Strange Posted May 16, 2017 Posted May 16, 2017 A suggestion that tiny fluctuations of expansion and contraction can average out to reduce the effect of vacuum energy.https://www.universetoday.com/135570/new-explanation-dark-energy-tiny-fluctuations-time-space/https://journals.aps.org/prd/abstract/10.1103/PhysRevD.95.103504 We investigate the gravitational property of the quantum vacuum by treating its large energy density predicted by quantum field theory seriously and assuming that it does gravitate to obey the equivalence principle of general relativity. We find that the quantum vacuum would gravitate differently from what people previously thought. The consequence of this difference is an accelerating universe with a small Hubble expansion rate H∝Λe−βG√Λ→0 instead of the previous prediction H=8πGρvac/3‾‾‾‾‾‾‾‾‾√∝G‾‾√Λ2→∞ which was unbounded, as the high energy cutoff Λ is taken to infinity. In this sense, at least the "old" cosmological constant problem would be resolved. Moreover, it gives the observed slow rate of the accelerating expansion as Λ is taken to be some large value of the order of Planck energy or higher. This result suggests that there is no necessity to introduce the cosmological constant, which is required to be fine tuned to an accuracy of 10−120, or other forms of dark energy, which are required to have peculiar negative pressure, to explain the observed accelerating expansion of the Universe. https://arxiv.org/abs/1703.00543 2
koti Posted May 17, 2017 Posted May 17, 2017 On one hand this seems thin because it relies on QFT and assumes obedience to GR on the quantum level but on the other hand it resolves the awful cosmological constant problem and dark energy weirdness. Very interesting, great find Strange.
KipIngram Posted May 17, 2017 Posted May 17, 2017 (edited) I thought QFTs were our very best theories - why is relying on that bad? ^ Honest question there - not a poke of any kind. Edited May 17, 2017 by KipIngram
koti Posted May 17, 2017 Posted May 17, 2017 I thought QFTs were our very best theories - why is relying on that bad? ^ Honest question there - not a poke of any kind. As far as I know, the behavior of gravity on the quantum level is unlcear and results in null theories and infinities when combined with GR. QFT's predictions are unfortunately impossible to confirm anytime soon (if ever) due to the small scale which cannot be probed experimentally without some ridiculous amounts of energy. As I understand these guys are assuming and basing their investigation on the above thats why I used the term "thin" By no means I'm an expert on QM so I might be wrong. Nevertheless, this seems very interesting and I will try to dig through it more thoroughly over the weekend which will be a challenge for me.
KipIngram Posted May 17, 2017 Posted May 17, 2017 Ok. I'd just read that QED is a QFT, and is stunningly, amazingly accurate.
koti Posted May 17, 2017 Posted May 17, 2017 Ok. I'd just read that QED is a QFT, and is stunningly, amazingly accurate. Sure. Unfortunately QED is missing one tiny detail just like any other quantum field theory so far - gravity.
Mordred Posted May 18, 2017 Posted May 18, 2017 (edited) Is gravity truly missing or can we simply not isolate gravity from all the contributors to spacetime? ie other forces, Higgs field etc. We have no problem isolating every other contributor to kinematic motion which via the stress tensor contributes to spacetime. So if all other contributors to spacetime can successfully account for all kinematic action. What does gravity itself contribute or is it simply the sum of all other contributors.? I'll leave that as food for thought. This is a tricky issue, finding a graviton to mediate the gravitational field would certainly answer the above. However we are far far far from ever producing the predicted energy levels to produce a graviton. Then the question remains does a graviton exist or does the spacetime geometry not require a mediator particle as with photons and the electromagnetic field? There is a quantum field of study that specifically deals with gravity. Quantum geometrodynamics. just and FYI now as far as the article is concerned I'm still going through it but it is definetely interesting. I was recently thinking of how to model spacetime under the Heisenburg uncertainty. So it is a nice coincidence seeing this paper. In a similar fashion via the HUP. The paper is also alluding to the cosmological constant as a sum of all contributors via the uncertainties inherent in all other fields. Thanks for posting it Strange. Edited May 18, 2017 by Mordred
koti Posted May 18, 2017 Posted May 18, 2017 Is gravity truly missing or can we simply not isolate gravity from all the contributors to spacetime? ie other forces, Higgs field etc. We have no problem isolating every other contributor to kinematic motion which via the stress tensor contributes to spacetime. So if all other contributors to spacetime can successfully account for all kinematic action. What does gravity itself contribute or is it simply the sum of all other contributors.? I'll leave that as food for thought. This is a tricky issue, finding a graviton to mediate the gravitational field would certainly answer the above. However we are far far far from ever producing the predicted energy levels to produce a graviton. Then the question remains does a graviton exist or does the spacetime geometry not require a mediator particle as with photons and the electromagnetic field? There is a quantum field of study that specifically deals with gravity. Quantum geometrodynamics. just and FYI now as far as the article is concerned I'm still going through it but it is definetely interesting. I was recently thinking of how to model spacetime under the Heisenburg uncertainty. So it is a nice coincidence seeing this paper. In a similar fashion via the HUP. The paper is also alluding to the cosmological constant as a sum of all contributors via the uncertainties inherent in all other fields. Thanks for posting it Strange. My thoughts exactly but you put them in a more coherent form than I did adding some meat to it. Not being able to isolate gravity from other contributors to spacetime is pribably a better aproach than what I said that its missing. By missing, I meant that gravity defends itself from team play within QM models. I'm thinking...in various modern theories, maybe gravity doesn't have to contribute to spacetime and maybe it is not a sum of all other contributors to spacetime. Maybe gravity is just a property of spacetime and it doesnt have to be analysed in such a way. If we look at GR, gravity doesnt seem to be a force anyway so maybe treating it only like a property of spacetime changing under the influence of conditions makes sense. In such a case would it make sense to refer to gravity as a contributor? I would love to know what are your thoughts after youre done with the article and let us know in this thread. As a side note, and Im only mentioning this as I noticed you make the same typo in many other threads - its Heisenberg not Heisenburg
Recommended Posts