AlphaG

AlphaG, written α_G, is the gravitational fine-structure constant in discussions of gravity at quantum scales. It is a dimensionless parameter that measures the strength of gravity relative to quantum mechanics for a given mass scale. The standard definition is α_G = G m^2 / (ħ c), where G is the gravitational constant, m is a particle or system mass, ħ is the reduced Planck constant, and c is the speed of light.

For a single elementary particle such as the proton, α_G is extremely small (approximately 5.9 × 10^-39), illustrating why gravity is negligible in ordinary quantum phenomena compared with electromagnetism and the other fundamental forces. Because α_G scales with the square of the mass, a system with greater mass increases its gravitational coupling, but the value remains small until masses approach the Planck scale.

AlphaG is not a universal constant; it is a scale-dependent quantity used mainly in theoretical contexts such as quantum gravity, semiclassical gravity, and discussions of the relative strengths of fundamental interactions. It serves as a convenient benchmark for comparing gravitational effects to those of other forces and for framing questions about the hierarchy between gravity and quantum mechanics. In many treatments, α_G is linked to Planck units, with the Planck mass defined by α_G ≈ 1.

Related concepts include the gravitational fine-structure constant, Planck units, and explorations of quantum gravity.