When
Newton formulates the
Gravitational Theory in the
17th century, you would never think that it would complicate things so much. Newton manages to explain how gravity works and its influence, but never explains why and the origin of this force. Objects, according to Newton and according to what we can now say with certainty, attract each other according to each other''s mass. Newton was able, through its various forms, to predict and describe this force; however, he couldn''t understand how it was that it worked.
Einstein, in the early
20th century, redefines the way of understanding Gravity with his theory of
General Relativity. Asserting that nothing could go faster than the speed of light comes into conflict with Newton, who affirmed that Gravity acted instantly at any distance. What Einstein formulates to integrate the ideas of gravity, and rethink Newton, without betraying the absolute speed of light, is the space-time mesh. Einstein raises that the universe can be understood on a spatio-temporal mesh. Heavier objects curve this mesh, producing what we mean by Gravity.
Einstein revolutionizes physics with his theory and aims with it (we know from his letters) to one much larger goal: a unifying theory to explain the cosmic order; i.e., that integrates the other known force until the time: Electromagnetism.
Maxwell had succeeded in integrating two forces which had an apparent relationship: electricity and magnetism. Einstein admired this achievement, and intended to unify
electromagnetism with the force he had restated: gravity. However, the differences between both forces increased, and thus Einstein failed ever to integrate them. Gravity worked perfectly to explain the behaviour of the big stars, but electromagnetism was much more powerful at the atomic level.
During the 1920s, a group of scientists began to develop, in parallel to Einstein''s attempts, a new vision of the subatomic behavior: quantum mechanics.
Quantum mechanics explained how the tiny particles that make up the atom are related to each other. Gravity and electromagnetism, at this level, did not work to explain anything. The main problem lies in the way of conceiving the behavior of particles: Einstein''s universe was orderly and harmonious, while the one posed by quantum mechanics, at the subatomic level, was a chaotic and random universe.
Quantum Mechanics is a science of probability. For this branch of physics, everything can happen, and goes as far as to say that if for a phenomenon there are a hundred possibilities, the hundred chances will be carried out. At the subatomic level the odds that something happened which challenged the laws of classical physics are equivalent to those which contradict them. In fact, for Quantum Mechanics, those odds happen in our everyday world as well; however, they are so remote that it would have to spend thousands of years experimenting. Einstein and Quantum Mechanics are inconsistent from the simple fact that Quantum Mechanics stated that it was impossible to know the outcome of an experiment.
The path towards a unifying theory is complicated further when Quantum Mechanics defines two new forces: the
strong nuclear force (which holds together neutrons and protons in the nucleus of the atom) and the
weak nuclear force (which allows that neutrons are transformed into protons, emitting radiation during the process). For this quantum mechanics, all forces (with the exception of gravity) work perfectly on a subatomic scale (electromagnetism, the weak nuclear force and the strong nuclear force).
Thus, the unification which would allow the explanation of the universe and the behavior of the whole, moved away. Einstein, already coming to his death, could not assume the discoveries of Quantum Mechanics. And other scientists did not believe themselves capable of integrating general relativity for electromagnetism and nuclear forces that explained the subatomic behavior.