http://discovermagazine.com/2011/dec/16-how-to-survive-the-end-of-the-universe/article_view?b_start:int=2&-C=
...few people have peered farther than University of California, Santa Cruz, astronomer Greg Laughlin, science’s leading soothsayer. As a graduate student in 1992, he was plugging away at a simple computer simulation of star formation when he broke for lunch and accidentally left the simulation running. When he returned an hour later, the simulation had advanced 100 million billion years, much further into the future than most scientists ever think (or dare) to explore...
The program itself didn’t reveal anything terribly startling—the simulated star had long since gone cold and died—but Laughlin was intrigued by the concept of using physical simulations to traverse enormous gulfs of time...
Laughlin teamed up with Fred Adams, a physics professor at the University of Michigan, to investigate the future of the universe more rigorously. Working in their spare time, the two researchers coauthored a 57-page paper in the journal Reviews of Modern Physics that detailed a succession of future apocalypses: the death of the sun, the end of the stars, and multiple scenarios for the fate of the universe as a whole.
For...futurists, the fun begins a billion years from now, a span 5,000 times as long as the era in which Homo sapiens has roamed Earth. Making the generous assumption that humans can survive multiple ice ages and deflect an inevitable asteroid or comet strike (NASA predicts that between now and then, no fewer than 10 the size of the rock that wiped out the dinosaurs will hit), the researchers forecast we will then encounter a much bigger problem: an aging sun...
Today’s sun is already 40 percent brighter than it was when it was born 4.6 billion years ago.... in a billion years the sun will unleash 10 percent more energy than it does now, inducing an irrefutable case of global warming here on Earth. The oceans will boil away and the atmosphere will dry out as water vapor leaks into space, and temperatures will soar past 700 degrees Fahrenheit, all of which will transform our planet into a Venusian hell-scape choked with thick clouds of sulfur and carbon dioxide. Bacteria might temporarily persist in tiny pockets of liquid water deep beneath the surface, but humanity’s run in these parts would be over...
Such a cataclysmic outcome might not matter, though, if proactive Earthlings figure out a way to colonize Mars first. The Red Planet offers a lot of advantages as a safety spot: It is relatively close and appears to contain many of life’s required ingredients...
The main deterrent to human habitation on Mars is that it is too cold. A brightening sun could solve that—or humans could get the job started without having to wait a billion years....
..let’s assume...humanity transitions successfully to Mars. By Laughlin’s calculations, life there could proceed relatively comfortably for another 4.5 billion years after Earth becomes uninhabitable and before the sun’s bloat once again forces a move. According to standard models of stellar evolution, around that time the sun will largely deplete the hydrogen reserves in its core and begin to balloon as its fusion reactions migrate outward. Through their telescopes astronomers have watched this scenario play out with many other stars, so they know with considerable certainty what happens next: In a dramatic growth spurt, the sun will swell to become a red giant star, 250 times as large and 2,700 times as bright as it is now, stretching farther and farther out into the solar system. It will vaporize Mercury, Venus, and Earth and turn Mars into a molten wasteland...
So where to next? Martian colonies could pack up the spaceship and relocate to Jupiter’s moon Europa, where scientists believe a large ocean of liquid water hides beneath an icy crust. Heated by a brightening sun, Europa could turn into a lush ocean planet. When Europa overheats, Saturn’s moon Titan—which already has a thick atmosphere rich in organic compounds—could be humanity’s next rest stop. But eventually the sun will fry that outpost and every other one in the solar system as well. Even the miserably cold Pluto (–400 degrees Fahrenheit at present) will be too hot for habitability. Finally, about 130 million years after the red giant phase, the sun will go through a final spasm and eject its outer layers into space, leaving behind a white dwarf: a hot, dense lump of carbon and oxygen no larger than Earth. Moving within the solar system during all that drama would be a bit like relocating the beach house an inch inland.
ON TO PROXIMA CENTAURI
Under these circumstances, Laughlin believes the continued survival of our species will depend on the development of high-occupancy starships propelled by nuclear fusion or matter-antimatter annihilation that can transport people rapidly to planets orbiting other stars. (Current chemical rockets are far too slow; they would take 100,000 years just to reach the closest stars.) Astronomers have already identified over 600 planets around other stars, some of them roughly the size of Earth, and believe many billions more exist within our galaxy.
For a long-term solution, Laughlin recommends colonizing a planet with a much more stable sun. Take Proxima Centauri, the very closest neighboring star—only 4.2 light-years from Earth. It is a red dwarf, considerably smaller and cooler than our current sun but with a life span of 4 trillion years, roughly 400 times as long. Astronomers have not found any planets orbiting it yet, but they have discovered planets orbiting similar stars. Red dwarfs also happen to be the most common type of star in the galaxy, so even though Proxima Centauri will not always be close, we’ll still have plenty of housing options...
When Proxima Centauri perishes, humanity can relocate to another red dwarf and then another, but that strategy won’t work forever....
As existing stars consume their last drops of fuel, they will wink out one by one, and the light of the universe will almost entirely disappear.
What then? How could humanity possibly survive without light and warmth? Laughlin says the answer lies in the universe’s secret fuel reserves: brown dwarfs, Jupiter-size balls of hydrogen too massive to be considered planets but that never achieved the heft to become full-fledged stars. In 2009 nasa launched the 1,433-pound wise satellite, carrying a wide-field infrared telescope designed in part to detect such stunted stars; it has since turned up 100 of them within 20 light-years of Earth. Judging from this sample, the galaxy may hold billions more. Laughlin envisions that those cold balls of gas could keep civilization thrumming even after the red dwarfs die out. When brown dwarfs occasionally collide, he explains, they can trigger the birth of a new life-
sustaining star. “For a long time there will always be about 10 to 15 stars shining in the galaxy, each lasting trillions of years,” Laughlin says. “Brown dwarf collisions should continue for another 10 billion billion years.” That would keep us going a thousand times as long as red dwarfs.
But we may not need to rely on chance collisions. Glenn Starkman, the physicist at Case Western, considered the starless era as well and came up with a contingency plan. By the time nature can no longer produce new stars, he says, we may know how to create our own...
When physicists project forward 100 trillion years, they see potential threats much more dire than a ballooning sun or even the dying of all the stars. Starkman says we must also consider the potentially game-ending influence of an all-pervasive cosmic force known as dark energy. “To put it simply,” he says, “dark energy is very bad for life.”
Scientists don’t know what dark energy is, but they do know that it exerts a repulsive effect that makes the universe expand faster and faster. At first glance that may seem like a good thing. An expanding universe creates more space, and by extension, an ever-growing frontier for life to explore and exploit. But dark energy has an unfortunate downside: It pulls galaxies away from each other.
In about 100 billion years, as future humans are enjoying
an extended stay near Proxima Centauri, some physicists ...believe that dark energy will drastically stretch out the vast amounts of empty space between the Milky Way and other galaxies, creating an impassable gulf between them. In this way, every galaxy outside our own would eventually become invisible and inaccessible; trying to travel between galaxies would be as futile as jogging in place. Even if future generations achieve the sci-fi dream of Star Trek–esque starships darting at the speed of light, they could never reach extragalactic destinations.
The result of this phenomenon, known to physicists as the Big Chill, would be a catastrophic limit on resources. With all matter and energy beyond the Milky Way fundamentally out of reach, we would no longer even be able to see stars and planets in other galaxies...In that scenario, humans would have to make the most of every remaining neutron star and brown dwarf in our galaxy. But once we consume every last parcel of matter and energy, there will be nothing more. Humanity will go extinct...
Dartmouth College physicist Robert Caldwell...explored the possibility that in the future dark energy will grow even stronger. At present it makes itself felt only over huge distances, such as the gaps between clusters of galaxies, but Caldwell says that some theories indicate that dark energy might just be kicking into gear. If that is the case, then within 20 billion years—fairly early in our sojourn around a red dwarf—dark energy could start to wreak havoc on much smaller objects.
Stars would be yanked away from galaxies. Then planets would be pulled from their stars. And in one extraordinary half hour, dark energy would progressively tear even the smallest pieces of the universe apart. Layer by layer, humanity’s home planet would be dismantled—first the atmosphere, then the crust, all the way down to the core—in a fantastic explosion. “Anything resting on the planet will just—whoosh—float off,” Caldwell says. In the final 10-19 second, dark energy would rip individual atoms apart. Finally, it will tear the very fabric of space-time at the seams, marking the official end of the universe. The only solace is that life’s extinction would be quick and painless.
