necessary and sufficient conditions for a quantum gravity

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necessary and sufficient conditions for a quantum gravity

#1

Post by notFritzArgelander »


This looks to be important and needs some digging. The article is kind of vague to me. So I will follow up with more detail.

Article:

https://phys.org/news/2019-08-key-piece ... lZV_ogoLpA

The paper is at https://journals.aps.org/prl/abstract/1 ... 123.041601
We show that uniformly accelerated detectors can display genuinely thermal features even if the Kubo-Martin-Schwinger (KMS) condition fails to hold. These features include satisfying thermal detailed balance and having a Planckian response identical to cases in which the KMS condition is satisfied. In this context, we discuss that satisfying the KMS condition for accelerated trajectories is just sufficient but not necessary for the Unruh effect to be present in a given quantum field theory. Furthermore, we extract the necessary and sufficient conditions for the response function of an accelerated detector to be thermal in the infinitely adiabatic limit. This analysis provides new insight about the interplay between the KMS condition and the Unruh effect, and a solid framework in which the robustness of the Unruh effect against deformations of quantum field theories (perhaps Lorentz-violating) can be answered unambiguously.
arXiv to the rescue: https://arxiv.org/abs/1804.00685
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

#2

Post by notFritzArgelander »


The issue at stake here is essentially a thought experiment involving how to vacuum looks to an accelerating observer. General Relativity uses the principle of equivalence (gravity is the same as being in an accelerated, non inertial reference frame). The Unruh effect predicts that an accelerating observer will see blackbody radiation while an inertial (non accelerating) observer sees none. The temperature of blackbody Unruh radiation is the same as the Hawking radiation from black holes. Essentially the accelerating and non-accelerating observers see completely different vacuum states. This is OK since there there isn't a globally defined coordinate transformation that links the accelerating and non accelerating frames of reference. Only local coordinate transformations are possible and that isn't enough to relate the two observed vacuums.

https://en.wikipedia.org/wiki/Unruh_effect#Explanation

OK that's installment #1. Must run errands.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


So an inertial observer sees a vacuum that looks different from that of an accelerated observer who sees a warm gas at some temperature that is proportional to the acceleration. This breaks the KMS conditions which quantum field theory usually requires for an equilibrium thermal state. The KMS conditions are described here:

https://en.wikipedia.org/wiki/KMS_state

Which looks likely to give folks headaches. I don't propose to go into detail translating it beyond remarking that it is the quantum field theory generalization of the Boltzmann distribution. The probability of a state is proportional to exp( -βEi ) where β = 1/(kT) and Ei is the its energy level. The fact that the vacuum looks different depending on whether the observer is moving implies violation of the KMS conditions and can be interpreted in one of two ways:

1) the Unruh effect doesn't happen (which a General Relativity person would find repugnant) or
2) the KMS conditions are too restrictive and small deviations associated with a cutoff length scale (something like the Planck length perhaps) are permitted along with the Unruh effect.

The authors proceed to look for permissible small violations or generalizations of the KMS conditions that will keep the Unruh effect in play.

To be continued.....
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


So to summarize, the Unruh radiation effect, the difference in appearance of the vacuum to an accelerated observer, requires that the KMS conditions are sufficient but not necessary for a quantum-gravity field theory. In particular the possibility of a high energy (Planck length?) cutoff. Can this "deformation" of Quantum Field Theory be performed and still allow Unruh radiation?

The answer to this is very technical. I'm going to dodge around those issues by stating that the intricate maths the authors perform is equivalent to looking at the axioms for Quantum Field Theory proposed by J A Wheeler's other (i.e. not Feynman) student, Art Wightman. Wightman did a critical examination of the logical foundations of Quantum Field Theory in the 1950s-60s. His axioms are here.

https://en.wikipedia.org/wiki/Wightman_axioms

Briefly the axions are:

1) Relativistic Quantum Mechanics (as formulated in the Copenhagen manner by John von Neumann with symmetries as described by Eugene Wigner) is fundamentally true.
2) The quantum fields are operator valued functions in the state space (simplifying a lot here)
3) The fields are invariant under Lorentz transformations
4) Microscopic causality holds, in that IF two fields are only nonzero on domains that are separated by a spacelike (not causally connected) spacetime interval THEN their operators either commute or anti commute. I.e. one can be measured without affecting the other. There is no Heisenberg uncertainty relation that holds for joint measurement.

So the next and final task is to see how the KMS conditions can be relaxed to allow both Unruh radiation and QFT to coexist and then glean hints about what is required of quantum gravity.

Sorry to trouble you all as I work my way through this....
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


Next the authors turn to technical mathematical discussion of how much the KMS conditions need to be generalized in order for the Unruh effect be preserved for accelerated observers. It's a technical morass. I was hoping for some clear conceptual issue to arise that would indicate a conceptual requirement for quantum gravity like for instance: Lorentz invariance must be discarded unless one is a long length scales compared to the cutoff (Planck?) length or micro causality has to be abandoned at shorter than the Planck length.

NO!

Thermal behavior is assured for all observers in the Unruh effect thought experiment. All the Wightman axioms are satisfied to a very high degree of approximation. Am I disappointed?

NO!

The result tells me that quantum gravity is not likely to require major tweaking in quantum field theory to achieve. Furthermore it tells me that it is quite possible that the attempts to find hints of quantum gravity behavior like Lorentz invariance violations or anomalous time delays for ultra high energy gamma rays are likely to fail just as they have. What I learned from this exercise is this.

A completely granular structure of spacetime at ultra high energy or ultra short distances is immune to experimental detection.

that was worth the price of admission for me. I hope it didn't try your patience too much.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

#6

Post by chasmanian »


"What I learned from this exercise is this."

"A completely granular structure of spacetime at ultra high energy or ultra short distances is immune to experimental detection."

nFA, would you please elaborate on this?


I googled and found an article I hope you enjoy:


http://physicsbuzz.physicscentral.com/2 ... chers.html
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


chasmanian wrote: Tue Aug 13, 2019 2:28 am "What I learned from this exercise is this."

"A completely granular structure of spacetime at ultra high energy or ultra short distances is immune to experimental detection."

nFA, would you please elaborate on this?


I googled and found an article I hope you enjoy:


http://physicsbuzz.physicscentral.com/2 ... chers.html
I did enjoy the article. It references the work of this paper whose abstract is quoted below the link.

https://journals.aps.org/prl/abstract/1 ... 122.221302
We argue that discreteness at the Planck scale (naturally expected to arise from quantum gravity) might manifest in the form of minute violations of energy-momentum conservation of the matter degrees of freedom when described in terms of (idealized) smooth fields on a smooth spacetime. In the context of applications to cosmology, such “energy diffusion” from the low energy matter degrees of freedom to the discrete structures underlying spacetime would lead to the emergence of an effective dark energy term in Einstein’s equations. We estimate this effect using a (relational) hypothesis about the materialization of discreteness in quantum gravity which is motivated by the strict observational constraints supporting the validity of Lorentz invariance at low energies. Arguments based on a simple dimensional analysis lead to an estimate of an effective cosmological constant agreeing in order of magnitude with its observed value. If correct, this would constitute remarkable empirical evidence for a Planckian granular aspect of spacetime.
Needless to say I bristle at a model that sets out with non conservation of energy-momentum but that might be fixable. For instance some folks have in recent years suggested that Dark Energy is a decay product of Dark Matter. That might be a useful idea that preserves energy-momentum conservation.

Anyway, I have found the paper's preprint on arXiv and will give it a read.

Other approaches to a sandy space time include Alain Connes Noncommutative Geometry
https://en.wikipedia.org/wiki/Noncommutative_geometry

His book is available as a free download https://www.alainconnes.org/docs/book94bigpdf.pdf but the maths are formidable.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by chasmanian »


thank you nFA!!
awesome, amazing and fascinating. :)
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Re: necessary and sufficient conditions for a quantum gravity

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Post by chasmanian »


hey nFA,

I thought this might be an interesting video for folks interested in Quantum Mechanics.
the woman presenting the subject is a big Feynman fan.



https://lookingglassuniver.wixsite.com/ ... n-your-own
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


chasmanian wrote: Thu Aug 15, 2019 2:27 am hey nFA,

I thought this might be an interesting video for folks interested in Quantum Mechanics.
the woman presenting the subject is a big Feynman fan.



https://lookingglassuniver.wixsite.com/ ... n-your-own
Very good taste. I'm not familiar with the Strang and Townsend books but the Feynman, Susskind and Sakurai are excellent and in my collection. One that she missed is Dirac.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by chasmanian »


very good. thank you for your reply nFA. :)

the Feynman book she recommends is free to read online.
she recommends volume 3.

http://www.feynmanlectures.caltech.edu/

http://www.feynmanlectures.caltech.edu/III_toc.html
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


chasmanian wrote: Thu Aug 15, 2019 3:19 am very good. thank you for your reply nFA. :)

the Feynman book she recommends is free to read online.
she recommends volume 3.

http://www.feynmanlectures.caltech.edu/

http://www.feynmanlectures.caltech.edu/III_toc.html
That's the only one with QM. Vol 1 is CM and vol 2 is EM.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by chasmanian »


ah, very good. thank you nFA!!
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Re: necessary and sufficient conditions for a quantum gravity

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Post by GCoyote »


I'm glad Gordon added a bookmark function to the site!
Any metaphor will tear if stretched over too much reality.
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Re: necessary and sufficient conditions for a quantum gravity

#15

Post by notFritzArgelander »


GCoyote wrote: Thu Aug 15, 2019 1:07 pm I'm glad Gordon added a bookmark function to the site!
I looked for a how to use it and came up empty. I found how to bookmark a thread but the retrieval end eludes me.... :)
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

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Post by chasmanian »


nFA,

I just did this and it worked.
I bookmarked this thread.
then I clicked on the little dude icon 4th from right, above the search box, (between Gallery and pm icons).
now click on user control panel.
on the left you will see manage bookmarks.
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Re: necessary and sufficient conditions for a quantum gravity

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Post by notFritzArgelander »


chasmanian wrote: Fri Aug 16, 2019 2:38 am nFA,

I just did this and it worked.
I bookmarked this thread.
then I clicked on the little dude icon 4th from right, above the search box, (between Gallery and pm icons).
now click on user control panel.
on the left you will see manage bookmarks.
Thanks, I see it now.....
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: necessary and sufficient conditions for a quantum gravity

#18

Post by chasmanian »


you're very welcome.
I wonder if the Moderators would consider
putting a bookmarked threads icon link
somewhere thats a little more convenient?
maybe right in the Toolbar menu?
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Re: necessary and sufficient conditions for a quantum gravity

#19

Post by GCoyote »


chasmanian wrote: Fri Aug 16, 2019 3:28 am you're very welcome.
I wonder if the Moderators would consider
putting a bookmarked threads icon link
somewhere thats a little more convenient?
maybe right in the Toolbar menu?
I'd say put this suggestion in the Feedback section of the forum.
Any metaphor will tear if stretched over too much reality.
Gary C

Celestron Astro Master 130mm f5 Newtonian GEM
Meade 114-EQ-DH f7.9 Newtonian w/ manual GEM
Bushnell 90mm f13.9 Catadioptric
Gskyer 80mm f5 Alt/Az refractor
Jason 10x50 Binoculars
Celestron 7x50 Binoculars
Svbony 2.1x42 Binoculars
(And a bunch of stuff I'm still trying to fix or find parts for.)
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Re: necessary and sufficient conditions for a quantum gravity

#20

Post by chasmanian »


I pm'ed a friend to suggest putting a Bookmarks link in an easier place to get to.
(not the Tools menu, though. that menu only appears when you are in a thread.)
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