MadSci Network: Physics

Re: What is the smallest object visible?

Date: Wed May 6 06:21:29 1998
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Physics
ID: 894371167.Ph

What is the smallest object visible?

I have searched and searched on the internet for ever and I was incapable of finding the smallest object visible. Keep in mind that this question means the smallest object visible, period (microscopes, anything) Not to the naked eye, just visible.

The answer to this question depends on what you are using to do the "seeing." You can't image anything smaller than the wavelength of the energy (or whatever) you use. (But there are ways around that, as we'll see.)

This means that, if you mean "seeing with the eye" (using a microscope, of course), you can't see anything smaller than about a micrometer, 10-6 m, because visible light has wavelengths about that size. (See one of my previous answers.)

Electrons -- which can be described as either particles or waves -- can also be used to "see" with, and electron microscopes are used to distinguish fine structure within cells. An electron micrograph can resolve features down to about a nanometer (10-9 m).

If you use X-rays, you can resolve things down to about 1/100 the size of an atom (one picometer, or 10-12 m); this is called X-ray diffraction, although you can't really call it "seeing" because you need to do a lot of processing before you can convert the diffraction pattern into an understandable picture.

Finally, instruments which use very fine probes (the tips are one atom wide) can be used to detect roughness at the atomic scale on solid surfaces. These probes are called scanning tunneling microscopes and atomic force microscopes (as I understand it, the terms refer to two different types of instrument using similar principles), and have been used not only to "image" individual atoms but also to move them around, one atom at a time! In a famous article which appeared in (I think) Science, physicists at IBM used an AFM (or was it an STM?) probe to arrange 36 xenon atoms into the letters "IBM" on a metal surface, then used the instrument to image the result.

All this has been a very long way of saying:

  Dan Berger
  Bluffton College

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