April 23rd, 2010 • 12:34 PM

Wave phenomena are characterized by what is called "interference." Transverse waves, such as those produced on the surface of water, are composed of both peaks and troughs. If two waves cross each other, the heights of the waves "add" to each other, in such a way that two peaks crossing will produce a wave whose height is enhanced, while a peak crossing a trough will produce one whose height is diminished.

If one wave encounters a barrier with two holes, each hole will become the source of a new set of waves, and thus two wave sets will propagate on the other side of the barrier. If a screen is set up further on that side, the waves will produce an interference pattern.

In the figure above, drawn by Thomas Young, two sets of water waves emanate from the slits at A and B. Each of the circles drawn represent a peak of a circular wave. At the far end is a screen. Between points D and E is the tallest wave, between C-D and E-F are shorter tall waves, and so forth. But, at C, D, E, and F the waves completely cancel each other.

If one wave encounters a barrier with two holes, each hole will become the source of a new set of waves, and thus two wave sets will propagate on the other side of the barrier. If a screen is set up further on that side, the waves will produce an interference pattern.

In the figure above, drawn by Thomas Young, two sets of water waves emanate from the slits at A and B. Each of the circles drawn represent a peak of a circular wave. At the far end is a screen. Between points D and E is the tallest wave, between C-D and E-F are shorter tall waves, and so forth. But, at C, D, E, and F the waves completely cancel each other.

A beam of light passed through two thin slits will also produce such a pattern on a screen. Thus, it was hypothesized that the light must have the same wave characteristics as water. This opened up the question, though, as to what, exactly, was waving?

—*Peter Martinson*

**Links:**

[1] http://archive.larouchepac.com/node/14253