Have you ever walked a very long way?  Maybe to the store or all the way to school?  You go for one mile, maybe two, but then you get tired.  You sweat.  You pant.  You fall to the ground.  You have run out of energy!  This is a lot different than light, which goes 92,960,000 miles to get to Earth from the sun.  And it still has energy when it gets here.  How does it do that?  And could we ever travel that quickly without breaking a sweat?


Light can travel around the world 7.5 times in just one second.  It could flash through every chore you will ever do, shoot to every place you will ever walk, speed through every race you will ever run, and still have a lot of that one second left over.  Right now, at least, no one could beat light in a race in space.  Space is the name for the place between the planets and stars with very little matter in it.  Since there's almost nothing there, it is very easy for light to move through it.  In order for us to move through space, we must use up our energy.  You use gas to go to the grocery store.  You burn up the food you eat to run races.  So what makes light so special?


The answer is that light is made up of very different stuff than anything you can hold in your hands.  It does not have any mass.  We can think of light as tiny little packets that fly through the air and don't weigh anything.  A photon is a piece of light, like a packet of energy that moves out from something that lets out light.  Since light has no mass, it does not have to follow the same rules that, say, a jelly doughnut does.  (In a race, a jelly doughnut would just fall and go splat on the ground).  So do not be mad about not being able to beat light in a race.  You have all your stuff to carry around, like your bones, your muscle, your skin, your hair, your clothes . . .  Cheer up.  Eat this jelly doughnut.  Oh, right.  It's on the ground.  Never mind.


So how could we move as fast as light?  Well, a good start would be to use some of its energy.  Just be careful when moving that fast, because if you crash into something, there will be a quick stop.  Maybe some headaches.  Maybe some crying.  That isn't what happens with light from the sun.  In fact, light is the only type of energy that doesn't need anything to get from one place to another.  This means it must hurt a lot less to crash.  Radiation is light energy that does not need matter to move from one place to another.  What happens when something has no mass and it crashes into something? 

One of two things can happen to this light.  It can either bounce off the thing it crashed against, like when you throw a bouncy ball against the wall.  Or it can stick, like if you were to throw a ball of cookie dough against the wall.  (Do not do this.)  Some photons are taken in by the things they crash into and this gives their energy to the thing.  The same thing would happen if you were to eat the cookie dough.  That's why things heat up when they are hit by light from the sun.  They are taking those heated bits of energy and it's becoming part of them.  Plants take in red light and turn it into energy we can eat.  We use that to run our race against light . . . and lose.  Hey, we can beat jelly doughnuts, though.


Let's throw a whole bunch of food at you.  Grapes, balls of cookie dough, hard boiled eggs.  You might only want to catch some of these to eat.  The light we can see is only one part of the light that comes from the sun.  Infrared light is the part of light that we feel as heat.  This light acts just like the light we can see that can bounce off or get stuck in things.  Your eyes can see the different colors of light, but not the heat part of light.  It is hard to tell this light apart from the light we can see, since the sun lets out both kinds at the same time.  Even though you can't see it, you will feel the warm part of the sunlight when it runs into you. 


Fun Fact!  We can use infrared light to see in the dark!  Infrared light sensors can read people's body heat and lets you know where they are.


So for the time being, no, we cannot beat light in a race.  We may have fast cars, we may have rockets, but they weigh thousands or even millions of pounds.  This makes them move a lot slower than photons.  Maybe one day we will find a way to beat light in a race.  Until that happens, we can be happy that light comes over 100 billion miles to give energy to our food.  That way we can run, jump, and crash, and work off that cookie dough we just ate.



References:

Universe Today.  "Radiation From the Sun"  Universe Today, 2010.  <http://www.universetoday.com/60065/radiation-from-the-sun/>

Top Documentary Films. "Through the Wormhole: Can We Travel Faster Than Light?"  Top Documentary Films, 2011.  <http://topdocumentaryfilms.com/through-the-wormhole-can-we-travel-faster-than-light/>

Ask a Physicist.  "How can photons have energy and momentum but no mass?"  Ask a Physicist, 2013.  <http://www.askamathematician.com/2010/09/q-how-can-photons-have-energy-and-momentum-but-no-mass/>

Science News For Kids.  "Higgs -- at last!"  Science News For Kids, 2012.  <http://www.sciencenewsforkids.org/2012/09/higgs-at-last/>