alt Hacker News> When researchers measure an individual particle, the outcome is random, but the properties of the pair are more correlated than classical physics allows, enabling researchers to verify the randomness.
Is this not possibly just random-seeming to us, because we do not know or cannot measure all the variables?
> The process starts by generating a pair of entangled photons inside a special nonlinear crystal. The photons travel via optical fiber to separate labs at opposite ends of the hall.
> Once the photons reach the labs, their polarizations are measured. The outcomes of these measurements are truly random.
I understand that obviously for our purposes (e.g. for encryption), this is safely random, but from a pure science perspective, have we actually proven that the waveform collapsing during measurement is "truly random"?
How could we possibly assert that we've accounted for all variables that could be affecting this? There could be variables at play that we don't even know exist, when it comes to quantum mechanics, no?
A coin toss is completely deterministic if you can account for wind, air resistance, momentum, starting state, mass, etc. But if you don't know that air resistance or wind exists, you could easily conclude it's random.
I ask this as a layman, and I'm really interested if anyone has insight into this.
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>I ask this as a layman, and I'm really interested if anyone has insight into this.
Another comment basically answered but basically you are touching on Hidden Variable Theorems in QM. Basically that there could be missing variables we can't currently measure that explain the seeming randomness of QM. Various tests have shown and most Physicists agree that Hidden Variables are very unlikely at this point.
It could still be a pseudo random number generator behind the scenes. For example, a typical quantum circuit simulator would implement measurements by computing a probability then asking a pseudo random number generator for the outcome and then updating the state to be consistent with this outcome. Bell's theorem proves those state updates can't be local in a certain technical sense, but the program has arbitrary control over all amplitudes of the wavefunction so that's not a problem when writing the simulator code.
If the prng was weak, then the quantum circuit being simulated could be a series of operations that solve for the seed being used by the simulator. At which point collapses would be predictable. Also, it would become possible to do limited FTL communication. An analogy is some people built a redstone computer in minecraft that would detonate TNT repeatedly, record the random directions objects were thrown, and solve for the prng's seed [1]. By solving at two times, you can determine how many calls to the prng had occurred, and so get a global count of various actions (like breaking a block) regardless of where they happened in the world.
This a difference between the ontological (as-is) and the epistemological (as-modeled). I asked pretty much the same thing, you might find some of the responses I got illuminating. [0]
I don’t think I’ll ever be convinced that there’s some kind of fundamental “randomness” (as in one that isn’t a measure of ignorance) in the world. Claiming its existence sounds like claiming to know what we don’t know.
Bell's Theorem (1964) describes an inequality that should hold if quantum mechanics' randomness can be explained by certain types of hidden variables. In the time since, we've repeatedly observed that inequality violated in labs, leading most to presume that the normal types of hidden variables you would intuit don't exist. There are some esoteric loopholes that remain possibilities, but for now the position that matches our data the best is that there are not hidden variables and quantum mechanics is fundamentally probabilistic.