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- If quantum theory is nothing but a set or rules to compute the probabilities of macroscopic measurement outcomes, then what is microscopic about it?

Quantum theory is widely thought to be a theory of the fundamental microscopic constituents of matter. It is supposed to tell us something about how matter behaves at the fundamental microscopic level, from which the classical macroscopic behavior should somehow emerge as an approximation based on averaging over a large number of microscopic constituents. But is that really so? Does quantum theory really tell us something about the microscopic world? Or is it just a macroscopic theory which only tells us that macroscopic apparatuses sometimes behave differently than classical macroscopic apparatuses?

No doubt, some

Contrary to a widespread belief, I think it doesn't. The minimal instrumental form of quantum theory is nothing but a set of rules to predict the probabilities of measurement outcomes. And since all measurement outcomes are

Or if you disagree, can you explain in what sense is quantum theory a microscopic theory? Can you really argue that quantum theory is a microscopic theory without assuming (either explicitly or implicitly) some interpretation that goes beyond the minimal instrumental view of quantum theory?

Sure, the minimal quantum formalism does contain objects, such as particle position operator or field operator, that are in a certain sense microscopic objects. But they are merely tools to compute the probabilities of macroscopic measurement outcomes. In this sense minimal quantum theory is not

No doubt, some

**interpretations**of quantum theory, such as the Bohmian interpretation,**do**explicitly tell us something about the microscopic world. But here I don't want to talk about such interpretations. I want to talk about the minimal instrumental view of quantum theory, which refrains from saying anything about quantum interpretations except that which is directly based on experimental evidence. So does such a minimal instrumental form of quantum theory tell as anything about the microscopic world?Contrary to a widespread belief, I think it doesn't. The minimal instrumental form of quantum theory is nothing but a set of rules to predict the probabilities of measurement outcomes. And since all measurement outcomes are

**macroscopic**events, the minimal instrumental quantum theory is not a theory of the microscopic world.Or if you disagree, can you explain in what sense is quantum theory a microscopic theory? Can you really argue that quantum theory is a microscopic theory without assuming (either explicitly or implicitly) some interpretation that goes beyond the minimal instrumental view of quantum theory?

Sure, the minimal quantum formalism does contain objects, such as particle position operator or field operator, that are in a certain sense microscopic objects. But they are merely tools to compute the probabilities of macroscopic measurement outcomes. In this sense minimal quantum theory is not

**about**local objects such as position or field operators. The minimal quantum theory is about macroscopic measurement outcomes, while the local objects above only make sense if they can be somehow used to predict the properties of macroscopic measurement outcomes. Hence the microscopic objects**by themselves**have no purpose, and hence no meaning at all, if the minimal instrumental view of quantum theory is adopted.
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