In two previous posts I dealt with the relation between the multiverse theories and the problem of fine tuning, noting that those theories do not solve the problem. This third post describes briefly what is the fine tuning problem.
In 1973 Brandon Carter formulated the anthropic principle, a name later deplored by its author, because it may be prone to misunderstandings. This principle is simply the verification that the universe must fulfill all the conditions necessary for our existence, since we are here.
Over a decade later, John Barrow and Frank Tipler published a book entitled The anthropic cosmological principle, which offered a stronger version of the anthropic principle, posing that the values of many of the universal constants are critical and minor variations would make life impossible. This finding raises the fine tuning problem, based on the analysis of the possible effects of changing the values of those constants. In other words, the universe seems designed to make life possible. Let’s look at a few examples:
1. The mass of the proton is 1836 times that of the electron. The mass of the neutron equals 1838.4 times the electron: 0.13% greater than the mass of the proton. If the neutron mass had been just 0.15% higher (i.e. 1841.2 times that of the electron, or 0.28% greater than that of the proton) stars would not be able to produce helium from hydrogen. They could still use the helium generated shortly after the Big Bang, but only for a few million years. In such a universe, life would not have time to appear.
2. Modern physics knows four fundamental interactions: gravitational, electromagnetic, weak and strong nuclear. If the strong nuclear force were 0.5% more or less intense than it is, carbon or oxygen could not be produced in stars. Without carbon or oxygen, earth-like life would not be possible, since both elements are indispensable for organic matter. The same would happen if the intensity of the electromagnetic interaction differed by more than 4% in both directions from its actual value.
3. In every nuclear fusion that occurs in stars, 0.7% of matter is converted into energy. If the value of this constant were 0.8% or more, all the hydrogen would have become helium during the Big Bang and there wouldn’t be any hydrogen in the universe to make living beings or to provide energy to stars. If it was less than 0.6%, hydrogen fusion would be impossible, the universe would consist only of hydrogen and stars would not exist.
4. The cosmological constant, introduced by Einstein in his cosmic equation and later rejected by himself, has recently re-risen with the discovery of the accelerated expansion of the universe. Its value, if its existence is confirmed, would be critical: if it were higher than it is, the universe would have expanded so fast that galaxies, or stars (or life) would never have formed. Lower values lead to a universe which would have stopped expanding soon and contracted toward a Big Crunch, with no time for life to appear.
All these parameters, plus a few more that I don’t have room to mention, have values in the field of real numbers. The probability of the existence of life is thus calculated by dividing the volume of configuration space compatible with the existence of life, between the volume of the total configuration space (the infinite continuum). Considering the above critical values, it follows that the part of configuration space compatible with life is ridiculously small. Some scientists believe that the probability that the universe fulfills all the necessary conditions could be between 0 and 10-500. Recall that the probability of the existence of something can be zero, even though we know that a favorable case exists. This was discussed in a previous article.