Gravitational Field Propulsion

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Randy introduces Jim to several ways in which people have theorized that gravity can be used to propel an object through space. In order of likelihood and in inverse order of coolness:

• The Slingshot Effect -- Using a gravitational well to increase the energy available to an object. (In use)
• The Penrose Process -- Using a rotating black hole to gain energy. (Penrose)
• Negative Inertia Mass -- If mass has both a negative charge and inertia, then you can build a device that moves perpetually (RL Forward)
• Induced Gravitational Dipoles -- Spinning half of a sphere will (supposedly) propel it in some direction or other. (Jeong)
• The Alcubierre Drive -- A process that would sneak around the laws of relativity and allow someone to travel faster than light. (Alcubierre, White)

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Notes:

1. The papers we read for this program:

• Wisdom, J., "Swimming in Space-Time: Motion by Cyclic Changes in Body Shape." Science 299, 1865 (2003).
• Longo, M.J., "Swimming in Newtonian Space-time: Orbital Changes by Cyclic Changes in Body Shape." American Journal of Physics 72, 1312 (2004).
• Forward, R.L., "Negative Matter Propulsion." Journal of Propulsion and Power 6, 28 (1990).
• Forward, R.L., "Space Warps: A Review of One Form of Propulsionless Transport." Proceedings of the 25th Joint Propulsion Conference (1989).
• Jeong, E.J., "Anomalous Center of Mass Shift: Gravitational Dipole Moment." [arXiv]
• Alcubierre, M., "The Warp Drive: Hyper-Fast Travel Within General Relativity." Classical and Quantum Gravity 11, L73 (1994). [arXiv]
• White, H., "Warp Field Mechanics 101." DARPA/NASA 100 Year Starship Conference (2011).

2. The slingshot effect is in common use and is a topic viable at the junior mechanics level in such books as Taylor's and Morin's.

3. There is a problem defining the center of mass in general relativity, and we've recorded at least one podcast related to the topic (although not directly addressing it) between the recording of this last June and its publication in March. But the problem is with defining mass, not the center of mass. And because of the simplicity of the space-time swimmers, I'm still not sure its as much of a problem as some people do.

4. Popular articles for this program:

• Gueron, Eduardo, "Adventures in Curved Spacetime." Scientific American 301(2), 38 (Aug 2009)

5. The video Randy keeps talking about in the podcast he found linking through The Hammock Physicist Blog of Johannes Koelman. You can download it here from the IOP. I haven't yet found the article IOP attached it to.

6. I'll make a video of the non-commutative motion diagrams that I sent Randy and put a link up here.

7. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.
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