1927: Copenhagen interpretation
While we have already discussed the Copenhagen Interpretation in the context of the pre-war years, it is probably worth putting this interpretation into some overall perspective of developments that have led to the current spread of ideas. In many ways, the Copenhagen interpretation might now be better described as the initial ‘holding position’ that sought to abstain from too much speculation following the early formulation of quantum wave mechanics based on:
- deBroglie’s matter waves (1924)
- Schrodinger’s wave equation (1926)
- Born's probability interpretation (1926)
- Heisenberg's uncertainty principle (1927)
- Bohr's complementarity principle (1928)
As such, this holding position was predicated on a number of assumptions linked to the idea that quantum knowledge depended on the state of the wave function. However, given the suggestion that a discrete particle does not exist prior to the wave function collapse, it was then inferred that objective reality itself may not exist prior to measurement. Bohr himself questioned the objective reality of quantum waves, since these waves required complex numbers, which he assumed had no physical meaning. However, he also took a somewhat contradictory position in arguing that atoms were ‘real’ and not just a mathematical construct.
- The double-slit experiment:
Here it was argued that the wave function collapse has to occur as soon as you know the path of the electrons. In some respect, it did not seek to speculate further and simply held to the position that this was simply a property of the quantum reality, which could not be explain any further.
- The EPR paradox:
Based on limited experimental data, it was initially assumed that quantum mechanics provided an accurate mathematical model of quantum reality, which simply bypassed the issue of objective reality by maintaining that any description of quantum reality had to be restricted to a probability function. However, in many respects, the full implication of the EPR paradox was not really understood within the pre-war years, and possibly not even now, such that any interpretation of locality and causality was initially highly speculative.
From a historical perspective, most commentaries suggest that Bohr argued his case against Einstein and won. It might also be said that in the 80+ years that have passed, there has been no significant breakthrough that can be used to absolutely refute the Copenhagen position. However, while the Copenhagen interpretation was generally accepted as a basis of the standard model, there was, and possibly still is, a sense of dissatisfaction in that it appears to simply side-step the key issue of objective reality by its assertion that science is simply denied further access to the quantum realm. As a result, others have sought an alternative interpretation that either avoids or better explains the perceived paradoxes in quantum mechanics.