Walk-in warp bubble: can it be done?

Question

My setting has alcubierre-drive-style technologies using negative energy to create buildings that can be larger on the inside than the outside container area.

I’ve heard of Van de Broeck warp drive concepts being associated with that function.

My question is, would it be possible to distribute the effects of the generated/harnessed energy causing this warp effect in the first place, so that instead of an abrupt shift from regular outside space to the expanded “bubble” interior, there’s some kind of smooth transition gradient in the spacetime warping allowing the bubble to be walked right into with essentially no noticeable difference or sensation?

This would allow it to be used as a continuous sort of architecture rather than an activated and deactivated transport “drive”.

EDIT: What would a plausible sounding, pseudo-realistic, technobabble explanation for this use case be like?

Answer 1

I study warp drive metrics and their associated energy densities to great extents at my research programs, and I will tell you that if you're talking about an Alcubierre/Van de Broeck/Natario-style warp drive, definitely super certainly surely not.

These metrics rely on the mass-energy density being roughly spherical around the ship in most cases, although they can be made to have toroidal geometries of mass-energy density instead. That doesn't mean that there can be regions where the energy density is small. The "shell" itself will be made of unobtainium fluid, which has energy densities on the order of trillions or quadrillions of quintillions of solar masses per cubic meter; if you safely modify the metric in such a way that a "hole" appears that would allow you to walk into the warp drive's area, it would need to be done in a smooth way, and without making the edge ultra-sharp (and thus making spacetime ultra-bent in that area), even the "hole" will be filled with solar masses' worth of energy.

Theoretically, there could be a configuration of negative mass-energy that would allow for a gap in the shell with energy density below $1000c^2\approx8.98\cdot10^{16}\,\mathrm{J}\,\mathrm{m}^{-3}\equiv1000\,\mathrm{kg}\,\mathrm{m}^{-3}$ (which, in the case of a non-flowing fluid/liquid, would make traversing the gap roughly like swimming through water), but that would be extremely difficult. Essentially, the issue is that the mass-energy densities of the warp drives are so astronomically high that even some distance away from the edge of the bubble, where the energy density is dozens of orders of magnitude lower than inside the shell, the mass density is still extremely high by human standards, and the fluid making up the bubble would be a virtually-impenetrable solid - in some cases even the density of the "gap" would be comparable to the density of an atomic nucleus, or equivalently a neutron star.

So unless you can walk through neutron stars like they were air, or if you can give me a lower-energy warp drive metric, this isn't going to work. If you can do the latter, please stop asking questions on WB:SE and prepare a paper to publish immediately.

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But it's no fun not being able to use warp drives and bigger-on-the-inside rooms and spacetime engineering of that sort!

Yeah, it's not. My solution is just to say that the civilization that has access to that tech (maybe humanity, maybe not) at some point figured out a very specific pattern that allowed them to do that kind of stuff at much lower energies. This is specifically what I study - low-energy warp drive solutions - and based on my work I theorize that it is at least sort of maybe possible in the future. With that in mind, as a writer, I just handwave "they figured out how to do it with a 1 GW fusion reactor instead of a Universe-evaporating vacuum-decay engine", and my readers tend to go with it. After all, unless you're writing for a science crowd (which in your case I don't think you are), exact scientific realism can sometimes be given a nudge in the name of something that drives the story and helps flesh out the world.

Answer 2

Not with the exact technologies you've described

Our modern understanding of Alcubierre drives is that they need to create a microscopically thin bubble of warped spacetime around a normal volume of space time. The whole point it that whatever is inside the bubble is not experiencing the intense space-time distortions as the bubble. This reduces the power requirements by many many orders of magnitude, but it is also a necessary consideration for the survivability of what is inside the bubble since passing matter through a contiguous field powerful enough to cause noticeable relativistic distortions would break down any known form of matter from gravitational sheer.

This means that an Alcubierre warp bubble will be the same size on the inside as the outside with only the wall of the bubble representing warped spacetime; so, this technology will not give you a bigger room, just the same size room that transitions through space a bit differently.

So use a different system to describe your technology

That said, there are other kinds of FTL drives in Sci-fi than the Alcubierre drive. Another common one is the idea of a subspace drive. The idea here is that we live in a multiverse, and not every reality shares the same speed of light. To go faster than the speed of light, you transition to another reality where things become faster. So to make a bigger room, you just need to find any alternate reality where the area of space you want your bigger room is not occupied by anything that would get in its way. So, you would create your dimensional doorway inside an airlock and go through it to find a reality where the speed of light may not be noticably different, but maybe you are now in a reality where very minor changes in the fundamental laws of science caused our Earth and Sun to now be somewhere many light years away; so, you've created a sort of bridge into the middle of interstellar space with plenty of room to build whatever you want.

In this since, your bigger room is actually a space station that is technically not very far away from your building, you are just traveling in an N-th dimensional direction to get there.

This has a few advantages over the Alcubierre drive explanation. One is that you do not need to exert the tremendous forces it takes to noticably warp space time. Instead you are just going somewhere else that has more room to build in. Secondly, because we have no scientifically or mathematically verifiable models for subspace travel, there is no way of saying how much, power, sheer, or N-th dimensional distance is required to get to a suitable alternate reality. This lack of verifiability gives you a lot more latitude as an author to describe the transition and mass/energy requirements however you want.

Answer 3

Superluminal travel == Time travel == Negative Mass == Paradoxon == Non-existence

With other words, current physics quite strongly says that it is impossible and that is it.

Alcubierre drive has two problems:

1. It can not happen without negative mass.
2. If you pack the Alcubierre drive into a box, you get a superluminal drive. With the same logical paradoxons.

Any superluminal travel, including information transfer, makes possible to send a message to your previous yourself into your past. It is not even too complex, just google for tachyonic antitelephone (essentially, a superluminal message send backward from a nearly light speed spaceship will arrive in the past of the original point).

Or negative mass matter has the problem that it had negative energy. First, if you push it by force, it will accelerate into the opposite direction. Or imagine a negative mass planet and a positive mass planet. The negative mass planet distracts the positive mass planet, the positive mass planet attracts the negative mass planet. They will start to fly with infinite speed into the infinity.

Of course it can not be said that it won't be possible ever, but no one can say anything about things not existing yet.