Repository | Book | Chapter

As physicists say, all basic laws of physics are invariant against time reversal. This holds for the fields of mechanics, quantum mechanics, electrodynamics, the theory of relativity and so on. What though, is actually, meant by "invariant against time reversal"? Let us consider the simple example of a pendulum (Fig. 1). We can lift it and let it swing downwards. At its lowest point, it will arrive with a velocity υ. We can invert this process by letting our pendulum start at its lowest position and give it a push so that it starts with a velocity — υ i.e. its original velocity but in the opposite direction. In the ideal case considered here, the pendulum will return to its initial position from which we had let it go before.

DOI: 10.1007/978-3-642-78685-3_11

Full citation: