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Navigation: Contents: Info: The anthropic
principle was set down by Dirac who analysed
Eddington’s magic numbers. Although the Copernican
anthropic principle had been around for quite awhile, it
was Dirac along with Dicke who reinvented it for the 20th
century. Sir Arthur Eddington revealed that the ratios of
the electromagnetic force between the proton and the
electron and the gravitational force of the proton and
the electron is about 1040. Also that the ratio of the
radius of the universe and the electron radius is also
1040. His theory led onto
the calculation of the square root of the number of
particles in the universe which turned out to be about
1040 for a universe where k=1. Two people who
studied these results were Robert Dicke and Paul Dirac.
Dirac deduced that these numbers remain the same at all
epochs of the universe, so that the fundamental constants
must change with time. Dirac’s analyses states that
gravity must grow weaker in inverse proportion to time
and the number of particles must increase in direct
proportion to the square of time. This became known as
Dirac’s large number hypothesis (LNH). Dicke however
proposed that we as observers are at a special epoch of
which life has had a chance to evolve for us to pose such
questions. Certain conditions have been set down by the
fundamental constants that allow life to exist. This
became known as the anthropic principle. From the Greek
word anthropos; man. Its’ underlying statement is
thus:- Why are we
here? Why does the
universe have such special properties to create
life? Is it pure
chance or is there a reason? Two versions of the
anthropic principle were developed- the weak and
strong. Intelligent life
can only develop in special places at particular times,
so observers see very special properties due to the
natural selection effect. The weak AP looks for those
coincidences in nature that create life, but offers no
insight as to why the universe is this way. The preconditions
of the early universe was such that it made it a
necessity for life to evolve. That is to say the universe
must have been constructed this way and could not have
come into existence any other way. For observers to
exist, the universe must be a certain age. This age is
governed by the fact that to create an observer, carbon,
oxygen and other heavy elements must be in abundance.
These elements are produced in supernova, so a rough time
estimate is the lifetime for a star to go from creation
to supernova. This time is:- Now So Now Dirac’s
conclusion to his LNH was that the gravitational constant
G decreases with time. Dicke used the above method to
prove that this is unnecessary and G can remain as a
constant in nature. This proves a selection effect that
we as observers occupy a special place at a special time
and strongly backs up the weak anthropic
principle. There are three
interpretations of the strong anthropic
principle. 1. There is one
universe with the sole intention of developing life.
Being religious in nature, this statement can neither be
proved nor disproved and is generally open to the
theologians and teleolgians for
interpretation. 2. Observers are
solely necessary for the universe to come into
being. 3. A number of
different universes or ‘worlds’ are needed for
the existence of our universe. This is the interpretation
that has the most significance to modern
science. The many worlds
interpretation of quantum mechanics was developed by Hugh
Everett who could not believe the idealistic Copenhagen
interpretation. He could not understand why the wave
function should collapse, and so developed for his PhD
thesis a paper on a many worlds theory. In the many worlds
interpretation, he proposed that the universe branches
off like a tree at every interaction between its
constituent particles. This then stated that instead of
the probability of a particle being at a point in space
time, it is either there or it isn’t.
SchrÖdinger’s cat could not be only 30% dead.
Brandon Carter went on to describe how the universe has
branched off a stupendous amount of times and that we
happen to lie on a branch where all the fundamental
constants are just right to produce life. This also says
that there must be a number of universes that were still
born and that when life has developed in a universe it
will always be there. This generalisation is part of the
final anthropic principle. Although the many
worlds interpretation seems a very improbable theory, the
methods of quantum mechanics along with experiment has
proved its hypothesis. Each constant in
the universe is at such a value just right for life. A
small change in G or e will make life impossible. Most of
the constants in nature can be described using
dimensionless fundamental constants, these
are:- For those studying
the anthropic principle it is needed that they know
whether the universe is a fortunate coincidence or to be
expected. The Universal
Gravitational Constant. If this was
slightly stronger, star formation would proceed more
effectively and all the stars would be more massive than
our sun. These stars would burn up too quickly to produce
life on any orbiting planet. If it was weaker, stars
would be smaller than our sun. It would be impossible to
form life because the heavy elements needed for planets
and life can only be produced in larger stars. Strong
Nuclear Force. If this was weaker,
multi-proton nuclei would not be held together. Any
element heavier than hydrogen would be impossible to
produce. On the other hand, if it was stronger, hydrogen
would be a very rare element in the universe and so
hydrogen fusion would be impossible. Weak Nuclear
Force. This effects
leptons and in particular beta decay. If the weak force
was slightly larger, neutrons would decay more and so
there would be less available to produce helium in the
fusion process. Charge On The
Electron. This binds the
electrons in the atom to the protons in the nucleus. If e
was smaller, no electrons would be held in the atom. If
it was stronger, an electron would not be able to share
an orbit with another electron. Either way life would be
impossible. The Ratio Of
Electron To Proton Mass. If this was
slightly higher or lower, then it would be impossible for
molecules to form. The Age Of
The Universe. It takes about
three billion years for the first stars to form. It then
takes another ten to twelve billion years to turn into
supernova and to throw enough heavy elements out to form
rocky planets suitable for life to evolve. The time
period for life is very narrow. The Velocity
Of Light. As this can be
represented using functions of other constants such as
the fine structure constant, a small change in c would
negate the possibility of life. It is seen that if
any of these constants were slightly different, then it
would be impossible for life to develop. Although
Copernicus stated that we do not occupy a central
position in the universe, we are privileged in some way
to get the correct conditions for life (i.e. temperature,
chemical abundance, age etc…). Most scientists
involved in the anthropic principle have come out against
the strong and for the weak. This is because of the
natural selection effect that allows us in
‘this’ universe to develop into the people that
we are. This does not mean the debate is closed, the
theory that Everett proposed is still a very good
contender to sway the argument towards the strong
anthropic principle. BIBLIOGRAPHY
COPYRIGHT 1999
= ratio of the electric force and gravitational force
between the electron and the proton.
= ratio between the age of the universe and the atomic
light crossing time.
and
where
N is the number of nucleons in the visible universe at
time t.
=
Gravitational fine structure coupling
constant.
=Electromagnetic
fine structure coupling constant.
=Strong
force fine structure coupling constant.
=
Weak force fine structure coupling constant.
=
Proton to electron mass ratio.
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