relativity

We spend our lives moving quite slowly compared to the speed of light. This can make some of the phenomena of relativity difficult to believe.

All of the changes that occur at close to light speed have been experimentally demonstrated – they are not science fiction.

When Albert Einstein carried out thought experiments to predict motion close to the speed of light he realized that the speed of light in a was actually a physical constant and could not change. It is given the symbol c and is approximately $$3 \times 10^{8}ms^{-1}$$

As the speed of light remains constant, this means that everything else has to change at these speeds.

, length and must all be redefined at speeds greater than 90 per cent of light speed (approximately $$2.7 \times 10^{8}ms^{-1}$$).