Proxima Centauri, is our nearest star, about 4 light years away.
A light year is the amount of time light travels in one year, or 9,460,730,472,581 kilometers. That’s 9.46 trillion kilometers, or about 5.88 trillion miles.
The fastest space ship we ever built was the Juno spacecraft, which in 2016 broke all speed records in space with a gravity assisted acceleration up to 164,700 mph.
The problem with going much faster than that is General Relativity and propulsion. Even with all the fuel in the solar system, it would still take an infinite amount of fuel to approach the speed of light. There’s no warp speed or aliens that have somehow “broken” the laws of physics. You can’t approach the speed of light.
If, however, you could go, say 40 times faster than Juno (there’s no existing technology that would come anywhere near this speed), you’d be going about 6.58 million miles an hour. That’s a hypothetical but impossible speed by either humans or space faring aliens, but none the less, for the sake of argument, let’s say you could go that fast.
Light travels at 670,616,629 miles per hour (as a layman and lazy American I think in miles more easily). So your space craft is amazingly, impossibly, traveling slightly less than 1% the speed of light. We’ll round it up for arguments sake. You’re going now 6.7 million miles an hour. Don’t crash into an asteroid at that speed!
How long would it take to make the trip to Proxima Centauri 4 light years away? Well, if you were going 1% the speed of light (6.7 million miles an hour) it would take you 400 years to reach the nearest star.
Unfortunately, you can’t just get up and go 6.7 million miles an hour. You’ve got to build up speed, which conceivably would take years burning some kind of fuel source that would weigh as much as the Moon because you’d need so much of it (which would slow your acceleration). The problem is the faster and longer you want to burn fuel, the more fuel you need, which increases your weight and decreases your acceleration. Remember, also, as you approach any percentage of the speed of light at all, the amount of fuel required to accelerate your spacecraft any faster begins to increase exponentially because of the law of General Relativity.
At the other end of the trip you’d need the same time and fuel to slow down so you don’t overshoot your target.
People have thought about using light propulsion. From somewhere in Earth orbit, shooting a powerful laser at a reflector at the back of the outgoing spaceship. It would be slow, but eventually it would increase in speed. They’d still need fuel at the other end to slow down.
It’s difficult to know how to figure in that acceleration and deceleration process, so I usually, for the sake of argument, just double the time, which probably isn’t far off.
That would mean it would take you about 880 years to start out, accelerate to 6.8 million miles per hour, and then slow down at the other end. That’s how long it would take to reach our nearest star.
As far as we know, there’s not even any interesting planets over there. If you want to go somewhere more interesting you’d probably have to go farther out in a different direction to the Trappist-1 system, which is 40 light years away.
That would only take you 8,000 years each way. We’re talking eight thousand years. You’d need generational spacecraft, where entire civilizations lived and died for thousands of years before they reach where they’re going, and would these descendants of the original pioneers have any idea what to do when they got there?
These, depressingly, are only the closest stars, right around our neighborhood. There are many more stars in our local group, and billions more in the galaxy, and millions of galaxies.
All we can do is watch them, study them, wonder about them and so on. We will, however, never be able to visit them, and those aliens out there unable to visit us.