The rare Earth doctrine, the conclusion that Earth has many unique features that enable it to support life and, in particular, advanced life, is well established within the scientific community.
The discovery of about 250 extrasolar planets, combined with spacecraft missions to explore the outer solar system, likewise is beginning to establish the rare solar system doctrine. Now, a new doctrine is emerging to complement the others—the rare Milky Way Galaxy doctrine.
Many features of a galaxy must be fine-tuned for life to be possible within it. Several are listed and described in The Creator and the Cosmos, pages 176-79, and 188-89. And a team of French astronomers has just added another. They discovered that among spiral galaxies (life is possible only in a spiral galaxy) the Andromeda Galaxy is typical, whereas the Milky Way Galaxy (MWG) is exceptional.
The MWG is exceptional in that it has escaped any major merging event with other galaxies over at least the last ten billion years. Not so for the Andromeda Galaxy. As a team led by the South African astronomer David Block (an RTB volunteer) recently demonstrated, the huge warp in the spiral arms of the Andromeda Galaxy was caused by a not-so-small galaxy passing through its center about 210 million years ago.
Major merging events can disturb the structure of a spiral galaxy for a billion years or more. A lack of such events over the history of a planetary system and during the billion years or so before the formation of that planetary system is necessary for the eventual support of advanced life in that system. Yet, for life to be possible within a planetary system its spiral galaxy cannot be totally without merging events. The relatively frequent accretion of dwarf galaxies by a spiral galaxy is critical for preserving the long-term spiral structure.
For advanced life to become a possibility within a spiral galaxy, the galaxy must absorb dwarf galaxies that are large enough to preserve the spiral structure, but not so large as to significantly disturb or disrupt the spiral structure. Also, the rate at which it absorbs dwarf galaxies must be frequent enough to preserve the spiral structure, but not so frequent as to significantly distort it. All these just-rights are found in the MWG. Astronomers know of no other galaxy that manifests all the qualities that advanced life demands. The rarity of the MWG in its capacity to support advanced life comprises one more argument in favor of a supernatural, superintelligent Being designing the universe for the benefit of life, and for human beings in particular.