Nanotechnology and Human Health

Advanced Quantum Mechanical Concepts

Quantum mechanics is indeed difficult to grasp and the implication is that our intuition is incorrect and that experiential knowledge gained from experiment is the only access we have to reality. In fact, much of quantum mechanics is so paradoxical that we can only indicate how things behave but can't even postulate on a mechanism for why reality behaves the way that it does. "Theorists whose prejudice inclined towards determinism were troubled, and they began to ask what was 'really' happening behind the scenes. Quantum mechanics not only gave no answer, but even declared that such questions ought not to be asked! Henceforth, intuition was to be regarded as a very fallible guide, and ideas which used to be regarded as obvious were to be viewed with reserve until experience either vindicated of invalidated them." ³² So in quantum mechanics we are bound to attempting to understand how matter and energy behave in a probabilistic manner without the ability to address why it behaves that way. In addition, measuring has a profound effect on reality. In regard to determining the polarization of a photon, until we decide what direction to set the measuring polaroid "it appears that we cannot talk of the photon having any definite polarization. It seems that our choice of the direction of the 'measuring apparatus' has an influence on the polarization of the photon! According to quantum mechanics, until we make a measurement, the direction of the polarization of the photon is apparently not just unknown but really indeterminate. Pascal Jordan, an author of some of the earliest papers on quantum mechanics, went so far as to say that 'observations not only disturb what has to be measured, they produce it.'" ³³ Consequently, the act of measurement, or even interacting with the world in some fundamental way, creates or defines the reality!

Einstein's objection

Because the objects we see around us have a comforting, solid, reality, they do not seem to be conjured into existence because we choose to look and make a measurement. According to Hey and Walters, "It is not surprising that Einstein would have none of this. He disliked Bohr's denial of an underlying physical reality and believed passionately that physical objects had real, physical properties whether or not we were there to measure them. In a conversation with Abraham Pais, Einstein highlighted what he felt was the absurdity of the situation by asking Pais: 'Does the Moon only exist when you look at it?' It was to attack Bohr's view of the world that Einstein devised his famous 'thought' experiment with two young colleagues at Princeton, Boris Podolsky and Nathan Rosen." ³⁴ John Bell consolidated these apparently philosophical questions into a mathematical formula that could be tested, which is known as Bell's inequality.

The most disturbing consequences of quantum mechanics are philosophical in nature. The classical notion that was formulated by Einstein, Podolsky and Rosen says that "once two systems have been in contact—no matter how long ago, and no matter how far apart they may be now-observing one system drastically alters our view of the other in ways which are difficult to understand. Such correlations are clearly and unambiguously predicted by conventional quantum mechanics; experimental evidence is in their favor; and yet we are unable to comprehend how they can happen. There is nothing wrong with correlation as such: life is full of it. A universe without correlation would be chaotic, uneventful and dull. But quantum mechanics appears to yield too much correlation, more than we can intuitively stomach without feeling compelled to ask what is really going on." ³⁵ There is a profound problem, and no-one has yet provided a satisfying resolution. Even if an acceptable mechanism were found, the amount of correlation would almost always have to be less than that predicted by standard quantum mechanics based on Bell's inequalities which need to be satisfied if our natural intuitions are right. "Conventional quantum mechanics violates Bell's inequalities in theory, and there is consequently a number of experiments designed to test if they are violated in real life. On balance, available results suggest that violation does indeed occur. It is therefore inevitable, for reasons of philosophical prejudice, that attempts to rebuild quantum mechanics will be made, to make any violation appear more 'reasonable. Conceivably, however, we may have to give up the riddle." ³⁶ Potentially, the underlying mechanisms of quantum mechanics may defy our comprehension or not exist at all.

Bell's response to the explanation of the wave collapse of the Copenhagen interpretation was oppositional. The experiment involves correlation. Two photons are released in opposite directions with the same undetermined polarization. Upon one encountering a polarizer or Polaroid, "this photon is in neither the V (vertical) or H (horizontal) state but a superposition of the two and 'has to make a choice' at the Polaroid and 'jump' into either V or H. The seemingly innocuous phrase, 'has to make a choice', is at the heart of the problem. How is this choice made? The photon cannot make the choice the quantum superposition evolves according to Schrodinger's equation and this does not describe a collapse to one state or the other. It must somehow be the act of observation with the polaroid that causes the collapse into one of the two photon polarization states. But exactly how can some 'classical' measuring apparatus like the piece of polaroid cause this 'collapse of the wavefunction'? After all, any so-called 'classical' measuring apparatus is actually made up of atoms and electrons and these are subject to quantum mechanics and Schrodinger's equation just like the photon. This is the nub of the 'measurement problem' of quantum mechanics and it troubled many of the founders of the theory." ³⁷ It was in response to these challenges that the orthodox Copenhagen interpretation of quantum mechanics was carefully put together by Niels Bohr and his colleagues. "The Copenhagen interpretation offers a very austere and abstract view of the world. Bohr believed that the language of classical physics was inadequate to describe phenomena at the quantum level of reality. Ordinary words are incapable of giving us a satisfactory and unambiguous definition of a quantum superposition. Bohr offers no mechanism to explain the collapse of the wave function on measurement. Instead, to obtain results from quantum theory to compare with experiment, Bohr instructs us to split the experimental system into two parts — one part a classical world containing classical measuring devices and a second part containing the quantum system under observation. This Copenhagen distinction between classical and quantum systems is sometimes called the 'Heisenberg split'." ³⁸ Such a split seems ambiguous, but it is clearly sufficiently unambiguous for physicists to use in practice with great success. Regardless, some physicists, especially John Bell, found such a "cookery book" approach to our most basic theory of matter unsatisfactory. John Bell detested this "shifty boundary" between Schrodinger's "wavy quantum states" on the one hand, and Bohr's "classical apparatus" on the other and insisted that, at its heart, quantum theory was "rotten".

However, Bell's Inequality was eventually shown to be violated and quantum mechanics' prediction proved to be accurate. "These experiments confirmed that Bell's inequality was indeed violated and that the predictions of quantum mechanics agreed with the data…most physicists now accept that quantum mechanics has passed this test. What do these experiments tell us about the nature of reality? The observed violation of Bell's inequality means that no hidden variable theory — without some explicit or implicit unpleasant action-at-a-distance property- can agree with experiment. Whilst Einstein would probably have preferred some underlying, deterministic hidden variable explanation for quantum mechanics, he would certainly not have wanted to accept the existence of such 'spooky action-at-a-distance' effects. ³⁹ This still does not leave quantum mechanics in a very comfortable state. As modern scientists we might have to accept this degree of discomfort.