Probing the universe. New tools will help scientists settle -- and raise -- nagging issues
| Batavia, Ill.
EVERY other Monday, Michael Turner's colleagues get together at his house for pizza and small talk about the origin and destiny of the universe. No dabblers here. As astrophysicists at the Fermi National Accelerator Laboratory, the particpants of these semimonthly ``primordial pizza fests'' are in the vanguard of civilization's grandest intellectual adventure. Between mouthfuls of pepperoni and cheese, this band of theorists exchanges the latest notions about quarks, photinos, and all the other real or imagined scraps from which everything in the universe is made.
``We cover a lot of ground,'' reports Dr. Turner, a theoretical physicist from the University of Chicago. ``The field is moving very quickly.''
In fact, a revolution is under way in the study of the cosmos which promises to give this group, and others like it, much to chew on.
Nearly all astrophysicists accept the notion that our universe started with a ``big bang.''
From a space roughly one-trillionth the size of a proton, our observable universe exploded under conditions of phenomenal compression and temperature to the expanse being studied today.
But there the questions start to mount. How could something so presumably chaotic as the roiling primordial soup of the early universe resolve itself into the apparent order we see today? And how could it be that for the last 15 billion years the universe has remained exquisitely poised between infinite expansion and immediate collapse?
Some of the answers may not be long in coming. The new era of orbiting astronomical observatories have given researchers a clearer window on the universe than ever before.
Cosmologists, who study the universe's structures on their most massive scale, and particle physicists, who concern themselves with the universe's tiniest constituents as they might have existed at the beginning of time, have recently joined forces to try to explain the origins of the cosmos.
As a result, groups such as Dr. Turner's at Fermilab are presenting what many scientists say are vastly more plausible explanations for our universe's beginnings and present structure. They say cosmology is in the midst of a number of historic discoveries that will force textbooks to be rewritten and philosophies to be overhauled.
``In the '60s, the big deal was in trying to calculate, say, cross sections for proton scattering at 5 GeV,'' says Alan Guth, a physicist at the Massachusetts Institute of Technology and a scientist who has recently made fundamental contributions to the understanding of the Big Bang. ``Now our goals are tremendously more ambitious. We want to be able to explain everything.''
To those ends, a number of scientific instruments, now nearing completion or at the final planning stages, promise to provide a torrent of information for the theorists at Fermilab and elsewhere to consider.
Among the most greatly anticipated devices is the Hubble space telescope, scheduled to be lofted into orbit by the space shuttle in August.
Circling Earth high above the atmospheric haze that hampers the vision of its terrestrial cousins, the space telescope is expected to expand our observable universe 350 times.
That means, says Princeton University astronomer James Peebles, ``an ability to see further and further back in time.'' The space telescope should be able to view objects up to 5 billion light years distant. That will enable scientists to study objects up to 5 billion years younger than those in our solar system.
Expectations are high that the instrument will provide important clues about the formation of galaxies, the composition of the universe, as well as its age and size.
``The prospects are tremendously exciting,'' says astronomer Edward Witte, also at Princeton. ``The space telescope is going to provide a staggering amount of data.''
Physicists are having their palates whetted by the prospect of a new generation of particle-smashing accelerators. CERN, the giant European atomic research consortium straddling the Franco-Swiss border, and Fermilab are building machines of unprecedented power. Both instruments, which smack oncoming beams of subatomic particles into each other at high energies, will re-create conditions thought to have existed at the very early stages of the universe's existence.
At the planning stage is the US's Superconducting Super Collider. Perhaps 100 miles in circumference, this behemoth would simulate the environment of the universe at an earlier stage of its life than has so far been possible.
``There are a lot of little theoretical threads that have been left hanging because we haven't had powerful enough machines to decide what's really going on,'' says Harvard University physicist Sheldon Glashow. ``Instruments like the one going up at Fermilab are going to help answer a lot of questions.''
Much attention is being paid to the destiny of the cosmos as well. No one can say for sure whether the universe will continue to expand like a loaf of rising dough, collapse on itself like a deflating tire, or simply dwindle away into listless drifts of energy. But nearly every theoretician has his or her own idea.
``Right now theorists have gotten a little bit ahead of themselves,'' admits Dr. Turner. ``Cosmology is not a smooth progression where scientist `A' thinks up a theory, proposes an experiment, which then either agrees or doesn't agree with the theory. It moves in jerks, and right now there's been a lot of theoretical activity. The experiments have to catch up, and they will.''
In one area, scientists are redoubling their efforts to solve a cosmic mystery of immense scale -- the apparent fact that 90 percent of the universe appears to be missing. Clusters of galaxies, superclusters, even individual galaxies appear to mankind's most powerful telescopes to be missing much of their mass. It could be hidden as small dark stars, so-called black holes -- stars so dense that even light cannot escape their immense gravitational pull -- exotic subatomic particles or, just as likely, something no one has yet imagined.
Scientists call it the ``dark matter'' problem. The solution to this riddle is important because it may hold the key to the universe's ultimate destiny. Albert Einstein's theory of gravity holds that the fate of the universe is determined by the amount of matter and energy it contains. If that amount is greater than a certain critical value, then the universe's pell-mell expansion since the Big Bang will slow to a stop and begin to hurtle inward. Eventually, the thinking goes, a ``Big Crunch'' will result -- everything in the universe will collapse back into a point.
If the amount of matter in the universe is less, however, then the cosmos is indeed infinite and will continue to expand forever. And if it is precisely critical, then the universe, though infinite, will cease expanding.
The problem is that calculations of the gravitational tugs on stars and galaxies tell astronomers that there has to be about 10 times more matter in the universe than has been observed.
``Otherwise,'' says University of Chicago astrophysicist David Shramm, ``the clusters of galaxies would have flown apart.''
Complicating the picture further is the fact, Dr. Schramm adds, that this missing mass has to be made of something other than ``everyday'' matter. By calculating the amounts of elements such as helium and deuterium in the universe, Schramm calculated that only a certain amount of such matter could have been formed during the Big Bang. The rest of the matter is of a type perhaps not yet thought of.
And while the universe may be teetering between infinite expansion and virtual collapse, many theorists ``like to think it's going to topple on the side of collapse,'' says physicist and New York Academy of Science president Heinz Pagels. In order for that Big Crunch to come about, researchers figure there would have to be at least 100 times more matter in the universe.
So studies have been going on to see if neutrinos -- packets of supposedly massless energy that do not react with normal matter -- do in fact have a mass, and are thus responsible for part of the discrepancy.
In the mid-1970s, for example, a team of Soviet researchers reported that they had found a mass for the neutrino. Almost instantly, scientists around the world thought that this might be a solution to the missing-mass question.
``The solution seemed perfect,'' recalls University of Arizona astronomer Simon White. ``Neutrinos weren't just speculation. They were known to exist and to be completely undetectable apart from gravitational effects. So that would make missing mass impossible to observe and, at the same time, explain away the evidence.''
No one has been able to duplicate the Soviet results. At the same time, the neutrino seems to be falling out of favor as an explanation for the missing mass problem: For one thing, computer studies by Dr. White determined that if neutrinos had mass, all the galaxies in the universe would be in the process of forming, rather than being largely complete.
Even if neutrinos should turn out to be massless after all, theoreticians have dreamed up an array of exotic particles with names like winos, gravitos, and axions that could cause a similar result. Some scientists at CERN think they have already found evidence for the existence of such ``supermatter'' -- matter that flickered in and out of existance during an unimaginably brief moment during the first second of the Big Bang.
Further confirmation of these particles may have to wait until after Fermilab's colliding accelerator reaches full power this fall, or in 1986, when CERN's collider is finished, or perhaps even in the 1990s, when the SSC may be ready to run.
Black holes also have been nominated as an explanation for the missing mass. Each black hole would have the equivalent mass of several million suns, and millions of them would have to be scattered around the edge of the galaxies.
The problem, Dr. White says, is that any ``missing mass'' would have to have originated at a very early stage of the universe's development. Black holes, on the other hand, are the last stage of a star's development and are therefore not likely to have existed in great numbers at such an early time.
The other alternative may be to come up with a new theory of gravity. But such an approach would require such titantic effort and destroy so many cherished assumptions about the nature of the cosmos that most physicists would rather find the particles or stars that have so far eluded them.
And what happens if the universe is slated to expand forever?
Scientists are focusing their efforts to determine whether protons -- once thought to be unchanging and eternal -- actually do decay into energy. If they do, they says, then all matter is similarly fated.
The idea comes from certain Grand Unified Theories (GUTs), which try to tie three of nature's four fundamental forces into one great force. They say that a proton will deteriorate after 1032 years -- that's 10 with 32 zeros after it. Other GUTs say it will take 1031 years.
Whatever the length, several experiments are under way around the globe to tackle such predictions.
One of them, in an abandoned salt mine underneath the shores of Lake Erie outside Cleveland, holds 10,000 tons of water containing well over 1033 protons. The assumption is that since one can't really conduct an experiment lasting 1033 years, then collect enough protons so that if one decays, it can be spotted in a more reasonable amount of time.
The experiment has been running contrary to the predictions of the GUTS for six years: No decaying protons have been detected.
The scientists running the experiment haven't given up, however. ``We're going to be at this for another three or four years,'' reports University of Michigan physicist John van der Veldy, a member of the team from the Universities of Michigan, California at Irvine, and the Brookhaven National Laboratory that is running the operation.
While they watch their protons, new theories are being invoked to explain the large-scale structure of the universe today. The clusters of galaxies, enormous voids, and gossamer strands of nebulae may be due to the existence of 11-dimensional cosmic ``super strings,'' produced abundantly in the early universe. By breaking up into three-dimensional strings, this exotic mix of particles may have acted as seeds for the galaxies and, scientists speculate, helped form the underlying skeleton of the heavens we see today. They could also account for some of the dark matter scientists have been scratching their heads over.
``It's a messy picture and a lot of it is no doubt going to be proven wrong,'' says John Wheeler, a physicist now at the University of Texas, whose work has set a standard for three generations of physicists. On the other hand, he adds, some of it will stand up to experimental tests, and the field will move on. ``We're getting there. I think we're about 10 percent of the way. Only 90 percent to go. Not all that bad, really.''