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.My thoughts:
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.
- As observers, we don't necessarily have to reside within a universe that is perfectly optimized for life—it just needs to be good enough to foster the emergence and sustenance of life. In the space of all possible life sustaining universes, ours may be but one example of many other viable models.
- Our universe may not be fine-tuned for life, but it may be optimized for something else. Our universe, for example, may actually be an exquisite black hole generator. Or something we don't yet know.