WHY is the Universe the way it is? Why do the many parameters that define it happen to be the very values that give rise to habitable planets and life?
Many cosmologists subscribe to the 鈥渁nthropic principle鈥� 鈥� for us to observe them, the parameters simply have to be the size they are. Not so, says one physicist. He says that at least one other arrangement of cosmological parameters would lead to life.
Some of the Universe鈥檚 parameters seem precisely set at values that allow us to be here. If they were only slightly different, the heavy elements essential for life would not have formed, for example. Many prominent cosmologists think this is no accident, and their view is enshrined in the 1986 book The Anthropic Cosmological Principle by John Barrow and Frank Tipler.
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But the principle could have its legs knocked from under it by a theoretical study by Anthony Aguirre of the Institute for Advanced Study in Princeton, New Jersey. He wondered if there might be another set of parameters that would permit life.
Aguirre began by defining the conditions necessary for biology. 鈥淐rudely speaking, the evolution of life requires heavy elements such as calcium and iron and the billions of years of stable temperatures found around a star of solar mass,鈥� says Aguirre.
To his surprise, Aguirre found that such conditions could also be satisfied in a universe that seems very alien. 鈥淚t鈥檚 hard to imagine a universe more different from our own,鈥� he says. In our 鈥渉ot鈥� big bang, a huge number of photons very quickly blasted apart any matter that formed. This meant that the light elements produced early on did not have time to fuse together to form heavier ones. Heavy elements were later formed in the central furnaces of stars.
Aguirre鈥檚 universe starts with a 鈥渃old鈥� big bang, and does not have to wait so long for its heavy elements to form. 鈥淚n a cold big bang universe, matter is much denser at a given temperature and all the heavy elements necessary for life get built up in the first seconds,鈥� says Aguirre.
His universe could also have an enormously large cosmological constant 鈥� a repulsive force which drives matter apart. At up to 100,000 trillion times bigger than the constant in our Universe, this would mean that after 13 billion years 鈥� the Universe鈥檚 current age 鈥� the alien universe would be eerily dark and devoid of stars. 鈥淚nstead of galaxies crowding space, only a few isolated star clusters would be adrift in a vast ocean of darkness,鈥� says Aguirre.
He suspects there could be other alternative universes, too. 鈥淧eople are going to have to think very carefully about using the anthropic principle,鈥� he says.
Supporters of the principle are not convinced. 鈥淢aking the cosmological constant 1017 times bigger might not be an option without a bad change in something else, or it might just not be permitted,鈥� says John Barrow, now at Cambridge University. 鈥淲e have no idea, since we don鈥檛 know the true explanation for the dimensionless parameters which define cosmologies.鈥�
More at:http://arxiv.org/abs/astro-ph/0106143