Are objects really as solid as they seem?

When I was a high school student, my teacher told me that we would never be able to see atoms with a microscope. But the year after I graduated high school (1986), three physicists - Ernst Ruska, Gerd Binnig, and Heinrich Roher - won the Nobel prize for inventing the scanning tunneling microscope (STM for short). This microscope, which uses electrons to "see" things, instead of using light, is actually able to see individual atoms. Some beautiful images of atoms on metal surfaces are available here.

When you look at STM images, the surfaces always look pretty solid. Why is that? Well, its because the STM sees the electrons that move around the atoms and these electrons move extremely fast. The image that the STM makes sees a blur that shows all the places the electrons visit while they are moving around. If it was possible to freeze the electrons at some instant in time, and then take a picture, the image would show lots of space between the atoms. In fact, empty space is about all you would see. Unfortunately, it will never be possible to take such an image because of the Heisenberg uncertainty principle.

So if materials are mostly empty space, why do they feel solid when you touch them? That's because the atoms in your hand are made up of positive and negative charges and the atoms in a surface (a table, for example) are made up of positive and negative charges. We've all learned that two charges of the same sign (positive or negative) repel one another, and when two atoms get close enough, the electrons zipping around them repel one another. This repulsion is enough to make a table feel solid.

-From Dr. Bill Atkinson, Physics at Trent University