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How fast is the speed of light really?

Update: Thanks to our readers for pointing out some of the problems with this piece. Mark Smith came up with a short and sweet analogy for what's going on in the video below:

The times given are how long *we* perceive it takes light to travel those distances. Relativity tells us that the faster you travel, the more compressed distances become in the direction you're travelling. At the speed of light, that distance becomes zero. So from a light beam's point of view (which the physics say doesn't actually exist), it takes no time at all to travel any of the distances mentioned.”

The speed of light is one of the universe's great constants. Since it's discovery, it's provided us with all sorts of measuring sticks, including the speed limit of matter, a better way to understand time and a wonderfully simple way of discussing vast distances in the universe. It's also incredibly useful simply because it's so fast, as it allows you to read this split seconds after I've posted it and for us to receive messages from our automated space craft millions of miles away in mere minutes.

But as fast as it is, it's still slow enough that were you to hitch a lift on the back of a beam of light, like a photon riding Silver Surfer, it would take you a long, long time to get anywhere, as this excellent video showcases.

If you were to start at the heart of our solar system, with your nose touching the sun's surface – preferably with something a little heftier than factor 50 covering it – and you shot off directly away from it at the speed of light, in just ten minutes you'd have travelled over 180 million kilometres, passing the orbit of Mercury, Venus and our own little blue marble on your way out.

NB. Though that would be how we on Earth would view it, rather you, the traveller.

You won't be able to see much on your fly by though, as when you're travelling at 299,792 kilometres per second, the distance between the Earth and the Moon is traversed in just 1.3 seconds. But consider that even at this monumental speed, the fastest that anything with or without mass has ever travelled as far as we know (except perhaps the universe's original expansion), you aren't even close to leaving our solar system after 20 minutes.


And you aren't much closer at the half hour mark either. Or at 45 minutes, when you fly by Jupiter and its many moons and the Sun just looks like a brighter pinprick in a sky of stars. At that point you've travelled over three quarters of a billion kilometres and you have so much further to go if you want to get somewhere new.

To reach Pluto, that once upon a time planet, you'd need to travel for over five hours at the speed of light and catching up to Voyager, humanity's furthest ever probe would take even longer.

Of course, travelling at the speed of light yourself isn't theoretically possible, as you have mass. You could potentially hit 99.9999 per cent  the speed of light, but you would need a ridiculous amount of energy to achieve it.

If you want to get really bizarre, consider that if you were travelling at that sort of speed, it would seem to take far less time for you, than those of us back home, thanks to time dilation.

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KitGuru Says: While I think I have the science right here, my brain hurts just proof-reading it. Feel free to correct any mistakes I may have made in the comments and I'll give the article an update.

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