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:

I hope I didn't miss any.

1 Thanks to Demeter and Gorgonzola for reminding me about Ender's Game et seq.

2 Thanks to Gorgonzola for calling me back to the ochre vegetation etc. Gorgonzola prefers to refer to John Carter's trick as "astral projection" rather than teleportation. He concedes that the distinction is a subtle one.
There is one kind of plot device you're forgetting:


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.

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.
But why are these three advances so vital? We were able to make it to the moon without such advances; why would we need additional advances? The reason is because space is big, bigger than anything imaginable.

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 violates 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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