Previous work seemed to conclude pretty strongly that superluminal warp travel required negative energy. What's the insight here that gets around that?
The goal of warp drive is to produce a modified region of spacetime that makes it feasible to travel faster than light. There are an infinitude of different approaches. The authors in this paper find that if you impose specific constraints on the way the modified region of spacetime is shaped and evolves over time, you don't need the negative energy anymore.
However, you do need a very high energy density, strong enough to create a black hole. And there is, of course, no guarantee that such an energy source is feasible or even possible. But you no longer need exotic matter — you just need enough regular matter in one spot.
The sociology of this is fascinating. For my whole life I've heard that travelling faster than light is not only impossible, but so obviously absurdly impossible that only loons and sci-fi writers bother to think about it at all. Now I'm reading that "There are an infinitude of different approaches" to the problem!
What exactly is the breakthrough that has led to this recent spurt of warp drive papers? As far as I can tell the results are all purely theoretical and just re-arranging equations. None of them appear to rely on any recently lab discovered physics. Why couldn't this have been done in 1950, I wonder?
> What exactly is the breakthrough that has led to this recent spurt of warp drive papers? As far as I can tell the results are all purely theoretical and just re-arranging equations. None of them appear to rely on any recently lab discovered physics. Why couldn't this have been done in 1950, I wonder?
By "recent", you have to go back almost 30 years to the Aclubierre Drive (https://en.wikipedia.org/wiki/Alcubierre_drive) described in 1994. It forms part of the "we can come up with some interesting solutions to general relativity" literature.
It's not like these are entirely new questions, but they used to be relegated to much smaller circles.
Hell, even recall any theoretical physics notions in other threads on HN and watch it burn.
It definitely seems like a bit of a philosophical change is sweeping throughout society, and it's probably mainly do to the increased speed and spread of information. It's easy to ignore, but those who don't are sort of forced to revaluate their world view and even their understanding of reality.
We have mainstream philosophers and neuroscientists giving talks on the limits of our perceptions in language "lay" people can understand. It's an interesting time to follow these developments.
It's almost like a new-age open-mindedness without the woo-woo. It was probably never really true, but growing up it felt like the answers were all written, and the universe was sticks and stones and the suggestion of anything else was nonsense. It seems more open now, and more intellectually encouraging, isn't it?
Bear in mind that the "infinitude of different approaches" means an infinitude of purely mathematical solutions, all of which seem to involve physically impossible concepts like negative energy.
As far as I can tell, there is no such insight here - in the middle of page 13 they admit that in their solution, the weak energy condition is violated, and even that:
"No amount of modification to the configuration could get rid of these WEC-violating regions."
If I'm reading this correctly, all they have done is found a solution that has positive Eulerian energy density according to one particular reference frame, but not according to other reference frames. (I'm not a physicist, so please correct me if I'm wrong.)
