COLUMN ONE : Rethinking Cosmic Questions : Scientists trying to solve the mysteries of the universe have been long on theories and short on data. Now, new telescopes and technology help them see the unseeable.

Ever since people first stood up amid the tall grasses and looked about the world in wonder, religion, mythology and science all have struggled to explain how the world came to be. But when it comes to creation stories, few can hold a candle to the tale cooked up by modern cosmologists.

Dialing back the cosmic clock about 15 billion years, they depict a time before time, a place before space existed. Out of nothing and nowhere, all the energy and matter in the universe exploded into existence in an event that came to be called--initially as a joke--the Big Bang.

But until quite recently, the scientific study of the universe--cosmology--was almost exclusively the playground of theorists, scientists who ply their trade primarily with pencils and brains. While masterful at spinning ideas out of faith and equations, cosmologists were pitifully short on data. They could not see or measure the phenomena they were trying to explain. “Twenty-five years ago, cosmology was very close to religion,” said physicist Roberto Peccei of UCLA.

Technology is changing all that. A new generation of telescopes with ever keener vision sees farther, and clearer, into space. New kinds of detectors look beyond light to signals carried by radio, microwave and gravity itself.

Cosmology is rapidly being transformed into an experimental enterprise, with scientists placing ever more sensitive stethoscopes on the pulse of the universe. For the first time, they can begin to see pieces of the puzzle that were nothing but theoretical constructs a decade ago.

Already, earthbound and space-based telescopes are scanning the skies for telltale winks of starlight and peculiar faint blue arcs--illusions created by huge mounds of invisible matter believed, by some, to make up most of the universe. Detectors in laboratories throughout the world lie quietly in wait, like so many fields of dreams, hoping that the mysterious particles of dark matter will come and proclaim their existence.

Meanwhile, scientists are preparing to survey 1 million galaxies, the better to see just how big structures in the universe can get. From the high cold desert to the barren South Pole, antennae are tuned to the whisper of background radiation that has persisted, unchanged, since light stopped interacting with matter about 300,000 years after the Big Bang.

And those are only the most mundane of the experiments.

Within the foreseeable future, mile-long laser beams strung like spider silk between mirrors will be ready to snare the first gravity waves rippling through the fabric of space from the crash of colliding black holes. Strings of light-sensitive detectors buried in the ice and under the ocean will flash like Christmas lights, signaling the arrival of elusive particles called neutrinos, which will carry tales of who knows what from deep space.

Using what they learn, the scientists will confirm some theories, and destroy others--making, and breaking, reputations in the process. If they succeed, they finally will be able to piece together an accurate picture of the universe. How big is it? How old? What is it made of? What will be its fate?

For now, experimenters are collecting data so fast that the immediate result is often confusion. “We’re just beginning to understand all this,” said astronomer Vera Rubin of the Carnegie Institution of Washington. “Some expect to do in a year what astronomers used to do in a lifetime.”

Added experimental cosmologist Chris Stubbs of the University of Washington: “You’ve got these things that are ridiculously far away and ridiculously faint, and . . you’ve got to make sense out of it.”

It’s an equally odd time for theorists. “At times, I miss the old days when I could just work in my office and not worry that someone would disprove my theory in a few weeks,” said Rocky Kolb of the Fermi National Accelerator Laboratory in Illinois. “It’s like being in Europe in the 15th Century and knowing a continent is out there, but you don’t know what, so you can tell all sorts of fanciful tales. Then you learn that somebody’s actually going to look at it.”

Some of those doing the looking would like nothing better than to discover the fatal crack in the existing theory that would lead to a whole new view of the universe. Universe-shattering discoveries are as good a way as any to win a Nobel Prize.

“Many of us who have worked in this field for decades still worry that the whole house of cards is going to collapse,” said Princeton cosmologist David Wilkinson. “It isn’t for lack of trying. Every young cosmologist would love to pull this thing down.”

What makes studying the universe so hard is that it’s so, well, universal. Answers to every big question tend to hang on the answers to all the rest.

Surprisingly, most of the pieces seem to fit--at least sort of--so far. The age of the universe has been narrowed to between 10 billion and 20 billion years, and the Big Bang theory looks more like reality all the time.

But many key mysteries have yet to be solved. Recent observations, for example, suggest that the universe is younger than its oldest stars--an enigma that has astronomers scrambling for explanations.

The biggest mystery, however, strikes even scientists as so astonishing as to be absurd: 99% of the universe, according to some estimates, is made of totally unfamiliar stuff. Commonly known as dark matter, it actually is mostly transparent; it neither shines nor casts a shadow. Whatever it is, it is not like us.

Solutions to the dark matter puzzle abound, and new dark matter candidates seem to proliferate like presidential hopefuls. Scientists, however, tend to be skeptical of simple answers--if only because the question is so complicated.

Until they get an answer, cosmologists will not be able to say with any confidence how old the universe is, or how big, or predict its fate.

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How do astronomers know what kinds of matter inhabit the universe? Clearly, it’s not possible to go out and inventory every speck. Matter that glows (such as stars) can be seen with telescopes. Other kinds of matter (such as planets) are harder to see.

But there’s another way to “see” matter--by watching its gravitational pull on other objects. Better telescopes have been able to track the motions of stars and galaxies with greater precision, indirectly measuring gravity’s influence with more accuracy.

All matter interacts with gravity.

In fact, the case for the existence of dark matter was first made convincingly on the basis of astronomer Rubin’s careful measurements of galaxy rotation. At the rate the galaxies were spinning, there simply was not enough visible gravitational glue to keep stars and dust from flying into space. But if gravity worked the way scientists think it does, the matter had to be hiding somewhere.

Clusters of galaxies also rotate at speeds that would tear them apart without some invisible wellspring of gravity. This is enough to convince most people that dark matter, in some form, exists.

What is dark matter? It could be something relatively simple--large, Jupiter-like planets too small to ignite into stars. Or small, dark stars, too dim to see. But dark matter has to do more than hold galaxies together.

According to some theories, it also is the glue that holds the universe together, and keeps it from expanding forever into endless space. In addition, dark matter should have the right properties to provide seeds for clumping of matter into galaxies.

Some people think that at least three varieties of dark matter may be needed to solve these problems. “Sometimes you have three puzzles and you find one answer that solves all three,” said Haim Harari, particle physicist at the Weizmann Institute of Science in Israel. “And sometimes you have three puzzles that all have a different answer.” No one is sure just what kind of puzzle dark matter is yet, which makes finding it tricky at best.

The problem is how to see something innately unseeable.

One of the most powerful new instruments for seeing invisible matter was only a theoretical glimmer in Albert Einstein’s eye a few decades ago. He saw that energy and matter are different forms of the same basic stuff.

Therefore, gravity should pull on light just as it pulls on matter. And light passing near a massive object should be bent just like light passing through a lens. While Einstein predicted that such gravitational lensing should occur, it was not actually seen until about 20 years ago. Today, it is rapidly becoming a common way of seeing invisible masses. Astronomers watch for distortions in the light from distant stars--a sure sign of unseen gravitational influences.

Experimental cosmologist Stubbs and his colleagues have been searching the skies for sudden flashes of light that signal the brightening of a star. The apparent flare-up is caused by an invisible hunk of matter that passes in front of the star, and momentarily bends its light into a focused spot. “The nice thing about these projects is that they exploit the one thing we think we understand about the dark matter--that it exerts a gravitational force,” said Stubbs.

These invisible, but ordinary, objects are collectively known as Massive Compact Halo Objects, or MACHOs, which is also the name of Stubbs’ group of researchers. MACHOs have also been seen by two other groups using gravitational lensing to look for dark matter (while competing for the least politically correct acronym for their organizations): the French group EROS and the Polish-American group OGLE.

Gravitational lensing is also behind another type of dark matter search. Instead of focusing on a distant star, the telescope looks at a background of millions of faint blue galaxies, known as “the wallpaper.”

Astronomers have seen evidence that invisible matter that sits between Earth and the wallpaper distorts the light from the galaxies into faint blue arcs. “For every patch of sky the size of the moon, if you look very deep, there are about a million galaxies,” said Kolb of the Fermi laboratory. “The junk that’s between us and them acts as a gravitational lens, so the wallpaper is distorted.”

The invisible matter that bends the light could be just about anything. “It doesn’t matter what it is,” Kolb said. It’s still one of the most direct means of mapping out where matter is in the universe.

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Almost all astronomers agree that dark matter is needed to explain why galaxies do not fly apart. But there is far less consensus about the somewhat different form of dark matter that would be required to keep the entire universe from expanding forever, eventually dissipating into nothingness. This is a particularly unsettling idea that violates some deep-seated prejudices among cosmologists, who have reasons to prefer a universe that will remain intact and eventually stop growing.

One key to this scenario, many believe, lies in proving that the elusive particle called the neutrino possesses some mass--enough, perhaps, to glue the universe together.

Until now, neutrinos have shown no signs of mass. But because there are billions in every speck of space, even a smidgen of mass would be enough to account for much of the universe’s missing mass.

Harari is pinning his hopes on an experiment being conducted at the European Center for Nuclear Research that he suggested some years ago. “I have an almost religious belief that the heaviest neutrino is the dark matter of the universe,” he said. “This experiment is designed to see if the (heaviest) neutrino has the correct mass, and it’s plenty sensitive to probe this.”

Meanwhile, in tunnels and mines under mountains, other groups continue to wait for neutrinos streaming from the sun. With the ground filtering out cosmic rays, scientists think they will be able to detect telltale streaks of light produced should a passing neutrino collide with a water molecule or another target.

By studying the aftermath of such a yet-to-be-observed collision, scientists expect to find out what, if any, mass neutrinos hold.

In all, about a dozen neutrino mass searches are planned or in progress worldwide. The Sudbury Neutrino Observatory in Canada, for example, is getting ready to lower a 58,000-pound geodesic sphere crammed with light-sensitive detectors into a 10-story-deep cavern filled with thousands of tons of water. Other experiments aim beams of neutrinos produced in accelerators at various targets, hoping to trigger a similar streak.

The galaxy rotation problem requires a slower, more sluggish kind of dark matter than neutrinos, most scientists believe. In addition, yet a third kind of dark matter may be needed to provide the seeds for the initial clumping of matter that took place in the earliest days of the universe.

The sky that astronomers see today is a canvas of pattern and structure. Galaxies group into well-defined clusters, and clusters align themselves along huge sheets of matter surrounding great voids. The question is: How did the clumping get started when the Big Bang is so formless and uniform? Where did the structure come from?

Most scientists think dark matter plays a central role. Many believe that the right recipe is likely to be a mixed bag. David Caldwell of UC Santa Barbara, along with Joel Primmack of UC Santa Cruz, has a paper coming out this month suggesting that dark matter consists of about 20% neutrinos, 5% ordinary matter and the rest more exotic varieties.

And other physicists are looking for varieties of dark matter far more exotic than neutrinos. Known as axions and WIMPs (Weakly Interactive Massive Particles), they are the subject of elaborate experiments in laboratories throughout the world. Neither of these species has yet made an appearance.

Not everyone believes the mysterious dark matter is necessary. According to Mordechai Milgrom of the Weizmann Institute, it may be more fruitful to rethink gravity. Perhaps it’s not as constant as people have thought. If gravity grew stronger over cosmological distances, then dark matter would not be required to hold things together; gravity could do it of its own accord.

Other astronomers, such as Arno Penzias at Bell Laboratories--one of the scientists who discovered the pervasive background radiation left over from the Big Bang--think cosmologists should stop searching for the missing mass and simply learn to live with the fact that the universe will expand forever.

“Certainly, the missing mass controversy is by far the most interesting (in cosmology),” he said. “Partly, because it tells us about the fate of the universe. But it also tells us something about the nature of our scientific theories. As (the universe) gets more testable, the tests don’t always work out according to people’s prejudices.”

Either way, the universe remains an enigma, wrapped in more than one mystery. And although the solution to the dark matter problem will point the way to answers about the size and age of the universe, it cannot answer them completely. For that, a half dozen other unsolved puzzles will have to show their hands.

NEXT: Soap bubbles, microwaves and the battle over size and age.

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The Big Bang and What Followed It

In the beginning, there was light--but also quarks and electrons. The Big Bang spewed out energy that condensed into radiation and particles. The quarks joined into protons and careened wildly about in a hot, dense, glowing goop as opaque as a star.

Time (300,000 years or so) passed. Space expanded. Matter cooled. The electrons and protons, electrically irresistible to each other, merged into neutral hydrogen, and from this marriage, the first atoms were born. Space between atoms became as transparent as crystal--pretty much the way it looks today.

The rest, as they say, is history. Atoms merged to form dust clouds, which grew into stars and galaxies and clusters. Stars used up their nuclear fuel, collapsed and exploded in recurring cycles, fusing elements in the process.

Occasionally, a stable planet condensed around a second-generation star, where carbon-based life forms grew into, among other things, cosmologists, the better to contemplate it all.

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Pieces of the Puzzle

Scientists all over the world are conducting experiments to answer fundamental questions about the universe. Many of the observations are interconnected, and answers to any one will provide critical clues for solving the others.

TRYING TO FIND: Structure of the universe

HOW: Using telescopes to pinpoint the locations and velocities of galaxies.

WHY: To figure out how matter is distributed.

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TRYING TO FIND: Objects of known brightness in the sky--called standard candles--such as supernovas and cepheid stars.

HOW: Using ground-based telescopes and the Hubble Space Telescope.

WHY: To determine how far away objects are. If both the distance and the velocity are known, scientists can calculate the expansion rate of the universe, and thus its age.

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WHAT: Dark matter.

HOW: Using telescopes to see distortions in the light from distant stars and galaxies as invisible masses pass in front.

HOW: Using enormous vats of water in caves or tunnels, and experiments with particle acclerators, to see if ephemeral particles called neutrinos have mass.

HOW: Using specialized laboratory-based detectors to search for exotic dark matter candidates, thus far unseen.

WHY: To find out what the universe is made of.

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TRYING TO FIND: Background microwave radiation

HOW: Using satellites, balloons and telescopes in deserts and at South Pole to look for subtle variations in temperature.

WHY: To find origin of structure in the universe. Cooler areas correspond to dense lumps of matter that would be the gravitational seeds necessary to get matter to clump into galaxies and clusters.

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TRYING TO FIND: High energy neutrinos from violent cosmic events

HOW: Using strings of light-sensitive detectors buried underground or on the ocean floor.

WHY: Objects that radiate neutrinos rather than light provide a new way to view the universe.

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TRYING TO FIND: Gravity waves rippling through space-time as a result of violent cosmic events.

HOW: Gravity wave detectors-long beams of laser light sensitive to subtle disturbances.

WHY: To learn more about gravity.

Researched by K.C. COLE / Los Angeles Times