I usually don't blog about physics. Actually, I don't think I ever have, which is not surprising given that I'm not a physicist. This unusual post was prompted by an ongoing series of encounters with people asking me how I can be so sure that the universe is indeterministic. I'm explicitly writing this as an interested layperson, even though I took elementary quantum mechanics as special subject in high school and was supervised during my PhD by Martin Heisenberg, the youngest son of Werner Heisenberg.

The reason why I'm reasonably sure that the universe is indeed indeterministic is rather simple: there is no empirical evidence to suggest that the universe is deterministic and plenty of evidence that it is indeterministic. Of course, that doesn't mean that the universe may not be deterministic after all, it only means that at the moment we don't have the slightest reason to believe in determinism - which is sort of analogous to belief in the supernatural.

Because there are different concepts which people use when they talk about determinism, let me briefly clarify which of these concepts I'm referring to with 'determinism'. The kind of determinism important for behavioral biologists like me, studying spontaneous actions, is 'causal determinism', i.e., the concept that everything in the universe has a cause and every such event can eventually, in theory, be traced back to the big bang. Adherents to this idea claim that the apparent indeterminism in Quantum Mechanics is merely a testament to the finite human brain not being able to accurately account for events which are determined, but seem, to us, random or indeterminate. In essence, this is what Einstein was expressing when he exclaimed that 'god does not play dice with the universe'. Which goes to show that even geniuses like Einstein don't get everything right.

One of the predictions that Einstein derived was Quantum Entanglement. He claimed that this 'spooky action at a distance' was, as a consequence of quantum mechanics, such an obviously silly idea that it had to falsify the whole theory, or at least show that it was incomplete. However, quantum entanglement is a very real phenomenon that has later been directly observed and is now used in some protocols of quantum cryptography.

The most commonly used metaphor is that of 'hidden variables' which would make every event in the universe deterministic, if only we would be able to know of these variables. However, Bell's Theorem suggests that at least the 'local' variety of these hidden variables is not possible.

A common misconception by many lay-determinists (non-physicists) is that Heisenberg's uncertainty principle describes a technical problem of our measurements rather than a principle of the universe. However, Stephen Hawking predicted the radiation named after him as stemming from virtual particle/antiparticle pairs being generated by quantum vacuum fluctuations right at the event horizon of black holes. A similar effect was claimed to have been observed in the lab. Just this week, another effect having to do with quantum fluctuations in a vacuum generating particle/antiparticle pairs has been observed. Forty years ago it was predicted that these same fluctuations which are thought to give rise to Hawking Radiation should become 'real', i.e., visible photons when they hit a mirror which moves at a significant fraction of the speed of light. It is this generation of photons which was directly observed and reported in the paper cited above.

Another problem for determinists is radioactive decay: all nuclei of a radioactive element are thought to be physically identical. Yet, some of these nuclei decay only fractions of a second after the were generated, while others exist for millennia. There currently exists no theory trying to explain this discrepancy or predict the decay of individual nuclei. On the contrary, these processes seem to so exquisitely follow the rules of statistics, that they are used to construct genuine random-number generators.

And there are many more such examples (see references below). In short, Einstein was one of the physicists who felt that there had to be something wrong with quantum mechanics and failed to show it. Now, more than eighty years later, there still is no hole in the theory and the universe is still as indeterminate as it was back in Einstein's time. Thus, as a biologist, I must say that my universe will remain indeterminate until someone unequivocally shows it to be determinate.

Consequently, this would also mean that brains are, at least to the extent as they are part of this universe, indeterminate. Unlike in algae or birds, the degree to which quantum effects affect biological processes in the brain is not yet known. However, unless the brain is a bubble in which quantum effects cannot occur, some of the fluctuations in the brain which are thought to underly the generation of spontaneous behavioral variability, have some quantum origin. We don't know the fraction of these contributions, but they must be larger than zero. We also don't know how relevant they are to behavioral variability, only that they somehow contribute, simply because they occur and the nonlinear mechanisms in the brain could in principle pick them up. This, in brief, is the physics underlying the biology of free will.

Further reading:

• Living in a quantum world
• Dynamics, Quantum Mechanics and the Indeterminism of Nature
• Free randomness amplification
• No extension of quantum theory can have improved predictive power

Many thanks to Bruno Landeros for providing most of the references linked to above!

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Wilson, C., Johansson, G., Pourkabirian, A., Simoen, M., Johansson, J., Duty, T., Nori, F., & Delsing, P. (2011). Observation of the dynamical Casimir effect in a superconducting circuit Nature, 479 (7373), 376-379 DOI: 10.1038/nature10561

Brembs, B. (2010). Towards a scientific concept of free will as a biological trait: spontaneous actions and decision-making in invertebrates Proceedings of the Royal Society B: Biological Sciences, 278 (1707), 930-939 DOI: 10.1098/rspb.2010.2325