"Would it help if I got out and pushed?"
- Princess Leia, concerning the Millennium Falcon
Definition of lightspeed travel:
This is your site guide speaking: I'm always here to help! Now sit back and imagine flying from Nevada to Germany in a few hours. We can do that. Some planes go at the speed of sound. Now imagine doing the same thing in a matter of moments. That is the speed of light. We have not been able to reach this speed yet, for various reasons explained below. And even if we could, would it be enough?
Let's do a little experiment. Han Solo blasts out of Mos Eisley spaceport in the Millennium Falcon. The stormtroopers on the planet below see this. But as he approaches the speed of light, several strange things happen. The stormtroopers pull out their scanners to take a look. The Falcon is now traveling at three-quarters the speed of light. But the ships mass seems to be one and a half times bigger than the landing records say it was after landing. That doesn't seem right, they think. Even if he jammed the whole ship full of spices it wouldn't weigh that much. And now the length of the ship has been shortened to two-thirds of what the records show! The stormtroopers compare notes for a moment, then check the scanners again. The Falcon is now traveling at .9 the speed of light. But now its mass is over twice as much as it should be, and it is less than half the original length. The stormtroopers look over their shoulders, making sure Darth Vader isn't nearby to witness their confusion, then check their scanners again. The Falcon is now traveling at .999 the speed of light! But now the ships mass is over 20 times as large as it should be, and its length is just one-twentieth of what it was. It is shrinking into nothingness! The stormtroopers, afraid crushed necks are in their futures, pull out their super-duper scanner, used only for emergencies. Using this, they look inside the Falcon itself. They scan the interior, noticing that the Falcon's clock is ticking very slowly. In fact, for every twenty seconds passing on the ground, only one second is passing in the ship! This is truly the most confusing case the stormtroopers have investigated. Checking to see theat they haven't been observed, they pack up the super-duper scanner and move quickly away.
But the ability to travel between planets is needed in almost every SciFi series conceived. Since travel between planets takes years at "sublight" speeds, and travel to another solar system can take much, much longer, science fiction authors have come up with various ways to get around the theory of relativity and have their characters travel at speeds equaling or surpassing that of light. As we all know (not!) light travels at exactly 299,792,458 meters per second (about 186,000 miles per second). This may seem like a lot, but the sun's nearest stellar neighbor, Alpha Proxima (part of the triple star Alpha Centauri) would take us 4.3 years to get to in a space ship at the speed of light. This means people in SciFi series must surpass the speed of light. But, because of reasons explained above, this is close to impossible and very impractical. Therefore SciFi authors have invented interesting ways of getting past this barrier. A very common one is to have their spaceships tunnel into another dimension (or something similar). Various names have been invented for this dimension, including Zero-Space, Hyperspace, and Gh (which stands for GALAXYhyperspatial).
What about the roadkill? Huh? Huh? If all these people travel are traveling through the universe, sometime or another they've got to hit something! Well, the fact is, almost all of these civilizations are smart enough to have thought of that. Usually they use a sort of machine or something like that to calculate the route that they take beforehand, thereby avoiding killing any galactic opossums (J). You can find out more about these navigational devices by clicking on the name of the series you want to find out about on the sidebar.
There are some very interesting theories concerning inertia, wormholes, warp drives, and quantum mechanics which would allow us to go from one place to another really fast (I mean really, really fast). A lot of them are detailed in chapter four of The Science of Star Wars, by Jean Cavelos. I strongly suggest (just like the IRS strongly suggests you pay your taxes before April 15) that you pick up this book if you are interested in the science behind any SciFi series, not just Star Wars.
Note: parts of paragraph two are paraphrased from Pg. 127 of The Science of Star Wars by Jeanne Cavelos (great book!).