Review and Response to Bobrick and Martire 2021

Hello all,

I have received quite a few requests by email, interview, reddit, social media, and even this blog for a response to the paper "Introducing Physical Warp Drives" (IPWD) by Alexey Bobrick and Gianni Martire (https://doi.org/10.1088/1361-6382/abdf6e). There has also some confusion about the difference between the papers. This paper came out very near to my own 'warp drive' paper (Hyper-Fast) and in the same journal, Classical and Quantum Gravity.  This post addresses questions I have received about IPWD and its reference to an unfinished version of my own paper. Suffice it to say, I am somewhat disappointed in their assessment. For ease of access, I will be working from the most recent  arXiv version of IPWD (https://arxiv.org/abs/2102.06824v2).

For disclosure, I have been in contact with the authors since July 2020 when I gave a virtual seminar on my own paper to CENTRA (Center for Astrophysics and Gravitation) in Lisbon, Portugal (https://tecnico.ulisboa.pt/en/events/centra-seminar-erik-w-lentz/). We exchanged several messages and discussed our respective papers over Zoom during the following months.

Questions on IPWD have fallen into three topics:

What are the differences between IPWD and Hyper-Fast?

The IPWD paper contains a review of the warp drive literature, defines a "general warp drive spacetime", studies a set of spherical (Schwarzschild) models of subluminal warp drives with positive energies as well as a set of axis-symmetric (Alcubierre) negative energy warp drives with some optimizations between shape and energy, and provides some comments concerning the acceleration of warp drives. 

My paper concentrates on deriving sufficient conditions for constructing a class of hyper-fast solitons (warp drives) that are capable of moving at an arbitrary speed (subluminal or superluminal) and are sourced by only positive energy densities. The process of constructing these new spacetimes is discussed rigorously in explicit mathematical detail. One example of a hyper-fast soliton is provided, and the properties of the sourcing energy and stresses are discussed in the context of a plasma. 

What is your take on the IPWD results?

Overall I appreciated their review treatment of the published literature to date, though I would have liked to have seen more technical detail throughout the rest of the paper. I found myself particularly interested in the discussion of acceleration among warp drives and stress-energy-momentum conservation, but was ultimately let down by the depth of discussion, which could effectively be summarized as 'put a rocket on it'.

The motivation for positive energy warp drives being limited to subluminal speeds seemed ad hoc, and the result seems to simply fall in line with previous work. I would expect a more thorough treatment of positive-energy soliton spacetimes to motivate their claim of a limit at light speed beyond the consideration of spherically symmetric (Schwarzschild) spacetimes.

Additional questions I have:
  • What are the conditions on the spacetime geometry, particularly the metric's shift vector, due to stress-energy-momentum conservation?
  • How does the IPWD's so-called general warp drive model include my solution? The discussion in Section 2 is unclear on this point.

Do you have a response to IPWD's reference of Hyper-Fast?

IPWD references my paper several times. References included statements that my findings of a positive energy soliton in general relativity capable of traveling superluminaly are done "without providing means to reproduce the study" and that the conclusions of IPWD "do not support the recent claim" of my paper. I am disappointed by this, considering the great detail I put into the manuscript laying out the conditions for creating such solutions.

Much of the meat of Hyper-Fast is in the description of the underlying mathematics of the solution geometry, and is very audit-able. Further, I gathered feedback from colleagues and experts in general relativity before publication and added further detail to the manuscript through the peer-review process, refining the results. Mostly, I am disappointed that their paper made a rush to judgement by criticizing a draft version of my paper and not the full peer-reviewed published article. The authors did not contact me to check what updates may have been made to my manuscript during the months between our first contact and the posting date of IPWD by the journal or on the arXiv.

Additional questions I have:
  • What further details would be helpful to understand and reasonably reproduce my positive energy soliton?
  • Is this satisfied by the published version of the paper?
It is an exciting time for space travel! Moving forward, it is my hope that we can thoroughly examine all possibilities and help make warp drive a reality.

Have a happy Wednesday,

Erik

Comments

  1. LorenzoApril 8, 2021 at 10:51 AM

    Will you publish any new paper about warp drive this year ?

    ReplyDelete

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