The anthropic principle is one of my favorite topics.
So many interesting ideas and personalities with many
controversies. IOW, science at its best :-). As a
brief illustration, people can't even agree on what
the anthropic principle is, some saying it is an answer
to the design argument while others claiming that it
*is* the design argument.
An example of the former view is:
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There does exist a line of thinking that _is_ in direct
competition with the anthropic principle. Edward Harrison,
in his textbook _Cosmology_, advises his readers early on:
"We shall occasionally refer to the anthropic principle,
and the reader may, if it is preferred, substitute the
alternative theistic principle." The theistic principle
is quite straightforward: the reason the universe seems
tailor-made for our existence is that it _was_ tailor-made
for our existence; some supreme being created it as a home
for intelligent life. Of course, some scientists, believing
science and religion mutually exclusive, find this idea
unattractive. Faced with questions that do not neatly fit
into the framework of science, they are loath to resort to
religious explanation; yet their curiosity will not let
them leave matters unaddressed. Hence, the anthropic principle.
It is the closest that some atheists can get to God.
-- Pagels, H. (1985). "A Cozy Cosmology," <The Sciences>
25(2):35-38. also in <Physical Cosmology and Philosophy>,
Ed. J. Leslie, Macmillan, New York, 1990, pp. 174-180.
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An example of the latter view (much shorter):
"The anthropic principle is the design argument in scientific
costume" --Timothy Ferris <The Whole Shebang>
OK, back to the subject at hand.
I had previously argued that not just any MWT will provide
an answer to fine tuning. The "answer" comes by way of
anthropic selection, so obviously there must be something
to select from. This implies then that the Many Worlds must
actually exist (as opposed to just being logically possible)
and that they must vary in their physical laws and constants
(they must vary in whatever happens to be finely tuned).
A review of many of the MWT's is available in Gale (1990)
[refs at end]. Gale claims that all MWT's (modern as well
as ancient) fall into one of three categories:
1) Spatially Multiple Universes
2) Temporally Multiple Universes
3) Other-Dimensional Multiple Universes
I believe the suggestion made previously by John Rylander
would fall into category (3). Interestingly, the first
attempt to explain fine-tuning with a MWT and anthropic
selection involved the scenario outlined by John.
This was proposed by Brandon Carter in 1974.
Category (3) MWT's are basically of the oscillatory,
bouncing universe type.
Here I'm going to concern myself only with category (1)
MWT's since I consider them to be the most promising.
One reason for this is that many worlds can arise from
the currently most popular version of the big bang,
the inflationary universe first proposed by Alan Guth.
Guth proposed the inflationary universe in an attempt
to solve some problems associated with the standard
big bang but apparently did not notice originally the
potentiality of the theory for producing many worlds.
A crude description follows, hopefully physicists will
forgive my crudity :). All the action takes place an
infinitesimal fraction of a second (about 10^-30 sec)
after the bang and then lasts only an infinitesimal
fraction of a second. During this short period there
is a tremendous exponential inflation of the universe.
The inflation is so rapid that some regions become
causally disconnected. These causally disconnected
regions become the "many worlds".
Well, as I argued before, more than many worlds is
required. The many worlds must have different laws
and constants. To get this one needs to add to the
inflationary universe an hypothesis about how laws
come into existence. One popular idea is that laws
come about by symmetry breaking bifurcations during
the early stages of the bang. A good analogy for this
is crystallization. The laws "crystallize". This
is considered to be a stochastic process. Thus, if
this crystallization occurred after the regions
become causally disconnected one could obtain many
worlds with widely varying physical laws and constants,
as required for the anthropic selection argument.
OK, now its disclaimer time. My presenting the above
should in nowise be considered an endorsement of same $-).
reference:
Gale, G. 1990. "Cosmological Fecundity: Theories of
Multiple Universes," in <Physical Cosmology and Philosophy>
J. Leslie, Ed., Macmillan.
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"It is not certain that all is uncertain,
to the glory of skepticism." -- Pascal