This GIF is a scale model that illustrates (in real time) the time it takes light to cross the distance between Earth and the Moon (about 1.26 seconds). I'm sure I've posted it before, but it's such a neat illustration of the fact that light does have a speed -- something to remember when reading about the recent hubbub surrounding a planet called Gliese 581 d.
Gliese 581 d is a planet orbiting a small red star in the Libra constellation. Picture a warm, wet world under a dusky red sun. It might have monsoons. It might even have oceans. Scientists are calling Gliese 581 d the most habitable of any exoplanet yet discovered. And (as many reporters seem keen to add) it's just 20 light-years away...
Only 20 light-years? That's not so bad. In a galaxy that's almost a hundred thousand light-years across, 20 light-years is practically right next door... Right?
Well let's remember that a "light-year" is the distance light travels in a year. And let's also remember that humans can't travel at the speed of light. We can't even come remotely close.
Apollo 10 set the speed record for any manned vehicle at 24,791 mph.
After that, the fastest manmade object ever is the Helios 2 probe. It clocked in around 157,000 mph.
Crazy fast stuff, right? But here's the kicker -- the speed of light is nearly 300 million meters a second. That's many times faster than the fastest thing humans have ever built. Ever.
Science fiction has relentlessly demystified the humbling distance of the light-year. We've all seen countless fictional spaceships zipping about from planet to planet with little more than the push of a button.
But sadly, this is the real world, and we don't have hyperdrives or warp drives or jumpdrives or stargates. What we have are rockets. Sure we've toyed with stuff like solar sails or ion engines, but nothing outside the plain Newtonian physics of just basically booking it from A to B as fast as possible. In that context, nothing outruns light, and crossing a 20 light-year distance means at least 20 years in a vacuum-sealed space capsule (and probably quite a bit longer).
Not that I believe opening a wormhole or bending spacetime are ultimately impossible goals, but they are goals well outside NASA's current budgetary restrictions. In a world wherein politically ambitious deficit hawks circle hungrily over every mundane space probe NASA proposes, defying the laws of physics is simply not on the table. (It's not even scheduled to be considered to be on the table.) In the here and now, 20 light-years may as well be a hundred million.
There's only so much ordinary people like you and me can do about all that, but it ain't nothing. Write your president. Write your congressperson. Tell them to make science a priority. Tell them to go to Mars and to keep going. Write tweets. Write blogs. Write stories. Write movies. Talk about it. Be your future's own evangelist. Dream big. Because big dreams cast long long shadows. Longer than light-years.
Look up tonight. Somewhere up in that huge night sky, there are unseen oceans shimmering under alien suns. You want to see them? Make someone else want it too.