New calculations shed light on one of science’s great puzzlesby Philip Ball / June 12, 2018 / Leave a comment
New calculations of “model universes” different from our own have shown that our existence might not be as special as has been supposed. According to these results, just published by a team of astrophysicists in the Monthly Notices of the Royal Astronomical Society, the problem of so-called “dark energy” in our universe becomes more puzzling than we thought. The work juggles with several speculative ideas in cosmology, but goes to the heart of one of the deepest problems in science.
At the centre of the issue is the so-called “fine-tuning problem,” which confronts the fact that our universe seems oddly “designed” for life to exist. Everything we see—atoms, matter, planets, stars and galaxies—can be largely explained by physical laws that govern, say, the forces of gravity and electromagnetism But those laws have within them a handful of numbers (“fundamental constants”) that just happen to have particular values—so that, for example, the strength of the electromagnetic force is much greater than that of gravity. It’s in these numbers that the fine-tuning is manifested.
For decades, physicists dreamed of finding a “Theory of Everything” that would not only unify our understanding of such forces in one over-arching theory but would also reveal why the fundamental constants of nature have to have the values we observe and not some other.
The trouble is, efforts to develop such a unified theory have led in the opposite direction. Many (though by no means all) physicists working on those problems regard string theory—which posits that all particles are made up of incredibly tiny one-dimensional vibrating entities called strings—as the best candidate. But string theory seems to imply that there is an absurdly huge range of possible “ways things could be,” all with different values of the fundamental constants.
That looked discouraging, but in fact it fits quite nicely with one of the favourite cosmological theories of how the Big Bang occurred that led to our expanding universe. This theory posits something called inflation: a period of incredibly rapid expansion very early on in the Big Bang, in which our universe ballooned suddenly from microscopic to cosmic size. Inflation potentially solves some puzzles about the large-scale distribution of galaxies and radiation that we observe. But if the theory of inflation is right, it seems to imply that this wasn’t a one-off event. There could have been a profusion…