Friday, 18 September 2015

determinism - How do we know that certain quantum effects are random?


I was looking at a website that claims to generate random numbers from observation of quantum effects. This lead me to question how we know that the numbers are truly random.


When we observe a probability wave and it collapses in one place into a particle, how do we know that the location of the particle is really random?


Do we have any evidence of the randomness, or is it just that no one can predict the location right now?



Answer



There are two main views. The first view relates to the Copenhagen interpretation of Quantum Mechanics. According to this interpretation, a particle does not have a specific path, but travels like a wave. Upon detection, the wave function collapses and the particle appears at a random point on the screen (according to the probability defined by the wave function).


The second view relates to the "Pilot Waves" theory. It states that a particle has a definite trajectory that ends up with a dot on the screen. However, the trajectory depends on the emission parameters, as the particle is emitted by the source at a certain angle, with a certain phase, etc. These parameters are random, so the result is exactly the same.


In the Copenhagen interpretation, the trajectory is unknown, because a definite trajectory does not exist. In the Pilot Waves theoty, the trajectory is definite, but cannot be known, because it depends on the random parameters of the emission.


In other words, whether we don't know the trajectory, because it doesn't exist, or we don't know it, because it exists, but we can't ever know it, the result is exactly the same. Whether randomness is at the end of the path or at the beginning, the result is unpredictable anyway.



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