Theoreticians ponder why we exist


Dec 4, 2006

Scientists debate how anthropic reasoning predicts cosmological constant

The emergence of humans in the universe might not tell us anything concerning the fundamental constants of nature as scientists have speculated, new theoretical findings argue.

The idea known as the anthropic principle states that human existence is possible only if fundamental constants such as the speed of light or the strength of gravity are not higher or lower than what is observed.

Scientists who support anthropic reasoning suggest they can understand fundamental properties of the universe by determining what conditions intelligent beings such as humans need to exist. For instance, if gravity was too strong, black holes ( would form too often and suck up all matter before humans could evolve, but if gravity was too weak, it could not attract matter to form stars or planets.

According to advocates of anthropic reasoning, in 1987 Nobel laureate Steven Weinberg used the logic to calculate the cosmological constant ( — the strength of the mysterious force driving the universe apart — with surprising accuracy, well before astronomical observations turned up similar findings. What astronomers have since observed is that the universe's expansion is accelerating, driven by a sort of mysterious force dubbed either dark energy ( or vacuum energy.

Quantum physics predicts the cosmological constant should be far larger than what is actually seen: roughly 10120 times larger, a number representing 1 with 120 zeroes behind it.

In comparison, Weinberg's original estimate was off just by roughly a hundredfold, and refined versions of this argument claim greater accuracy, suggesting anthropic reasoning could provide answers quantum physics currently cannot.

However, theoretical physicist Glenn Starkman of Case Western Reserve University in Cleveland and cosmologist Roberto Trotta at Oxford University in England take issue with how anthropic reasoning predicts the cosmological constant.