Last year the Yankees won the World Series... Three years ago France won the soccer World Cup. Everyone knows that. But does anyone know who is the World Champion next November, or who will raise the World Cup in Japan in 2002? I doubt.

Why is that? What is the difference between past and future?
The sensation of the progression of time from a definite past to an uncertain future is deeply rooted in us. There is a distinct direction from past to future. Past carries the cause and future the effect.
However, past and future can not be distinguished physically. (Physical equations will remain the same if we replace t by -t)

 Imagine a glass of water resting on a coffee table. If you push the glass, it will undoubtedly break on the floor and spill the water all over the place. Now suppose that you have recorded the incident on videotape and that you run the film backward. You will see the shattered glass pieces coming together to form the original glass and the water jump back in the glass while the glass finds its place back on the table. Unbelievable! The reason these things never happen in reality is because of what is called the Entropy law or the second law of thermodynamics. This law states that in an isolated physical system, the degree of disorder (or entropy) increases with time. When the glass was broken, its entropy increased. In order to bring it back you need to lower its entropy and that is not possible.

That is why it is impossible for us to imagine that the broken glass was brought back to its original state.
The second law of thermodynamics actually defines a direction of time, and this unables us to distinguish past from future.

 Other questions in this section : • Why do we know the past and not the future?  • Why can't science answer all our questions?  • Why doesn't a spider get caught in its on web?  • Why being reasonable is really unreasonable?  • Why water is wet?