After reading your comment, I agree that this is probably just a semantic question with no real meaning. This is interesting, because I completely failed to realize this myself and instead constructed an elaborate rationalization for why the distinction exists.

While reading the wikipedia page, I found myself interpreting meaning into these two viewpoints that were probably never intended to be there. I am mentioning this both because I find it interesting that I reinterpreted both theories to be consistent with my own believes without realizing it, and because I would like to see what others have to say about those reinterpretations. I should point out that I am currently really tired and only skimmed the article, so that probably wouldn't have happened under ordinary circumstances, but I still think that this is interesting because it shows the inferential gap at work:

I am a computationalist, and as such the distinction between the two theories was pretty meaningless to me at first. However, I reinterpreted the two theories in ways that were almost certainly never intended, so that they did make sense to me as a reasonable distinction:

• the A theory corresponds to living in a universe where the laws of physics progress like in a simple physical simulation, with a global variable to measure time and rules for how to incrementally get from one state to the next. I assume for the purpose of this theory that quantum-mechanical and relativistic effects that view time non-linearly can be abstracted in some way so that a single, universal time value suffices regardless. I interpreted it like this because I thought the crux of the theory was having a central anchor point for past and future.

• the B theory corresponds to living in a highly abstracted simulation where many things are only computed when they become relevant for whatever the focus of the simulation is on. For instance, say the focus is on accurately modelling sapient life, then the exact atomic composition of a random rock is largely irrelevant and is not computed at first. However, when the rock is analyzed by a scientist, this information does become relevant. The simulation now checks what level of detail is required (i.e. how precise the measuring is) and backpropagates causal chains on how the rock came to be, in order to update the information about the rock's structure. In this way, unnecessary computations are avoided. I interpreted it like this because I thought the crux of the theory was the causal structure between events.

In essence, the A theory would correspond to a mindless, brute-force computation, while the B theory implies a deliberate, efficient computation that follows some explicit goal. This is nowhere near what the A and B theory actually seem to say now that I have read the article in more detail. In fact, the philosophical/moral implications are almost reversed under some viewpoints. I find it very interesting that this is the first thing that came to mind when I read it.

I probably should have used the words "presentism" and "eternalism" instead of "A-theory" and "B-theory". I've added a footnote which I hope clarifies this.

The point is that these are theories about what exists, and not just theories about how we should talk about time. To say that all of time is even "there" to be coordinatized is, in essence, to sign onto the B-theory as opposed to the A-theory.

How is this just a change of basis? To me it seems more like B-theorists have an appropriately coordinate-independent conception of the underlying reality whereas A-theorists are privileging one particular coordinate representation.

I personally can say that I had a very strong belief that if I awake and the last day I remember is Tuesday it should be Wednesday and not Monday. It was quite a shock to learn that isn't true.

Yes, it can be very distressing to have a strong intuition challenged. It would be very distressing to learn that arithmetic for large integers didn't work the way I assumed it did.

But in math, the intuition precedes the emotional significance. I don't start out being emotionally attached to a certain answer. Rather, I start out emotionally neutral about the question, I form an intuition about the answer, and then I am emotionally attached to being right.

So, the emotional significance can't be used to explain where the intuition came from. In the case of math, the universality of the intuitions can be explained by our common biological and cultural heritage, and by our common experience with how the enumeration of things works.

In the case of time, we have the same biological and cultural heritage, and we have the same experience with time itself, but we arrive at different intuitions about the relationship between time and ontology. This is what I find puzzling.

Different perception can easily lead to different intuitions.

What are the different perceptions that would explain the different intuitions about whether the future exists?

Thanks for this data point.

In the post, I unthinkingly used "A-theory" and "B-theory" as code for "presentism" and "eternalism". I'd be curious to know how you react to the positions in these articles.

Except it is testable, I think. If the A-theory of time is true, we would expect our best theory of space-time to contain an objectively definable notion of "present". However, our best theory of space-time contains no such notion, and in fact actively militates against it. It is, of course, possible to posit an undetectable preferred foliation of space-time or some such, but this just shows that you have to complicate your physical theory in order to sustain A-theory.* Plain relativity, interpeted naturally, is simply incompatible with it. So the experimental success of the general theory of relativity is strong evidence against the A-theory.

In addition, the fact that our experience of the passage of time can be adequately explained within B-theory in terms of the Second Law of Thermodynamics means that pretty much the only argument for A-theory (the supposed inability of B-theory to account for our experience of time) fails. So A-theory is a theory that requires us to complicate our best physical understanding of the world for no perceivable explanatory benefit. That is a bad theory in scientific, not just philosophical, terms.

* I see this move as a slightly more respectable version of protecting biblical creationism from empirical refutation by saying that God created the universe 6000 years ago but made it look exactly as if it was billions of years old.

I don't think B-theory, broadly construed, would be incompatible with that. B-theory is basically just treating space-time as an integrated entity, rather than having radically different ontologies for space and time. It doesn't require time to be partially ordered, any more than it requires spatial directions to be partially ordered.

There are spacetimes, most notably the Godel Universe, where time is both a loop and not a loop. Some time directions (from the same spatial point) loop around, others go on forever, never getting close to the point of origin. You can still say, however, that it is compatible with the timeless B-like approach. There is no way to construct this spacetime by taking an A-like fixed spatial slice and evolving it forward in time using the Einstein equations. (There is a loophole, however, where one can lift the Godel universe from flat space using a twisted timelike fiber, but that's a different story.)