''cGh'' physics refers to the historical attempts in physics to unify relativity, gravitation and quantum mechanics, in particular following the ideas of

Matvei Petrovich Bronstein Matvei Petrovich Bronstein (russian: Матве́й Петро́вич Бронште́йн, , Vinnytsia – February 18, 1938) was a Soviet theoretical physicist, a pioneer of quantum gravity, author of works in astrophysics, semiconductors, quan ...

and

George Gamow George Gamow (March 4, 1904 – August 19, 1968), born Georgiy Antonovich Gamov ( uk, Георгій Антонович Гамов, russian: Георгий Антонович Гамов), was a Russian-born Soviet and American polymath, theore ...

. The letters are the standard symbols for the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...

(''c''), the gravitational constant (''G''), and Planck's constant (''h''). If one considers these three universal constants as the basis for a 3-D coordinate system and envisions a cube, then this pedagogic construction provides a framework, which is referred to as the ''cGh'' cube, or physics cube, or cube of theoretical physics (CTP). This cube can used for organizing major subjects within physics as occupying each of the eight corners. The eight corners of the ''cGh'' physics cube are: *

Classical mechanics Classical mechanics is a physical theory describing the motion of macroscopic objects, from projectiles to parts of machinery, and astronomical objects, such as spacecraft, planets, stars, and galaxies. For objects governed by classical ...

(_, _, _) *

Special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The law ...

(''c'', _, _), gravitation (_, ''G'', _),

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, q ...

(_, _, ''h'') *

General relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. ...

(''c'', ''G'', _),

quantum field theory In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity, and quantum mechanics. QFT is used in particle physics to construct physical models of subatomic particles a ...

(''c'', _, ''h''), non-relativistic quantum theory with gravity (_, ''G'', ''h'') *

Theory of everything A theory of everything (TOE or TOE/ToE), final theory, ultimate theory, unified field theory or master theory is a hypothetical, singular, all-encompassing, coherent theoretical framework of physics that fully explains and links together all asp ...

, or relativistic

quantum gravity Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics; it deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the v ...

(''c'', ''G'', ''h'') Other ''cGh'' subjects include Planck units,

Hawking radiation Hawking radiation is theoretical black body radiation that is theorized to be released outside a black hole's event horizon because of relativistic quantum effects. It is named after the physicist Stephen Hawking, who developed a theoretical ar ...

and

black-hole thermodynamics In physics, black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons. As the study of the statistical mechanics of black-body radiation led to the developmen ...

. While there are several other physical constants, these three are given special consideration, because they can be used to define all Planck units and thus all physical quantities. The three constants are therefore used sometimes as a framework for philosophical study and as one of pedagogical patterns.

Overview

Before

Ole Rømer Ole Christensen Rømer (; 25 September 1644 – 19 September 1710) was a Danish astronomer who, in 1676, made the first measurement of the speed of light. Rømer also invented the modern thermometer showing the temperature between two fi ...

made the first successful estimate of the speed of light in 1676, it was not known whether the speed of light (''c'') was infinite or not. Because of the tremendously large value of ''c'' (i.e. 299,792,458 metres per second in vacuum) compared to the speeds of things in our daily experience, the propagation of light seems to us to be instantaneous. Hence, the ratio 1/''c'' was hidden from our view making

relativistic mechanics In physics, relativistic mechanics refers to mechanics compatible with special relativity (SR) and general relativity (GR). It provides a non-quantum mechanical description of a system of particles, or of a fluid, in cases where the velocities of ...

irrelevant. At speeds comparable to the speed of light (''c''), special relativity takes the finitude of the speed of light into consideration by the aid of

Lorentz transformation In physics, the Lorentz transformations are a six-parameter family of linear transformations from a coordinate frame in spacetime to another frame that moves at a constant velocity relative to the former. The respective inverse transformation i ...

. A non-relativistic theory is recovered from a relativistic theory when the limit 1/''c'' is set to zero. The gravitational constant (''G'') is irrelevant for a system where gravitational forces are negligible. For example, the special theory of relativity is the special case of general relativity in the limit ''G'' → 0. Similarly, in the theories where the effects of quantum mechanics are irrelevant, the value of Planck constant (''h'') can be neglected. For example, setting ''h'' → 0 in the

commutation relation In mathematics, the commutator gives an indication of the extent to which a certain binary operation fails to be commutative. There are different definitions used in group theory and ring theory. Group theory The commutator of two elements, ...

of quantum mechanics, the uncertainty in the simultaneous measurement of two

conjugate variables Conjugate variables are pairs of variables mathematically defined in such a way that they become Fourier transform duals, or more generally are related through Pontryagin duality. The duality relations lead naturally to an uncertainty relation— ...

tends to zero, approximating quantum mechanics with classical mechanics.

In popular culture

chose "C. G. H." as the initials of his fictitious character, Mr C. G. H. Tompkins.

References

{{Branches of physics Theoretical physics