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How long would it take to travel a light year?

By Harriet Piercy

Nov 27, 2020

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Our universe has a speed limit, and this limit is set by the speed of light which travels at the mind boggling pace of 186,282 miles per second, or 299,792 kilometres per second. That’s 670.6 million miles per hour, or 1.1 billion kilometres per hour. Basically, if you had the ability to travel at the speed of light, you would be able to do a darting cycle around the Earth seven and a half times each second. Windburn will get ya, that’s for sure. So, when human hour’s turn to years, we’re talking light years in particular—how long would a light year take in human time?

How long would it take to travel a light year?

Thanks to Albert Einstein’s theory of relativity, which is based on two key concepts; special relativity and general relativity, we can figure this out. An overview of the thought that these theories trigger is that, well, everything is relative, but the speed of light is constant. To warp your thinking a bit: rulers and clocks, the tools that mark time and space, are not the same for different observers. However, if the speed of light is constant, as Einstein said, then time and space cannot be absolute or uniform, they must instead be subjective. Einstein read the relationship between space and time, and noticed that their consequences were intertwined. In fact, space and time can no longer be independent.

We as humans have many misconceptions of time and space, because time for one, feels like it’s relentlessly moving forward. Time to us flows, and has a direction that advances in an orderly fashion. Time has become like a backdrop in which all events take place in space, sequence and durations are measured. However, this smooth concept is challenged by Einstein’s theory of relativity whereby space and time convert into each other in such a way as to keep the speed and light constant for all observers, in other words, they depend on the motion of the observer who measures them, this is why moving objects appear to shrink. The theory is the infrastructure of our current understanding of the universe. What does this relate to in terms of calculating the speed of light then?

Keeping the perspective of a viewer in mind, and bringing in an object that travels (which is essentially what we are measuring here) let’s say, a human, that is travelling at the speed of light. To an observer, the size of the human would be miniature, but to the human travelling, they would remain their own size. Time also passes slower the faster one goes, and mass also depends on speed. The relationship between mass and speed (or energy) is calculated with the formula: E=mc^2, where E is energy, m is mass and c is the speed of light.

Now to get back to figuring out how long it would take us to travel a light year. If we were to measure distances in miles or kilometres, we would be working with enormous numbers, so we measure cosmic distances in light years according to how fast light can travel in a year. According to Futurism, 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 5.9 trillion miles (9.4 trillion kilometres) which is the distance that light travels in one year.

The time that it takes us humans to travel one light year is considerably longer than a year. To put it into context, it takes between six months and a year for us to reach Mars, which is in light year terms, 12.5 light minutes away. It took NASA’s New Horizons spacecraft almost ten human years to reach Pluto from Earth (which is ‘just around the corner’), only 4.6 light hours away.

Saying we were a space shuttle that travelled five miles per second, given that the speed of light travels at 186,282 miles per second, it would take about 37,200 human years to travel one light year. That’s a long time, and what would you see? Well, not much unfortunately. You’d be closer to the centre of our own galaxy, but with a further 26,000 light year distance still to travel. All I can really say after writing this piece is that i’m exceptionally relieved that I’m travelling at my own pace, which seems almost too fast even in relation to myself some days, but hey, it’s all relative.