For decades scientists have noticed that if small changes were made in the parameters and constants of the physical universe, the universe would not be able to support life, or would not be as hospitable to life as it is now. The universe in many ways seems to be kind of “tailor-made” to support the evolution of intelligent life, either by design or by an astonishingly improbable series of lucky coincidences. You can find information on this topic by doing a google search on the word “anthropic” and the terms “anthropic principle” and “cosmic fine-tuning.” The wikipedia article on “anthropic principle” offers a good overview of the topic.
An author named Victor Stenger disputed this idea with a recent book The Fallacy of Fine-Tuning: Why the Universe is Not Designed for Us. However, Stenger's book is rather thoroughly demolished by a recent 77-page paper by Luke A. Barnes of the School of Physics at the University of Sydney.
The scientific paper by Barnes is entitled “The Fine-Tuning of the Universe for Intelligent Life.” It is a quite thorough scientific discussion of all the main reasons for thinking that there is something very, very special about this particular cosmos we inhabit. A link to the paper is below:
Let us focus on one particular part of this paper which is particularly compelling.
Barnes cites a graph from a 2007 scientific paper by Barr and Khan relating to two particle mass parameters in our universe. The graph is shown below. Notice the tiny little green triangle. That triangle represents a universe in which intelligent life could exist. Our universe (thankfully) happens to be inside that tiny little "potentially viable" triangle. Universes with parameters outside of the tiny little triangle are those which (for one reason or another) intelligent life could not exist, or could not have evolved.
I will quote Barr and Khan's explanation of the colored lines in this graph:
1. Above the blue line, there is only one stable element, which consists of a single particle
++. This element has the chemistry of helium, an inert, monatomic gas (above 4
K) with no known stable chemical compounds.
2. Above this red line, the deuteron is strongly unstable, decaying via the strong force.
The fi rst step in stellar nucleosynthesis in hydrogen burning stars would fail.
3. Above the green curve, neutrons in nuclei decay, so that hydrogen is the only stable
4. Below this red curve, the diproton is stable. Two protons can fuse to helium-2 via a
very fast electromagnetic reaction, rather than the much slower, weak nuclear pp-chain.
5. Above this red line, the production of deuterium in stars absorbs energy rather than
releasing it. Also, the deuterium is unstable to weak decay.
6. Below this red line, a proton in a nucleus can capture an orbiting electron and become
a neutron. Thus, atoms are unstable.
7. Below the orange curve, isolated protons are unstable, leaving no hydrogen left over
from the early universe to power long-lived stars and play a crucial role in organic
8. Below this green curve, protons in nuclei decay, so that any atoms that formed would
disintegrate into a cloud of neutrons.
9. Below this blue line, the only stable element consists of a single particle, which
can combine with a positron to produce an element with the chemistry of hydrogen. A
handful of chemical reactions are possible, with their most complex product being (an
analogue of) H2.
All of these reasons listed above are factors which would preclude the existence of creatures like us. For example, reason 9 is talking about a universe in which there is only a single element, hydrogen; but life could not exist in such a universe, as life requires additional elements such as carbon.
Now, you may look at the graph cited above, with its tiny green triangle, and you may say: it looks like we got lucky, but not all that lucky. In the graph above, the green triangle is about .5% of the total graph, so you might think that the likelihood of the universe randomly landing inside this green triangle is perhaps 1 in 200. That's interesting, but not as much as a “1 in a million” type of thing.
However, the graph shows something much more improbable than a “1 in 200” coincidence. This is because the graph is a logarithmic graph. The actual chance of randomly landing inside the green triangle is actually many times smaller than 1 in 200.
Let me give a simple example that illustrates this point. Let us imagine that you are ordered to create a golf ball, but you know absolutely nothing about golf; you don't even know that golf is a sport. You might then create the golf ball with any size between .0001 centimeter and 10000 centimeters. However your chance of success is low, because a golf ball will not be suitable for playing golf unless it is between about 3 centimeters and 7 centimeters in size. Golf balls smaller than 3 centimeters will get lost in the grass, and golf balls larger than 7 centimeters will have too small a chance of fitting into the golf hole.
So you randomly generate a number between 1 and 10000, and you then flip a coin. If the coin is heads, you make your golf ball that fraction of a centimeter. If the coin is tails, you make your golf ball that multiple of a centimeter. So, for example, if your random number was 300, and your coin flip produced a tails, you would make your golf ball 300 centimeters in size; but if the coin flip was heads, you would make your golf ball a three hundredth of a centimeter.
Now the logarithmic graph below illustrates the total range of possibilities, and the much smaller range of successful outcomes. The green rectangle shows the suitable range for golf balls. Golf balls larger or smaller than this size won't work. The scale is in centimeters.
Now, if you were looking at this graph, you might estimate that the chance of success under this procedure is about 1 in 100, because the green rectangle is about one hundredth of the total graph. But the logarithmic scale of the graph misleads you. The actual chance of success using this procedure is only about 1 in 10,000. I figured that out by doing a computerized “Monte Carlo” simulation.
My point here is that a logarithmic graph showing “range of possible outcomes” and “range of successful outcomes” will typically make it look much more likely that the successful outcome will occur. A “1 in 10000” chance may look like a “1 in 100” chance when graphed on a logarithmic graph. A “1 in 300” chance may like like a “1 in 10” chance” when graphed on a logarithmic graph.
So look again at the tiny green triangle shown in the above scientific graph near the top of this blog post. Getting a random result that falls within the life-suitable green triangle is not a “1 in 200” probability. It is a much smaller probability – something like a one in a million probability.
The coincidence shown in the first graph is rather like the coincidence of hitting a “hole in one” when playing golf – getting the golf ball to luckily land in the hole on the first try.
In fact, our universe somehow managed not only to land the particular “hole in one” described in the first graph of this blog post, but it also managed to land quite a few other “holes in one,” all of which were necessary for beings like us to exist. These “lucky coincidences” are described fully in Barnes' paper.
This is why scientists use the term “fine-tuned” to describe our universe. As to whether there was a fine-tuner, or some mindless fine-tuning process, that is a matter of debate, and no consensus explanation has emerged. There are a variety of attempts to explain this situation, with a rich variety of speculations having been put forth. I will discuss some of those explanatory attempts in later blog posts.