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I got a bit lost at the double slit experiment with superdeterminism. Can someone clarify what is supposed to be going on? * We send one photon at a time throu
by raylad 5y ago
I got a bit lost at the double slit experiment with superdeterminism. Can someone clarify what is supposed to be going on?
* We send one photon at a time through a double slit, don't measure them, and an interference pattern is formed, presumably because the probabilities of the particle going through each slit interfere with each other.
* If we measure the position of the particle, it goes through only one slit, and there's no interference pattern created.
* Standard QM says that the probability wave function representing the position of the particle "collapses" when measured and the particle then goes through only one slit with no interference when we measure it.
* Superdeterminism says that the initial state of the universe determined that we would measure the particle, and therefore it goes through one slit and there's no interference.
* What I don't understand is: why would there ever be interference in that case? If it's not probabilities interfering with each other what causes single photon interference in the double slit experiment in superdeterminism?
- Koshkin 5y agoWell, the thing is, neither the standard (non-local) quantum mechanics nor the superdeterminism answer this question, as they both simply talk about a wave function and its taking a different shape depending on what measurement is made; the only difference is that one completely gives up on futher clarification of what the wave function physically represents while the other encourages looking for hidden variables.
- raylad 5y agoI've heard the interference discussed as an "interference of probability amplitudes". But in superdeterminism, it seems as if there are no probabilities in that sense, or am I missing something?
- Koshkin 5y agoSuperdeterminism does not deny probabilities (just like, say, classical mechanics does not deny statistical mechanics).
- raylad 5y agoNot following. If everything is predetermined, there are no actual probabilities except as an artifact lack of knowledge of what the outcome must be. If that is the case, how can the probability amplitudes interfere with each other?
- Koshkin 5y agoEven as an artifact of a lack of knowledge, probabilities can do many things - correlate, interfere...
- raylad 5y agoI don't see how one's lack of knowledge can cause lines to form differently (different interference patterns). If anyone has any more insight into this, please do weigh in.
- shellac 5y agoIt's a good question. The interference pattern is a result of two things: 1) Quantum mechanics: the pilot wave or whatever you want to call it. 2) Incoming particles' positions having a broad statistical distribution. With a cunningly skewed / rigged distribution you wouldn't see fringes (e.g. suppose they all come in on the same trajectory). However such distributions are atypical.* But we talk about probability being a 'measure of ignorance' here because we don't know where these particles are exactly, but we know they must have gone through the initial slit, and QM says: in that case, here's the probability it will end up at this final destination. * This the same story as statistical mechanics. (Having said that we do have the issue there that our systems start in low entropy, or 'atypical', states. That's a whole other topic)
- raylad 5y agoRight, in classical QM. But in superdeterminism unless I'm really misunderstanding, they are basically saying that there are no probabilities at all because everything is predictable given the initial conditions of the universe, if you knew the hidden variables. Any "probabilities" are just what one observes to happen, but they aren't doing anything any more, they are just the result of incomplete knowledge. If you knew the hidden variables, you would be able to predict everything exactly and there would be no probabilities as such. In that case, what is creating the interference pattern and why?
- rafaelero 5y ago> Superdeterminism says that the initial state of the universe determined that we would measure the particle, and therefore it goes through one slit and there's no interference. Where did you get this from? I don't think Sabine implied that. From what I understood, it is more like the measurement interacted with the particle and it changed its behavior. I don't see why we need to consider that it was always meant to be that way.
- 8note 5y agodeterminism implies that afaik?
- raylad 5y agoIt seems that can't be true, because if you randomly decide after the particle is launched whether to measure it or not, the interference pattern still appears. So it's not the measuring that does anything in superdeterminism apaprently, it's that if you do measure it, that was "known" in advance by the state of the universe. If not that, what is supposed to be going on (physicists please respond).
- rafaelero 5y ago> if you randomly decide after the particle is launched whether to measure it or not, the interference pattern still appears. So, if you run an experiment and in 50% of the time the machine measures the particles and in 50% don't, does it still form an interference pattern in both cases? That does seem odd. I would expect that whenever a measurement is made, the interference pattern would disappear.
- lmm 5y agoIt forms a weaker interference pattern - imagine superimposing 50% of the interference pattern and 50% of the non-interfering look. There's also the fun of the delayed-choice quantum eraser experiment, where if you measure (or not) which slit the photon went through after measuring the interference pattern (or not), you see (or don't see) the interference pattern.
- 8note 5y agoNit: the single slit case still gives you an interference pattern. It's just that it's a single slit pattern and not a double slit one
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