I don’t understand what, if anything, you would consider non-arbitrary.
I’m not sure this is actually an important disagreement; I’m ok with dropping it if you want. However, you are the one who suggested that entropy could be calculated in a non-arbitrary way; but I don’t think you’ve offered an example of such a calculation.
And why does that conflict with what anyone says about the “arrow of time”?
It conflicts with the notion that entropy is a good way to consider the problem; entropy is a non-full-information heuristic that doesn’t appear in the actual laws of physics.
neither of us is a quantum field theorist
Well, I’m not a theorist, no. I do have a PhD in experimental particle physics. I will admit that the QFT classes tended to fry my brain like an egg, which is one reason I went experimental.
so far as I know no one knows how to do the QFT calculations on anything like the scale required to understand what’s happening when you fry an egg
That’s true. I do think, however, that an intuitive understanding is sufficient to get a grasp of how a microlevel asymmetry can become macrolevel.
Do you have any actual evidence that it’s so?
It seems that such evidence would have to be in the form of simulations or calculations, since you can’t very well turn off the weak interaction and see what happens when you fry an egg without it. I am not aware of any such calculation, no. But, again, there’s such a thing as a qualitative insight.
you are the one who suggested that entropy could be calculated in a non-arbitrary way
All I actually said was “not-so-arbitrary”. I think that’s pretty much all one can say about anything, which is why I asked what if anything you would consider non-arbitrary.
It conflicts with the notion that entropy is a good way to consider the problem; entropy is a non-full-information heuristic that doesn’t appear in the actual laws of physics.
I don’t see the connection between the two halves of that sentence. There seems to be some implicit premise along these lines: “When contemplating the ‘arrow of time’ we should not consider anything that doesn’t explicitly appear in the laws of physics.” but I don’t see any reason to accept such a premise.
an intuitive understanding is sufficient to get a grasp of how a microlevel asymmetry can become macrolevel
If you mean that that’s enough to appreciate that in principle something of that sort is not entirely ruled out—yeah, I agree. If you mean that your intuition tells you that weak parity violation really is the reason why we can fry eggs but not un-fry them then, well, I’m afraid I don’t trust your intuition as much as you might.
If I talked to a bunch of theoretical physicists—a group whose intuition in such things I think we should probably trust more than that of either experimentalists like you or pure mathematicians like me—would you expect them to agree with you, to say “yes, of course, weak parity violation is probably the cause of the familiar macroscopic time-asymmetries we see in the world”? My impression—which I admit is not based on actually finding lots of theoretical physicists and asking them—is that they mostly would not say any such thing.
As one example, I’ll cite Sean Carroll again; although he is an author of pop-science books he is also a working scientist and this is pretty much in his field of expertise. And he says: Time reversal violation is not the arrow of time.
There seems to be some implicit premise along these lines: “When contemplating the ‘arrow of time’ we should not consider anything that doesn’t explicitly appear in the laws of physics.” but I don’t see any reason to accept such a premise.
I would say “explicitly or implicitly”, and then it seems to me that we have every reason to accept that premise, because where the Devil else are you going to look? Noting that entropy does not appear in the laws of physics even implicitly; it’s a heuristic, not a derived quantity.
If I talked to a bunch of theoretical physicists—a group whose intuition in such things I think we should probably trust more than that of either experimentalists like you or pure mathematicians like me [...]
I would rather phrase it as “micro-level time violation is the cause”; we’re talking about weak parity violation only because that’s much more easily measured, and implies time violation. That aside, yes, I would expect a poll of theorists to find at least a sizable minority who think micro-level time violation is the cause of macro-scale time asymmetry.
I’m not sure this is actually an important disagreement; I’m ok with dropping it if you want. However, you are the one who suggested that entropy could be calculated in a non-arbitrary way; but I don’t think you’ve offered an example of such a calculation.
It conflicts with the notion that entropy is a good way to consider the problem; entropy is a non-full-information heuristic that doesn’t appear in the actual laws of physics.
Well, I’m not a theorist, no. I do have a PhD in experimental particle physics. I will admit that the QFT classes tended to fry my brain like an egg, which is one reason I went experimental.
That’s true. I do think, however, that an intuitive understanding is sufficient to get a grasp of how a microlevel asymmetry can become macrolevel.
It seems that such evidence would have to be in the form of simulations or calculations, since you can’t very well turn off the weak interaction and see what happens when you fry an egg without it. I am not aware of any such calculation, no. But, again, there’s such a thing as a qualitative insight.
All I actually said was “not-so-arbitrary”. I think that’s pretty much all one can say about anything, which is why I asked what if anything you would consider non-arbitrary.
I don’t see the connection between the two halves of that sentence. There seems to be some implicit premise along these lines: “When contemplating the ‘arrow of time’ we should not consider anything that doesn’t explicitly appear in the laws of physics.” but I don’t see any reason to accept such a premise.
If you mean that that’s enough to appreciate that in principle something of that sort is not entirely ruled out—yeah, I agree. If you mean that your intuition tells you that weak parity violation really is the reason why we can fry eggs but not un-fry them then, well, I’m afraid I don’t trust your intuition as much as you might.
If I talked to a bunch of theoretical physicists—a group whose intuition in such things I think we should probably trust more than that of either experimentalists like you or pure mathematicians like me—would you expect them to agree with you, to say “yes, of course, weak parity violation is probably the cause of the familiar macroscopic time-asymmetries we see in the world”? My impression—which I admit is not based on actually finding lots of theoretical physicists and asking them—is that they mostly would not say any such thing.
As one example, I’ll cite Sean Carroll again; although he is an author of pop-science books he is also a working scientist and this is pretty much in his field of expertise. And he says: Time reversal violation is not the arrow of time.
I would say “explicitly or implicitly”, and then it seems to me that we have every reason to accept that premise, because where the Devil else are you going to look? Noting that entropy does not appear in the laws of physics even implicitly; it’s a heuristic, not a derived quantity.
I would rather phrase it as “micro-level time violation is the cause”; we’re talking about weak parity violation only because that’s much more easily measured, and implies time violation. That aside, yes, I would expect a poll of theorists to find at least a sizable minority who think micro-level time violation is the cause of macro-scale time asymmetry.