The speed of light is constant but length and time can change when objects travel at close to the speed of light. These changes depend on the relative motion of the observer and the object.
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 â 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 vacuumA volume that contains no matter. 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.
massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g)., length and timeTerm that describes the order and duration of events. For example, the Physics lesson was 50 minutes long. must all be redefined at speeds greater than 90 per cent of light speed (approximately \(2.7 \times 10^{8}ms^{-1}\)).