Talk:Quantum gravity/Archive for 2016

Causal Fermionic Systems

"Causal fermionic systems" refers to a theory essentially known only by one "F. Finster". It probably shouldn't even be mentioned in the "other approaches" list, and certainly not beside string theory and LQG. The detail that the theory "gives general relativity and quantum field theory as limiting cases" is also superfluous given that no such details are given for any other theory. (198.84.200.2 (talk) 07:18, 24 February 2016 (UTC))

Assessment comment

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Putting statements such as "they are so astronomically small" in the overview leaves this reader dazed and confused, he finds it in stiff competition with such concepts as "a worldwide bottleneck". I know it is being pedantic and in this case nobody is deceived but there are very many disputed matters in wiki where real confusion arises because the matters are explained in a similarly confused way. In this case leaving out "astronomically" would reinforce the idea to be conveyed--Damorbel 06:57, 13 April 2007 (UTC) == This sentence "one can demonstrate that the structure of general relativity essentially follows inevitably from the quantum mechanics of interacting theoretical spin-2 massless particles" I don't think is correct == It's followed by five citations from the 1950s and 60s (most by a single author), none of which are available online. My understanding is that its incorrect. It seems that there's a theoretical argument by Weinberg, coming much later than the citations following the sentence, for why a massless spin-2 particle would have to be a graviton in the sense that it would have to couple to the stress-energy tensor or angular momentum tensor, unless there are additional particles. Anyone have a view? — Preceding unsigned comment added by 50.138.1.245 (talk) 03:37, 12 December 2013 (UTC)

Last edited at 03:38, 12 December 2013 (UTC). Substituted at 03:37, 30 April 2016 (UTC)

About quantum gravity

In an article you need to add the following point. The main role in the quantum theory of gravity will play the uncertainty relation $\Delta r_{s}\Delta r\geq \ell _{P}^{2}$, where $r_{s}$ is Schwarzschild radius, $r$ is radial coordinate, $\ell _{P}$ is the Planck length, which is another form of Heisenberg's uncertainty relation between the momentum and coordinate. In fact, this ratio can be written in the form $\Delta (2GM/c^{2})\Delta r\geq G\hbar /c^{3}$, where $G$ is the gravitational constant, $M$ is mass, $c$ is the speed of light, $\hbar$ is Dirac's constant, or what is the same, the Heisenberg's uncertainty relation $\Delta (Mc)\Delta r\geq \hbar /2$. This uncertainty relation predicts the emergence of virtual black holes at the Planck scale. It indicates that the photon velocity fluctuations depend on the square of the Planck length $\ell _{P}^{2}$, but not the Planck length $\ell _{P}$. These fluctuations is immeasurably small. Therefore, images of distant stars should be visible without distortion on intergalactic distances. At the same time the emergence of virtual black holes (quantum foam, which is the basis for "fabric" of the Universe) is energetically most favorable in three-dimensional space. This gave rise, most likely, to the three-dimensionality of the observed space. See more here in the proofs. 178.120.22.229 (talk) 08:10, 10 December 2016 (UTC)