Introducing Physical Warp Drives
Alexey Bobrick · Gianni Martire
Abstract and summary · read the original at the source
In one page
Alexey Bobrick and Gianni Martire, at the Advanced Propulsion Laboratory of Applied Physics in New York, take the warp drive out of the exotic-solutions box and give it a general definition: a shell of material, ordinary or exotic, wrapped around a flat passenger region and moving inertially through flat space. Every warp metric in the literature, Alcubierre’s 1994 solution included, sits inside that definition. Two results follow. Subluminal warp drives can be built from purely positive energy — they give the first explicit spherically symmetric example, whose signature effect is that time inside the shell runs slower than outside. And because a warp drive is a shell like any other object, it cannot accelerate itself: it needs propulsion, and Alcubierre’s time-varying velocity quietly broke energy conservation. They also cut the negative energy an Alcubierre drive demands by about two orders of magnitude, by flattening the bubble and choosing a better shape function. Warp geometry, stated as ordinary general relativity.
Why it matters hereChapter 4 treats the metric as something you build rather than something you accept, and this is the paper that turns the warp bubble into an engineering object: a mass shell, described by known physics, with a price tag you can compute. It also names the bill honestly — the shell still needs a power source and a way to push, which is where chapters 6 and 13 pick the thread up.
What it claims
01A warp drive spacetime is defined generally as an asymptotically flat vacuum background enclosing a compact curved shell, which in turn encloses a flat extended passenger region; every existing warp drive metric, the Alcubierre solution included, falls inside this single definition.Section 2.1, definition of a general warp drive spacetime; Figure 1
Published and peer-reviewed02Stationary warp drive spacetimes split into exactly four classes, according to whether the remote comoving observer moves subluminally or superluminally, and whether the internal observer has the same character as that comoving observer (mild) or a different one (extreme).Section 2.1, Classes I to IV
Published and peer-reviewed03The first manifestly positive-energy warp drive spacetime is constructed: a spherically symmetric subluminal shell. For such a shell built of non-exotic matter the only achievable modification of the interior is that time inside passes more slowly than for a remote comoving observer — an Earth-mass shell of 10 metre radius slows the rate of time by about four parts in ten thousand.Section 3.1, Equations 5 to 9
Published and peer-reviewed04Any warp drive is a shell of regular or exotic material moving inertially, so it has no way of changing its own velocity: every warp drive requires propulsion, and the time-variable velocity assumed in the original Alcubierre construction does not satisfy the continuity equations.Sections 5.1 and 5.2, what is a warp drive and constructing warp drives
Published and peer-reviewed05Flattening the Alcubierre bubble along its direction of motion by a factor reduces its total energy by the same factor, and a variational choice of shape function — the slower-decreasing profile that minimises the energy integral — cuts the requirement by a further factor of about three.Section 4.2 and Section 5.3; derivation in Appendix A.3
Published and peer-reviewed06Extreme flattening yields superluminal solutions that satisfy the semiclassical quantum inequalities without extreme energy densities; the authors note these solutions still violate the averaged null energy condition, so they may be probing the limits of the inequalities themselves — a question they hand to analogue-gravity experiments and numerical relativity.Section 4.2, third implication of Equation 12; Section 5.4
What to watch
Read it · abstract
Abstract
The Alcubierre warp drive is an exotic solution in general relativity. It allows for superluminal travel at the cost of enormous amounts of matter with negative mass density. For this reason, the Alcubierre warp drive has been widely considered unphysical. In this study, we develop a model of a general warp drive spacetime in classical relativity that encloses all existing warp drive definitions and allows for new metrics without the most serious issues present in the Alcubierre solution. We present the first general model for subluminal positive-energy, spherically symmetric warp drives; construct superluminal warp-drive solutions which satisfy quantum inequalities; provide optimizations for the Alcubierre metric that decrease the negative energy requirements by two orders of magnitude; and introduce a warp drive spacetime in which space capacity and the rate of time can be chosen in a controlled manner. Conceptually, we demonstrate that any warp drive, including the Alcubierre drive, is a shell of regular or exotic material moving inertially with a certain velocity. Therefore, any warp drive requires propulsion. We show that a class of subluminal, spherically symmetric warp drive spacetimes, at least in principle, can be constructed based on the physical principles known to humanity today.
The way in
https://arxiv.org/abs/2102.06824Posted to arXiv under the arXiv.org perpetual non-exclusive licence, so this page carries the summary, the claims and the authors’ own abstract, and sends the reader to the source. Published as Classical and Quantum Gravity 38, 105009 (2021).
How to cite it
Alexey Bobrick, Gianni Martire (2021) Introducing Physical Warp Drives. doi:10.1088/1361-6382/abdf6e
Where it sits in the curriculum
The metric, warp drives and wormholesThe unified pictureWhat the vacuum is