Some months back, discussing books I had been rereading lately, I spoke of Olaf Stapledon’s epic of the far future, Last and First Men—the quintessential far-future epic, the key title in that entire subspecies of science fiction. Stapledon purports to be writing a history of the next two billion years or so of human evolution, carrying us through eighteen successive human species until the race, having weathered disaster after disaster and now dwelling on a terraformed Neptune, is confronted with a challenge beyond its immense ingenuity: the sun has come under “a continuous and increasing bombardment of ethereal vibrations, most of which were of incredibly high frequency, and of unknown potentiality,” evidently emanating from a nearby supernova. This has caused old Sol to behave in a “deranged” way, and, as a result, says Stapledon’s far-future narrator, “Probably within thirty thousand years life will be impossible anywhere within a vast radius of the sun, so vast a radius that it is quite impossible to propel our planet away fast enough to escape before the storm can catch us.”

So it is the end for our solar system, and the end as well for the highly evolved, dazzlingly endowed Eighteenth Men. But the narrator, speaking to us from the very brink of extinction, provides this lovely epilog by way of summing up humanity’s two billion years of cyclical striving: “Man himself, at the very least, is music, a brave theme that makes music also of its vast accompaniment, its matrix of storms and stars. Man himself in his degree is eternally a beauty in the eternal form of things. It is very good to have been man. And so we may go forward together with laughter in our hearts, and peace, thankful for the past, and for our own courage. For we shall make after all a fair conclusion to this brief music that is man.”

It has always seemed quite sad to me that our splendid species is fated to be snuffed out in a mere two billion years, if we are to take Stapledon’s elegant fantasy as embodying an accurate prediction. All our cleverness gone for naught, Shakespeare and Mozart and the iPod and penicillin and high-definition television and all the rest of our glorious achievements not only gone but not even forgotten, for there will be nobody here to forget us! But now the calculations of two astronomers, Klaus-Peter Schroeder of the University of Guanajato in Mexico and Robert Connon Smith of England’s University of Sussex, have put my mind at rest. The clock is ticking for us, yes, and doomsday is approaching, but it is not nearly as close as the author of Last and First Men suggested, and, unlike Stapledon’s Eighteenth Men, we have plenty of time to deal with the problem. They, two billion years in our future, had a mere thirty thousand years to figure out a solution, and couldn’t do it. But we, say Drs. Schroeder and Smith, have a full 7.59 billion years to come up with an answer. How comforting that extra 5.59 billion years is! And what a nice sense of scientific precision is provided by “.59 billion years,” so much more scientific-sounding than the vulgar “590 million years.”

What is going to happen to our world, in the Schroeder-Smith version of the future, makes all our current little ecological scramblings around with hybrid automobiles and fluorescent lighting seem pretty much beside the point. We can be as green as can be, and give ourselves many brownie points for Saving the Planet, but the planet isn’t going to be saveable, because the sun is going to keep on getting warmer and warmer and eventually conditions will become downright intolerable. We’re not talking about global warming here. That’s a purely local phenomenon resulting from our offloading of carbon dioxide and other so-called “greenhouse gases” into our own atmosphere. No, this is solar warming, an expansion of the sun’s output. Most astronomers believe that such expansion goes on gradually but inexorably throughout the life-span of any star, and that our sun, in the 4.5 billion years of its life, has already increased its luminosity by 40 percent. And nothing we could do will halt the process.

So, we are told, things will keep on getting hotter and muggier on Earth, until, about a billion years from now, the oceans will boil away. That will deal with the humidity problem, I suppose, but will create other serious but not wholly insoluble problems. We—if anything like “us” is still here, a billion years from now—aren’t likely to be able to withstand the scorching heat of the expanded sun, but, given this much notice, we surely ought to be able to find some more comfortable place to live.

We see that in Last and First Men: Stapledon’s Fifth Men, some four hundred million years in our future, organize a mass migration to Venus upon learning that our moon is about to disintegrate and bombard us with big troublesome fragments; and when, another half a billion years down the line, the Eighth Men discover that the sun is about to go nova and cook all the inner worlds, a second migration to Neptune is successfully carried out. So, too, I suppose, we, having been properly warned, will find ways of coping with the increased temperatures of Earth in the year One Billion, perhaps by burrowing underground but, more probably, by escaping from our overheated planet altogether. That would mean saying goodbye, of course, to the Great Pyramid of Giza and the Taj Mahal and the Grand Canyon, and all of Earth’s other familiar wonders, but it’s a safe bet that geological forces will have removed all those cherished landmarks from our ken anyway, even the Grand Canyon, long before those billion years have elapsed.

Bigger trouble is in store, though, and coping with that won’t be nearly as simple. Go another 5.5 billion years down the line, say Drs. Schroeder and Smith, and we find the sun using up the last of the hydrogen in its core—that is, the fuel that it has been burning to generate its heat—and starting to burn the hydrogen in its outer layers. This will cause the core to shrink and the outer layers greatly to expand, turning the sun into a vast, tenuous red-giant star. That means sayonara for Mercury and Venus, which will be within the perimeter of our inflated sun. Earth has some chance of escaping the fate of those worlds, because the altered sun’s gravitational pull will have diminished, causing Earth to move outward to something like the present orbit of Mars, where it might just escape being engulfed by the expanded solar mantle.

Even so, the prognosis isn’t good. The risk is that Earth will gradually drift back sunward from its new orbit until it, too, is gobbled up. Calculations made in 2001 by two European scientists indicated a reasonable chance that that would not happen, but new figures developed by Dr. Schroeder of Guanajato and Manfred Cuntz of the University of Texas give our little globe no hope. Their numbers show that the transformations going on within the sun will cause it to throw off much more mass—and thus, paradoxically, grow much larger, increasing greatly in diameter even while becoming far more attenuated in substance. Instead of losing 25 percent of its mass while undergoing metamorphosis into a red giant, as was previously predicted, the sun will lose about one third—resulting in a star with a diameter 256 times as great as today’s sun, and a luminosity 2,730 times greater. Not only will our inner-world neighbors be devoured, but the hapless Earth will find itself skimming just a short distance above the surface of the solar monster, and tidal forces will create a bulge in the sun that will exert a gravitational pull on the Earth, slowing its speed of revolution and tugging it inexorably downward toward its doom. In the even longer run the sun itself will fare little better, going through a standard cataclysmic cycle of shrinking and expanding and shrinking again that will turn it, eventually, into a white dwarf star heading toward its ultimate burnout, further billions of years ahead in the future that we are not going to see.

So, then, the Schroeder-Smith clock is ticking, and we have a mere 7.59 billion years to deal with the problem.

Stapledon, who arrived at an intuitive vision of approximately this sort of bleak destiny back in 1930, made the men of his fictional distant future nimble enough to escape first to Venus and then to Neptune. But then, as the final solar catastrophe approached, even they had run out of places to hide, and the best they could manage was to look upon their coming doom with philosophical detachment: “Man is a fair spirit, whom a star conceived and a star kills.” Even then, the stubborn humanity in them led them to conceive a plan to create “an artificial human dust capable of being carried forward on the sun’s radiation, hardy enough to endure the conditions of a trans-galactic voyage of many millions of years, and yet intricate enough to bear the potentiality of life and of spiritual development.” And so, as the book closes, they are about to seed the stars with their own successors, who, perhaps, will continue the human saga in some unimaginably alien manner under the light of some distant sun.

We, having more notice of the end than Stapledon’s Last Men, are free to follow a similar path. Earth may be doomed, but the universe awaits us. At the moment, of course, political and financial difficulties seem to have stymied any sort of movement very far into space, but it’s folly to think that the present slump in human space exploration is going to last forever. There’s nothing like an imminent vast expansion of the sun to stimulate our agile species in the direction of self-defense. So we may—not soon, mind you, but sooner than it seems right now—start thinking about colonizing Mars or one of the more suitable moons of Jupiter or Saturn, which would get us out of reach of the first phase of the big temperature rise. We could even go one step beyond Stapledon’s soaring vision and consider moving Earth itself into a safer orbit by making use of the gravitational force of comets or asteroids, as several astrophysicists have quite seriously proposed. (Though one of them, Dr. Gregory Laughlin of the University of California at Santa Cruz, has noted that “There are profound ethical issues involved, and the cost of failure . . . is unacceptably high.”) And, finally, when the red-giant sun has begun its metamorphosis into that white dwarf and the entire solar system is without a source of heat, the beings who then inhabit the Earth—not the Eighteenth Men of Stapledon, but perhaps the Ninetieth Men or the Thousandth Men—will have to find some way to export their brand of humanity to the stars.

Dizzying stuff to think about, yes. A billion years ago there was nothing but microscopic life on Earth, and here we are talking about the “human” life-forms that will inhabit this place billions of years in the future. How likely are they to resemble us in any significant way?

Most science fiction abjures such Stapledonian vistas and deals instead with short-range stuff like the way computers will work in the twenty-second century, or the problem that space pirates will cause in the twenty-third. Stories like that don’t leave one’s mind whirling giddily, the way pondering the astrophysical problems of the year Five Billion can do. Would that our best writers would spend more time dealing with such things, say I, dizzy though they may make their readers in the process. It’s the good kind of dizziness, the kind that science fiction excels at generating, the sort of vertiginous sensation that brought most of us to science fiction in the first place.