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Non-philosophically inclined experts in relativistic QFT often insist that QFT is a local theory. They are not impressed much by arguments that quantum theory is non-local because such arguments typically rest on philosophical notions such as ontology, reality, hidden variables, or the measurement problem.

But how about the Reeh-Schlieder theorem? The Reeh-Schlieder theorem (recently explained in a relatively simple way by Witten in https://arxiv.org/abs/1803.04993 ) is an old theorem, well-known in axiomatic QFT, but relatively unknown in a wider QFT community. In somewhat over-simplified terms (see Sec. 2.5 of the paper above), the theorem states that acting with a suitable (not necessarily unitary)

What I would like to see is how do non-philosophically inclined experts in QFT, who insist that relativistic QFT is local, interpret Reeh-Schlieder theorem in local terms? How can it be compatible with locality?

But how about the Reeh-Schlieder theorem? The Reeh-Schlieder theorem (recently explained in a relatively simple way by Witten in https://arxiv.org/abs/1803.04993 ) is an old theorem, well-known in axiomatic QFT, but relatively unknown in a wider QFT community. In somewhat over-simplified terms (see Sec. 2.5 of the paper above), the theorem states that acting with a suitable (not necessarily unitary)

**local**operator (e.g. having a support only on Earth) on the vacuum, one can create an**arbitrary**state (e.g. a state describing a building on Mars). As all other theorems that potentially can be interpreted as signs of quantum non-locality, this theorem is also a consequence of quantum entanglement. However, unlike other theorems about quantum non-locality, this theorem seems not to contain any philosophical concepts or assumptions. The theorem is pure mathematical physics, without any philosophical excess baggage.What I would like to see is how do non-philosophically inclined experts in QFT, who insist that relativistic QFT is local, interpret Reeh-Schlieder theorem in local terms? How can it be compatible with locality?

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