# Designing a plausible faster than light drive: the Space Skip Drive [duplicate]

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I'm designing a plausible faster-than-light (FTL) drive for a SF universe. Here's what I have so far. I'm aware of existing attempts, e.g., Alcubierre's warp drive. I'm taking a different approach, and would appreciate comments from physicists on where I am (too) implausible.

The drive is what I call a "space-skip" drive. You have a drive and an matter/anti-matter battery attached to it (typically half-full.) When you activate the drive, you instantaneously change your spatial coordinates only; any change in your gravitational potential energy is added to or taken away from the battery. Your momentum doesn't change. You do end up interpenetrating whatever matter there is at your destination so it's a good idea to skip into high vacuum areas (e.g, into the wake of a planetoid.)

Since you're changing only your coordinates, your kinetic energy does not change. Infinite energy isn't needed, nor do you need immense shielding to protect against .999c particles or radiation hitting your ship.

A skip conserves energy, linear momentum, angular momentum, charge, etc. Did I miss anything?

If you need to match velocity vectors with your destination, a simple way is to skip near a sun and simply fall for a bit (with the falling vector's direction matching the velocity change vector you need.) You'll deplete the battery somewhat when you do that, of course.

The universe "cooperates" with the drive to preserve causality. Specifically, you can not skip to any coordinate until your resulting light cone will not violate causality.

Note that special relativity (as I understand it) does in fact allow superluminal travel as long as causality isn't violated; if I skipped to Pluto, was careful not to change my velocity, and skipped back to Earth, I believe I don't actually break anything.

If two ships are involved, say A and B, and A skips from Earth to Pluto, and B at Pluto has a non-zero velocity with respect to A, then "censorship" occurs and B will find that the drive refuses to work in any attempts to travel back to Earth until enough time passes in B's frame that causality is preserved.

So what do you think? Anything obviously impossible here (assuming you can actually make stuff skip?)

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## marked as duplicate by Qmechanic♦, Manishearth♦, Colin K, David Z♦Jul 12 '12 at 19:24

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

– Qmechanic Jul 12 '12 at 10:09

## 1 Answer

There is something in general relativity that sounds similar to your skip space concept, it is called "space-time swimming" and it involves twisting around in curved space (very much like a cat would), and you eventually get a net displacement without violating or changing any conserved Noether quantities (and without propellant of any kind). See this question.

The only problem is that the current estimates for space-time swimming as a drive concept make it something like 30 orders of magnitude slower than foot walking. But since this is for SF, you are free to speculate that some discovery made it extremely more efficient.

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