Einstein and Quantum Theory
|I write weekly articles on my other website Chronon critical points and will provide links to any of these which are relevant, but I also intend to add articles to this website if they seem to fit in better here|
With the centenary of Einstein's 1905 Annus Mirabilis now upon us, we are hearing much about Einstein's life, and in particular how he 'wasted' the latter part of it battling against quantum theory. My intention on this website is to question this assertion. Einstein's early successes were a result of his wonderful intuition about physics, and my belief is that he still had this intuition in the later part of his life. Rather, it was other physicists who 'wasted' this intuition, being seduced by a more mystical view of physics, which was based on the philosophical fashions of the time.
Clock-in-a-boxThe turning point seems to be marked with Einstein's thought experiment, in which a box has a shutter which opens at a precise time and lets out a single photon of light. Seemingly we can know when the photon left the box as precisely as we wish. We can also find out the energy of the photon by weighing the box before and after (since mass and energy are equivalent). This seems to contradict quantum theory, which says that the product of the uncertainty of the energy and that of the time must exceed Planck's constant. Niels Bohr answered this by saying that weighing it would mean that it would move within a gravitational field, and then Einstein's own general theory of relativity would say that the rate at which the clock ran would change, and we would end up with an uncertainty in the time. This gedanken experiment is mentioned pretty often, and the implication seems to be that Einstein couldn't even figure out the consequences of his own theory, and so his productive life was at an end.
What these accounts don't mention is that Bohr's 'explanation' just doesn't hold water. If true it would imply a deep link between general relativity and quantum theory, leading to a possible unification of the two theories, which didn't happen then, and has been a major problem of physics ever since. As far as I can tell the argument was based on the idea that the measurement of the time and energy would involve the pointer of some apparatus moving until it comes to rest in a given position so a result could be read off. This involvement of position and momentum of the apparatus would introduce the usual uncertainty relations between these quantities. In this case the apparatus involves a gravitational field, and this is used in the argument. However, there are two serious problems. Firstly, the uncertainty deduced seems to relate the time of measurement rather than the time of the photon emission. Secondly, the involvement of the gravitational field would seem to work as well with the classical theory of gravity, and doesn't need the more advanced theory of GR.
The other reason we know Bohr's response was faulty is that three-quarters of a century of experience of quantum theory has taught us what the real response is. Since light has wave-like aspects, trying to open the shutter for a very short time would affect the light passing through, resulting in a photon with a different energy. Nothing to do with general relativity.
Local RealismThe fundamental question is whether one believes in what is called local realism, that is the idea that it should be possible to have a theory which doesn't require any signals to travel faster than light. I don't like this name, particularly the realism part, which seems to be muddling the issue with unrelated philosophical questions. I have written more about this in the article Local Realism - what does it mean?. But accepting the name for the moment, the consensus is that local realism does not hold. In the 1960's John Bell devised the Bell inequalities, which were inequalities which would have to be satisfied if local realism were true. Recent experiments have shown that these inequalities do not hold, implying that the universe is fundamentally nonlocal.
However, it is possible to challenge this view. One critic is Caroline Thompson, who approached the subject by looking at the statistics of the experiments, and claims that much of it is suspect - that it wouldn't be accepted in other areas of science. Unfortunately, this hasn't been taken very seriously. In a way this is hardly surprising as elsewhere on her website (the Forgotten History page) she lends support to ideas which definitely fall into the "crank" category.