Æther as an Inevitable Consequence of Quantum Gravity

Round 1

Reviewer 1 Report (New Reviewer)

The authors propose aether as an inevitable consequence of quantum gravity. This is an interesting topic for theoretical physics. However, the discussions based on the vacuum state, vacuum energy, size of eicheon and decoherence are not enough to connect  with the aether  and quantum gravity. In addition, the existence of aether breaks the local Lorentz invariants. How do it  compatiability with special and general relativities? The authors should discuss this issue in the revised version.

Author Response

We are grateful to reviewer for the interest to our paper and
the comments.  Reply to the reviewer comments is in pdf file. 

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

The authors study the quantum vacuum.  Initially, they show that there is no vacuum state in the vicinity of the small-scale factor because of an absence of field oscillators.  They go on to make contact with previous results associated with the Wheeler-DeWitt equation within the Gowdy model.  They go on to look at a string-like quantization.  Eventually, they go on to define the vacuum state on a classical background of space-time. The authors spend a good portion of the manuscript examining a class of conformally-unimodular metrics and some astrophysics applications associated with the metrics.

I think this is an interesting manuscript that is well thought out with interesting physics.  I would recommend this manuscript for publication.

A few things I noticed:

Page 3: "qausi-Heisenberg" should be "quasi-Heisenberg"

Page 5:  "We will not discuss this subject carefully considered in string theory textbooks." might be better said, "We will not discuss this subject any further since it is widely considered in many string theory textbooks."  and a few citations may be needed.

I am not sure...but the Appendix is labeled G.

Author Response

We are grateful to the reviewer for his positive estimation of our
work and intention to improve the quality of our paper. We introduced the suggested corrections into the text and added some references.

Reviewer 3 Report (New Reviewer)

The manuscript treats the question of aether and claims its existence is inevitable in quantum gravity theories due to their lack of Lorentz invariant vacuum state.

 

Although the set up is well built, and -apparently- mathematically sound, however the authors rely on a set of papers they authored, some of which are very little cited by others, which indicate they are espousing ideas which may not fall inside mainstream physics. 

 

1) although one can argue classically that by Unruh effect, the 'emptiness state (vacuum)' of an inertial observer would look, for an accelerated observer (say, due to gravity), like a state in thermodynamic equilibrium with a bath whose temperature is not zero, thus showing that -classically- emptiness is not frame-independent leading to vacuum in QFT as being full of virtual particles, no mention of this effect in the whole paper. 

 

2) The work relies heavily on the authors previous work on Fast Vector Theory of Gravity [reference 15], which is published in a journal of zero impact score and h-index!     

 

3) Putting this aside, am not convinced by 

restricting the metrics to a limited class (eq. 19): Isn't the general Equivalence Principle sacrified away thus? For me, FVT gravity has nothing to do with actual world, even if it were mathematically correct, exactly as the resulting Milne cosmology is irrelevant to actual universe. 

 

4) Lines 131-132 state that eq 19, on which the work is heavily relying, ensures an absence of dipole anisotropy. Thus, how can they account for the 10^-5 anisotropy observed in the CMBR? 

 

5) Also, the prediction of the FVT of the absence of BH (lines 146, 147) then leads to the question of how to interpret the gravitational waves observed recently and attributed to BH collisions?

Author Response

We appreciate the third Reviewer for the useful remarks. We tried
to improve our manuscript by following these remarks. Reply to the reviewer's comments is in pdf file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (New Reviewer)

The authors answer the referee's questions and add a few paragraphs to  discuss the connection between vacuum state, the preferred reference frame and the violation of Lorentz symmetry. The present form may be consided for publication.

Author Response

We thank the reviewer again for the careful reading of our paper
and  the remarks.

Reviewer 3 Report (New Reviewer)

The revised version represents an improvement compared to the past one. Although, I am still not  convinced at all by the authors' arguments about the physicality of their model, I do understand that some in the community may get interested in reading such out of mainstream ideas. Thus, I accept it.  

Author Response

Dear Reviewer, Thank you very much for your comment. We understand
that some indisputable achievement, like explanation of CMB
acoustic peaks, is needed for this model to accept it as
describing  reality. We are going to work in this direction.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The paper tried to argue that Quantum Gravity (QG) does not admit a diffeomorphism-invariant vacuum state, thus ether exists in QG. The paper listed several different things trying to argue about this, but I do not think they support the statement the paper is trying to make. My comments are as follows

1. From the paper's title and abstract, it seems that the author is trying to talk about the vacuum in “Quantum Gravity”, however, the paper mostly talks about “classical gravity”.
2. The author did not show that the vacuum state of QG is not diffeomorphism-invariant, thus it is hard to understand what the author is actually arguing about.
3. The paper listed several things, like decoherence, but they are not really related or relevant, and none of them support the statement the paper is trying to make. It may be more compelling if the author can analyze an example in more detail to argue why we need ether.
4. Most of the things that the paper talked about are just rewriting things in a different coordinate system. The paper talked about some alternate theories to General Relativity (they cited the authors' previous papers), but it seems that it's just writing things in a different coordinate system.
5. In the last paragraph of the paper, the authors said that black holes are absent in their theory. This is rather confusing. We do have pretty good evidence that black holes exist in reality.

I do not think the paper meets the standard for publication in Particles

Reviewer 2 Report

I have read the revised draft of the manuscript and the authors’ reply letter carefully. However, neither the revised text, nor the authors’ reply, address the central questions raised in my first report. These are:

Is $P^{m}(x)$ a physical (observable) vector field?
Is the class of “conformally unimodular metrics” compatible with GR or not?
In either case, what are the resulting “Einstein” field equations?

Therefore, I cannot recommend this paper for publication in Particles.

In addition, if the authors intend to submit the manuscript to another journal, I strongly advise them to drop the use of their chosen acronym for “conformally unimodular metrics”.

Comments for author File: Comments.pdf