Question

Discuss possible ways to resolve the following paradox: both Newton's equations and Schrodinger's equations are the same when time moves forwards and backwards, yet we know that in the real world in which we live time only moves in one direction.

Answer 1

Quantum mechanics is widely viewed as being imposed on the well-understood classical world of Newtonian mechanics and Maxwell’s electromagnetism.

Here is a typical textbook question. Your car has run out of petrol. With how much force do you need to push it to accelerate it to a given speed? The answer comes from Newton’s second law of motion: F=ma

When people first started considering the world at the smallest scales, for example electrons orbiting the nucleus of an atom, they realised that things get very weird indeed and that Newton's laws no longer apply. To describe this tiny world you need quantum mechanics, a theory developed at the beginning of the twentieth century. The core equation of this theory, the analogue of Newton's second law, is called Schrödinger's equation.