6 ms·

I don't understand. Isn't action at a distance this: you take red and green marble and randomly put them in two bags. You take one bag with you to Pluto. Then y

by dvh 9y ago

I don't understand. Isn't action at a distance this: you take red and green marble and randomly put them in two bags. You take one bag with you to Pluto. Then you open the bag and see the red one, now you instantly know what marble is in the bag that stayed on Earth. This doesn't break any law so what's the problem?

Twisol 9y ago
In the hidden variables case (yours), it was predetermined which marble was in the bag before you opened it. In the retrocausal case, the information about which marble is in the bag simply isn't part of reality until you've checked. With macroscopic objects like bags and marbles, this is ridiculous, because someone had to put the marble in the bag (a "shared cause"). However, Bell's Theorem shows that entanglement isn't a sufficient "shared cause" to explain his experiment. Thus, we either need superdeterminism (the "shared cause" is the origin of the universe!), spooky action at a distance, or retrocausality.
- RobertoG 9y ago
  >>" the information about which marble is in the bag simply isn't part of reality until you've checked" It seems to me that the universe uses lazy evaluation (1). (1) https://en.wikipedia.org/wiki/Lazy_evaluation https://en.wikipedia.org/wiki/Lazy_evaluation
  - Twisol 9y ago
    It's even weirder than that, though, because with lazy evaluation you still have a complete description of the state involved; it's just a matter of unpacking it by executing the description. That's more analogous with a hidden variables theory. With retrocausality, it seems that performing an observation fundamentally adds information to that which has been observed. If retrocausality can be likened to a computational mechanism, I'd be really interested to know what it is! Like I said in another comment, it seems like there's some element of monotonic computation involved, but the brand of monotonicity is quite unusual.
    - deleted 9y ago
      [deleted]
    - RobertoG 9y ago
      >>"it seems that performing an observation fundamentally adds information to that which has been observed." disclaimer: I have not idea what I'm talking about. Is it not that the "adds information" that you mention, it's like sampling a probability distribution? Of course, then your program, the universe, it's not deterministic anymore (but I think that it's already the case when quantum physics is involved). So, your lazy function, don't do anything until is required and then it returns a sample from a probability mass function (not a pdf because we are talking quantum here).
      - cma 9y ago
        No. See the Kochen-Specker theorem. You can choose which way to measure in ways that sort of interact with one another statistically even after two particles are far separated.
    - neolefty 9y ago
      Can anything be "forgotten" once it's been determined? For example--can two entangled particles be created, then forced to interact in a way that collapses their wave functions, then sucked into a black hole, without having been observed by anything that isn't sucked into that black hole--does their collapse matter? Does the universe forget it? If so, then could the whole universe be a reversible computation, once it's summed up from big bang to big ... whatever happens at the end?
      - lurquer 9y ago
        This makes me think of dangling pointers and memory leaks.
  - marcosdumay 9y ago
    That can also be called "retro causality".
taneq 9y ago
The problem is that Bell's theorem (which is supported by all of our experimental data so far, afaik) states that "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." Basically, hidden variables models can't explain the results of some of our experiments and no-one's found a way to make the two match up. Reference: https://en.wikipedia.org/wiki/Bell's_theorem https://en.wikipedia.org/wiki/Bell's_theorem
- naasking 9y ago
  > "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." It's more accurately phrased as, "No physical theory of local hidden variables with observations that are statistically independent can ever reproduce all of the predictions of quantum mechanics." This is actually a new loophole that 't Hooft is exploring in his cellular automata interpretation of quantum mechanics, ie. it has local hidden variables, but because all matter shares a common history from the Big Bang, no observations we can possibly make can be statistically independent of each other.
  - khafra 9y ago
    It also changes things from "local hidden variable" to "universal hidden variable," it's just a different implementation of universal hidden variables than the Many Worlds Interpretation.
  - 09bjb 9y ago
    > no observations we can possibly make can be statistically independent of each other. Yep. When I'm reading these articles, "Everything Connects" is a pretty useful heuristic for flowing with apparent discrepancies in theories...although of course nailing down concrete theories and finding precise explanations for phenomena is important.
  - John_KZ 9y ago
    Great point, more people need to know about this "small" detail.
marcosdumay 9y ago
The problem is that the state of the your particle, in Pluto, changes when somebody on Earth observes it. The marbles were neither exactly green nor red before somebody looked. It is not as simple as you'll get with macroscopic things, but yes it is not as crazy as some people imply either.
- lostmsu 9y ago
  I always though the problem is with the "collapse" thingy. You don't observe Green marble. You just entangle yourself with the marble pair. And so does the guy with other marble. In the end two marbles, you, and the other observer become a single entangled system, who has two states: you've seen green marble (and the other guy red), and you've seen red marble (...). And now if I "observe" that system, I also become entangled, and also will have two states: "I saw you claiming you saw green", and "I saw you claiming you saw red", and so on. From a physical point of view, in that description there's no mystery. What might be interesting is how you (as in your mind) seemingly experience only one outcome. I even suspect we don't.
  - kgwgk 9y ago
    > From a physical point of view, in that description there's no mystery. There is no explanation either.
    - lostmsu 9y ago
      What do you need explained? This is the nature of things according to the Standard Model.
      - kgwgk 9y ago
        how you seemingly experience only one outcome (the Standard Model? of particle physics?)
d0mine 9y ago
The correlation in the quantum case is stronger https://youtu.be/ZcpwnozMh2U?t=18m10s https://youtu.be/ZcpwnozMh2U?t=18m10s
empath75 9y ago
Imagine instead of Green and Red, it could be either Green or Red, or Blue or Yellow. If you measure it's Red/Green-ness, one will be red, and the other will be green. If you measure it's Blue/Yellow-ness, one will be blue and the other will be yellow. You can't measure the blue/yellow-ness of one and the red/green-ness of the other. As soon as one is measured, the other collapses into a particular color.
John_KZ 9y ago
There's no problem. The copenhagen interpretation is a joke, same as the "spooky action at a distance". The formula to reproduce this mess is too many PhDs with zero intuition, a hierarcical system based on seniority where status=correctness, and jokes gone wrong (ie copenhagen interpretation). The "collapsing universe" is simply the realization that the other marble is blue, and so is the "instant" information transfer.

by dvh 9y ago

Twisol 9y ago

In the hidden variables case (yours), it was predetermined which marble was in the bag before you opened it. In the retrocausal case, the information about which marble is in the bag simply isn't part of reality until you've checked. With macroscopic objects like bags and marbles, this is ridiculous, because someone had to put the marble in the bag (a "shared cause"). However, Bell's Theorem shows that entanglement isn't a sufficient "shared cause" to explain his experiment. Thus, we either need superdeterminism (the "shared cause" is the origin of the universe!), spooky action at a distance, or retrocausality.

RobertoG 9y ago
>>" the information about which marble is in the bag simply isn't part of reality until you've checked" It seems to me that the universe uses lazy evaluation (1). (1) https://en.wikipedia.org/wiki/Lazy_evaluation https://en.wikipedia.org/wiki/Lazy_evaluation
- Twisol 9y ago
  It's even weirder than that, though, because with lazy evaluation you still have a complete description of the state involved; it's just a matter of unpacking it by executing the description. That's more analogous with a hidden variables theory. With retrocausality, it seems that performing an observation fundamentally adds information to that which has been observed. If retrocausality can be likened to a computational mechanism, I'd be really interested to know what it is! Like I said in another comment, it seems like there's some element of monotonic computation involved, but the brand of monotonicity is quite unusual.
  - deleted 9y ago
    [deleted]
  - RobertoG 9y ago
    >>"it seems that performing an observation fundamentally adds information to that which has been observed." disclaimer: I have not idea what I'm talking about. Is it not that the "adds information" that you mention, it's like sampling a probability distribution? Of course, then your program, the universe, it's not deterministic anymore (but I think that it's already the case when quantum physics is involved). So, your lazy function, don't do anything until is required and then it returns a sample from a probability mass function (not a pdf because we are talking quantum here).
    - cma 9y ago
      No. See the Kochen-Specker theorem. You can choose which way to measure in ways that sort of interact with one another statistically even after two particles are far separated.
  - neolefty 9y ago
    Can anything be "forgotten" once it's been determined? For example--can two entangled particles be created, then forced to interact in a way that collapses their wave functions, then sucked into a black hole, without having been observed by anything that isn't sucked into that black hole--does their collapse matter? Does the universe forget it? If so, then could the whole universe be a reversible computation, once it's summed up from big bang to big ... whatever happens at the end?
    - lurquer 9y ago
      This makes me think of dangling pointers and memory leaks.
- marcosdumay 9y ago
  That can also be called "retro causality".

taneq 9y ago

The problem is that Bell's theorem (which is supported by all of our experimental data so far, afaik) states that "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." Basically, hidden variables models can't explain the results of some of our experiments and no-one's found a way to make the two match up. Reference: https://en.wikipedia.org/wiki/Bell's_theorem https://en.wikipedia.org/wiki/Bell's_theorem

naasking 9y ago
> "No physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics." It's more accurately phrased as, "No physical theory of local hidden variables with observations that are statistically independent can ever reproduce all of the predictions of quantum mechanics." This is actually a new loophole that 't Hooft is exploring in his cellular automata interpretation of quantum mechanics, ie. it has local hidden variables, but because all matter shares a common history from the Big Bang, no observations we can possibly make can be statistically independent of each other.
- khafra 9y ago
  It also changes things from "local hidden variable" to "universal hidden variable," it's just a different implementation of universal hidden variables than the Many Worlds Interpretation.
- 09bjb 9y ago
  > no observations we can possibly make can be statistically independent of each other. Yep. When I'm reading these articles, "Everything Connects" is a pretty useful heuristic for flowing with apparent discrepancies in theories...although of course nailing down concrete theories and finding precise explanations for phenomena is important.
- John_KZ 9y ago
  Great point, more people need to know about this "small" detail.

marcosdumay 9y ago

The problem is that the state of the your particle, in Pluto, changes when somebody on Earth observes it. The marbles were neither exactly green nor red before somebody looked. It is not as simple as you'll get with macroscopic things, but yes it is not as crazy as some people imply either.

lostmsu 9y ago
I always though the problem is with the "collapse" thingy. You don't observe Green marble. You just entangle yourself with the marble pair. And so does the guy with other marble. In the end two marbles, you, and the other observer become a single entangled system, who has two states: you've seen green marble (and the other guy red), and you've seen red marble (...). And now if I "observe" that system, I also become entangled, and also will have two states: "I saw you claiming you saw green", and "I saw you claiming you saw red", and so on. From a physical point of view, in that description there's no mystery. What might be interesting is how you (as in your mind) seemingly experience only one outcome. I even suspect we don't.
- kgwgk 9y ago
  > From a physical point of view, in that description there's no mystery. There is no explanation either.
  - lostmsu 9y ago
    What do you need explained? This is the nature of things according to the Standard Model.
    - kgwgk 9y ago
      how you seemingly experience only one outcome (the Standard Model? of particle physics?)

d0mine 9y ago

The correlation in the quantum case is stronger https://youtu.be/ZcpwnozMh2U?t=18m10s https://youtu.be/ZcpwnozMh2U?t=18m10s

empath75 9y ago

Imagine instead of Green and Red, it could be either Green or Red, or Blue or Yellow. If you measure it's Red/Green-ness, one will be red, and the other will be green. If you measure it's Blue/Yellow-ness, one will be blue and the other will be yellow. You can't measure the blue/yellow-ness of one and the red/green-ness of the other. As soon as one is measured, the other collapses into a particular color.

John_KZ 9y ago

There's no problem. The copenhagen interpretation is a joke, same as the "spooky action at a distance". The formula to reproduce this mess is too many PhDs with zero intuition, a hierarcical system based on seniority where status=correctness, and jokes gone wrong (ie copenhagen interpretation). The "collapsing universe" is simply the realization that the other marble is blue, and so is the "instant" information transfer.