In 1999, astrophysicist and mathematician Jeanne Cavelos wrote a book titled The Science of Star Wars: An Astrophysicist's Independent Examination of Space Travel, Aliens, Planets, and Robots as Portrayed in the Star Wars Films and Books. Timed with the release of The Clone Wars, Scientific American has posted excerpts from Cavelos's book, including bits about the power of the Death Star, light speed travel, and Darth Vader's bionics. From SciAm:
The Death Star: Could It Destroy A Planet?
The Death Star's planet-destroying weapon is said in the Star Wars Encyclopedia to be a super-laser. While a laser is basically just light, it is light that can be focused onto a precise spot and can have high, extremely concentrated power. Lasers can produce a steady beam for long periods, or they can produce a very intense beam in short pulses, occurring thousands or millions of times per second. The amplified light of lasers can also be very powerful. A series of pulses can drill through hard materials like titanium or diamond.
A megawatt laser can burn a hole through a jet up to six miles away–though it needs to maintain contact with the aircraft for one to two seconds. In a 1998 test, MlRACL, a 2.2-megawatt laser, was able to hit a satellite in Earth orbit. MlRACL purposely did not destroy the satellite, since the test was designed merely to show that the laser could target and hit the satellite. But researchers say the laser could just as easily have melted it.
Thus it seems the lasers we have today would be capable of doing many of the things we see in Star Wars. We could injure or kill people; we could burn structures or melt holes in walls; we could destroy targeted areas of spaceships, assuming we could keep a beam on them for long enough. The main difference between Star Wars lasers and ours is the size. While we can create lasers that emit extremely powerful energies, we need to pump great energies into them to make them work. That energy source takes space, which the Death Star, at least, provides.