Physicist Leonard Susskind on time: why does time (appear to) have a direction? There's some very interesting remarks (in response to a question) at roughly 1:09:00 ff. Susskind is talking about telling time. In the talk he's presented versions of the cosmos when there are very long periods of thermal equilibrium in which nothing happens. Itty bitty particles just bump into one another in a random way but nothing develops in an interesting way.
So, how much time passes during such a phase? Well, Susskind remarks, it depends on how you measure time. If you measure time by a clock "which is geared to things happening, practically no time takes place...If you keep time by events that happen and change the system from one thing to another, nothing happens during those periods. It's a tiny tiny time. If you follow each molecule and ask how many times it's banged ... it's a huge amount of time." I like this.
This lecture was delivered at the Santa Fe Institute in 2013. Here's there description of the talk:
Anyone can see that the past is different from the future. Anyone, that is, but theoretical physicists, whose equations do not seem to distinguish the past from the future. How, then, do physicists understand the "arrow of time" — the fact that the past and future are so different? Leonard Susskind will discuss the paradox of time's arrow and how physicists and cosmologists view it today.
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