What is time? and Janus Point.

I watched the following discussion between Julien Barbour and Brian Keating:

Here are my thoughts on this:

I think scientists always say that microphysics is time-reversible. IMO a more correct way to say it is that microphysics is velocity reversible with time still moving forward. For example, when we are asked to imagine a film of "two billiard balls colliding and flying away" being run forward and backward, we cannot tell if the scene is playing out in forward or backward flowing time. The example of idealized billiard balls is supposed to be similar to microphysics. But notice that in that imagined experiment the film runs backward but time is still running forward. This is the point Tim Maudlin makes. And this kind of ties into what Julien's theory of time is. Time is something that happens when the configuration of constituents parts of the universe changes from one state to the next. So as soon as there is a configuration change from one state to the next, time falls out of it. That is what time is. This fundamental time is without any rate yet. This time is another name for the phenomenon of change of configuration from current state to next state. This by definition is the forward flowing time. In other words, when we say that the current configuration changes to the next configuration. This use of the word like next is what gives us the direction of time flow implicitly and automatically. In fact, that can be called the definition of fundamental time. Also, note that even if the configuration goes from A to B and back to A on and on we can get time out of it. Also, note if the configuration does not change across the whole universe then the notion of time is rendered meaningless. Now, how do we get to the rate of the flow of time? Well, when we build comparative instruments from some parts of the universe, we call clocks, to compare the relative change of configuration of other parts of the universe. This choice of the clock is what gives us the rate of flow and the familiar day-to-day time we are used to. The clocks are usually subparts of the universe that cyclically go thru the same set of configurations. The hour hand goes back to the same place on the dial after 12 hours. The other subparts whose time clocks measure may or may not be cyclic.

About Janus Point

If the complexity was not 0 at Julien's Janus point (maybe he is using this as another name for big bang) then it could be a local minimum. In other words, there may be many more Janus Points. In that picture, we can think of only one direction of time from the earliest configuration to later configuration which may go thru many local minimums. In other words, the direction of time is unidirectional - an idea suggested by Tim Maudlin and different from Julien's idea of reverse direction of time on the other side of THE Janus point he talks about. Needless to say, I agree with Time Maudlin.

BTW Janus point refers to the two-headed Roman god Janus.