by Denyse O'Leary
Here's a recent exercise in cosmological imagination – or science fiction, if you like: In "Looking for Life in the Multiverse: Universes with different physical laws might still be habitable" Scientific American Magazine (December 16, 2009) By Alejandro Jenkins and Gilad Perez make clear what is and is not accepted in science (as they understand it) and why:
The laws of physics-and in particular the constants of nature that enter into those laws, such as the strengths of the fundamental forces-might therefore seem finely tuned to make our existence possible. Short of invoking a supernatural explanation, which would be by definition outside the scope of science, a number of physicists and cosmologists began in the1970s to try solving the puzzle by hypothesizing that our universe is just one of many existing universes, each with its own laws. According to this"anthropic" reasoning, we might just occupy the rare universe where the right conditions happen to have come together to make life possible. Amazingly, the prevailing theory in modern cosmology, which emerged in the1980s, suggests that such "parallel universes" may really exist-in fact, that a multitude of universes would incessantly pop out of a primordial vacuum the way ours did in the big bang. Our universe would be but one of many pocket universes within a wider expanse called the multiverse. In the overwhelming majority of those universes, the laws of physics might not allow the formation of matter as we know it or of galaxies, stars, planets and life. But given the sheer number of possibilities, nature would have had a good chance to get the "right" set of laws at least once. Our recent studies, however, suggest that some of these other universes-assuming they exist-may not be so inhospitable after all. Remarkably, we have found examples of alternative values of the fundamental constants, and thus of alternative sets of physical laws, that might still lead to very interesting worlds and perhaps to life. The basic idea is to change one aspect of the laws of nature and then make compensatory changes to other aspects.
Our work did not address the most serious fine-tuning problem in theoretical physics: the smallness of the "cosmological constant," thanks to which our universe neither recollapsed into nothingness a fraction of a second after the big bang, nor was ripped part by an exponentially accelerating expansion. Nevertheless, the examples of alternative, potentially habitable universes raise interesting questions and motivate further research into how unique our own universe might be.
Well, the supernatural may be "outside the scope of science," but universes whose existence is not demonstrated, which are imagined principally to get out of a jam with the evidence from this universe, are reasonably doubted, despite thought experiments. The tentative tone here is well justified. It should be used more often.
Also just up at Colliding Universes (Colliding Universes is my blog on competing theories of our universe (and Earth, in one case))
– American Physical Society reacts to physicist Hal Lewis's accusation: APA "…has accepted corruption as the norm"
– Exoplanets: The planet with 100% life has 0% existence?
See other multiverse stories here.
See other fine tuning stories here