### What is the Theory of Relativity?

Wednesday, September 12th, 2012When Einstein penned his Theory of Relativity in 1905 he probably did not realize the impact this would have on physics. In particular, the notion challenged Newton’s theory of Mechanics which reined for 200 years prior. Specifically the theory contended that all motion is relative.

The theory stems from two postulates:

- The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity).
- The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

Using these two simple postulates Albert Einstein was capable of showing some very amazing facts including that mass and energy as equivalent. This paved the way to the famous equation *E* = *mc*^{2}. E is energy, m is mass and c is the speed of light. Hence the amount of energy stored in a given unit of mass is incredibly high! Note that the speed of light is squared which is multiplied by itself. This famous equation resulted in the development of the atomic bomb as well as the basis for deriving energy from nuclear fuel.

Relativity

One interesting point to make about the theory of relativity is that all motion is relative. Einstein used a number of interesting thought experiments to show that travelling clocks run slower for an external observer. For instance, he theorized that a clock in possession by a person traveling at close to the speed of light would appear to slow down to an external observer. For the person traveling it would appear normal. This lead the way to theorize that the person traveling would in fact appear to be traveling in time. A person (let’s say) on a rocket traveling close to the speed of light may appear to have traveled for about 10 minutes, however a person back on earth may see the event as having taken place after many thousand of years!

Another interesting fact is that as a body travels close to the speed of light its mass gets larger. In theory you couldn’t travel at the speed of light because based on the mathematical model your mass would go to infinity. As you would approach this infinity it would take more and more energy to bring you closer to the speed of light and hence this energy would also approach infinity.

Scientific Evidence

The theory of relativity has been shown in many experiments. Traveling clocks have been show to slow down. In effect airline pilots do in fact experience time travel. Although their speed is not at all close to the speed of light – however their faster than normal speeds coupled with the many hours of flight do result in a slowing of their “clock”. Although this has been shown in experiment, the amount of time travel is limited to perhaps a few seconds a year.

Other experiments using particle accelerators show that as a particle is accelerated towards the speed of light their mass increases.