“Seeing is believing.” “I trust my own eyes.” “Let me see for myself.” We’ve all heard such phrases. They linger in the language because they help cope with lots of things we encounter in life. But how do we deal with things too small to see? Nanotechnology is one of the hottest new sciences. By definition, it manipulates objects so tiny that people can’t relate to them. One reader, responding to last week’s column, asked in an e-mail, “What are the smallest things people can see?”
This is like questions kids ask innocently and scientists spend years trying to answer, such as, “What makes a rainbow?” and “Why can’t I see air?”
My reply, developed years ago when I worked as a volunteer at a science center, is, “The smallest thing you can see with your unaided eye is a star.”
Stars are huge, but most are so distant that only a few photons reach our eyes. So, the smallest thing you can see is the faintest star — or, as some children pointed out, maybe a galaxy — your eyes can detect.
My friend obviously meant to ask, “What’s the smallest object we can see in our hands?” You can check this for yourself. As an experiment, put a piece of cardboard against your nose, the height extending from your forehead to your cheek and the cardboard itself extended straight outward. Now put your thumb or a finger at the far end of the cardboard and slowly slide it along the side toward your face, focusing on the skin’s lines or pores. Stop when you can no longer focus, take the cardboard away from your face and measure how far away the thumb was from your eye. For most people, the distance will be 5 to 10 inches. The closer you can focus, the smaller the object you can see unaided.
At 6 inches, people can make out grains of salt or very fine sand, thin hairs and strands of lint — objects down to about 4 thousandths of an inch. Some people with naturally good eyesight, or who have trained their eyes in occupations that require good close-up vision, will see individual grains of flour, pollen or mold spores down to about 1.5 thousands of an inch. And that’s the human limit.
Talcum powder is probably the finest substance you have around the house. I’ve done this experiment with sharp-eyed kids who claim to be able to see individual grains of talc. Every time we double-checked their vision with a magnifying glass or small microscope, what they actually saw was a small clump of particles, not a single piece.
Talcum powder is milled to 10 microns’ width (a micron is 1 millionth of a meter) — about a tenth the width of a human hair.
The largest object in the world of nanotechnology is hundred times smaller than talc.
Comparing a grain of talcum powder to one of the 100-nanometer-wide crystals in my wife’s eye shadow is like comparing an NBA-regulation basketball with the diamond on her wedding ring. From a nanobot’s viewpoint (a nanobot is an ultrasmall robot) one strand of my wife’s soft, lovely hair looks bigger than Pilot Mountain appears to me — in fact, nearly twice as tall. For that matter, each cell in my wife’s body — I love every single one — is 100 to 200 times larger than the biggest object in nanospace.
And this is what concerns me about nanotechnology.
It’s been less than 50 years since Richard Feynman first proposed forging moleculescale tools, a little more than 30 since Norio Taniguchi described how to manufacture nano-sized substances and 20 years since Eric Drexler invented the idea of creating small robots that could copy themselves and assemble nanoscopic machines.
Scientists and engineers now have atomic-force probes and scanning electron microscopes that can manipulate individual atoms. European engineers have demonstrated robots that can inject fluid into specific cells and assemble and solder microcircuits. The Europeans’ Project Micron also developed an onboard digital camera that could give “eyes” to a nanobot. Most of those projects remain at the experimental level, but some could show up in commercial uses within three to five years.
Meanwhile, scientists and engineers have raced ahead with development and commercial use of nanotech products. That “clear” sunscreen you wear contains nanometer-scale particles of titanium dioxide, the same chemical used into regular sunscreen where it appears white because the particles are larger. When carbon nanotubes replace carbon fibers, golf clubs get extraordinarily strong shafts without greater stiffness. Many cosmetics use nanotech-sized particles to create special color effects; whether the ultrafine particles produce promised benefits for skin remains to be seen.
I can’t help wondering what happens if those nanoscopic particles fall through people’s skin. At nanotech sizes, a pore must seem as big as a four-lane tunnel. And if they slip through, where do those nanoparticles end up — as mascara on a heart or eye shadow on the brain?
Since I can’t see where those particles are going, I’ll watch closely where nanotechnology is headed ... in the future.