Space opera cut its teeth on the ray gun, that futuristic weapon that makes stuff disappear with a concentrated beam of light. It wiped out whole cities in War of the Worlds (both the 1950s version and Tom Cruise’s remake.) They kept Leslie Nielsen’s crew safe in Forbidden Planet. And they are responsible for the deaths of countless aliens, Klingons, and red shirts in Star Trek. Star Wars, set in a civilization far more advanced than anything we can realistically envision, uses it for everything from swords to guns to a substitute for hokey religions and ancient superstitions.
But the ray gun, or rather the energy weapon seems to have fallen out of favor. Starship Troopers, the rebooted Battlestar Galactica, and others prefer good old fashioned bullets, bombs, and sophisticated versions of throwing rocks. Even Star Trek has reduced the phaser to essentially firing bullet-like bolts of energy.
Some of this has to do with research that has come about in the years since World War II. In the forties and fifties, when we had no idea how interstellar travel might work or what aliens might look like, ray guns were sufficiently futuristic. But since then, not only have lasers become common place – You can buy one at Target – but we know what nuclear weapons will do on Earth and away from it. Since that time, we’ve come up with the concept of the rail gun, the smart bullet, and the “rod from God” (or less flashily, “kinetic weapons”), a block of something – rock, metal, metallic handwavium – fired at a high rate of speed at a target. Impact would smash a spaceship and have the same great effects of a nuclear weapon without the radioactive fallout.
But the most compelling theoretical weapon is also how we might get to the stars. It’s been said that, if a power source can be used for FTL flight or even high velocity interplanetary flight, it’s powerful enough to be a weapon. David Weber uses this to great effect as his warships use components of their FTL drives to disable other ships and as a means of defense.
But still, I kinda miss the ray gun. There was something about it that, despite its destructive power, was kind of cool, that we could pack that much power into a handheld weapon that could dangle off your belt or fit in your pocket. But then they belong to an era when space opera was little more than futuristic Westerns.