- Zeit ist das, was man an der Uhr abliest.
Albert Einstein (1879-1955)
Time provides an ordering of the happenings in the world. It is our way of keeping track of our events as condensed in the saying: “the only reason for time is so that everything doesn't happen at once” (often attributed to Albert Einstein, but probably to be credited to the writer Ray Cummings, 1919). Without time, the world would be completely still. But what is time?
The philosophical analysis of time is as old as philosophy itself, starting around 500 BC with the opposition between Heraclitus, who famously maintained that everything constantly changed, and Parmenides, who felt that if not change, then at least time was an illusion. This pre-Socratic opposition between 'becoming' and 'being', or 'change' and 'existence', continued with Aristotle and on to this day.
Clocks can tell you what time it is, but they cannot tell you what time is. Time can mean the duration between events; It can mean the temporal location of an event, or it can mean the temporal structure of the universe. But it may not be what it seems. Perhaps it is only a human construct to help us differentiate between now and our perception of the past. It may even be an illusion made up of human memories; everything that has ever been and ever will be is happening right now, as some people say.
- The scientific definition of time does not address the fundamental questions about the nature of time. Science has adopted the relational view of Aristotle who wrote “there is no time apart from change….”. We see change, and change is the variation of properties with respect to time.
- Time itself is not an observable. Time manifest itself through change and is measured by clocks, as summarized in Albert Einstein’s famous quote above.