Time is not an artificial or human construct. It is very much as real as things that we can touch and see.
Time is only as real as the experience of the phenomenon we call time. I would propose that if you either extinguish the human race or the make the universe in which humans live disappear, time will cease to exist.
Ok, maybe the former wouldn't work, as time is a property of the universe and the interaction between measurable entities inside it as defined by mathematical relationships, not of human perception.
Yet, I would argue that "time" is only as real as its practical usefulness in a human being's personal life journey. The less practically useful it is, the less real it becomes.
People often complain that time flies. They get so busy doing something that they lose track of time. This is what I mean. The numerical quantity means much less than the experience of itself. The experience of time somehow escaping from our iron grip doesn't seem real and we are surprised (and often shocked and horrified
-- oh no I've got an exam tomorrow! I forgot study! Ahhhhh!!!!!!) at how much "time" has numerically elapsed.
In fact, physics has proven the equivalence of time with the other three spatial dimensions!
I'm not so sure about equivalence. Time is temporal and not spatial, though the temporal dimensions may indeed have some spatial properties.
My guess is that in one of those other dimensions I am rich and handsome
You aren't? Oh what a shame!
Anyone have a time machine
That's the thing, once you build a time machine, the observable and accessible universe ceases to be four-dimensional.
Time as we know it before the advent of time travel is the time-line of the three spatial dimensions. At the moment, time travel has been "invented" as an idea. It just hasn't been implemented. When that happens, the observable and accessible universe is no longer four-dimensional, but at least five-dimensional, because if you can travel back and forth in time, not only do you have a time-line of the first three spatial dimensions, but you also have a time-line of the fourth dimension (ie. the fifth dimension, second temporal dimension). You have a time-line of time-lines. The fourth dimension is merely the first temporal dimension. The fourth dimension becomes semi-spatial because of time travel.
But this is where it gets interesting. What if, instead of moving in the first (4th) temporal dimension, you want to travel within the second (5th) temporal dimension, or a combination of both. You want to move in a direction that isn't parallel or anti-parallel to the unit vectors of the either of the first two temporal dimensions.
In what direction, for example, does the progression or propagation of time travel? The question, therefore, of whether you're changing history or changing the time-line is a question of whether you're moving parallel or anti-parallel to the direction of propagation of time. In a sense, it doesn't matter then if we are moving in the first or second temporal dimension. All that matters is that we are moving parallel or anti-parallel to the direction of propagation of time.
But having said that, it's probably not possible to know if we are moving in the fourth or fifth dimensions at all. The universe doesn't have a compass for the three spatial dimensions, so why would it have one for temporal dimensions?
The important thing then is to be able to sense the direction of propagation of time and bias the time machine in that direction (or against it).
We could develop a whole theory (maybe more for fictional purposes
) for the physics of time-travel as we would like to think of it. What causes the propagation of time?
Maybe it's a bit like gravity. The universe is being pulled in a particular direction. The time machine is like a kind of rocket ship exploring the depths of the universe. But instead of a
space ship, it's a
time ship.
Maybe it's like electromagnetic propagation, the propagation of light and photons, which, actually wouldn't be much different to the idea of gravity if you believe in so-called "gravity waves," where the influence of the force of gravity propagates at the speed of light -- and that gravity is just another force in the universe that emits particles and waves just like electric and magnetic fields and forces.
So . . . time is propagating at a fixed speed independent of its orientation.
