3\. WHY MATTER ALONE IS NOT ENOUGH!

\"Nonlocality gets more real\". This is the provocative title of a
bulletin in a recent issue of \"Physics Today.\" It reports some
experimental results that imply that causal influences must in some
cases act over large distances faster than the speed of light. These
experiments, carried out in Switzerland, are similar to many others
performed over the past thirty years, but they are more spectacular
because the distance involved was not just a laboratory interval of a
few meters, but a geographic separation of more than ten kilometers. The
results of these experiments are incompatible with the materialist
conception of nature that ruled science from the time of Isaac Newton
until the dawn of the twentieth century. There is a theory that
perfectly describes all of these experimental results, but it is based
on a non-material conception of the universe, and a new kind of
mathematical law.

According to Einstein\'s theory of relativity, any faster-than-light
action would be, from some point of view, instantaneous. But instant
transfer of information is anathema to many scientists, on aesthetic and
intuitive grounds. Of course, Newton\'s theory of gravity postulated a
force that acted with no time delay over a planetary scale, and gave no
hint of what was transmitting this action. His theory was severely
criticized on that account, and even Newton himself was troubled by this
feature. In a letter to his friend Bentley, he expressed his own
skepticism about unmediated force, and by implication, I think, about
any sort of instantaneous action at a distance:

\",...that one body may act upon another at a distance

through a vacuum, without the mediation of anything else, by

and through which their action and force may be conveyed

from one to another, is to me so great an absurdity, that I

believe no man, who has in philosophical matters a

competent faculty of thinking, can ever fall into it. Gravity

must be caused by an agent acting constantly according to

certain laws, but whether this agent be material or immaterial

I have left to the consideration of my readers.\"

Newton had, in fact, made huge efforts to find a satisfactory physical
explanation of this force, but failed. More than two centuries later
Einstein explained gravity as being due to the warping of space-time by
the presence of matter. According to this theory, the gravitational
effect is indeed conveyed from point to point by a local contact
interaction that transfers information no faster than the speed of
light. Thus Einstein achieved what Newton had intuited, the abolition of
instantaneous action at a distance. His theory of relativity implied,
moreover, that *no physical influence of any kind* could act faster than
the speed of light.

But why should we be concerned here with this rather esoteric question
of whether faster-than-light influences exist? Our topic is human
beings, and their place in the causal structure of Nature. On the time
scale of biological processes in human brains and bodies the speed of
light is so fast as to be essentially infinite anyway. So why worry
about this seemingly irrelevant question?

There are three important reasons.

The first concerns the constitution of the world: the question of what
the world is made of. Neither matter nor energy can travel faster than
the speed of light. Nor could anything else in a world composed of
matter and energy alone. Thus the proved existence of such influences is
a compelling and easy to understand reason to abandon the tenets of
materialism, and move on to the more adequate quantum framework, which
is relies on a causal interplay of the idea-like and matter-like
properties of nature.

The next reason pertains to size. It is often argued quantum theory
concerns only very small-scale phenomena, and hence can be ignored when
dealing with something as big as your brain, or even a neuron in your
brain. But the faster-than-light quantum effect entailed by the Swiss
experiment acts over a distance of more than ten kilometers: quantum
effects are obviously not confined to small regions. Indeed, in the von
Neumann formulation of quantum theory to be adopted here there is a
brain-sized event associated with each of your knowings: with each of
your experiential graspings of a meaning. These macroscopic brain events
enter dynamically, by means of a well understood quantum process that
has no classical analog, into the formation of your thoughts and
actions.

The final reason concerns *understanding*. In the book *John von Neumann
and the Foundations of Quantum Physics* the philosopher Wesley C.
Salmon, in a contribution entitled *Scientific Understanding in the
Twentieth Century* begins his section on \"The Possibility of Scientific
Explanation\" with the following paragraph:

\"Between the triumph of the atomic theory of matter early in the
century and the middle of the twentieth century it would not have been
incoherent to claim that we can *describe* the nature and behavior of
atoms, molecules and subatomic particles, and that we can make
successful predictions on the basis of such knowledge, but to deny that
we have achieved anything that deserves the honorific title of
explanation or understanding. To appreciate the transition from that
position to our *fin de siecle* confidence in the possibility of
scientific explanation and understanding, we must turn to the work of
philosophers.\"

He goes on to say that \"According to an old doctrine, going back at
least to Aristotle, we seek to know, not only *what*, but also *why*.\"

Salmon is contrasting here to two different ideas of science. One claims
science is only about *knowledge*, *description,* and *prediction*;
whereas the other says science can provide also *understanding*.

During the first fifty years of the twentieth century the ascendant
position of philosophers of science was the first view, but now,
according to Salmon, philosophers are coming back to the old idea that
science can provide also understanding. That shift supports,
philosophically, the aim of this book, which is to provide not merely a
description of the quantum world, but also an understanding of it.

It is probably not coincidental that the ascendant views of philosophers
during that first half of the century dovetailed with those of the
quantum physicists. The essential core of Bohr\'s message was precisely
that scientists should focus on *knowledge*, *description*, and
*prediction*, and forego the endeavor to *understand* in terms of
traditional concepts and categories.

But why should scientists, of all people, have abandoned the effort to
understand nature?

The reason is clear: Quantum theory, as a mathematical structure, is
built on the idea of non-microscopic events and instantaneous actions.
Yet the scientist were reluctant to admit that such things could
actually exist: they preferred abandoning understanding, to abandoning
locality However, if understanding is ever to be achieved, non-locality
must surely be acknowledged.

No reasonable person should accept on hearsay a revolutionary new idea
of reality that overturns everything that has been believed for
generations, and is, moreover, wildly counter-intuitive: might not the
physicists who are setting forth this \"craziness\" be carried away by
enthusiasm, or be so beguiled by the power of their mathematical tools
that they lose touch with reality. This abrogation of the formerly
well-established science has such far-reaching consequences that serious
thinkers need to understand for themselves the empirical evidence and
its logical implications. I shall therefore describe here the experiment
performed in Switzerland by members of the Applied Physics Group of the
University of Geneva, and then explain how their results contradict the
basic idea that Nature is built of matter and energy alone.

The general idea of the Swiss experiment is this: A sequence of pairs of
photons is generated in Geneva, and one member of each pair is sent by
optical fiber to the village of Bellevue, and the other is sent to
Bernex. In each village a random choice is made to perform one or the
other of two alternative possible experiments. Each performed experiment
gives a result Yes or No. But the operations are all carried out so fast
that the information about which random choice is made in a village
cannot, even by traveling at the speed of light, get to the other
village before the result appears there.

It needs to be emphasized that the experiment does not demonstrate a
direct \"mechanical\" influence of the choice made in one regions upon
the result appearing in the other. The situation is more subtle than
that. A \"mechanical\" influence would be one such that, for an
*actually performed* sequence of measurements in the two villages, the
answer Yes or No appearing in one village is correlated to the choice
made in the other village. (For example, each time the \"first\"
possibility is chosen in one region the result \"Yes\" appears in the
other region, and each time the \"second\" choice is made the result
\"No\" appears.) Such a correlation, if it existed, could be used to
send a telegraph message from one village to the other faster than
light. But the possibility of sending such messages faster-than-light is
strictly excluded by quantum theory. Correspondingly, the existence of
such a \"mechanical\" faster-than-light influence is not what this
experiment demonstrates!

Classical physical theory imposes, however, also a stronger
no-faster-than-light condition. Because all casual connections are
carried by matter or energy the theory allows no influence of the choice
made in one village on the outcome of *either one of the two experiments
that could be chosen in the other village.* It is this stronger
condition that is incompatible with the predictions of quantum theory
confirmed (to within the limits imposed by the experimental exigencies)
by the Swiss experiment.

I turn now to a more detailed description of the Swiss experiment, and
to the proof of the violation of this no-faster-than-light condition.
Readers more interested in general ideas than in detailed proofs can
skip at any time to the last paragraph of this chapter without loss of
continuity.

The initial phase of the Swiss experiment occurs at a lab in downtown
Geneva. A pair of associated twin photons is born there. This birthing
is achieved by directing a laser beam at a crystal. Most of the laser
light goes through the crystal, but each laser photon in a small subset
is split into a pair of photons, with each member of the pair carrying
about half the energy of its laser-photon parent.

For some of these pairs one partner is sent by optical fiber to a lab in
the village of Bellevue, while the other partner is sent to a lab in the
town of Bernex. These two labs lie more than ten kilometers apart.

At each lab the arriving twin is sent into an \"interferometer\".

Interferometers are, themselves, very interesting devices, and they need
to be understood if the experiment is to be made clear.

There are different kinds of interferometers. To simplify the
explanation without altering the principle I shall consider one that is
slightly different from what was used in the Swiss experiment.

This interferometer involves two ordinary (i.e., fully silvered)
mirrors, each of which reflects all the light falling on it, and two
half-silvered mirrors. In half-silvered mirrors the layer of silver is
so thin that it reflects (like a mirror) only half the light incident
upon it, and transmits (like a plate of clear glass) the other half.

**AN** **INTERFEROMETER**

\[*The light enters the device horizontally, and eventually exits either
horizontally, or vertically downward. Photon detectors H and V signal
the emergence of the photon in the horizontal and vertical exit beams,
respectively. The two 45-degree slanted lines on the lower side of the
rectangle represent half-silvered mirrors, the two upper 45-degree
slanted lines represent fully silvered mirrors. Thus half the light
takes the short direct path between the two half-silvered mirrors,
whereas the other half takes the longer roundabout path. Each detector,
H or V, gets half of its light via the direct path and half via the
roundabout path*.\]

Experiments with an interferometer of this kind reveal an interesting
\"interference\" phenomena: the fraction of the photons detected in
detector H depends upon the *difference between the lengths of the two
alternative paths available to the photon;* i.e., on the *difference* of
the lengths of short (direct) and the long (roundabout) paths between
the two half-silvered mirrors. This fraction can easily be computed by
imagining the photon to be a wave, like the wave on the surface of a
pond. This wave divides at the first half-silvered mirror into two
parts, which move along the two different paths to the second
half-silvered mirror. At the second half-silvered mirror the direct and
roundabout parts of the wave are reassembled, and one reconstituted
combination is sent to H, and the other reconstituted combination is
sent to V.

The wave consists of a long regular sequence of crests and troughs, and
the \"wavelength\" of the light is distance between successive crests.
The key point is that the laws of wave optics say that the process of
reflection off of a slanted 45-degree (half-silvered or fully-silvered)
mirror *shifts the crest* of the reflected wave *backward by one quarter
of a wave length*, relative to the geometric distance traveled by the
wave. *Transmission* through the half-silvered mirror generates no such
shift.

The wave in, say, the horizontal exit beam will be the sum of a part
coming via the direct path and a part coming via the roundabout path.
Suppose that the difference in the lengths of these two paths is an
integral (i.e., whole) number of wavelengths. Then, *without* *the
quarter-wavelength shifts associated with the reflections*, the crests
of the waves in this exit beams that come via the direct and roundabout
routes will exactly coincide: the extra distance traveled by the light
that takes the roundabout path would not produce any *net shift* in the
position of the crests, relative to the wave that takes the short path,
because a shift by an integral number of wave lengths just shifts each
crest into coincidence with another crest. Thus the contributions from
the long and short routes would, after being recombined at the second
half-silvered mirror, be exactly \"in phase.\" The same would be true in
the vertical exit beam.

But when the shifts at the 45-degree reflections are taken into account
the situation is more interesting. Consider first the light that goes to
the detector H. The light that travels the roundabout route to the
detector H is reflected four times and hence will have its crests
shifted by four quarter-wavelengths (which add up to one full
wavelength). The light that travels the short direct route is not
shifted at all. Since a shift by a full wavelength keeps the crests
aligned, the part going to H via the roundabout route will be completely
in phase with the light going to H via the short (direct) route. Thus
there will be *complete constructive interference* between the two parts
of the wave that go to H.

But consider next the two parts that go to V. The wave going via the
roundabout path to V is shifted backward by three quarters of a
wavelength, whereas the wave that goes via the short path to V gets
shifted backward by one quarter of a wavelength (because it is
*reflected* only once.) Therefore the relative shift is seven
quarter-wavelengths minus one quarter-wavelength. This is six
quarter-wavelengths, or one and a half wavelengths, which is equivalent
to a half wavelength, since a shift by a full wavelength keeps the
crests aligned. But a half wavelength shift moves each crest of one part
onto a trough of the other part, and the two waves will cancel each
other out. Thus there will be complete destructive interference: no
light will go to V. This \"wave optics\" calculation matches the
empirical facts.

Thus if the difference in the lengths of the long and short path lengths
is an integral number of wave lengths of the light, then *all of the
photons* will get detected in H, and none in V. But if, say, the
roundabout path is now lengthened by a half wave length the situation
will be reversed and all of the light will go to V and none to H.

These wave optics calculations are easy to do, and to understand, and
they give predictions about the fractions of the light going to H and to
V, respectively, that are in full accord with experiment. These results
demonstrate clearly the wave nature of light. This wave nature persists
undiminished even when the beam is attenuated so strongly that two
photons are never (or at least hardly ever) in transit at the same time.

Having thus establishing the wave nature of the light we arrive at an
interesting puzzle! If one places detectors in the two paths just
*before* they reach the second half-silvered mirror, then for each
photon that enters the interferometer *only one or the other* of the two
detectors will fire, never both. This seems to show clearly that the
photon travels *along one path or the other*, not both.

But how can one reconcile this particle-type (single-path) behavior with
the empirically validated wave-like behavior just described, which
depends upon the interference between the light that travels the two
paths?

This problem is, of course, the famous \"wave-particle duality\" puzzle.

The simplest answer is to assume that there is both a \"particle of
light\", the photon, *and* a wave. The wave obeys the laws of wave
optics, but also *guides* the photon to places where the waves interfere
constructively, and away from places where the waves interfere
destructively. So there is no really serious problem at this one-photon
level. It is only when one considers *two paired photons* that a real
puzzle arises.

So let us return to the Swiss experiment. In that case there are two
interferometers in each village, and hence four altogether.

![](media/image1.wmf){width="5.9847222222222225in" height="2.83125in"}

**The Experimental Set up**.

\[*The laser beam is split at D. The two R\'s indicate the two random
processes, each of which randomly sends the photon that arrives in its
laboratory to either the \"upper\" or the \"lower\" of the two
interferometers in that village. H and V label the photon detectors in
the horizontal and vertical exit channels, respectively. There are four
alternative possible cases. In Case One the two selected interferometers
are the two lower ones, one in Bellevue and one in Bernex. In Case Four
the two selected interferometers are the two upper ones. The two lower
interferometers are mirror images of each other, and the two upper
interferometers are mirror images of each other. All four of the short
paths (between the two half-silvered mirrors in an interferometer) have
the same length, but the roundabout paths are slightly longer in the
upper two interferometers than in the lower two. In the lower two
interferometers the difference between the long and short paths is an
integral numbers of wavelengths.\]*

Some of the photons get lost along the way and do not reach a detector.
But there are many pairs whose two members both reach detectors, one in
Bellevue, the other in Bernex. Signals from those detectors are sent
back by ordinary wires to a central processor in Geneva.

Consider first Case One. In this case the two selected interferometers
are the two lower ones in the diagram. These two interferometers are
mirror images of each other. This means, in particular, that the length
of the short path in the Bellevue device is the same as the length of
the short path in the Bernex device. Likewise, the lengths of the two
long paths are the same.

Each pair of photons is created at an event in Geneva. One member goes
to Bellevue the other member goes to Bernex, and then each generates a
signal that goes back to Geneva. Bellevue and Bernex do not lie at the
same distance from Geneva. Thus the signals from these two villages will
not arrive in Geneva simultaneously: there will be a *time lag.* This
delay depends upon whether the photons traverse the short or the
roundabout routes inside the interferometers. However, if both photons,
one in each village, take the short route then this time lag will be the
same as when both take the long route. (This is because the *difference*
between the lengths of the long and short routes is the same for the two
photons, and hence the *difference in transit times* is the same.) But
if one photon of the pair takes a roundabout route whereas the other
takes the direct route then the time lag between signals from Bellevue
and Bernex will be either longer or shorter than the common lag time for
the cases in which both photons traverse the direct route or both
traverse the roundabout route.

This difference in lag times allows the experimenters to keep only those
pairs of photons such that both members take the long path or both take
the short path. The slight lengthening of the long paths in the upper
two interferometers (in our diagram) is too small to upset this
restriction of the data to the contributions in which both of the two
siblings take the roundabout route or both take the direct route.

When *coincidences* of detection events, one in each village, are
considered it is the *sum of the two phases* that is pertinent. In Case
One the long path in each interferometer is longer than the short path
by an integral (i.e., whole) number of wavelengths. Consequently, there
will be constructive interference if both photons are detected in the H
detectors, or if both are detected in the V detectors, but destructive
interference if one photon is detected by a V detector, but the other is
detected by an H detector.

These results are easy to deduce. Note that in the case where both
photons are detected in an H detector the contribution from the two long
paths gives a total shift of eight quarter wave lengths (there are
altogether eight 45-degree reflections on the path to the two detectors
H) and the two short paths give no shift. Thus we get a two-wavelength
shift, and hence complete *constructive* interference. In the case of
two V\'s the two long paths give a backward shift of six quarters (three
reflections in each village) whereas the two short paths give a total
backward shift of two quarters, for a net difference of one full
wavelength, and hence, again, complete constructive interference. In the
case of H in one region but V in the other, the contribution from the
two long paths will be shifted back by seven quarters, whereas the
contribution from the two short paths will be shifted back by only one
quarter of a wavelength, for a net difference of one and a half
wavelengths. Thus the crests coming from the long paths will coincide
with the troughs coming from the short paths, which means complete
destructive interference.

The rate at which the pairs are detected is slow enough so that each
pair of particles, one detected in Bellevue the other in Bernex, can be
distinguished from all the other pairs by fast electronics. A pair is
classified as \"matched\" if both members are detected in a horizontal
exit channel or both are detected in a vertical channel. They are
\"unmatched\" if one partner is detected in a horizontal exit channel
and its mate is detected in a vertical exit channel.

Quantum theory predicts, and the empirical results confirm (to within
the limits imposed by experimental exigencies) that the fraction of the
pairs that are unmatched will be the *sine* *squared* of L/2 minus S/2,
where L is the *sum* of the two long paths, one in each village, and S
is the *sum* of the two short paths. The sine-squared function
oscillates smoothly between zero and one, and touches zero each time L/2
minus S/2 reaches some half-integral multiple of the wavelength of the
light. This agrees with the result in Case One that was just described:
there L/2 minus S/2 is an integral number of wavelenghts, and hence the
sine square of L/2 minus S/2 is zero.

For ease of explanation, I shall use just one simple property of this
formula: if for some original value of L/2 minus S/2 none of the pairs
are unmatched then for small shifts of L/2 minus S/2 away from this
original value the number of unmatched pairs *will grow like the square
of this small shift.* In particular, if for some small value of this
shift in L/2 minus S/2 the value of this fraction of mismatches is f,
then a doubling of this small shift will multiply the fraction of
mismatches by about 4: the fraction of mismatches will *more than
double!*

What is so astonishing about that?

What is puzzling and interesting is this. The experiment is done with
very high-speed equipment. The speed is so high that the information
about which of the two interferometer is randomly chosen for the photon
in one village cannot get to the other village before its twin photon is
detected there, without that information traveling faster than light.
Under these conditions the principles of classical physics ensure that
the random choice *of what is done to a twin in one village* can have no
influence on the behavior of its faraway sibling. But this condition of
no faster-than-light influence cannot be reconciled with the quantum
results just described.

How is this remarkable result proved?

Case Two is the same as Case One up until the moment that the two random
choices are made, but the random choice in Bellevue goes the other way:
the upper interferometer is picked by the random process there, but
nothing is changed in Bernex. Now a small fraction f of the pairs will
be \"unmatched\". Since nothing has changed in Bernex, this small
fraction f of unmatched events must arise from a switching of this
fraction f of the events in Bellevue from what they were in Case One.
That is, if in Case One the sequence of detection events is, say (H, V,
V, H, H, H, V, H, etc.) in both Bellevue and Bernex then in Case Two the
fraction f, say 1%, of these values will be reversed from their Case One
values in Bellevue, *but none will be reversed in Bernex*. This is the
first key consequence of the no-faster-than-light-influence condition:
it ensures that the random choice made in Bellevue does not disturb the
outcomes in Bernex.

Case Three is the same as Case One in Bellevue, but the upper
interferometer is chosen in Bernex instead of the lower one. Hence the
same fraction f of the detection events, but now in Bernex, must be
opposite to what they were in Case One.

In Case Four the changes that were made in Bellevue in Case Two, and in
Bernex in Case Three are now made simultaneously in both Bellevue and
Bernex. Hence in this final case the changes that occur in Bellevue must
be the same as the changes made there in Case Two, since no influence of
the choice made in Bernex can be present in Bellevue. Similarly, in this
Case Four, the changes made in Bernex must be the same as the changes
that were made there in Case Three.

But then the total number of mismatches in Case Four can be no greater
than the sum of the number of mismatches in Cases Two and Case Three.
Thus the fraction f\* of mismatches in Case Four can be no larger than
2f. But this contradicts the empirically verified prediction of quantum
theory that f\* is roughly 4f.

This large-scale failure of the core causality idea of relativistic
classical physics suggests that we must be prepared for a profound
revision of our conception of the nature of the physical world. Bohr,
Heisenberg, Pauli, and the other founders of quantum theory partially
achieved this by bringing conscious human observers into basic physical
theory in a way that permits the idea-like aspects of reality to be more
deeply involved in the causal structure of the Nature than classical
ideas allow. So let us look now more closely at what they did.