Historical research guide · 0459 · 2024
Constant velocity physical warp drive solution
Jared Fuchs · Christopher Helmerich · Alexey Bobrick · Luke Sellers · Brandon Melcher · Gianni Martire
In one minute
A warp drive has always come with a bill attached: negative energy, exotic matter, energy conditions broken. Jared Fuchs and his colleagues at Applied Physics and the University of Alabama in Huntsville pay that bill a different way. Instead of drawing a bubble in empty space, they begin with something ordinary — a stable shell of real matter, the kind of object general relativity has described since Schwarzschild — and then add a shift vector inside it, the term that carries passengers along a geodesic without their feeling any acceleration. Working numerically with their Warp Factory toolkit, they show that the combination satisfies all four energy conditions, null, weak, strong and dominant, with no violation above the numerical noise floor. And the warp is real rather than a change of coordinates: light sent through the shell one way and back comes home about 7.6 nanoseconds out of step with light sent the other way, a linear frame dragging of the same family a spinning mass produces. The drive is subluminal and at constant velocity; acceleration is the next problem.
Connection
Chapter 4 has waited thirty years for a warp spacetime that does not require exotic matter, and this is it: the first constant-velocity solution that keeps Alcubierre’s geodesic transport and satisfies every energy condition. It belongs to chapter 1 as much as to chapter 4, because the whole result is numerical and the toolkit that produced it is public, so the claim is one another group can rerun rather than only read.
From the source
The Natario class of warp solutions — those built from a shift vector on a unit lapse and a flat spatial metric — has been shown always to violate the energy conditions, and one reason is that such metrics lack the gravitational effect of ordinary matter: the Alcubierre metric and its relatives have zero ADM mass, where a Schwarzschild solution of equivalent energy density would have a positive one.Sect. 1.3, The Problem of Physicality
The likely ingredients of a physical warp drive can be stated simply: the asymptotically flat spacetime should have a positive ADM mass; the energy density in the non-vacuum bubble should be much larger than both pressure and momentum flux as measured by Eulerian observers; and the motion should be subluminal.Sect. 1.3, the three numbered ingredients
A stable shell of ordinary matter — inner radius 10 m, outer radius 20 m, mass 4.49 times 10²⁷ kg, about 2.365 Jupiter masses — built by solving the Tolman-Oppenheimer-Volkoff equation and smoothing the density and pressure profiles, carries non-isotropic pressures that hold it against its own gravity and violates none of the null, weak, strong or dominant energy conditions.Sect. 3, Eqs. (16) to (25); Figs. 4, 6 and 7
Adding a shift vector of magnitude 0.02 inside that shell, smoothly transitioned to zero at the outer boundary, produces a constant-velocity warp drive that keeps the flat, tidal-force-free passenger interior of the Alcubierre solution and still satisfies all four energy conditions, with no violation above the double-precision floor of about 10³⁴ against stress-energy terms of order 10³⁹. The authors record it as the first constant-velocity subluminal physical warp drive solution.Sect. 4, Eqs. (26) to (28); Figs. 9, 10 and 14; Sect. 6
The warp effect is a measurable physical quantity, not a coordinate choice: light rays sent through the centre of the shell and back, one along the shift direction and one against it, return about 7.6 nanoseconds apart for the Warp Shell and exactly together for the plain matter shell. That difference is a Lense-Thirring effect, a linear frame dragging, and the same test gives 8.0 ns for Alcubierre, 9.1 ns for Van Den Broeck and 6.7 ns for the modified-time metric at a warp velocity of 0.04 c.Sect. 5.1, Measuring Shift; Table 1; Fig. 15
Because this solution has a changing lapse rate, light crossing it is delayed in the Shapiro sense rather than advanced as in the Alcubierre metric — which the authors suggest may itself be a requirement of physicality. The open problems they name are the acceleration phase, the upper limit on shift magnitude before momentum flux exceeds energy density, and optimising the radial profiles of density, pressure and shift, which they expect could cut the required mass by orders of magnitude.Sect. 5.2 and 5.3; Sect. 6, Conclusion
The way in
https://doi.org/10.1088/1361-6382/ad26aaHow to cite it
Jared Fuchs, Christopher Helmerich, Alexey Bobrick, Luke Sellers, Brandon Melcher, Gianni Martire (2024) Constant velocity physical warp drive solution doi:10.1088/1361-6382/ad26aa