Science: The Universe at Notre Dame

The sun radiates energy at the rate of about 77,000 horsepower from every square yard of its surface. On the sun there are so many square yards pouring out this energy that little Earth, 93,000,000 miles away, intercepts 127 trillion solar horsepower, and this is only about one-half of one billionth of the total solar energy constantly radiating out into space.

The sun is not “burning”—that is, forming oxygen compounds—but if it were, the equivalent of seven quadrillion tons of coal would have to be consumed every second to maintain its temperature, which is measured at 6,000° C. on the surface, estimated at 40,000,000° at the core. It is generally agreed that the sun continues to radiate by converting mass into energy in accordance with the Einstein equation: mass equals energy multiplied by the velocity of light.

At Notre Dame University last week was held a symposium on “The Physics of the Universe and the Nature of Primordial Particles,” attended by two Nobel Prizewinners (Arthur Holly Compton of Chicago and Carl David Anderson of Caltech), and a handful of men with radiant names in physics and astronomy. One of them, William Draper Harkins of the University of Chicago, gave his analysis of the sun’s energy-producing mechanism.

In Dr. Harkins’ opinion, the key “fuel” of the sun is hydrogen, the lightest element. In building up heavier elements— helium, carbon, oxygen, iron, etc.—the hydrogen atom is not destroyed, but becomes another kind of atom, losing in the process about eight parts in 1,000 of its mass. This small fraction, called the packing fraction, becomes energy. The process would require only about 200 million tons of hydrogen per second to maintain the sun’s estimated temperature. Hydrogen constitutes about half the matter of the sun in its present state. If it contained nothing but hydrogen originally, the half that has been converted would have served for 100 billion years. In this view, the sun is neither an oldster nor a youngster, but an early middle-aged body which has used up about half of its stellar life-substance.

On hand at the symposium last week was Canon (formerly Abbe) Georges Lemaitre of Belgium, who has been a visiting professor at Notre Dame this year, and at whose feet Einstein once respectfully sat for instruction in cosmology. Lemaitre is the proponent of the “exploding universe,” which is a sort of special case of the Expanding Universe. In this theory the universe is pictured billions of years ago as a single vast atom which blew up, so that its fragments flew in every direction like shrapnel, are still flying. The force behind this explosion is the cosmical constant of repulsion X, which opposes the force of gravity in large-scale regions of the cosmos. Last week Canon Lemaitre defended his theory against an apparent anomaly caused by the sky surveys of Harvard’s Harlow Shapley.

Dr. Shapley, who was at Notre Dame also, agrees with Lemaitre that the universe is actually expanding. But his surveys of the distant star-galaxies or island universes has shown irregular distribution —a tendency to cluster—in certain regions, although at first glance the exploding-universe theory would require a fairly uniform dispersion of the fragments.

Canon Lemaitre argued that, in the regions where clustering is observed, the cosmological constant of repulsion has got into balance with the opposing force of gravity, so that the star-swarms there are in a state of unstable equilibrium. * Any small disturbance might give gravity the upper hand, causing an increasing “local” tendency to contract or cluster. But in general, throughout the expanding universe, the cosmological constant would still hold sway.

* The mathematical consequences of the unstable equilibrium theory yield a figure for the mass of an average star-swarm, and Lemaitre finds it to be about 700 million times the mass of the sun. This is in good agreement with the figure given by Mount Wilson’s Edwin Powell Hubble.