Space is big. I mean, really friggin’ big.
Even light, the fastest thing known to humankind, would take years to travel across the Milky Way, let alone travel to another galaxy.
By comparison, our fastest spacecraft (Voyager 1) only travels at 0.005% the speed of light. This means that it would take 80,000 years for Voyager 1 to reach the closest star, Alpha Centauri! So if humans are ever going to visit another star (let alone a distant planet such as Neptune), we certainly need to speed things up.
The good news is that theoretically, we are capable of achieving faster speeds for our spacecraft using technology that’s already available. As first proposed by Freeman Dyson in 1968, we could potentially reach speeds up to 10% of the speed of light by simply relying on nuclear pulse propulsion (essentially a series of controlled nuclear explosions). While we do have the means to go after such a technology, the major world governments have signed a pact agreeing never to detonate any nuclear devices in space, even if the device isn’t meant as a weapon. So until that changes, nuclear-propelled spaceships are not going to happen.
With nuclear-based technology out of the question, researchers at the University of Michigan are working on an alternative (and quite promising) way to increase flight speed, using a device known as the nanoparticle field emission thruster (NanoFET). In essence, NanoFET works like the Hadron Collider in that it is able to accelerate teeny-tiny nanoparticles up to very high speeds, except it can do so using an area no bigger than a postage stamp. NanoFET then ejects these fast-moving nanoparticles to create a forward-thrusting force (as per Newton’s third law of motion). Theoretically, if you eject enough nanoparticles over a long enough period of time, such constant acceleration could get you pretty close to the speed of light. Like all things though, there is a caveat. A postage stamp-sized engine isn’t going to be able to move a giant spaceship. So while this technology might help us to reach Alpha Centauri within our lifetime, at this point we’d only be able to send out a very small probe.
Now of course, any discussion of space travel would be incomplete without also mentioning some of the crazy speculative ideas that scientists have come up with. The most feasible of these would be the so-called “anti-matter rocket”. While antimatter does exist and we’ve successfully stored it in the past (albeit, for only 17 minutes), it is extremely expensive to produce and store. We’re talking $62.5 trillion dollars per gram expensive. Another fun concept is the “black hole starship”, a spacecraft that would be propelled by the forces of Hawking radiation emitted from a human-made black hole. And if complete and utter speculation is your cup of tea, then you’ll love the Alcubierre drive, a spacecraft that would be able to collapse the fabric of space at one end while simultaneously expanding it on the other end, thus forming a traveling space bubble!
Still, no matter what method of propulsion we can or cannot use, the ultimate question is will we ever reach another star system? Some experts seem to doubt that we’ll ever be able to explore beyond our solar system. Space is so gigantic that they think the energy requirements to get to the nearest star system are simply impossible to obtain.
But hey, it never hurts to dream big!