Quantum weirdness is everywhere in life • Hacker News Board

Re: Quantum weirdness is everywhere in life

#81

Post by n4r9 » Tue, Aug 11, 2015, 11:32 AM UTC

williamjennings wrote: post #72

n4r9 wrote: post #66

Earlier quoted context omitted.

Not sure what you mean by "contradict". Certainly you won't easily find experiments for which the two offer different predictions. They are very different in terms of their ontology though: DeBroglie states that particles have definite positions and momenta at all times whereas Copenhagen does not.

Most of the contradictions arise as epistemological forks in the context of molecular spectroscopy with nuclear decay events. Thusly, it is a question of whose theories to use, and the Born rule is moot when the distribution of particles is not gaussian. DeBroglie himself states that matter waves propagate according to a defined distribution; whereas Copehagen interprets that they are probabilistically distributed. I…

What do you mean by "moot"? The Born rule is simply that the probability of measuring a particle to be in a certain location is given by the squared amplitude of the wavefunction. This squared amplitude will generate the same predictions whether you are using deBroglie-Bohm or "Copenhagen" to imagine your underlying ontology.

The difference in ontology being that deBroglie-Bohm is deterministic, i.e. particles have definite positions of which we are merely ignorant, whereas "Copenhagen" is (usually) non-realist, i.e. it is not meaningful to talk about the positions of particles until the moment we measure it.

Re: Quantum weirdness is everywhere in life

#82

Post by renox » Tue, Aug 11, 2015, 1:18 PM UTC

VLM wrote: post #37

sklogic wrote: post #13

Earlier quoted context omitted.

Our intuition is so poor that it even gets many classical mechanics problems wrong. Most hilariously the various resonance-related things (my favourite practical example is a pendulum swinging upwards, which looks like pure magic). Intuition is also very poor in dealing with nonlinear things (think soliton waves and all that stuff). So, trusting an intuition is always wrong and intuition got no place in science anywa…

> Our intuition is so poor Even better example, "Heavy things fall faster". Or "The sun revolves around the earth". As a greater cultural trend there is often a bit of quantum-whitewashing that everything in physics is obvious and straightforward except quantum mechanics because I suffered thru the annoying math and need to show off superiority at being one of the few humans (on a percentage of entire population) who…

> Even better example, "Heavy things fall faster". Or "The sun revolves around the earth".

Except that those two particular examples are very easy to explain to (nearly) everybody: 1- you think that heavy things fall faster because this is true when there is air resistance.

2-Q:if you have one 'fixed' object and one rotating object, what do you see from the rotating object? A: the same thing as from the 'fixed' object. So is it the Sun which is revolving or the Earth? You don't feel like the Earth is moving but observation of remotes stars have shown us that this is the case.

Which is NOT the case for QM! A good example: QM 'spooky action at distance', QM predicts that there are non-local instantaneous (FTL) effects, but they cannot be used to send data FTL and this has been measured to be true (mostly).

Re: Quantum weirdness is everywhere in life

#83

Post by sklogic » Tue, Aug 11, 2015, 1:43 PM UTC

renox wrote: post #82

VLM wrote: post #37

Earlier quoted context omitted.

> Our intuition is so poor Even better example, "Heavy things fall faster". Or "The sun revolves around the earth". As a greater cultural trend there is often a bit of quantum-whitewashing that everything in physics is obvious and straightforward except quantum mechanics because I suffered thru the annoying math and need to show off superiority at being one of the few humans (on a percentage of entire population) who…

> Even better example, "Heavy things fall faster". Or "The sun revolves around the earth". Except that those two particular examples are very easy to explain to (nearly) everybody: 1- you think that heavy things fall faster because this is true when there is air resistance. 2-Q:if you have one 'fixed' object and one rotating object, what do you see from the rotating object? A: the same thing as from the 'fixed' objec…

> those two particular examples are very easy to explain

Explanations do not affect intuition at all, it's too primal to listen to any reason. Even despite the fact that everybody heard this explanation from the elementary school, watching this in action is still mind-blowing. Check it out yourself [1], and answer honestly - was your intuition puzzled by what you've seen?

[1] http://www.iflscience.com/physics/dropping-bowling-ball-and-...

Re: Quantum weirdness is everywhere in life

#84

Post by n4r9 » Tue, Aug 11, 2015, 2:38 PM UTC

omalleyt wrote: post #69

n4r9 wrote: post #20

Earlier quoted context omitted.

There's a lot of truth in that, and the orthodox interpretation is indeed riddled with incoherence. But what fascinates me is that after so much effort, the quantum community seems to be further away than ever from coming to a consensus on interpreting the theory. Every proposed interpretation does away with some foundational issue, yet introduces another in the process.

Pilot wave theory: the "weird effects" that QM displays are really just the result of space time being a thing that vibrates in a wave-like pattern influenced by mass. And the reason this is cool is because when you put everyday objects in situations like that stated above, they exhibit quantum interference and everything else.

So this is essentially what is meant by the "deBroglie-Bohm" interpretation. There is an underlying definite configuration of all matter, but it is "guided" deterministically by the wavefunction psi. This avoids issues associated with wave function collapse, but by no means does it rid us of all the "weird effects". In particular, the pilot wave is explicitly non-local, in that for a Bell-type experiment the choice of measurement in one location will (instantaneously) affect the physical state of affairs in the other location.

Re: Quantum weirdness is everywhere in life

#85

Post by williamjennings » Wed, Aug 12, 2015, 3:14 AM UTC

n4r9 wrote: post #81

williamjennings wrote: post #72

Earlier quoted context omitted.

Most of the contradictions arise as epistemological forks in the context of molecular spectroscopy with nuclear decay events. Thusly, it is a question of whose theories to use, and the Born rule is moot when the distribution of particles is not gaussian. DeBroglie himself states that matter waves propagate according to a defined distribution; whereas Copehagen interprets that they are probabilistically distributed. I…

What do you mean by "moot"? The Born rule is simply that the probability of measuring a particle to be in a certain location is given by the squared amplitude of the wavefunction. This squared amplitude will generate the same predictions whether you are using deBroglie-Bohm or "Copenhagen" to imagine your underlying ontology. The difference in ontology being that deBroglie-Bohm is deterministic, i.e. particles have d…

In this context, the word moot is a synonym for false. You are omitting the word "normalized wave function" from your description of the Born Rule; it is a key part of the mathematical justification. The squared amplitude does not generate the same predictions under every theory, because the probability function is different.

That is also the difference between the theories of DeBroglie and Bohm, the former is stochastic while the latter is deterministic. Copenhagen theories describe the positions of particles probabilitistically; and the word 'measure' is not being used in the precise mathematical way that it should be. A better translation from Danish would be 'convolute'.

The thing to remember is that when one writes about physics which are centuries old, one must be historiographically consistent. If there is a hyphen between two names for a theory, such that one name is being attributed posthumously; then the student should infer the most recent name is making some error in translation.

When you separate DeBroglie and Bohm, on the basis of their lack of real cooperation, then it is clear to see who was ahead of their time. Bohm is abusing statistical terms in his translations from French, and the meaning of those words is an extremely important detail in the context of Quantum Information Theory. John Von Neumann was contemporaneously working in that context, but it was classified until recent times.