Materialism is an atheistic philosophy that says that all of reality is reducible to matter and its interactions.
This article originally appeared on Big Questions Online. / by Stephen M. Barr; Not in any direct way. That is, it doesn’t provide an argument for the existence of God. But it does so indirectly, by providing an argument against the philosophy called materialism (or “physicalism”), which is the main intellectual opponent of belief in God in today’s world.
Materialism is an atheistic philosophy that says that all of reality is reducible to matter and its interactions. It has gained ground because many people think that it’s supported by science. They think that physics has shown the material world to be a closed system of cause and effect, sealed off from the influence of any non-physical realities — if any there be. Since our minds and thoughts obviously do affect the physical world, it would follow that they are themselves merely physical phenomena. No room for a spiritual soul or free will: for materialists we are just “machines made of meat.”
Quantum mechanics, however, throws a monkey wrench into this simple mechanical view of things. No less a figure than Eugene Wigner, a Nobel Prize winner in physics, claimed that materialism — at least with regard to the human mind — is not “logically consistent with present quantum mechanics.” And on the basis of quantum mechanics, Sir Rudolf Peierls, another great 20th-century physicist, said, “the premise that you can describe in terms of physics the whole function of a human being … including [his] knowledge, and [his] consciousness, is untenable. There is still something missing.”
How, one might ask, can quantum mechanics have anything to say about the human mind? Isn’t it about things that can be physically measured, such as particles and forces? It is; but while minds cannot be measured, it is ultimately minds that do the measuring. And that, as we shall see, is a fact that cannot be ignored in trying to make sense of quantum mechanics. If one claims that it is possible (in principle) to give a complete physical description of what goes on during a measurement — including the mind of the person who is doing the measuring — one is led into severe difficulties. This was pointed out in the 1930s by the great mathematician John von Neumann. Though I cannot go into technicalities in an essay such as this, I will try to sketch the argument.
It all begins with the fact that quantum mechanics is inherently probabilistic. Of course, even in “classical physics” (i.e. the physics that preceded quantum mechanics and that still is adequate for many purposes) one sometimes uses probabilities; but one wouldn’t have to if one had enough information. Quantum mechanics is radically different: it says that even if one had complete information about the state of a physical system, the laws of physics would typically only predict probabilities of future outcomes. These probabilities are encoded in something called the “wavefunction” of the system.
A familiar example of this is the idea of “half-life.” Radioactive nuclei are liable to “decay” into smaller nuclei and other particles. If a certain type of nucleus has a half-life of, say, an hour, it means that a nucleus of that type has a 50% chance of decaying within 1 hour, a 75% chance within two hours, and so on. The quantum mechanical equations do not (and cannot) tell you when a particular nucleus will decay, only the probability of it doing so as a function of time. This is not something peculiar to nuclei. The principles of quantum mechanics apply to all physical systems, and those principles are inherently and inescapably probabilistic.
This is where the problem begins. It is a paradoxical (but entirely logical) fact that a probability only makes sense if it is the probability of something definite. For example, to say that Jane has a 70% chance of passing the French exam only means something if at some point she takes the exam and gets a definite grade. At that point, the probability of her passing no longer remains 70%, but suddenly jumps to 100% (if she passes) or 0% (if she fails). In other words, probabilities of events that lie in between 0 and 100% must at some point jump to 0 or 100% or else they meant nothing in the first place.
This raises a thorny issue for quantum mechanics. The master equation that governs how wavefunctions change with time (the “Schrödinger equation”) does not yield probabilities that suddenly jump to 0 or 100%, but rather ones that vary smoothly and that generally remain greater than 0 and less than 100%. Radioactive nuclei are a good example. The Schrödinger equation says that the “survival probability” of a nucleus (i.e. the probability of its not having decayed) starts off at 100%, and then falls continuously, reaching 50% after one half-life, 25% after two half-lives, and so on — but never reaching zero. In other words, the Schrödinger equation only gives probabilities of decaying, never an actual decay! (If there were an actual decay, the survival probability should jump to 0 at that point.)
To recap: (a) Probabilities in quantum mechanics must be the probabilities of definite events. (b) When definite events happen, some probabilities should jump to 0 or 100%. However, (c) the mathematics that describes all physical processes (the Schrödinger equation) does not describe such jumps. One begins to see how one might reach the conclusion that not everything that happens is a physical process describable by the equations of physics. /sources: article; image (cern);.
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