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Part Feynman's idea is that that the electron when travelling backwards through the slicing plane (current moment) become positive electrons that are travelling

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.
    - samograd 13y ago
      I have a problem with the image of 'a single electron on a twisty path through spacetime' that you are describing. The image in my mind is the vibrating, twisty path /out there/, not necessarily in spacetime. Through this path passes a continuous surface that could be be thought of as the 'current moment' of our observable reality. Each crossing/intersection of the electron path through this surface would result in an observable electron. This would then result in the 'single electron' being be the intersection of a uniform diameter path along the reality surface. But now that I've thought about it more it's starting to make less sense :) I was thinking these intesections would be pure, geometric points, but a google shows that electrons have a physical radius and I'm having a hard time coming up with any way that these intersection points would have a spin. What would be the appearance of the electron in your model? I couldn't see it being what we would call an electron travelling along this spacetime path because it would have a need to be in multiple places at the same time; althought I'm sure the 'holographic universe' could somehow take this into account. Does your single electron have a form similar to what I described above?
- nimble 13y ago
  Just sew the end of time up to the beginning of time and the electrons never need to turn around.
  - pdonis 13y ago
    There are mathematical descriptions of universes like this, but their predictions don't match our observations of the actual universe. For example, the Godel universe contains closed timelike curves through every event, but it predicts that we should see distant galaxies rotating with respect to nearer stars, with the rotation getting faster the farther away the galaxies are. We don't observe that.
    - samograd 13y ago
      Why do we have to think that this electron is moving through spacetime? With the 9(?) other dimensions that String Theory has given us, I would think that it could be passing through any subset of them. My impression is that thinking this electron curve is moving through spacetime ignores a lot of modern physics.
      - pdonis 13y ago
        When Wheeler and Feynman originally came up with this model, string theory was still decades in the future. Also, string theory even today is speculative; a lot of physicists think it's a good theory, but it is experimentally untested, because nobody can think of a way to test it; we can run plenty of experiments that are consistent with string theory, but they're also consistent with lots of other theories. We don't know how to run experiments that will help us to distinguish between string theory and the others. And in any case, the point of the model is to describe observations of electrons that we can make directly; those observations don't involve extra dimensions even if there are any. They directly involve the four dimensions we can directly observe, three spatial dimensions plus time, i.e., spacetime. Even if there were string theory machinery "behind the scenes", so to speak, it would still have to be describable at some level as electrons moving through spacetime.

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.
  - samograd 13y ago
    I have a problem with the image of 'a single electron on a twisty path through spacetime' that you are describing. The image in my mind is the vibrating, twisty path /out there/, not necessarily in spacetime. Through this path passes a continuous surface that could be be thought of as the 'current moment' of our observable reality. Each crossing/intersection of the electron path through this surface would result in an observable electron. This would then result in the 'single electron' being be the intersection of a uniform diameter path along the reality surface. But now that I've thought about it more it's starting to make less sense :) I was thinking these intesections would be pure, geometric points, but a google shows that electrons have a physical radius and I'm having a hard time coming up with any way that these intersection points would have a spin. What would be the appearance of the electron in your model? I couldn't see it being what we would call an electron travelling along this spacetime path because it would have a need to be in multiple places at the same time; althought I'm sure the 'holographic universe' could somehow take this into account. Does your single electron have a form similar to what I described above?
nimble 13y ago
Just sew the end of time up to the beginning of time and the electrons never need to turn around.
- pdonis 13y ago
  There are mathematical descriptions of universes like this, but their predictions don't match our observations of the actual universe. For example, the Godel universe contains closed timelike curves through every event, but it predicts that we should see distant galaxies rotating with respect to nearer stars, with the rotation getting faster the farther away the galaxies are. We don't observe that.
  - samograd 13y ago
    Why do we have to think that this electron is moving through spacetime? With the 9(?) other dimensions that String Theory has given us, I would think that it could be passing through any subset of them. My impression is that thinking this electron curve is moving through spacetime ignores a lot of modern physics.
    - pdonis 13y ago
      When Wheeler and Feynman originally came up with this model, string theory was still decades in the future. Also, string theory even today is speculative; a lot of physicists think it's a good theory, but it is experimentally untested, because nobody can think of a way to test it; we can run plenty of experiments that are consistent with string theory, but they're also consistent with lots of other theories. We don't know how to run experiments that will help us to distinguish between string theory and the others. And in any case, the point of the model is to describe observations of electrons that we can make directly; those observations don't involve extra dimensions even if there are any. They directly involve the four dimensions we can directly observe, three spatial dimensions plus time, i.e., spacetime. Even if there were string theory machinery "behind the scenes", so to speak, it would still have to be describable at some level as electrons moving through spacetime.