The central hypotheisis in this book is that if any of just six numbers, were different, our universe would be entirely different. Some critical consequence such as planets not been able to form, stars not emitting enough energy or evolution not having enough time for our species to develop would be the result of any of these numbers being different.
When I first heard of this book, I was naievly thinking the numbers would include PI, the speed of light or some of the well other known constants from the scientific world. The numbers and their associated concepts are far more abstract.
The six numbers are:
1. N This is the ratio of electrical force to gravitational force between atoms. This is 10 pow 37. If this number were slightly lower, molecules would behave similarly but less atoms would be needed to make a star and it wouldn't last as long. The star would die sooner, meaning planets such as our own wouldn't get the length of time needed for evolution to bring species such as our's into existence.
2. E This is the percentage of mass that is converted into energy, when hyrogen atoms fuse to form helium. Strong nuclear force, is the force which the particles that make up an atomic nucleus (protons and nuetrons) together. This force acts is the dominant force in the microworld where it overcomes the electrical repulsion which would cause the protons to fly apart. The amount of energy released when atoms undergo nuclear fusion depends on the strength of strong nuclear force as this force that is overcome.
If E was lower (say 0.006) it would mean, that the strong nuclear force or nuclear glue was weaker and protons and nuetrons would never overcome the electrical repulsion and attach. Elements such as helium would never form.
If E was larger (say 0.008) no hyrdogen (which has one proton, no nuetron) would have survived from the big bang. Two protons would have been able to bind as they would have easily overcome the electrical repulsion to each other. This would have happened in the early universe so that all hydrogen would quickly be gone. No hydrogen, amongst other things means no water.
3. Omega. The universe is quite empty. Omega is the ratio of actual density to critical density. If the universe were closer to critical density, gravitational force would over come explosive energy and the universe could collapse. If the actual density was too small, no stars or galaxies would have formed because gravitational energy would not be strong enough.
4. Lambda. This controls the expansion of the universe. It relates to the anti gravitational force (a new force and recent discovery) which determines the speed of expansions of the universe. I gathered that not a lot is known about this other than it is a small number. Had it not have been galaxies etc would not have formed.
5. Q: 10 pow -5. This ratio of ratio of energy required to break up stars and galaxies to their rest mass energy (i.e. E = mC pow2). This is 10 pow -5. If Q were less the universe would be structureless. If Q were too large no stars or solar systems would survive.
6. D: Number of spatial dimensions which is 3. If D was 2 or 4 life could not exist.
Although this book is well written some of the concepts in it are difficult to grasp. There is a lot more in this book than just simple numbers. There are some very sophisticated concepts in this book. If you are doing a PhD in Theoritical Physics its probably quite easy, but I found myself having to re-read several passages to grasp the ideas. Other Universe-esque books such Stephen Hawkings' 'Brief History of Time' or Simon Singh's 'The Big Bang', I found a lot easier to understand and arguably better.
That said, the overall hypotheisis that just 6 numbers play a critical role in shaping our universe is fascinating, mind boggling and well presented.