Response to new paper: "Generic warp drives violate the null energy condition"

 Hello all,

I was pointed to a paper that appeared on the arXiv yesterday (https://arxiv.org/abs/2105.03079v1). I am glad to see people taking a close look into my paper (https://doi.org/10.1088/1361-6382/abe692, and the latest arXiv version https://arxiv.org/abs/2006.07125v2) and the other recent papers on the topic of warp drives (https://doi.org/10.1088/1361-6382/abdf6e, https://arxiv.org/abs/2104.06488). I have also been contacted in the last months by several other researchers working to reproduce and expand upon my results. I wanted to make a running post on this paper and a series of posts on other appraisals of my work in this field and the resulting discussions.

After reading through their entire paper, I noticed that this new manuscript seems to have overlooked my complete discussion of the weak energy condition (WEC) contained in my published paper, instead referring to an early arXiv manuscript that tracked quantities of energy, momentum, etc. in only an Eulerian frame. This single frame of reference does not cover the breadth of the WEC, which requires an examination of the energy from the reference frames of all time-like observers. This is the new paper's stated central issue with my work, that it does not fully address the WEC. Fortunately, this limitation was addressed in the peer-review process and the final version of the paper published by Classical and Quantum Gravity contains a presentation of the WEC in full. 

I contacted the authors of the new paper to point this out and they supplied a reply this evening as I was writing this post. I will make an update when I have had a chance to think through their new comments. At this point, I will say that the disagreement has yet to be resolved. 

Enjoy your Tuesday evening,

Erik

Update (6/25/21):

The conversation with the authors of `Generic Warp Drives' continued for a few days after the initial post. The reply to my initial message reiterated and elaborated on their positions in their manuscript. These new details that much of the confusion was regarding the origin of some components used in the WEC calculations. The authors assumed that the stress tensor principle values had been introduced ad hoc using an assumed form of the stress-energy from the plasma instead of directly from the soliton geometry and therefore did not demonstrate non-negative energy. In my response, I pointed out that every term used in the calculation was derived directly from the soliton's space-time metric, and therefore was a valid test of the WEC. There were other comments addressed in the correspondence, but this was the central point.

Also, the same group put out another paper this month (https://arxiv.org/abs/2106.05002), as indicated in the comments. The new manuscript introduces engineered metrics in the form of beams of space-time curvature that can induce stresses such as pressure or tension forces or more general shearing stresses onto objects that pass into the beam path. This is an interesting paper exploring another science-fiction technology (tractor beams) within the scope of general relativity. I am still absorbing the paper's contents and may have more to say soon.

Update (7/25/21):

I recently gave a talk the (virtual) 16th Marcel Grossmann meeting (http://www.icra.it/mg/mg16/) where there was a mini-session warp drives. I mention this here as Matt Visser, one of the authors to the two papers above, was also invited to give a talk in that session. Dr. Visser mostly focused on the more recent tractor/pressor/stressor beam (https://arxiv.org/abs/2106.05002), but also took the opportunity to review the shortcomings of the recent warp drive papers (Fell/Heisenberg, Bobrick/Martire, and my own). My own talk directly followed Dr. Visser's, allowing me to directly address his comments and demonstrate ow my soliton persists as an example of a positive energy warp drive. Discussion continued in the Q&A, where I think we were able to make progress.

You can watch the whole session on YouTube, which was recently released by the International Center for Relativistic Astrophysics Network (https://youtu.be/NqN1c-2fv8Y).

Update (11/2/21):

The 16th Marcel Grossmann meeting is putting out a proceedings, where speakers submit an article on the topic of their talk and the set is published as a collection (in this case by World Scientific). Matt Visser and his co-authors posted their contribution to the proceedings on the arXiv (https://arxiv.org/abs/2110.14926). Unfortunately, not much from our conversation at the meeting made its way into the article, which essentially follows the contents of their tractor/pressure/stressor beam paper.