Download Quantum Mechanics Booklet

1
What are the key ideas of
Quantum Mechanics?
Does light behave as a wave or a particle?
This question is central to quantum mechanics. In the 19th Century,
most physicists agreed that light behaved like a wave. However, as
the 20th Century began, the idea of light as a wave was called into
question.
Problem One: Light doesn’t need a medium to travel through
Some scientists were confused, as waves like sound waves, need a medium, or substance
to travel through. Sound waves can only travel through a medium, like air. For instance, a
bell in a vacuum, where there is no air, will not make a sound. However, light can travel
without a medium. We know this, as the light from the sun and other stars travels to us
through empty space. Did this mean that light was made up of particles, which could
travel without a medium?
Problem Two: The prediction of ultraviolet catastrophe is wrong
A black body is an object which absorbs all light it encounters. When a black body is
cold, it appears black because it radiates no energy. However, a black body which is hot
will emit visible wavelengths. The hotter the black body, the higher up the spectrum the
light which is emitted. For example, a black body at room temperature will emit infrared
energy, but as it gets hotter, we will see energy emitted which is red, then orange, then
yellow, then white and then blue. Finally, at the hottest temperatures, ultraviolet energy
is given out.
Twentieth Century physicists predicted that a perfect black body would give out
radiation of an infinite density when it reached thermal equilibrium (when the black
body was absorbing the same amount of energy as it was giving off) This prediction was
called the ‘ultraviolet catastrophe’. “If this were true, all objects should appear
violet in colour.” (Alastair Rae) However, this is not the case; the ultraviolet
catastrophe did not occur, which physicists found very hard to explain.
2
The Solution: Max Planck
In 1901, Max Planck discovered that light did not flow in a
continuous stream, but that it came in little packets called quanta.
(‘Quanta’ is the plural for ‘quantum’ which is Latin for ‘amount). All of
the quanta in a beam of light are of the same size and contain the
same amount of energy. The energy of a quantum is determined by
the following formula:
Frequency of the wave
x
a constant number.
This constant number is one of nature’s constants, like Newton’s law of gravity. As
Planck was so influential in the formulation of quantum mechanics, this constant is
termed ‘Planck’s constant’.
To aid our understanding of the idea of ‘quanta’,
Alister McGrath asks us to imagine a sand dune in
an African desert. He states that from a distance,
the sand dune appears to be smooth, but when we
look at it more closely, we see that it is made up of
tiny grains of sand. Similarly, energy, like light,
appears to be a continuous wave, but in actuality,
it is made up of little packets of energy. (Quanta)
Albert Einstein
Einstein’s ideas and experiments gave more weight to Planck’s
argument that light is not only a wave. He stated that all
electromagnetic energy contain photons, which should be treated
like particles.
Einstein’s Photoelectric Effect (1905)
Einstein proved that when light hits a metal surface, the metal gives out electrons. This
means that particles (or quanta / photons) of light containing energy, hit the metal and
eject the electrons. Therefore, there must be packets of energy contained within the
light. The amount of energy these ejected electrons contain is always equal to the
amount contained within the light ‘quantum’ minus a fixed amount. (This amount is the
amount of energy required to eject the electron from the metal and is called the ‘work
function’.)
3
“Einstein’s brilliant theoretical account for the photoelectric effect suggested that
electromagnetic radiation had to be considered as behaving as particles under certain
conditions.” (Alister McGrath)
“We therefore have evidence … that light is a wave, while the photoelectric effect
indicates that it has the properties of a stream of particles. This is what is known as
‘wave-particle duality.’ (Alastair Rae)
In the Twentieth Century, it was becoming clear that atoms did not behave in a normal
way. It became accepted that light could behave as a wave and a particle, and the term
‘wave-particle duality’ was coined to explain this idea. Thus, it was no longer sensible to
ask the question, “Is light a wave or a particle?” because it is both of these things at
the same time. Whether light behaves as a wave or a particle at a particular time
depends upon what type of experiment is conducted and how an observation is carried
out.
Is it only light which displays wave-particle
duality?
The Nature of the Electron
Further experimentation on wave-particle duality, found that electrons
also behave as both a wave and as a particle. All atoms contain
electrons which are forced to remain in a small space by an electrical
charge which links them to the centre of the atom, the nucleus.
The Double Slit Experiment
The Double Slit Experiment is used to show that
energy, such as light and electrons, behave as both
waves and particles. The experiment was originally
done with light, but eventually it was used with
electrons also. In the experiment, electrons are fired
through two slits on a plate. There is a screen behind
this plate. If electrons behave as particples, the
number of electrons hitting the screen at the back of
the plate should be equal to the sum of the electrons
which are fired through BOTH slits.
If electrons are fired through two slits, the wave
4
However, physicists found that this does not happen. The number of electrons which
hit the screen is LESS than the sum of the electrons which pass through the two slits.
This means that the electrons are behaving as a wave as well as a particle. When two
waves which are out of step with each other meet, they ‘interfere’ with each other, or
cancel each other out. Thus, when the waves of electrons pass through the two slits,
‘interference’ takes place and some of the electrons are cancelled out. This is why the
number of electrons which reach the screen is less that physicists predicted.
Therefore, electrons also have wave-particle duality.
Einstein hated quantum mechanics. One of his famous quotes is, “God does not play dice
with the universe.” He believed that everything in nature is determined and that laws
can be found to explain everything that happens in the world and that these laws can be
used to make predictions about future events. However, advances in quantum mechanics
have shown that things do not always behave in a predictable manner. Paul Davies
explains this by stating, “… two identical situations might produce different outcomes.
For instance, imagine firing an electron directly at an atom: it may deflect either to the
left or to the right with equal probability.” Therefore, in quantum mechanics there is a
lot of uncertainty.
Heisenberg’s Uncertainty Principle
Heisenberg argued that it is impossible to predict the value of the
position and the momentum of a particle at the same time. Thus an
observer can predict where a particle is, or can make a prediction
about its momentum, but these two measurements cannot be taken
at the same time. The greater the certainty of the position, the
lesser the certainty about the momentum and the greater the
certainty about the momentum, the lesser the certainty about the
position. It is the observer that causes this uncertainty. The
observer’s measurement of the position of the particle affects its
momentum in an uncertain way and his/her measurement of
momentum affects the particle’s position in an uncertain way. This is
known as ‘observer effect.’
5
Therefore, it seems that the observer causes uncertainty, “What we observe, we
influence” (Mel Thompson). This uncertainty is not down to a failure of scientific
apparatus and will not disappear as science progresses. The uncertainty is fundamental
to quantum physics and will never go away, “an object has no existence independent of
our observation of it. We cannot get ‘outside’ our process of observation to see what is
‘really’ there – it makes no sense to speak in those terms.” (Mel Thompson)
All physicists can do at quantum level is base ideas on probabilities, “Quantum theory
cannot predict the action of individual particles, but describes the atomic world in
terms of probabilities, based on observations of very large numbers.” (Mel Thompson)
Fritjof Capra – “The Tao of Physics”
Capra tried to show that quantum mechanics has several links with
Eastern Mysticism. He stated that “Physicists do not need
mysticism and mystics do not need physicists, but humanity needs
both.” He believes that the views of quantum mechanics are very
similar to the ideas which Eastern mystics have held for
generations. For instance:
 Eastern mysticism holds that everything in the universe is interrelated and
connected. Capra argues that, like the mystic, “…the modern physicist … has come to
see the world as a system of inseparable, interacting and ever-moving components “
 Capra states that Eastern mysticism has always been able to deal
with the paradoxes of nature. He states that mystical ideas can help
scientists to come to terms with the apparent paradox of waveparticle duality. For example, the Yin-Yang sign embraces opposites
and brings them together as one whole.
 The central role of the human observer, Capra argues, is central to both mystical
thought and quantum physics, “In Eastern mysticism, the universal interwoveness
always includes the human observer and his or her consciousness, and this is also
true in atomic physics.”
 The world of quantum physics is difficult for scientists to explain and they often do
not understand why things at quantum level happen in the way that they do.
Similarly, in mysticism, it is difficult for believers to describe mystical experiences
of God.
6
What are the implications for religion?
Science has often seen to be in conflict with religion. Many
scientists see themselves as uncovering new ideas which get rid
of religion and superstition and shrink the gaps left for God in
the modern world.
If the new ideas discovered by quantum physicists can be linked to mystical and
religious thought, as Capra suggests, perhaps science has discovered evidence for
religion. Capra argues that God could be a unifying force which binds the whole of
nature together. Perhaps God is the ultimate essence which links everything together
and allows things like light and electrons to be two things at once. Has science found
proof of God?
However, perhaps religious people are clutching at straws here. Have scientists really
found evidence of God? Is putting God in as an explanation of wave-particle duality
another example of ‘God of the gaps’? Do we really have evidence of a God recognisable
by religious believers of traditions such as Christianity, Islam and Judaism?
Jeremy Bernstein: “Science Observed”
Bernstein argues that Capra has made very weak links between
science and mysticism. “At the heart of the matter is Mr
Capra’s methodology – his use of what seems to me to be
accidental similarities of language as if these were somehow
evidence of deeply rooted connections.”
Leon M. Lederman: “The God Particle”
Lederman argues that Capra is wrong to simplify all of the advances
of quantum mechanics by stating that they have only discovered
things which Eastern mystics have known for centuries. “Starting
with reasonable descriptions of quantum physics, he constructs
elaborate extensions, totally bereft of the understanding of how
carefully experiment and theory are woven together and how much
blood, sweat and tears go into each painful advance.”
Eddington
The quantum physicist Eddington argued that any form of ‘quantum
mysticism’ is wrong to state that great God of classical theism can be found
in quantum mechanics, “We should suspect an intention to reduce God to a
system of different equations. That fiasco should be avoided.”
Alister McGrath: “Science and Religion – An Introduction”
McGrath argues that a parallel can be made between wave-particle
duality of quantum physics and Christology. He states that
Christianity has struggled to explain how Jesus can be both a
human being and God at the same time, “The Christological issue of
critical importance was that the biblical portrayal of Jesus of
Nazareth at times suggested that he behaved or functioned as
God, at others as a human.”
7
If science can hold that light, electrons etc can be both waves and particles at the same
time, without being able to fully explain this phenomena, then this could, McGrath
argues, help Christians to assert that Jesus was both God and a human being at the
same time.
Religion has often been challenged by advances in science. For
example, Copernicus’ realisation that the sun was the centre of our
galaxy, rather than the earth, greatly challenged Christian teaching
at the time. However, religion has managed to survive these
challenges from science. Some religions have attempted to
incorporate science into their religion, for example, Liberal
Christians accept the scientific ideas of the Big Bang and Evolution.
Other religious groups have rejected scientific ideas, for example,
Literal Christians, who still believe in the creation of the world by
God in 6 days as presented in Genesis.
 Religious people may argue that they do not need to have agreement with science
as they have faith. Science may dispute some of their ideas, but they believe in
God and trust in His teachings and so this does not matter.
 Some religious believers may champion the efforts of those, like Capra, who try to
make links between religion and science. They want their religion to be acceptable
to modern people. Keith Ward states that, “There are millions of things we do not
understand, including the fundamentals of quantum mechanics.” Perhaps God is
behind the workings of quantum mechanics and that is why we cannot understand
them properly. However, it could be said that trying to find God in quantum
mechanics is another example of ‘God of the Gaps’ – pushing God in to explain
something not yet understood by scientists.
8
As we have seen, Capra argues that developments in
quantum physics have led to truth which has been
known by Eastern mystics for generations. For
example, the discovery of the behaviour of electrons
on earth has led to the discovery of electron behaviour
throughout the universe, suggesting that everything in
the universe is unified – a teaching of Eastern
mysticism.
However, these attempts to link religion to quantum physics have been widely criticised.
The physicists who worked so hard to make these discoveries about quantum mechanics
are appalled at claims that they have just discovered something that was already known.
(E.g. Lederman in “The God Particle”) They argue that the discoveries they have made
have involved much experiment and observation and that likening the results to
mysticism because of some accidental similarities in language is nonsensical. (Bernstein).
Quantum mechanics is based upon empirical evidence gained of the physical world. All
physicists can perform the same experiments to see the same (albeit bizarre) results.
This is different from the subjective ideas of mystics which are not based on any
evidence at all. Quantum physics uses the language and strict methodology of science,
not the language of mysticism.
9
If the fundamentals of quantum physics can be
linked to mysticism (Capra) and can be used to
explain the human and divine nature of Christ
(McGrath), does this mean that science, rather than
being the enemy of religion, can now be said to be
religious itself?
Yes!
 Capra states that science and mysticism can work
hand-in-hand to discover the truth behind the
universe.
 Similarly, McGrath states that science can help
Christians to explain how Jesus can be both human and
divine at the same time.
 Quantum mechanics reveals that there are some things that science cannot, and
will never be able to, understand. Scientists need to realise that there is another
force working outside the world which has given it the regular laws of nature
(Newton’s laws) as well as the strange laws of quantum mechanics. The reason that
we cannot understand the workings of quantum physics is because this is where
God can be found and God is too difficult to comprehend. Science needs to learn
that it cannot explain everything, but needs a helping hand from religion “The
whole of science proceeds on the assumption that a reason can be found for why
things are as they are, that it is the end of science if one finds an ‘uncaused’
event, or one for which there is no reason at all.” (Keith Ward: “God, Chance and
Necessity)
10
No!
 Wittgenstein states that religion and science are
playing different ‘language games’. Just as the
rules of rugby cannot be used to judge the game
of football, so the language of science must not
be confused with the language of religion.
Therefore, science cannot be religious and
religion cannot be scientific.
 Stephen Jay Gould argues that religion and science must remain separate. Science
cannot comment on religion and therefore, science cannot be religious, “We can
neither affirm or deny it: we simply can’t comment on it as scientists.”

Dawkins believes that scientific advances have removed the need for God
altogether. To look for God in quantum mechanics is an example of ‘God of the
Gaps.’ Dawkins states that, “the alleged marriage between religion and science is a
shallow, empty, spin-doctored sham.”

Religious believers may argue that if science is taken as religious, ‘Reductionism’
may occur. If religion is ‘reduced’ to the links which can be made with science,
then there is a serious risk that the essence of the religion may be lost. For
example, Eastern mysticism involves a religious way of life and embodies ideas
beyond the concept of unity which Capra argues can be found in quantum physics.
Bernstein argues that the trial, error and constant revision involved in science
means that Eastern mystics would probably not want their beliefs and philosophy
of life compared to it, “…if I were an Eastern mystic the last thing in the world
that I would want would be a reconciliation with modern science." (Bernstein)
11