Regarding the question of scientific paradigms, the cyclic-universe paper
I mentioned a few days ago made an interesting point.  The paper may be
found at http://arxiv.org/abs/astro-ph/0204479.

The main author, Paul Steinhardt, is a successful physicist who has done
a great deal of original work in conventional cosmology, particularly
inflation theory.  (Inflation is the theory that the universe expanded
extremely quickly at an early stage, which helps to explain why the
larger universe is as uniform as it is seen to be.)  Steinhardt now
presents what may strike many physicists as an exotic, even "oddball"
theory which denies the existence of inflation, one of the cornerstones
of modern cosmology.  In his second paragraph he takes pains to show
the promise of his new theory:

   The purpose of this paper is to introduce a new type of cosmological
   model - not a variant of an older model, but, a genuinely new
   cosmological framework.  This new paradigm turns cosmic history
   topsy-turvy.  And yet, as you will see, it is able to reproduce all
   of the successful predictions of the consesnsus model with the same
   exquisite detail.  Perhaps you will even conclude that the cyclic
   Universe accomplishes the feat more economically.

Later in the paper he indirectly comments on the difficulty he knows he
faces in persuading people to give the new theory a fair hearing:

   The cyclic model could have been proposed at the same time as
   inflation, in which case it would have been interesting to see which
   proposal would have emerged as the more appealing idea.  As it is,
   the cyclic model has arrived twenty years late, after cosmologists
   have become attached to the inflationary paradign, so there can be
   no fair measure.

Let me say first that, although I am no physicist, I think Steinhardt
is somewhat over-selling his theory here.  There were a number of holes
in the picture where he promised that ongoing work was showing excellent
signs of filling in these remaining details.  But still, inflation has 20
years of testing, development and refinement behind it.  His new theory
really cannot be said to be quite on the same firm footing as inflation.

Nevertheless, he has a point, which is that to some extent in science
the historical accident of which theory comes first may be influential
in terms of the theory becoming better accepted.  It will be interesting
to see how Steinhardt's cyclic model fares vis a vis inflation, if both
models truly do turn out to explain the observations equally well.

Hal Finney

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