The Dancing Wu Li Masters (52 page)

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The EPR argument for the incompleteness of quantum theory rests squarely on the assumption that the real factual situation in one region cannot depend on what an experimenter does in a far-away region (the principle of local causes).
      Einstein, Podolsky, and Rosen point out that we could have chosen to place the axis of the magnet in area A either in the vertical position or in the horizontal position, and that in each case we would have observed a definite result—either
up
or
down
in the vertical case, or
right
or
left
in the horizontal case. They also assert that what we do (choose to measure or observe) in area A cannot affect the real factual situation in area B. Thus they conclude there must exist
simultaneously
in area B a definite spin,
up
or
down
, and also a definite spin,
right
or
left
, to account for all the possible results that we can get by orienting the magnet in area A one way or the other.
      Quantum theory is not able to describe such a state and hence Einstein, Podolsky, and Rosen concluded that the description which quantum theory provides is not complete; the quantum description cannot represent certain information about the system in area B (the simultaneous existence of different spin states) that is needed to completely describe the situation there.

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The original version of Bell’s theorem involves spin ½ particles. Clauser and Freedman’s experiment (keep reading), like this one, involves photons.

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The Einstein-Podolsky-Rosen argument for the incompleteness of quantum theory was based upon the assumption of local causes. This assumption seemed plausible to most physicists because most physicists doubted that the real factual situation in one area of the EPR experiment actually was being influenced by the actions of a faraway observer. Their doubts arose from the fact that the quantum state composed of equal parts
up
and
down
is exactly equivalent to the quantum state composed of equal parts
right
and
left
. These two combinations are experimentally indistinguishable. Thus the actions of the far-away observer, by themselves, can have no observable effects here. Hence it is not clear that the real factual situation here is being changed.
      The Einstein-Podolsky-Rosen argument (and the principle of local causes) was demolished by Bell in 1964. Bell showed that several assumptions that are implicit in the Einstein-Podolsky-Rosen argument imply that what happens experimentally in area B
must depend
on what the experimenter does in area A, or vice versa. The sufficient assumptions are: (1) that the observer in each area can orient the magnetic field in his area in either of the two alternative directions; (2) that some particular (although generally unknown) experimental result can be assumed to occur in each of the four alternative experimental situations; and (3) that the statistical predictions of quantum theory are valid (say to within 3%) in each of the four alternative cases. Bell’s argument demonstrates by simple arithmetic that these three assumptions imply that the experimental results in one of the two areas must depend on what the observer in the other area chooses to observe (i.e., on how he orients the magnetic field of his Stern-Gerlach device). This conclusion contradicts the locality assumption of the Einstein-Podolsky-Rosen argument.

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A tacit assumption is made here that the choice of the orientation of the polarization detector, which can be made by a random quantum process (like radioactive decay), or by the free will of an experimenter, has no deterministic roots in the past which are important in this context.

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“Superluminal transfer of information” refers to a fundamental phenomenon of nature, but not one that can be controlled, i.e., used to send messages. The possibility of utilizing superluminal information transfer to transmit encoded messages was proposed in 1975 by J. Sarfatti. However, H. Stapp and N. Herbert independently have pointed out, following Heisenberg (1929) and Bohm (1951), that any phenomenon which is described adequately by the quantum theory cannot be used to transmit messages superluminally.

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The phenomenon of superluminal information transfer between space-like separated events may be related to Jung’s concept of synchronicity.

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If the Big Bang theory is correct, the entire universe is initially correlated.

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The nonlocal aspect of nature illuminated by Bell’s theorem is accommodated in quantum theory by the so-called collapse of the wave function. This collapse of the wave function is a sudden global change of the wave function of a system. It takes place when any part of the system is observed. That is, when an observation on the system is made in one region the wave function changes instantly, not only in that region, but also in far-away regions. This behavior is completely natural for a function that describes probabilities for probabilities depend on what is known about the system, and if knowledge changes as a result of an observation, then the probability function (the amplitude of the wave function squared) should change. Thus a change in the probability function in a distant region is normal even in classical physics. It reflects the fact that the parts of the system are correlated with each other, and hence, that an increase of information here is accompanied by an increase of information about the system elsewhere. However, in quantum theory this collapse of the wave function is such that what
happens
in a far-away place must, in some cases, depend on what an observer here chooses to observe, what you see there depends on what I
do
here. This is a completely nonclassical nonlocal effect.

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There are some notable exceptions, chief among which are Harold Puthoff and Russell Targ, whose experiments in remote viewing at the Stanford Research Institute are presented in their book,
Mind-Reach
, New York, Delacorte, 1977.

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A branching also occurs at the choice between results. This can be illustrated by the EPR experiment. On the original branch where, for example, the axis of the magnetic field is vertical and the result is either spin
up
or spin
down
, there is a branching into two “twigs.” In the first twig the result is spin
up
, and in the second twig the result is spin
down
. Similarly, on the second branch, where the axis of the magnetic field is horizontal, there is also a branching into two twigs. On the first of these twigs the result is spin
right
, and on the second of these twigs, the result is spin
left
. Thus, on any given twig of any branch there is a definite result (spin
up, down, right
, or
left
), but the idea of “what would have happened if one had chosen the ‘other branch’ ” makes no sense, for both results (
up
or
down
, or
right
or
left
) occur on different branches. Thus the results on “the other” branch are not definite.

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Physicists usually express philosophical phrases (like “free will”) in more precise terms. For example, the concept of free will is defined within this experimental situation as the tacit assumption that “each of the two observers, one located in area A, and the other located in area B, can choose between two possible observations [experiments].” These two choices are considered “free variables” in the context of the study of the observations made on the two-particle system.

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In fact, most physicists do
not
believe that it is worthwhile to think about these problems. The main thrust of the Copenhagen Interpretation, which is the interpretation of quantum theory accepted by the bulk of the scientific community, is that the proper goal of science is to provide a mathematical framework for organizing and expanding our experiences, rather than providing a picture of some reality that could lie behind these experiences. That is, most physicists today side with Bohr, rather than with Einstein, on the question of the utility of seeking a model of a reality that can be conceived of independently of our experience of it. From the Copenhagen point of view, quantum theory is satisfactory as it is, and the effort to “understand” it more deeply is not productive for science. Such efforts lead to perplexities of just the sort that we have been discussing. These perplexities seem to most physicists to be more philosophical than physical. Thus most physicists choose the “no model” option shown in the diagram on page 335.