# What was Einstein’s most famous invention?

• Asked on January 3, 2010

Einstein’s most famous invention was not an invention so much as a discovery.  Einstein is known for the theory of relativity, represented by the famous equasion E = mcSquared.  E stands for Energy, M for mass, and “c stands for the speed of light in vacuum, ( which is: c = 2.99792458 108 m/s )” according to (http://www.physlink.com/Education/AskExperts/ae3.cfm?CFID=24199692&CFTOKEN=7e09ad1f2e9699a-F473F1E8-15C5-EE01-B95C763DDD4648DD).

A great quote on the importance of the theory, copied from the article in the first citation, is:

The theory of relativity was revolutionary because it showed how the speed at which time happens is mutable; that space and time are not discrete entities: time and space and motion (ie, movement through space) collapse into a fourth dimension, in which all act on each other. It is impossible to say “now” without saying “here” and “how fast”.

Or, to put it another way, imagine you have a twin. You stay on earth, your twin goes into space on a fast rocket ship for 10 years; when they come back, they’re a couple of years younger than you are. It even works with aeroplanes: circle the earth, flying low; when you return to your starting point, your watch will be slightly behind. “If you were actually moving at the speed of light (which you couldn’t do, but suppose you could),” says Penrose, “your watch would stop altogether.” It’s a rather more expensive method of age-defiance than CrÃ¨me de la Mer, but then again, it has the advantage of being a physical law of the universe.

Basically, it means that time and length are all relative to our speed.  Another example of “relativity,” while it doesn’t actually apply to speeds of light or E = mcSquared, is simply that when we put our fingers on a hot stove it can feel like they were there for many seconds, but if you are doing something you like, hours can seem like minutes.  The point of all this is that time is not as fixed a concept as we thought!