You may find the idea of “charge as a pump” appealing; fair enough. I am at a loss to see why that is a reason for thinking that T symmetry is simpler than CPT symmetry.
Well, if true, it is a reason to think T symmetry or PT symmetry holds—since then charge would reverse itself automatically if T was reversed.
Depending on the nature of the pump. For instance, a pump made out of Standard Model stuff would not exactly reverse itself if T were reversed. Presumably, then, you have something more specific in mind; would you care to say more exactly what it is?
a pump made out of Standard Model stuff would not exactly reverse itself if T were reversed.
Pumps usually reverse if T is reversed. Most pumps contain something like a rotating fan blade. Reverse T and the momenta all reverse, so the blade turns the other way—and the pump pushes in the opposite direction.
What about C and P you ask? Well, we are talking about a pump inside charged particles, whose action is responsible for charge. C is hardly likely to be relevant. If T symmetry holds, you would just have to reverse T. If PT symmetry holds (but not T symmetry alone), and the components of the pump are sensitive to the sign of P, then you might have to reverse both P and T to get the pump to run backwards.
Whether pumps “usually” reverse exactly when T is reversed depends on whether the universe is actually T-symmetric or not. If you assume that they do then you’re begging the question.
Do you have any actual evidence that charged particles such as electrons and quarks are actually likely to contain pumps? This seems, on the face of it, monstrously implausible; of course it might be right—anything might be right—but why does the idea even deserve taking seriously, never mind using as the basis for your opinions about whether CPT symmetry is more likely than T symmetry?
Whether pumps “usually” reverse exactly when T is reversed depends on whether the universe is actually T-symmetric or not. If you assume that they do then you’re begging the question.
It is not “begging the question” it is “explaining one way it could work”. If charged particles contain pumps with moving parts, that would make simple T symmetry more plausible, since then there would be a clearer mechanism for explaining why reversing T would lead to all the charges in the universe reversing.
Do you have any actual evidence that charged particles such as electrons and quarks are actually likely to contain pumps? This seems, on the face of it, monstrously implausible; of course it might be right—anything might be right—but why does the idea even deserve taking seriously [...]
We don’t know the details of how electromagnetic and gravitational fields are generated. Something generates fields following an inverse-square law. A pump would be likely to have that effect—and seems about as plausible as anything else. Why do you describe the idea as being “monstrously implausible”?
I think it’s monstrously implausible because it requires charged particles to have intricate internal structure of a very curious sort, a thing for which we have no evidence whatever. (Assuming you actually mean a pump, rather than (e.g.) “a source of some substance that can flow”, in which case I see no reason whatever for thinking it should be T-symmetric.)
Your justification seems to be that “charged particles contain pumps” would somehow explain the inverse square law, but I don’t see that at all. The idea that they are sources/sinks of some substance that spreads out geometrically might (though I don’t know how you’re going to make that work in the quantum context) but what you’re suggesting is both more specific (pumps as such are not required for an inverse square law) and less specific (pumps as such do not imply an inverse square law).
I think it’s monstrously implausible because it requires charged particles to have intricate internal structure of a very curious sort, a thing for which we have no evidence whatever.
So: charged particles are very tiny, we have limited knowledge about how they do what they do. To reverse under T=>-T you need something that rotates, or something that cycles through more than two states, or something like that—it need not be particularly intricate. Sources could reverse their operation under T=>-T too—it depends on the details of how they are constructed. It doesn’t take very much to reverse under T=>-T. Rotating is enough to do it, for example.
Sources make slightly more sense for gravity than electromagnetism, IMO. With electromagnetism you typically need sources and sinks—and a pump does both of those jobs pretty neatly.
I am entirely unable to understand how you can say “a pump does both of those jobs pretty neatly” without actually having at your disposal anything remotely resembling a theory that does any sort of job of matching observation in which charged particles are pumps.
You might as well point to some property of elementary particles and say “a billiard ball does this pretty neatly”. Except that we do at least have models of some of physics in which particles are a bit like billiard balls, which appears to put that proposal ahead of explaining electric charge via pumps.
Actual working models trump handwaving, for me, because the problem with handwaving is that without working out the details you have nothing remotely resembling an upper bound on the actual complexity of the theory—if any even exists—that the handwaving might be gesturing towards.
I am entirely unable to understand how you can say “a pump does both of those jobs pretty neatly” without actually having at your disposal anything remotely resembling a theory that does any sort of job of matching observation in which charged particles are pumps.
I just meant that a pump can act as a source—or a sink—depending on which way around you use it.
A specific model would probably not help much. My position is that there are a whole class of models which are isomorphic to conventional physics and exhibit T symmetry. We don’t yet know which of those models are correct, or indeed if any of them are.
Well, if true, it is a reason to think T symmetry or PT symmetry holds—since then charge would reverse itself automatically if T was reversed.
Depending on the nature of the pump. For instance, a pump made out of Standard Model stuff would not exactly reverse itself if T were reversed. Presumably, then, you have something more specific in mind; would you care to say more exactly what it is?
Pumps usually reverse if T is reversed. Most pumps contain something like a rotating fan blade. Reverse T and the momenta all reverse, so the blade turns the other way—and the pump pushes in the opposite direction.
What about C and P you ask? Well, we are talking about a pump inside charged particles, whose action is responsible for charge. C is hardly likely to be relevant. If T symmetry holds, you would just have to reverse T. If PT symmetry holds (but not T symmetry alone), and the components of the pump are sensitive to the sign of P, then you might have to reverse both P and T to get the pump to run backwards.
Whether pumps “usually” reverse exactly when T is reversed depends on whether the universe is actually T-symmetric or not. If you assume that they do then you’re begging the question.
Do you have any actual evidence that charged particles such as electrons and quarks are actually likely to contain pumps? This seems, on the face of it, monstrously implausible; of course it might be right—anything might be right—but why does the idea even deserve taking seriously, never mind using as the basis for your opinions about whether CPT symmetry is more likely than T symmetry?
It is not “begging the question” it is “explaining one way it could work”. If charged particles contain pumps with moving parts, that would make simple T symmetry more plausible, since then there would be a clearer mechanism for explaining why reversing T would lead to all the charges in the universe reversing.
We don’t know the details of how electromagnetic and gravitational fields are generated. Something generates fields following an inverse-square law. A pump would be likely to have that effect—and seems about as plausible as anything else. Why do you describe the idea as being “monstrously implausible”?
I think it’s monstrously implausible because it requires charged particles to have intricate internal structure of a very curious sort, a thing for which we have no evidence whatever. (Assuming you actually mean a pump, rather than (e.g.) “a source of some substance that can flow”, in which case I see no reason whatever for thinking it should be T-symmetric.)
Your justification seems to be that “charged particles contain pumps” would somehow explain the inverse square law, but I don’t see that at all. The idea that they are sources/sinks of some substance that spreads out geometrically might (though I don’t know how you’re going to make that work in the quantum context) but what you’re suggesting is both more specific (pumps as such are not required for an inverse square law) and less specific (pumps as such do not imply an inverse square law).
So: charged particles are very tiny, we have limited knowledge about how they do what they do. To reverse under T=>-T you need something that rotates, or something that cycles through more than two states, or something like that—it need not be particularly intricate. Sources could reverse their operation under T=>-T too—it depends on the details of how they are constructed. It doesn’t take very much to reverse under T=>-T. Rotating is enough to do it, for example.
Sources make slightly more sense for gravity than electromagnetism, IMO. With electromagnetism you typically need sources and sinks—and a pump does both of those jobs pretty neatly.
I am entirely unable to understand how you can say “a pump does both of those jobs pretty neatly” without actually having at your disposal anything remotely resembling a theory that does any sort of job of matching observation in which charged particles are pumps.
You might as well point to some property of elementary particles and say “a billiard ball does this pretty neatly”. Except that we do at least have models of some of physics in which particles are a bit like billiard balls, which appears to put that proposal ahead of explaining electric charge via pumps.
Actual working models trump handwaving, for me, because the problem with handwaving is that without working out the details you have nothing remotely resembling an upper bound on the actual complexity of the theory—if any even exists—that the handwaving might be gesturing towards.
I just meant that a pump can act as a source—or a sink—depending on which way around you use it.
A specific model would probably not help much. My position is that there are a whole class of models which are isomorphic to conventional physics and exhibit T symmetry. We don’t yet know which of those models are correct, or indeed if any of them are.
The Wheeler–Feynman Time-Symmetric theory appears to be one such idea.