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Not Only Is Earth One Nice Planet Among Many, but Our Entire Universe Is Lost in a Crowd
by Denyse O'Leary
Your patience is earnestly requested. We're a bit delayed finding those habitable planets, their myriad life forms, and that dense throng of alien civilizations. Fine-tuning remains a problem. So, more boldly go. What if not just Earth, but our whole universe, is seen as one mere Copernican blip?
Should the fine-tuning turn out to be real, what are we to make of it? There are two widely-discussed possibilities: either God fine-tuned the universe for us to be here, or there are (as string theory implies) a large number of universes, each with different laws of physics, and we happen to find ourselves in a universe where the laws happen to be just right for us to live. After all, how could we not?
A large number of hitherto unnoticed universes? No sooner asked than granted: Nima Arkani-Hamed and others have proposed over 10^500 universes because fewer of them would not obviate fine-tuning. Why believe in them? As a New Scientist writer has explained
But the main reason for believing in an ensemble of universes is that it could explain why the laws governing our Universe appear to be so finely turned for our existence ... This fine-tuning has two possible explanations. Either the Universe was designed specifically for us by a creator or there is a multitude of universes -- a multiverse.
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Cosmologists deserve credit for making the choice so clear. In that spirit, Discover Magazine offers the multiverse as "Science's Alternative to an Intelligent Creator" (2008). And New Scientist's editors promise, in addition, a "multiverse-fuelled knowledge revolution". As David Berlinski puts it, "The Big Fix has by this maneuver been supplanted by the Sure Thing."
Three multiverse concepts worth knowing (because they turn up time and again in pop science media) are inflation, string theory, and M-theory:
inflation: Cosmologist Alan Guth champions a particle, the "inflaton," which caused the universe to expand faster than the speed of light, thus (accidentally) smoothing the Big Bang into its present delicate balance between too loud and too soft. In Guth's eternally inflating universe:
... anything that can happen will happen; in fact, it will happen an infinite number of times. Thus, the question of what is possible becomes trivial -- anything is possible, unless it violates some absolute conservation law.
Guth's signature statement is "The recent developments in cosmology strongly suggest that the universe may be the ultimate free lunch."
string theory: In a theory that became popular in the late 1970s, to reconcile gravity with quantum mechanics in a ten-dimensional spacetime, the building blocks for all the universes are strings of vibrating energy. The extra six spatial dimensions curl up inside our four conventional ones (3D plus time). The resulting string landscape is a huge increase in possible solutions to equations. Key string theorist Leonard Susskind is blunt about one attraction of the theory: "Without any explanation of nature's fine-tunings we will be hard pressed to answer the ID critics…