Recently in the news, an experiment from 2008 has scientists scratching their heads. Sometimes it takes a while for a good experiment to be recognized as important. In this case, a paper titled “Chaos, entanglement and decoherence in the quantum kicked top,” published by physicists Ghose, Stock, Jessen, Lal, and Silberfarb in the journal Physical Review A, is raising fundamental questions about the nature of the universe at the macroscopic level.
The experimenters created what is called a quantum top. This is a system of atoms in which the overall spin of the system can be influenced from the outside by magnetic fields in such a way that the quantum spins of the component atoms can change direction and become entangled with one another. In general, the system acts like a spinning top that can be made to wobble about its spin axis. An actual macroscopic top, when bumped, wobbles chaotically.
However, in a quantum system, there are different rules. There are certain stable states, which are generally preferred so long as the system can find them. Outside of these stable states, there are other states, which are less stable. The question that the experimenters were looking at involved the nature of those unstable states – whether or not they are chaotic in nature. The experimenters discovered that they the unstable states are, in fact, chaotic.
When the system begins in a stable spin state, the regime of change, when “kicked” by the external magnetic field, keeps the system in that set of stable states. If the beginning state was not one of these stable ones, the experimenters found that the changes became chaotic. Not only did the spin states of the system become chaotic, but also the entanglements between the system components did as well.
The experiment gives the impression that entangled quantum systems tend to behave like a strange attractor unless they find a set of stable states. In the real world, the effect of so much bumping from other particles would tend to limit the amount of time that any quantum system could remain in such a stable state. So, in general, quantum systems should behave chaotically.
Many physicists and other scientists and philosophers have pointed to quantum mechanics and entanglement in particular as the potential source of the chaos seen in so many macroscopic classical systems. So far, this has just been speculation, a way of trying to explain where all this chaos comes from in such highly deterministic systems. That idea has really been based on the elimination of, or just a plain lack of, other ideas. After all, what else could it be? Of course, that is not any proof that the quantum world is actually the source of chaos.
This experiment seems to be the clincher that indicates that quantum mechanics is indeed the source of chaos in the universe. It gives a basis to the concept that chaos is fundamentally built into the mechanics of the universe itself.
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