I think Leonard Susskind touched this point in one of the theoretical minimum lectures [1] but I really can not tell which one. While we can quite easily imagin

I think Leonard Susskind touched this point in one of the theoretical minimum lectures [1] but I really can not tell which one. While we can quite easily imagine adding and removing space dimensions, nobody ever figured out what it would mean to have more than one time dimension. I think he also talked about time traveling in this context - you can go back and forth in space because there is more than one space dimension and so you can turn around and walk the other direction. Unless you instantaneously flip around that is nothing you can do with just one dimension like our one time dimension. But those things aside, the order of spatially separated events is not in general well defined if you take general relativity into account. There is a causal ordering all observers agree on but that still allows some observers to see some events in one order or another. I skimmed the papers linked in the article but they are quite a bit above what I can immediately grasp. But one thing I noticed was that they talked a lot about observable changes, so now I am wondering whether the entire system they are talking about is really static or whether we are just unable to observe the evolution of the entire system? If it is really static like the block universe, then I have not the slightest idea of how two subsystems can experience time if you think of one as a clock and the other as an observer watching the clock. In case of the block universe I can totally understand how everything is deterministic and all times exist in parallel, but I never understood what mechanism picks out the slice that is my or your now. [1] http://theoreticalminimum.com http://theoreticalminimum.com