Problems with Quantum Mechanics

Problems with Quantum Mechanics

Since its discovery in the first half of the 20th century, the unique predictions of quantum mechanics have been intensely scrutinised and never proven false. In fact the theory has been used to explain a wide variety of phenomena including the behaviour of all known subatomic particles and all forces but gravity. It has also been used in chemistry and biology to explain, amongst other things, how our brain interprets different smells (Brookes et al., 2007) and how photosynthesis works (Engel et al., pp.782-786). Almost all modern technology relies on the laws of quantum mechanics to work, including transistors, microchips, lasers, digital cameras and USB drives. Quantum mechanics has solved a wide variety of problems, but in doing so it has created more of its own.

Quantum mechanics challenges classical notions of space, time, matter and probability. Proponents of the collapse approach state that when we measure a property of a quantum system, the different possibilities given in Schrodinger's wave equation collapse into a single result. The probability of any given result can be determined using the Born rule. Yet we have never found these collapse dynamics and there is nothing like them within quantum theory itself.

We could put this problem aside and hope that these dynamics will be discovered in time, but then we still have to solve the problem of how quantum states can interact with ordinary matter at all. This is known as the measurement problem. The measurement problem is similar to the problem faced by mind-body dualists like Descartes, who argued that there are two fundamentally different substances in the universe which interact, despite exhibiting different properties and obeying different laws.

Einstein's theories of relativity have also caused problems for quantum mechanics. There is reason to believe that a quantum theory of gravity will eventually be found but instantaneous action at a distance poses a more serious philosophical problem. The Bohm approach solves all of these problems by dropping the idea of a collapse but it is then unable to explain why all but one of the possibilities given in the Schrodinger equation are suppressed without relying on extra dynamics.

These problems could all be solved with instrumentalism, the view that we should not take physical theories literally when they invoke objects that we cannot see. Instrumentalists argue that all previous scientific theories have been proven false and so we should not take the invisible entities postulated by our current theories literally either. This argument is countered by the fact that instruments have been built which rely on these invisible entities to work. In fact, the immense technological progress that we have made would be miraculous if they did not exist.

References

Brookes, J.C., et al., 2007, 'Could Humans Recognize Odor by Phonon Assisted Tunneling?', Physical Review Letters, Vol.98

Engel, G.S., et al., 2007, 'Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems', Nature, Vol.446