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.
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So how do minds enter the picture? The traditional understanding is
that the “definite events” whose probabilities one calculates in quantum
mechanics are the outcomes of “measurements” or “observations” (the
words are used interchangeably). If someone (traditionally called “the
observer”) checks to see if, say, a nucleus has decayed (perhaps using a
Geiger counter), he or she must get a definite answer: yes or no.
Obviously, at that point the probability of the nucleus having decayed
(or survived) should jump to 0 or 100%, because the observer then knows
the result with certainty. This is just common sense. The probabilities
assigned to events refer to someone’s state of knowledge: before I know
the outcome of Jane’s exam I can only say that she has a 70% chance of
passing; whereas after I know I must say either 0 or 100%.
Thus,
the traditional view is that the probabilities in quantum
mechanics and hence the “wavefunction” that encodes them refer
to the state of knowledge of some “observer”. (In the words of the
famous physicist Sir James Jeans, wavefunctions are “knowledge waves.”)
An observer’s knowledge and hence the wavefunction that encodes it
makes a discontinuous jump when he/she comes to know the outcome of a
measurement (the famous “quantum jump”, traditionally called the
“collapse of the wave function”). But the Schrödinger equations that
describe any physical process do not give such jumps! So something must
be involved when knowledge changes besides physical processes.
An obvious question is why one needs to talk about knowledge and
minds at all. Couldn’t an inanimate physical device (say, a Geiger
counter) carry out a “measurement”? That would run into the very
problem pointed out by von Neumann: If the “observer” were just a purely
physical entity, such as a Geiger counter, one could in principle write
down a bigger wavefunction that described not only the thing being
measured but also the observer. And, when calculated with the
Schrödinger equation, that bigger wave function would not jump! Again:
as long as only purely physical entities are involved, they are governed
by an equation that says that the probabilities don’t jump.
That’s why, when Peierls was asked whether a machine could be an
“observer,” he said no, explaining that “the quantum mechanical
description is in terms of knowledge, and knowledge requires somebody
who knows.” Not a purely physical thing, but a mind.
But what if one refuses to accept this conclusion, and maintains that
only physical entities exist and that all observers and their minds are
entirely describable by the equations of physics? Then the quantum
probabilities remain in limbo, not 0 and 100% (in general) but hovering
somewhere in between. They never get resolved into unique and definite
outcomes, but somehow all possibilities remain always in play. One would
thus be forced into what is called the “Many Worlds Interpretation”
(MWI) of quantum mechanics.
In MWI, reality is divided into many branches corresponding to all
the possible outcomes of all physical situations. If a probability was
70% before a measurement, it doesn’t jump to 0 or 100%; it stays 70%
after the measurement, because in 70% of the branches there’s one result
and in 30% there’s the other result! For example, in some branches of
reality a particular nucleus has decayed --- and “you” observe that it
has, while in other branches it has not decayed and “you” observe
that it has not. (There are versions of “you” in every branch.) In the
Many Worlds picture, you exist in a virtually infinite number of
versions: in some branches of reality you are reading this article, in
others you are asleep in bed, in others you have never been born. Even
proponents of the Many Worlds idea admit that it sounds crazy and
strains credulity.
The upshot is this: If the mathematics of quantum mechanics is right
(as most fundamental physicists believe), and if materialism is right,
one is forced to accept the Many Worlds Interpretation of quantum
mechanics. And that is awfully heavy baggage for materialism to carry.
If, on the other hand, we accept the more traditional understanding
of quantum mechanics that goes back to von Neumann, one is led by its
logic as Wigner and Peierls were to the conclusion that not everything
is just matter in motion, and that in particular there is something
about the human mind that transcends matter and its laws. It then
becomes possible to take seriously certain questions that materialism
had ruled out of court: If the human mind transcends matter to some
extent, could there not exist minds that transcend the physical universe
altogether? And might there not even exist an ultimate Mind?
