[jackson1372]

I should disclose: I'm an A-theory-supporting philosopher. (Sigh. Why are philosophers and physicists always disagreeing?! We should be friends!)

My above analogy to the left/right issue is the example I use to introduce students to the A- vs. B-theory.

The A- vs. B-theory debate is, of course, complicated, and you point to one possible complication: can we separate the issue of temporal asymmetry from the issue of temporal change?

As I see it, the answer to this question is "No".

We can talk about how some physical object 'changes' its spatial properties as we move from one spatial slice to another. For instance, as we move from the pointy-end of a cone to its base, each circular slice of the cone 'changes': they keep getting bigger until you reach the base.

This use of 'change' is symmetrical. There's no preferred direction of 'change' here. It makes equal sense to speak of changes "from bigger circle-slices to smaller-circle slices" as it does the other way around.

But in the context of the temporal dimension, talk of 'change' is not symmetrical. It's fine to say "The President changed from Obama to Trump", but you can't say "The president changed from Trump to Obama".

The point of all this just is: the issue of whether (temporal) change is symmetrical is tied up with the issue of whether time itself is symmetrical. You can't have your cake and eat it too. There's either an objective temporal ordering of physical events from past to future (as A-theory posits) or there isn't (as B-theory posits). If you're a B-theorist, you have to say that "Trump came after Obama" is like saying "The cup is on the left".

This is not a refutation of B-theory. But it, I hope, makes clearer what the stakes are. And when those stakes are made clearer, B-theory, in my view, looks less attractive.

[adrianratnapala]

Ok, I think I accept your point about distinguishing a symmetrical concept of "change" applied to asymmetrical things from a truly asymmetrical concept of change. That clarifies what I was getting at in my last paragraph. But I am still surprised to see it as a characterisation of the A vs. B debate[1]

So please help me check I am understanding the terms of that debate correctly.

(1) Even if it is not the way you explain it to students, do you accept my claim that A-theory considers time and change as being more fundamental than physics?

(2) If I further said "... as opposed to considering time change to be properties of the history of the universe", then would you accept the implied dichotomy?

[1] And I say the A-B is in turn not truly a debate reality of time, which was just an unfortunate framing by McTaggart.

[jackson1372]

1. I wouldn't put it in terms of time being "more fundamental than physics". We can mean two things by 'physics': the thing that is the object of study in the Physics department or the theory that gets generated by that study. Time, I take it, is one aspect of the object of study, one aspect of the natural world. So the question is: does the natural world, at the most fundamental level, have asymmetric temporal order? Or, rather, is asymmetric temporal order mearly an 'illusion' that gets explained away once you have the most fundamental picture of the world?

That's likely still unclear, but that's to be expected. We typically can't ask questions about fundamental structure without invoking that fundamental structure itself. That's why I find the analogy to left/right so helpful. We have a pretty good idea of what it means for left/right orientation not to be built into the fundamental structure of nature. And so that can provide a way of testing various claims about the fundamentality of asymmetrical temporal ordering.

2. I'm not sure I have a grip on what this additional thing is supposed to add. But I'll note that you reference 'history' and one might reasonably think that that is a temporal notion. If you meant 'history' to mean something like "the universe's extension in the temporal direction", that doesn't quite seem to allow for the distinction I took you to be trying to make.

(And, yes, McTaggert's framing is highly unhelpful.)