Abstract
Despite almost a century’s worth of study, it is still unclear how general relativity (GR) and quantum theory (QT) should be unified into a consistent theory. The conventional approach is to retain the foundational principles of QT, such as the superposition principle, and modify GR. This is referred to as ‘quantizing gravity’, resulting in a theory of ‘quantum gravity’. The opposite approach is ‘gravitizing QT’ where we attempt to keep the principles of GR, such as the equivalence principle, and consider how this leads to modifications of QT. What we are most lacking in understanding which route to take, if either, is experimental guidance. Here we consider using a Bose–Einstein condensate (BEC) to search for clues. In particular, we study how a single BEC in a superposition of two locations could test a gravitizing QT proposal where wavefunction collapse emerges from a unified theory as an objective process, resolving the measurement problem of QT. Such a modification to QT due to general relativistic principles is testable near the Planck mass scale, which is much closer to experiments than the Planck length scale where quantum, general relativistic effects are traditionally anticipated in quantum gravity theories. Furthermore, experimental tests of this proposal should be simpler to perform than recently suggested experiments that would test the quantizing gravity approach in the Newtonian gravity limit by searching for entanglement between two massive systems that are both in a superposition of two locations.
Highlights
We examined how, if we attempt to make quantum theory (QT) consistent with the equivalence principle of general relativity (GR), a possible resolution is to consider making modifications to QT that would lead to a violation of the superposition principle of QT where the degree of violation is dependent on the gravitational interaction and configuration of the system. Since this increases for more massive systems, the proposal can provide an objective state reduction that is consistent with current experiments, resolving the measurement problem of QT, which would, on other hand, be expected to persist for the ‘quantizing gravity’ approach and conventional quantum gravity theories
QT is predicted to breakdown when the mass of a quantum system is near the Planck mass scale, allowing for experimental tests that are far more achievable than those generally required for distinguishing conventional quantum gravity theories, where the relevant effects are anticipated near the Planck length scale
In the proposal considered here for a unified theory of GR and QT, quantum superposition states are expected to decay to localized states with an average lifetime that is reciprocally related to the self-energy of the difference between the mass distributions of the localized states, EG [3], which is dependent on the mass and configuration of the system
Summary
At the turn of the previous century, Newtonian mechanics was advanced by two revolutionary theories, quantum theory (QT) and general relativity (GR). If entanglement is observed in the Feynman-inspired experiments this would be a remarkable and significant result, this does not rule out the gravitizing QT approach since QT could still be modified, for example via a GQSR at some other scale such as the Planck length scale This is because the tested effect derives in the nonrelativistic limit of quantum gravity, and so arguably the experiments cannot provide the specifics of how GR should be modified in order to be consistent with QT in the conventional quantizing gravity approach (see [27] for a possibility of extending the experiments with much heavier masses to achieve this). Predictions of the conventional quantizing gravity approach, such as searching for entanglement between two massive quantum systems
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