Additional Math Pages & Resources

Monday, December 21, 2009

Bending Light Around Corners

Light radiates outward from its source in straight lines. That means if you are around the corner from a light, you are in darkness. It's the reason we have shade. If light poured around corners and filled up darkness like liquid fills up a container, we would have no shade.

Here's an example showing my friend Steve driving us across the desert in his 1956 Jaguar. The hat is providing shade on part of his face. The rest is in the direct path of the sunlight.

Sometimes we want light to shine around dark corners, so we have learned how it bends. And sometimes we can help it bend round corners!

Light hits drops of moisture in the air and shines through those drops. But in the process, the rays of light change speed. Because it is more difficult for light to travel through water than through air, some beams slow down slightly. Light is made up of a number of different frequencies and some slow more than others. That causes the beams of light to curve. The various frequencies hit our eyes in a different way than normal, so we suddenly see the colors that make up clear light.

A prism is a specially-cut and polished piece of glass or plastic whose purpose is to bend and separate rays of light. It's a mechanical means of making a rainbow.

If we want to transport light from one place to another, we use optical fibers. These consist of a core of plastic strands enclosed in a sheath of slightly different plastic. The light that goes into the fiber can bounce back and forth between the core and the sheath until it comes out the other end. Even if the fiber is bent, most of the light continues to travel through.

We can send light through optical fibers to illuminate a space at the other end, or we can receive light through optical fibers and see what's going on at the other end. There are lots of neat experiments that you can do to curve light. Just search Google for Bending Light and try some.

You'd have a hard time making this at home, but astronomers theorize that light bends when it encounters a tremendous gravitational field emanating from a star or galaxy. We think that gravity travels too. When the light and the gravity interact, light curves. This is the basis of the science fiction terms: time warp and warp speed.

Einstein and others predicted this effect, but it was not actually observed until 1979. On that car trip across Arizona and New Mexico I saw a Very Large Array of space antennas. They are hard to see in the picture, but they are scattered across the desert behind us. This is where scientists from around the world learn about Gravitational Lenses.

This NASA image shows the effect of a Gravitational Lens. You can see how the white beams of light go across a galaxy, bending around the blue (gravity field) space surrounding the planet(s).

If we can learn precisely how light is bent and reflected or refracted, scientists think we can create a way to shield or camouflage ourselves or other objects. Experiments have produced devices that can shield objects from certain types of light.

This is a popular theme in science fiction, such as H.G. Wells'  The Invisible Man, the invisibility cloak in the Harry Potter series, the alien in Predator, and the Romulan Cloaking Device in Star Trek.

You can click this link to get a scientist's take on invisibility, from Duke University.

Here are some more photos of the Jaguar - it's got curves in all the right places.

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