How do scientists slow light down? (Intermediate)

Recent experiments involve slowing down the speed of light to very much below its value in vacuum (c). How is this possible?

Here's a link to a news article on one such experiment.

Although the speed of light in a vacuum is constant, light slows down when travelling through a medium. This doesn't make much difference when it is travelling through air, but it does make a difference in many other media. For example, light going through glass slows down to two-thirds its speed in a vacuum. Just like it's harder for a person to move through water than through air (so people swim slower than they run), photons (massless particles that make up light) move slower when going through a medium that is difficult for them. Certain states of matter slow light down a huge amount (imagine a person trying to run through a tank of molasses or silly putty), and by using these states of matter, scientists can slow light down to a "human" speed. I'm not an expert on the physics involved, so here's a link that will provide you with more information. 

About the Author

Cathy Jordan

Cathy got her Bachelors degree from Cornell in May 2003 and her Masters of Education in May 2005. She did research studying the wind patterns on Jupiter while at Cornell. She is now an 8th grade Earth Sciences teacher in Natick, MA.

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