Indeterminacy in ScienceIs the universe really indeterminate at the smallest level?
by T.J. Nelson
uantum physics tells us that at a fundamental level everything is random. Radioactive alpha decay, for example, occurs by a process called quantum tunneling, which is said to be a purely random, non-deterministic process. But scientists have been reluctant to conclude that fundamental particles exhibit true random behavior. Einstein summed up this feeling when he famously said “God does not play dice with the universe.” So is the universe truly random, or is the mechanism just not understood?
There have been many attempts to find so-called ‘hidden variables’ that might explain quantum phenomena deterministically. But John Bell proved that local hidden variables do not exist, which means one of two things: either particles can communicate with each other faster than the speed of light, or our idea that an object can only be in one place at one time is wrong.
The latter idea is called a non-local theory, and one example is the de Broglie-Bohm approach, which takes the particle's position to be a hidden variable. A particle's position is hard to pin down. A popular problem in introductory QM textbooks is to calculate the probability that a neutron floating around in your back yard is actually on the Moon. The probability is easy to calculate, and though it is small it's not zero. We might have to accept that objects in the universe do not have to be in one single place, and it is our intuitive ideas about objects that need changing.
Indeterminacy is sometimes associated with the Heisenberg uncertainty principle, which states that a particle's position and momentum cannot both be measured precisely. But we need to be careful: there are two different uncertainty relations, and even on a macro level, uncertainty is a property of measuring complementary variables—which makes it a property of waves. You cannot, for example, measure the pitch of a note on a piano accurately unless you sample for a sufficient period of time. When you do a Fourier analysis you always have to choose between high frequency resolution and high time resolution. It is impossible to get both at the same time.
But quantum waves interact with matter in such a way as to appear nondeterministic. Quantum states don't tell us the outcome of a particular measurement, but only the probabilities of each outcome. This discussion gets technical very quickly; a great explanation can be found in Maximilian Schlosshauer's book Decoherence and the Quantum-to-Classical Transition. Many scientists prefer to remain agnostic about the whole issue, while others, notably David Bohm and Murray Gell-Mann, the quark guy, take the view that indeterminacy is a fundamental component of the universe.
But by opening the door of randomness even by a tiny crack, it seems to imply that a big part of the world is unknowable. The question is: if we allow randomness, have we effectively abolished causality? If we throw up our hands, saying it is unexplainable, it seems that demons will enter into those unexplored spaces.
What physicists are really saying is that our understanding is abstract, because the world is too strange and mysterious to understand intuitively from our everyday experience.
One of the strangest and most mysterious facts is that whenever you give a lecture on free will, all the physicists sit in the back and go to sleep. But scientists from other branches of science are sneaking in the back door. Psychologists like P. W. Glimcher, for example, argue that human behavior may be indeterminate.
The processes that Glimcher and others cite—membrane channel stochasticity and behavioral test variation—are not quantum effects, and they can be more easily explained by natural variability. Although this is popularly called ‘random,’ it is a totally different meaning of the word, with little connection to true indeterminacy.
Schrödinger argued in What is Life that true indeterminacy would be lethal to living organisms, and that for this reason living organisms must be large enough that quantum effects are negligible. It is generally accepted that quantum effects are many orders of magnitude too small to affect nerve cells, let alone the human brain (although Henry P. Stapp and a few others have argued otherwise).
These ideas are driven by a desire to preserve the concept of free will: if our minds are mere computers obeying only the laws of physics and biology, how can we be free to choose our actions?
In fact, it is indeterminacy, not determinism, that takes away free will. Our brains follow strict rules of logic: our neurons and the biomolecules within them use complicated mechanisms to ensure that ‘random’, uncontrolled signals are kept to a minimum. For sure there is lots of variability and noise, but even a little bit of true randomness would cause our actions to make no sense—a random event in our brain might cause us to steer left instead of right while driving, or decide that 2 + 2 = 5. Our thoughts would be at the whim of whatever random event happened to occur, and we would have no free will at all.
Our free will depends on making rational choices, not random ones; the sheer complexity of our brains and brain-environment interactions are more than enough to ensure that no two people think exactly alike. Can we then call this free will? No. The question cannot be answered, because the concept of free will is too ill-defined.
Albert Einstein did not believe in free will, and quoted Schopenhauer, who said: “Man can do what he wants, but he cannot will what he wills.” Today we would go even farther and say that, very often, we do not even know what we want. Defining free will in the light of our new understanding of the brain will create challenges not only for ethicists and theologians, but for anyone concerned about freedom.
So far the answer seems to be both: the universe appears to contain randomness, and the mechanism is not understood—once again proving the fundamental axiom in science, known as MRIN: More Research Is Needed™.
mar 01, 2015