Physics doesn't define time. The definition isn't buried in the math. It assumes its existence. For a definition of time we need to turn to a philosophy of time.
Sure, whatever. My point is that when physics talks of 'time' it means what clocks measure.
Feel free to clarify where necessary but the basic logic for a perspective using Einstein's relativity as a basis for a philosophy of time appears to be as follows:
- Time is assumed to be a dimension within a spacetime coordinate system, because it is convenient to do so for one's calculations
- The math proceeding from the assumptions predicts time dilation
- We assume that what the math says is correct because time dilation is observable
- Because we have assumed that what the math says is correct, we assume time must be a dimension in reality, implying that time is traversible in reality, which in turn implies that there exists pasts or futures which can be traveled to (eternalism)
- The math results in a possible situation wherein a single location in our spacetime coordinate system has at least two distinct time coordinates
Usually, in a multi-dimensional coordinate system, this would be impossible. Consistency is key, especially for a coordinate system.
One error here is that Einsteinian relativity is a
model to describe & explain what we observe. Time dilation and other observations are consistent with this model. We know it is not a complete model, even of our own observations, let alone reality, whatever that may be. But in the domain where it does accurately fit our observations, we can explore its implications - it may make predictions that turn out to be inconsistent with what we observe, in which case we'll learn something.
Whether it predicts that a single event can have two time coordinates, I seriously doubt, but I would like to see the maths behind that claim.
Special Relativity has two postulates, the first being "the laws of physics are invariant in all inertial frames of reference". If what it is that would be perceived as the passage of time as governed by the laws of physics is occurring more slowly in one inertial frame of reference than another, and those laws of physics are invariant within each inertial frame of reference, this implies a transformation of certain functions responsible for what it is that we perceive as the passage of time.
The important concept you didn't mention here is relativity - time runs more slowly in an inertial frame
moving relative to an observer. All observers see their proper time passing at one second per second, so they always perceive the passage of time to be the same (ignoring perceptual distortions).
I don't think Einstein was so quick to jump onto an eternalism bandwagon, though I'm sure he must have thought about it.
Who knows? perhaps his comment that time is an illusion was referring to that idea. The relativity of simultaneity seems to imply that events in your past and in your future can be real for other observers, and events in their past and their future can be real for yet other observers.
See my post #111 for Godel's response to his solutions for Einstein's equations. A solution doesn't imply reality. Anyone can cook up any system we want and there is no guarantee that it will be congruous with the world of the senses.
Sure; as above, these are models based on observation. We know that Einstein's model has a limited domain of applicability, and we know that it's extraordinarily accurate within that domain, but it's quite possible that none of the ways of obtaining closed time-like curves are actually possible - perhaps, for example, because they don't account for the effects of quantum mechanics. But if they are possible, they're almost certainly not practical for anything less than a Kardashev type III civilization, maybe not even that.
