NATURAL selection has been proved wrong 鈥� at least for the ancestry of our universe. For more than a decade, a novel theory that used Darwinian evolution to explain why our universe seems improbably well-suited for life has defied criticism. Now a cosmologist claims to have falsified it, once and for all.
Lee Smolin, then at Pennsylvania State University in University Park, first proposed his theory that multiple universes follow a kind of natural selection in the early 1990s. It attempts to explain why the physical constants in our universe seem perfectly tuned for life to evolve. Smolin was inspired when other physicists suggested that at the centre of black holes space-time can become so warped that it breaks off and forms a new, disconnected universe. He proposed that each such baby universe would inherit similar physical constants to its parent (快猫短视频, 15 January 1994, p 38).
In this scenario, universes with physical conditions that promote the maximum number of black holes would be the most productive parents, and would pass on these favourable black-hole-producing characteristics to their own offspring. Over time, such universes would dominate the population, making it highly probable that we find ourselves in one, says Smolin.
Advertisement
鈥淯niverses that promote the maximum number of black holes would be the most productive parents鈥�
鈥淚t鈥檚 a very clever idea because the conditions for producing stars that turn into black holes are the same as the ones needed for producing the stellar systems needed for life to evolve,鈥� says cosmologist Alexander Vilenkin at Tufts University in Medford, Massachusetts.
Smolin, now working in Canada at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, admits that the theory may sound fanciful. 鈥淚t鈥檚 surprised me that nobody so far has managed to disprove it,鈥� he says. He has challenged other cosmologists to falsify his idea by showing that our universe isn鈥檛 tuned to produce the maximum number of black holes.
Now Vilenkin believes he has done just that. The key point, he says, is to realise that baby universes would be formed not only within massive black holes produced by collapsing stars but also inside the so-called 鈥渕ini black holes鈥� that are predicted to pop out of quantum fluctuations in empty space.
Vilenkin calculated the rate at which these mini black holes would appear in universes with different values of the cosmological constant (CC), which describes the accelerated expansion of the universe. Each universe reaches a constant temperature, determined by its CC, after a few billion years, and this temperature controls mini-black-hole production after this point (). Vilenkin found that raising the CC above the value seen in our universe dramatically increases the number of black holes produced in the later part of a universe鈥檚 life. 鈥淥ur universe is very far from being the optimum black hole factory,鈥� says Vilenkin.
鈥淩aising the cosmological constant above the value in our universe dramatically increases the number of black holes鈥�
Smolin isn鈥檛 convinced, though, and has prepared a paper to say so (). He points out that Vilenkin鈥檚 calculations assume that the CC will behave the same way across the universe and for billions of years in the future, but some recent observations of the cosmic microwave background hint otherwise (快猫短视频, 22 October 2005, p 19).
Vilenkin is undeterred. 鈥淚 used the best physical theories that we have,鈥� he says. 鈥淚f they are wrong, I will be happy to test Smolin鈥檚 theory again.鈥�
