The Alcubierre warp drive metric has been criticized on the points of requiring a large amount of exotic matter with negative energy, and conditions deadly for human travellers inside the bubble. What if the Alcubierre metric is used to just span a tiny bubble around a single spin-1/2 particle to transport either classical or quantum information faster than light? Wouldn't known small-scale effects, such as the Casimir force, suffice to provide the exotic conditions required for an Alcubierre bubble large enough to fit at least one particle? My question explicitly addresses the feasibility of a microscopic bubble using known microscopic effects.
[Physics] Faster-than-light communication using Alcubierre warp drive metric around a single qubit
casimir-effectfaster-than-lightgeneral-relativityquantum-information
Related Solutions
Warp drives are not allowed by the basic laws of physics, in particular the theory of relativity prohibits any superluminal motion or superluminal propagation of usable information. So whatever "exotic matter" or other wordings are proposed to justify the superluminal warp drives is banned, too. The typical "exotic matter" needed for warp drives would need to admit a negative energy-mass density. If Nature allowed the energy density to go negative, the vacuum itself would be unstable.
The laws of physics also ban the transfer of an object from a universe to a different universe through a black hole, whether it is primordial or not. Wormholes allowed by the laws of physics, if there are any, have to be non-traversable. It means that by jumping into such a black hole, he is guaranteed to end up in the singularity. At most, the singularity where he ends may be shared between a pair (or perhaps a higher number) of black holes. Such a pair of black holes is known as the non-traversable wormhole or the Einstein-Rosen bridge (at least the simplest one). But whoever falls into a black hole can never escape to the "liberated space" outside it, in any Universe, by the very definition of a black hole. Incidentally, the technical reason why a traversable wormhole can't be built is the very same why the warp drives are impossible: negative energy density would be needed for them, too.
Sagittarius A* is in no way the nearest black hole to the Earth. For example, V404 Cygni has a black hole in it that
is 7,800 light years away, and there are probably many closer ones, too.
It wasn't my plan to correct statements in the question but I have to. While an idealized empty large black hole is indeed mildly curved and one may survive the fall behind the horizon, that's not true for realistic black holes, especially Sagittarius A*. The latter is surrounded by plasma, matter that the black hole devours. A good description of the plasma around Sgr A* is the two-temperature plasma. The temperature of the electron component of the plasma is about 100 billion kelvins. No material that could be used to build a spaceship could survive these conditions. We would need a much more isolated black hole to avoid this thermal hell but it isn't clear whether such astrophysical black holes exist.
This new question links a recent paper
- J. Santiago, S. Schuster and M. Visser, 2021, “Generic warp drives violate the null energy condition”, arXiv:2105.03079.
which counts as “technical analysis” of Erik Lentz's solution as well as Bobrick & Martire's (already linked in OP) and Fell & Heisenberg's solutions (that I mentioned in a comment). According to the authors:
The key observation is that WEC requires all timelike observers to see positive energy density, whereas the analyses of references [1–3] only investigate the energy density as seen by one class of timelike observers (the co-moving Eulerian observers). Thus the claims made in references [1–3] are at best incomplete, and in many key specific details, wrong.
So, this “new idea” seems to be a non-starter.
Best Answer
The reason why the Alcubierre drive is not feasible as an FTL drive has nothing to do with absence of exotic matter; in fact, we likely had plenty of the required matter during cosmic inflation era, or something with identical geometrical effects. Physicists that dismiss it as impossible because "there is no exotic matter" play ignorance to the fact that inflation era happened, and it cannot be accounted by some magic variation of the cosmological constant, because the cosmological constant is a constant, otherwise you are referring to some scalar field, which is not GR, so dismissing exotic matter (or something equivalent) amounts to dismissing inflation and General Relativity
Now, obviously we don't have any idea about how to create "inflation" fields, but even if we were able to have some way to create some "inflation" field, it would still not help us to create a FTL drive. The reason is that the Alcubierre metric assumes that the field is already distributed over the spacetime at previous times before the tube is formed. Since all this field is arranged over space-like distances, the only way to distribute those fields so that you are able to "surf" over them is by travelling faster-than-light to set them up. So, you need a FTL drive in order to be able to build an Alcubierre drive.
If you want, you can lay out that field over the space beforehand so ships can then use it to travel, but since you are already changing the geometry, you are not travelling FTL anymore, since the metric has been distorted significantly. Also, there are be better ways to construct FTL drives if exotic matter was to be accessible, like wormholes
So in short; no amount of exotic matter will make the Alcubierre metric work as it was intended