A Fifth Force?

In the famous anecdote, Galileo Galilei clambered to the top of the Leaning Tower of Pisa, simultaneously dropped cannonballs of different sizes and found that they all hit the ground at the same time. He thus convinced the world–and in the years to come, Sir Isaac Newton and Albert Einstein as well–that in a vacuum all objects, regardless of mass, fall at the same speed. Galileo’s work went unchallenged until last week, when Purdue University Physics Professor Ephraim Fischbach, three of his graduate students and S.H. Aronson, a physicist at Brookhaven National Laboratory in New York, reported discerning a previously unknown force that causes objects of different masses to fall at different rates.

If Fischbach is proved right, his hypothetical force, which he calls hypercharge, would be the fifth known basic force. (Four forces are known to exist: gravity; electromagnetism; the strong force, which binds the atomic nucleus; and the weak force, which is responsible for certain types of radioactivity.) Hypercharge, Fischbach reports in Physical Review Letters, is an extremely weak repulsive force that acts between objects no more than about 600 feet apart and varies in strength from element to element. It is strongest in iron and weakest in hydrogen. Thus, the physicists contend, if an iron ball and, say, a feather were released simultaneously in a vacuum, the iron’s repulsive hypercharge would act more strongly than the feather’s to counteract the earth’s gravity–and the feather would hit first.

The team began looking for evidence of hypercharge after perceiving what Fischbach calls “funny results” in two contemporary experiments, one involving gravity tests in a deep mine, the other the behavior of subatomic particles. “We felt the results could be explained with an additional force,” says Fischbach, “so we went back to the data published by Baron Roland von Eötvös in Hungary in 1922 to see if we could find evidence.” Eötvös had indirectly measured the speeds at which objects fall and found small discrepancies, which he attributed to limitations in his equipment. Re-examining the data, the team decided that the aberrations were caused by hypercharge. But other physicists caution that more experiments are necessary before a firm conclusion can be reached. Says Harvard University’s Sheldon Glashow: “The work suggests an interesting direction, but by no means should be taken as a real discovery.”