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That solution doesn't work in the general case. Say I have an anti-correlated EPR pair of electrons, such that measuring spin-up for one particle means I will

by wetmore 13y ago

That solution doesn't work in the general case. Say I have an anti-correlated EPR pair of electrons, such that measuring spin-up for one particle means I will subsequently measure spin-down for the other. Then your solution doesn't work. Also the EPR paradox applies to quantum states that are not necessarily electrons. FWIW the EPR paradox is no longer a paradox anyway since you cannot use entanglement to transmit information faster than the speed of light, therefore preserving locality. The reason Einstein et al. termed it a paradox was because they thought it represented some sort of instantaneous information transfer.

_dark_matter_ 13y ago
You are mostly correct, except for the last part. EPR denied that it was faster than light transfer, but instead thought that the information was already present in the second particle, thus implying that the theory was incomplete. This was also more exciting since it left open an avenue for further development in physics.
- unclebucknasty 13y ago
  Right. Either relativity or our understanding of quantum mechanics had to be "violated" in order to explain their observations. Einstein & Co. chose the latter with their idea of hidden parameters (i.e. information already present in the second particle). But, later experiments based on Bell's theorem seriously challenged the hidden parameter explanation, preserving quantum mechanics in the process. So, that takes us back to instantaneous information transfer or a third option: one electron (or any particle for that matter)!
samograd 13y ago
Part Feynman's idea is that that the electron when travelling backwards through the slicing plane (current moment) become positive electrons that are travelling backwards in time. This then leads people to ask, where are all the positive electrons? I propose that the electron when going 'backwards' across the reality projection/slicing plane are not actually travelling in time and producing 'negative' electrons with a positive charge, but are actually the 'electrons' we observe with opposite spin. This brings us back to a single electron on a twisted path with a single spin but giving us observations showing multiple electrons with 2 spins. Paradox again resolved ;-)
- pdonis 13y ago
  The "backwards" electrons can't be just "forwards" electrons with opposite spin, for two reasons: (1) Ordinary "forwards" electrons exist in both spin states, and both states have negative charge, not positive charge. So the anti-electrons that we observe with positive charge can't be just ordinary electrons with their spins flipped. (2) The spin reversal operator (also called the "parity operator") is unitary, but the time reversal operator, the one that changes a "forward" electron into a "backward" electron, is anti-unitary. So they can't possibly be the same operator.
  - samograd 13y ago
    But the article is talking about a single electron on a twisted path that is intersected by the projection surface[1] of reality. Your statement (1) depends on the existence of multiple electrons, where the whole idea of this article idea is that only one electron exists, which is where my argument comes from. (2) sounds like math and not something physical or 'real'. If this operator actually existed in reality such that a single electron's spin can be flipped by applying it to an actual physical electron? I'll answer that by saying, I doubt it, but I am not a particle physicist. If this operator does exist, then one could not say that there was a single electron on a path, unless all electrons in the universe changed spin direction instantly after the application such an operator. [1] Edit: changed 'plane' to 'surface'.
    - pdonis 13y ago
      Your statement (1) depends on the existence of multiple electrons No, it doesn't. The single electron could still be acted on by various operators in the course of its twisty path through spacetime, which could make it appear in various different ways. Which operators might be acting is then deduced from the different ways electrons appear. Your hypothesis amounts to the claim that the only operator that is required to act on the single electron, to explain all its different appearances, is the spin reversal operator. My point is that that hypothesis only accounts for the appearance of "electrons" (more precisely, different views of the single electron) with opposite spins and the same charge; it does not account for the appearance of "electrons" (different views of the single electron) with opposite charges, because no unitary operator can change the charge, and the spin reversal operator is unitary. If this operator actually existed in reality such that a single electron's spin can be flipped by applying it to an actual physical electron? Sure it does; there are many different kinds of experimental setups that can realize this operator. One of the simplest is an inhomogeneous magnetic field. The "operator" language is just a way of linking the math describing electrons with the physical setup that does things to them. If this operator does exist, then one could not say that there was a single electron on a path, unless all electrons in the universe changed spin direction instantly after the application such an operator. No, this is not correct. The operator can be localized, so it only operates on one "electron" (i.e., one particular segment on the single electron's entire worldline) at a time. In fact, regardless of which operator acts on the electron, it has to be localized for the hypothesis that there is only one electron to make sense. The whole point of the hypothesis is that the single electron follows a highly twisted path through spacetime, so that it crosses any single spacelike slice of spacetime multiple times, with each crossing potentially having a different appearance (different spin, etc.). That means whatever operator acts on the electron to make its path through spacetime twist has to be localized--otherwise all the appearances of electrons everywhere in the universe at a given instant of time would be exactly the same, which they obviously aren't.
unclebucknasty 13y ago
>Then your solution doesn't work. It's a measurement artifact, based on our presumption that there is more than one electron. That is, measurement itself is simply a way to quantify what we perceive and understand. So, our perception that we are measuring more than one particle is the same lens through which that measurement is produced. Or, garbage in, garbage out. Instead, let's assume that there is one electron. Then, we would have to derive different metrics for explaining what we observe (spin, locale, charge, etc.). How does that electron appear to be in multiple places simultaneously? Why does it appear to possess multiple properties? What mechanism do we have to explain that? And what is missing in our understanding or ability to perceive that makes us believe it's impossible? Is there another dimension? Or is it truly a function of time that we don't understand?

by wetmore 13y ago

_dark_matter_ 13y ago

You are mostly correct, except for the last part. EPR denied that it was faster than light transfer, but instead thought that the information was already present in the second particle, thus implying that the theory was incomplete. This was also more exciting since it left open an avenue for further development in physics.

unclebucknasty 13y ago
Right. Either relativity or our understanding of quantum mechanics had to be "violated" in order to explain their observations. Einstein & Co. chose the latter with their idea of hidden parameters (i.e. information already present in the second particle). But, later experiments based on Bell's theorem seriously challenged the hidden parameter explanation, preserving quantum mechanics in the process. So, that takes us back to instantaneous information transfer or a third option: one electron (or any particle for that matter)!

samograd 13y ago

Part Feynman's idea is that that the electron when travelling backwards through the slicing plane (current moment) become positive electrons that are travelling backwards in time. This then leads people to ask, where are all the positive electrons? I propose that the electron when going 'backwards' across the reality projection/slicing plane are not actually travelling in time and producing 'negative' electrons with a positive charge, but are actually the 'electrons' we observe with opposite spin. This brings us back to a single electron on a twisted path with a single spin but giving us observations showing multiple electrons with 2 spins. Paradox again resolved ;-)

pdonis 13y ago
The "backwards" electrons can't be just "forwards" electrons with opposite spin, for two reasons: (1) Ordinary "forwards" electrons exist in both spin states, and both states have negative charge, not positive charge. So the anti-electrons that we observe with positive charge can't be just ordinary electrons with their spins flipped. (2) The spin reversal operator (also called the "parity operator") is unitary, but the time reversal operator, the one that changes a "forward" electron into a "backward" electron, is anti-unitary. So they can't possibly be the same operator.
- samograd 13y ago
  But the article is talking about a single electron on a twisted path that is intersected by the projection surface[1] of reality. Your statement (1) depends on the existence of multiple electrons, where the whole idea of this article idea is that only one electron exists, which is where my argument comes from. (2) sounds like math and not something physical or 'real'. If this operator actually existed in reality such that a single electron's spin can be flipped by applying it to an actual physical electron? I'll answer that by saying, I doubt it, but I am not a particle physicist. If this operator does exist, then one could not say that there was a single electron on a path, unless all electrons in the universe changed spin direction instantly after the application such an operator. [1] Edit: changed 'plane' to 'surface'.
  - pdonis 13y ago
    Your statement (1) depends on the existence of multiple electrons No, it doesn't. The single electron could still be acted on by various operators in the course of its twisty path through spacetime, which could make it appear in various different ways. Which operators might be acting is then deduced from the different ways electrons appear. Your hypothesis amounts to the claim that the only operator that is required to act on the single electron, to explain all its different appearances, is the spin reversal operator. My point is that that hypothesis only accounts for the appearance of "electrons" (more precisely, different views of the single electron) with opposite spins and the same charge; it does not account for the appearance of "electrons" (different views of the single electron) with opposite charges, because no unitary operator can change the charge, and the spin reversal operator is unitary. If this operator actually existed in reality such that a single electron's spin can be flipped by applying it to an actual physical electron? Sure it does; there are many different kinds of experimental setups that can realize this operator. One of the simplest is an inhomogeneous magnetic field. The "operator" language is just a way of linking the math describing electrons with the physical setup that does things to them. If this operator does exist, then one could not say that there was a single electron on a path, unless all electrons in the universe changed spin direction instantly after the application such an operator. No, this is not correct. The operator can be localized, so it only operates on one "electron" (i.e., one particular segment on the single electron's entire worldline) at a time. In fact, regardless of which operator acts on the electron, it has to be localized for the hypothesis that there is only one electron to make sense. The whole point of the hypothesis is that the single electron follows a highly twisted path through spacetime, so that it crosses any single spacelike slice of spacetime multiple times, with each crossing potentially having a different appearance (different spin, etc.). That means whatever operator acts on the electron to make its path through spacetime twist has to be localized--otherwise all the appearances of electrons everywhere in the universe at a given instant of time would be exactly the same, which they obviously aren't.

unclebucknasty 13y ago

>Then your solution doesn't work. It's a measurement artifact, based on our presumption that there is more than one electron. That is, measurement itself is simply a way to quantify what we perceive and understand. So, our perception that we are measuring more than one particle is the same lens through which that measurement is produced. Or, garbage in, garbage out. Instead, let's assume that there is one electron. Then, we would have to derive different metrics for explaining what we observe (spin, locale, charge, etc.). How does that electron appear to be in multiple places simultaneously? Why does it appear to possess multiple properties? What mechanism do we have to explain that? And what is missing in our understanding or ability to perceive that makes us believe it's impossible? Is there another dimension? Or is it truly a function of time that we don't understand?