3 ms·

> Why does probability seem to follow an arrow of time, it doesn't seem symmetrical like the rest of physics. One cannot really oppose probability to "the rest

by kgwgk 2y ago

> Why does probability seem to follow an arrow of time, it doesn't seem symmetrical like the rest of physics. One cannot really oppose probability to "the rest of physics". Probability is not "a part of" physics. Probability is what we use to describe imperfect knowledge of a physical system - and we know more about the past than we do about the future.

ninetyninenine 2y ago
No, probability is a mathematical game with axioms and theorems. Why the rules of this game happens to describe systems where we have imperfect knowledge... nobody knows. Another thing is all of these systems have probability travel in a single direction. Things with high probability are more likely to happen. If time were to go backwards, low probability events will start to spontaneously occur.
- kgwgk 2y ago
  Ok, so we agree that probability is not a part of physics. I also agree that the question of how to apply probability in physics is interesting. I’m not sure about the “nobody knows” though. I would say that statistical mechanics has been quite successful in “knowing”: https://arxiv.org/pdf/cond-mat/0501322 https://arxiv.org/pdf/cond-mat/0501322
  - ninetyninenine 2y ago
    Haven't you heard of quantum mechanics. The probability wave makes it a foundational part and not just a macro phenomena. Statistical mechanics is just a study of the application of probability to that macro phenomena. We still don't know why all of it works.
    - kgwgk 2y ago
      > Haven't you heard of quantum mechanics. Haven't you looked at the article I sent which says "quantum" in every other page. Haven't you heard of its author Roger Balian and his (two-volume) book From microphysics to macrophysics: methods and applications of statistical physics. > Statistical mechanics is just a study of the application of probability to that macro phenomena. We still don't know why all of it works. "We" may "know" different things - and have a different view on the relative importance of what is known and what it isn't.
- kgwgk 2y ago
  > Another thing is all of these systems have probability travel in a single direction. Things with high probability are more likely to happen. If time were to go backwards, low probability events will start to spontaneously occur. If I shoot a pool ball to strike a heavier second ball which is at rest they will end up moving in opposite directions. If "time were to go backwards" - whatever that means - they would approach at the end one would be at rest. That's seems indeed unlikely with "time going forwards" because we wouldn't be able to do that if we tried (at least not systematically). I don't think there is a conceptual problem or anything surprising there: we know how balls move given their initial conditions but we cannot control those initial conditions with the precision required to obtain a precise outcome. There are also cases were we can prepare systems in the right configuration and produce "low probability" events even with "time going forwards": https://en.wikipedia.org/wiki/Spin_echo https://en.wikipedia.org/wiki/Spin_echo
  - ninetyninenine 2y ago
    >If I shoot a pool ball to strike a heavier second ball which is at rest they will end up moving in opposite directions. If "time were to go backwards" - whatever that means - they would approach at the end one would be at rest. That's seems indeed unlikely with "time going forwards" because we wouldn't be able to do that if we tried (at least not systematically). in a vacuum no ball will ever go to rest if it's moving. It will move forever because there is no resistance. What's happening in the pool table is that the ball is losing it's movement energy to the table. Table is absorbing it, the air is resisting it and slowly that vibrational energy becomes more and more spread out until it's basically imperceptible heat (which is also technically atoms vibrating). What happens when time goes backwards is a bunch of tiny low probability events start happening. Heat from the background vibrating atoms by pure random luck happen to align and happen to produce motion that's noticeable. This happens from several places and by pure luck all of this vibrational motion concentrates on one place, the pool table and the ball. The kinetic vibrations just happen to push the ball slowly in one direction more and more with all kinetic vibrations by pure luck speeding up the ball. The ball being picking up speed until you with the tip of the pool cue catch the ball and ease it into a perfect stop, absorbing all the kinetic energy into the stick and your body. All within the laws of physics but all extremely low probability events. >There are also cases were we can prepare systems in the right configuration and produce "low probability" events even with "time going forwards": https://en.wikipedia.org/wiki/Spin_echo https://en.wikipedia.org/wiki/Spin_echo When you put an intelligence in the system it's sort of cheating as you can manipulate random events to be non random and thus violate the laws of probability by intelligent choice. There's some computational theory here that states that the act of thinking itself produces entropy thus it's sort of conserved in a way but that' some other theory stuff that's another rabbit hole to dive into.

by kgwgk 2y ago

ninetyninenine 2y ago

No, probability is a mathematical game with axioms and theorems. Why the rules of this game happens to describe systems where we have imperfect knowledge... nobody knows. Another thing is all of these systems have probability travel in a single direction. Things with high probability are more likely to happen. If time were to go backwards, low probability events will start to spontaneously occur.

kgwgk 2y ago
Ok, so we agree that probability is not a part of physics. I also agree that the question of how to apply probability in physics is interesting. I’m not sure about the “nobody knows” though. I would say that statistical mechanics has been quite successful in “knowing”: https://arxiv.org/pdf/cond-mat/0501322 https://arxiv.org/pdf/cond-mat/0501322
- ninetyninenine 2y ago
  Haven't you heard of quantum mechanics. The probability wave makes it a foundational part and not just a macro phenomena. Statistical mechanics is just a study of the application of probability to that macro phenomena. We still don't know why all of it works.
  - kgwgk 2y ago
    > Haven't you heard of quantum mechanics. Haven't you looked at the article I sent which says "quantum" in every other page. Haven't you heard of its author Roger Balian and his (two-volume) book From microphysics to macrophysics: methods and applications of statistical physics. > Statistical mechanics is just a study of the application of probability to that macro phenomena. We still don't know why all of it works. "We" may "know" different things - and have a different view on the relative importance of what is known and what it isn't.
kgwgk 2y ago
> Another thing is all of these systems have probability travel in a single direction. Things with high probability are more likely to happen. If time were to go backwards, low probability events will start to spontaneously occur. If I shoot a pool ball to strike a heavier second ball which is at rest they will end up moving in opposite directions. If "time were to go backwards" - whatever that means - they would approach at the end one would be at rest. That's seems indeed unlikely with "time going forwards" because we wouldn't be able to do that if we tried (at least not systematically). I don't think there is a conceptual problem or anything surprising there: we know how balls move given their initial conditions but we cannot control those initial conditions with the precision required to obtain a precise outcome. There are also cases were we can prepare systems in the right configuration and produce "low probability" events even with "time going forwards": https://en.wikipedia.org/wiki/Spin_echo https://en.wikipedia.org/wiki/Spin_echo
- ninetyninenine 2y ago
  >If I shoot a pool ball to strike a heavier second ball which is at rest they will end up moving in opposite directions. If "time were to go backwards" - whatever that means - they would approach at the end one would be at rest. That's seems indeed unlikely with "time going forwards" because we wouldn't be able to do that if we tried (at least not systematically). in a vacuum no ball will ever go to rest if it's moving. It will move forever because there is no resistance. What's happening in the pool table is that the ball is losing it's movement energy to the table. Table is absorbing it, the air is resisting it and slowly that vibrational energy becomes more and more spread out until it's basically imperceptible heat (which is also technically atoms vibrating). What happens when time goes backwards is a bunch of tiny low probability events start happening. Heat from the background vibrating atoms by pure random luck happen to align and happen to produce motion that's noticeable. This happens from several places and by pure luck all of this vibrational motion concentrates on one place, the pool table and the ball. The kinetic vibrations just happen to push the ball slowly in one direction more and more with all kinetic vibrations by pure luck speeding up the ball. The ball being picking up speed until you with the tip of the pool cue catch the ball and ease it into a perfect stop, absorbing all the kinetic energy into the stick and your body. All within the laws of physics but all extremely low probability events. >There are also cases were we can prepare systems in the right configuration and produce "low probability" events even with "time going forwards": https://en.wikipedia.org/wiki/Spin_echo https://en.wikipedia.org/wiki/Spin_echo When you put an intelligence in the system it's sort of cheating as you can manipulate random events to be non random and thus violate the laws of probability by intelligent choice. There's some computational theory here that states that the act of thinking itself produces entropy thus it's sort of conserved in a way but that' some other theory stuff that's another rabbit hole to dive into.