General relativity and quantum mechanics don't get along. A theory of everything, such as the string theory was meant to reconcile them. But they are mutually incompatible, and they cannot both be right. General relativity is a theoretical framework that only focuses on gravity for understanding the Universe in regions of both large scale and high mass: stars, galaxies, clusters of galaxies, etc. Quantum mechanics is a theoretical framework that only focuses on three non-gravitational forces for understanding the Universe in regions of both small scale and low mass: sub-atomic particles, atoms, molecules, etc. A theory of everything is a hypothetical single, all-encompassing, coherent theoretical framework of physics that thoroughly explains and links together all physical aspects of the Universe. Axions and the string theory The string theory says that at the beginning of the Universe, up to 10\u221243 seconds after the Big Bang, the four fundamental forces were once a single fundamental force. It provides a unified description of gravity and particle physics, which makes it a candidate for a theory of everything. This self-contained mathematical model describes all fundamental forces and forms of matter. The novelty is that 200 million light-years away, in a galaxy cluster, no axions were found. The axion is a hypothetical elementary particle that, if existent, is of interest as a possible component of cold dark matter. The most important aspect of the axion is that, if it'd exist, it could solve the most underrated puzzle in all of physics: why does quantum chromodynamics seem to preserve CP-symmetry? CP-symmetry plays an important role both in the attempts of cosmology to explain the dominance of matter over antimatter in the present Universe and the study of weak interactions in particle physics. The string theory strongly supports the axion's existence, by predicting that large numbers of particles that behave as axions exist. The theory calls them axion-like particles. The new study on the string theory Scientists used the Chandra X-ray Observatory to study the active nucleus of a galaxy called NGC 1275 that sits at the heart of a cluster of galaxies called the Perseus cluster. Astrophysicist Christopher Reynolds of the University of Cambridge in the UK observed that they couldn't detect the hypothetical axions. And their observations were as sensitive as about a millionth of a billionth of the mass of an electron. "These constraints dig into the range of properties suggested by string theory, and may help string theorists weed their theories," says astronomer Helen Russell of the University of Nottingham in the UK.