The
fine-tuned Universe is the idea that the conditions that allow
life in the
Universe can only occur when certain universal
physical constants lie within a very narrow range, so that if any of several fundamental constants were only slightly different the universe would be unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is presently understood.
[1]There is no firm scientific consensus that the fine-tuning hypothesis is correct. Among scientists who find the evidence persuasive, a variety of scientific explanations have been proposed, e.g., the anthropic principle. The idea has also attracted discussion among philosophers and theologians, as well as creationists.
The premise of the fine-tuned universe assertion is that a small change in several of the dimensionless fundamental physical constants would make the universe radically different.
If, for example, the strong nuclear force were 2% stronger than it is (i.e., if the coupling constant representing its strength were 2% larger), diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium. This would drastically alter the physics of stars, and presumably preclude the existence of life similar to what we observe on Earth. However, many of the fundamental constants describe the properties of the unstable strange, charmed, bottom and top quarks and mu and tau leptons which seem to play little part in the universe or the structure of matter.
