UNIVERSE IS DYING, BUT THERE'S TIME.

Byline: David L. Chandler The Boston Globe

If you like to plan far, far ahead, a report Wednesday by two astrophysicists brings good news: The universe, they say, will look pretty much the same for the next 100 trillion years or so - about 10,000 times as long as it has existed so far.

After that, though, things will start to go downhill - very, very slowly.

The new study, presented here at a meeting of the American Astronomical Society by Fred Adams and Gregory Laughlin of the University of Michigan, is titled ``The Long Term Fate and Evolution of the Universe,'' and they aren't kidding. The next 100 trillion years is just the first phase of their four-step analysis.

We're now in what they call the ``stelliferous era,'' in which stars are the most important component of the cosmos. But stars eventually die off, and the time will come, they say, when there will be no stars left in all the vastness of space.

At that point, the only thing left will be a bunch of degenerates. These are not, as the name suggests, perverts hanging around the dark alleys of the universe, but things like black holes, white dwarfs and neutron stars - the burned-out hulks of long-dead stars that physicists call ``degenerate matter.''

``The galaxy will have a very different flavor than it does today,'' Laughlin said, but it won't be as bleak as it sounds.

There will still be some brown dwarfs around - lukewarm objects that were too small to become stars.

Occasionally, a couple of brown dwarfs might bump into each other and form a mass large enough to ignite and become a star, just like in the good old days.

But the universe will be a dark and lonely place, and it will stay that way, they say, until about 10 trillion trillion trillion years from now. Then things will get worse.

This is serious stuff, despite the absurdly large numbers. The theories on which this scenario is based are well established - Adams and Laughlin just extrapolated them further into the future than anyone has bothered to look in recent years.

Previous extrapolations, like the attempt by physicist Freeman Dyson of the Institute for Advanced Study in Princeton, are a couple of decades old. Some theories have changed since then, so the two young astrophysicists decided it was time for a fresh look. Their paper ``A Dying Universe'' will appear in a forthcoming issue of Reviews of Modern Physics.

After the ``degenerate era,'' even the white dwarfs and neutron stars will be gone, they say. There will be nothing left but black holes, very far apart from each other in the utterly cold and dark emptiness.

The third phase, the ``black hole era,'' will persist, they say, until about 10,000 trillion trillion trillion trillion trillion trillion trillion trillion years from now. (That's a 1 with 100 zeros after it, also known as a googol, but that's another story).

Even black holes don't last forever, though, as physicist and best-selling author Stephen Hawking discovered some years ago. Black holes radiate away energy over time, Hawking found (the phenomenon is now called ``Hawking radiation.''). The black holes gradually lose mass and finally evaporate.

What's left when all the black holes are gone? Not much. In the fourth phase, Adams and Laughlin say, the universe will contain nothing except four kinds of subatomic particles: electrons, positrons, neutrinos and photons.

And let's not forget that we live in an expanding universe - which by now has been expanding for an awfully long time. According to some theories, the rate of expansion may even be accelerating. So the few remaining particles are very, very far away from their nearest neighbors.

This phase, the ``dark era,'' will go on forever, say Adams and Laughlin. The universe will be cold, dark, lonely and featureless - at least as far as we can now imagine.

But maybe that conclusion simply reflects our provincial ways of thinking. ``It seems like these distant eras are seriously impoverished,'' Adams conceded, ``but that probably has more to do with the limitations of our own understanding.''

What's the point of thinking about a future so impossibly far off? The two astrophysicists say such extrapolations can help us understand nearer-term physics and pinpoint areas that could turn out to play a crucial part in the universe's long-term fate.

For example, their scenario shows that one of the major factors that determine what happens to the universe is the decay of fundamental particles called protons.

When protons decay, that's the end of matter, so when they have all decayed, there can be no more stars, planets or people. (On the plus side, no more death or taxes either). By that time - the beginning of the third phase, the ``black hole era'' - ``the character of the universe will change perhaps more than with any of the other changes we've looked at,'' Adams said.