Einstein and the Speed of Time

The world experienced a great leap in science when Einstein proposed his theories of Special and General Relativity. For about 200 years physics depended on Newtonian laws. It was thought then that time was constant; an hour is the same all over, under any conditions.

Understanding of time soon changed, and time was different ever since.

Let's view the way Newton thought of time. It was said that time can be related to the running of water in a river. Should the speed of the water be measured at any point, it would yield equal results. The same was thought of time; if time was measured at any point in the universe it would be the same.

Suppose George and Bill synchronised their watches. George left on a super fast spaceship, and came back an hour later (according to his own watch). Newton would say that Bill would have waited an hour for George to come back, and their watches would read the same time.



Einstein disagrees! According to his theories, time is relative, and it depends on the speed at which one travels. Suppose that George left earth on the same spaceship at 1:00 p.m. travelling at a speed close to that of light, and suppose that Bill was in some way was looking at George's watch. Bill would realise that George's watch is advancing very slowly compared with his. So if Bill's watch said 2:00 p.m. then George's watch would have said 1:05 p.m. for example. On the other hand, George would see that Bill was acting a bit strange; he would see him doing everything pretty fast, as if he was in a movie that was being fast forwarded.
Strange indeed! This time difference applies to everything surrounding both George and Bill. If George returns one year later (according to his own time), he would find out that Bill aged 12 years. Not only this, but both George and Bill, separately, feel normal; George does not feel that his life was moving any faster than normal, nor does Bill feel that his life was moving any slower than normal.