When will we meet again?"
"When the autumn leaves that fall from the trees
Are green and spring up again."
– The Unquiet Grave
Recently I watched the Feynman Messenger Lectures, from 1964.
In this lecture Feynman discusses past and future, in a way that in some ways has never been bettered. Only recently has Carlo Rovelli explained it as well. The direction of time is driven by the fact that things easily become intermingled. If I drop some food colouring into a glass of water, then after a time the water will all be the same colour. In principle the food colouring might one day all collect together again, and the water once more be clear. But this is very unlikely to occur. An inconceivably large number of ink and water molecules would have to randomly make their way back to the start line.
The Unquiet Grave is a medieval folk song, that expresses the thought that things decay, and time cannot be reversed, at least as far as livings things are concerned. Joan Baez sang it, in the same era as the Feynman lectures, and I've always thought she performed it very beautifully.
Search for 'Joan Baez Unquiet Grave BBC 4' and you will find it.
Incidentally she has a cousin John Baez, who is a physicist, and a great teacher.