Einstein was not the only scientist to try to develop a unified field theory. Other physicists working at about the same time had similar interests. Their main discoveries, though, were in other aspects of science and physics. Erwin Schrödinger and Werner Heisenberg were two scientists whose work would be fundamental to the furthering of Einstein's thinking in terms of a unified field theory.
Don't expect to find unified field theory headlining the newspapers anytime soon. It has not been proven, and it currently exists solely as a scientific hypothesis. But perhaps ongoing research will one day turn unified field theory into fact.
Erwin Rudolf Josef Alexander Schrödinger was an Austrian scientist, one of Einstein's contemporaries. He entered the University of Vienna in 1906 and studied theoretical physics, such as Maxwell's equations, thermodynamics, optics, and mechanics. He received his doctorate degree in 1910 and, after a brief stint in the military, took a job working in experimental physics. This break from theoretical physics would prove invaluable to his later work in theory because it provided him with a practical backdrop for his research.
Beginning around 1921, Schrödinger engaged in studies of the nature of the atom. He worked with quantum statistics in the mid-1920s, and he was aware of the work of Louis de Broglie. Schrödinger began conversing with Albert Einstein in 1925, and the two exchanged letters on the subject of physics and contemporary scientists. By 1926 Schrödinger had published new papers on wave mechanics and was gaining worldwide fame. He won the Nobel Prize in physics in 1933.
By the 1940s, Schrödinger was starting to work actively on creating a unified field theory. He published a paper on it in 1943, and in 1946, Schrödinger corresponded with Einstein on the subject. Although he never reached a conclusion of any significance, he would continue this elusive quest for the remainder of his life.
“The Present Situation in Quantum Mechanics,” Schrödinger's work from 1935, discusses his famous cat paradox. A cat placed inside a closed box would live or die depending on a quantum event, Schrödinger rationalized. The paradox was that, until the box was opened, both scenarios existed.
Werner Heisenberg was one of the primary physicists responsible for discovering quantum mechanics. As such, his contribution to the creation of a unified field theory was enormous, because he laid the foundation for one of its four corners. Heisenberg's research focused on developing the “uncertainty principle” of quantum theory, which states that as the position of a subatomic particle is known with more and more certainty, its momentum is known with less and less precision. Position and momentum are therefore coupled, and only one can be known with any certainty. This idea forms the basis for many aspects of quantum theory.
Heisenberg would go back and forth with Schrödinger, as the two scientists developed competing theories. Heisenberg's idea of uncertainty lent itself to an explanation of quantum theory known as the “matrix form,” while Schrödinger actively pursed his research in wave mechanics. Schrödinger would eventually come up with a proof, showing that the two methods arrived at the same conclusions.
Heisenberg's uncertainty principle would later be paraphrased into the notion of the “probability field,” the idea that particles had a tendency to exist at certain places in the space-time continuum, although the exact position of any single particle was impossible to determine. Probability was seen as a potentially unifying factor of all the forces of nature. It couldn't be created or destroyed, and its total amount held constant. While this idea never gained universal recognition or proof, it fed into Einstein's idea that such a universal binder might exist.