The portrait of reality painted by relativity and quantum mechanics is so far from common sense that it raises problems of interpretation. The mathematics of the theories are precise, and the predictions work fantastically well. But translating mathematics into human terms, especially for quantum mechanics, has remained exceedingly difficult.
The perplexing implications of quantum mechanics were greeted with shock and awe by the developing scientists. Many physicists today believe that a proper explanation of reality in light of quantum mechanics and reliability requires radical revisions of one or more common-sense assumptions: reality, locality, causality or continuity.
Given the continuing confusions in interpreting quantum mechanics, some physicists refuse to accept the idea that reality can possibly be so perplexing, convoluted, or improbable - compared to common sense, that is. And so they continue to believe, as did Einstein, that quantum mechanics must be incomplete and that once "fixed" it will be found that the classical assumptions are correct after all, and then all the quantum weirdness will go away. Outside of quantum physics, there are a few scientists and the occasional philosopher who focus on such things, but most of us do not spend much time thinking about quantum mechanics at all. If we do, we assume it has no relevance to our particular interests. This is understandable and in most cases perfectly fine for practical purposes. But when it comes to understanding the nature of reality, it is useful to keep in mind that quantum mechanics describes the fundamental building blocks of nature, and the classical world is composed of those blocks too, whether we observe them or not. The competing interpretations of quantum mechanics differ principally on which of the common-sense assumptions one is comfortable in giving up.
Copenhagen Interpretation – This is the orthodox interpretation of quantum mechanics, promoted by Danish physicist Niels Bohr (thus the reference to Copenhagen, where Bohr's institute is located). In an overly simplified form, it asserts that there is no ultimately knowable reality. In a sense, this interpretation may be thought of as a "don't ask–don't tell" approach that allows quantum mechanics to be used without having to care about what it means. According to Bohr, it means nothing, at least not in ordinary human terms.
Wholeness – Einstein's protg David Bohm maintained that quantum mechanics reveals that reality is an undivided whole in which everything is connected in a deep way, transcending the ordinary limits of space and time.
Many Worlds – Physicist Hugh Everett proposed that when a quantum measurement is performed, every possible outcome will actualize. But in the process of actualizing, the universe will split into as many versions of itself as needed to accommodate all possible measurement results. Then each of the resulting universes is actually a separate universe.
Quantum Logic – This interpretation says that perhaps quantum mechanics is puzzling because our common sense assumptions about logic break down in the quantum realm. Mathematician John von Neumann developed a "wave logic" that could account for some of the puzzles of quantum theory without completely abandoning classical concepts. Concepts in quantum logic have been vigorously pursued by philosophers.
NeoRealism – This was the position led by Einstein, who refused to accept any interpretation, including the Copenhagen Interpretation, asserting that common sense reality does not exist. The neorealists propose that reality consists of objects familiar to classical physics, and thus the paradoxes of quantum mechanics reveal the presence of flaws in the theory. This view is also known as the "hidden variable" interpretation of quantum mechanics, which assumes that once we discover all the missing factors the paradoxes will go away.
Consciousness Creates Reality – This interpretation pushes to the extreme the idea that the act of measurement, or possibly even human consciousness, is associated with the formation of reality. This provides the act of observation an especially privileged role of collapsing the possible into the actual. Many mainstream physicists regard this interpretation as little more than wishful New Age thinking, but not all. A few physicists have embraced this view and have developed descriptive variations of quantum theory that do accommodate such ideas.
It should be emphasized that at present no one fully understands quantum mechanics. And thus there is no clear authority on which interpretation is more accurate.
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