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I think the confusion here is "in space", maybe you can expand on that. Is space itself not the medium? Localization is precisely what prevents backwards causal

I think the confusion here is "in space", maybe you can expand on that. Is space itself not the medium? Localization is precisely what prevents backwards causality and is at the basis of relativity, where spacetime is invariant. And from what I understand that's also the source of conflict in the quantum world where that's not necessarily the case, retrocausality is entirely possible, spooky interactions at a distance are entirely possible. Like the problem of gravity is described by the curvature of spacetime. Does spacetime "exist"? If not it's just a tool, and not an actual observation that maps onto reality. In other words we don't know how gravity actually "works" and interacts or what "spacetime" is, if it is a thing, regardless of how powerful the description is. The description is just a mathematical tool that is very useful, but that's just about it. "You can still try to define the word, pick something within that description and call it a medium if you like" Yes... that's how language works. "Spacetime" is mapped onto something. Language is a medium of communication. Spacetime is a medium of interaction/causality. Whether such things "exist" is an epistemic discussion or a discussion for experimentalists. But any medium is just the means by which something occurs or happens. So what is the means by which gravity "happens", or exerts influence on other bodies if not the curvature of "spacetime", which itself hasn't really been established. Does gravity just magically happen?

tux3 3y ago
>I think the confusion here is "in space", maybe you can expand on that. Is space itself not the medium? I think using that definition is fine! I tried to talk about things positioned in space directly instead of using a notion of medium because that word comes with a lot of imagery, and it can make discussion difficult, it's easy to talk past each other when we start using words that don't have a very well settled definition I was originally responding to a formulation where the medium is defined as something "present in a vacuum" that allows propagation of things. This is where imprecise language creates trouble, and why I don't like that word. You can say space is the medium, but you can't say space is a thing present in the vacuum that allows propagation. Vacuum is located in space, there's not a very meaningful sense in which space is a medium found within vacuum that helps things propagate, or at least that definition of the word is not very helpful to my understanding of the world For gravity, I'm okay with calling spacetime the medium, as long as you're careful to not imagine that there's some more ethereal thing within the vacuum that physics doesn't say anything about >But any medium is just the means by which something occurs or happens That's fine. That's not an invalid definition. I just think it's important to separate the concept of a physical medium from more philosophical notions that everything happens in a medium, even if that sometimes means defining the word medium as an immaterial concept whose existence makes people question the definition of the word "exist". In response to the original post, that definition of a medium inside the vacuum is something that doesn't exist. With your definition of space as the medium for gravity, you can make that work, as long as you can communicate what you really mean to other people when using that particular word!
- denton-scratch 3y ago
  > For gravity, I'm okay with calling spacetime the medium I thought spacetime was supposed to be identical with the gravitational field. It can't be gravity's "medium" if that medium is itself gravity. I find this extremely hard to think about; gravity both generates spacetime, and warps it. It's really hard to escape from the earthman's experience of space as a sort of instantaneous volume; we don't really experience time at all, except in the sense that we have a sense of certain events as being not the present (i.e. the past). We know that time exists in some sense; but all we experience of spacetime is the space bit.
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tux3 3y ago

>I think the confusion here is "in space", maybe you can expand on that. Is space itself not the medium? I think using that definition is fine! I tried to talk about things positioned in space directly instead of using a notion of medium because that word comes with a lot of imagery, and it can make discussion difficult, it's easy to talk past each other when we start using words that don't have a very well settled definition I was originally responding to a formulation where the medium is defined as something "present in a vacuum" that allows propagation of things. This is where imprecise language creates trouble, and why I don't like that word. You can say space is the medium, but you can't say space is a thing present in the vacuum that allows propagation. Vacuum is located in space, there's not a very meaningful sense in which space is a medium found within vacuum that helps things propagate, or at least that definition of the word is not very helpful to my understanding of the world For gravity, I'm okay with calling spacetime the medium, as long as you're careful to not imagine that there's some more ethereal thing within the vacuum that physics doesn't say anything about >But any medium is just the means by which something occurs or happens That's fine. That's not an invalid definition. I just think it's important to separate the concept of a physical medium from more philosophical notions that everything happens in a medium, even if that sometimes means defining the word medium as an immaterial concept whose existence makes people question the definition of the word "exist". In response to the original post, that definition of a medium inside the vacuum is something that doesn't exist. With your definition of space as the medium for gravity, you can make that work, as long as you can communicate what you really mean to other people when using that particular word!

denton-scratch 3y ago
> For gravity, I'm okay with calling spacetime the medium I thought spacetime was supposed to be identical with the gravitational field. It can't be gravity's "medium" if that medium is itself gravity. I find this extremely hard to think about; gravity both generates spacetime, and warps it. It's really hard to escape from the earthman's experience of space as a sort of instantaneous volume; we don't really experience time at all, except in the sense that we have a sense of certain events as being not the present (i.e. the past). We know that time exists in some sense; but all we experience of spacetime is the space bit.
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