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.
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