#qbism

(via Wine, Quantum, a Life Worth Living -- Is Quantumness in the Eye of the Beholder? - YouTube)

The conflict arising from the violation of Bell's inequalities is often reduced to a binary one: Either we have to give up "realism" or we are forced to give up "locality". Though I asked the same binary question in an older entry, this way of stating the problem ignores important subtleties of possible interpretations of quantum mechanics. In the following I will present you an approach of interpreting quantum theory that relies on the notion participatory realism (you can find a more general entry about realism here). We will study the approach called QBism, developed primarily by Chistopher Fuchs, Rüdiger Schack and David Mermin.

What is QBism?

The term Qbism is an abbreviation for Quantum Bayesianism - therefore denoting the bayesian understanding of probability as the fundament of this interpretation. To be more precise: The underlying interpretation of probability is the one of Bruno de Finetti. A view in which probabilities are merely personal degrees of belief and have nothing to do with the representation of physical objects. De Finetti claims radically: PROBABILITY DOES NOT EXIST. In the same manner, QBists state: QUANTUM STATES DO NOT EXIST. [1]

Quantum states are therefore no elements of the observer independent physical reality. Quantum mechanics itself is regarded to be rather an extension of probability theory than a theory about elements of reality. According to the binary categorization above, they give up "realism". Instead they regard quantum mechanics to be a strictly "local" theory, since "no agent can move faster than light". [4]

Solipsism? Instrumentalism? No - It's participatory realism!

Following the simplified binary categorization, QBists seem to give up "realism" (because they deny the quantum state to be an object of the observer inependent physical reality). As a result QBists are often accused to be instrumentalist or even solipsist - since their radically subjective view of quantum mechanics as a "single user theory" might suggest so. But the opposite is the case; QBists regard their interpretation neither as instrumentalist nor as solipsist. Why? Though denying the reality of the quantum state, they do not deny the existence of a world "out there": In Qbist thinking the Born rule is a statement about the world, it is empirical [3]. In addition the subjective character of the theory is not supposed to be a defect, it rather abolishs the strict division between reality and observer - consequently the observer becomes part of reality as well. As Fuchs put it: "That’s not less reality, that’s more." [2]

Randomness and participation in Qbist thinking

In a quantum measurement the "irreducible randomness" or "genuine autonomy"[2] of the world manifests itself. There are no hidden variables or whatsoever that predict with any certainty the measurement outcomes - measurements are rather "moments of creation" [1] in which the agent's participation plays a crucial role. This perspective definitely does not deny realism: "in such a quantum measurement we touch the reality of the world in the most essential of ways" [2].

Then, what are the laws of the world "out there"?

We already encountered the terms "irreducible randomness" and "genuine autonomy" [2] Their meaning can be subsumed in a very strong statement QBists do about the nature of physical reality - they go along with John Wheeler's declaration: "The only law of nature is that there is no law". [2]

The main point I want to convey with this entry is, one needs to be aware that we should not ask oversimplified questions, because doing so dangerously narrows our horizon of possible answers. Bell's theorem does not simply give us the possibility to decide between "realism" and "locality". There are much more possible facettes to explore.

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References

[1] Fuchs: QBism, the Perimeter of Quantum Bayesianism

[2] Fuchs: On participatory Realism

[3] Fuchs, Schack: QBism and the Greeks: why a quantum state does not represent an element of physical reality

Amanda Gefter has an article at Nautilus a couple of you have asked me about: Reality Exists Without Observers? Boooo! The title is an accurate summary of her thesis. Gefter is responding to a book by Vlatko Vedral, where he reportedly argues for a reality that doesn’t require observers. In terms of quantum mechanics, Vedral is an Everettian, although he seems to downplay the many-worlds aspect,…

RE: I see this as the narrative to explain the increasing fragmenting of society & verbal attacks that arise from disagreements over the tiniest things.. let's just admit to it, ppl generally do not like others due to our selfish tendencies & to a degree GOD labels that as greed.

The other month I was shocked when I looked up that verse where JESUS tells of this rich man who says to himself how he can relax because he has torn down his old barn & built a monumental monstrosity to store his wealth.. to which JESUS scolded or warned him: "You fool! This very night your life is required of you, who then will inherit what you have worked so hard to accumulate?"

This is the shocker: HE was not only saying you idiot, your wealth is not for you to kick back & enjoy yourself, rather it was given to you as a test to see if you'd do the right thing & provide for those who have not. Essentially now that your ego has mis-spent your windfall for the year, now all your neighbours will come kill you. The ancients knew to be generous with what they have bc they knew full well the ups & downs of life; that they were all reliant on one another's generosity to see them through the years of famine to share in the feast of others, and vice versa. But in modern times, we assume we can hang on to what we have through all the technological advances & educational forums, we have done away with our fear of GOD & how HE levels out the playing field for the have-nots to survive.