Timeline for Do we actually need negative probabilities in quantum mechanics?
Current License: CC BY-SA 4.0
27 events
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| Mar 28, 2023 at 5:08 | comment | added | FlatterMann | @kludg It's actually worse than that: there is no description of individual copies of a quantum system. We can say a few general things about it (that it will preserve energy, momentum and angular momentum, for instance), but there is no way to predict when and where that energy will be transferred by the system. We can only make statements about the distributions of those processes in the ensemble. That is, IMHO, the hardest to get over if we come from a classical perspective in which the individual system copy has a meaningful physical behavior. | |
| Mar 28, 2023 at 4:12 | comment | added | kludg | @FlatterMann True, but I meant a different thing. Quantum physics is very different from Classical physics then it comes to description of individual systems, not ensembles. Still, probability theory as math remains the same, and there is no reason to think that Quantum physics needs negative probabilities. | |
| Mar 27, 2023 at 18:43 | comment | added | FlatterMann | @kludg In physics we are always counting frequencies. Probabilities enter into it only through assumptions like the law of large numbers, which is not always a safe bet (see e.g. martingales for a trivial counterexample of why even infinitely many experiments can not guarantee a well defined average). | |
| Mar 27, 2023 at 18:19 | answer | added | akhmeteli | timeline score: 2 | |
| Mar 27, 2023 at 15:51 | comment | added | kludg | I think probability theory as Math is the same in Classical and Quantum physics. Physics only is different. | |
| Mar 27, 2023 at 14:23 | comment | added | Vladimir F Героям слава | How does QFT interpret the Negative probability problem of the real scalar fields' Klein-Gordon equation? | |
| Mar 27, 2023 at 10:45 | answer | added | Dast | timeline score: 4 | |
| Mar 27, 2023 at 7:15 | history | became hot network question | |||
| Mar 27, 2023 at 0:31 | comment | added | ZeroTheHero | On a lighter note: maybe (Jason) Bourne rules the screen, but it is (Max) Born who “rules” QM…. Hopefully I corrected all the occurrences of “Bourne”…. ;) | |
| Mar 27, 2023 at 0:30 | vote | accept | Mikayla Eckel Cifrese | ||
| Mar 27, 2023 at 0:29 | history | edited | ZeroTheHero | CC BY-SA 4.0 |
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| Mar 27, 2023 at 0:12 | comment | added | tparker | @Amit Subtracting probabilities is not the same thing as negative probabilities. If you subtract two positive numbers, then they're still both positive. | |
| Mar 27, 2023 at 0:09 | answer | added | tparker | timeline score: 43 | |
| Mar 27, 2023 at 0:08 | comment | added | FlatterMann | @MikaylaEckelCifrese The same as with the talk of "collapse". It simply doesn't have an equivalent in nature. It is somebody's failed mental model. You are not required to make it yours. | |
| Mar 27, 2023 at 0:06 | answer | added | ZeroTheHero | timeline score: 15 | |
| Mar 27, 2023 at 0:05 | comment | added | Mikayla Eckel Cifrese | @FlatterMann, but the what's the deal with the talk of probability amplitudes and negative probabilities? Even the that famous comic, "The Talk" that clarifies a bunch of misconceptions about quantum computing, mentions probability amplitudes. And there's a whole Wikipedia article about them, so it doesn't seem like they're some fringe concept that no actual physicist takes seriously. I just don't understand the need for them, or if they're even really their own thing or just an alternative label for the magnitude of the wavefunction. | |
| Mar 27, 2023 at 0:02 | comment | added | Mikayla Eckel Cifrese | @hyportnex, Not specifically, or at least, I didn't know it was called that. What prompted my question was actually someone on Quora claiming that QM doesn't have PDFs only wavefunctions. I knew he was wrong about that, but he also started talking about probability amplitudes and negative probabilities, which I had previously heard about in the context of QM, and it got me curious to learn more about it, hence why I was reading the other two threads I linked to and asked questions about. | |
| Mar 26, 2023 at 23:54 | history | edited | Mikayla Eckel Cifrese | CC BY-SA 4.0 |
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| Mar 26, 2023 at 23:45 | comment | added | Amit | @tparker I very purposefully started by writing "It's not only in QM"... I didn't mean to say it applies to QM. Only that negative probabilities occurring as an intermediate step in calculating a total probability is nothing special / unique to QM. | |
| Mar 26, 2023 at 23:45 | comment | added | FlatterMann | @Amit The interpretation of probabilities as the limit of the frequencies of outcomes of the repetition of the same experiment (aka statistical or quantum mechanical ensemble) is not a philosophical issue. These experiments are completely independent. You can even imagine them taking place in distinct universes, if you like. Therefor they can not have a causal relationship and it is not possible to negate what has happened in one experiment by another one. That is the first and foremost reason for the linearity of quantum mechanics to begin with. | |
| Mar 26, 2023 at 23:42 | comment | added | hyportnex | are you thinking of this en.m.wikipedia.org/wiki/Wigner_quasiprobability_distribution ? | |
| Mar 26, 2023 at 23:39 | comment | added | Amit | @FlatterMann Whether the minus sign that arises as the square of a specific probability amplitude is interpreted as a negative probability, or as a subtraction of a positive probability is somewhat philosophical I think. I think the question is whether it will be possible to justify it in a similar way or not, e.g. , avoiding counting the same event twice or something like that. But for that we need of course to talk about a specific example... | |
| Mar 26, 2023 at 23:38 | comment | added | tparker | @Amit That has nothing at all to do with complex amplitudes or destructive interference in quantum mechanics. Moreover, it's a very misleading analogy. | |
| Mar 26, 2023 at 23:35 | comment | added | FlatterMann | @Amit Where do you see a negative probability in that formula? All probabilities are positive. The only minus sign occurs in the formula itself, but the negative term alone does not represent a meaningful process. One can not undo the outcome of an experiment with another experiment. | |
| Mar 26, 2023 at 23:33 | comment | added | FlatterMann | I would disregard what you have been reading there. Probabilities in quantum mechanics are what you get AFTER you apply the Born rule, i.e. after a projection and after taking the square of the modulus of the wave function. That is, by definition, a positive number. The wave function itself does not have a physical interpretation and it is complex, anyway, which means that it isn't "negative" in any meaningful mathematical sense. | |
| Mar 26, 2023 at 23:33 | comment | added | Amit | It's not only in quantum mechanics. Consider the general formula: $$P(A \cup B) = P(A) + P(B) - P(A \cap B)$$ You need to subtract the probability that both events happen to avoid counting it twice | |
| Mar 26, 2023 at 23:15 | history | asked | Mikayla Eckel Cifrese | CC BY-SA 4.0 |