DRAFT
OF A CHAPTER
Charles
P. Poole, Jr.
CONTENTS
1.
Introduction
2. Anthropic Cosmological Principle
3.
Specific Cosmological Principles
4.
Implications of the Weak Anthropic Principle
5.
The Fine Tuning of the Proton-proton Cycle
6.
7. Critical Density and Flatness of the Universe
1. INTRODUCTION
In
1986 the astronomer John T. Barrow and the mathematical physicist Frank J. Tipler wrote The Anthropic Cosmological Principle which provides an
important missing link in the framing of a comprehensive world view or
Weltanschauung. Such a world view should
take into account both current scientific explanations of the origin and
development of the universe, as described in the chapters Big Bang Theory and
Background for the Big Bang Theory (BBB), as well as traditional Christian
beliefs about the creation of the world and the providence of God acting in the
world. The present chapter will explain the Anthropic
Principle, and the Weltanschauung chapter will make use of it in formulating a
Christian Worldview.
2. ANTHROPIC COSMOLOGICAL
PRINCIPLE
Until the invention of the telescope, there
was a belief common to mankind that human beings have a privileged position in
the Universe. Our universe is the earth
surrounded by the sky containing the sun, the moon, many stars, and a few
planets. When Galileo
looked through his telescope. he found that the
planet Jupiter had moons which also cycled through phases such as new moon,
first quarter, full moon, and last quarter.
Our planet Earth no longer seemed so privileged. Astronomers, other scientists, and soon
academia adopted the world view or Copernican Principle that Man does not
occupy a privileged position in the Universe.
This idea remained dominant until the last few decades of the twentieth
century. At that time some cosmologists
began to wonder to what extent we as intelligent observers unfairly influence the
type of description that we offer, and the conclusions that we arrive at,
concerning the nature of the universe.
In 1974 Brandon Carter suggested that the Copernican Principle is not
absolute, but should be limited by an Anthropic
Principle which states that: “our location in the Universe is necessarily
privileged to the extent of being compatible with our existence as observers.” In other words, since observers are offering
a description of the Universe, it follows that the Universe which they describe
must have had the capability of evolving intelligent life so that these
observations could be made. More
specifically, conditions close enough to the region of observation must have
been suitable for the development of biological evolution leading to the
appearance of Man.
3. SPECIFIC ANTHROPIC
PRINCIPLES
Barrow
and Tipler put an emphasis on what they refer to as
the weak, strong, and final anthropic
principles. These principles are defined
by them as follows:
Weak Anthropic Principle: 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 the Universe be old enough for it to have
already done so.
Strong Anthropic Principle: The
Universe must have in it those properties which allow life to develop in it at
some stage of its history.
Final Anthropic Principle (FAP): Intelligent information processing must come
into existence in the Universe, and once it comes into existence, it will never
die out.
Mitigated
Final Anthropic Principle (FAP): Intelligent
information processing must come into existence in the Universe.
Participatory Anthropic Principle: Observers
are necessary to bring the Universe into being.
Theistic Anthropic Principle: The
physical universe was created in such a manner that it is compatible with the
presence of life, more specifically human life, for a duration exceeding
several centuries.
Barrow
and Tipler argue that the weak principle is merely a
restatement of the general adage that the interpretations made by an observer
must take into account the limitations of his measuring apparatus. The remaining ones are speculative in nature. The Theistic Principle provides a rationalization for the
pseudoscience Creationism which is discussed in the Intelligent Design
chapter.
4. IMPLICATIONS OF THE WEAK
ANTHROPIC PRINCIPLE
According
to the Weak Anthropic Principle the observed values
of all physical and cosmological quantities must satisfy the requirements that
there exist sites where carbon based intelligent life can evolve, and the
present Universe is now old enough for this to have already happened. The universe is at present finely tuned with
the values of the fundamental constants that are listed in the table of
BBB. It is easy to show that small
changes in some of these quantities, or in some of the dimensionless constants
constructed from them, could produce dramatic changes in our present Universe. According to the Anthropic principle small changes of this type which
upset the ability of the Universe to evolve toward the production of life are
not a possibility.
The next three sections will discuss examples where small changes in particular physical quantities would dramatically alter the manner in which the Universe develops, and thereby provide no opportunity for the appearance of life. Some of the material in these sections is very technical in nature, and will draw on background presented in BBB.
5. THE FINE TUNING OF THE
PROTON-PROTON CYCLE
An
example of this from BBB is the first interaction (20) of the proton-proton
cycle for the generation of nuclear energy in the sun:
1H +
1H Y 2H +
positron + neutrino (1)
where 1H denotes a
hydrogen nucleus, which is a proton p. The symbol 2H,
sometimes written D or 2D, corresponds to a deuteron, a heavy
hydrogen nucleus, which consists of a proton plus a neutron. Using this notation the interaction (1) can
be written:
p
+ p Y D
+ e+ + < (2)
where e+ is a positive
electron called a positron, and the Greek letter nu, <, denotes a neutrino. This reaction may be looked upon as
proceeding via the formation of an intermediate transitory state in which one
of the protons transforms to a neutron n plus a positron, and then the neutron
combines with the other proton to form the deuteron, corresponding to the
overall process:
p
+ p = p + n + e+
+ < Y D
+ e+ + < (3)
The step p + n Y D involves very little energy because the
deuteron is very weakly bound. The other
possible interaction p + p Y 2He where two protons combine to
form light helium-2 cannot occur because
2He does not have a bound state. In other words the strong interaction is not
strong enough to form 2He, and it is barely strong enough to form
D. If the strong interaction were weaker
then deuterons would never form, and the sun would be unable to burn its
hydrogen fuel by the proton-proton cycle.
If, on the other hand,
this interaction were stronger then the cycle would end with
helium-2, and helium-4 would never form.
Nature has established a delicate balance whereby the strong interaction
is just the proper strength so stars like the sun can burn their hydrogen fuel
in a manner that eventually leads to the appearance of life.
6.
Another
example of the application of the Weak Anthropic
principle is the stability of atomic nuclei.
A nucleus tends to contain equal numbers of protons and neutrons because
they are held together by the strong attractive forces acting between these
nucleons. As a result light nuclei have
equal numbers of protons and neutrons.
When nuclei become larger the repulsive electromagnetic interactions
between the positively charged protons become appreciable so more neutrons are
added to reduce this repulsion. Bismuth,
with atomic number 83, has the heaviest nucleus that is not radioactive. All larger nuclei are unstable. We showed in BBB that the strong interaction
is 137 times as strong as the electromagnetic interaction. If the electromagnetic interaction were
relatively stronger then nuclei much lighter than bismuth would become radioactive
and unstable, hence unsuitable for playing roles in biological organisms. A number of heavy atoms play important roles
in the human body, such as iodine (I, atomic number 53), tin (Sn, 50), and molybdenum (Mo, 42), and they would not be
available to do so if the electromagnetic interaction were much stronger. The dimensionless fine structure constant " discussed in BBB is what
determines the relative strengths of the strong and electromagnetic
interactions, and this sets limits on values of " that would support human
life.
7. CRITICAL
DENSITY
A
third example of the delicate balance of forces that exists in the Universe
involves its large scale structure. The
Universe is found to be very close to isotropic, that is, its structure is
almost the same in all directions. It is
also found to be homogeneous, that is, every large region of space looks the
same. The fact that the Universe is
homogeneous and isotropic is called the Cosmological Principle.
One
important parameter that characterizes the Universe is its density, meaning the
average density, or the amount of mass per unit volume averaged over galaxies,
galaxy clusters, and the space between them.
This density is very low, about four hydrogen atoms per cubic meter of
space. If the density of the Universe is
less than a certain critical density, then the curvature of space is negative,
and it will be an open system destined to expand forever. If the density is less than the critical
density the curvature of space is positive, the Universe is closed, and it will
eventually contract and collapse.
Astronomers find that our actual Universe has close to the critical
density, so it is an almost flat Universe with zero curvature of space. It will also undergo continual expansion, but
at a continually decelerating rate. It
will take an infinite duration in time to come to a stop at its final maximum
size.