In order for everything to work exactly the same, there essentially would have to be water, since physics would have to figure out what water could do. That being said, it could just be similar. If it models how XeYZn should behave approximately, subtracts that from how XeYZn actually behaves, and adds how H2O should behave approximately, and has some force to hold the XeYZn together, you’d have to model XeYZn to predict the future.
Come to think of it, it would probably be more accurate to say that water is made of physics at this point, since it’s really more about how physics are acting crazy at that point than it is about the arrangement of protons, neutrons, and electrons. In any case, it’s not H2O.
You didn’t answer the question. Does XYZ behave like water in every way, or not? If it does, what’s the difference? If it doesn’t, you can no longer say it replaces water.
Is the thrust of the thought experiment preserved if we assume that the two versions of water differ on a chemical level, but magically act identically on the macro scale, and in fact are identical except to certain tests that are, conveniently, beyond the technological knowledge of the time period? (Assuming we are allowed to set the thought experiment in the past.)
Surely it’s not necessary that the two worlds be completely indistinguishable?
It doesn’t behave just like water. It behaves like a simpler model of water. If you look more closely, the difference isn’t what you’d expect between a good model of water and a bad model of water. It’s what you’d expect between a good model of XeYZn and a bad model of XeYZn.
In other words, it would act like water to a first approximation, but instead of adding the terms you’d expect to make it more accurate, you add the terms you’d use to make an approximation of XeYZn more accurate.
In order for everything to work exactly the same, there essentially would have to be water, since physics would have to figure out what water could do. That being said, it could just be similar. If it models how XeYZn should behave approximately, subtracts that from how XeYZn actually behaves, and adds how H2O should behave approximately, and has some force to hold the XeYZn together, you’d have to model XeYZn to predict the future.
Come to think of it, it would probably be more accurate to say that water is made of physics at this point, since it’s really more about how physics are acting crazy at that point than it is about the arrangement of protons, neutrons, and electrons. In any case, it’s not H2O.
You didn’t answer the question. Does XYZ behave like water in every way, or not? If it does, what’s the difference? If it doesn’t, you can no longer say it replaces water.
Is the thrust of the thought experiment preserved if we assume that the two versions of water differ on a chemical level, but magically act identically on the macro scale, and in fact are identical except to certain tests that are, conveniently, beyond the technological knowledge of the time period? (Assuming we are allowed to set the thought experiment in the past.)
Surely it’s not necessary that the two worlds be completely indistinguishable?
It doesn’t behave just like water. It behaves like a simpler model of water. If you look more closely, the difference isn’t what you’d expect between a good model of water and a bad model of water. It’s what you’d expect between a good model of XeYZn and a bad model of XeYZn.
In other words, it would act like water to a first approximation, but instead of adding the terms you’d expect to make it more accurate, you add the terms you’d use to make an approximation of XeYZn more accurate.