May 2, 2017
##### In Brief
• As we, as humans, explore further and further into the Universe, some have wondered what it would take for us to travel a light-year?
• Specifically, for us to walk one light-year it would take about 225 million years...if we didn't take any breaks.

Thanks to Albert Einstein’s Theories of Relativity, we know that our Universe has a speed limit. This limit is set by the speed of light, which travels at a staggering  299,792 km/sec (186,282 miles per second).  If we are looking at hours, that translates to 1.1 billion km/h (670.6 million mph). For a little context, if you were traveling at the speed of light, you would be able to whip about the Earth 7.5 times each second (though you probably (definitely) wouldn’t survive the journey).

It’s pretty dang fast, which comes in handy for measurements.

Since the Universe is such a vast place, if we measured distances in miles or kilometers, we would be working with some incredibly huge numbers. As such, we measure cosmic distances according to how fast light can travel in a year. If you are wondering, there are just about 31,500,000 seconds in a year, and if you multiply this by 186,000 (the distance that light travels each second), you get 9.4 trillion km(5.9 trillion miles)—the distance that light travels in one year.

In short, on Earth, we talk about things in relation to feet or meters, but in the cosmos, we talk about things in relation to light.

For example, the Milky Way galaxy is some 100,000 light-years across, and our closest galactic neighbor, Andromeda, is some 2.5 million light-years away. In other words, it takes light 2.5 million years just to travel from our galaxy to the one that is right next to us. Remember that the next time that you see a Hubble image that shows a host of galaxies dancing across the cosmos—what you are looking at is amazingly far away.

The time that it takes for us to travel one light-year is (unsurprisingly) considerably longer than a year. In fact, it takes between six months and a year just to reach Mars, which is only 12.5 light-minutes away. And, it took New Horizons nearly a decade to make its way from Earth to Pluto, which is just “around the corner”, 4.6 light-hours away.

This duration is a bit of a problem, as it makes space exploration a painstakingly slow process.

Even if we hopped aboard the space shuttle discovery, which can travel 5 miles per second, it would take us about 37,200 years to travel one light-year. Walking? That would take us some 225 million years (that’s assuming that you managed a constant speed of 20 minutes for every mile and didn’t stop for any bathroom breaks…it would be a little trying, to say the least, especially when one considers that modern humans have only been around for about 200,000 years).

The worst thing? Even after all that time, we still wouldn’t be anywhere even remotely interesting. The closest star, Proxima Centauri, is more than four light-years away.