We may occupy a preferred place or preferred time in the Universe (we may also occupy a preferred universe). This uncomfortable idea may follow from several vexing facts about our Universe:

• Horizon problem
• Flatness problem
• Matter/Anti-matter asymmetry
• Cosmological constant
• ....

It does appear as though we live in a special universe. Some quantities assume highly improbable values, for example, the flatness of the Universe is disturbing. Several questions are:

• Are these special values simply the way our Universe is (that is, is it a coincidence that our Universe has these properties)?
• Is there a deeper level to the physical nature of the Universe which we do not understand (which makes our type of Universe the most probable type of Universe)?
• .....

These questions are interesting in the sense that if we can understand the origins of the above problems, this would imply that we understand how the Universe was constructed (in the beginning) which would be intellectually satisfying and would also offer the admittedly rather far-fetched notion that we could perhaps engineer the space-time structure of the Universe.

Anthropic Principle

Note that if some of the finely-balanced quantities were not finely-tuned then our Universe would have grossly different properties. The properties would, in fact, be so different that it is highly likely that life (as we know it) would not develop and we would not be around to ask the question of why does the Universe appear special:

• if the Univerese is strongly closed, it would have recollapsed by now and we have sped through the galaxy/star/planet/life-forming phases too quickly
• if the Universe is very open, expanding very quickly, then the time when the Universe was dense enough to be in the galaxy/star/planet/life-forming phases would be too short

That is, life is likely to develop in Universes which expand at about the rate and has roughly the properties of the current Universe. Therefore, selection effects would say that it is only in universes where the conditions are right for life (thus pre-selecting certain universes) is it possible for the questions of specialness to be posed.

This statement and variants of this statement are the gist of the Anthropic Principle. Note that the Anthropic Principle is probably true in some sense, and says that there is nothing mysterious about why our Universe is special in terms of the development of life. However, it does not rule out the possibility that there is a deeper level to our understanding of the Universe which makes our Universe (and its finely tuned parameters) the most probable universe from the plethora of all possible universes. This still may be true but is not required philosophically or scientifically.