#unniverse

They introduce us to their favourite movies and music – and their wry sense of humour is not without value. This is an unusual popular science book in which the authors have humanised themselves. Congratulations Geraint and Luke!

Big questions

Cambridge University Press

This book is for anyone who has ever wondered: “Why is it so?” With colourful analogies and admirably accurate simplifications, Geraint and Luke have succeeded in making much of modern physics and cosmology comprehensible.

They address the biggest questions of science. What is dark energy? What is dark matter? Why is there something rather than nothing? Why is there more matter than antimatter? Where did the laws physics come from? Do we live in a multiverse? Do we live in a simulation? How different could the universe have been? If God is omnipotent, why does evil exist?

Not even the popular scientist and writer Paul Davies tries to address so many important big questions in one book – and fortunately, Paul only puts God in his book titles.

Here is how Geraint and Luke describe the main thesis of their book:

We scratched our heads … and wondered deeply about how things could have been different. This quickly leads to the realisation that life would be very difficult, if not impossible, in the vast sea of possible universes.

You may be asking yourself ‘how could the universe have been different?’ and the answer is the fundamental laws of matter and energy could have been different. There are basic quantities that theorists cannot calculate; we have to cheat by getting the answer from experiments. These loose ends cry out for a deeper understanding.

My comment on that is: “Hmmm … maybe.”

Why the constants?

We physicists are always trying to come up with better equations to describe the universe. In our equations for gravity, for example, there is a constant that we call “G”. It represents the strength of gravity.

Geraint and Luke seem comfortable imagining universes with different values of G. If G were ten times larger, gravity would be so strong that you couldn’t walk. If G were ten times smaller, there wouldn’t be an Earth to walk on.

We have tried to derive the value of G from a more fundamental theory, but have had little success. The only thing we can do with G is measure it. So in some sense, G seems arbitrary. The only explanation for its arbitrary value – according to Geraint and Luke – is that it has been fine tuned to allow life to exist in our universe.

They call this fine tuning “a fact” and then spend most of the book trying to explain this “fact”.

Geraint and Luke define fine tuning like this:

Something is fine tuned if, to explain the data, you must make an unmotivated but suspiciously precise assumption.

I agree with that, but notice that in this sentence, the “something” that is fine tuned could be the theory (which is the normal way physicists use the term fine tuning), or it could be the universe.

If you hang around theoretical physicists for more than an hour in a pub talking shop, you will hear the phrase “fine tuning”. It is the most common insult that we heap on each other’s pet theories: “You’re trying to explain the remarkable spatial flatness of the universe with a remarkably flat inflaton potential. That’s fine tuning. You’re cheating. Your theory stinks.”

We try hard to make our theories natural, but to fit the universe we live in, our equations need what seem like arbitrary constants that we haven’t been able to explain at any deeper level.

Rather than blame our current theories for this shortcoming, and rather than calling the theories fine tuned, the authors think that our universe is fine tuned.

For something to be fine tuned, there have to have been other possibilities. Geraint and Luke explain:

[…] what if almost all of the possible universes are sterile, with conditions too simple or extreme for life of any conceivable type to arise? Then we are faced with a conundrum. Why, in the almost infinite sea of possibilities, was our universe born with the conditions that allow life to arise? That is the subject of this book.

Imagining an almost infinite sea of unfortunate possibilities would make anyone feel fortunate not to be in that sea.

Geraint and Luke argue, if you take the number of universes that are compatible with life and divide by the number of all possible universes, that ratio must be tiny. Hence the title of the book A Fortunate Universe.

Fine tuned by what?

We can’t currently derive those pesky physical constants (such as G) so we have to resort to only measuring them.

Interpreting this as evidence for a supernatural being who fine tunes the universe so that we can exist is not a very humble interpretation of the data. But for 25 pages near the end of the book, Luke argues that God is the fine tuner.

Saying that the universe is fine tuned for life makes as much sense to me as saying that my legs are fine tuned to reach the ground. The case for our theories being incomplete and not as fundamental as we would like, is more compelling to me as a scientist than the idea that any god fine tuned the universe for us.

To paraphrase the American theoretical physicist and cosmologist Lawrence Krauss: The lack of understanding of physical constants is not evidence for God. It’s evidence of a lack of understanding.

If you’re a scientifically minded theist looking for your God in the universe, this book is invaluable. If you’re a strident atheist, this book is a long god-of-the-ultimate-gap argument and just another theistic salvo for intelligent design.

I enjoyed the book a lot, but I disagreed with the main thesis. No matter what your religious beliefs are, this book will make you think.

A Fortunate Universe: Life in a Finely Tuned Cosmos

By Geraint Lewis and Luke Barnes

Published by Cambridge University Press 

Charley Lineweaver is a Researcher at Research School of Astronomy and Astrophysics and the Research School of Earth Sciences, Australian National University.