Interstellar Journey

I recently enjoyed a chat with Dr Jose Natario, author of several influential warp drive papers. Arguably one of Dr Natario’s most notable contributions to the field is his demonstration that a mutual contraction/expansion of spacetime is not a required feature of a warp drive, as was commonly believed. You can read the highlights of our conversation below.

[Obousy] Could you briefly describe your research interests and also your contributions to the field of warp drives?

[Natario] My research field is General Relativity. Besides warp drives, I have done work on the geometry of the space of light rays, various types of 4 and higher dimensional black holes, spinning objects and the quasi-Maxwell formulation of the Einstein equations.

I have written 2 papers on warp drives. In the first one I set up a fairly general model for a warp drive spacetime, which includes the Alcubierre model as a particular case. I showed that it is possible to have models where there is no overall contraction or expansion of space (although space does get severely distorted on the warp bubble wall). My hope was that one would then get less severe violations of the energy conditions, but that turned out not to be the case: one can easily prove that these
models always violate the positivity of energy. I also showed that there are two other (in my view more serious) problems with the warp drive concept, namely the existence of horizons and infinite blueshift regions.

The second paper studied warp drive spacetimes which have a classical Newtonian analogue. It showed that in these Newtonian versions the gravitational field inside the warp bubble is uniform whenever the bubble is accelerating, thus avoiding tidal forces; all nonuniform gravitational fields are confined to the bubble wall.

[Obousy] What got you interested in warp drives in the first place?

[Natario] The first time I heard about the warp drive was reading the daily newspaper back in Portugal, when I was still an undergrad. I thought it was a nice idea, but didn’t really think too much about it. A few years later, when I was in Oxford doing my DPhil, a fellow student showed me the Alcubierre paper, and I made a copy to read at home. The idea was clear: one makes space move around in unusual ways, dragging the spaceship with it. What I didn’t understand was why was it necessary for space to expand and contract: couldn’t one make it move without expansion? That was the beginning of my first warp drive paper.

[Obousy] It appears on arXiv that far more papers are released on wormhole research than warp drive. Why do you think that this is?

[Natario] For one thing the wormhole idea is much older (going back to the Einstein-Rosen bridge), and has been pursued by well known physicists. It is also mathematically more interesting, and probably more realistic (as science fiction ideas go). Finally, it could be relevant to quantum gravity.

[Obousy] What do you see as the biggest questions/challenges in current warp drive research?

[Natario] The question of the horizons. The problem is the following: in all currently known warp drive models part of the warp bubble wall (i.e. the place where the negative energy fields are located) is causally disconnected from the interior. This means that it is impossible for someone inside the warp bubble to send a signal to (hence to control) these regions of the wall. Intuitively, you cannot set up a bubble which is moving faster than light from inside the bubble, because your signals, which travel at most at the speed of light, cannot reach the front part of the bubble wall. (Some people call this the “you need one to make one problem”). A related problem is that whenever the bubble starts travelling faster than light an infinite blueshift region (the analogue of a sonic boom) forms behind it.

[Obousy] Warp drive… theoretical curiosity or deep future technology?

[Natario] Because of the two problems I mentioned, I think it will remain a theoretical curiosity.

[Obousy] What are you currently working on?

[Natario] Higher dimensional black holes