Hot Universe

Man's growing interest in space and the universe is producing an ever-increasing list of theories on one of the biggest of all scientific questions: Why is the universe expanding? Why do its galaxies fly apart like marbles in an explosion, while the galaxies themselves do not expand?

Last spring, British Mathematicians Raymond A. Lyttleton and Hermann Bondi attributed the expansion of the universe to the presence of thin hydrogen gas between the galaxies, suggesting that the hydrogen atoms may have slight positive charges and therefore push one another apart by electrostatic repulsion (TIME, June 22). A still-later theory comes from Professors Thomas Gold of Cornell and Fred Hoyle of Cambridge. England. Gold and Hoyle also think that the mysterious force comes from intergalactic hydrogen gas, but they argue that its urge to expand comes from high temperature, not from electrical repulsion.

Gold and Hoyle, like Lyttleton and

Bondi, are backers of the theory of continuous creation, which holds that matter is still being created. The newly created matter is generally believed to appear throughout space in the form of hydrogen atoms (one proton and one electron each), but Gold and Hoyle now think it may first appear as neutrons. Since neutrons are unstable, they break up almost immediately, yielding equal numbers of protons and electrons. This neutron decay releases so much energy that the resulting "cosmological material" has the temperature of 1,000,000,000DEG K.*

At that temperature, the hydrogen is hotter than the center of an exploding nuclear bomb. But the gas is spread so thin between the galaxies (fewer than ten atoms per cubic yard of space) that there is no appreciable heating effect on objects it surrounds. The heat merely makes it expand like any hot, unconfined gas; and since it fills the whole universe, the universe as a whole expands.

What about the galaxies, which do not expand but merely move farther apart? Gold and Hoyle believe that great clouds of the hot cosmological gas radiate some of their heat away over the course of several billion years. As heat drops, each gas cloud cools and shrinks. At last, it reaches the critical point where gravitational attraction between its gas particles is greater than their tendency to fly apart. Then the great cloud collapses, forming a galaxy or a cluster of galaxies, each of which contains billions of stars. The galaxies, being immersed in the hot gas, continue to move away from one another. But within their narrow confines, gravitation reigns as supreme as it does on the little planets revolving around their stars.

-Kelvin: the absolute temperature scale, which starts at absolute zero, 273DEG below zero on the centigrade scale.

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