In 1956 Hugh Everett III published his Ph.D. dissertation titled “The Theory of the Universal Wave Function.” In this paper Everett argued for the relative state formulation of quantum theory and a quantum philosophy, which denied wave collapse. (DOWNLOAD HERE)
Initially, this interpretation was highly criticized by the physics community and when Everett visited Niels Bohr in Copenhagen in 1959 Bohr was unimpressed with Everett’s most recent development. In 1957 Everett coined his theory as the Many Worlds Interpretation (MWI) of quantum mechanics. In an attempt to circumvent the problem of defining the mechanism for the state of collapse Everett suggested that all orthogonal relative states are equally valid ontologically. What this means is that all-possible states are true and exist simultaneously.
Everett left the field of pure physics and went on to work for the Department of Defense until his untimely death in 1982. Since his seminal work many have had their reserves due to the mere weirdness, B.S. DeWitt, whose work was critical for Everett, stated,
[I] still recall vividly the shock I experienced on first encountering this multiworld concept. The idea of 10100 slightly imperfect copies of oneself all constantly splitting into further copies, which ultimately become unrecognizable, is not easy to reconcile with common sense. Here is schizophrenia with a vengeance.
However, there are still those who find the interpretation attractive. The Oxford philosopher David Wallace puts it this way:
[I]n recent work on the Everett (Many-Worlds) interpretation of quantum mechanics, it has increasingly been recognized that any version of the interpretation worth defending will be one in which the basic formalism of quantum mechanics is left unchanged. Properties such as the interpretation of the wave-function as describing a multiverse of branching worlds, or the ascription of probabilities to the branching events, must be emergent from the unitary quantum mechanics rather than added explicitly to the mathematics.
 Jonathan Allday, Quantum Reality: Theory and Philosophy (Boca Raton, FL: Taylor & Francis, 2009), 439.
 An orthogonal state is one that is mutually exclusive. A system cannot be in two orthogonal states at the same time. As a result of the measurement interaction, the states of the observer have evolved into exclusive states precisely linked to the results of the measurement. At the end of the measurement process the state of the observer is the sum of eigenstate—or a combination of the sums of eigenstates, one sum for each possible value of the eigenvalue. Each sum is the relative state of the observer given the value of the eigenvalue. Allday, 442-43.
 Quoted in Allday, 455.
 David Wallace, “Everettian Rationality: Defending Deutsch’s Approach to Probability in the Everett Interpretation,” arXiv:quant-ph/0303050v2 (Mar. 2003): 1.