How would you describe an atom? The most popular picture is that of a tiny solar system, with the atomic nucleus as a solid, planet-like sphere orbited by one or more electrons in a series of concentric rings. The image is simplistic, and wrong. Particle physicists know that the actual bits and pieces of which atoms are made—the protons, neutrons, and electrons—do not act much like any objects or processes with which we are familiar.

Some physicists talk about the “wave/particle duality” of the subatomic. In that scenario, sometimes an electron acts like a particle, other times it acts like a wave. Others scientists explain that the laws of nature which exist at the infinitesimal size of atomic particles simply are different from the laws that govern airplanes, trees, baseballs, and water puddles. They describe electrons as “probability waves,” or “wave packets.” Electrons are are neither particles nor waves alone, but both at the same time.

Subatomic particles even react differently to energy. Add a little energy to a proton, and nothing happens. Add a little more, and the proton jumps to what scientists call a new “quantum energy level.”

Think of the guitar string that vibrates only at a certain frequencies. Like that string, a proton or neutron can exist only at certain energy levels, and at no others. Physicists know that it is impossible to add energy continuously to a subatomic particle. But if a particle is hit with enough energy in one burst, it will transition into a higher energy state. In fact, add more and more energy, and the result is a variety of different particles.

Physicists say that such “creation” of such new particles from nothing but energy is clear eveidence that mass and energy are equivalent, as Albert Einstein argued.

Protons and electrons carry electric charges. As a result, scientists can use forces such as magnetism and electricity to control, accelerate, and detect these subatomic particles. To conduct meaningful research in this tiny world, experimental physicists such as ASU’s Ricardo Alarcon and Joseph Comfort must use massive pieces of equipment known as particle accelerators.

Accelerators come in two basic types: machines that send electrons zooming into a target, and those that speed protons into atomic collisions. Each type of accelerator is used for a different purpose.

Electrons are much less massive than protons—almost 1,800 times less massive. As a result, when electrons are speeded up inside a particle accelerator, they have much less energy than a proton speeding at the same velocity. Picture a baseball and a large truck zooming along at 90 miles per hour. The baseball is the electron; the truck is the proton.

Even though electrons essentially have no mass, electron beam accelerators allow researchers such as Alarcon and Comfort to use them as tools for probing deep into the structure of the atomic nucleus.—John Svetlik

Go to: Physical Science: Physics

Home Page | Arts | Business | Education | Engineering | Health | Life Sciences | Physical Sciences | Social Sciences

Who we are | Contact Info