# Is it possible to "swim" in a vacuum, taking advantage of relativity, and make a useful amount of headway? [closed]

His situation seems hopeless. However, he remembers the lessons he received as rookie astronaut on swimming in empty space. By applying a weird degenerative form of breaststroke the astronaut slowly moves toward the spaceship and makes it safely back before he runs out of oxygen.

Science 20 cites and MIT paper by Jack Wisdom in support of the claim, although the latter makes no mention of astronauts.

My question is: could an astronaut doing a space 'walk' in space move their center of mass by a useful amount (or even a detectable amount) by moving their arms about by taking advantage of relativity?

Background: On this page is this comment (by the user "Skyler") that was upvoted twice:

In fact, you can "swim" in a vacuum, taking advantage of relativity: science20.com/hammock_physicist/swimming_through_empty_space. However, this is a very subtle effect, and takes hours to move a foot or two.

Similar to this question (except for asking whether an astronaut could really make enough headway to save his own life as claimed by Science 20 and Skyler).

• More directly relevant is the paper istelf: web.mit.edu/wisdom/www/swimming.pdf rather than a circuitous link through a magazine that is pay-walled. Apr 23 at 20:56
• Possible duplicates: physics.stackexchange.com/q/886/2451 and links therein. Apr 23 at 21:01
• I’m voting to close this question because it asks for a critical review of a published paper without specifying which passage the OP had difficulty following. Apr 23 at 22:46
• @WillO The question does not ask for a critical review of any paper. It simply asks whether an astronaut really could save his own life as claimed by Skyler and by Science 20 website. Apr 24 at 3:13
• @MatthewChristopherBartsh: You say the question "simply asks whether an astronaut really could save his own life as claimed". But the answer to that question is in the paper. So presumably there is something in that paper you don't understand, or that you believe is wrong. If you don't specify what passage in the paper is bothering you, then you are implicitly asking people to comment on the correctness of every part of the paper. The name for that is a critical review. Apr 24 at 12:22

The idea that an astronaut could 'swim' a noticeable amount in a vacuum is not supported by the MIT paper by Jack Wisdom http://web.mit.edu/wisdom/www/swimming.pdf because it says "The curvature of spacetime is very slight, so the ability to swim in spacetime is unlikely to lead to new propulsion devices. For a meter-sized object performing meter-sized deformations at the surface of the Earth, the displacement is of order (sic) $$10^{-23}$$ m."
In plain English, that means that the astronaut would have moved his body, after a trillion strokes (which at one stroke per second would take just over $$30,000$$ years), less than a millionth of a millimeter.