The Physics 242 Puzzler

Newton's Law of Gravitation and Coulomb's Law for electric charges look very similar. Both the gravitational and electric force decrease as the inverse square of the distance between the point sources F ~ 1 / r 2 And both forces are directly proportional to the sources themselves F ~ m1m2 or q1q2 But there is one very significant difference. Mass comes in only one "type" which we arbitrarily label as positive. Charge comes in two types, positive and negative. The single type of mass means that all masses attract one another. (Mathematically, it would be just as meaningful for all masses to repel one another, but we wouldn't be here to wonder why.) But the existence of two types of charge means that charges can either attract or repel one another. In this week's lab, you will perform a series experiments that will confirm the rule that "like charges" repel and "unlike charges" attract. Here's the puzzle: Consider the possiblility of a parallel (or perhaps orthogonal) Universe with two distinct charges, but one in which like charges attract and unlike charges repel. The top picture shows a hydrogen atom from our Universe, in which the positive proton attracts a negative electron. The lower picture shows a positive proton attracting a positive electron in the parallel Universe. (Incidently, positive electrons do exist in our Universe. They are called positrons.) Would the parallel Universe be a different place if this were the only difference? Explain your reasoning, giving an example of how nature would or would not be different.

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