Examples of fine tuning #4 - The Strength of Dark Energy
The strength of dark energy is an example of fine tuning. It’s much less than expected. Yet if it were more, there could be no life in the universe.
Dark energy is blowing the universe apart. It first surfaced in Albert Einstein’s Theory of Relativity. Gravity pulls everything in the universe together: Einstein’s equations said that the universe ought either to be expanding or collapsing under the effects of gravity. At the time, everyone thought the universe was static - neither expanding nor contracting - so Einstein introduced into his equations a ‘fudge factor’ called the cosmological constant (always symbolised by a Greek letter Λ (lambda)). This amounted to a kind of energy that would cause the universe to expand, exactly balancing the contracting force of gravity.
Later, when it became clear that the universe is indeed expanding, Einstein called the cosmological constant his ‘greatest blunder.’ The cosmological constant should have been set =0.
For a couple of generations, astronomers believed that (a) the universe is expanding because of the Big Bang, (b) the expansion is slowing down because of gravity, and (c) Λ=0. Then in 1998, they discovered – contrary to all expectations - astronomical evidence that the expansion of the universe is speeding up. Einstein’s cosmological constant is not =0 after all.
Another way to look at this is to say that space itself contains some mysterious energy that is pushing the universe apart.
Nobody really knows what this dark energy is, although we now believe that it makes up around 70% of the universe. Physicists have some ideas which enable them to predict the strength of dark energy - and this is where things get interesting: this prediction comes out to be 10120 times its actual value. Nobel prize-winning physicist Steven Weinberg famously said that
'This must be the worst failure of an order of magnitude estimate in the history of science.'
But here’s the important point: if the strength of dark energy was much more than it actually is, the universe would have been blasted apart much faster. There would be no way for galaxies to form – or stars, or complicated things like people.
(Please note: this doesn't just mean that people like us would be impossible. Any kind of complicated life would be impossible. There would be no possibility of 'life, Jim, but not as we know it.')
Professor Felix Bloch of Stanford University, put it like this:
‘The fact that we are just on the knife-edge of existence, if the dark energy were very much bigger we wouldn’t be here, that’s the mystery.’
The strength of dark energy is another critical example of the fine tuning of the laws of physics without which we would not be here.
David A Couchman MA M.Sc M.Min FRAS, August 2011