quantum gravity « General Relativity

Every old style, Newtonian theory in modern physics – which is all of them except General Relativity, do not fit well with GR itself. This is curious, as for instance the Dirac equation, the Standard Model, QM, QFT all work well with each other (hence the Standard Model). In an attempt to unify everything else with GR, the well worn (almost proven impossible by now one would think) trail is to quantize GR on some perturbed Minkowski space.

It doesn’t work. Or rather has not worked.

Since it’s virtually impossible to prove that something can’t be done in physics (see von Neuman’s ‘no hidden variables proof’ as an example), we are left with hundreds of PhDs per year being granted trying to add another brick to a wall that is sinking in mud, hoping that the mud is only so deep, so that another few thousand postdocs life efforts piled up will hit the rock bottom.

It won’t. It’s pure folly.

An alternative is what I present on this site, namely that one can and indeed must build on General Relativity – that in a very real sense all future successful theories will be phenomena inside the Riemannian manifold controlled by the Einstein Equations that we live in.

Examples provided on this site show how one can make electric fields, quantum waves and particles from nothing more than GR. Of course, it’s a minority viewpoint, one I’m willing to stand on.

In this essay I argue for the case of simply trying, in the sense of a toy model, to build parts of the universe out of nothing more than 4D, standard Einstein General Relativity. Its already the norm for a postdoc to spend a decade looking at some 2D toy model of a field that is known not to be able to work, just because it’s easier to do some calculations.

But apparently doing the same thing with a model (4D GR) that we know works extremely well is, well wrong, boring and silly.

I don’t think so.

Physics needs new trial balloons. To the fundamental physics establishment – you can’t actually pop a balloon unless you at least get it in front of you.

Only Gravity Download

T C Andersen 2019 J. Phys.: Conf. Ser. 1275 012038 – 9th International Workshop DICE2018 : Spacetime – Matter – Quantum Mechanics

Abstract. The recent experimental proposals by Bose et al. and Marletto et al. (BMV) outline a way to test for the quantum nature of gravity by measuring gravitationally induced differential phase accumulation over the superposed paths of two ∼ 10−14kg masses. These authors outline the expected outcome of these experiments for semi-classical, quantum gravity and collapse models. It is found that both semi-classical and collapse models predict a lack of entanglement in the experimental results. This work predicts the outcome of the BMV experiment in Bohmian trajectory gravity – where classical gravity is assumed to couple to the particle configuration in each Bohmian path, as opposed to semi-classical gravity where gravity couples to the expectation value of the wave function, or of quantized gravity, where the gravitational field is itself in a quantum superposition. In the case of the BMV experiment, Bohmian trajectory gravity predicts that there will be quantum entanglement. This is surprising as the gravitational field is treated classically. A discussion of how Bohmian trajectory gravity can induce quantum entanglement for a non superposed gravitational field is put forward.

andersen_2019_j._phys.3a_conf._ser._1275_012038 Download

This paper is a result of a talk I gave at DICE2018. The trip and the talk allowed me to sharpen the math and the arguments in this paper. I’m convinced that the results of a BMV like experiment would show these results – namely that gravity violates QM! Most physicists are of course on the opposite side of this and would assume that QM would win in a BMV experiment.

For those of the main camp, this paper is still important, as it describes another way to approximate quantum gravity – one that works better than the very often used Rosenfeld style semi-classical gravity. Sitting through talks where researchers use the semi-classical approximation in order to do sophisticated quantum gravity phenomenology has convinced me that often the results would change significantly if they had of used a Bohmian trajectory approach instead. The chemists figured this out a while ago – a Bohmian approximation is much more accurate than semi-classical approximations.

In some sense semi-classical gravity seems more complicated than Bohmian trajectory gravity, as in semi-classical gravity the gravitational field has to somehow integrate the entire position space of the wave function (a non local entity) in real time (via the Schr ̈odinger – Newton equation), in order to continuously use the expectation value as a source for the gravitational field. In Bohmian mechanics, the gravitational field connects directly to an existing ’hidden’ particle position, which is conceptually simpler.