Evidence emerges that laws of physics are not fine-tuned for life
The value of the cosmological constant suggests that the laws of nature could not have been fine-tuned for life by an omnipotent being.
One of the more curious debates in science focuses on the laws of physics and why they seem fine-tuned for life.
The problem is that the laws of physics contain various constants that have very specific, mysterious values that nobody can explain. These constants are balanced in such a way that life has evolved at least once, in one small part of the Universe. But why do the constants have these values? Various scientists have calculated that even the tiniest of changes to these constants would make life impossible. That raises the question of why they are so finely balanced.
One explanation is that this is pure accident and that there is no deeper reason for the coincidence. Another idea is that there is some deeper law of nature, which we have yet to discover, that sets the constants as they are. Yet another is that the constants can take more or less any value in an infinite multitude of universes. In ours, they are just right, which is why we have been able to evolve to observe them.
None of these arguments is easy to prove or disprove, although that may change as other evidence accrues, says Don Page, a theoretical physicist at the University of Alberta in Canada.
But there is a fourth line of thought which Page says is easier to attack. This is the idea that the constants have been fine-tuned by some unseen omnipotent being who has set them up in a way that maximises the amount of life that form. So instead of directly creating life, God simply sets the conditions to maximise the chances of it forming.
Today, Page says this idea is potentially falsifiable and says we already have evidence that does the trick.
Here’s the thinking. The cosmological constant is a number that determines the energy density of the vacuum. It acts like a kind of pressure that, depending on its value, acts against gravity to push the universe apart or acts with gravity to pull the universe together towards a final Big Crunch.
Until recently, cosmologists had assumed that the constant was zero, a neat solution. But the recent evidence that the universe is not just expanding but accelerating away from us, suggests that the constant is positive. But although positive, the cosmological constant is tiny, some 122 orders of magnitude smaller than Planck’s constant, which itself is a small number.
So Page and others have examined the effects of changing this constant. It’s straightforward to show that if the the constant were any larger, matter would not form into galaxies and stars meaning that life could not form, at least not in the form we know it.
So what value of the cosmological constant best encourages galaxy and star formation, and therefore the evolution of life? Page says that a slightly negative value of the constant would maximise this process. And since life is some small fraction of the amount of matter in galaxies, then this is the value that an omnipotent being would choose.
In fact, he says that any positive value of the constant would tend to decrease the fraction of matter that forms into galaxies, reducing the amount available for life. Therefore the measured value of the cosmological constant, which is positive, is evidence against the idea that the constants have been fine-tuned for life.
An interesting argument and one that adds to the fine body of work that attempts to prove or disprove the existence of an omnipotent interferer. But not one that is likely to settle the matter one way or the other.
• Source: MIT Technology Review
• The paper is available at http://arxiv.org/abs/1101.2444.pdf