of rigorous attempts to look far into the future — long-term climate-change modelers, say, or radiophysicists who consider where to stash nuclear waste. But more often, Bostrom says, speculation about the future has been “a projection screen, on which we display our hopes and fears.” Think of Karl Marx, laying out a path for history based mostly on his own aspirations, rather than on anything that would today qualify as science. “Even just trying to get it right is something that distinguishes [us] as a small subset,” Bostrom says.

This newfound appreciation for the depths of time has led a handful of thinkers like Rees, a theoretical cosmologist by training, to begin venturing some of humanity’s first real educated guesses about what may lie far, far, far ahead. Serious futurologists are not a large group yet. “It’s a fairly new area of inquiry,” says Nick Bostrom, an Oxford University philosophy professor who heads the school’s Future of Humanity Institute. But they are trying to give a first draft of a map of the future, using the kinds of rigor that theologians and uneducated guessers from previous generations didn’t have at their disposal.

Humans have been interested in the future for millennia, mostly as a subject for theologians. But theologians were, along with everyone else, thinking small. Most humans who have ever lived have died in conditions almost exactly like the ones into which they were born, and without written history had no way to grasp that the future might be different at all. Only now have we gained the scientific knowledge necessary to appreciate how exactly how deep a rabbit-hole the future really is: not just long enough to see empires rise and crumble, but long enough to make all human history so far seem like a sneeze of the gods.

The occasion for Rees’s mind-bending assertion was his acceptance of the 2011 Templeton Prize, an annual cash award of $1.7 million, payable to individuals who have made “an exceptional contribution to affirming life’s spiritual dimension” — in Rees’s case, by looking millions of years into the future and venturing a guess as to what might be waiting.

“Our sun formed 4.5 billion years ago, but it’s got 6 billion more before the fuel runs out,” Sir Martin Rees, the Astronomer Royal, told the audience seated among the busts and weathered books of the institution’s second-story library. “It won’t be humans who witness the sun’s demise: It will be entities as different from us as we are from a bug.”

The Royal Institution of Great Britain has stood on the same site since 1799, and on most days it would seem one of the older and fustier buildings in central London. But on April 6, time did a funny thing: The institution’s 212 years of existence suddenly contracted, and went from seeming unimaginably long to unimaginably short.

The community of thinkers on distant-future questions stretches across disciplinary bounds, with the primary uniting trait a willingness to think about the future as a topic for objective study, rather than a space for idle speculation or science fictional reverie. They include theoretical cosmologists like Sean Carroll of the California Institute of Technology, who recently wrote a book about time, and nonacademic technology mavens like Ray Kurzweil, the precocious inventor and theorist. What binds this group together is that they are not, says Bostrom, “just trying to tell an interesting story.” Instead, they aim for precision. In its fundamentals, Carroll points out, the universe is a “relatively simple system,” compared, say, to a chaotic system like a human body — and thus “predicting the future is actually a feasible task,” even “for ridiculously long time periods.”

Nick Bostrom’s Future of Humanity Institute is in St. Ebbes, central Oxford, a district named for the site of a church that has been built and rebuilt over about a thousand years. The Faculty of Theology, he says, would have been the home for his institute in any other century. But when the institute was founded in 2005, the natural home for it had shifted toward the secular. It straddles a departmental boundary between Oxford’s Faculty of Philosophy and its Martin School, a creation of the computer-science whiz James Martin, meant to encourage interdisciplinary thought about science, policy, and risk.

Most important, they’re systematically analyzing for the first time the worryingly numerous ways in which humanity might fail to survive to see that long future. Having a clearer sense of the future will give hints about how to act now to keep the real doomsday scenarios at bay. In the past, thinking about the world in a thousand years meant thinking about a religious apocalypse, as in Norse mythology’s prediction that humanity and the universe will conclude when Yggdrasil, the tree that holds up the world, begins to creak and shrug. Academics today, including Rees, are finding such predictions wanting — even if the reality could turn out to be in some ways just as dark.

Their methods are scientific and philosophical, and they all come down to trying to understand what all those zeroes in numbers like “6 billion” really mean. Scientists now have firmly grounded hypotheses about how Earth and the solar system will be different in 50 million years, for example, as distinct from 500 million or 50 billion, and can rule out some possibilities for what will happen at each point. Armed with data from history, they can use rough computer models to simulate how human populations might rise and fall, how their technology might accelerate, and how thousands or millions of years of human activity might or might not change the planet.

For Rees, then, and many other thinkers about the future, a central preoccupation is making sure that humans survive to see it. Only 0.01 percent of all species that have ever existed continue to do so. We happen to be one of them, for now. When Rees looked at the myriad ways in which the present is more perilous than the past in his 2003 book “Our Final Hour,” he set the odds of human extinction in the next century at 50 percent.

While an essential part of the toolkit of a futurologist is knowledge of the past, science is now crossing a line where the past may be less helpful as a guide: It has moved beyond replicating the work of nature, and begun introducing eventualities never before seen on earth. A seemingly benign example is chilling materials to within a fraction of absolute zero, many times colder than the coldest place in the universe. Potentially less benign are certain types of high-energy physics research, or DNA experimentation that creates beings unknown on this planet.

Also among the cosmologists is Rees, the speaker at the Royal Institution, who turned his attention to the end of time after a career in physics reckoning with time’s beginning. An understanding of these vast time scales, he contends, should have a large and humbling effect on our predictions about human evolution. “It’s hard to think of humans as anything like the culmination of life,” Rees says. “We should expect humans to change, just as Darwin did when he wrote that ‘no living species will preserve its unaltered likeness into a distant futurity.’ ” Most probably, according to Rees, the most important transformations of the species will be nonbiological. “Evolution in the future won’t be determined by natural selection, but by technology,” he says — both because we have gone some distance toward mastering our biological weaknesses, and because computing power has sped up to a rate where the line between human and computer blurs. (Some thinkers call the point when technology reaches this literally unthinkable level of advancement the “singularity,” a coinage by science fiction writer Vernor Vinge.)

Indeed, to a cosmologist steeped in the vastness of time, 6 billion years may not even seem so long. Carroll puts the sun’s remaining years in stark perspective, noting that one can go further and set one’s cosmological egg timer for the burnout of all the stars in the universe (about one thousand million million years from now) and for the evaporation of the last black holes (about a googol, or one followed by a hundred zeroes, years from now). “After that, the universe will simply continue to expand and dilute, and that will go on forever,” he says.

Bostrom, the Oxford philosopher, puts the odds at about 25 percent, and says that many of the greatest risks for human survival are ones that could play themselves out within the scope of current human lifetimes. “The next hundred years or so might be critical for humanity,” Bostrom says, listing as possible threats the usual apocalyptic litany of nuclear annihilation, man-made or natural viruses and bacteria, or other technological threats, such as microscopic machines, or nanobots, that run amok and kill us all.

This is quite literally the stuff of Michael Crichton novels. Thinkers about the future deal constantly with those who dismiss their speculation as science fiction. But Bostrom, who trained in neuroscience and cosmology as well as philosophy, says he’s mining the study of the future for guidance on how we should prioritize our actions today. “I’m ultimately interested in finding out what we have most reason to do now, to make the world better in some way,” he says.

So if we really understood the future, how would we behave? “It turns out that the reduction of existential risk turns out to be one of the most important things we can do,” he says. “It turns out, if you act and consider all good — including that of future generations — you could outweigh the good you can do today by eliminating world hunger, say, or curing malaria.” Saving a billion from famine today is, by this calculation, a minor concern compared with making sure no extinction-level event snuffs out the opportunity for a trillion more to live in the centuries to come.

There is, both in Bostrom’s scenarios and in Rees’s, the possibility of a long and bright future, should we manage to have any future at all. Some of the key technologies capable of going awry also have the potential to keep us alive and prospering — making humans and post-humans a more durable species. Bostrom imagines that certain advances that are currently theoretical could combine to free us some of the more fragile aspects of our nature, such as the ability to be wiped out by a simple virus, and keep the species around indefinitely. If neuropsychologists learn to manipulate the brain with precision, we could drug ourselves into conditions of not only enhanced happiness but enhanced morality as well, aiming for less fragile or violent societies far more durable than we enjoy now, in the nuclear shadow.