I wasn't going to put this section in, but I have to. I wanted to keep the website as free from handwavium as possible. However, while Faster-Than-Light travel is about as handwavium as you can get, it is unfortunately the sine qua non of interstellar space opera. Space opera with no StarDrive is like chocolate cake without the chocolate.
The standard physics term for "the speed of light in a vacuum" is lower-case letter c. "Vacuum" is because light and other electromagnetic radiation travels slower in spaces filled with matter, such as water. Science fiction commonly uses "lightspeed" as a synonym for c.
- FTL: Faster Than Light
- STL: Slower Than Light
- NAFAL: Not As Fast As Light. Non-relativistic flight, say below 14% c. (Ursula K. LeGuin)
- AAFAL: Almost As Fast As Light. Relativistic STL flight, say, above 14% c but below 100% c.
- Superluminal: faster than light, from Latin terms for superior and pertaining to light
- Sublight: lower than light
- Fittled: to travel at FTL velocities. (Ken MacLeod)
- Tesser: to travel FTL by space warp. Term comes from Tesseract. (Madeleine L'Engle)
- Wrinkle: to travel FTL by space warp. Synonym for Tesser. (Madeleine L'Engle)
For FTL drives that travel to their destination at a certain rate (as opposed to "jump" drives that appear instantly at the destination), science fiction authors generally talk about how much faster than the speed of light in a vacuum the starship travels. No jokes about Han Solo and the Kessel Run (see the frantic retconning at this website). This allows one to easily calculate how long the starship will take to travel a trip of x light years. Assuming no complications from relativistic time dialation, but if you are traveling faster than light then relativity has been kicked to the curb already.
- 1,000 c: one thousand times the speed of light in a vacuum. 0.5 c is half lightspeed.
- 100,000% lightspeed: one thousand times the speed of light in a vacuum, because the percentage is the factor times 100.
- Mike 1,000: one thousand times the speed of light in a vacuum, from Robert Heinlein's Starship Troopers. Presumably "Mike" refers to Michelson–Morley. "Under Cherenkov drive she cranks Mike 400 or better—say Sol to Capella, forty-six light-years, in under six weeks."
- 1 kilolight: one thousand times the speed of light in a vacuum, from Iain M. Banks Culture novels. The term "lights" is used like the navy term "knots". And it is in metric: 1 decalight = 10c, 1 megalight = 1,000,000c, etc.
- Ninety parsecs an hour: 2,570,184 times the speed of light in a vacuum, in E. E. "Doc" Smith's LENSMAN series the starship speed at full blast in intragalactic space. The top extragalactic speed at full blast is 100,000 pc/hr or 2,855,760,000c.
Jump drives commonly have a maximum jump distance, a minimum time between successive jumps, but the jump proper is instantaneous. Or they have a maximum jump distance and the jump takes a certain amount of time. These two factors can be combined to give an effective speed. You calculate how long it takes to go a given distance, and divide that time by how long it takes light to go the same distance.
In vintage SF, the propulsion was commonly termed "hyperdrive", since the starships evaded Einstein by entering a dimension called "hyperspace" where there was a higher speed limit. Star Trek has its "warp drive" that reduces the distance to be traveled by warping space. The RPG Traveller has its "jump" drive that teleports the ship from point A to point B. In his "Lucky Starr" novels, Isaac Asimov uses the term "Hyperatomic spaceships", presumably since the spacecraft had both a faster-than-light Hyperspace engine and a more conventional atomic engine. Go read the "Faster Than Light" entry in Wikipedia.
The two main catagories of science-fiction-invented FTL travel center around modifying one of the two terms in the travel time = distance / rate of travel equation. Modifying distance is usually called a "warp drive" while modifying rate-of-travel is usually called a "hyperspace drive", but not always. There are some modifying distance types that are called hyperspace drives because there is always one in every crowd.
Fred Kiesche says that a faster than light starship should have a license plate that reads "ME = MC2"
The important point is to keep the fracture under control. Hack writers will assume that "if we have to break a few laws of physics for FTL, why not just throw all the laws out the window?" Don't give in. Omitting physics will degrade your novel to a pathetic lack of accuracy worse than an average Space Ghost cartoon.
What to do? Keep all the physics you can. And when you break the laws for your FTL drive, at least establish some limitations and rules. Then stick to them! Internal self-consistency is better than nothing.
The general rule is what physicists call the correspondence principle or the Classical limit. This states that any new theory must give the same answers as the old theory where the old theory has been confirmed by experiment. Newton's laws and Einstein's Relativity give the same answers in ordinary conditions, they only give different answers in extreme conditions such as near the speed of light, refining the accuracy of the GPS system, or calculating the orbit of Mercury (none of which Newton could confirm by experiment).
The point is: you, as a science fiction author inventing a FTL drive, have to explain why current scientific theory didn't discover FTL travel decades ago. Harry Turtledove turned the problem on its head and turned the explanation into the plot of the short story.
As a general rule, a given science fiction novel has one faster than light method. Two notable exceptions are The Halcyon Drift by Brian Stableford and Startide Rising by David Brin. Both of those novels have half a dozen stardrives used by various races and factions, each with different capabilities and limitations.
That old spoil-sport Einstein ruined FTL travel when he created his theory of General and Special Relativity.
Now according to common sense (and as codified by Isaac Newton), velocities will add to each other. If you are travelling at twenty kilometers per hour due north, and you add five kilometers per hour northward to your velocity, you should now be travelling at twenty-five kilometers per hour due north. Everybody (including Newton) knows that 20 + 5 = 25.
Unfortunately for us, Einstein is not everybody. In Special Relativity, no matter how fast you are moving, a beam of light appears to be moving at exactly the speed of light (the technical term is The Principle of Invariant Light Speed). One of the unobvious consequences is that velocities do NOT add. At least not when one gets close to the speed of light. Only a percentage of the new velocity is actually added.
What percentage? Well, the faster you go, the lower the percentage. And at the speed of light, the percentage is zero. So in theory, once you are at light speed, no matter how much velocity you try to add, the amount actually added is zero. Which means you can never exceed lightspeed.
Almost every single FTL drive you read about in science fiction is based on some clever way to avoid the light speed barrier.
However, very few SF novels deal with the second problem. The aphorism at rec.arts.sf.written goes "Causality, Relativity, FTL travel: chose any two."
Your average physicist holds Relativity quite strongly. It has been tested again and again with an accuracy of many decimal places. They hold onto Causality even tighter. Without Causality the entire structure of physics crumbles. Causes must preceed effects, or it becomes impossible to make predictions. If it is impossible to make predictions, it would be best to give up physics for a more profitable line of work.
Therefore, they chose to jettison FTL travel.
Please note that as far as Causality is concerned, FTL communication is every bit as bad as FTL travel.
Why only two?
Time travel makes Causality impossible, since it can be used to create paradoxes.
- So if you have Relativity and FTL, Causality is impossible
- If you do not have Relativity, then FTL is not Time travel, so you can have Causality.
- Or more mundanely you can have Relativity and Causality, but no FTL/Time travel
∴ Causality, Relativity, FTL travel: chose any two.
Clever readers will have already spotted a possible loop-hole. What if there was some law of physics that prevented Time travel from creating paradoxes? In that case, FTL/Time Travel would not make Causality impossible.
The classic Time-travel paradox is the so-called "Grandfather paradox" (though it actually should be called the "Grandmother paradox"). Boris Badenov sneaks into Mr. Peabody's Wayback Machine (actually the WABAC machine, but who cares?) and travels back in time to when Boris' grandfather was a baby. Boris then gives his infant grandfather a lit stick of dynamite then cackles evilly as his grandfather is blown to bits. Bah-hah-hah!
But wait! Boris' grandfather is now smithereens, he'll never grow up, beget Boris' father, who will beget Boris. In other words, Boris will never exist.
But if Boris never exists, then he will never travel back in time to assassinate his grandfather. In which case grandpop will beget Poppa Boris, who will beget Boris. Who will then proceed to assasinate his grandfather. Start back at the beginning and repeat.
Does Boris' grandfather get blown up? Both Yes and No! A paradox.
Hinson shows there are four ways of enforcing a "no-paradox" rule for time travel. Parallel Universes, Consistency Protection, Restricted Space-Time Areas, and Special Frames. In some ways Special Frames is the best, though it directly contradicts part of Relativity (the first postulate of special relativity is that there are no special frames, "no privileged inertial frames of reference"). Oh well. For details, you'd best read the Hinson article.
The latter three are examples of the Novikov self-consistency principle.
In some late-breaking news, physicists Daniel Greenberger and Karl Svozil have shown that the laws of quantum mechanics enforces Consistency Protection. You can read their paper here, but it makes my brain hurt. Translated into English, they maintain that time travellers going back into the past cannot alter the past (i.e., the past is deterministic). This is because quantum objects can act sometimes as a wave. When they go back in time, the various probabilities interfere destructively, thus preventing anything from happening differently from that which has already taken place.
As a side note, those interested in the various ways time-travel seems to work in SF novel should run to the Guide To SF CHRONOPHYSICS.
Why have you not read about this in any science fiction novel?
It is absent from some because the authors do not know enough relativity theory to spot the FTL equals Time Travel implication.
It is absent from the rest because of those who do know enough relativity, practically no author wants to deal with the huge squirming can of worms opened by time travel. They just wants a quick and easy way to get their hero from star to star.
This is why the time travel connection is the dirty little secret of science fictional FTL travel.
It seems to me that an FTL drive ruled by the Novikov self-consistency principle would operate in a very strange and non-intuitive way. It might be that occasionally the starship pilot would set up a trip and the FTL drive would refuse to operate. Then the pilot would know that somehow someway the proposed trip would cause a paradox.
Or even worse, after an FTL trip, the pilot and any passengers would discover that if they try certain actions the entire universe throws up random events preventing said actions. Indeed the entire universe might throw up random events forcing a passenger to perform some action. Because if certain actions happen or certain actions do not happen, a paradox will ensue.
If the FTL drive has an elaborate mechanism described in detail, the mechanism can suggest appearances. For instance, if the spacecraft travels from star to star through stargates, obviously one would expect to see a stargate involved. A ship that enters hyperspace might fade out and vanish. The Starship Enterprise streaks off with a rainbow contrail and vanishes in a flash. The Millennium Falcon just streaks off until it vanishes in the distance.
Regardless of that, it still looks like whatever the author damn well pleases. Or looks like whatever jazzy eye-candy scientifically-ridiculous ILM special effect which catches the movie director's fancy and is within the special effects budget.
But if the FTL drive somehow makes the starship move superluminal while still being visible in our mundane space-time continuum, that's when Newtonian and Einsteinian physics have a say in how it looks.
There are two main dodges. You may remember from Physics 101 that travel time = distance / rate of travel. For example, if you have to travel 100 miles, and you maintain a speed of 50 miles per hour in your automobile, the travel time will be two hours.
The laws of physics forbids any rate of travel faster than the speed of light. Since the distances between stars are so astronomically huge, this means the travel time will be measured in decades or centuries. This is unacceptable in a fast-paced science fiction novel.
Dodge #1 is to handwave some technobabble way of increasing the starship's rate of travel to faster than light. From the equation you can see this will reduce the travel time. In Geoffrey Landis' Canonical List of StarDrives, this includes Continuous Drives and Modifying the Universe: Modify the speed of light.
"Hyperdrives" often talk about the starship entering a magic dimension called "hyperspace" where that pesky speed limit does not apply. E.E. "Doc" Smith's interialess drive removes the inertia from the matter composing the ship and crew, so again the speed limit is side stepped (sort of). Also covered are FTL drives that convert the starship and crew into FTL tachyons, then convert back to ordinary matter at the destination.
Dodge #2 is to handwave some technobabble way of reducing the distance to the starship's destination. From the equation this also reduces the travel time. This includes stardrives that warp or fold space. There is a second kind of hyperspace in science fiction, one where the speed of light is the same as in our dimension, but distances are compressed by a factor of a billon or so. The 4.2 light-year distance to Alpha Centauri might therefore be only 40,000 kilometers in hyperspace. Pop into hyperspace, move 40k km in the Alpha-C direction, pop back into our dimension, and find yourself at our neighbor star.
Taken distance reduction to extremes, the distance can be reduced to zero along with the travel time. These are "jump" or teleportation drives where the ship vanishes at point A and instantly appears at point B. In the Landis list, this includes Discontinuous Drives and Modifying the Universe: Modify distance in space.
Sometimes a jump drive is a machine inside a starship, sometimes it is an external installation called a "jumpgate" or "stargate". Star Trek's "warp drive" was originally intended to use this method, but the method has sort of changed with each new generation of writers. Travel by wormholes also uses this technique.
Why do these dodges violate the laws of physics? Well, that is complicated, but there are two main problems: the Light-speed barrier and Causality. This is explained with some depth at Jason Hinson's authoritative "Relativity and FTL" website, so I'm just going to give a short summary. Refer to Hinson for details.
It is unclear if reducing the distance is allowed or not, and nobody is sure how to warp space on a commercial level. Suggestions generally involve gravity fields of intensities only found around black holes and/or wormholes (aka Einstein-Rosen bridge). Warping the fabric of space would seem to require astronomical amounts of energy, and heaven help any solar systems that got wadded up in the warp.
One of the classic faster-than-light dodges was for the starship to enter "another dimension" where the speed of light was faster or otherwise allowed the starship to violate Einstein's relativity with extreme prejudice. The standard name was "hyperspace."
Though considered somewhat passé now, in the 1940's hyperspace was a synonym for the dreaded "Fourth Dimension."
Yes, I know some call "time" the fourth dimension, this is talking about the fourth spatial dimension. Forwards/backwards, left/right, up/down, ana/kata (terms coined by Charles Hinton). The fourth dimension is a valid scientific concept, even though our puny three-dimensional intellects cannot truly comprehend it. It can be worked with using mathematics, and crudely visualized by using the magic of analogy.
0: A point has no dimensions. There is no width, there is no height, there is no thickness, there are zero dimensions.
1: If we take a point and move it in the X axis, the point becomes a line. It now has width. It still has no height or thickness, so it only has one dimension.
2: Take the line, and move it down in the Y axis (in a direction 90 degrees to the X axis). The line becomes a square. Now it has both width and height. No thickness so it only has two dimensions. There are four lines enclosing one square plane.
3: Take the square and move it towards you out of the plane of the computer monitor in the Z axis (in a direction 90 degrees to both the X axis and the Y axis). The square becomes a cube. It has width, height, and thickness, three dimension. There are six square planes enclosing one cubical volume
4: By analogy, take the cube and move it in the direction of the fourth dimension in the W axis (in a direction 90 degrees to the X, Y , and Z axes). The square becomes a tesseract or hypercube. It has width, height, thickness, and ana. There are eight cubes enclosing one hyper-cubical hyper-volume.
Your brain has started to hurt. It won't be the last time it hurts in this section.
The first major use of analogy to explain the fourth dimension was in the classic Flatland: A Romance of Many Dimensions, a 1884 satirical novella by the English schoolmaster Edwin Abbott Abbott. If you are interested in the fourth dimension, you should read it. There are quite a few free downloadable versions, but ensure that you get one that has the illustrations.
Mathematician Rudy Rucker wrote a slender textbook along the lines of Flatland with equations and everything, entitled Geometry, Relativity, and the Fourth Dimension. It is a bit dry. He later wrote a more popularized version with entertaining illustrations by David Povilaitis entitled The Fourth Dimension: A Guided Tour of the Higher Universes. Both are excellent.
If you want to delve more into the nitty-gritty details of the life and technology of two dimensional creatures, may I recommend The Planiverse by A. K. Dewdney? The appendix in the back has the details of various 2D items, such as a NOR logic gate where the wires do not cross, and a two dimensional steam engine.
In Flatland and The Fourth Dimension, a two-dimensional character named A. Square encounters dimensional weirdness when the 3D Sphere from the third dimension invades. The reader is then shown how by analogy the same thing can happen if they encounter the 4D Hypersphere invading from the fourth dimension.
Sometimes the 2D square character from the 2D flatland universe encounters the 1D line character living in the 1D "lineland" universe. A. Square is usually very annoyed at how the line character fails to comprehend two dimensional weirdness. In a case of the pot calling the kettle black, A. Square then finds himself incapable of comprehending three dimensional weirdness exhibited by the 3D sphere. The reader then squirms in their chair as they uncomfortably realize they would be just as incapable of comprehending four dimensional weirdness if the 4D hypersphere showed up and started messing with their mind.
One can imagine A Square to be like a square of paper on a tabletop. He can move around on the two dimensional table surface, but has no ability to move in the third dimension. He cannot even comprehend what direction that is. He knows all about north and sound, east and west. But an "up and down" at ninety degrees to the first two? Inconceivable.
In Flatland, A Square's adventures start when he dreams about encountering Lineland. The inhabitants are points and line segments, they can move east and west but not north or south. Nor can they comprehend what direction that is.
A Square tries communicating with the King of Lineland, but finds it to be quite frustrating. The king can hear A Square but his voice seems to be coming from nowhere. A Square's attempts to explain that he is "north" of the king (90 degrees to east-west) go nowhere. And A Square's visit to Lineland are weird. The king can only see that part of A Square which intersects Lineland. So when A Square passes through Lineland, as far as the king is concerned he just sees a line segment pop out of nowhere, exists for a while, then vanishes. A Square tries to explain that his body is composed of a series of line segments stacked in the second dimension, which is total gibberish to the king.
Now it is time for A Square to be flummoxed.
A Square is in his locked two-dimensional house with his wife when the Sphere from the third dimension comes to call. Just like the king of lineland, A Square thinks the Sphere's voice is coming from nowhere. The Sphere's attempt to explain that he is "above" A Square (90 degrees to north-south and east-west) goes nowhere. And the Sphere's visit to Flatland is weird. A Square can only see the part of the Sphere that intersects Flatland. So when the Sphere passes through Flatland, as far as A Square is concerned he just sees a dot pop out of nowhere, becoming an expanding circle, then contracting back down to a dot, then vanishing. The Sphere tries to explain that his body is composed of a series of circles stacked in the third dimension, which is total gibberish to A. Square.
The reader sits there smugly feeling superior to the stupid King of Lineland and A. Square. Then they receive a visit from the Hypersphere from the fourth dimension.
Just like A Square, the reader thinks the Hypersphere's voice is coming from nowhere. The Hypersphere's attempt to explain that he is "ana" the reader (90 degrees to north-south, east-west, up-down) goes nowhere. And the Hypersphere's visit to the third dimension is weird. The reader can only see the part of the Hypersphere that intersects the third dimension. So when the Hypersphere passes through, as far as the reader is concerned they just sees a dot pop out of nowhere, becoming an expanding sphere, then contracting back down to a dot, then vanishing. The Hypersphere tries to explain that his body is composed of a series of spheres stacked in the fourth dimension, which is total gibberish to the reader.
A Square's mind was blown by a simple sphere from the fourth dimension. Just imagine if a irregularly shaped human being came for a visit! A Square would probably see several apparently separate blobs, the intersections of your torso, arms and legs. If you tried to explain that they were all connected in the third dimension, A Square would tell you that now you were just makin' stuff up. He would also have difficulty understanding how your parts keep changing shape and texture.
And of course if the reader was visited by some living being from the fourth dimension, it would also be just as disjointed and terrifying.
Imagine that flatland was the surface of a lake. A Square floats on the surface, but can only see the outline of where your body pierces the surface of the water. If you tried to grab A Square, you'd stick your fingers into the water. A Square would see five apparently separate irregular circles appear out of nowhere, which converge on him. By analogy if a large hyper-person in the fourth dimension tried to grab you, you would see five apparently separate irregular flesh-colored spheres appear out of nowhere, which converge on you.
Remember that when the Sphere from the third dimension visited A Square in Flatland, it appeared inside A Square's locked house. How did it manage that? Because even though the house was closed in the second dimension, it was quite open in the third.
If you are constrained to stay in two dimensional Flatland, there is no way to move into the house without first encountering the walls of the house. But if you can enter the third dimension, you can "hop" over the wall and enter the house anyway. By analogy, locking yourself inside your home will not prevent the Hypersphere from entering the fourth dimension and "hopping" over the walls and thus entering your locked home.
This also means that your space dreadnought coated in adamantium armor and guarded by impenetrable force fields will be quite defenseless to an enemy warship in the fourth dimension. They can fire all their weapons over the armor and force fields, and gut your dreadnought from the inside.
And "walls" do not just apply to houses, they apply to an organism's skin as well. Pictured below is a two dimensional being from the Planiverse. Remember that 2D creatures can only see things in the 2D plane they exist in. So when they look at another inhabitant, they see their skin.
But a 3D observer is "looking down" at the 2D creature. So they see the 2D creature's internal organs. In the same way, a hyper-observer looking at you would mostly see all your internal organs. And they could reach inside you and touch said organs without breaking your skin first.
Finally getting to the point, the fourth dimension might be used as a method of faster-than-light travel. The basic idea is that our 3D space might be crumpled up in the fourth dimension without us being aware of it. So points that were far apart in 3D space might be adjacent if one could only make a little hop in the fourth dimension.
If of course we are lucky enough that our space is all crumpled up in the fourth dimension. Or if our FTL drive is powerful enough to crumple up light-years of space all by itself. That could be dangerous, some passing cosmic four dimensional being might inadvertently have its lower left tentacle suddenly pleated into painful Origami, with unfortunate consequences. And any advanced 4D civilization might take exception to having their entire solar system wadded up like piece of used facial tissue.
Since FTL drives are ruled more or less impossible by current science, you have to invent your own. In such cases, the best way to start is to focus on effects instead of causes. Many novice SF novelists and game designers make the mistake of inventing a cause first and may not even try designing the effects.
An example of an effect is "The star drive can move the ship at ten light-years per hour".
An example of a cause is "The Mason Field is generated by the amplification of the interaction of the Alpha and Omega sub-particles contained in the Xanthe crystal when bombarded by pseudo electron valients in a charged hydrogen field."
Effects help you avoid unintended consequences, and define the implications of your drive. Causes are fluffy technobabble explanations that a good SF story might avoid all together. As Gene Roddenberry noted, in a police TV show a policeman does not explain to the viewers how the primer of the bullet ignites the main charge propelling the lead slug down the barrel every time he shoots his handgun. Neither should Captain Kirk explain the operating principles of his phaser weapon, the fact that it is some species of sidearm is enough for the viewers.
Causes can also get you into trouble if your explanation implies new effects that you did not intend. They also give more weak points that a scientifically minded reader can use to poke holes in your theory.
- How much faster than light is the ship? (that's the one effect you have to establish.)
- How big a ship can be moved?
- Does it require large intricate starships, or can you just mount it in a submarine?
- Does it require huge amounts of energy?
- Does it require the ship to be outside any planetary or solar gravity wells?
- Can the ship only enter FTL flight at special locations ? ("jump points")
- Does each FTL "jump" require days of tedious mathematical calculations?
- Can a ship in FTL flight be detected by another ship also in FTL flight?
- Can a ship in FTL flight be detected by another ship or base not in FTL flight?
- Does FTL flight make the crew vomit, hallucinate, have epileptic fits?
- Is the supply of FTL drive units limited due to a tight monopoly on their manufacture, or due to the fact that they can no longer be manufactured at all?
- Is a required component a person with some kind of mystical psionic power?
- Do the drive units require rare and hard to get materials? (the Traveller RPG required Lanthanum, H. Beam Pipers' ships required Gadolinium, Captain Future's ship required a ring of Terbium. All of these are rare earth elements, emphasis on the "rare")
These are just off the top of my head, you can find more by reading SF novels, or from your imagination.
If your ship is twice as fast as the speed of light, it can go 100 light years in a mere 50 years. Therefore most of the action in your universe will take place close to Sol, if the average interstellar journey is two years. On the other hand if your ship is 36,500,000 times as fast as the speed of light, your ship can cross the Galaxy the long way in about one single day. The action in this universe will therefore be galactic in scope.
If the only ships that can be moved are ones smaller than a Greyhound Bus, one implication is that you will not have titanic ships the size of Star Wars Imperial Star Destroyers, much less any Death Stars.
If there are only large intricate starships, they will be few in number and crewed by the cream of the crop. If any fool can build an FTL drive from plans downloaded from the internet and convert a septic tank into a starship, there will be zillions of starships crewed by a wide range of eccentric people.
If ships require huge amounts of energy for their FTL drives, you have to decide upon the source of said energy. Antimatter fuel implies antimatter factories or antimatter "mining." There is also the unintended consequences of a given starship containing enough energy to, say, vaporize Greenland. The further implication is that starship captains will be on a very short leash (John's Law). If on the other hand a starship can run on one AAA battery, you start having problems with FTL missiles the size of bullets.
A very common limit is that the FTL drive can only be entered if the ship is "not too deep in a gravity well", that is, farther than a certain distance from either a planet or the primary star. Again keep in mind that if ships can only enter or leave FTL at about Pluto's orbit, the ships will either require unreasonably powerful normal-space rocket drives that run afoul of Jon's Law, or the ships will take years to travel between Terra and the FTL take-off point.
Ships that can only enter/exit FTL flight at special locations make those locations into military choke points. Ships that can exit FTL flight anywhere coupled with ships that cannot be detected while FTL will open the possibility to genocidal interstellar wars that last all of five minutes.
In John Maddox Roberts novels Space Angel and Spacer: Window of the Mind, the "Whoopee Drive" makes the crew suffer projectile vomiting, violent diarrhea, and hallucinations. Before each jump they have to attach a barf bag over their mouth, strap themselves on to a toilet, and try to ignore the paisley Peter Max metal termites eating the hull. Naturally this made troop ships a nightmare. In Gordon Dickson's The Genetic General, closely spaced FTL jumps made without a recovery period in between would rapidly incapacitate the crew.
In David Lynch's movie adaptation of Frank Herbert's novel DUNE, mutated Guild Steersmen move starships between stars with their psychic abilities. Thus the Spacing Guild has a monopoly on starships, and the total number of starships was limited to the available supply of mutated Guild Steersmen. The same general situation occurs in SPI's StarForce and SPI's Universe RPG. Other stardrives have to be controlled by a human being, they cannot be automated or computer controlled. For more details go here
In John Brunnner's Interstellar Empire and Frederik Pohl's Heechee novels (Gateway et al) the starships are artifacts from some long lost alien race, humans can fly them but cannot construct them.
In SPI's game Freedom in the Galaxy all stardrives are manufactured by the Empire, and contain a thermonuclear booby-trap to discourage attempts at reverse-engineering. The empire takes its monopoly on stardrives very seriously.
This concept dates all the way back to the 1930s, with E. E. "Doc" Smith's LENSMAN series. Say Lensman Kimball Kinnison's starship is moving seven kilometers per second towards Galactic North. When Kim turns on his ship's FTL inertialess drive, he can fly all over the place in any direction at a speed of 90 parsecs per hour, or even become perfectly stationary. But when Kim turns off the inertialess drive, the starship reverts back to moving 7 km/sec towards Galactic North. Doc Smith calls this the starship's "intrinsic" velocity.
The point being that even though Kim's ship can travel from Sol to Alpha Centauri in 52 seconds, when he gets there he will have to use normal space thrusters to match the ship's intrinsic velocity to the ship (or solar system) that is his destination.
This can be a real problem if the target ship is moving relativistically, or the solar system is around a runaway star. Or worse, a hypervelocity star. You are going to need a huge amount of reaction mass, or a reactionless drive (plus the threat of RocketCat's Atomic Wedgie).
Doc Smith takes this to an extreme, because inertialess drives can be made small enough for a person to wear on their belt. So if starship Alfa and person Bravo are both currently inertialess and both have moderate differences in intrinsic velocity, they can match velocity by using the spring room. Person Bravo enters the ship, goes to the spring room, enters the padded leather form fitting coffin which is attached to all the walls with huge strong springs, and both the person and the ship turns off their inertialess drives. The person in the coffin jolts around the room until the velocity is matched.
Larry Niven gets around the problem with a handwaving gizmo called a Gravity Drag. It uses zero reaction mass and very low amounts of power. The handwaving is that it somehow converts a ship’s momentum relative to the "nearest powerful mass" into heat. So all you need is a large heat radiator. If the intrinsic velocity difference is too great one might have to bleed off the momentum in stages. You bleed off all the momentum you can until you are too close to the destination planet. Then you use your hyperdrive to move further away from the planet, reenter normal space, and use the gravity drag to bleed off some more.
Poul Anderson turned the problem of no reactionless drives into a plot point. In The Bitter Bread there are starships with an FTL drive with the intrinsic velocity problem of Doc Smith's drive. One exploration starship is investigating a pair of massive stars in close orbit with each other. Oh noes! The FTL drive malfunctions while the ship is too close. Such star pairs can be used as a gravitational catapult. It grabs the starship and gives it near relativistic intrinsic velocity. More to the point, too much intrinsic velocity for the ship to get rid of with its on board reaction mass, by several orders of magnitude. So they are trapped. They fly back to Terra, but nobody can leave the ship (or their intrinsic velocity will sent them out of the solar system at a large percentage of lightspeed), and they cannot load more reaction mass to slow down (since intrinsic velocity can only be shed with the stardrive turned off, and the instant you do that the newly loaded reaction mass will shoot off at near lightspeed and destroy the ship).
For reasons that are unclear to me, I've seen more than one science fiction universe where starships were detectable at a distance of many parseces as long as they were moving faster than light, but are practically invisible once they turn off their FTL drive. Or when the drive shuts off due to a malfunction or something.
This tends to appear in order to support one of two possible story plots:
- The protagonist's starship is being hotly pursued by an enemy starship with too many guns, so the protagonist turns off the stardrive hoping to become a microscopic needle hiding inside an astronomically sized haystack.
- The protagonist's starship is off on a jaunt somewhere, suffers a drive malfunction, and the rescue ships have to try and find them before the oxygen runs out.
Matter transmitters (transmats) or stargates come under the Landis classification of [1.0] Discontinuous Drives ("teleport-like"). Basically the starship vanishes at point A and suddenly appears at point B, without traveling through the points in between.
The transmat type with the fewest nasty unintended consequences is the kind that requires both a transmitter and a receiver. And there are quite a few science fiction stories that impose the same restriction on their starships in order to make interesting implications.
The fundamental idea is that FTL starships can travel between transmat pairs instantaneously (or at least vastly faster than light would take). BUT before starships can travel to a new star, some poor SLOWER-than-light starship has to take several decades slogging through the light years in order to transport a transmat to the new destination. Once it arrives, it activates the transmat and suddenly the new star is part of the stargate network.
There are a few interesting implications:
- The rate of expansion of an interstellar empire is limited to less than the speed of light, quite a bit less if the slower-than-light ships are underpowered.
- If a star system only has one transmat and that is rendered inoperable, the system is cut off from the stargate network. At least until a new one can be manufactured (in some science fiction they cannot) or until an STL ship takes several decades to ship a new one.
- If both transmitting and receiving transmats have to cooperate, then it is very difficult to invade another star system. In Stargate SG-1, the Earth stargate is equipped with a metal iris to prevent the emergence of alien invaders.
- Some transmats have a aperture size. Meaning a starship with a cross-section larger than the aperture cannot travel through the stargate, at least without slicing off parts of the hull. This is used in John Lumpkin's Human Reach novels.
- A star system that wanted to break away from their interstellar empire would gain independence by destroying all the transmats connected to the empire. They now have time to build defences, up to the point when an imperial STL ship arrives with a replacement transmat.
- It is very difficult to invade another star system by STL ship lugging a transmat. The defender wil have decades to detect the incoming STL ship and attack it. The invader's task is even more difficult since STL ships are always severely mass limited; i.e., it cannot afford fancy extra like weapons or armor. It takes unreasonable amounts of energy to delta V the STL ship's mass up to relativistic velocities. This is used in the game Web and Starship.
- There has been a science fiction story or two where the expanding Terran civilization sends a starship through a transmat and the ship accidentally arrives at an alien built transmat of which the Terrans were unaware. This is used in Poul Anderson's The Enemy Stars.
- If rival starfleets are doing battle in a star system, they generally are scrupulously careful not to damage the transmat. Since doing so can cut off the star system from the transmat network for times ranging from several decades to forever, deliberate destruction is considered to be the nuclear option. War to the knife, in other words. This is used in Babylon-5.
We must not forget the masterful selection of FTL limitations which created the fascinating tactical situation in the wargame Web and Starship (keep in mind this is a paper-and cardboard tabletop game, not a computer game). The game designer (the legendary Greg Costikyan) wanted to create the world's first balanced three-player game. Up until now, all three player games in practice tend to devolve into two players ganging up on the third player (i.e., they are unbalanced). Mr. Costikyan wanted to design a game that avoided this. The mechanism depended upon the constraints of the FTL system.
The situation starts with two alien races: the Gwynhyfarr (hereafter referred to as "Birds") and the Pereen (hereafter referred to as "Moles"). Each has a totally different type of FTL transport system. And, as will become an important point later, neither can use or even comprehend the others FTL system.
The Birds have FTL starships that can travel anywhere in the universe at will. No special launch or landing sites are required. The trouble is that the starships are expensive to build (i.e., there are not many of them), and each has a limited cargo capacity.
The Moles have FTL teleportation devices. A teleporter unit must be present both at the start and at the destination. Teleportation is instantaneous. Unfortunately in order to teleport to a new planet, a teleporter unit must by shipped to the planet by a Slower-than-light robot ship. This of course takes years. The advantage of teleporter units is that they have huge cargo capacities. The Moles can move entire armies through a teleporter in a matter of hours.
When the Bird Empire and the Mole Empire expanded to the point where their borders contacted each other, war was inevitable, but futile. Both empires wanted to destroy the other and take over the enemy's habitable planets. Unfortunately, due to the limitations of their respective FTL, war was impossible.
Say the Birds want to invade a Mole planet. The Bird starships can go anywhere, so the Birds load up their limited number of starships with the few numbers of solders each ship can carry, and invade the Mole planet. Whereupon the Moles use their teleporters to instantly transport in the planetary armies of all the other Mole planets, and the combined Mole armies turn the pathetically small Bird invasion force into a smoking crater.
Say the Moles want to invade a Bird planet. The Moles load a teleport unit into a STL robot ship, aim it at the Bird planet to invade, and wait a few years for it to arrive. Years later, as it approaches the Bird planet, it is noticed by Bird space patrols, who promptly shoot it to pieces.
Until one fine day both the Birds and the Moles notice radio waves being emitted by a small planet set right in between the two empires. A planet called Earth.
Naturally both empires want to conquer Earth. It is in a very strategic position and it has an industrial base that can produce war material once the population has been enslaved. And since Earth has no empire (or even FTL capability of any kind), it should be an easy conquest.
However, Earth has a few things in its favor. For one, it knows that one empire cannot attempt to conquer it without the other empire trying to prevent it. Earth has limited diplomatic contact with both empires, so it can make deals and otherwise try to keep the two empires off balance. And in the long term, Earth has a wild card. Unlike the two empires, Earth can comprehend and eventually produce both types of FTL system. In fact, they can eventually produce the game-changing "Web Starship". This is a Bird style starship which ferries a Mole style teleport unit to strategic locations.
So as you can see, careful selection of the limits on ones FTL drive can force the desired situation to come to pass.
In the story Northshield's Triumvirate by Joseph F. Patrouch, Jr. the author deliberately mandates some limitations on the FTL drive in order to force some limitations on spacecraft design, for purposes of the plot.
If you want to do the job right, work backwards. Decide what type of universe you want for your book, figure out what implications it must have, then figure what constraints on the FTL will create the desired implications. Finally add a bit of colorful technobabble to describe the cause.
If you want to explore uncharted terrain, work forwards. Create a few unusual constraints, spend some time deducing some implications from the constraints, and see what sort of SF universe flows from the implications. You might stumble over an interesting universe for your next novel and/or game.
If you want to write science fiction stories about starship combat, you jolly well better have a set of limitations on your FTL drive that allows starship combat. Or your readers are going to point at you and laugh, and not buy any more of your books.
For instance, you do not want your FTL to permit nuclear sucker-punches.
If your FTL warships can fly through hyperspace (a "continuous" drive) and cannot be detected until they re-enter normal space, they can sucker-punch. Or if your FTL warships can instantly "jump" or teleport from one spot to any other spot they chose (a "discontinuous" drive), they too can sucker-punch.
By "nuclear sucker-punch" I mean that interstellar wars only last long enough for your hyperspace bombers to fly to the enemy's unsuspecting planets, then surprise them with an emergence into normal space only long enough to spit out a hellburner, a planet-wrecker nuclear bomb, a planet-sterilizing torch warhead, a planet-cracker antimatter warhead, or a planet-buster neutronium-antimatter warhead. Or take a bit more time to simply carpet-bomb the planet with old-school nuclear bombs. The enemy planets will be caught flat-footed, and be seared clear of life before they realized what hit them. The hyperspace bombers then fly home, only to discover that the enemy's bombers were on a similar mission and your homeworlds have also been burnt off.
Sort of like the US and Russia armed with invisible ICBMs. The first who launches will win.
The war, the lifespan of everything on Terra, and your novel will be over far too quickly (like five minutes, tops). As will the number of readers you have, because reading about such wars is intensely boring.
A defender can attempt to surround all their planets with defending fleets and orbital fortresses to counter sucker-punches, but this is a losing game. The attacking enemy always has the initative, and they can show up with a much larger fleet. Unless you happen to have enough surplus manufacturing capacity so you can park a defending fleet as large as the enemy's entire star fleet around every single one of your worlds. Which is still a waste of good manufacturing ability.
Even if for some reason such FTL drives are not used to incinerate enemy planets at the earliest opportunity, the other problem is that it makes all interstellar battles occur only by mutual consent. No intercepting incoming starfleets, no heading them off at the pass, no dry gulching, no nothing. No dramatic tales of piracy either. Your fleet and the enemy will have to come to an agreement on when and where the battle will happen. As will the pirate corsair and the hapless merchant ship, which presents a bit of a problem for the pirate. Again, quite boring. And also damaging to sales of your novels.
Another annoying part of FTL combat is keeping your opponent from running away. If you are fighting in normal space (not hyperspace or something) and have shot enough holes in your opponent to convince them that they are losing, they'll dodge into hyperspace and flee at many multiples of the speed of light. They will travel to a repair dock and return to fight another day. The same thing will happen when a pirate corsair attacks a merchant ship. The merchant will skedaddle into hyperspace like a scared jack rabbit.
Limitations to prevent this include:
- The FTL drive requires a long time to charge up the capacitors to the point where the drive can be activated. And/or require energy to be diverted from weapons and defenses into the FTL drive.
- The FTL drive can only be activated if the ship is at a certain location (see jump points). If the FTL method is some kind of stargate or other installation, you can position your ships to interdict the gate, forcing your opponent to run the gauntlet.
- If your ship grabs your opponent with a "tractor beam" or other handwaving device it will prevent your opponent from escaping.
- Mandate that combat occurs within hyperspace (not normal space), so enemy ships cannot escape unless they can out-run you. And out-run your missiles.
Otherwise you the author can just assume enemy ships fleeing is just one of those unpleasant aspects of starship combat. And forego writing romantic tales of pirates.
Greg Costikyan created a rather interesting military situation in his tabletop wargame Web and Starship. One race uses a Continuous drive (hyperspace starships), the other uses a Discontinuous drive (stargates). The consequence is side neither can invade each other due to how each FTL method's advantages and disadvantages interact with the other.
If your spacecraft use a continuous drive (hyperdrive, warp drive, or other drive where they "fly" through space instead of teleporting), there are three limits that together will allow starship combat:
- Invading starship must travel slow enough that a defender has enough time to try and stop them. if the time between being spotted at the limits of detector range and arriving at bombing positions over Terra is two nanoseconds, mutual combat is impractical. The same goes for a pirate corsair trying to jump a merchant ship.
- There must exist some kind of faster-than-light radar that can detect the invading ships. It will warn the defender planet about the invading fleet, and it will allow the defending starships to intercept said fleet. This can be a large hyper-radar installation on the planet, a network of patrolling scoutships armed with FTL radar and FTL radios to shout the alert, interstellar spy satellites, whatever. The defender ships need such radar or they won't be able to find the invaders. Nor can the pirates find the merchants.
- There must exist some kind of anti-ship weapons that will function under FTL drive. The defender has to be able to shoot at the invaders or the invaders will just go whizzing by while flipping you the bird. If your ship is travelling at twenty times the speed of light, firing a laser beam at only light speed will just have the beam pile up in front of the cannon like unrolling a roll of glowing toilet paper.
The idea is to set up some sort of situation similar to wet navy combat in the Pacific ocean in the period after the time the navy was equipped with radar, but before the advent of orbital spy satellites that can see every ship on the ocean. This is more or less the situation in the Star Trek TV show(s).
Note that Star Wars does not have FTL radar, so they can do nuclear sucker-punches. The only reason the Empire is still around is because they have thousands of times more ships than the rebels. Apparently the ships in Star Wars have no weapons that operate under FTL drive, they always exit hyperspace for normal space before they start shooting.
Often the weapons take the form of missiles equipped with their own little FTL drives. Sometimes they are laser-like directed energy weapons using some sort of energy that is faster than light. Other novels postulate that conventional weapons will work as normal, provided that you and the enemy are in the same continuum. That is weapons will work if you are both in hyperspace or both in normal space, but not if you are in one and they are in the other.
In his Polesotechnic series, Poul Anderson postulated that starship moved FTL by microjumping at a certain frequency. If the enemy ship was at a different frequency, or at the same freqency but out of phase, your ship would be transparent to the enemy's weapon fire. At least until the enemy adjusted their frequency and phase to match yours, so watch out! In Star Trek phaser beams are "warp-accelerated" to faster than light speeds, whatever that technobabble means. In David Gerrold's Yesterdays' Children the warp drive ships fire warp-drive missiles. The missiles have no explosive warhead, instead they try to ram the target. The intersection of the two warp fields will overload the target's stasis generators, instantly destroying the enemy ship.
The standard way to allow combat with discontinuous drives (jump drives or teleporting drives) is to drastically limit the locations a jump drive ship can travel to. A faster-than-light jump drive that can jump anywhere is too powerful. It can do nuke sucker-punches at will.
- A matter transmitter needing both transmitter and receiver, large enough to teleport an entire starship. Ship requires no FTL drive, the external transmitter is the drive. The locations are the sites of the transmitters and receivers. Sometimes a transmitter can send a ship to any receiver in range, sometimes they can only send ships to its paired receiver.
- A portal-to-portal "stargate". When energized this opens a hole in space between two fixed points that lots of starships can pass through. Once the power is off the gate closes. Again the ships require not FTL drive, the external stargate is the drive. Like matter transmitter these might be paired, or to selectable destinations as in Stargate SG-1.
- A permanent gate or "wormhole". This is like a stargate except it requires no power and is always open. The two ends of the wormhole are fixed, starting at one end the only possible destination is the other end.
- A multiple-connection jump drive. Fixed locations in space are "jump points", paired to another jump point light-years away. A starship equipped with a jump drive can enter a jump point location, energize its jump drive, and the ship will instantly teleport to the paired jump point. Discovering new jump points is usually difficult and tedious.
The locations ("jump points") become military choke points, thus allowing starship combat. The combat occurs in normal space so conventional weapons can be used (generally the starship is not in normal space for no longer than a fraction of a second, most are instantaneous).
Arguably this was invented by Larry Niven and Jerry Pournelle (contracting Dan Alderson), under the name "Alderson Drive". It has been used in many tabletop SF starship combat games since game designers knew a good thing when they saw it. I think the first was the game Starfire.
In science fiction, jump points are generally very limited in number within a star system.
If jump points occur naturally, there are usually fewer than 10 in any given star system.
If jump points are artificial, they are either very difficult to construct, or they are left-over technology from some long-gone Forerunner culture (i.e., they are impossible to construct, by us). In either case battle fleets will generally never ever destroy such a point, for reasons supplied by the author.
Now, in most science fiction, jump points are always detectable. If it is a permanent wormhole gate, the jump point is pretty obviously the swirly hole thingy throwing off sparks. If it is an ordinarily invisible "jump point", special detection equipment can locate them ("clumping of isogravity lines" or similar technobabble). Usually exploration scout ships when entering a new star system will use such equipment to locate all the system's jump points. After the system has been scouted, each new jump point will be explored by a scout ship.
The main exception I ran across was with the Starfire game and related novels. The reason was to craft a militarily interesting setup. There were a small number of jump points that were undetectable by sensor (the game called them "closed warp points"). The only way they could be found is if a ship entered the paired jump point (which had to be a detectable kind of course). The ship who transited the jump point would discover the location of the undetectable jump point, as would anybody nearby who noticed the transiting ship appearing out of nowhere (presumably there exist jump point pairs where both points are undetectable, but for practical purposes they do not exist since they are unfindable).
What was the game designer's motiviation to make such points? To allow (one-time) strategic surprise.
Say there was no such thing as an undetectable jump point. When a new star system was colonized, the owner would naturally build bastion space forts around all the jump points. An invasion would automatically be a slog through an endless series of defended jump points. Very boring.
Things become much more exciting if undetectable jump points exist. The star system may think it is utterly safe behind a wall of heavily defended jump points. Up until the moment when the enemy invasion fleet comes pouring through a previously unknown and totally undefended jump point, turning the system of space forts into a worthless Maginot Line.
The star system can now fortify this undetectable previously-unknown jump point. Assuming it survives the invasion fleet. The surprise only works once, but sometimes once is enough.
Undetectable jump points can provide strategic surprise more than once if the nobody else observes you using it.
For example, say one of system Alfa's jump points links to system Bravo, and Bravo only has a link to system Alfa and system Charlie. You have an inhabited planet at Alfa and Charlie, Bravo is uninhabited.
If Alfa is part of the heavily defended inner empire, system Charlie might not bother setting up space forts around the jump point to Bravo. Those forts are expensive so it is better to fortify the other jump points and assume that system Alfa will be guarding the Bravo point.
Up until the point when the enemy discovers the undetectable jump point into Bravo.
As long as the enemy is lucky, they can use the hidden jump point multiple times. As long as there are none of your ships present in system Bravo to see the enemy ships. Or if one is present, and the enemy manages to destroy it before it can escape system Bravo and sound the alarm. The enemy can vacate system Bravo through the hidden jump point, leaving you the mystery of the vanishing ship when you send your own ships into Bravo looking for the lost stray.
Later, the enemy can use system Bravo as a staging point for their invasion of system Charlie.
With jump points, you have choke points that can be defended. Battles occur because the enemy has no choice but to invade though the jump point. Though it does become difficult and fuel intensive for the defenders, since Alderson points do not orbit their primary star, while planets, orbital fortresses, anti-ship mines and blockading tasks forces have to. The defending forces must constantly be thrusting for the entire tour of duty just to maintain their position. In The Gripping Hand, sequel to The Mote in God's Eye, there is some mention of a constant stream of tanker ships travelling between the defending forces and the gas giant fuel sources. And there are only blockading spacecraft, orbital fortresses and mines are impractical.
Well, maybe not totally impractical. For mines a possibility is Dr. Robert Forward's statite concept. This uses a carefully angled solar sail to generate the constant thrust required to keep the mine stationary. I haven't done the math, but my gut feeling is that if the jump point is too far from the primary star the solar flux will be so low that even for low mass miles the sails will have to be huge. However, I am quite proud of making the jump point/statite connection, since this is actually an original idea by me (unlike almost all of the rest of this website).
While I haven't done the math on statites, David Harris did! Here is his analysis:
ClaysGhost's points out that the magnitude of the constant thrust problem depends upon how far the jump points are from the primary star.
This will make stealth difficult for a minefield. Even such low thrust from a rocket will be readily detectable, and a statite sail will be large enough to be hard to hide.
If you want to roll your own, you might find the following useful. Noted physicist and Hugo & Nebula award-winning SF author Geoffrey A. Landis has created a catalog of every kind of StarDrive that has ever existed in science fiction. It appears here with Dr. Landis' permission.
|NASA STFDS Starship|
|Wet Mass||230,000 kg|
|Normal FTL power||0.5 GW|
|Peak FTL power||0.7 GW|
This is from Vision-21: Space Travel for the Next Millennium, page 357 "Spaceport Operations for Deep Space Missions" by Alan C. Holt (1990).
I must confess that at first I thought this was some kind of April-Fools joke, since I was unaccustomed to encountering detailed specifications of a faster-than-light starship constructed out of pure handwavium in a NASA document. But there it is.
The author explains that the spacecraft can move faster than light by virtue of a "Space-Time Field Disengagement System" (STFDS), which by some hand-waving means disconnects the ship from whatever it is in the universe that constrains material objects to only move slower than c. The system uses 16 field disengagers which conveniently also provides near perfect protection against radiation and micro-meteoroids. Somehow this interacts with magnetic fields to accelerate the spacecraft.
No explanation is given for the laws of physics that would create this sci-fi marvel, only an unsubstantiated claim that the STFDS will require a sustained power of 0.5 gigawatts with 0.7 gigawatts of peak electrical power. I presume these are figures that were pulled straight out of the author's derrière.
The author does mention that interstellar exploration will be incredibly difficult at slower-than-light velocities. But it maintains that the only reason we do not have an FTL drive already is because we did not look hard enough. Helpfully the author gives a list of several fields of physics at the frontiers of science that scientists should get cracking on.
A cursory Google search uncovered another paper by the same author titled Prospects for a Breakthrough in Field Dependent Propulsion. It gives more details, but no justification is given for the alternate physics he proposes. And the propulsion system looks suspiciously like something designed for a UFO.
For slower-than-light propulsion the spacecraft uses a handwaving fusion drive with a specific impulse of 1,000 to 3,500 seconds (which is reasonable) and an array of 8 engines with a total variable thrust of 220,000 to 1,300,000 Newtons (which is unreasonable). Divided among 8 thrusters translates to 27,500 to 162,500 Newtons for each thruster. Unfortunately fusion engine thrusts are typically closer to 2,500 Newtons.
Larry Niven and Jerry Pournelle took the bull by the horns. Before they wrote their award-winning classic The Mote in God's Eye, they went to physicist Dan Alderson. Niven and Pournelle gave Alderson a list of things they wanted the proposed FTL to allow, and things to forbid. Dr. Alderson then custom designed a mostly plausible FTL drive to spec, but with additional limits. Niven and Pournelle kept within those limits, and the novel was improved as a consequence.
Antares Series, Foldpoints are areas about a thousand kilometers in diameter which are weak points in the space-time continuum. They occur in pairs, one at each end of a "foldline". A starship with a foldspace generator can enter the fold point, radiate a precise pattern of energy, and be instantly transported along a "foldline" to the foldpoint at the other end of the line (in another solar system). Foldlines do not usually connect one solar system to the next nearest, they randomly connect to a solar system tens or hundreds of light-years away.
Another FTL system that was carefully crafted in order to force a specific situation was the one created by Redmond Simonsen for the wargame StarForce: Alpha Centauri (keep in mind this is a paper-and cardboard tabletop game, not a computer game).
In the game, starships or "TeleShips" are jumped or "shifted" instantaneously from one location to another several light-years away by teams of women with psionic powers. Shifting cannot be done by a machine, it has to be done by a person. The supply of psionic or "telesthetic" women is limited. There is no way to genetically engineer them, they naturally occur at the rate of one First Order Telesthetic per million females (why? because Redmond Simonsen is trying to force a specific situation). Energy is cheap, any ore or element can be synthesized, any material good can be manufactured.
So the only valuable interstellar commodity are telesthetic women.
This has several implications. In interstellar warfare, there are no carpet bombings of planetary populations with mass destruction weapons. This would destroy the only valuable item the planet has: a population that can produce more telesthetic women. Obviously, there are no restrictions placed on population growth, and large families are encouraged by the planetary governments.
Since the population of telesthetics is so limited, they sort of know each other. They are also all members of the same Telesthetics Guild. Therefore, in ship-to-ship combat, weapons are not designed to kill.
Instead, the anti-ship weapon is sort of a telepathic command to the enemy teleship to make an uncontrolled interstellar shift into a random awkward location. Such a shift can be up to five times the distance of a safe shift, so a teleship will take a while to crawl back to the battle but will be essentially unharmed. And in any event, a teleship that can jump between the stars is not going to have any difficulty avoiding something as sluggish as a laser beam.
The main point to be aware of is that the telesthetics are not just the propulsion system, they are the anti-ship weapon as well.
Against planetary populations, teams of telesthetics can create the so-called Heissen Effect. This sedates the inhabitants, sending them to sleep. The ships then land squads of StarSoldiers in gravity sleds to take control. The inhabitants later wake up with migraine headaches and a newly installed government.
Teleships have a maximum safe shift limit of five light years. If a friendly teleship does nothing but sit stationary and telesthetically "enhance" its location, another friendly can do a safe shift to that enhanced location from up to ten light years.
Attempting to shift a distance greater than the safe limit is called "over-shifting." There is a small chance that the shift will go as planned. There is a greater chance that the shift will malfunction. A bad shift will be either a "mirror shift" where the teleship moves in the exact opposite vector, or a "randomization" where the teleship appears in a random location within twenty light-years of Sol (i.e., up to four safe shifts away from Sol).
A "Star Gate" is a nine kilometer ring of chanplastic, crammed with telesthetics intimately familiar with the fabric of local space. A teleship starting at a star gate and shifting to an unenhanced location has a safe range of ten light-years, fifteen light-years to an enhanced location. Shifting from one star gate to another has a safe range of twenty light-years.
Since telesthetics are at a premium, there are no warships or orbital fortresses. Instead in times of war, merchant ships and star gates are converted into warships and forts. Otherwise, in between wars, you would have part of the limited supply of telesthetics tied up as the propulsion system for idle warships. This does nothing except reducing the maximum size of the merchant fleet. And the same goes for star gates. They can get away with having no warships since the telesthetics are not just propulsion, they are also the weapon system.
You see the basic effect that flows from the FTL drive is that wars are relatively bloodless. The secondary effect is that pressures were created that caused wars. The latter effect is desirable, since a wargame simulation requires wars to simulate.
There are a few semi-plausible FTL methods out there. One of the most famous is Dr. Miguel Alcubierre "Warp Drive", along with Chris Van Den Broeck's improvement. Dr. Alcubierre specifically set out to make a warp drive similar to the one in Star Trek, but obeying the laws of physics. The ship is enclosed in a highly distorted bubble of spacetime. The ship technically is not moving faster than light, the warp bubble is and the ship is carried along for the ride. Problems include: it requires more energy than is contained in the entire universe to set it up, the ship inside cannot see where it is going, the ship inside cannot release the warp bubble and is thus permanently trapped without outside help, quantum mechanics says the bubble will rapidly fill up with deadly Hawking radiation and will otherwise be very unstable, and when the bubble is stopped all the interstellar particles swept up will be emitted as a planet-destroying burst of gamma-rays and high energy particles in the direction of travel.
There are others at Dr. John Cramer's Alternate View archives, Edward Halerewicz, Jr.'s Warp Physics site, Marcelo B. Ribeiro's Warp Drive Theory site, Lawrence H. Ford and Thomas A. Roman's Scientific American article Negative Energy, Wormholes and Warp Drive, David Waite's Modern Relativity site (if you can understand the math), and NASA's Warp Drive When?
More on the fringe is Burkhard Heim and his theory of everything. If the theory describes reality, it could give a form of FTL travel with an artifical gravity propulsion system at no extra charge. You can read the research paper and the expanded version here.
- Hainish Cycle by Ursula K. Le Guin: Ansible (name comes from "anserable"). The term has also been used by Terry Bisson, Orson Scott Card, L. A. Graf, Elizabeth Moon, Dan Simmons, Vernor Vinge and Jason Jones.
- Singularity Sky and Iron Sunrise by Charles Stross: causal channels communicates using entangled particles. Each particle can send one bit of information then becomes worthless. In theory the communication is impossible to be eavesdropped. In a fascinating twist there does exist FTL spacecraft, but if such spacecraft transport entangled particles they become unentangled and worthless. The causal channel particles have to be shipped slower than light by Starwisp at great expense.
- The Quincunx of Time and others by James Blish: The Dirac communicator was named after Paul Dirac who predicted antimatter. It communicates instantly and has infinite range. So all sentient creatures in all the galaxies can listen in to what you say. As it turns out it is even worse than that. Each transmission starts with a "beep" noise. As it turns out, the beep is the sum total of all Dirac messages ever sent in all the past and all the future. By demultiplexing you too can receive messages from the future and violate causality.
About every six months or so, some science writer stumbles over a reference to "quantum entanglement" or "Bell's Inequality" or "spooky action at a distance", then immediately writes an article or blog post about OMG! Quantum Mechanics can send radio messages faster than light!
Short answer: No, it won't work.
Slightly longer answer: When you send the message, it will technically arrive faster than light. But the message will be in two parts: a scrambled sequence of numbers at the source, and a second scrambled sequence at the destination. The only way to decode the message is with both sequences. So the source has to send the first scrambled sequence to the destination over conventional just-as-fast-as-light radio. Which sort of defeats the purpose.
After receiving both parts of the message at a rate equal to the speed of light, you can find out after the fact that yes indeed there was some faster-than-light communication. Oh, my, wasn't that pointless?
Back in 1930, several physicists in general and Albert Einstein in particular were quite upset when Quantum Mechanics was invented. Everything about QM was offensive to those who like their physics logical, deterministic, and non-weird. Einstein and co-authors Boris Podolsky and Nathan Rosen wrote a paper in 1935 demonstrating that Quantum Mechanics had to be utterly wrong, or at the very least quite incomplete. The paper set forth a paradox. The two solutions were [a] Quantum Mechanics is wrong or incomplete or [b] there exists bizarre spooky action at a distance which travels faster than light (actually it is instantaneous). Since [b] was obviously impossible, Einstein and his co-authors smugly sat back and waited for Quantum Mechanics to be discarded into the dust-bin of history.
Unfortunately for Einstein et al, in 1964 some clown named Dr. John Stewart Bell wrote a paper showing how to test the paradox (called "Bell's Inequality"), and to the horror of the foes of quantum mechanics it turned out that bizarre spooky action at a distance which travels faster than light actually happens.
This saved quantum mechanics from the EPR paradox, but now all the physicists had to deal with this obnoxious FTL action at a distance. As mentioned above, physicists hate FTL because it destroys causality and thus makes the entire structure of Science collapse into a flaming ruin.
As it turns out: yes, the FTL effect is real but no you can't use it for anything useful. Physicists heaved a sigh of relief (and science fiction writers became quite angry).
Why can't you use it for anything useful? Well that's complicated. Here is how Heinz R. Pagels puts it: