The Fate of the Earth & the Universe (Astronomy Cast: Dr. Pamela Gay & Fraser Cain)

http://www.astronomycast.com/ Astronomy : Life, the Universe, and Nothing: Life and Death in an Ever-expanding Universe Current evidence suggests that the cosmological constant is not zero, or that we live in an open universe. We examine the implications for the future under these assumptions, and find that they are striking. If the universe is cosmological constant--dominated, our ability to probe the evolution of large-scale structure will decrease with time; presently observable distant sources will disappear on a timescale comparable to the period of stellar burning. Moreover, while the universe might expand forever, the integrated conscious lifetime of any civilization will be finite, although it can be astronomically long. We argue that this latter result is far more general. In the absence of possible exotic and uncertain strong gravitational effects, the total information recoverable by any civilization over the entire history of our universe is finite. Assuming that consciousness has a physical computational basis, and therefore is ultimately governed by quantum mechanics, life cannot be eternal. Our universe could end in one of two ways. Either the observed expansion could terminate and be followed by collapse and a Big Crunch, or the expansion could continue forever. The evidence is overwhelmingly in favor of the latter possibility. Indeed, recent direct (Perlmutter et al. 1999; Riess et al. 1998) and indirect (Krauss & Turner 1995; Ostriker & Steinhardt 1995; Krauss 1998) measurements suggest that the expansion is accelerating, implying that it is driven by an energy density which at least mimics vacuum energy, a so-called cosmological constant. As dramatic as this result may be for our understanding of fundamental processes underlying the big bang, it has equally important consequences for the long-term quality of life of any conscious beings that may survive the more mundane challenges of daily existence. In an eternally expanding universe life might, at least in principle, endure forever (Dyson 1979). While global warming, nuclear war, and asteroid impacts may currently threaten human civilization, one may hope that humanity will overcome these threats, expand into the universe, and perhaps even encounter other intelligent life forms. In any case, if intelligent life is ubiquitous in the universe, it is reasonable to expect that no local threats can ever wipe the slate entirely clean. But are there global constraints on the perdurability or on the quality of conscious life in our universe? These are the questions we examine here. We find that the future is particularly discouraging if we live in a cosmological constant--dominated universe. In this case, very soon, on a cosmic timescale, our ability to gather information on the large-scale structure of the universe will begin to forever decrease. The decreasing information base in the observable universe is associated with a finite and decreasing supply of accessible energy. Life's long-term prospects are only slightly less dismal in any other cosmology, however. We argue that the total energy that any civilization can ever recover and metabolize is finite, as is the recoverable information content, independent of the geometry or expansion history of the universe. Faced with this inevitable long-term energy crisis, life must eventually either identify a strategy for reduced energy consumption or cease to exist. In a cosmological constant--dominated universe, the de Sitter temperature fixes a minimum temperature below which life cannot operate without energy-consuming refrigerators. In any cosmology, the need to dissipate excess heat may fix a minimum temperature at which a biological system can operate continuously. http://iopscience.iop.org/0004-637X/531/1/22/fulltext Lawrence M. Krauss and Glenn D. Starkman