We know that several of the distinctive features of the large scale structure of the visible universe play a role in meeting the conditions needed for the evolution of biochemical complexity within it.
The first example is the proximity of the expansion dynamics to the
``critical'' state which separates an ever-expanding future from one of
eventual contraction, to better than ten per cent. Universes that expanded
far faster than this would be unable to form galaxies and stars and hence
the building blocks of biochemistry would be absent. The rapid expansion
would prevent islands of material separating out from the global expansion
and becoming bound by their own self-gravitation. By contrast, if the
expansion rate were far below that characterising the critical rate then the
material in the universe would have condensed into dense structures and
black holes long before stars could form
[16],
[17],
[4],
[19],
[18].
The second example is that of the uniformity of the universe. The
non-uniformity level on the largest scales is very small, 
10-5. This is a measure of the average relative fluctuations in the
gravitational potential on all scales. If were significantly
larger then galaxies would have rapidly degenerated into dense structures
within which planetary orbits would be disrupted by tidal forces and black
holes would form rapidly before life-supporting environments could be
established. If were
significantly smaller then the
non-uniformities in the density would be gravitationally too feeble to
collapse into galaxies and no stars would form. Again, the universe would be
bereft of the biochemical building blocks of life
[20].
In recent years the most popular theory of the very early evolution of the
universe has provided a possible explanation as to why the universe expands
so close to the critical life-supporting divide and why the fluctuation
level has the value observed. This theory is called ``inflation''. It proposes
that during a short interval of time when the temperature was very high (say
~ 1025 K), the expansion of the universe accelerated. This
requires the material content of the universe to be temporarily dominated by
forms of matter which effectively antigravitate for that period of time
[21].
This requires their density 
, and pressure, p, to satisfy the inequality
[19]
The inflation is envisaged to end because the matter fields responsible
decay into other forms of matter, like radiation, which do not satisfy this
inequality. After this occurs the expansion resumes the state of
decelerating expansion that it possessed before its inflationary episode
began.
If inflation occurs it offers the possibility that the whole of the visible
part of the universe (roughly 15 billion light years in extent today) has
expanded from a region that was small enough to be causally linked by light
signals at the very high temperatures and early times when inflation
occurred. If inflation does not occur then the visible universe would have
expanded from a region that is far larger than the distance that light can
circumnavigate at these early times and so its smoothness today is a
mystery. If inflation occurs it will transform the irreducible quantum
statistical fluctuations in space into distinctive patterns of fluctuations
in the microwave background radiation which future satellite observations
will be able to detect if they were of an intensity sufficient to have
produced the observed galaxies and clusters by the process of gravitational
instability.
As the inflationary universe scenario has been explored in greater depth it
has been found to possess a number of unexpected properties which, if they
are realised, would considerably increase the complexity of the global
cosmological problem and create new perspectives on the existence of life in
the universe [22],
[23],
[19].
It is possible for inflation to occur in different ways in different places
in the early universe. The effect is rather like the random expansion of a
foam of bubbles. Some inflate considerably while others hardly inflate at
all. This is termed ``chaotic inflation''. Of course, we have to find
ourselves in one of the regions that underwent sufficient inflation so that
the expansion lasted for longer than t* and stars
could produce
biological elements. In such a scenario the global structure of the Universe
is predicted to be highly inhomogeneous. Our observations of the microwave
background temperature structure will only be able to tell us whether the
region which expanded to encompass out visible part of the universe
underwent inflation in its past. An important aspect of this theory is that
for the first time it has provided us wit ha positive reason to expect that
the observable universe is not typical of the structure of the universe
beyond our visible horizon, 15 billion light years away.
It was subsequently been discovered that under fairly general conditions
inflation can be self-reproducing. That is, quantum fluctuations within each
inflating bubble will necessarily create conditions for further inflation of
microscopic regions to occur. This process or ``eternal inflation'' appears to
have no end and may not have had a beginning. Thus life will be possible
only in bubbles with properties which allow self-organised complexity to
evolve and persist.
It has been found that there is further scope for random variations in these
chaotic and eternal inflationary scenarios. In the standard picture we have
just sketched, properties like the expansion rate and temperature of each
inflated bubble can vary randomly from region to region. However, it is also
possible for the strengths and number of low-energy forces of Nature to
vary. It is even possible for the number of dimensions of space which have
expanded to large size to be different from region to region. We know that
we cannot produce the known varieties of organised biochemical complexity if
the strengths of forces change by relatively small amounts, or in dimensions
other than three because of the impossibility of creating chemical or
gravitational bound states,
[24,
25,
26,
4,
27].
The possibility of these random variations arises because inflation is ended
by the decay of some matter field satisfying (4). This corresponds
to the field evolving to a minimum in its self-interaction potential. If
that potential has a single minimum then the characteristic physics that
results from that ground state will be the same everywhere. But if the
potential has many minima (for example like a sine function) then each
minimum will have different low-energy physics and different parts of the
universe can emerge from inflation in different minima and with different
effective laws of interaction for elementary particles. In general, we
expect the symmetry breaking which chooses the minima in different regions
to be independent and random.
