Dec. 21 - Looking for Life in the Multiverse‏

Dear Friends,

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http://www.scientificamerican.com/article.cfm?id=looking-for-life-in-the-multiverse

Be Well.

David

Looking for Life in the Multiverse

Universes with different physical laws might still be habitable

By Alejandro Jenkins and Gilad Perez

Key Concepts

• Multiple other universes—each with its own laws of physics—may have emerged from the same primordial vacuum that gave rise to ours.
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• Assuming they exist, many of those universes may contain intricate structures and perhaps even some forms of life.
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• These findings suggest that our universe may not be as “finely tuned” for the emergence of life as previously thought.

The typical Hollywood action hero skirts death for a living. Time and again, scores of bad guys shoot at him from multiple directions but miss by a hair. Cars explode just a fraction of a second too late for the fireball to catch him before he finds cover. And friends come to the rescue just before a villain’s knife slits his throat. If any one of those things happened just a little differently, the hero would be hasta la vista, baby. Yet even if we have not seen the movie before, something tells us that he will make it to the end in one piece.

In some respects, the story of our universe resembles a Hollywood action movie. Several physicists have argued that a slight change to one of the laws of physics would cause some disaster that would disrupt the normal evolution of the universe and make our existence impossible. For example, if the strong nuclear force that binds together atomic nuclei had been slightly stronger or weaker, stars would have forged very little of the carbon and other elements that seem necessary to form planets, let alone life. If the proton were just 0.2 percent heavier than it is, all primordial hydrogen would have decayed almost immediately into neutrons, and no atoms would have formed. The list goes on.

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 the 1970s 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 the 1980s, 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.

The Weakless Way of Life

The conventional way scientists find out if one particular constant of nature is finely tuned or not is to turn that “constant” into an adjustable parameter and tweak it while leaving all other constants unaltered. Based on their newly modified laws of physics, the scientists then “play the movie” of the universe—they do calculations, what-if scenarios or computer simulations—to see what disaster occurs first. But there is no reason why one should tweak only one parameter at a time. That situation resembles trying to drive a car by varying only your latitude or only your longitude, but not both: unless you are traveling on a grid, you are destined to run off the road. Instead one can tweak multiple parameters at once.

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