The unidirectionality of time
There doesn’t seem to be a definition of time anywhere. Does that mean it’s not real?
The Big Questions by Richard Morris has a chapter on this exact question. The book was quite terrible. However, the first chapter, regarding time, was thought provoking if a little sparse on hard facts.
The entire chapter revolved around the idea of time’s direction. Does time flow in one direction? Is that direction reversible? Anyone who is familiar with some science has heard of the laws of thermodynamics. The sort of basic, most important, laws of physics. Well one of them has an impact on time, or at least its direction. That is the law about entropy. Time seems to indicate increased entropy. Because entropy has not been found to reverse itself in nature it’s assumed time could not reverse itself either.
A second “arrow of time” Morris describes is a subatomic particle called the kaon. Apparently the kaon’s decay is time asymmetrical. All other particles decay in a manner that can be reversed. A uranium-238 atom can decay into a thorium atom (releasing an alpha particle in the process) but when bombarded with alpha particles the thorium will create a uranium-238 atom. Well this is not so with the kaon. It decays into two or three particles (no one knows why yet) and those particles can never be brought back together to make a kaon. Don’t ask me how kaons are created in the first place.
I suppose neither of these things proves time’s direction, as these events may not have been observed yet. Absence of evidence is not evidence of absence. The book doesn’t resolve the issue, as it does not any other it discusses. I know I certainly seem to have a psychological urge to believe that time is unidirectional and irreversible. Anyone else have that feeling?