ScienceWise - Mar/Apr 2008

Bend it like Bosons

Article Illustration
These two magnifiers employ the same basic principle, but getting from left to right took humanity about 3000 years. Fortunately in the century since this beautiful brass microscope was made, we’ve picked the pace up a little.

The Editors Corner

We’re covering a couple of stories on optics in this issue, one about human engineered optical materials (page6) and one about an amazing natural instrument - the eye (page 10). Both human engineers and nature tend to employ much the same principles. Sometimes because we copy nature but often because when faced with a given set of physical laws and a given problem, there is only one good solution. This situation can been seen time and again in the history of invention. It’s easy to make the mistake of thinking that one has a good idea and that it’s new and amazing. Then to discover many others have reached the same conclusion. Throughout history widely separated groups of humans have often developed similar technologies and social traditions in response to being faced with similar biology and similar problems. I suppose its what makes all cultures more similar than they are different.

During prehistory many humans must have noticed that drops of water bend light in strange ways and that if correctly placed, have the ability to make things appear larger. Those fortunate enough to live in regions where natural crystals like quartz were polished round by rivers would doubtless have made use of these natural magnifiers. Some archeologists argue that an ancient biconvex quartz crystal found in Nineveh (now a part of Iraq) is evidence for use of lenses at least 2500 years ago. Others suggest that this is putting a modern functional interpretation on an ancient object. Whichever is true, the lens’ original owner would have been just as intelligent as you and I and surely can’t have failed to notice that it magnified objects.

What I personally find strange is that it took humans so long to develop better optical instruments. Perhaps that’s the perspective of a scientist interpreting history using modern concepts? Perhaps that’s why they don’t let scientists teach history? But whatever the reason, the development of lenses and the instruments they are used in took a very, very long time. Any simple biconvex lens will magnify but there’s a practical limit on how much. The apparent magnification depends on the ratio of the lens to eye, and lens to object distance. When this becomes about ten, you are either too close to the object to allow any light in or so far back that the field of view is tiny. The way round this took more than a thousand years to discover. Two lenses in combination, separated by a distance make a far better magnifier than one. It took another 300 years to perfect the art of designing and grinding two lenses to the required tolerance to make a microscope. Even with two lenses, you are limited to about 1500 times magnification in visible light because of diffraction. The way around this is to use electrons rather than visible light. The effective wavelength is much shorter so the diffraction limit is greatly extended. But it’s still there. Physics is a bit annoying like that, beyond every breakthrough lies another obstacle.

So what does this have to do with bosons? Well Bosons are a family of particles with integer spin that include photons of light. Their trajectory bends when entering or leaving refractive media and well, sometimes I’m stumped for a snappy title!

The Editors Corner
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