The precise formulation of the idea is made difficult by the fact that physicists do not yet know how many independent physical constants there are.The current standard model of particle physics has 25 freely adjustable parameters with an additional parameter, the cosmological constant, for gravitation.For example, the cosmological constant may be a fundamental constant, but attempts have also been made to calculate it from other constants, and according to the author of one such calculation, "the small value of the cosmological constant is telling us that a remarkably precise and totally unexpected relation exists among all the parameters of the Standard Model of particle physics, the bare cosmological constant and unknown physics." An older example is the Hoyle state, the third-lowest energy state of the carbon-12 nucleus, with an energy of 7.656 Me V above the ground level.According to one calculation, if the state's energy level was lower than 7.3 or greater than 7.9 Me V, insufficient carbon would exist to support life.The fine-tuned Universe is the proposition that the conditions that allow life in the Universe can occur only when certain universal dimensionless 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 understood.Various possible explanations of ostensible fine-tuning are discussed among philosophers, scientists, theologians, and proponents and detractors of creationism.This would drastically alter the physics of stars, and presumably preclude the existence of life similar to what we observe on Earth.
In 1913, the chemist Lawrence Joseph Henderson (1878–1942) wrote The Fitness of the Environment, one of the first books to explore concepts of fine tuning in the Universe.
He compares "the chance of obtaining even a single functioning protein by chance combination of amino acids to a star system full of blind men solving Rubik's Cube simultaneously".
John Gribbin and Martin Rees wrote a detailed history and defence of the fine-tuning argument in their book Cosmic Coincidences (1989).
However, because the standard model is not mathematically self-consistent under certain conditions (e.g., at very high energies, at which both quantum mechanics and general relativity are relevant), physicists believe that it is underlaid by some other theory, such as a grand unified theory, string theory, or loop quantum gravity.
In some candidate theories, the actual number of independent physical constants may be as small as one.