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| Ilya Prigogine |
We know Einstein
believed that the passage of time is an illusion. In a letter of condolence he
wrote in 1955 he said: ...the
distinction between past, present and future is only a stubbornly persistent
illusion. To assert this, he relied on the fact that Newton’s equations
of gravitation, his own equations of General Relativity, Maxwell’s equations (which
apply to electromagnetic waves) and Schrödinger’s equation (which gives the
wave function of a particle in quantum mechanics) are all symmetric with
respect to time.
How then can we
explain the fact that it seems so obvious that time goes from the past to the future? Usually,
physicists who believe that time is an illusion explain it by saying that, at
the microscopic level, time is actually reversible, but when we move to the macroscopic level, new, emerging phenomena
appear, one of which is the irreversibility of time. Let's give an
example:
According to
the usual theories, the movement of the molecules of a gas is perfectly
reversible. If we reverse the
direction of time, all the particles behave exactly the same and continue
colliding with each other, only they would move in the opposite direction. However,
when we consider all the trillions of particles that make up a gas, we see
irreversible phenomena arising, such as the fact that the gas always tends to
occupy as much space as possible, while its accumulation in a corner of the
container is much less likely.
The problem is that
our physical theories are based on approximations. Mathematics is a very
important tool for physics, but in mathematics there are several kinds of very
different problems, which differ in their difficulty to be solved. Let us look
at a few:
