Against the Copenhagen Interpretation of Quantum Mechanics

7/31/2019 Against the Copenhagen Interpretation of Quantum Mechanics

1/16

Against the Copenhagen interpretation

of quantum mechanics in defence of

MarxismWritten by Harry Nielsen Wednesday, 13 July 2005

Quantum mechanics has given scientists and engineers a new and deeper

understanding of physical reality. It explains the behaviour of electrons, atoms and

molecules, the nature of chemical reactions, how light interacts with matter, the

evolution of stars, the bio-chemistry of life and the evolution of mankind itself.

Despite its successes it remains an intensely controversial theory. It suggests thatvery small objects such as electrons or photons behave in ways that contradict the

common sense ideas. Yet many scientists to this day refuse to accept the fact that

contradiction is an essential part of all matter.

Quantum mechanics is the part of science that deals with the motion of matter on the scale

of atoms and sub-atomic particles. It was the experimental and theoretical response of

scientists in the first half of the 20 th century to a series of contradictions that had emerged

in 19th century physics.

Quantum mechanics has given scientists and engineers a new and deeper understanding of

physical reality. It explains the behaviour of electrons, atoms and molecules, the nature ofchemical reactions, how light interacts with matter, the evolution of stars, the bio-chemistry

of life and the evolution of mankind itself. Semiconductors, transistors, computers, lasers,

plastics, all result from insights gained from this part of physics. When tested by experiment,

the predictions of quantum mechanics have been successful to extraordinary levels of

precision. In conjunction with the other great breakthrough of 20th century physics,

Einsteins theory of relativity, it leads to the possibility of enormous advances in human

society through the limitless supplies of energy from nuclear fusion or the possibility of

humankinds destruction by atomic weapons.

Yet despite its successes it remains an intensely controversial theory. It suggests that very

small objects such as electrons or photons (particles of light) behave in ways that contradict

the common sense ideas and physical intuition that derive from the world of objects that we

see around us. Very small objects appear to behave very differently from large objects - from

things we can see and hold. Light spreads out through a diffraction grating like a wave, then

thuds into a detecting screen as if it was a particle. Strange effects occur when electrons are

scattered by crystals that seem to suggest an electron is not a particle but a wave but not

always.

Worryingly for many physicists, quantum mechanics seems to fail exactly where it should be

strong in describing the motion of individual small particles of matter. It describes only the

relative probability of, for example, a moving particle arriving at one place or another, or ofan electron in an atom having one energy level or another. It has nothing to say about why
http://www.marxist.com/quantum-mechanics-copenhagen130705.htmhttp://www.marxist.com/quantum-mechanics-copenhagen130705.htmhttp://www.marxist.com/quantum-mechanics-copenhagen130705.htmhttp://www.marxist.com/component/option,com_mailto/link,915589aef83b453e237ca3979459493df266deda/tmpl,component/http://www.marxist.com/quantum-mechanics-copenhagen130705/print.htmhttp://www.marxist.com/component/option,com_mailto/link,915589aef83b453e237ca3979459493df266deda/tmpl,component/http://www.marxist.com/quantum-mechanics-copenhagen130705/print.htmhttp://www.marxist.com/quantum-mechanics-copenhagen130705.htmhttp://www.marxist.com/quantum-mechanics-copenhagen130705.htmhttp://www.marxist.com/quantum-mechanics-copenhagen130705.htm


2/16

or how the particle arrives here but not there, why the electron has this energy but not that,

why an atom of a radioactive substance decays at this time but not another. This is

acceptable, and very useful, when there are many particles, as in a transistor for example,

when the probability that an individual particle can behave in various ways translates into the

predictable overall behaviour and an observable and useable effect. But physicists would

like to know more, and several generations of physicists have had to live with an uneasyfeeling about quantum mechanics that something is missing, that the theory is in some

sense not complete.

Why should Marxists concern themselves with this part of science? Best leave it to the

scientists, perhaps, those experts who know best. But bourgeois ideology permeates every

aspect of life under capitalism. Scientists claim to be objective, simply dealing with the facts.

There are countless examples that prove the opposite, from the cover-up for decades of the

health-effects of smoking to the Nazi experiments in eugenics. Anyway, how can a scientist

be objective when under capitalism science and technique are the key to vast profits?

Those most conservative academics who developed quantum mechanics inserted into the

subject a direct attack on the philosophical basis of Marxism dialectical materialism - at the

most fundamental level. This was their chosen response to the incompleteness of quantum

theory. Almost unbelievably perhaps, they chose to interpret the strangeness of quantum

behaviour by denying the existence of physical reality. And as a standard textbook

interpretation of quantum mechanics, physicists have been taught for the last 80 years that

physical reality therefore only exists as a result of the act of observation. This is the

Copenhagen interpretation of quantum mechanics, developed in the late 1920s by Niels

Bohr and Werner Heisenberg. To quote Heisenberg: I believe that the existence of the

classical path can be pregnantly formulated as follows: The path comes into existence only

when we observe it[1].

If ideas are weapons, then, like religion, this is another weapon in the armoury of the

bourgeois, another part of the defences that surround the unmentionable - the private

ownership of the means of production. But there is nothing particularly new in this. The

bourgeois are consistently obliged to deny reality to justify their rule. Bush and Blair pray

together to the Almighty for guidance (for their precision bombing of civilian targets,

perhaps?). The educated elite in the universities and government research laboratories

meekly fall into line with their discussions on whether the notion of physical reality is an

ambiguous one and thatquantum mechanics is a discussion of measurement phenomena

without any relevance to a reality that is not observed. The more astute may have other

ideas, but they keep these to themselves. Like the old Soviet bureaucracy, they think one

thing, say another, and do a third.

The heart of quantum mechanics: the double-slit experimentQuantum mechanics is often associated with advanced mathematics, and mathematics can

be used to develop the ideas of quantum mechanics to applications in complex situations.

The mathematics, however, is only a vehicle for the physical ideas. The central ideas of

quantum mechanics the wave-like behaviour of matter and the particle-like behaviour of

light can be accurately described without the need to use any mathematics. The essence

of the subject lies, however, in a description of physical reality and behaviour at small scales,

which is very different from that of everyday objects that we are familiar with.
http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#1http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#1http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#1http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#1


3/16

One of the clearest, and more consistently materialist, introductions to quantum mechanics

is that given by the physicist Richard Feynman in his small book Six easy piecesand, in a

slightly more mathematical presentation, in the first few chapters of volume 3 of his Lectures

on Physics. Feynman introduces the subject by describing the double slit experiment,

which he says in a famous quote is absolutely impossible to explain in any classical way,

and which has in it the heart of quantum mechanics. In reality it contains the only mystery.This is an experiment from classical optics that explicitly demonstrates the contradictory

behaviour of matter at small scales that matter can behave simultaneously as both

particles and waves. It also reveals the roots of the idealism of the Copenhagen

interpretation, and that the denial of physical reality was Heisenberg and Bohrs response to

this contradiction.

Waves are a process of energy transport, as we can see from the motion of the sand and

pebbles on a beach when a wave breaks on the shore. Waves on the surface of a body of

water disturb the surface as they pass by, moving it up and down. If two waves from different

directions come together at some point on the surface the movement adds up locally therecan be a bigger peak or a deeper trough. If one wave is moving the surface upwards while

another is moving it down then the total movement will be less than from each individual

wave. At a place where the disturbances from different waves cancel each other out, the

total movement will be zero.

These patterns of motion and interference between different waves are characteristic of how

waves behave; particles lumps of matter do not do this. If two moving particles, say two

pieces of rock, happen to meet they do not normally add up in some way. They collide, and

depending on the force of the collision they might break into smaller pieces of rock or they

might bounce off each other and continue moving in new directions. A bullet hits a target.

Another bullet might hit the target in the same place. It never cancels out the first thereare simply two bullets where there previously was one.

From the beginning of the 19 th century it was accepted that light had the properties of a

wave. Thomas Young presented experimental evidence to the Royal Society of London that

appeared to demonstrate this conclusively. In this classic experiment he showed that if light

is passed through two slits in an otherwise opaque barrier and then allowed to fall on a

screen, the screen will show a pattern of light and dark bands. The prevailing view prior to

that time, due to Newton , was that light consisted of small particles of matter. But the

pattern that Young observed could only be explained by waves from each slit adding up

not by particles. ...It will not be denied by the most prejudiced that the fringes [which are

observed] are produced by the

interference of two portions of light. [2]


4/16

Youngs perspective that light was waves

and not particles was accepted for over

100 years. It was extended by the

experimental work of Michael Faraday and

the theoretical work of James Clark

Maxwell, who showed that light waveswere a form of electromagnetic radiation.

In the same way that water waves are a

disturbance in the surface of water, light,

they said, was the result of disturbances in

electrical and magnetic fields. In 1887

these results were confirmed by the

physicist Heinrich Hertz, who produced

electromagnetic radiation at lower

frequencies than light, in the form of radio

waves. The wave theory of light seemedfirmly established.

At the end of the 19 th century, however,

this solid piece of classical physics came

apart. Several scientists showed that when

light shines on certain metals it can cause

an electric current. Classical physics said that the strength of the current should depend on

the intensity of the light but not its frequency. It didnt. When the frequency was increased,

the current increased. When the frequency was decreased, below a certain frequency the

current stopped, no matter how strong the light was. Electromagnetic waves should not do

this, but light did.

In 1905 Einstein showed that this could be explained by assuming that light was not waves,

but small particles photons. He suggested that when light shines on a metal the photons

collide with electrons in the metal and produce an electric current. Each particle of light -

each photon - has an energy that is proportional to its frequency. If the photon has enough

energy if its frequency is high enough - it can knock an electron out of an atom and then

the electron can move freely throughout the metal.

Then in 1909 the physicist Geoffrey Ingram Taylor reported the results of an experiment in

which interference fringes were produced with a very weak light source. The light was so

weak that only one photon at a time passed through the apparatus. Yet interference fringes

were still observed. The experiment has been repeated many times since. With the

development of sensitive photo-detectors in the second half of the 20th century it has

become possible to perform interference experiments that actually observe the arrival of

individual photons. The images shown here are the results from one such experiment by

Robert Austin and Lyman Page of Princeton University .

(Seehttp://ophelia.princeton.edu/~page/single_photon.html)

Water waves passing through two gaps in a

screen. The waves interfere and add up

in some places, cancel out in others. Young

saw the same effect with light when it was

passed through two slits - a pattern of light

and dark interference fringes.

Clickherefor an animation.
http://ophelia.princeton.edu/~page/single_photon.htmlhttp://ophelia.princeton.edu/~page/single_photon.htmlhttp://ophelia.princeton.edu/~page/single_photon.htmlhttp://www.colorado.edu/physics/2000/schroedinger/small_interference.htmlhttp://www.colorado.edu/physics/2000/schroedinger/small_interference.htmlhttp://www.colorado.edu/physics/2000/schroedinger/small_interference.htmlhttp://www.colorado.edu/physics/2000/schroedinger/small_interference.htmlhttp://ophelia.princeton.edu/~page/single_photon.html


5/16

The photons arrive at positions which appear initially to be completely random. With time,

more photons arrive, but mainly at the strong parts of the interference pattern and never at

the completely dark parts. Eventually when thousands of photons have arrived (and in

normal light intensities, there would be trillions of photons) we see the interference

pattern created by the arrival of individual photons.

How can this happen? Interference is a wave phenomenon, but the localised dots imply that

light is made up of small particles, not waves. Why are there dots on the screen at the bright

parts of the interference pattern and none at the dark? We cant explain this by saying that

the photons interfere with each other - the same happens even when there is only one

photon in the apparatus. Does the photon split into two and go through both slits? Or

perhaps, as the quantum physicist Paul Dirac mystically asserts each photon interferes only

with itself[3]. (Dirac is one of the leading physicists of the 20th century, but his philosophical

statements are symptomatic of the idealism that has infected modern physics; take for

example the quote: This result is too beautiful to be false; it is more important to have

beauty in one's equations than to have them fit experiment.[4])

One hundred years later physicists are still asking how it is that a single particle can show

interference, and are repeating these basic experiments, as in the Princeton examples, to

see if there is something new to learn. The problem posed by Einstein in 1938 still has no

answer for them: But what is light really? Is it a wave or a shower of photons? . It seems

as though we must use sometimes the one theory and sometimes the other, while at times

we may use either. We are faced with a new kind of difficulty. We have two contradictory

pictures of reality; separately neither of them fully explains the phenomena of light, but

together they do.[5]
http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#3http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#3http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#3http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#4http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#4http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#4http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#5http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#5http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#5http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#5http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#4http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#3


6/16

The situation becomes even more puzzling if instead of light we shoot electrons through thetwo slits. J. J. Thomson in 1897 performed experiments that showed that electrons were

small charged particles of matter. This was the prevailing view in physics for the next 30

years. But in 1927 Clinton Davisson and Lester Germer observed diffraction(wave) effects

when electron beams were scattered by crystals; George (G P) Thompson saw the same

effect with thin films of celluloid and other materials shortly afterwards. These experiments

alerted physicists once more to the strange behaviour of waves and small particles that not

only can light waves behave like particles, but sub-atomic particles can behave like waves.

The double-slit experiment with electrons was not technically possible at that time, but it was

nonetheless proposed as a thought-experiment used by early quantum physicists to

explore their ideas about the wave-like behaviour of matter. The electron double-slit

experiment was eventually performed in 1961, by Claus Jnsson of Tbingen; the single

electron double slit experiment was performed by Pier Giorgio Merli, GianFranco Missiroli

and Giulio Pozzi in Bologna in 1974, and repeated by Akira Tonomura and co-workers at

Hitachi in 1989. The results of these experiments were as anticipated by the early quantum

physicists; electrons, even single electrons, can interfere like waves even when they are

detected like particles. An image from the Hitachi experiment is shown here and a film of the

Bologna results can be obtained from

http://lotto.bo.imm.cnr.it/educational/main_educational.php.

The soundtrack of the film includes a rephrase of Diracs statement when it says that each

electron interferes only with itself and fades out to the triumphant sound of baroque violinsand flutes.

Single electron events building up an

interference pattern in a double-slit experiment.
http://lotto.bo.imm.cnr.it/educational/main_educational.phphttp://lotto.bo.imm.cnr.it/educational/main_educational.phphttp://lotto.bo.imm.cnr.it/educational/main_educational.php


7/16


8/16

this Heisenberg derived his uncertainty principle: the more precisely the position is

determined, the less precisely the momentum is known in

this instant, and vice versa.[7]

This result is a consequence of the geometry of the

experiment, and the particle behaviour of light (that light ofa certain wavelength is equivalent to photons with a

certain momentum). Niels Bohr, working with Heisenberg

in the University of Copenhagen, preferred to derive the

result in a different way. Suppose, he said, that we are

able to produce a short pulse of light by switching a light

source on and then off very quickly. From a particle

perspective, the source sends out a large number of

photons that all travel in the same relatively small region of

space. But if we try to understand the experiment from a

wave perspective, we find that that a large number ofwaves of different wavelengths are needed in order to

produce a short pulse. Wavelength is equivalent to

momentum, because of wave-particle duality, so in a short

pulse there is a large range of momentum, even though

the position of each photon is known accurately. For a

long pulse we have the opposite result - the momentum is

known accurately, but the position of the photons is known

less accurately. This is the uncertainty principle again but without the microscopes, the

disturbance produced by an observer, or any of the other paraphernalia introduced by

Heisenberg. For Bohr, this approach put the wave-particle duality of matter at the centre,

with the uncertainty principle as an inherent consequence, whilst for Heisenberg it was the

act of observation that was more important.

For both Heisenberg and Bohr, however, the uncertainty principle became the opportunity to

construct the mathematical and philosophical edifice of the Copenhagen interpretation of

quantum behaviour the mathematical expression (or more accurately, the mathematical

alibi) for a rejection of material reality. They asserted that Heisenbergs analysis of the

double slit experiment, and similarly Bohrs analysis of the properties of a pulse of light, were

examples of a general law which became known as Bohrs principle of complementarity: it

is impossible ever to observe both wave and particle behaviour simultaneously. It is possible

to either observe particles a localised piece of matter detected on its way through a slit,with no interference pattern or observe waves a non-localised disturbance going through

both slits, with an interference pattern. But any attempt to observe both simultaneously must

fail. Thus the contradiction was resolved, by asserting that the question is simply not to be

asked, for if asked it can never be answered. You will see either waves or particles but

never both.

Furthermore - all that can be done is to make observations; physics must be viewed as the

science of outcomes of measurement processes, and speculation beyond that cannot be

justified. The question of where the particle was before its position was measured is

meaningless. The particle materialises as a result of the act of observation. In the jargon

the act of measurement causes an instantaneous collapse of the wave function. What

happens, you see, is that the measurement process randomly picks out exactly one of the

A short pulse is the sum of

many

waves of different wavelengths,

which cancel everywhere except

where the pulse is strong.


9/16

many possibilities allowed for, and the wave instantaneously changes into a localised event

to reflect that pick.

Caustically, and quite accurately, Feynman was known to refer to this as the magic of the

wave-function collapse[8]. That the observer can influence what is observed is not a new

idea. But this is something far different. For Heisenberg and Bohr the observer not onlyaffects what is observedthe observer creates it.

This is little more than an attempt to shore up the inadequacies of formal logic in the face of

the evidence for the combined wave and particle aspects of matter. The alternative would

have been to accept wave-particle duality as a deep-seated example of the union and

interpenetration of opposites in motion at small scales; in other words, to accept that in

motion rigid concepts are not adequate. Such an approach could be the starting point for a

deeper investigation, for more experimental observations and more theory. What

fundamental aspect of the interaction of matter with matter or with light is it that leads

simultaneously to both particle and wave behaviour? What assumptions, observations,

mathematical tools, should we revisit to obtain a deeper understanding of this phenomenon?

But instead for political reasons because dialectical materialism (Marxism) has been

outlawed from the bourgeois professors study - we arrive at a dead end, where all further

enquiry is deemed impossible in the face of the unknowable:

The whole point is that the laws of formal logic break down beyond certain limits. This most

certainly applies to the phenomena of the subatomic world, where the laws of identity,

contradiction and the excluded middle cannot be applied. Heisenberg defends the

standpoint of formal logic and idealism, and therefore, inevitably arrives at the conclusion

that the contradictory phenomena at the subatomic level cannot be comprehended by

human thought at all. The contradiction, however, is not in the observed phenomena at thesubatomic level, but in the hopelessly antiquated and inadequate mental schema of formal

logic. The so-called "paradoxes of quantum mechanics" are precisely this. Heisenberg

cannot accept the existence of dialectical contradictions, and therefore prefers to revert to

philosophical mysticismwe cannot know,and all the rest of it.[9]

Challenges to the Copenhagen interpretationUnfortunately for Heisenberg, developments

in modern technology have allowed

scientists to show that the path of a sub-

atomic particle is very real. It is common to

observe particle paths in high-energy

physics experiments, where both the

position and the velocity can be determined

to within less than the uncertainty limit.

Heisenberg defended his position against

such evidence by saying that his uncertainty

principle was only relevant to predictingthe

future. But he also said that this knowledge

of the past is of a purely speculative

natureIt is a matter of personal belief

A bubble chamber photograph showing the

paths of charged particles in a magnetic field.
http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#8http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#8http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#8http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#9http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#9http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#9http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#9http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#8


10/16

whether such a calculation concerning the past history of the electron can be ascribed any

physical reality or not.[10]This lets the cat out of the bag, to use an English expression

it is a matter of personal belief. Heisenberg himself is admitting here that his idealistic

interpretation of quantum behaviour is an ideological choice. And his alternative escape

route - that the uncertainty principle is only relevant to predicting the future is a distinctly

bland statement. If the momentum is only known to a certain degree of accuracy, we canonly predict the future position to a certain degree of accuracy. There is nothing new or

particularly profound in this.

The physicist Max Born[11]developed an alternative interpretation of wave-particle duality

that avoided the idealism of the Copenhagen interpretation. Erwin Schrodinger had shown

how to compute the quantum mechanical wave-function of a system; Born interpreted

Schrodingers wave functions not as physical objects but as a way of describing the

probability that a particle is at a particular location. For example, in the double slit experiment

there is a wave-function for arriving by one slit and there is a wave-function for arriving from

the other slit. The probability of arriving there is the magnitude of the superposition of thewave-functions for that position, in much the same way that the amplitude of a water wave is

the sum of the different waves at a point on the surface of the water. Einstein explained the

idea like this:

. it proved impossible to associate with these Schrodinger waves definitemotions of the

mass points - and that, after all, had been the original purpose of the whole construction.

The difficulty appeared insurmountable until it was overcome by Born in a way as simple as

it was unexpected. The de Broglie-Schrodinger wave fields were not to be interpreted as a

mathematical description of how an event actually takes place in time and space, though, of

course, they have reference to such an event. Rather they are a mathematical description of

what we can actually know about the system. They serve only to make statistical statementsand predictions of the results of all measurements which we can carry out upon the

system.[12]

As Einstein points out, an important aspect of this view of quantum behaviour is that the

wave-functions are not assumed to have a physical existence. Particles of matter exist, they

interact, pass through slits, move around in atoms. But the wave functions associated with

them are a means to an end, a mathematical device that allows the physicist to compute the

probability of a state or a combination of states the probability that an electron in a

hydrogen atom has a particular energy, or the probability of a particle of light arriving at a

detector by a variety of different possible paths. When there are many particles, the

probabilities become translated into the densities of the arrivals more at the bright peak in

a double-slit experiment, none at the dark peak.

This insight into quantum mechanical behaviour is essentially the approach taken in all

practical applications of quantum mechanics. It has sometimes been described as the shut

up and calculate method (an expression often credited, probably wrongly, to Richard

Feynman) as an understandable reaction to the idealism and mysticism of other

interpretations. When, for example, a scientist in industry sets about designing a TV screen,

it is this approach that he will use. The electrons leave the heated filament herewith this

probability, giving rise to thiscurrent; they are accelerated by the magnetic field there, and

deflected to thatposition on the screen. (If asked by the research department manager,however, it is clear of course that the path does not exist.)
http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#10http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#10http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#10http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#11http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#11http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#11http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#12http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#12http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#12http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#12http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#11http://www.marxist.com/quantum-mechanics-copenhagen130705.htm#10


11/16

Feynman himself used this approach particles plus probabilities in his work on quantum

electrodynamics, described in his very readable and accessible book QED - The Strange

Theory of Light and Matter. Quantum electrodynamics is itself an extremely successful

theory, with predictions that match experimental observations to a very high level of

accuracy.

A different type of double slit experiment has been performed recently by the scientist

Shahriar Afshar, at Rowan and Harvard Universities . Results from these experiments,

published on the web, directly contradict Bohrs principle of complementarity. The

complementarity principle asserts that it is not possible to observe both wave and particle

behaviour simultaneously. But Afshars results suggest otherwise. His experiments are the

subject of a detailed discussion on weblogs at http://irims.org/blog/index.php/questions (a

good example of how the internet can open up the discussion of new scientific results to a

wider audience, in contrast to the secretive review process used by traditional scientific

journals). A copy of a paper describing some of his results is available

athttp://irims.bluemirror.net/quant-ph/030503/.

In contrast to Heisenbergs thought

experiment about how to detect which

slit the particle passes through, Afshar

uses a lens and photodetectors

positioned behindthe interference

fringes in order to observe photons

passing through the slits. In the single

photon form of his experiment

(described verbally on the web, butresults from which are not yet publically

available) a light flash at the position of

the image of a slit shows

unambiguously that the photon passed

through that slit. The photon is localised

at that slit and is behaving like a

particle. According to Bohrs

complementarity principle, an

interference patternwave-like

behaviour should then not beobserved.

Afshar checks to see whether or not

interference is still present by placing

thin wires at previously measured

positions of the dark parts of the

interference pattern. Even when he

observes photons going through the

slits, he can show that the wires are still

in the dark parts of an interference

pattern; the photon has been observed behaving both as a particle and a wave. The results

of all of Afshars experiments are not yet available publically, and his experiments have not
http://irims.bluemirror.net/quant-ph/030503/http://irims.bluemirror.net/quant-ph/030503/http://irims.bluemirror.net/quant-ph/030503/http://irims.bluemirror.net/quant-ph/030503/http://irims.bluemirror.net/quant-ph/030503/http://irims.bluemirror.net/quant-ph/030503/


12/16

yet been repeated by others, which will be an important test of their accuracy. But if Afshar is

correct, Bohrs complementarity principle is dead.

Order from chaos

Dialectics is a method of thinking and interpreting the world of both nature and society. It isa way of looking at the universe, which sets out from the axiom that everything is in a

constant state of change and flux. But not only that. Dialectics explains that change and

motion involve contradiction and can only take place through contradictions. So instead of a

smooth, uninterrupted line of progress, we have a line which is interrupted by sudden and

explosive periods in which slow, accumulated changes (quantitative change) undergoes a

rapid acceleration, in which quantity is transformed into quality. Dialectics is the logic of

contradiction.[13]

The picture of reality that has emerged from quantum mechanics and modern science is one

of restless continual motion and change on an atomic and sub-atomic level. Atoms are

bound together by a continuous interchange of particles between particles; electrons in

molecules move from atom to atom; energy and matter interchange; particles turn into their

opposite and then recombine. A central, distinguishing feature of this theory is change

through steps, not as a continuum.

The developments of modern science in this sense confirm and deepen dialectical

materialism. Yet, slowly decaying in the basement of modern physics, there is an absurdity

a logical, not a dialectical, contradiction. Without a dialectical approach to motion and

change there is no way out of this contradiction.

Modern physicists have been forced to accept that concepts which had previously beenconsidered separate must be linked, that they can not be thought of as separate but are

different yet interconnected aspects of the physical world. In particular, the physicists

concept of motion has to be extended to acknowledge the simultaneous wave and particle

aspects of matter. When matter moves, a physicist can describe the process by momentum,

which is the mass of the moving body times its velocity. A wave, on the other hand, is a

different type of physical process. It is a disturbance, of the surface of a body of water or of

an electrical field for example, and is a process in which energy moves. A physicist might

describe a wave by its wavelength, the distance from one peak of the disturbance to the

next. Momentum and wavelength are two quite distinct abstractions used to describe two

different processes. Yet after Einsteins work on the photoelectric effect, and after the

theoretical work of the founders of quantum mechanics, physicists were forced to accept that

momentum, a characteristic of matter behaving like a particle, is directly related to

wavelength, a characteristic of matter behaving like a wave.

Much of the confusion surrounding quantum mechanics, added to and propagated by Bohr

and Heisenberg, relates to the insistence that concepts such as wave and particle, or

momentum and wavelength, must be kept separate - we have two contradictory pictures of

reality as Einstein put it. This confusion is deeply rooted in the rejection or the lack of

awareness - of dialectics by modern scientists. On the one hand, but then on the other

says the academic as he agonises over his choice between apparently contradictory options,

wondering why the world is always like this. That apparently contradictory properties can bepresent simultaneously is not only possible but also universal. Light and dark, hot and cold,


13/16

north and south, wave and particle, an inevitable and unavoidable combination, the

existence of one being impossible without the other, and out of which comes change and

motion:

Whereas traditional formal logic seeks to banish contradiction, dialectical thought embraces

it. Contradiction is an essential feature of all being. It lies at the heart of matter itself. It is thesource of all motion, change, life and development. The dialectical law which expresses this

idea is the law of the unityand interpenetration of opposites.[14]

Not only that, but in their insistence on reductionism one particle, one photon - scientists

unwittingly and unconsciously destroy the living reality that they originally set out to

investigate. In the images from the Hitachi electron double-slit experiment, at what stage

does the wave behaviour of matter become visible? After 8 electrons? Definitely not the

electrons appear to have arrived at random, with no obvious pattern. After 270? After 2000?

Even after 6000, the pattern is still blurred. Borns probability interpretation allows the

physicist to compute the relative probability of the particle arriving at a certain position. But

the probability, or the wave-function, is only a statistical property of the system, and each

individual arrival can be (almost) anywhere. We become aware of the wave behaviour of

matter only when we have many particles. Similarly, in a gas we observe the laws that

connect temperature, volume and pressure only when we have many molecules. Wave-like

qualities emerge in a transition from quantity to quality; one particle or molecule is

unpredictable, but many obey well-defined laws conforming to their statistical properties.

Both waves and particles are observed individual particles, which in large groups have the

properties (interference patterns) of waves.

In that sense, single particle experiments and images of the sort obtained from the Hitachi

experiment also directly contradict Bohrs principle of complementarity. In the face of thisevidence, supporters of the Copenhagen interpretation, like Dirac, have to wriggle around,

imitating the photons they describe, saying that a photon goes through both slits and

interferes with itself and then in a puff of smoke, when the magician waves his wand - the

wave function collapses.

It is common to draw pictures, as here, of an atom

surrounded by an electron cloud. An interpretation of

this image that is common among physicists is that the

electron is somehow stretched over the region

occupied by the cloud. True, the electron is moving

very fast. A cloud is perhaps one way of representing

the rapidity of the motion, and the fact that the electron

could be anywhere in the shaded region. But there is

only one electron in the hydrogen atom. During any

small instance of time the electron is moving through a

definite small, localised, region of space. It is no more

stretched over space than a single photon is stretched

through both slits in a double-slit experiment. To

assume otherwise would be to arrive back once more

at Diracs mystical the photon interferes only with

itself and the magic of the wave-function collapse.

One of the possible wave-functions

for the single electron in

a hydrogen atom.


14/16

If we had many atoms and superimposed a picture of each, then we would see a cloud; we

would see the wave function and its magnitude, the relative probability of the electron being

at a particular position. The wave function describes the behaviour over many atoms, but

says little about the motion of the electron associated with an individual atom. There lies

both the strength and the weakness of quantum mechanics.

But does the path exist? Yes, providing that motion is understood dialectically. The path is

the trajectory along which the particle moves. When the particle is in motion, it is not at any

one position; it is in the process of moving from position to position. It moves along a definite

trajectory. But to say it is here, or there, at some point in time means nothing. It is moving

from here to there. It is the confusion that comes from an undialectical understanding of

motion, the attempt to say that the particle is here at a particular point in time, that is

exploited by Heisenberg to develop the mysticism that the path does not exist.

In the two slit experiment it is not possible to predict where the particle will go after the slits,

other than on average. There is an indeterminancy, in the sense that the precise trajectory

cannot be predicted in advance. But this is different from acausality. The particle arrives

where it does as a causal chain of events. The apparatus fires the particle at the slits; it

passes through one of them; it arrives at the detecting screen. And there are many examples

in nature of causal but non-deterministic systems. A toboggan sliding down a bumpy hill

arrives at a position at the bottom which is impossible to predict beforehand. If it starts from

a slightly different position at the top it will arrive at a widely different position at the bottom.

Unpredictability does not preclude causality. In fact modern science is beginning to

understand that often causality is expressed through unpredictability that necessity is

expressed through chance:

At first sight, we seem to be lost in a vast number of accidents. But this confusion is onlyapparent. The accidental phenomena which constantly flash in and out of existence, like the

waves on the face of an ocean, express a deeper process, which is not accidental but

necessary. At a decisive point, this necessity reveals itself through accident.[15]

Quantum mechanics, the new physics, incorporated large elements of the old physics into its

mathematical description. The mathematics of wave theory, techniques for solution of

integral equations, and also the matrix representation of wave functions (which has been

revisited and developed in recent years due to the applicability of matrix and vector

formulations to digital signal theory) are elements of the mathematical methods of classical

physics which are an essential component of quantum mechanical theory. The old is present

in the new. It was a powerful boost to the development of quantum mechanics that a large

range of mathematical tools of this sort were available that could be incorporated from

classical physics. To develop further, however, perhaps quantum mechanics needs to

overcome the limitations of the old in particular its dependence on linear and low order

differential equations.

Non-linear systems with a sensitive dependence on initial conditions that leads to

unpredictability are the subject of chaos theory. The similarities between the behaviour of

chaotic systems and the unpredictability of the behaviour of matter at small scales is

suggestive of a possible similar explanation, and this is currently an active subject of

scientific research. That large numbers of particles exhibit a well-defined wave-likebehaviour could be evidence of the nature of the underlying dynamics much in the same


15/16

way that the patterns in the strange attractors of non-linear systems are a symptom of an

underlying causality. An individual particle is unpredictable; many particles have a precisely

defined behaviour. Order comes out of chaos quantity becomes quality - as in other

complicated, many-body, non-linear systems.

With the development of computers a direct product of the understanding ofsemiconductors that derives from the insights of quantum mechanics science is now able

to explore these non-linear systems which classical mathematics cannot. Perhaps it will be

in this region, in the physics of chaotic non-linear systems, that a deeper understanding of

wave-particle duality will become possible. Or perhaps not. Perhaps the solution lies in more

experimental data. As technology advances it will become possible to perform more exact,

more complete, and new experiments. We will learn more about physical reality. Some ideas

will be overturned, some revised, some developed further, some incorporated into the new.

New theories that ignore the dialectical nature of material reality that deal with rigid fixed

concepts, that ignore or dismiss the contradictions of motion will ultimately fail

experimental tests. This already appears to be the case with the Copenhagen interpretation

if Afshars experiments are confirmed. The interaction between the observer and the

observed is many-sided, and to separate one from the other inevitably leads to mistakes, as

in the mysticism of the Copenhagen interpretation. Cause and effect can change position,

the observer can effect the observed, and the observed can effect the observer. But

fundamentally, at base, reality is material, it exists, and is not created by the act of

observation.

That matter has properties of both waves and particles is intriguing, but not justification for

abandoning physical reality. At a macroscopic level we have developed abstractions that

help us describe, understand and use the material world around us. We see a rock, a(slightly large) particle of matter, and find it can be made into a tool or a weapon. We see

waves on the sea and build boats that can travel through them. Why should it be so

disastrous to find that at small scales matter sometimes has the properties of a wave and

sometimes of a particle? A photon passes through a slit. It arrives at a screen, most often at

places where the interference fringes are strong and never where they are dark. According

to Afshars (as yet unpublished) results it is possible to see which slit it went through it is a

particle. Yet where many of them go, on average, is determined by a wave equation it is a

wave. Interesting. Something to think about. But please no more wave function collapses

or pregnant paths. Science and technology could advance dramatically with a deeper,

dialectical, and materialist, understanding of how these phenomena come about, and with a

thorough clear out of the mystical and unscientific absurdities that currently masquerade as

the philosophy of science.

Future scientists and engineers will understand physical reality better. And with the future

technology that humanity will collectively plan and develop, it will be possible raise

humankind far beyond the current struggle for lifes necessities. The savage barbarity of the

capitalist system, the ugly inequalities, all the brutality and the savagery, will be nothing

more than a distant unpleasant memory. And that too, like an electron dot on a screen, will

fade with time.

July 2005


16/16

Documents

Against the Copenhagen Interpretation of Quantum Mechanics