True randomness in QM

[deleteduser12345]

I've read a bit about determinism and indeterminism and browed a bit but I haven't found a clear answer to my question:
Does true randomness exist?
If so, how does it "work"?

[TheRealJoeFish]

I've read a bit about determinism and indeterminism and browed a bit but I haven't found a clear answer to my question:
Does true randomness exist?
If so, how does it "work"?

Well, in a way, it may only be proper to call it "true randomness" if there's no sufficient answer to the question "how does it 'work'".

Consider 100 molecules of some radioactive element.  We know the element's half life, and we know that 50 will decay over the half life, but we cannot predict which 50 will decay and which 50 will not.  My understanding is, essentially, there are two possibilities:

1) There's something underlying all of this, behind the veil of physics, or observation or something, that says which molecule is ready to decay and when
2) There's not, and there is literally nothing that could allow us to determine which one will decay when - essentially, it is a property of the universe that you can't know which molecule is going to decay until it has decayed.

If that 2nd is the case, it's "true randomness" in a strong sense.  Even if the first is the case, it's still "true randomness" in a weak sense, until we have empirically determined the underlying mechanism.

The consensus seems to be that #2 is indeed the case, iirc - please, some physicist (ALEXK WHERE ARE YOU) correct me if I'm wrong.

[Alex K]

I think it goes too far to say that the consensus is that #2 true randomness is at the bottom of Quantum uncertainty. There is a consensus to use something like the Copenhagen interpretation (or should I say prescription) for all practical calculations in order to not get bogged down with metaphysical questions. That means that virtually everyone, for pragmatic reasons, uses a prescription to calculate results which does not contain rhe additional information (so called hidden variables) which would uniquely determine the result of a measurement involving quantum uncertainty. I believe people don't necessarily choose to do that because they believe in their hearts that there must be true randomness at the bottom of QM, but rather because it makes no difference for the result of any calculation if we included a (usually more complicated) deterministic description with hidden variables : we don't know the values of these hidden variables anyways, and they are constructed precisely such that ignorance of the hidden variable reproduces the same statistical distribution as true quantum randomness. Someone who "believes" in a deterministic interpretation of qm will generally still use the copenhagen or similar prescriptions to calculate concrete results because it is simple.

The Everett "many worlds" interpretation is a special case because it is relatively simple, and it is deterministic, but it has no hidden variables and is not deterministic from the perspective of any single observer. There is no way to determine in principle what a randomly chosen observer in the mwi will measure, because everything happens to some observer, and it is your selection of observer which determines the result xe observes, not any variable.

[Little lunch]

I had number 2 randomness just this morning. :-)

[Alex K]

I had number 2 randomness just this morning. :-)

It is important to eat enough fibre bundles

[Little lunch]

Well, I'm blaming Cadbury's and Pizza Hut.

[Time Traveler]

I think it goes too far to say that the consensus is that #2 true randomness is at the bottom of Quantum uncertainty. There is a consensus to use something like the Copenhagen interpretation (or should I say prescription) for virtually all practical calculations in order to not get bogged down with metaphysical questions. That means that virtually everyone uses a prescription to calculate results which does not contain rhe additional information (so called hidden variables) which would uniquely determine the result of a measurement involving quantum uncertainty. I believe people don't necessarily choose to do that because they believe in their hearts that there must be true randomness at the bottom of QM, but rather because it makes no difference for the result of any calculation if we included a deterministic description with hidden variables : we don't know the values these hidden variables anyways, and they are constructed precisely such that ignorance of the hidden variable reproduces the same statistical distribution as true quantum randomness. Someone who "believes" in a deterministic interpretation of qm will generally still use the copenhagen or similar prescriptions to calculate concrete results because it is simple.

Is there an uncertainty principle for Quantum physicists themselves which prevents them from all reaching the same conclusions? Perhaps we should be studying the scientists instead of tiny particles.

[Alex K]

@TT

No, if you have different theories which are not experimentally distinguishable and all have philosophical strengths and weaknesses, you simply can't expect everyone to agree on one.

[Time Traveler]

@TT

No, if you have different theories which are not experimentally distinguishable and all have philosophical strengths and weaknesses, you simply can't expect  everyone to agree on one.

I understand, just a tease.

[TheRealJoeFish]

THAT's the kind of response I was hoping for when I invoked the name of our resident physicist