In SF (as in life), there is always a problem with interstellar travel: Those damn stars are really far apart. Now consider physics: There's not much room to hope that we'll ever travel faster than the speed of light. If a science fiction author wants to send characters from one star to another and have them arrive before dying of old age, something's got to give. There are several standard solutions to the problem:
Faster than light travel
This one is simplest for the author, and interferes least with the plot. For those reasons, it's popular in movies where there's limited time to spend on exposition. Star Wars is an obvious example: When Luke Skywalker wants to go visit Yoda, he just hops in his spaceship and hits the gas. Iain M. Banks uses this in his Culture series. It's great for space opera and other "soft science fiction" writing, where the author doesn't want to swamp the action in elaborate lies about physics.
Cold sleep
The passengers and crew of a ship are put in suspended animation for the duration of the trip; see Orson Scott Card's The Worthing Saga for one example, and the three Alien movies for another. In the first of that series, Alien, cold sleep was not merely depicted, but used as a plot device. That was cool. In fact, cold sleep is often used as a plot device, because it's both creepy and seriously obtrusive.
Immortality
James Blish chose immortality for his Cities in Flight novels: It takes a hell of a long time to get there, but they've got time to spare. This isn't necessarily much use in a movie. There's not much to say about it, either: People get real old. They don't die. They get even older. They still don't die. Yeah, yeah, yeah. Next?
Time dilation
It takes a hell of a long time to get there, but they're travelling so fast that relativistic effects kick in, and the subjective transit time experienced within the ship is relatively brief. Those on the space ship might age two years while those on the planets of departure and destination age fifty. Vernor Vinge's A Deepness in the Sky is an example (with cold sleep thrown in too), or Robert Heinlein's Methuselah's Children (which also involves very long life spans, though no actual immortality). Then there's Orson Scott Card's Ender novels, wherein time dilation figures prominently1.
If you want to try to explain this one to an average movie audience, you're welcome to try. Nobody in Hollywood has given it a shot, as far as I know.
Teleportation
A couple of classic examples would be The Stars My Destination by Alfred Bester and Tunnel in the Sky by Robert Heinlein. Necromancer by Gordon R. Dickson pops into my head as well. Oh, and how could anybody forget John Carter, Warlord of Mars, in Edgar Rice Burroughs' classic Mars novels? John Carter just walks out into his back yard in Virginia, spreads his arms, and *poof!*, he's striding manfully across the soft carpet of ochre vegetation on the floors of the dead seas of ancient and fabulous Mars!2
There are variations on this one. Sometimes they do it by massaging their temples and vanishing; sometimes they use a machine. Still, both of those have a very high "bullshit factor". The super-duper magic-handwave nonsense in Card's Xenocide and Children of the Mind is a depressing example of how bad the bullshit factor can get when an author paints himself into a corner with the plot.
Some less blatantly wish-fulfilling ideas involve "loopholes" around the speed of light problem, such as wormholes, or other phenomena dreamed up for the occasion. Larry Niven and Jerry Pournelle invented a handwave called "tram points" for The Mote in God's Eye. Good hard science fiction writers that they are, they made the plot (not to mention the whole history of the galaxy) hinge on it. The idea is that there are certain points in space, near stars, which have a peculiar property: If you approach them at just the right speed, from just the right direction, you vanish and pop up someplace else. They never use the word "teleportation", you see, so it's still "science"!
Generation ships
The space ship is large enough (miles long) to support a self-sufficient population with adequate genetic diversity, farming, etc. The characters don't get there alive: Their descendants do. This would have caused plot problems in Star Wars, for example. "Generation ship" stories tend to focus on the trip itself, usually a small segment of it (e.g. Orphans of the Sky), but sometimes the whole journey from soup to nuts (Mayflies by Kevin O'Donnell, Jr. is a mind-blowing example of this, if you can get your hands on a copy).
This is a classic, classic science fiction gimmick. It's been done and done again, from Heinlein's Orphans of the Sky to Clarke's Rendezvous with Rama, and the prenominate Mayflies (which ought to be better known; read it if you can find it). Gene Wolfe has done a whole series on it, something about "The New Sun" or something. Personally, I find Wolfe unreadable. Then there's Eon by Greg Bear and Lovelock by Orson Scott Card and Kathryn H. Kidd (cough up the damn sequel, Orson!).
I hope I didn't miss any.
Hyperspace
Hyperspace is another plane, located outside normal space, where you can open a wormhole or jumpgate and enter hyperspace, go a few AUs, then re-enter normal space and you'll have gone the equivalent of 10 light years. It figures prominently in the Babylon 5 universe, where hyperspace can drift your ship away from navigation beacons and be lost forever, or where alien races can hide. In Babylon 5 it's done through jump gates, massive devices which open the entrance to hyperspace, or by ships powerful enough to create their own jump points. The Shadows' vessels are capable of fading in and out of hyperspace. Star Wars uses this as well. Star Trek has subspace which is a similar concept. In the Mechwarrior series, ships use hyperspace to travel quickly. The game Starlancer uses this as well.
Actually, it's misleading to say that Faster than Light travel "interferes least with the plot." That depends entirely on the author. For example, in Frank Herbert's Dune, some of the consequences of FTL travel are central to the plot.
<Dune spoiler>
Arrakis is the only place in the universe where are found the silicon-based organisms called "Worms." Worms create melange, or "spice."
Aside from spice's narcotic effects, it also induces precognition after prolonged use.
The Space Guild buys spice in copious quantities. Arrakis is the most important planet in the universe, as far as human civilisation goes, because it is the only source of the spice the Guild Navigators need so desparately. The Navigators immerse themselves in high-spice environments; aside from giving them a nasty addiction, it alters their physiology in bizarre ways.
Now, this was never really explained in Dune itself, and I haven't had the patience to read its sequels, so I had to deduce this for myself. It's pretty obvious that prophecy is a power that anyone would want to private for themselves if possible; but why it was specifically necessary for civilization to function was never quite explained. Here's what I came up with.
If you're flying a ship at faster than light speeds, you're flying blind. Unless you also have some faster than light information medium, your knowledge of your destination will, by necessity, be very out of date, possibly by millions of years, because you're gazing at stars as they were millions of light years ago, not as they are today, which is when you need the information.
Furthermore, you're going too fast to be able to make rapid course corrections, and if the star courses are more erratic than calculated, you could be off by hundreds or even millions of light-years, depending on exactly where you were aiming for and how wrong your calculations were. Who knows what obstructions may be in the way? And you could run out of fuel. And then you'd be adrift, and no one would ever, ever find you.
So, in effect, you have to have some sort of faster than light information medium. And given our knowledge of particle physics, there's no particle which travels faster than the speed of light, because when you accelerate to the speed of light, space contracts to a singularity and time dilates to eternity, so you really have nowhere to go and all the time in the universe to get there. That's the wonder of physics, you see; although light "travels" at the "speed of light" to stationary observers (which includes all non-accelerating bodies), from the light's "perspective," if you will, the particle is not travelling at all. It is already everywhere.
Of course, the ships themselves don't accelerate to this velocity; they warp space so that they actually don't have as far to go. But all the same obstructions will be there, crammed into a single warp conduit. And that's bad, very very bad, especially if you happen to hit a star on the way. Bye-bye spaceship.
So if you're looking for an FTL information medium, you need magic – or prophecy.
Hence the importance of Arrakis. Hence the plot of the damn story.
</spoiler>
State of the Universe or, a layman's factual guide to interstellar travel Where we are, and Where we want to go or, There and Back Again: A Human's Tale
Have you ever wondered when humankind will be able to travel to other planets and solar systems as easily as described in popular science fiction? This writeup is a summary of where we are and where we need to go to achieve this goal.
What's So Challenging About Interstellar Travel? The ideal propulsion system to travel between stars would be one that could transport you quickly and comfortably to other stars; envision the Enterprise from Star Trek, for example. However, before this becomes a reality, we need to achieve three distinct scientific breakthroughs:
Discovery of a means to exceed light speed All of the light that you see consists of waves that are moving extremely fast; your eyes are able to transmit these waves into, well, the images that you see. We need to be able to figure out how to move faster than these waves.
Discovery of a means to propel a vehicle without propellant When we travel about today in automobiles or trains, a great deal of space is occupied by the propellant, usually gasoline (petroleum). Since a lot of energy is needed to travel in space, we need to figure out a way to greatly reduce or eliminate the amount of space needed to store propellant.
Discovery of a means to provide energy for these devices Once we have the above problems solved, they will still need energy to start up and run. We need to figure out a method for providing this energy.
The Size of Space The distances between stars are so immense that it is almost impossible to effectively describe or even imagine the distance. What follows are a few attempts to describe these distances.
An Analogy: Let's imagine that the sun were a marble roughly half an inch in diameter. If that were the case, the Earth would be about as thick as a piece of paper, and it would be about four feet away from the "sun." The moon would revolve around the Earth at a distance of about 1/8 of an inch. Thus, we would have to travel about 400 times farther than the trip to the moon to reach the sun. If that were our goal, it would possibly be achievable using current technology. However, given this same scale, the nearest star to the sun would be about 210 miles away.
Here's another example: in the 1970s, we constructed the Voyager II spacecraft to explore our own solar system. It took approximately 14 years for this ship (which was extremely light and propelled using some of our best technology) to reach the edge of our solar system. It moves along at a speed of 37,000 miles per hour, which means it could go around the entire planet almost twice in a single hour. But it will take 80,000 years for Voyager II to reach the nearest star to Earth.
A Related Problem: The Amount of Propellant Needed Let's say, for starters, that we use the type of chemical engine used on the current space shuttles, and our goal was to use these engines to reach the nearest star in, say, 900 years. How much propellant would we need to get there? Believe it or not, we could use all of the fuel in the entire universe... and it would not be enough.
OK, so let's use plutonium-based rockets, which are 20 times more efficient (but not currently viable for space travel; this is merely theoretical). If we used these, we would have to use approximately one billion school bus sized pieces of plutonium; more than what exists on earth.
Now, let's say we were able to use the absolute bleeding edge technology for engines in space shuttles, which would probably be an ion drive engine, which is roughly 100 times more efficient, it would still take 100 school buses worth of fuel to get there.
That's reasonable, right? Except for a few things... once we got there, there would be no fuel to make us able to slow down, nor would there be any fuel at all for the return trip.
So, obviously, we need some method of propulsion with no fuel.
Research Possibilities Many general theories have sprung up addressing some potential solutions to the above problems, but most of these theories are just that, theories. Here are a couple of examples:
General Theory of Relativity In a simplified form, this states that gravity coupled with electromagnetic effects can slow time and has been observed many times in simple experimental situations. A slowing of time could enable interstellar travel.
Casimir Effect The Casimir Effect shows that plates near each other with an absence of light between them are pulled together, producing some force with no matter needed. This could potentially be the core of propulsion without fuel.
The primary problem with converting these theories into practical elements we could potentially use in interstellar travel is cost. Someone has to provide the funding for such research, and quite often areas of the government that would support such research (the National Science Foundation, NASA, etc.) are woefully underfunded. What can we do? Contact our local congressmen and tell them that they should encourage research in such areas by increasing funding to the National Science Foundation or to NASA.
Can We Do It? Given enough time and enough research, the answer is likely yes. None of what is needed violate fundamental laws of the universe, and the human race is consistently moving forward in many ways. However, a timeframe is impossible to put into place; no one can predict the birth of the next Michael Faraday or the next Albert Einstein who will lead us down the road of such discoveries. But just as Isaac Newton stood on the shoulders of giants, much research needs to be done, and that will take all of us working to make it possible by encouraging research in these areas.
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