I tend to think of time as flowing in one direction. But it could flow in the exact opposite direction, throughout the entire universe, and still make sense physically. So the way I like to make the distinction, the way to tell which direction time is flowing, is to observe the tendency of events towards entropy or order. Our universe tends towards entropy.

As humans, we have found that most order is achieved through effort, work, and often great amounts of time, and that structures of order are susceptible to destruction. Things fall apart over much smaller time spans than took to build them, in general. This tells me that time flows in the direction in which events tend towards entropy.

If time flowed backward, it would make sense to me that things would take effort, work, and often great amounts of time to fall apart, and structures falling apart would be susceptible to come together (tend toward order).

If anyone knows more about this topic than I do (which is probably a lot of people here), please tell me if this makes sense!

I tend to think of time as flowing in one direction. But it could flow in the exact opposite direction, throughout the entire universe, and still make sense physically. So the way I like to make the distinction, the way to tell which direction time is flowing, is to observe the tendency of events towards entropy or order. Our universe tends towards entropy.

As humans, we have found that most order is achieved through effort, work, and often great amounts of time, and that structures of order are susceptible to destruction. Things fall apart over much smaller time spans than took to build them, in general. This tells me that time flows in the direction in which events tend towards entropy.

If time flowed backward, it would make sense to me that things would take effort, work, and often great amounts of time to fall apart, and structures falling apart would be susceptible to come together (tend toward order).

If anyone knows more about this topic than I do (which is probably a lot of people here), please tell me if this makes sense!

The 2nd law of thermodynamics has its own arrow of time. Entropy always increases in the Universe. Even if I build a highly ordered system, the disorder I create in doing so outside that system outweighs the order I create. Booklearnin' for instance: the heat my brain gives off adds to the disorder of the Universe much more than the ordering of neurons in my brain subtracts.

The relationship between the thermodynamical arrow of time and the others (cosmological and psychological) is interesting. The cosmological arrow of time is in the direction of Universal expansion. As the universe expands, the number of possible configurations of matter within the universe necessarily increases. Entropy is simply a count of this number of configurations, so there is some link there.

A firmer link lies between thermodynamic and psychological time. Building memories, that is storing information about events, necessarily lowers the entropy of the brain and increases the entropy of the Universe as a whole. The reverse is something we'd probably have no control over: reducing entropy would likely yield information spontaneously rather than practically. So the psychological arrow of time is probably built on the thermodynamic one.

The way I see it, if time moves forward, then entropy increases. Also, if time moves backward, then entropy decreases.

Overall, I believe that it is impossible to know the direction that time is flowing at any given moment in time.