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[http://www.extremetech.com/article2/0,1697,1855303,00.asp
The Science in Science Fiction
By M. David Stone
September 1, 2005
Science fiction writers - well, good science fiction writers - rarely make up their science out of whole cloth. One reason is that a surprisingly large percentage are scientists or engineers themselves, and even those who aren't tend to know a lot about this stuff. It was, after all, science fiction writer Arthur C. Clarke who wrote the first technical paper that suggested placing communications satellites in geosynchronous orbit - the altitude where satellites take exactly one day to circle Earth, staying stationary in relation to it.
When you know what you're talking about, borrowing from the pool of scientifically valid speculation is just as easy as making things up. The Borg's nanotechnology in Star Trek comes under that heading, for example. So does the mass driver in Robert Heinlein's The Moon is a Harsh Mistress.
Of course, some of the science in science fiction comes after the fact (read: accidentally). Science fiction writers like E.E. "Doc" Smith came up with the faster-than-light drive in the 1920s and 30s. The only grounding in then-current science was a recognition that the speed of light was a physical maximum - but they had to come up with something to get on with the story. They had no idea that by the 1990s, ideas for traveling faster than light would be showing up in scientific journals like Physical Review.
So just how much real science and technology is there in science fiction? We're glad you asked. If any of what we're about to look at seems a little far out, keep Clarke's third law in mind (we'll get to the first and second a little later): Any sufficiently advanced technology is indistinguishable from magic.
Transportation at Home
Between the beginning and end of the 20th century, traveling around the world went from slow, uncommon, and expensive to fast, routine, and affordable. A raft of science fiction stories assume the same will happen for space travel in this century. If it does, it probably won't be with rockets. One sure bet is ion drives. Science fiction writers have been using them since Jack Williamson's 1947 story The Equalizer.
You've seen them in the first (or is that fourth?) Star Wars movie too, on the Empire's T.I.E. fighters - that's short for Twin Ion Engine, of course, the ideal fighter for defending the Deathstar. In the real world, ion thrusters keep communications satellites in position. And their first use as a main drive was on NASA's Deep Space 1, launched in 1998.
Ion drives are computer controlled and have essentially no moving parts and offer over 90 - percent efficiency compared with a maximum of about 35 percent for chemical rockets. The drives use inert gasses like xenon as propellant, so they can't explode, and although they don't have enough thrust to reach Earth escape velocity, their relatively low thrust over a long period of time can boost spacecraft to much faster speeds on much less propellant than chemical rockets.
As with the chicken soup recipe that instructs you to, "first steal a chicken," an ion drive must first steal ions. Current NASA designs use a cathode to fire high energy electrons into a propellant, making individual atoms into positively charged ions by knocking electrons off. That accomplished, positive and negative electric grids accelerate the ions and spit them out at tremendous speeds - better than 88,000 mph in the case of the Deep Space 1 probe.
The really good news, though, is that there's plenty of room for improvement. The limiting factor for the speed of the ejected propellant ions, and for the thrust they produce, is voltage at the grids, and that - in theory - is unlimited.
Mass Driver
Another alternative to the rocket is the mass driver like the one in Robert Heinlein's The Moon is a Harsh Mistress.
The device is essentially an electric motor, but one with the electromagnets unwound into what's called a linear motor. This motor accelerates payloads in a straight line, firing them out the end the way a gun spits bullets from its barrel.
Prototypes have been around since 1975, thanks to research sponsored by the Space Studies Institute (SSI), a group founded by former Princeton physicist Gerard K. O'Neill. Mass drivers are designed to produce higher acceleration than humans can tolerate. SSI's goal, largely realized, was to show that the technology would work for sending material mined on the moon to construction sites in space, as a preferred alternative to hauling everything up from Earth's much stronger gravity well.
Space Elevator
Although ion drives are a good way to move around in space, they won't help you get there.
For that, one of the more promising alternatives to rockets is a space elevator, as described in Arthur C. Clarke's Fountains of Paradise. You may also remember seeing one in an episode of Star Trek: Voyager.
The basic idea is simple: Extend a cable from Earth into space. Build in a way that puts the center of gravity at geosynchronous orbit altitude, and the cable will remain stationary in relation to the Earth. You can then ride up and down the cable, just as with an elevator.
NASA examined the idea in a 1999 conference and concluded it's a realistic possibility with technology likely to be available by the end of the 21st century. Current plans, for example, suggest using the same maglev (short for magnetic levitation) technology already used on a small scale in people-movers at some airports and under development for maglev trains.
Inter - Stellar Travel Farther Away
Puttering around the solar system is all well and good, but why not cruise the galaxy?
Little things like the light-speed barrier certainly never stopped science fiction writers. Now physicists are getting in on the act. We spoke with Marc G. Millis, the project manager of the Breakthrough Propulsion Physics Project at NASA's Glenn Research Center. "Space drives, warp drives, and wormholes may sound like science fiction," Millis told us recently, "but they are being written about in reputable journals. New theories and phenomena in recent scientific literature could eventually lead to voyages to other star systems."
When serious researchers want to discuss warp drives and transportation by wormhole - but head off the giggles that can sometimes follow - metric engineering is the term they use. The term fits well, actually. The warp drive and wormhole methods take you from point A to point B by adjusting the metrics of space-time so you don't have to go faster than light.
Think of space as a sheet of paper. Mark two spots on the page about 10 inches apart, then fold the sheet over so the spots touch. A bug on the paper could then go from point A to point B in a single step (assuming you didn't crush it), rather than walking 10 inches. Do the same with space-time, bringing points together that are light years apart, and you can travel a vast distance in a hurry without getting anywhere near the speed of light. That's a wormhole.
The problem with wormholes is creating them. One approach requires cosmic strings with negative mass. While theoretically possible, such building blocks are not exactly handy. Warp drives may be more promising. In 1994, theoretical physicist Miguel Alcubierre mathematically described a warp drive's workings - not how to build one so much as what abilities you'd need to do so.
Warp Drive
Creating a warp bubble using an Alcubierre warp drive would scrunch up spacetime in the direction of motion and expand it behind. But although the bubble itself would be surfing along faster than the speed of light, space-time inside would be unaffected, and a ship there would stand still.
For a good analogy, imagine that you're on a moving sidewalk in an airport. The walkway can whisk you along at a pretty rapid clip, but relative to the other people on the belt, you're standing still, of course.
Since the ship would be standing still relative to the bubble, you'd get the added benefit of not slamming yourself and the crew off the cabin walls due to sudden acceleration and deceleration.
Teleportation
Okay. Worm holes and warp drive are possibilities, but surely something like Star Trek's transporter must be impossible, right? Well, maybe.
Until the early 1990s, most physicists would have said that transporters are impossible in principle. That changed in 1993, with the first experiment establishing quantum teleportation.
As of 2005, various research teams have teleported the quantum states of individual photons, coherent light fields, and in 2004, individual atoms. The technique qualifies as teleportation because the original is destroyed in the process of scanning it. The teleported replication is assembled from the information gained by scanning the original.
In principle, if you can teleport an atom, you can teleport a person. There's the minor issue of destroying the original in the process, of course. That doesn't sound very pleasant for the original, even if there is a replica to carry on. This wouldn't matter for freight, but there's a practical problem as well: the sheer amount of data you'd need to track every quantum state of every particle in the shipment. On the other hand, none of this may be an issue. Most researchers will tell you that as the technology works its way out of the lab, it's more likely to wind up as the basis for quantum computing than daily commuting.
Nanotechnology
Science fiction isn't just about interstellar travel over vast distances.
It also deals with the very small-scale world of nanotechnology, with sizes measured in nanometers, or billionths of a meter.
Credit for the basic concept behind nanotechnology goes to the physicist Richard Feynman, who gave a talk in 1959 suggesting a way to develop tools that could manipulate atoms and molecules directly. The term itself was first coined in a different context in the 1970s, but was redefined in the mid-80s by K. Eric Drexler to apply to technology that could do what Feynman had suggested. Drexler also explored in depth the implications of nanotechnology for everything from manufacturing to medical treatment, and he discussed the technology's potential dangers as well.
From the late 1980s to the present, nanotechnology has increasingly crept into both science fiction and reality.
In the Star Trek universe, nanotechnology is a core Borg tool, used for assimilating individuals and repairing injuries. In I, Robot, Will Smith's cop character immediately recognizes a container of nanites - another name for nano-machines or nano-bots - implying that nanites are widely used and well known. And in Terminator 3: Rise of the Machines, nanotechnology is part of the model T-X Terminatrix's arsenal that the governor of California must protect John Connor from.
All of these examples deal with nanotechnology in Drexler's original sense: machines that can control individual atoms and molecules. In the real world, the definition has changed to include any technology, in the 1-to 100-nanometer range, that also has novel properties.
The changed definition covers a category of materials that sorely needed a name. Because of quantum mechanics, the behavior of many substances alters when they come in smaller pieces or with their atoms arranged differently. And having some way to refer to nano-scale materials as a group is handy.
The carbon nano-tube, a nano-tech star, falls under the newer definition. Individual tubes, just 1 to 5 nano-meters in diameter, are essentially 1-atom thick sheets of carbon rolled into cylinders. The strands are 100 times as strong as steel, one-sixth the weight, and 20 percent more flexible. They hold heat better than copper and can carry an electrical charge at twice the speed of circuits in silicon. They are also prime candidates for building a space elevator, far more efficient power cables, a new generation of computer chips, and greatly improved armor for the military.
The nanotechnology described by this wider definition is already showing up in consumer products from clear sunscreens to stain-repellent clothing. But there's also a very different kind waiting in the wings.
Molecular Nanotechnology
To distinguish his original vision from mere technology on the nano-scale, Drexler has coined the terms molecular nanotechnology and molecular manufacturing. The underlying conceit is that machines, built on a molecular scale and modeled after those that nature uses for tasks such as proteins assembly, could build just about anything.
Drexler's new terms actually complement each other. Carbon nano-tubes, for example, are notoriously difficult to produce reliably in large quantities. Molecular manufacturing would solve that problem. We don't have a clear idea of how long molecular nanotechnology will take to move from concept to reality, but there are already some primitive nano-machines: a sensor with a switch approximately 1.5 nano-meters across counts specific kinds of molecules in a chemical sample.
This more fundamental kind of nanotechnology stands to have far more impact than what passes for nanotechnology today. At one extreme are the doomsday scenarios: self-replicating nano-bots escape a lab, multiply explosively, and turn the world into a mass of gray goo. Drexler and other researchers insist that scenario is highly improbable. (Phew!)
More likely, we'll see nano-bots assisting in areas like medicine and manufacturing. Tiny medical robots might hunt out and destroy cancer cells, clean plaque from arteries, speed bone healing, and more. Manufacturing nano-bots could build formerly inconceivable products by assembling them a molecule at a time.
In some of these capacities, though, nano-bots might replace people. That seems to make economic impact a more immediate worry than gray goo.
Above all else, nanotechnology demonstrates Clarke's third law: Any sufficiently advanced technology is indistinguishable from magic. But given arguments by some researchers that molecular manufacturing is impossible, some other laws seem appropriate: Clarke's first and second, as well as physicist and science fiction writer Gregory Benford's corollary to Clarke's third law:
The First law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
The Second Law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
And finally, Benford's Corollary: Any technology that does not appear magical is insufficiently advanced.
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