Chalnoth said:
Yup. Forward in time is a direction. It's just not a direction you can point.
That was my initial response, there is only forward "in time".
But then the OP question becomes meaningless!
Can time be approached from a physical viewpoint at all. IMO to speak of direction is misleading. Along with different spacetime coordinates, time exist in latent form everywhere in the universe. I always thought of it as a non-causal universal potential.
In wiki, I saw the section of sets, but that is merely an exercise in probabilities. So the direction of time is a probability? A set of indicators which suggest the direction of time in the future?
This can be demonstrated by the double slit experiment, which shows a probability function of possible events, but what does that have to do with time itself or more to the point, direction?
OK, allow me to clarify this in my mind. If tomorrow is an (as yet) unspecified direction how can we make calculations for anything other than a generalized statement that time will be moving in an unspecified direction toward "somewhen", but always along with a series of chronological events, such as me traveling west on a train. The actual duration in time to complete my trip is affected by my physical speed, but not by my direction of travel.
It makes no sense to me. It is the worldline, the continuation of a series of events that creates a chronological time frame for that series of events. It stands to reason that there needs be change in the physical conditions (which require time) for time to become measurable by the duration of the event.
IMO, time ONLY comes into existence as result of a physical action which 'requires' and 'creates' time to be able to become instantiated in physical space at a specific coordinate, which undergoes change or is different than the starting coordinate. This bridging of physical events creates time in the process as a byproduct, a result.
Time does not exist by itself, it is a latency, a potential of spacetime, which becomes measurable only as a result of a change or action "in physical space". Whithout any physical change to measure, what is the need for time? Let alone direction.
The use of space by physical events creates a simultaneous "forward in time" chronology for those physical events, but only at the "time" of the event, no matter what direction the physical event itself follows. Time is a directionless latency, which allows reality to instantiate in chronological order, no more, no less..
Time is a result and cannot be measured at all without physical change. We can "assign" an estimate of the "time it will take" for an event to complete itself, but that is probabilistic and completely depends on the actuation of the event. But as soon as the event begins, time will record the actual time used going always forward in time along with the unfolding of the event.
How about a definition which states that time is a non-causal latency which becomes measurable only as a result of change and the duration of that event in spacetime. Therefore time can be measured (or even projected into the future) along with the direction of the event, but not independently by itself as a direction of time.
Fredrik,
The only thing that can define a direction of time is the kind of stuff that WannabeNewton is talking about. First you slice up spacetime into 3-dimensional hypersurfaces labeled by a real parameter t, so that each event belongs to exactly one of these hypersurfaces. Now if we want to find the direction of time at an event p, we would look at the hypersurface that p belongs to. There are two directions that are orthogonal to this hypersurface at p. In one of these directions, t is increasing, and in the other direction, t is decreasing. The direction that's orthogonal to the hypersurface and such that t is increasing, can then be considered the direction of time at p.
Note that this direction depends on our choice of how to do the "slicing".
This brings the question; can time be associated with a single point "p" at all? Then the conclusion the time in one direction "increases" and "decreases" in the other direction, sounds odd. If time does indeed increases or decreases in certain directions it is because space increases or decreases in size in those directions. IOW, the directions are spatial, not temporal.
Time follows no temporal direction other than the direction of spatial events, which may be in any direction. As the spatial events progress, time progress along with that worldline. But the counting of time is always forward, as it cannot do anything else, it is a non-causal result of a previous action.
Please consider any of my "assumptions" as probing questions. As a fan of Bohmian mechanics I am really interested in this discussion. Moreover, I do not seek to dispute any accepted theories, but try to stay within established knowledge.