Why does the uncertainty principle imply randomness

[Sleve123]

I'm trying to get my head round this. I don't see why our inability to measure the world around us means that at the quantum level things must be random. I understand that measuring momentum of a particle to a high degree of accuracy means losing accuracy in it known position. But I don't understand how this translates to randomness. For example a photon hits an electron, replay the same thing, time after time it should be the same (given exact same starting positions). Or doesn't the particle know where the photon is, so doesn't know what to do.

I understand the reasons we (humans) can't measure certain things to a given accuracy, but why does this mean nature is random. It just says we (humans) can't put a position on a object therefore can't predict what it will do next. Therefore we can't find the positions and momenta of everything, say in a box and work out there positions in the future (or past). It doesn't say that when a particle meets another particle it would do difference things if the situation was replayed exactly.

 

[LostConjugate]

The uncertainty principle is not a statement about measuring instruments. It is a statement about fundamental uncertainty. However it does not imply randomness at all, everything can be measured exactly. There are just some things that do not commute, and they never did even classically.

You can not say your car has some momentum as it travels down the road and is also at some exact position on the road. This is because momentum requires two positions in order to define.

What does imply randomness in QM is the wave function of probabilities.

 

[DrChinese]

I'm trying to get my head round this. I don't see why our inability to measure the world around us means that at the quantum level things must be random. I understand that measuring momentum of a particle to a high degree of accuracy means losing accuracy in it known position. But I don't understand how this translates to randomness. For example a photon hits an electron, replay the same thing, time after time it should be the same (given exact same starting positions). Or doesn't the particle know where the photon is, so doesn't know what to do.

I understand the reasons we (humans) can't measure certain things to a given accuracy, but why does this mean nature is random. It just says we (humans) can't put a position on a object therefore can't predict what it will do next. Therefore we can't find the positions and momenta of everything, say in a box and work out there positions in the future (or past). It doesn't say that when a particle meets another particle it would do difference things if the situation was replayed exactly.

Hard to know how to answer this, really.

For starters: observation of quantum particles yields random values. And we have no theoretical basis for there existing a cause which predetermines this. So that is mighty strong evidence per se. So your question then boils down to "yes, I know all that, but I want to believe the contrary even though there is no evidence to support my position other than it seems reasonable."

For instance: it is possible to create photons that are exact clones of each other (same polarization, frequency, etc.). And yet when we perform certain tests on these clones, we get completely random results. So the idea you suggest is not correct, the results are not the same.

Further, this is simply a consequence of the Heisenberg Uncertainty Principle, which is the theoretical rule which relates to this.

So there is a lot for you to overcome, since particles don't actually act as you expect, and the quantum theory is born out to great accuracy by experiment.

 

[zaybu]

There are things that just happen spontaneously (uncaused in the old language). For instance, beta decay and quantum fluctuations, off the top of my head. QM is a theory that deals quite remakably with that reality.

 

[haael]

I understand the reasons we (humans) can't measure certain things to a given accuracy, but why does this mean nature is random. It just says we (humans) can't put a position on a object therefore can't predict what it will do next. Therefore we can't find the positions and momenta of everything, say in a box and work out there positions in the future (or past). It doesn't say that when a particle meets another particle it would do difference things if the situation was replayed exactly.

So you propose some hidden variables theory. That's the exact meaning of the statement: "the particles have some exact position and momentum, but we can not measure it". Sadly, hidden variables theories do not agree with special relativity.

However, all experiments up to this date show that special relativity holds and uncertainity pronciple holds. If you also believe that the macroscopic world is classical, randomness is the only answer.

 

[wawenspop]

if quantum randomness is perfect, how does it achieve it? I am having difficulty with the whole random thing. we cannot produce random numbers however hard we try, so how do collidibg particles do it? what is the process or engine making these random events?
confused.

 

[zaybu]

if quantum randomness is perfect, how does it achieve it? I am having difficulty with the whole random thing. we cannot produce random numbers however hard we try, so how do collidibg particles do it? what is the process or engine making these random events?
confused.

I don't know what you mean by "perfect". All we can say is that randomness is part of nature at the sub-atomic level.

 

[Nervous]

Perfect randomness = Pure randomness
Which as stated above, HsUP doesn't imply randomness.