Apr/May 2000 Book Reviews

Just Six Numbers (The Deep Forces that Shape the Universe)

Sir Martin Rees
Orion Publishing Group (December 1999)
ISBN: 0 297 84297 8

reviewed by Ann Skea

The author of this book, Sir Martin Rees, is the Royal Society Research Professor at Cambridge University and holds the title of Astronomer Royal. One must assume, then, that the arguments that he puts forward in this book represent the very best thinking of what is to me a very esoteric science. He apologies for the slow gestation of this book, written especially for the Science Masters series. But in my mind he need not apologise as has completed a formidable assignment--that of explaining in everyday terms some of the leading-edge theories in the realm of cosmology.

In this book Sir Martin shows how just six numbers, imprinted in the "big bang," determine the essential features of the physical cosmos. He also shows that cosmic evolution is highly sensitive to the values of these numbers and that if any one of them were "untuned" there could be no stars and no life. Or at least not in the way that we know them today.

So what are these six fundamental numbers?

The first is a ratio of the strength of the electrical forces that hold atoms together divided by the force of gravity between them. It is very large, about 1036, and were it a few zeros shorter, only a short-lived miniature universe could exist and there would be no time for biological evolution.

The second number is also a ratio and is the proportion of energy that is released when hydrogen fuses into helium. This number is 0.007, and if it were 0.006 or 0.008 we could not exist.

The third number, also a ratio, relates the actual density of matter in the universe to a "critical" density. At first sight this number appears to be about 0.4. If this ratio were too high the universe would have collapsed long ago: if too low, galaxies or stars would not have formed.

The fourth number, only recently discovered, is a cosmic "antigravity" and appears to control the expansion of the universe even though it has no discernible effect on scales less than a billion light years.

The fifth number is the ratio of the energy required to break apart a galaxy compared to its "rest mass energy" and is about 10-5. If this ratio were smaller the universe would be inert and structureless: if much larger the universe would be so violent that no stars or sun systems could survive.

The sixth number, surprisingly, is the number of spatial dimensions in our world (3). Life could not exist if this was 2 or 4.

In this book Sir Martin discusses each of the above and develops reasons for the limits that he gives. He postulates that perhaps there are some connections between these numbers but states that at the moment we cannot predict any one of them from the values of the others. Perhaps a "theory of everything" will eventually yield a formula that interrelates them.

More thought provoking is Sir Martin's discussion of what or who "tuned" these numbers. He identifies three scenarios.

One is the hard-headed approach of "we could not exist if these numbers weren't adjusted in this special way: we manifestly are here, so there's nothing to be surprised about."

Another is that the "tuning" of these numbers is evidence of a beneficent Creator, who formed the universe with the specific intention of producing us.

For those who do not accept the "providence" or Creator arguments, and Sir Martin places himself in this category, there is another argument, though still conjectural. This is that the "big bang" may not have been the only one. Separate universes may have cooled down differently, ending up governed by different laws and defined by different numbers.

Certainly, reading this book (and its no light task in coming to grips with the scale or immensity of the numbers) has been rewarding for me and has awakened in me an interest in looking further into other discussions regarding the "big bang," time and parallel universes.


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