Imagine if some huge extraterrestrial spaceship were to appear in a fixed position above some US city. Suppose the extraterrestrials wanted to get started communicating with us. How could they start the conversation, if their language was so different from ours that English was utterly unintelligible to them? One way would be for them to place 1836 identical small objects in a field. Every physicist would understand the meaning of this. 1836 is the ratio between the proton mass and the electron mass, a constant throughout the universe.
Or if the extraterrestrials wanted to do something similar that wouldn't require so many objects, they could place 137 identical small objects on a field. Every physicist would recognize what this meant. 137 is the number associated with a universal constant of nature known as the fine-structure constant. Its value is normally represented as 1/137 (or more exactly, 0.007297351). The behavior of stars crucially depends on the value of the fine-structure constant.
A few days ago the Daily Galaxy web site had an article involving the rather prosaic topic of the fine-structure constant. Following the Daily Galaxy's standard rule of “spice things up to the max,” the article had this sensational title: Our Solar System “Is In a Unique Place in the Universe – Just Right for Life.”
Such a title must have excited those who like to believe the egotistical idea that man is the centerpiece of the universe. But the facts cited by the Daily Galaxy story do not warrant the article's sensational title implying something special about the position of our solar system.
The article in question refers to some research published in 2012 by John Webb and his colleagues at the University of New South Wales. The relevant scientific paper can be found here. Studying the fine-structure constant (a fundamental constant generally believed not to vary in time or space), the scientists claimed to find evidence that the fine-structure constant “increases with increasing cosmological distance from Earth.”
But the variation reported was only about 1 part in 100,000. There is probably insufficient basis for thinking that a variation of only 1 part in 100,000 in the fine-structure constant would rule out the habitability of a particular region.
There are some reasons for thinking that stars like the sun could not exist if the fine-structure constant were much larger or smaller. The fine-structure constant controls the strength of electromagnetism. On page 73 of his book The Accidental Universe, Paul Davies states the following:
If gravity were very slightly weaker, or electromagnetism very slightly stronger, (or the electron slightly less massive relative to the proton), all stars would be red dwarfs. A correspondingly tiny change the other way, and they would all be blue giants.
But we see yellow stars like the sun all over the galaxy, and in many other nearby galaxies. So a space-dependent variation of 1 part in 100,000 cannot justify any claim that our solar system is in a “unique place in the universe – just right for life,” not unless you mean “place” to mean some large fraction of the universe. The problem with such a claim is not the "just right for life" part, but the "unique" part implying some special zone of habitability in just one part of the universe.
Bubble around a bright star (Credit: NASA)
There has been other research on the fine-structure constant that does not agree with that of Webb and his colleagues. A more recent paper (published in June 2016) found no evidence for variation in the fine-structure constant, not even 3 parts in a million.
So the Daily Galaxy's article title seems to be unwarranted. Another interesting result on the fine-structure constant was reported in 2016 in a scientific paper by scientist McCullen Sandora. Sandora dealt with the “inverse fine structure constant,” which is the fine-structure constant divided by 1 (this has been measured to be 137.036). The iron lying around our planet (needed for technical civilizations) is believed to have arisen in the core of a distant star (stars shoot out iron when they explode in supernova explosions). Sandora found that for stars to produce iron, the inverse fine-structure constant must have a value of 145, give or take 50.
Sandora also found a more sensitive requirement, finding that for a planet to have plate tectonics like the Earth, the inverse fine-structure constant must be 145, give or take 9. Sandora gives some complicated reasons why such plate tectonics are a requirement for the appearance of creatures such as us.
The latter finding puts the measured value of the inverse fine-structure constant (137.036) just barely inside the range consistent with a planet like Earth (a range between 136 and 154). This finding is consistent with the claim in this scientific paper, which says that an inverse fine structure constant “close to 137 appears to be essential for the astrophysics, chemistry and biochemistry of our universe.”
The fine-structure constant is actually derived from three other fundamental constants of nature. The formula for the fine structure constant is that it is equal to e2/hc, where e is the charge of the proton, h is Planck's constant, and c is the speed of light.
According to Sandora, planets just like ours (with plate tectonics) could not exist if the fine-structure constant varied by more than 6%. If the fine structure constant must fall in a very narrow range, then think of how fine-tuned the proton charge must be, if the fine structure constant depends on the square of the proton charge.
This is only one way in which the proton charge must be exquisitely fine-tuned. There is the additional fact (involving a far-greater sensitivity) that planets will not hold together unless the proton charge and the electron charge match each other to many decimal places (the only difference being that the electron charge is negative). For if there were not so precise a match (far more unlikely than you randomly guessing correctly someone's Social Security number), the electromagnetic force (more than a trillion trillion trillion times stronger than the gravitational force) would cause repulsion exceeding the gravity holding the planet together (as mentioned here). Experiments have shown that the proton charge and the electron charge do actually differ by less than 1 part in 1,000,000,000,000,000,000. This fact is unexplained by our physicists, and is extremely surprising given that each proton has a mass 1836 times greater than each electron.