arrange the properties of elementary particles into curious arrays, he speculated that these patterns stemmed from groupings of yet more fundamental objects called quarks. If he had turned out to be wrong, his methods would have been deemed numerological hokum. But he was right, and his insight led to the modern field of quantum chromodynamics—the theory of the strong nuclear interaction that binds protons and neutrons together.

Following a similar hunch, Dirac bet that the coincidence he discovered between various large numbers in the universe stemmed from a fundamental principle of nature. He proposed that the ratio of the strengths of the gravitational and electromagnetic forces was equal in the cosmic beginning but diminished proportionally with each atomic interaction. That is, each time the “clock” of a hydrogen atom ticked, gravity would become slightly weaker. Consequently, by 1040 ticks, gravity would be that much scrawnier than still-brawny electromagnetism—the unequal match we witness today. In general form the LNH states that large dimensionless numbers should vary with the epoch of the Universe.

Is Dirac’s result profound or simply prestidigitation? In purest numerical form it is almost certainly not correct, since it does not match up with any known gravitational theory. However, there are compelling ways of altering general relativity to produce a changing gravitational strength that have attracted their share of supporters over the decades.

CHANGING GRAVITY

Spurred by Dirac’s curious notion, other physicists have attempted to develop explanations in cosmology and particle physics for why the Newtonian gravitational constant would vary. This parameter, G, an important component of general relativity as well as Newton’s law of gravitation, sets the scale of gravity. If G drops in value, the gravitational attraction between any set of masses grows correspondingly weaker.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement