Space is vast.
Light travels at just under 300,000 kilometres per second or about a billion kilometres per hour. Yet even at that nippy speed light takes about a second to reach us from the Moon, 8 minutes from the sun and a staggering 4 years to reach us from Proxima Centauri, the nearest star outside our solar system.
The laws of physics as we understand them include a ban against travelling faster than light - and we have no way to reach anything close to that speed anyway. That's why fictional interstellar voyagers usually have some convenient trick to get from to from one star to the next without really covering the yawning gulf of space: a warp drive, a wormhole, some kind of quantum thingamajig or the like. Because nothing brings the story to a halt faster than a dose of realism in the interstellar travel department.
But just because realistic interstellar travel is unattractive to authors and screenwriters doesn't mean it's beyond our abilities. Despite the the mind-boggling scale of interstellar distances it is possible to contemplate ways to cross them, even with our current level of technology.
We don't know how to reach the speed of light but we might, with some patience, be able to accelerate a ship to a small fraction of it. Not with the chemical rockets we presently use to reach orbit; those are peashooters good only for puddling around our own and nearby planets. No, to reach the stars we'd have to go nuclear.
Probably the best known interstellar design is the system known as Project Orion that was seriously considered in America in the middle of last century, and occasionally pops up again in modified form. An Orion spacecraft is driven by nuclear pulse propulsion which involves setting off nuclear bombs just behind the ship - hundreds or thousands of them, in quick succession. The explosions act on a heavy "pusher plate" at the rear of the spacecraft and accelerate it forward.
Spacecraft of the Orion type or similar could reach about 1 per cent to 10 per cent the speed of light, allowing us to reach a nearby star in a few centuries. Barring a revolution in extending the human lifespan anyone who embarked on this voyage would die along the way so the crew of an interstellar spacecraft would have to be a breeding population, a veritable space colony. Several generations would come and go in space just so their descendants could reach the destination. Ironically, without a crew of fragile humans complicating matters the trip could probably be done within a human lifespan.
These machines are certainly possible - though perhaps not practical since the cost would cripple any nation that tried to build one. But as our abilities improve, interstellar travel may start to look reasonable.
Mind you there are dozens of other knotty problems that must be solved: the International Space Station is dirty and smelly after just 12 years of use let alone a hundred or 500.
Interstellar travel is an exciting prospect - but it's not like on TV.
- The Press