Reactionless Drive: Difference between revisions

Obviously this would be an awesome invention! So why don't we have them? Well, naively it would shatter the fundamental basis of all physics since [[Isaac Newton]], as detailed [http://www.projectrho.com/rocket/reactionlessdrive.php here], and modern theories predict effects too small to be useful. Thoughtful [[Speculative Fiction]] writers have also noted that any sort of reactionless drive would provide those who possess it with an ''infinitely'' powerful weapon (compare [[Weaponized Exhaust]], which is the use of a reaction drive as a weapon). Note that this would not be a problem if they required truly massive amounts of power <ref> to accelerate at 1G a "photon drive" would need ~2.9TW per ton, not an easy task</ref> but many examples don't.

 

{{examples}}

 

 

== Comic Books ==

* Most super heroes who can [[Flight|fly]] under their own power in space have some form of reactionless drive, [[Required Secondary Power|even if the comic's authors don't call it this]]. [[Superman]], for example, can accelerate, decelerate, and turn in Earth orbit, with no (obvious) rocket exhaust coming out.

 

* In ''Stone'' by [[Adam Roberts]], reactionless propulsion is achieved by extremely rapid teleportation in infinitesimal steps. This can even be applied to an individual, who can be wrapped in a protective shell, with life-support equipment and a teleportation device, and then sent off to their destination through interstellar space. The speed of this mechanism is affected by gravitational fields, where a stronger field requires more complex calculation (and thus less rapid steps). The reader may notice this sounds exactly like the Stutterdrive mentioned for ''[[Sword of the Stars]]'' under Video Games. As Stone was published in 2003, and the game in 2006, I can only assume it was half-inched.

** [[Larry Niven]] proposed more-or-less this design in his "The Theory and Practice of Teleportation", originally a speech at [[Fan Convention|Boskone]] in 1969.

 

 

== Tabletop Games ==

* The various reactionless drives in ''[[GURPS]]: Spaceships'' are most obviously useful in that they save a tremendous amount of space because even the best reaction engines require a large fraction of the ship's mass in order to reach useful speeds. All of them require a great deal of power to operate, but not nearly enough to explain the thrust through anything but superscience.

* Later versions of ''[[Traveller]]'' used reactionless "thruster plates" for spaceship movement.

* The Ion Drive engines of ''[[Starfire]]'' are probably reactionless drives -- they let a starship instantly switch back-and-forth between a dead stop and 10% of the speed of light at the flick of a switch, so they definitely ignore pesky details of physics like ''inertia'' -- but we are never told outright whether they spew exhaust or not.

 

== Real Life ==

{{quote| The Dean Machine, the Dean Machine <br />

You stick it right in a submarine <br />

** A photon drive fits our definition; photons do exert pressure, and they are massless. A photon drive only consumes power. Unfortunately, a photon drive is horribly inefficient.

** The Ambient Plasma Wave Drive would use ambient plasma as its reaction medium, generating waves in it to propel itself. Sort of like how a propeller uses ambient air (or water) to create thrust.

** But since the inside of its "bubble" is causally unconnected to the past, present and and future of the outside universe, it's questionable whether it meaningfully counts as a form of transportation, or even as something that can be said to physically exist at all.

*** And, of course, the Alcubierre drive is an interesting thought experiment that gives absolutely no indication of how you'd generate the "spatial bubble" it requires, or turn it off when you'd done. Odds are that if you could engineer spacetime in that way you probably wouldn't need to.

** In fact, most of current cosmological theories ''require'' our Universe as a whole to be of negative mass to match the currently known pattern of expanding. Well, they mostly express it as a negative energy, but E=mc^2, y'know...

* The [http://physics.fullerton.edu/~jimw/nasa-pap/ Mach Effect] (AKA "Woodward Effect", but Dr Woodward prefers the former), the claim is it can be derived fairly directly from Relativity, and so involves no new physics, plus we already have most of the technology to try it in a lab... The claim is it is reactionless without violating any conservation laws, cool stuff if it works. NOTE: we may have most of the tech to build a test device, but it won't be very efficient, and the effect will be small. It will probably take several years of work to develop capacitors and piezoelectric materials that will make a useful version. That's assuming that the thing works at all.

** It should be noted that the ''Mach Effect'' DOES conserve momentum, the "equal and opposite reaction" is spread out over a vast amount of mass outside the engine (possibly the entire universe).

* [http://groups.csail.mit.edu/mac/users/wisdom/swimming.pdf Spacetime swimming] is another viable alternative for propulsion in a curved spacetime. This is analogous to how you can change the orientation of an office chair without touching anything (try it, unless [[Hilarity Ensues|someone is watching]]). It is also a small effect, and it is unclear whether or not it would be useful. This device exploits quirks in general relativity that allows one to sidestep the issue of conservation laws -- let's just say general relativity is a bit sticky on this subject, and that since this sort of drive would not work in the usual manner, i.e., it does not apply a continuous force, accelerating the craft, but instead [[Space Is an Ocean|needs to operate continuously in order for the craft to continue moving]], ensuring that no conservation laws are harmed. [http://www.brophy.net/Downloads/AIL%20Class%20on%20Reality%20&%20Unreality/READING%20MATERIAL%20IN%20PDF%20FORMAT/87%20SWIMMING%20in%20curved%20spacetime.pdf Here] is a more palatable description. This is the method of propulsion chosen by the alien Xeelee, in [[Stephen Baxter]]'s novels.

* [http://arxiv.org/abs/0912.1031 Effects of the quantum vacuum] on magnetoelectric materials exhibit this, but again, it is unclear whether technological applications will ever be possible.

 

{{reflist}}

[[Category:Spacecraft]]

[[Category:Reactionless Drive]]