"Benford-TheFarFuture" - читать интересную книгу автора (Benford Gregory)

H.G. Wells foresaw in The Time Machine a dim sun, with a giant crablike thing
scuttling across a barren beach. While evocative, this isn't what astrophysics
now tells us. But as imagery, it remains a striking reflection upon the deep
problem that the far future holds -- the eventual meaning of human action.

About 4.5 billion years from now, our sun will rage a hundred times brighter.
Half a billion years further on, it will be between 500 and a thousand times
more luminous, and seventy percent larger in radius. The Earth's temperature
depends only slowly on the sun's luminosity (varying as the one fourth root), so
by then our crust will roast at about 1400 degrees Kelvin, room temperature is
300 Kelvin. The oceans and air will have boiled away, leaving barren plains
beneath an angry sun which covers thirty-five degrees of the sky.

What might humanity -- however transformed by natural selection, or by its own
hand -- do to save itself? Sitting further from the fire might work. Temperature
drops inversely with the square of distance, so Jupiter will be cooler by a
factor of 2.3, Saturn by 3.1. But for a sun 500 times more luminous than now,
the Jovian moons will still be 600 degrees Kelvin (K), and Saturn's about 450 K.
Uranus might work, 4.4 times cooler, a warm but reasonable 320 K. Neptune will
be a brisk 255 K. What strange lives could transpire in the warmed, deep
atmospheres of those gas giants?

Still, such havens will not last. When the sun begins helium burning in earnest
it will fall in luminosity, and Uranus will become a chilly 200 K. Moving inward
to Saturn would work, for it will then be at 300 K, balmy shirtsleeve weather --
if we have arms by then.

The bumpy slide downhill for our star will see the sun's luminosity fall to
merely a hundred times the present value, when helium burning begins, and the
Earth will simmer at 900 K. After another fifty million years --how loftily
astrophysicists can toss off these immensities! -- as further reactions alter in
the sun's core, it will swell into a red giant again. It will blow off its outer
layers, unmasking the dense, brilliant core that will evolve into a white dwarf.
Earth will be seared by the torrent of escaping gas, and bathed in piercing
ultraviolet light. The white-hot core will then cool slowly.

As the sun eventually simmers down, it will sink to a hundredth of its present
luminosity. Then even Mercury will be a frigid 160 K, and Earth will be a frozen
corpse at 100 K. The solar system, once a grand stage, will be a black relic
beside a guttering campfire.

To avoid this fate, intelligent life can tinker -- at least for a while -- with
stellar burning. Our star will get into trouble because it will eventually
pollute its core with the heavier elements that come from burning hydrogen. In a
complex cycle, hydrogen fuses and leaves assorted helium, lithium, carbon and
other elements. With all its hydrogen burned up at its core, where pressures and
temperatures are highest, the sun will begin fusing helium. This takes higher
temperatures, Which the star attains by compressing under gravity. Soon the
helium runs out. The next heavier element fuses. Carbon bums until the star
enters a complex, unstable regime leading to swelling. (For other stars than