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Q & A: Understanding Light Through Lenses

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Most recent answer: 10/22/2007
Q:
I was doing some research on lenses and it seems that though they are useful, they haven’t really helped us (as a race) understand light in anyway (except perhaps in some experiments). Has the lens had any impact on our understanding on light, or for that matter, andything else?
- Chris (age 15)
Australia, Sydney
A:
Actually, without lenses, we would not know nearly as much about light and other sciences as we do now.

The key to lenses is an idea called Fermat's Principle. Fermat's Principle says that light will take the path that minimizes the time of travel. If you work through all the math (trust me because I've done it at least 5 times), you get the equations that describe how a lens works. In fact, very similar principles of minimization can be used to derive the laws governing mechanical motion, and they play a key role in formulating quantum mechanical descriptions of the same systems. Lenses provide a convenient, accessible example of some of the deepest principles of physics.

Lenses are then used to gather and focus light. For example, we can gather a lot of light from a very distant object and focus it all into our eyes. This is how a telescope works. A similar idea leads to microscopes. Both telescopes and microscopes have been vital in understanding many parts of science.

The benefit doesn't stop with lenses. You can carry it further to fiber optic communication, which in the backbone of the Internet and other communication systems. The same equations we used to understand the lens can be modified to transmit data down a tiny glass fiber with next to no loss.

As for understanding light, the lens still has importance. Many things that we learn about light require a very very long distance (to infinity works best) in order for us to use and experiment with. As my coherent optics professor likes to say, "Lenses bring Infinity closer." By using lenses, we can compress a system down in order to understand the wave nature of light better where we wouldn't have had the space to before.

So, yes, lenses have had a profound impact on our understanding of light and of other things in science. However, they tend to stay more in the background and are easily overlooked.

(and where would many of us be without our glasses?)

Adam (and Tom)

(published on 10/22/2007)

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