In order not to further irritate Marcus, let us move this off-topic discussion from the Rovelli thread.(adsbygoogle = window.adsbygoogle || []).push({});

Whether the foliation is bent or not has nothing to do with my argument. By talking about a foliation, you are making a hidden assumption about classical observers. However, since the observer's trajectory is a quantum variable, it can only be specified if we leave the observer's momentum completely undetermined. Or vice versa. This means that the foliation itself is subject to quantum fluctuations, which is the essential physical novelty. Careful said:** In conventional QM, time just marches on independent of what happens. Time must operationally be defined by ticks on the observer's clock, and thus the observer does not accelerate.**

??? There is no problem whatsoever in defining QFT with respect to (non-uniformly) accelerating observers (and bending the foliation according to local eigentime - as long as one does not encounter focal points).

In typical accelerator experiments, the detectors weigh several tonnes, and measurements are related to the detector's rest frame. The assumption that such a detector does not recoil at all is an excellent approximation, which is implicit in the assumption that the detector follows a sharp, classical trajectory. However, it is an approximation, which amounts to replacing several tonnes by infinity. When gravity is turned on, this becomes a problem, because an infinite mass will immediately collapse into a black hole. This is an essential difference between gravity and other interactions. Careful said:** This is no problem we observe an electric phenomenon, say. Then F = ma = qE, where q is the observer's charge and E the electric field generated by the system. That q and E are non-zero and a = 0 is OK, since m = infinity is a good approximation to reality. **

??? The m in the Newton formula is the physical mass and not the bare mass, for an electron that is still the very tiny number of 10^{-30} kilo at least when it moves smaller than c wrt an inertial observer. You can find such information in Eric Poisson, ``An introduction to the Lorentz Dirac equation´´ gr-qc/9912045 where such understanding is offered at a classical level.

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