3 ms·

> "The whole state of system-plus-clock doesn’t change in time" How is this different from the classical view of the universe as deterministic? In a Newtonian

> "The whole state of system-plus-clock doesn’t change in time" How is this different from the classical view of the universe as deterministic? In a Newtonian universe, all future states can be determined from the current state, so the universe can be seen as a "frozen" 4-dimensional object.

contravariant 10y ago
Well, it's similar, except in this case the universe wouldn't have to be deterministic. As far as I can tell there's no law saying you can't have two clocks, where observers entangled with either observe a different sequence of events.
- danbruc 10y ago
  I think Leonard Susskind touched this point in one of the theoretical minimum lectures [1] but I really can not tell which one. While we can quite easily imagine adding and removing space dimensions, nobody ever figured out what it would mean to have more than one time dimension. I think he also talked about time traveling in this context - you can go back and forth in space because there is more than one space dimension and so you can turn around and walk the other direction. Unless you instantaneously flip around that is nothing you can do with just one dimension like our one time dimension. But those things aside, the order of spatially separated events is not in general well defined if you take general relativity into account. There is a causal ordering all observers agree on but that still allows some observers to see some events in one order or another. I skimmed the papers linked in the article but they are quite a bit above what I can immediately grasp. But one thing I noticed was that they talked a lot about observable changes, so now I am wondering whether the entire system they are talking about is really static or whether we are just unable to observe the evolution of the entire system? If it is really static like the block universe, then I have not the slightest idea of how two subsystems can experience time if you think of one as a clock and the other as an observer watching the clock. In case of the block universe I can totally understand how everything is deterministic and all times exist in parallel, but I never understood what mechanism picks out the slice that is my or your now. [1] http://theoreticalminimum.com http://theoreticalminimum.com
chrischen 10y ago
The frozen 4 dimensional object creates a projection of the other dimensions, including time and relative time. Time is hen a subsystem within the system. Their analogy, aptly for HN, is that of computer code which is in one dimension interpreted amd executed linearly, being able to project something like a 3D game. Think something like minecraft's source code being interpreted and creating an infinite procedurally generated world that constantly evolves with an in game timer despite the source code still being static. Quantum mechanics, the mechanics governing the source code could still make it timeless and indeterministic, but output of the code (the projection), is still bound by the in game physics and timer much like time in general relativity.
- SomeStupidPoint 10y ago
  But is their proposal that, like Minecraft, we can detect properties of the background execution through apparent non-determinism (or other mechanism)? Cause Minecraft actually has two detectable, distinct notions of time: a game tick and update ordering of the underlying computation. Minecraft can even be viewed as having quantum effects caused by a universal nonlocal variable, Bohmian mechanics styles, with the apparent non-determinism resulting from that non-local hidden variable interacting woth the update engine. (The hidden variable is the ordering of the updates in real time rather than MC time.) I always thought we should teach physics with Minecraft, but the engine sucks too much for me to seriously recommend it. Ed: Imgur album on detecting MC update ordering via redstone; pictures somehow got out of order. http://imgur.com/a/e9YKi http://imgur.com/a/e9YKi
raattgift 10y ago
The article's a bit scattered but its central theme seems to be the Problem of Time. There's a wikipedia article on that, of course, and it's not so bad. https://en.wikipedia.org/wiki/Problem_of_time https://en.wikipedia.org/wiki/Problem_of_time The structure of the the paragraph you quoted and the one following it is similar to the first two long paragraphs under the "Proposed solutions to the problem of time" section of the wikipedia article. There is a bit more here: https://en.wikipedia.org/wiki/Canonical_quantum_gravity#The_problem_of_time https://en.wikipedia.org/wiki/Canonical_quantum_gravity#The_... and a technical overview in the first section of https://arxiv.org/abs/1009.2157 https://arxiv.org/abs/1009.2157 I wrote "seems", because I found it hard to focus on an article whose second paragraph is a grotesque of General Relativity and in subsequent paragraphs brings in a not especially clearly related set of links to the author's previous articles on the recent Verlinde paper on emergent gravity and the amplituhedron, among others. :-(

contravariant 10y ago

Well, it's similar, except in this case the universe wouldn't have to be deterministic. As far as I can tell there's no law saying you can't have two clocks, where observers entangled with either observe a different sequence of events.

danbruc 10y ago
I think Leonard Susskind touched this point in one of the theoretical minimum lectures [1] but I really can not tell which one. While we can quite easily imagine adding and removing space dimensions, nobody ever figured out what it would mean to have more than one time dimension. I think he also talked about time traveling in this context - you can go back and forth in space because there is more than one space dimension and so you can turn around and walk the other direction. Unless you instantaneously flip around that is nothing you can do with just one dimension like our one time dimension. But those things aside, the order of spatially separated events is not in general well defined if you take general relativity into account. There is a causal ordering all observers agree on but that still allows some observers to see some events in one order or another. I skimmed the papers linked in the article but they are quite a bit above what I can immediately grasp. But one thing I noticed was that they talked a lot about observable changes, so now I am wondering whether the entire system they are talking about is really static or whether we are just unable to observe the evolution of the entire system? If it is really static like the block universe, then I have not the slightest idea of how two subsystems can experience time if you think of one as a clock and the other as an observer watching the clock. In case of the block universe I can totally understand how everything is deterministic and all times exist in parallel, but I never understood what mechanism picks out the slice that is my or your now. [1] http://theoreticalminimum.com http://theoreticalminimum.com

chrischen 10y ago

The frozen 4 dimensional object creates a projection of the other dimensions, including time and relative time. Time is hen a subsystem within the system. Their analogy, aptly for HN, is that of computer code which is in one dimension interpreted amd executed linearly, being able to project something like a 3D game. Think something like minecraft's source code being interpreted and creating an infinite procedurally generated world that constantly evolves with an in game timer despite the source code still being static. Quantum mechanics, the mechanics governing the source code could still make it timeless and indeterministic, but output of the code (the projection), is still bound by the in game physics and timer much like time in general relativity.

SomeStupidPoint 10y ago
But is their proposal that, like Minecraft, we can detect properties of the background execution through apparent non-determinism (or other mechanism)? Cause Minecraft actually has two detectable, distinct notions of time: a game tick and update ordering of the underlying computation. Minecraft can even be viewed as having quantum effects caused by a universal nonlocal variable, Bohmian mechanics styles, with the apparent non-determinism resulting from that non-local hidden variable interacting woth the update engine. (The hidden variable is the ordering of the updates in real time rather than MC time.) I always thought we should teach physics with Minecraft, but the engine sucks too much for me to seriously recommend it. Ed: Imgur album on detecting MC update ordering via redstone; pictures somehow got out of order. http://imgur.com/a/e9YKi http://imgur.com/a/e9YKi

raattgift 10y ago

The article's a bit scattered but its central theme seems to be the Problem of Time. There's a wikipedia article on that, of course, and it's not so bad. https://en.wikipedia.org/wiki/Problem_of_time https://en.wikipedia.org/wiki/Problem_of_time The structure of the the paragraph you quoted and the one following it is similar to the first two long paragraphs under the "Proposed solutions to the problem of time" section of the wikipedia article. There is a bit more here: https://en.wikipedia.org/wiki/Canonical_quantum_gravity#The_problem_of_time https://en.wikipedia.org/wiki/Canonical_quantum_gravity#The_... and a technical overview in the first section of https://arxiv.org/abs/1009.2157 https://arxiv.org/abs/1009.2157 I wrote "seems", because I found it hard to focus on an article whose second paragraph is a grotesque of General Relativity and in subsequent paragraphs brings in a not especially clearly related set of links to the author's previous articles on the recent Verlinde paper on emergent gravity and the amplituhedron, among others. :-(