cGh physics refers to the mainstream attempts in physics to unify relativity, gravitation and quantum mechanics, in particular following the ideas of Matvei Petrovich Bronstein and George Gamow. The letters are the standard symbols for the speed of light (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 (_,_,_)
Special relativity (c,_,_), Gravitation (_,G,_), Quantum mechanics (_,_,h)
General relativity (c,G,_), Quantum field theory (c,_,h), Non-relativistic quantum theory with gravity (_,G,h)
Theory of everything, or relativistic quantum gravity (c,G,h)
Other cGh subjects include Planck units, Hawking radiation and black hole thermodynamics.
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.[5]

Matvei Petrovich Bronstein (Russian: Матвей Петрович Бронштейн, December 2 [O.S. November 19] 1906, Vinnytsia – February 18, 1938) was a Soviet theoretical physicist, a pioneer of quantum gravity, author of works in astrophysics, semiconductors, quantum electrodynamics and cosmology, as well as of a number of books in popular science for children.
He introduced the cGh scheme for classifying physical theories. “After the relativistic quantum theory is created, the task will be to develop the next part of our scheme, that is to unify quantum theory (with its constant h), special relativity (with constant c), and the theory of gravitation (with its G) into a single theory.”
He was married to Lydia Chukovskaya, a writer, prominent human rights activist, and a friend of Andrei Sakharov.
During the Great Purge, in August 1937 Bronstein was arrested. He was convicted by a list trial (“по списку”) in February 1938 and executed the same day in a Leningrad prison. His wife was told that he was sentenced to 10 years of labor camps without the right of correspondence.
Bronstein’s books for children “Solar matter” (Солнечное вещество), “X Rays” (Лучи X), “Inventors of Radio” (Изобретатели радио) were republished after he had been rehabilitated in 1957.
The “Bronstein Prize in Loop Quantum Gravity” is offered to Post-doctoral scholars in the field, the inaugural winner of which was Eugenio Bianchi in 2013.

The path integral formulation of quantum mechanics is a description of quantum theory that generalizes the action principle of classical mechanics. It replaces the classical notion of a single, unique classical trajectory for a system with a sum, or functional integral, over an infinity of quantum-mechanically possible trajectories to compute a quantum amplitude.
This formulation has proven crucial to the subsequent development of theoretical physics, because manifest Lorentz covariance (time and space components of quantities enter equations in the same way) is easier to achieve than in the operator formalism of canonical quantization. Unlike previous methods, the path integral allows a physicist to easily change coordinates between very different canonical descriptions of the same quantum system. Another advantage is that it is in practice easier to guess the correct form of the Lagrangian of a theory, which naturally enters the path integrals (for interactions of a certain type, these are coordinate space or Feynman path integrals), than the Hamiltonian. Possible downsides of the approach include that unitarity (this is related to conservation of probability; the probabilities of all physically possible outcomes must add up to one) of the S-matrix is obscure in the formulation. The path-integral approach has been proved to be equivalent to the other formalisms of quantum mechanics and quantum field theory. Thus, by deriving either approach from the other, problems associated with one or the other approach (as exemplified by Lorentz covariance or unitarity) go away.
The path integral also relates quantum and stochastic processes, and this provided the basis for the grand synthesis of the 1970s, which unified quantum field theory with the statistical field theory of a fluctuating field near a second-order phase transition. The Schrödinger equation is a diffusion equation with an imaginary diffusion constant, and the path integral is an analytic continuation of a method for summing up all possible random walks.
The basic idea of the path integral formulation can be traced back to Norbert Wiener, who introduced the Wiener integral for solving problems in diffusion and Brownian motion. This idea was extended to the use of the Lagrangian in quantum mechanics by P. A. M. Dirac in his 1933 article. The complete method was developed in 1948 by Richard Feynman. Some preliminaries were worked out earlier in his doctoral work under the supervision of John Archibald Wheeler. The original motivation stemmed from the desire to obtain a quantum-mechanical formulation for the Wheeler–Feynman absorber theory using a Lagrangian (rather than a Hamiltonian) as a starting point.

https://en.wikipedia.org/wiki/Path_integral_formulation