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 true that the original formulation of GR is covariant, i.e. has no time evolution built in, only a “block” spacetime manifold whose curvature is precisely its matter content. Similarly, classical EM, though originally formulated as an initial value problem, also looks better in a “timeless” form, where second derivative of the 4-vector potential is charge-current density.
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.*
I disagree. You have to recast GR into an initial value problem and then pick a foliation to model interesting physical phenomena, like stellar collapse and black hole collision. Completely independent of any underlying ontology. There is no intent to “sustain A-theory”, that’s just silly. You want to know how to detect the dying cry of a star torn apart by a supermassive black hole in the center of a galaxy, not whether to pick A or B from some book.
Plain relativity, interpreted naturally, is simply incompatible with it. So the experimental success of the general theory of relativity is strong evidence against the A-theory.
Are you saying that this A-theory predicts that there is a preferred foliation? By that logic, wouldn’t B-theory predict that no foliation is possible at all? Or that all foliations are equal, whether they are timelike, null or spacelike? If so, the B-theory has been clearly falsified (if you can ever falsify anything in philosophy of physics).
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
This seems like a major category error to me, mixing qualia (“experience of the passage of time”) with statistical mechanics. They are about a dozen of abstraction and energy levels removed from each other. I can’t take arguments like this seriously.
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.
What requires us to “complicate our best physical understanding of the world”, such as recast the beautiful Einstein equation into an ugly ADM form, is the drive to explain and predict what we see or will see. The ontological narrative is a byproduct.
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.
This was almost verbatim the Hoyle’s criticism of the Big Bang model, wasn’t it?
Are you saying that this A-theory predicts that there is a preferred foliation?
Not to speak for pragmatist, but, yes, that is my understanding. But, importantly, the foliation isn’t just preferred by some distinguishing physical characteristic (the way a preferred reference frame would be, for example). Rather, the foliation is preferred in a more ontologically fundamental sense: When one leaf exists, no other leaves of the foliation exist at all, nor do the parts of spacetime that they would “foliate”. For the presentist/A-theorist, at this moment, a completely exhaustive ontology of the world contains nothing that is not in the present leaf.
By that logic, wouldn’t B-theory predict that no foliation is possible at all? Or that all foliations are equal, whether they are timelike, null or spacelike? If so, the B-theory has been clearly falsified (if you can ever falsify anything in philosophy of physics).
The B-theory allows foliations to be different from one another in physically real ways. The B-theory doesn’t allow that leaves of one special foliation “pass into and out of existence”, which is what the presentist/A-theoretic approach requires.
(That is my understanding of what a presentist would say, anyway. But, as I said, I can’t really make sense of presentism, so I might not be portraying the view accurately.)
I disagree. You have to recast GR into an initial value problem and then pick a foliation to model interesting physical phenomena, like stellar collapse and black hole collision. Completely independent of any underlying ontology. There is no intent to “sustain A-theory”, that’s just silly. You want to know how to detect the dying cry of a star torn apart by a supermassive black hole in the center of a galaxy, not whether to pick A or B from some book.
None of these amounts to picking a single foliation and stating, “This (and no other) is the correct foliation of space-time.” A-theory requires a single privileged foliation. The fact that we often use foliations when modeling physical phenomena has nothing to do with sustaining A-theory, you’re right, but I didn’t say that any use of a foliation would have that role.
Are you saying that this A-theory predicts that there is a preferred foliation? By that logic, wouldn’t B-theory predict that no foliation is possible at all? Or that all foliations are equal, whether they are timelike, null or spacelike?
No. The B-theory predicts that there is no single preferred foliation. That is not equivalent to saying that no foliation is possible. Nor is it equivalent to saying that all foliations are equal.
This seems like a major category error to me, mixing qualia (“experience of the passage of time”) with statistical mechanics. They are about a dozen of abstraction and energy levels removed from each other.
There is, of course, a mystery about how (or even if) particular qualia are produced by physical processes. I don’t claim that statistical mechanics can answer that mystery, but that is not a mystery that A-theory claims to answer, either. However, if you grant (as I think you should) that our experience of the passage of time is related to the way in which our brain performs various computations, then stat. mech. becomes immediately relevant, and isn’t dozens of levels removed. There is a rich literature applying statistical mechanics to understand constraints on computational processes.
The beauty of stat. mech. methods is that they are not constrained to a particular energy level. They can be applied to understand the behavior of molecules in a gas, but also to understand the behavior of galaxies in a supercluster. In any case, my mention of stat. mech. in this context wasn’t just a throwaway. Part of my dissertation was about understanding the experience of time direction (in particular, the fact that cognitive systems record memories in one temporal direction and intervene in the opposite temporal direction) in statistical mechanical terms. I’d be happy to summarize the argument if you’d like, when I have the time.
What requires us to “complicate our best physical understanding of the world”, such as recast the beautiful Einstein equation into an ugly ADM form, is the drive to explain and predict what we see or will see.
As I said before, the motivations and consequences of the ADM formalism (at least when applied to obtain numerical solutions to initial value problems) are quite distinct from those of the A-theory. Now it may turn out that in our ultimate theory of quantum gravity, we do have to specify a single preferred foliation of space-time, in which case I will readily admit that this particular objection to A-theory no longer holds. But that just highlights how this debate is responsive to empirical confirmation and disconfirmation.
This was almost verbatim the Hoyle’s criticism of the Big Bang model, wasn’t it?
Perhaps it was, I don’t know. But if it was, then he was wrong, because the criticism certainly doesn’t seem to apply to the Big Bang model as we know it. Just because the criticism can be misapplied doesn’t mean it’s never valid.
Part of my dissertation was about understanding the experience of time direction (in particular, the fact that cognitive systems record memories in one temporal direction and intervene in the opposite temporal direction) in statistical mechanical terms. I’d be happy to summarize the argument if you’d like, when I have the time.
Drool—I would very much like to get a copy of this part of your dissertation, or the whole thing, or a summary, whatever and whenever is convenient to you. I think I sorta get it on an intuitive level, but to fill in more of the physics would be wonderful.
Well, I guess I sort of agree that “B-theory” is not as constraining, even if both use the term “exist” in a way I disagree with. In any case, they seem to be more of an inspirational value, like the Mach principle (wrong if quantified) was for Einstein.
I am not clear on how one can use stat.mech to explain our time perception, feel free to elaborate some time. Maybe in a separate post, if the argument is long. I agree that humans only experiencing the present is not an argument against “static” block spacetime.
Anyway, I get frustrated by these discussions online, too much is left unsaid, the back-and-forth is slow and selective, only bits and pieces of the argument and motivation get expressed. Could be just my lack of communication skills, of course. If you are ever in Vancouver and feel like meeting up, lunch/dinner/drinks are on me.
I appreciate the offer. The next time I’m in the vicinity of Vancouver (I currently live over 10,000 km away, unfortunately) I’d love to take you up on it.
It is true that the original formulation of GR is covariant, i.e. has no time evolution built in, only a “block” spacetime manifold whose curvature is precisely its matter content. Similarly, classical EM, though originally formulated as an initial value problem, also looks better in a “timeless” form, where second derivative of the 4-vector potential is charge-current density.
I disagree. You have to recast GR into an initial value problem and then pick a foliation to model interesting physical phenomena, like stellar collapse and black hole collision. Completely independent of any underlying ontology. There is no intent to “sustain A-theory”, that’s just silly. You want to know how to detect the dying cry of a star torn apart by a supermassive black hole in the center of a galaxy, not whether to pick A or B from some book.
Are you saying that this A-theory predicts that there is a preferred foliation? By that logic, wouldn’t B-theory predict that no foliation is possible at all? Or that all foliations are equal, whether they are timelike, null or spacelike? If so, the B-theory has been clearly falsified (if you can ever falsify anything in philosophy of physics).
This seems like a major category error to me, mixing qualia (“experience of the passage of time”) with statistical mechanics. They are about a dozen of abstraction and energy levels removed from each other. I can’t take arguments like this seriously.
What requires us to “complicate our best physical understanding of the world”, such as recast the beautiful Einstein equation into an ugly ADM form, is the drive to explain and predict what we see or will see. The ontological narrative is a byproduct.
This was almost verbatim the Hoyle’s criticism of the Big Bang model, wasn’t it?
Not to speak for pragmatist, but, yes, that is my understanding. But, importantly, the foliation isn’t just preferred by some distinguishing physical characteristic (the way a preferred reference frame would be, for example). Rather, the foliation is preferred in a more ontologically fundamental sense: When one leaf exists, no other leaves of the foliation exist at all, nor do the parts of spacetime that they would “foliate”. For the presentist/A-theorist, at this moment, a completely exhaustive ontology of the world contains nothing that is not in the present leaf.
The B-theory allows foliations to be different from one another in physically real ways. The B-theory doesn’t allow that leaves of one special foliation “pass into and out of existence”, which is what the presentist/A-theoretic approach requires.
(That is my understanding of what a presentist would say, anyway. But, as I said, I can’t really make sense of presentism, so I might not be portraying the view accurately.)
None of these amounts to picking a single foliation and stating, “This (and no other) is the correct foliation of space-time.” A-theory requires a single privileged foliation. The fact that we often use foliations when modeling physical phenomena has nothing to do with sustaining A-theory, you’re right, but I didn’t say that any use of a foliation would have that role.
No. The B-theory predicts that there is no single preferred foliation. That is not equivalent to saying that no foliation is possible. Nor is it equivalent to saying that all foliations are equal.
There is, of course, a mystery about how (or even if) particular qualia are produced by physical processes. I don’t claim that statistical mechanics can answer that mystery, but that is not a mystery that A-theory claims to answer, either. However, if you grant (as I think you should) that our experience of the passage of time is related to the way in which our brain performs various computations, then stat. mech. becomes immediately relevant, and isn’t dozens of levels removed. There is a rich literature applying statistical mechanics to understand constraints on computational processes.
The beauty of stat. mech. methods is that they are not constrained to a particular energy level. They can be applied to understand the behavior of molecules in a gas, but also to understand the behavior of galaxies in a supercluster. In any case, my mention of stat. mech. in this context wasn’t just a throwaway. Part of my dissertation was about understanding the experience of time direction (in particular, the fact that cognitive systems record memories in one temporal direction and intervene in the opposite temporal direction) in statistical mechanical terms. I’d be happy to summarize the argument if you’d like, when I have the time.
As I said before, the motivations and consequences of the ADM formalism (at least when applied to obtain numerical solutions to initial value problems) are quite distinct from those of the A-theory. Now it may turn out that in our ultimate theory of quantum gravity, we do have to specify a single preferred foliation of space-time, in which case I will readily admit that this particular objection to A-theory no longer holds. But that just highlights how this debate is responsive to empirical confirmation and disconfirmation.
Perhaps it was, I don’t know. But if it was, then he was wrong, because the criticism certainly doesn’t seem to apply to the Big Bang model as we know it. Just because the criticism can be misapplied doesn’t mean it’s never valid.
Drool—I would very much like to get a copy of this part of your dissertation, or the whole thing, or a summary, whatever and whenever is convenient to you. I think I sorta get it on an intuitive level, but to fill in more of the physics would be wonderful.
I’ve been meaning to make a couple of posts summarizing my dissertation, since it is rationality-relevant. This is an added impetus. I’ll get on it.
Well, I guess I sort of agree that “B-theory” is not as constraining, even if both use the term “exist” in a way I disagree with. In any case, they seem to be more of an inspirational value, like the Mach principle (wrong if quantified) was for Einstein.
I am not clear on how one can use stat.mech to explain our time perception, feel free to elaborate some time. Maybe in a separate post, if the argument is long. I agree that humans only experiencing the present is not an argument against “static” block spacetime.
Anyway, I get frustrated by these discussions online, too much is left unsaid, the back-and-forth is slow and selective, only bits and pieces of the argument and motivation get expressed. Could be just my lack of communication skills, of course. If you are ever in Vancouver and feel like meeting up, lunch/dinner/drinks are on me.
I appreciate the offer. The next time I’m in the vicinity of Vancouver (I currently live over 10,000 km away, unfortunately) I’d love to take you up on it.