How Do Electrons Experience Interference?

Electrons

• As science has explained today, electrons are the negatively charged particles of an atom. For a long time, however, scientists believed Newton's idea that light and electricity were composed of particles. Before 1897, nobody in the field of science knew that electrons existed, or that atoms existed. Newton's idea of particles in light meant that the particles in electricity, too, would act like a BB shot from a gun and ricochet around if they hit anything. The problem was, both light and electricity did not always behave in this manner, leaving many scientists confused.

Two-Slit Experiment: General

• Thomas Young's 1803 double-slit experiment was an attempt to prove his then-wild theories that light wasn't a particle, but a wave. In the experiment, Young divided a beam of light with two openings of the same dimensions in a screen. He shone the light toward a second screen beyond. By noting where the darker areas and lighter areas shone, and comparing them to the ripple effect of water waves, Young tried to show that photons (light) moved like waves rather than particles.

Two-Slit Experiment: Electrons

• In 1897, the cathode ray tube helped scientist J.J. Thompson discover the then-mysterious electron, which he considered a particle. The electrons showed the same interference patterns as light when used in Young's two-slit experiment; however, they also still behaved as particles. Particles, when used one at a time, would bounce off and ricochet into the same place every single time whenever the gun was aimed at the same spot on the wall. Even one electron at a time behaved like a wave, though. Electrons were therefore found to be both particles and waves.

Wave Properties of Electrons

• If electrons behave as waves, then they have wave properties. This includes a wavelength. A wavelength is Planck's constant (known as h) divided by momentum (or mass multiplied by velocity (mv)). Another property is that waves are not stuck in one place. They spread through space and are never in one location - which means that electrons never sit still and their speed can't be measured. And, of course, they show interference -- for example, the way two waves combine to become one, like in a tank of water.