Time

[Alex K]

Except that doesn't explain anything. It's like someone asking what is life and someone else answering it's that which stops you from being dead.

Ok then, time is a dimension in 4 dimensional space time down which we can only move one way.

my bold

Well... I'd say movement is defined as a change (of position in a literal or abstract sense) over time, and therefore your last statement is a tautology. Or actually a statement about the word "movement" rather than about time, which would be fine, but a different thing.

[Pyrrho]

I still don't have a simple coherent understandimg of how time works after 10 years of research in fundamental physics. Im quantum field theory, time is a continuous parameter like the three+ space directions, but distinguished from space via the metric tensor. Yet, time is not entirely separate from space because in relativity, which direction in the four dimensions one calls time is not uniquely defined.

The *direction* of time, i.e. the reason why past and future are so different, im classical physics seems to be a purely statistical phenomenon. A space like boundary of the 4D universe with low entropy is the past. But once I thought I got that a little bit, I got confused again because  in quantum theory (at least in the usual picture) we have wave function collapse which fundamentally seems to distinguish past from future as well.

With that, I think it is safe to conclude that it is unlikely that someone is going to easily understand what time is.  And one can pretty well guess that someone who claims to have a firm grasp on the concept is likely mistaken.

Of course I, in my infinite wisdom, perfectly understand what time is.  But I am not going to tell anyone what it is.