20 light years is ~ 117,569,996,000,000 miles.
That is, roughly one hundred seventeen and a half TRILLION miles.
Can't exactly hop in the prius and drive there on a weekend.
The distance to the moon is about 240,000 miles.
It took Apollo 11 around 4 and a half days to get to the moon. Let's be nice and round it off to four. That would mean it covered about 60k miles a day (my dad's station wagon looks on in envy).
That means, at current propulsion levels (and I don't think we travel a whole lot faster in space these days), it would take about 1,959,499,933 days to get there.
1.9 billion days. Hard to wrap your head around a number so big. Maybe if we switch to years...
5,368,492 years. Five point three six eight MILLION years.
You know what happened even around 3 million years ago?
Homo erectus.
It would take us longer to get there than OUR ENTIRE SPECIES HAS EXISTED TO THIS POINT.
Your grand, or great grand, or great great grandchildren will NOT be colonizing this planet. We stand a better chance of terraforming a planet in our own solar system before we reach this one, unless there's a sudden breakthrough in space folding.