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Teacher Resource Bank
GCE Religious Studies
Other Guidance:
• Unit D: Religion, Philosophy and Science
A Guide to Quantum Mechanics
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
A GUIDE TO DELIVERING QUANTUM MECHANICS
What this guide will do…
The intention of this guide is primarily to encourage more centres to tackle Q4 on the Science,
Religion and Philosophy paper. In it, there are notes on each of the four elements of quantum
mechanics specified in the specification. There are also notes on the implications of quantum
mechanics for philosophy, science and religion. These notes are intended to be the starting
point of study into this area.
…and what it will not do
The guide is not written specifically with students in mind. It is written for teachers but it is
hoped that its language will make it accessible to students as well.
In addition, the guide does not cover all the implications of quantum mechanics for religion. It
concentrates on the actual details of the science.
Finally, the guide necessarily provides a broader context than the specification demands. The
intention of this is to make the specification easier to understand.
Introduction
The specification requires candidates to know some quite specific details about the science of
quantum mechanics.
It is as well to point out at this stage that the significance of quantum mechanics is not readily
understood by most scientists never mind philosophers of religion. As John Polkinghorne
amusingly puts it:
“The average quantum mechanic is about as philosophically sophisticated as the average
motor mechanic”.
Anybody who is daunted by quantum mechanics is, therefore, in very good company.
However, it is also sometimes said that explaining quantum mechanics to a beginner is easier
than explaining it to a Newtonian physicist. This is, in part, because a Newtonian physicist
approaches physics with a set number of ideas about reality which are well established by
observation and experiment whereas a beginner in this field carries no such baggage.
In order to understand each of the elements within the specification it is essential to
understand what went on before quantum physics. After all, the reason why candidates are
being asked to study this topic in a Religious Studies course is not because they want to get to
grips with physics but because they want to know how this work affects religious and
philosophical belief. And the only way that they can see how this works is if they understand
how quantum mechanics has changed the thinking which went before it.
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
Before quantum mechanics
Until the end of the nineteenth century (more or less), science was conducted within a
framework established by Newtonian thinking. It would probably be wrong to assert that
Newton himself would have been happy to see how his science had been interpreted after his
death but he remains, nevertheless, the well-spring of the classical view of science. The
characteristics of this view may be summarized as follows:
•
Reductionism: a view that seemingly complex physical processes can be understood by
reducing that complexity to a few simple laws;
•
Determinism: a view that all moving things within the universe are caused;
•
Objectivity: a view that the truth about reality is something which can be known
independently of any personal prejudice;
•
Mechanism: a view that the universe is like a giant machine set in a framework of
absolute time and space.
Quantum mechanics changes all these characteristics radically. Albert Einstein’s work on the
nature of light and Max Planck’s work on black-body radiation kick started a debate amongst
physicists which was to take physics well into the twentieth century.
Quanta
In 1962, Richard Feynman, a giant in the world of quantum physics, expressed the following
truth:
“If…all scientific knowledge were to be destroyed and only one sentence were to be passed
on to future generations…it is…that all things are made up of atoms – little particles that move
around in perpetual motion, attracting each other when they are a little distance apart, but
repelling upon being squeezed into one another.”
One of the things which may surprise us at the start of the 21st century is how recent the proof
of the existence of atoms actually is. The ancient Greeks had some idea that all matter was
divisible into smaller things (Democritus actually called these things ‘atoms’) but the idea did
not really take off until the 18th century with the work of chemists like John Dalton. Even
during the nineteenth century, many scientists worked on the assumption that atoms were like
mini-billiard balls but they needed to assume this because, as yet, there was no proof that
atoms were real. It would take the work of physicists of the highest calibre (Einstein himself
amongst them) to prove beyond doubt that atoms really did exist.
Having discovered that atoms do actually exist, attention quickly switched to what was inside
them. To a certain extent, work on this had already begun. J. J. Thomson had already
announced to the Royal Institution in 1897 that the atom (still at this stage unproven) should
not be considered to be the smallest part of reality and, in 1899, further experiments
demonstrated the existence of the electron.
Another pioneer in this field was Ernest Rutherford. His work on the structure of atoms took
him through his whole life. Rutherford’s atom was conceived according to strict Newtonian
principles. After a great deal of experimentation he was able to announce in 1911 that atoms
consisted of a nucleus and, in 1919, he added the idea that the nucleus of the atom also
contained positively charged particles called protons (neutrons themselves were finally proved
to exist in 1932). So, the model of the atom which many of us still picture is a planetary one
with the nucleus acting as the sun and the electron acting like the planets.
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
Unfortunately, as described above, several problems with this model remain unsolved.
These problems arose long before the neutron was officially proved to exist. One of the most
significant was: how could the electron stay in orbit around the nucleus? Why did it not
collapse back into the nucleus of the atom? Why would it collapse back into the nucleus, you
may ask? The answer lies in understanding the concept of radiation.
Moving things radiate. It is easiest to think of this radiation as either heat or light. Heat itself is
best thought of as a sort of vibration. So, as the electron orbits the nucleus, it radiates energy.
The only energy provided to the electron comes about as the result of its motion. In due
course, however, the electron will have radiated all of its energy away. Under the Rutherford
model, this would mean that, in time (fractions of second!), the amount of energy it had would
eventually dry up and it would no longer be able to maintain its orbit.
For a solution to the problem, it is necessary to go back to 1900 and the work of an Austrian
physicist called Max Planck. Planck was steeped in the classical tradition of Newtonian
physics and spent nearly the whole of his life trying to disprove the discoveries which he had
made which undermined this tradition. From his work on the nature of light, scientists such as
Niels Bohr were able to construct a model of the atom which explained, in part, the conundrum
of the orbit of the electron.
Planck’s experiments demonstrated that radiation could be emitted in chunks or ‘amounts’
called ‘quanta’. We might be quite happy with this idea today but, at the time, this was an
awkward discovery. Largely, this was because of the prevailing view of the time which treated
electro-magnetic radiation like light as a form of wave. It could not be the case that radiation
could both be given off in wave form and in the form of particles. These two pictures seemed
to be completely contradictory. Putting it more simply, a picture of the nature of light as a
squiggly line on the page did not fit in with the picture of light as a series of bullet marks.
The exact science of Planck’s discoveries into quanta is more complicated than candidates
need to know. It is sufficient on this course for them to know that Planck’s discoveries helped
Bohr to overcome some of the problems posed by Rutherford’s picture of the atom.
Henceforward, the basic understanding of the atom we use today is known as the RutherfordBohr model. That is not to say that this model has not itself been amended and improved
since but, for the purposes of this course, it is as far as we need to go.
So, there we have it. The word ‘quanta’ describes chunks of energy and the phrase ‘quantum
mechanics’ describes the behaviour of these chunks of energy.
Now, quantum effects only affect very small things. So, an electron which is exceedingly
small, is significantly affected by quantum effects whereas an elephant will be affected so
slightly as to be barely observable. Actually, quantum effects reduce considerably for anything
much bigger than an atom. To give some sense of scale, the scale at which quantum
processes dominate is as much smaller than a sugar cube as a sugar cube is smaller than the
universe.
Light as a wave and a particle
Up until the work of Planck, it had long been established (by Thomas Young in 1805) that light
(a form of electro-magnetic radiation) only came in wave-form. Ironically, this directly
contradicted Newton’s work that light was made up of particles. The irony was that Young’s
idea dominated the 19th century and Newton’s idea was ignored but a particulate
understanding of light would return with a vengeance at the start of the 20th century.
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
It is difficult to see what describing light as a wave means. A simple way of understanding this
is to look at how Young established the wave form of light. He used something now referred
to as the double slit experiment. He took a beam of light and shone it through 2 slits which
were held in an otherwise opaque screen. Behind the screen was placed a white screen.
When the light was shone through the 2 slits, a pattern of light and dark bands (called an
interference pattern) was produced on the white screen giving rise to Young’s assertion that
light consisted of waves.
At the end of the nineteenth century, Max Planck hit upon a problem with this understanding of
light. Essentially, the wave theory of light did not explain what happened when a body
capable of absorbing light completely (called a ‘black body’) radiated heat. It seemed to
Planck that the emissions from such a body were not the kind you might expect if radiation
was wave-like. Rather, the radiation appeared to be in particle form. This discovery was to
become the basis of quantum mechanics. Einstein himself established through something
known as the photoelectric experiment that light did, indeed, act like a particle. The particle
was to become known as the photon.
So, there appeared to be a problem. On the one hand, a great deal of science depended on
the notion that light was in wave-form but on the other hand, this notion did not cover all the
ground. It seemed that neither view of light was wrong and, yet, neither view of light appeared
to be exactly correct either. The significance of this problem is not to be underestimated.
Remember that until this time, classical or Newtonian physics operated according to the
principles outline above on page 2. A summary of these principles would make science
certain, factual and straightforward. Now, however, there appeared to exist a scientific truth
which was neither certain nor straightforward and which, indeed, appeared to challenge the
very factual basis of science itself. What was going on?
The first thing to say in answer is that much of the Newtonian view of reality was not to be
jettisoned at this first sight of trouble. The idea of electro-magnetic radiation (established by
Maxwell) was still valid. The message to scientists at this time was to be: DON’T PANIC!
Equally, the wave-particle duality of light was forcing scientists to wake up to a new reality:
that of the apparent truth of contradictory states.
The second thing to say is that, at the level of the sub-atomic particle, the old characteristics of
science would have to be ignored. For example, if light could be understood both as a wave
and a particle, it would not be possible to reduce all of science to a few simple rules. Further,
as will be explained in the next section, the reason why light appears to behave in these
mutually contradictory ways has a lot to do with the way light is actually being measured. This
sounds obvious until you consider that, up until discovery of wave-particle duality, scientists
had always assumed that the process of observing was a purely objective, passionless
exercise. What the new physics was discovering was that scientists were themselves
influencing the outcome of their experiments. They could no longer take the stand of impartial,
objective observers. They had to accept that they were not spectators of the drama but actors
on the stage.
The nature of the electron
Problems with the Rutherford-Bohr model of the atom persisted for much of the first twenty
years of the twentieth century. For example, despite the fact that the electron was pictured
whizzing around the nucleus of the atom, atoms themselves still presented a smooth, ‘hard’
surface. Even the hydrogen atom behaves as though its nucleus is entirely surrounded by the
electron. How could this be?
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
The answer was presented by a French aristocrat and physicist, Louis de Broglie. He
proposed to turn Planck’s work on light on its head and apply it, in reverse, to the electron.
Simply put, he reasoned that, if light (which was previously understood to be wave-like) could
be understood to be particulate perhaps the electron (which was previously understood to be
particulate) could be understood to be wave-like. To put it more scientifically, the equation
which uses Planck’s constant to relate the wavelength of light to the equivalent energy for a
particle (the photon) could be turned around. De Broglie proposed in his PhD thesis that, in
certain circumstances, electrons could be viewed in wave form. Initially, this idea was treated
with a great deal of suspicion: de Broglie’s own supervisor could not decide whether it was
genius or complete rubbish and decided to send the thesis to Einstein. Fortunately, it struck a
chord which Einstein who had, himself, come to the inescapable conclusion that all things subatomic appeared to suffer from the wave-particle schizophrenia.
How does this solve the problem of the smoothness of atoms? Every electron in the cloud
around the nucleus of the atom has to be seen not as a tiny ball but as a wave spread out
around the entire nucleus. The single electron in the hydrogen atom really does form a
spherical cloud around the nucleus all by itself. This presents us with the possibility of thinking
about the atom not as a mini solar system but rather like a series of onion skins.
So now a picture of reality was emerging which was, to say the least, bizarre. Scientific work
was demonstrating that sub-atomic particles were wave-like and particle-like. According to
classical physics, if two mutually exclusive possibilities presented themselves, one of them
must be wrong. Niels Bohr worked hardest in this field to provide an explanation (now part of
the Copenhagen Interpretation) for this behaviour by using what has been called the Principle
of Complementarity which asserts that two mutually exclusive pictures can both be truth.
At the very least, the work was showing scientists that our understanding of this reality could
only be based on models. The models formed a story about reality rather than presented an
absolute objective truth. In this respect, science could be understood to be one (highly
successful) way to describe reality but one which should take its place alongside other ways to
describe reality not least a theological one.
The role of the observer in resolving uncertainty
All this leads nicely onto the final part of the specification. Obviously, wavy things are not
precise things. Electrons and photons are wavy so being able to picture them precisely at a
dot will not be possible. There will always be some uncertainty about these particles. The
uncertainty will not be the result of a failing in human knowledge. Neither will the uncertainty
be the consequence of unsophisticated methods of measurement. The uncertainty is real –
objectively there. Walter Heisenberg discovered in 1926 that there was a mathematical way of
talking about this uncertainty. He stated that the closer you got to understanding where a
particle (like an electron) is the further away you were from discovering where it is going and,
similarly, the closer you got to discovering where a particle is going the further you were from
understanding where it is. John Gribbin expresses the same idea using the idea of the coiled
spring. If you squeeze a strong spring between your fingers, you know that it will, eventually,
ping out in some entirely, unpredictable direction. The more closely you try to measure the
behaviour of particles, the greater will be the uncertainty. So, an electron does not have a
precisely defined position and a precisely defined velocity at the same time or, to put it another
way, it does not ‘know’ simultaneously both where it is and where it is going. This
understanding became known as the Uncertainty Principle.
Mathematically, of course, it is perfectly possible to understand what is going on. At this point,
it is as well to say that many quantum physicists use maths (in this case, probability) as the
language of choice because it avoids many of the problems that plain English presents. In
some ways, too, it explains why it is possible both to be a good quantum physicist but be a
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
relatively poor philosopher and also why it is possible to be a poor quantum physicist yet
understand the significance of quantum mechanics for human thought in general.
In what ways, then, does the role of the observer help us? Observations of the behaviour of
sub-atomic particles will only get half the story. We have already established that a good way
to think about how electrons behave is to use wave-like imagery. This means, by definition,
uncertainty will always be a factor. If, however, the uncertainty is too much to bear, the
observer may wish to look more closely at how they behave. The bizarre thing is that,
whenever that happens, electrons behave like particles. In other words, when you are not
looking, electrons wave and when you are, they don’t. The observer massively changes what
there is to see.
From the perspective of classical physics, all this is too much to bear. It is worth repeating
that a Newtonian physicist would have believed his vantage point to be passionless and
impartial. His observations of reality were true, objective and factual. Now, quantum
mechanics was telling us that observers were getting in the way of finding out everything there
was to find out but, frustratingly, if they did not do this, the thing they would like to be
observing was uncertain anyway. This was a no-win situation for traditional science.
Theological implications
The specification raises a number of issues which candidates may wish to consider but three
are mentioned here for further consideration:
Quantum mechanics does not prove the existence of God! The field is so complex that there
have been all kinds of hare-brained attempts to link it with religious and pseudo-mystical claptrap. What quantum mechanics does for science is highlight the cloud of unknowing. The
theologian Eric Mascall once said that the development of knowledge was a bit like walking
into a thick fog with a bright light. The light helps to guide your way and you can see a great
deal because of it. Even more importantly, however, you can use the light to see just how
much you can’t see. In the same way, the new physics reminds scientists that knowledge is a
human and, therefore, a contingent thing. There will always be a provisionality about it and,
very probably, an incompleteness. Many theological traditions (the via negativa tradition for
one) also stress the contingency of human knowing especially in relation to God. This type of
theology does not undermine human efforts at knowledge but it does underscore it with a
certain humility in the face of both the physical reality of the universe and the spiritual reality of
God.
Some aspects of quantum mechanics demonstrate the unity of reality. The most extraordinary
thing about the new physics is the understanding that the laws which seem to apply locally on
this tiny planet apply across the entire expanse of the universe. Using quantum mechanics,
for example, scientists can show how the behaviour of individual electrons in this piece of
paper affect the behaviour of individual electrons in galaxies billions of light years away. This
underlying unity is appealing to mystical traditions which have a long history of stressing the
unity of all reality – material and spiritual.
Finally, the story of quantum mechanics is not a cold, scientific, ‘mechanical’ story. It is a story
of real people who have followed their thinking with passion, surprise and courage. On many
occasions, it is a story characterized by leaps of faith and significant jumps into the unknown.
Physics is the better for the inspiration of thinkers like Bohr and Heisenberg who were
prepared to risk ridicule in the pursuit of what they sensed to be true. The story of faith,
likewise, is a story marked by people of courage whose example reminds us that the
impersonal reality of the physical universe has really given birth to something remarkable: the
spiritual, thinking beings we call us.
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Teacher Resource Bank / GCE Religious Studies / Other Guidance: A Guide to Quantim Mechanics / Version 1.0
Sources and thanks
One World
Almost Everyone’s Guide to Science
John Polkinghorne
John Gribbin
SPCK (1986)
Phoenix Science (1998)
Quantum Theory for Beginners
McEvoy and Zarate
Icon Books (1996)
Dr Jonathan Allday for agreeing to deal with my irritating questions and helping to unlock the
secrets of quantum mechanics with such enthusiasm.
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