Laurel Hurlburt, age 12, of Phoenix, Ariz., for the question:
How big is an atom?
A sheer cliff can stop the waves at the shore and turn them back. But those same waves flow over and around a little pebble without missing stride. The light by which we see also travels in waves. They are more complex infinitely smaller and faster than the waves on the shore. An object becomes visible because it stops the passage of light. The light turns back, carrying an image of the object for our eyes to see. An atom is too small to stop the passage of light.
For this reason an atom is invisible and always will be invisible. It is too small to be seen, even under the most powerful microscope. That little pebble was smaller than the waves on the shore and could not stop them. An atom is smaller than the wavelength of visible light. So it cannot stop the passage of light and bounce back a picture of itself.
However, this big‑little problem did not stop our scientists. They have figured out the size of an atom and checked their findings from different angles. The figures say that the atom measures 100 million to the centimeter. A centimeter is one hundredth part of a meter and a motor is slightly more than a yard. Thus a centimeter is somewhat less than half an inch.
Such a figure does not mean much to our minds. So here are some comparisons to help us grasp the size of an atom. Think of an ordinary round marble. Now think of that marble shrinking until it is 10,000 times smaller. It is now so small that it can only be seen under a very powerful microscope. But it is not so small as an atom. It must shrink until it is another 10,000 times smaller.
We are told that two billion atoms could dance on the head of a pin. Crowded together, they would fit on the point of a pin. So, if humans were as small as atoms, the world population could be housed on the top of a pin.
Another trick is to compare an atom with a pin prick in a sheet of paper. Let's magnify them both at the same rate until the pin prick is a mile wide. The atom would then be as large as the original pin prick. And, if all the atoms in a drop of water were grains of sand they would cover the whole earth.
These examples help us realize that a single atom is too small for our minds to grasp. Before we recover, we are even more amazed to learn that each atom is composed of still smaller particles. And the particles all work together in perfect order.
An atom is an orderly little solar system with a central sun and a number of whirling planets. Excepting that the sun and the planets are tiny atomic particles.
Most amazing of all is the fact that our whole world, everything in the universe, is made of atoms. Single atoms are too small to stop a sunbeam. Bulked together in countless, countless numbers they have size and weight. Your body and everything around you, even the air you breathes all are made of bitsy atoms.