Guided tour leaves us a lot less lost in space
In Candide, Voltaire satirises Gottfried Wilhelm Leibniz’s dictum that we live in the best of all possible worlds. The naive Dr Pangloss clings to this as an essential truth, despite enduring a chain of terrible mishaps. By the end of Candide, it is hard to agree with the good doctor.
Australian astrophysicists Geraint Lewis and Luke Barnes open their charming, intelligent and well-written book by arguing that we live in “a fortunate universe”. The Earth “is a special place” for humans, “a relative cosmic paradise where the conditions are just right for life”.
Not only that, but “at every level, we find that our universe’s ability to create and sustain life forms is rare and remarkable”. The University of Sydney duo then proceed to convincingly show why we should share their belief.
This requires a gentle stroll through the details of the standard model of particle physics, as well as the standard model of cosmology, but the authors lead us with such a light hand, streak of humour and lack of pedantry that the information is easily absorbed.
Atomic nuclei are made up of neutrons and protons, and these in turn are composed of quarks. But what determines the mass of the quarks and electrons that surround the nuclei? Or, for that matter, what sets the strength of the forces that hold the quarks together or of those that bind the electrons to the nuclei? Despite decades of valiant research, we still don’t know.
A more technical statement of our puzzlement is that the standard model of particle physics has 19 so-called free parameters, numbers whose values have been determined experimentally but have evaded explanation.
But those parameters are not free in the sense that the world would be relatively unchanged if they had slightly different values. Here’s where the subtitle Life in a Finely Tuned Cosmos enters the picture.
Lewis and Barnes show us how small changes lead to a variety of disasters. (“Ruining a universe is easy,” Barnes quips.) Neutrons and protons are primarily composed of up and down quarks. A little shift in the masses of those quarks causes protons to decay into neutrons rather than vice versa. In another version, the shifts produce a universe where hydrogen and helium are the only elements present.
After an introduction to the concept of finetuning in particle physics, Lewis and Barnes turn to cosmology and come face-to-face with the great dilemmas posed in understanding how our universe has come about and what its future is likely to be. The establishment of the standard model of cosmology is regarded as one of the great triumphs of modern science.
According to the model, the universe began with a big bang a little less than 14 billion years ago and has been expanding since then. Atoms formed about 400,000 years after the big bang, and, as expansion and cooling continued, stars, galaxies and planets formed.
Is this all a happy coincidence, as the authors ask each other in an amusing mock debate modelled on one that Galileo instigated 400