STM-D-0781Paper2012Published and peer-reviewed

Alcubierre warp drive: On the matter of matter

Brendan McMonigal · Geraint F. Lewis · Philip O’Byrne

Abstract and summary · read the original at the source

In one page

An Alcubierre warp bubble carries a ship by deforming spacetime around it, so the ship never moves through local space and its crew feels no acceleration at all. Brendan McMonigal, Geraint Lewis and Philip O’Byrne, at the University of Sydney, asked the question the design literature had largely skipped: what happens to the ordinary matter the bubble meets on the way — the dust, the gas, the starlight. They integrated the free-fall paths of light and of massive particles across the full range of starting speeds, through bubbles travelling both below and above the speed of light, and through bubbles that speed up and slow down mid-flight. The picture that comes out is specific and useful. Particles the bubble catches from the front pile up against an inner horizon, gain enormous energy and become ’time locked’, ageing almost not at all while inside. Particles that pass through come out with the energy they went in with, displaced a little. And when the bubble drops back below light speed, everything it has collected is released forward at once.

Why it matters hereChapter 4 treats metric engineering as engineering, and this is the paper that first mapped, in detail, how a warp bubble interacts with the ordinary matter it flies through — which makes shielding and beam aiming design parameters rather than afterthoughts. Every result in it is a geodesic integration in a written-down metric, so anyone can repeat it.

What it claims

01The Alcubierre spacetime is asymptotically flat except at the walls of a small spherical bubble around the ship: spacetime is deformed so that the chosen path becomes a timelike free-fall geodesic, the travellers therefore experience no inertial effects at all, and their proper time equals the coordinate time of observers at the origin and destination however large the global velocity.Section II, line element Equation 1 and the shape function Equation 2
Published and peer-reviewed
02Horizons form only above light speed. Solving the null condition gives two positions, one on the side the bubble is moving towards and one behind it, at a separation from the ship set by the reciprocal of the bubble velocity; when the global velocity is subluminal these positions lie outside the bubble radius and the horizons do not exist.Section III, Equation 14; Figures 1 and 2 for subluminal velocity 0.5 and superluminal velocity 4
Published and peer-reviewed
03Particles that pass clean through the bubble are blueshifted at the ship by a factor of one minus the product of the ship velocity and the particle velocity, but leave the far side with their original velocity and energy, displaced in space by an amount that grows with the time spent inside and with the ship velocity.Section III A, null and massive particles; Section IV, Conclusions
Published and peer-reviewed
04Particles moving in the same direction as a superluminal bubble are captured instead: they asymptote towards the front horizon, obtain extremely high blueshifts, and become ’time locked’ for the duration of their stay, experiencing very little proper time between entering and eventually leaving the bubble.Abstract; Section III A 2; Section IV, Conclusions
Published and peer-reviewed
05Changing the bubble’s speed shifts the particles it is carrying. Under acceleration a particle inside gains or loses velocity magnitude according to whether it is moving towards the front or the rear of the bubble, and deceleration reverses the effect, with the size of the boost scaling with the size of the acceleration — while Eulerian matter, stationary in the rest frame of the origin and destination, is left unaffected by bubble accelerations and decelerations.Abstract; Sections III B and III C, one-way and round trips; Section IV, Conclusions
Published and peer-reviewed
06The engineering consequence the authors state plainly: the space behind a superluminally travelling bubble is left almost entirely devoid of forward-travelling particles and holds only a sparse population of greatly reduced energy, while the space in front of a bubble decelerating from superluminal to subluminal velocity receives a concentrated beam of extremely high energy particles — so a crewed Alcubierre ship requires shielding, and where the released beam is pointed at arrival is a design parameter to be set.Section IV, Conclusions, final two paragraphs
What to watch

Read it · abstract

Abstract

The Alcubierre warp drive allows a spaceship to travel at an arbitrarily large global velocity by deforming the spacetime in a bubble around the spaceship. Little is known about the interactions between massive particles and the Alcubierre warp drive, or the effects of an accelerating or decelerating warp bubble. We examine geodesics representative of the paths of null and massive particles with a range of initial velocities from -c to c interacting with an Alcubierre warp bubble travelling at a range of globally subluminal and superluminal velocities on both constant and variable velocity paths. The key results for null particles match what would be expected of massive test particles as they approach +/- c. The increase in energy for massive and null particles is calculated in terms of v_s, the global ship velocity, and v_p, the initial velocity of the particle with respect to the rest frame of the origin/destination of the ship. Particles with positive v_p obtain extremely high energy and velocity and become "time locked" for the duration of their time in the bubble, experiencing very little proper time between entering and eventually leaving the bubble. When interacting with an accelerating bubble, any particles within the bubble at the time receive a velocity boost that increases or decreases the magnitude of their velocity if the particle is moving towards the front or rear of the bubble respectively. If the bubble is decelerating, the opposite effect is observed. Thus Eulerian matter is unaffected by bubble accelerations/decelerations. The magnitude of the velocity boosts scales with the magnitude of the bubble acceleration/deceleration.

Brendan McMonigal, Geraint F. Lewis and Philip O’Byrne, Sydney Institute for Astronomy, School of Physics, University of Sydney. Physical Review D 85 (2012) 064024; author preprint arXiv:1202.5708, 26 February 2012.

(Abstract only. The author version is free to read at https://arxiv.org/abs/1202.5708 and the published article at https://doi.org/10.1103/PhysRevD.85.064024 — see the rights note for why the full text is not reproduced here.)

The way in

https://doi.org/10.1103/PhysRevD.85.064024Licence checked directly. The arXiv page for arXiv:1202.5708 carries the arXiv perpetual non-exclusive distribution licence, which is not a Creative Commons licence, and the published article is under the APS default licence, so this page carries the summary, the claims and the authors’ own abstract and sends the reader to the source. Published as Physical Review D 85, 064024 (2012), by the Sydney Institute for Astronomy, School of Physics, University of Sydney; the article carries the title ‘The Alcubierre Warp Drive: On the Matter of Matter’ on its own first page. The summary, the claims and the locators below were written from the full author text.

How to cite it

Brendan McMonigal, Geraint F. Lewis, Philip O’Byrne (2012) Alcubierre warp drive: On the matter of matter. doi:10.1103/PhysRevD.85.064024

Where it sits in the curriculum

The metric, warp drives and wormholes