From Weinberg, The Quantum Theory of Fields, Vol. 1, there is the statement that "the only way" to merge Lorentz invariance with the cluster decomposition property (a.k.a. locality) is through a field theory.

He uses this argument basically to justify that any quantum theory at low energies will be an (effective) field theory.

But this leaves out string theory: string theory is not a field theory, but it is thought as a candidate for a quantum theory. Is string theory not respecting Lorentz invariance and / or the cluster decomposition property?

Edit: from https://arxiv.org/pdf/hep-th/9702027.pdf , Weinberg states "(...) the whole formalism of fields, particles, and antiparticles seems to be an inevitable consequence of Lorentz invariance, quantum mechanics, and cluster decomposition, without any ancillary assumptions about locality or causality."

He uses this argument basically to justify that any quantum theory at low energies will be an (effective) field theory.

But this leaves out string theory: string theory is not a field theory, but it is thought as a candidate for a quantum theory. Is string theory not respecting Lorentz invariance and / or the cluster decomposition property?

Edit: from https://arxiv.org/pdf/hep-th/9702027.pdf , Weinberg states "(...) the whole formalism of fields, particles, and antiparticles seems to be an inevitable consequence of Lorentz invariance, quantum mechanics, and cluster decomposition, without any ancillary assumptions about locality or causality."

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