Fine Tuning and Anthropic Principle

Fine Tuning and Anthropic Principle

by : Aria Ratmandanu 

          In 1919, physicist Hermann Weyl expressed his puzzlement that the ratio of the electromagnetic force to the gravitational force between an electron and a proton is such a huge number, N1 = 1039.1 Weyl wondered why this should be the case, expressing his intuition that “pure” numbers occurring in the description of physical properties, such as π, which do not depend on any system of units, should most naturally occur within a few orders of magnitude of unity. Unity, or zero, you can expect “naturally.” But why 1039? Why not 1057 or 10-123? Some principle must select out 1039. This is called the large number puzzle.

                In 1923 Arthur Eddington commented: “It is difficult to account for the occurrence of a pure number (of order greatly different from unity) in the scheme of things; but this difficulty would be removed if we could connect it to the number of particles in the world—a number presumably decided by accident.”2 He estimated that number. “now called the “Eddington number,” to be N = 1079. Well, N is not too far from the square of N1. This coincidence was no doubt accidental, since we now know that it corresponds just to the number of atoms in the visible universe, which contains a billion times as many photons and neutrinos and many billions of times more beyond our horizon.

               These musings may bring to mind the measurements made on the Great Pyramid of Egypt in 1864 by the Astronomer Royal for Scotland, Charles Piazzi Smyth. He found accurate estimates of π and the distance from Earth to the sun, and other strange “coincidences” buried in his measurements.4 However, further analysis revealed that these were simply the result of Smyth's selective toying with the numbers. Still, even today some people believe that the pyramids hold secrets about the universe. Ideas like this never seem to die, no matter how deep in the Egyptian sand they may be buried.

              Look around at enough numbers and you are bound to find some that appear connected. Most “physicists, therefore, did not seriously regard the large number puzzle until one of their most brilliant members, Paul Dirac, took an interest. Few physicists ignored anything Dirac had to say. Dirac pointed out that N1 is the same order of magnitude as another pure number, N2, that gives the ratio of a typical stellar lifetime to the time for light to traverse the radius of a proton. That is, he found two seemingly unconnected large numbers to be of the same order of magnitude. If one number being large is unlikely, how much more unlikely is another to come along with about the same value ?

              In 1961 physicist Robert Dicke pointed out that N2 is necessarily large in order that the lifetime of typical stars be sufficient to generate heavy chemical elements such as carbon. Furthermore, he showed that N1 must be of the same order as N2 in any universe with heavy elements.7 This was the first of the anthropic coincidences: if N1 did not approximately equal N2, life as we know it would not exist.

            The heavy elements did not get fabricated straightforwardly. According to the big bang theory, only hydrogen, deuterium (the isotope of hydrogen containing one proton and one neutron in its nucleus), helium, and lithium were formed in the early universe. Carbon, nitrogen, oxygen, iron, and the other elements of the chemical periodic table were not produced until billions of years later. These billions of years were needed for stars to form and in their death throes, after burning all their hydrogen, to assemble these heavier elements out of neutrons and protons. When the more massive stars expended their hydrogen fuel, they exploded as supernovae, spraying the manufactured elements into space. Once in space, these elements cooled, mixed with the interstellar medium, and eventually formed newer stars accompanied in many instances by planets.”

               Billions of additional years were needed for our home star, the sun, to provide a stable output of energy so that at least one of its planets could develop highly complex life. But if the gravitational attraction between protons in stars had not been many orders of magnitude weaker than the electric repulsion, as represented by the very large value of N1, stars would have collapsed and burned out long before nuclear processes could build up the periodic table from the original hydrogen and deuterium. The formation of chemical complexity is possible only in a universe of great age in terms of nuclear reaction times or at least in a universe with other parameters close to the values they have in this one.

The Anthropic Principles

          In 1974, physicist Brandon Carter introduced the term anthropic principle to describe the anthropic coincidences. In the weak form of the principle, the location in the universe in which we live must be compatible with the fact that we are here to observe it. In the strong form, at least at some stage, the universe itself must have been compatible with the existence of observers.

         In its weak form, the anthropic principle simply points out the obvious fact that if the laws and parameters of nature were not suitable for life, we would not be here to talk about them. As a simple example, physical constants and the laws that contain them determined that the atmosphere of Earth would be transparent to wavelengths of light from about 350 nanometers to 700 nanometers, where a nanometer is a billionth of a meter. The human eye is sensitive to the same region”

        One possible natural explanation for the anthropic coincidences is that multiple universes exist with different physical constants and laws and our life-form evolved in the one suitable for us. Theists vehemently object that we have no evidence for multiple universes and, furthermore, we are violating Occam's razor by introducing multiple entities “beyond necessity”

      Modern cosmological theories do indicate that ours is just one of an unlimited number of universes. In this book I do not spend a lot of time with philosophical or “commonsense” reasoning. Rather I look directly at the various parameters that have been proposed as being fine-tuned and see if plausible explanations can be found within existing knowledge.

“Barrow and Tipler defined three different forms of the anthropic principle, the first of which is as follows:

Weak Anthropic Principle (WAP):

           The observed values of all physical and cosmological quantities are not equally probable but they take on values restricted by the requirement that there exist sites where carbon-based life can evolve and by the requirement that the Universe be old enough for it to have already done so.

             This is essentially the same as Carter's definition. As we saw above, all the WAP seems to say is that if the universe were not the way it is, we would not be here talking about it. If the mass of the electron were different, people would look different. However, it does not tell us why the constants have the values they do rather than some other value that would make life impossible.

Barrow and Tipler formulated the strong anthropic principle as follows, which differs from Carter's definition:”

Strong Anthropic Principle (SAP):

The universe must have those properties that allow life to develop within it at some stage in its history.