The paper explains why the de Broglie-Bohm theory reduces to Newtonian mechanics in the macroscopic classical limit. The quantum-to-classical transition is based on three steps: (i) interaction with the environment produces effectively factorized states, leading to the formation of effective wave functions and hence decoherence; (ii) the effective wave functions selected by the environment–the pointer states of decoherence theory–will be well-localized wave packets, typically Gaussian states; (iii) the quantum potential of a Gaussian state becomes negligible under standard classicality conditions; therefore, (...) the effective wave function will move according to Newtonian mechanics in the correct classical limit. As a result, a Bohmian system in interaction with the environment will be described by an effective Gaussian state and–when the system is macroscopic–it will move according to Newtonian mechanics. (shrink)

The paper explains why the de Broglie–Bohm theory reduces to Newtonian mechanics in the macroscopic classical limit. The quantum-to-classical transition is based on three steps: (i) interaction with the environment produces effectively factorized states, leading to the formation of _effective wave functions_ and hence _decoherence_; (ii) the effective wave functions selected by the environment—the pointer states of decoherence theory—will be well-localized wave packets, typically Gaussian states; (iii) the quantum potential of a Gaussian state becomes negligible under standard classicality conditions; therefore, (...) the effective wave function will move according to Newtonian mechanics in the correct classical limit. As a result, a Bohmian system in interaction with the environment will be described by an effective Gaussian state and—when the system is macroscopic—it will move according to Newtonian mechanics. (shrink)

The purpose of this contribution is to examine the current state of the de Broglie-Bohm theory (dBB) in light of Bohm’s vision as he explicitly set it out in his book Quantum theory [In Bohm, D., Quantum theory, Courier corporation, (1961b)]. In particular, two programmes that differ in many crucial respects are currently being pursued. On the one hand, the Bohmian mechanics school, founded by Dürr Goldstein and Zanghì, considers the theory to be Galilean invariant, regards particles’ motion as determined (...) by a nomological entity, the universal wave function, upholds the quantum equilibrium hypothesis and explains probabilities in terms of typicality. On the other hand, the Pilot-wave school advocated by Valentini considers the theory to be based on Aristotelian dynamics, regards the wave function as a physical field displaying a contingent nature, and explains quantum equilibrium as the result of a process of relaxation from quantum non-equilibrium. Looking at Bohm’s work [In Bohm, D., Quantum theory, Courier corporation, (1961b)], it is clear that his intention was to construct a theory that was empirically different from standard quantum mechanics, so that it would be testable and falsifiable. Only this way could he defend dBB from the criticism that accused the theory of being 'metaphysical'. These methodological concerns about the falsifiability of the theory constitute, in my opinion, a strong reason for regarding Valentini's programme as methodologically valuable, even if it might turn out to be wrong. Indeed, the programme of the Pilot-wave school aims to be falsifiable with respect to standard quantum mechanics and can in principle defend the empirical status of particle trajectories. (shrink)