I’ve already said, and so has Luke_A_Somers, that “fubs” are 3d spatial slices of 4d spacetime regions.
Ah! I didn’t catch that. Thanks. Suppose a man-made satellite (Fubly 1) is released into (non-geosynchronous) orbit around the earth directly over Phoenix, Arizona. Each time it orbits the earth, it passes over Phoenix, and we can count its orbits this way. One orbit of Fubly 1 is extended in time in the sense that it takes one month (say) to get around the whole planet. In any time less than one month, the orbit is incomplete. So the orbit of Fubly 1 is temporally divisibile in the sense that if I divide it in half, I get two things neither of which is an orbit of Fubly 1, but both of which are parts of an orbit of Fubly 1.
Now, Fubly 1 itself seems different. Suppose Fubly 1 only completes one orbit and then is destroyed. Supposing it’s assembled and then immediately released, the spaciotemporal region that is Fubly 1 and the spaciotemporal region that is the orbit of Fubly 1 have the same extension in time. If I divide the spaciotemporal region of the orbit in half, time-wise, I get two halves of an orbit. If I divide the spacio-temporal region of Fubly 1 itself, I don’t get two halves of a satellite. Fubly 1 can’t be divided time-wise in the way its orbit and its lifespan can. Does that make any sense? My question, in case it does, is this ’Is the distinction I’ve just made likely to be meaningful in the correct physics, or is this a mere artifact of intuition and natural language?
Fubly 1 can’t be divided time-wise in the way its orbit and its lifespan can.
It’s already the result of such a division. As for orbits and lifespans, they are not physical objects but rather logical abstractions, just like language is (as opposed to the air released from the mouth of the speaker and the pressure waves hitting the ear of the listener).
If you mean that Fubly 1 is a given 3d slice, can Fubly 1 persist through time? I mean that if we take two temporally different 3d slices (one at noon, the other at 1:00PM), would they be the same Fubly 1? I suppose if we were to call them ‘the same’ it would be in virtue of a sameness of their 3d properties, abstracted from their temporal positions.
I don’t know what sameness is, sorry. It’s not a definition I have encountered in physics, and SEP is silent on the issue, as well. I sort of understand it intuitively, but I am not sure how you formalize it. Maybe you can think about it in terms of the non-conservation of the coarse grained area around the evolved distribution function, similar to the way Eliezer discussed the Liouville theorem in his Quantum Sequence. Maybe similar areas correspond to more sameness, or something. But this is a wild speculation, I haven’t tried to work through this.
Ah! I didn’t catch that. Thanks. Suppose a man-made satellite (Fubly 1) is released into (non-geosynchronous) orbit around the earth directly over Phoenix, Arizona. Each time it orbits the earth, it passes over Phoenix, and we can count its orbits this way. One orbit of Fubly 1 is extended in time in the sense that it takes one month (say) to get around the whole planet. In any time less than one month, the orbit is incomplete. So the orbit of Fubly 1 is temporally divisibile in the sense that if I divide it in half, I get two things neither of which is an orbit of Fubly 1, but both of which are parts of an orbit of Fubly 1.
Now, Fubly 1 itself seems different. Suppose Fubly 1 only completes one orbit and then is destroyed. Supposing it’s assembled and then immediately released, the spaciotemporal region that is Fubly 1 and the spaciotemporal region that is the orbit of Fubly 1 have the same extension in time. If I divide the spaciotemporal region of the orbit in half, time-wise, I get two halves of an orbit. If I divide the spacio-temporal region of Fubly 1 itself, I don’t get two halves of a satellite. Fubly 1 can’t be divided time-wise in the way its orbit and its lifespan can. Does that make any sense? My question, in case it does, is this ’Is the distinction I’ve just made likely to be meaningful in the correct physics, or is this a mere artifact of intuition and natural language?
It’s already the result of such a division. As for orbits and lifespans, they are not physical objects but rather logical abstractions, just like language is (as opposed to the air released from the mouth of the speaker and the pressure waves hitting the ear of the listener).
If you mean that Fubly 1 is a given 3d slice, can Fubly 1 persist through time? I mean that if we take two temporally different 3d slices (one at noon, the other at 1:00PM), would they be the same Fubly 1? I suppose if we were to call them ‘the same’ it would be in virtue of a sameness of their 3d properties, abstracted from their temporal positions.
I don’t know what sameness is, sorry. It’s not a definition I have encountered in physics, and SEP is silent on the issue, as well. I sort of understand it intuitively, but I am not sure how you formalize it. Maybe you can think about it in terms of the non-conservation of the coarse grained area around the evolved distribution function, similar to the way Eliezer discussed the Liouville theorem in his Quantum Sequence. Maybe similar areas correspond to more sameness, or something. But this is a wild speculation, I haven’t tried to work through this.
Well, thanks for discussing it, I appreciate the time you took. I’ll look over that sequence post.