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.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.
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.
See other multiverse and fine tuning stories:
Cosmology: If you needn't worry about paying the rent Friday, you can worry about this stuff
Cosmology: Science's leader in things that don't make sense
Cosmology: Crisis of the month: gravitation
Cosmology: Multiverse - getting comfortable with a zillion of everything that is unique.
Cosmology: I seem to have yanked particle physicist Lawrence Krauss's chain
Cosmology: Wow. It takes guts to wage warwith Stephen Hawking. He appeared in Star Trek
Cosmology: Arguments against flatness (plus exposing sloppy science writing)
Cosmology: If the universe has free will, where do I go to file a claim for damages?
New podcasts on fine tuning of the universe
Also: Gravity doesn't make sense? Hold on to that thought!
Multiverse: Getting comfortable with a zillion of everything that is unique?
Can the laws of physics evolve?
Like clouds in our coffee, all these other universes
Major media, imagining themselves sober, think there are many universes, not just double vision
The Big Bang exploded; seriously, is there room for reasonable skepticism about the Big Bang?
Could God live in an infinite sea of universes? It depends.
Will the cosmic multiverse landscape ensure the triumph of intelligent design?
Now, remind me again why we need multiverse theory in the first place?
Multiverse theory: Replacing the big fix with the sure thing?