Title: Relativity - Experimental evidence for general relativity | Britannica
Headings: Experimental evidence for general relativity
Experimental evidence for general relativity
Applications of relativistic ideas
Elementary particles
Particle accelerators
Fission and fusion: bombs and stellar processes
The global positioning system
Know about the application of gravitational waves in science and our day to day life
Cosmology
Relativity, quantum theory, and unified theories

Content: Relativity, quantum theory, and unified theories
Cosmic behaviour on the biggest scale is described by general relativity. Behaviour on the subatomic scale is described by quantum mechanics, which began with the work of the German physicist Max Planck in 1900 and treats energy and other physical quantities in discrete units called quanta. A central goal of physics has been to combine relativity theory and quantum theory into an overarching “theory of everything” describing all physical phenomena. Quantum theory explains electromagnetism and the strong and weak forces, but a quantum description of the remaining fundamental force of gravity has not been achieved. After Einstein developed relativity, he unsuccessfully sought a so-called unified field theory with a space-time geometry that would encompass all the fundamental forces. Other theorists have attempted to merge general relativity with quantum theory, but the two approaches treat forces in fundamentally different ways. In quantum theory, forces arise from the interchange of certain elementary particles, not from the shape of space-time. Furthermore, quantum effects are thought to cause a serious distortion of space-time at an extremely small scale called the Planck length, which is much smaller than the size of elementary particles. This suggests that quantum gravity cannot be understood without treating space-time at unheard-of scales. Although the connection between general relativity and quantum mechanics remains elusive, some progress has been made toward a fully unified theory.