Fresh evidence has been found to suggest that the universe will cease to expand, then start to contract until it gets so dense and overheated that the act of creation is repeated in another awesome fireball.
The evidence suggests that the universe will go on expanding for another 40 billion years, then will begin to shrink and fall back on itself for another 50 billion years until the stars and planets and dust and gas throughout the whole universe are so close together that they will explode in an event as catacylsmic as the one that formed the universe more than 10 billion years ago.
Evidence for this comes from a pair of scientific satellites circling the Earth and even more recent findings by the world's largest radio telescope at Arecibo in Puerto Rico.
With the help of the satellites and the telescopes at Arecibo, scientists have learned that there is far more dust, gas and other matter in the voids of deep space than can be seen with optical telescopes or measured with conventional instruments. There is so much more matter, in fact, that it makes up almost half of what astronomers have come to call the "missing mass" that disappeared after the primordial Big Bang, the scientists say.
In the last 30 years, astronomers have evaluated the visible stars and galaxies at about 3 percent of the mass that would have had to be present at the time of creation to explain the size of the universe and the way it seems to be expanding. The other 97 percent has always been called the "missing mass."
If the missing mass should prove to be forever missing, if in fact the 97 percent does not exist, that would mean the universe would go on expanding forever. It would mean there is not enough mass in the universe to stop its expansion and force it to start contracting again.
"It would mean the stars would all burn out and the universe would become dark," said Dr. Herbert Friedman of the Naval Research Laboratory, an authority of the missing mass."It would mean the dark mass would then expand into infinity . . ."
The satellites that have helped discover fresh evidence for the missing mass are the Small Astronomy Satellite and the High Energy Astronomical Observatory, both of which were flown into earth orbit in the last two years by the Natonal Aeronautics and Space Administration. Both satellites are equipped with instruments to detect distant sources of x-rays which have their origins in superheated stars or ingalactic gas that's been heated to temperatures as high as 100 million degrees.
Astronomers have long figured that much of the missing mass lies as gas between galaxies. Both the SAS and HEAO satellites have discovered gas between the galaxies in at least three clusters of galaxies whose temperature appears to be as hot as 20 million degrees.
Gas that hot would be heated by cosmic rays and the energy of thousands of nearby stars and would be so hot that it would be unable to asborb any visible light. The gas itself would therefore radiate only x-rays. This kind of gas has been found in the Coma, Virgo and Abell galactic clusters, which are thousands of galaxies tied together by some unknown binding force.
In a galactic cluster called Virgo-A the HEAO satellite has found x-ray emissions that suggest there may be as many as 1,000 billion stars in the cluster, fully 30 times as many stars as can be seen with telescopes in Virgo-A.
"If this is typical of all clusters," said NRL's Dr. Friedman, "that might add up to enough mass all by itself to close the universe."
What the giant radio telescope at Arecibo has contributed to solving the puzzle of the missing mass is that, in looking at some 80 spiral galaxies, it cannot find the outer limits of the galaxies. No matter how far from the galactic center the telescope has searched, it still finds clouds of gas and dust dense enough to get a radar echo, even though nothing is visible where it is loking.
"In any of the galaxies we've looked at we've never come to the end of the mass in the galaxy. Never," said Dr. Frank Drake, director of the National Center for Ionospheric Research, which operates the Arecibo telescope. "What that says about the missing mass is that is a lot of it's right there in the outer parts of the galaxies and in a dark form. It just doesn't shine like stars."
Together, the clues furnished by the two satellites and the telescope at Arecibo add up to as much as half the missing mass. That still leaves a lot that's missing but Drake thinks it may all be in the form of primordial black holes - stars formed at the time of creation that collapsed immediately to objects so dense they weigh one billion tons but so small they are invisible.
"They could be all through space and we'd never know it," Drake said. "They're literally so small the only ay you'd ever find one is by running right into one."