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.



                     The figure is missing from this plain text file.





                                           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. 

                         The figure is missing from this plain text file.


                                         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.