This fall Lord Rees completes his five-year term as president of The Royal Society. He continues as Britain's Astronomer Royal and Master of Trinity College, Cambridge. His books include Just Six Numbers: The Deep Forces that Shape the Universe and Our Final Hour.

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President of the Royal Society, England's Astronomer Royal, Lord Martin Rees brings a lifetime of cosmological inquiry to a crucial question: What if human success on Earth determines life's success in the universe?

He thinks that civilization's chances of getting out of this century intact are about 50-50. He is hopeful that extraterrestrial life already exists, but there's no sign of it yet. But even if we are now alone, he notes that we may not even be the halfway stage of evolution. There is huge scope for post-human evolution, so that "it will not be humans who watch the sun's demise, 6 billion years from now. Any creatures that then exist will be as different from us as we are from bacteria or amoebae."

Appropriately, Rees's Long Now talk will be at the Chabot Space & Science Center in the hills above Oakland, in the planetarium.

Cosmic Life

The pace of astronomic discovery, said the Astronomer Royal, keeps increasing with the constant improvement in our sensing technology. The recent discovery of the accelerating expansion of the universe (dark energy) revolutionized cosmology, and with the launch of the Kepler Telescope in 2009, we are beginning to detect and study Earth-sized planets around distant stars.

Since the Moon landings, humans in space have done little of scientific interest, but unmanned probes have delivered revelations from the planets and moons of the solar system, with much more to come. The best prospects for finding life elsewhere in our solar system appear to be on Mars, on Saturn's moon Titan, or on Jupiter's moon Europa. (Human space exploration is best pushed by private individuals such as Elon Musk, Jeff Bezos, and Richard Branson, rather than governments, Rees feels. Governments aren't allowed to be realistic about the dangers of space travel.)

"We are the nuclear waste of stellar fusion," Rees noted, the ash from long-dead stars all over the galaxy exchanging their gases in a complex ecology, and the galaxies show a mega-structure of density contrasts generated by gravity. Poised midway in scale between atoms and stars, biological life appears to be the peak of complexity in the universe---a flea is more complicated than a star.

Since we don't know how our own life emerged and haven't discovered any elsewhere, we still have no idea whether life is common in the universe or if we are unique. We can be certain that we are not the culmination of life forms here, because we are less than halfway through the Sun's lifespan. In the six billion years to come, there are likely to be creatures as far beyond humans as we are beyond microbes, and science as far beyond our present understanding as quantum theory is remote to a chimpanzee.

Now that we are stewards of this planet, we are responsible for maintaining life's possibilities in this cosmic neighborhood.