What is Quantum Theory?
The study of physical laws that apply on very small microscopic scale, normally the size of Atoms and smaller.
At the heart of Quantum Theory lie two linked concepts – what are they?
The concepts of wave-particle duality and uncertainty
What are the basic concepts of Newtonian Physics?
- Matter was considered to be solid and predictable.
- Bodies of matter obeyed fixed laws and it was possible to predict their behaviour in every situation.
- One day all natural laws would be discovered.
What challenged Newtonian certainty?
What is Quantum Mechanics?
QM is the study of the behaviour of matter and energy at the molecular, atomic, nuclear and subatomic particle level.
What did Max Planck discover?
That radiation was not produced in a continuous stream (as was thought) but in packets of energy of a definite size – he called these quanta.
Newton thought that light was made of a steady stream of particles – what did Thomas Young discover?
That light had the character of wave motion
It was shown though experimentation that light could behave like both a wave and a particle depending on the circumstances – what is this called?
Apart from light, what else can be shown to have wave-particle duality?
Whether a particle behaves like a wave of a particle can depend on what?
Whether it is being observed or not.
What was Albert Einstein’s biggest contribution to QM?
The Photo-Electric Effect
What is the Photo-Electric Effect?
It's been determined experimentally that when light shines on a metal surface, the surface emits electrons. For example, you can start a current in a circuit just by shining a light on a metal plate.
Who discovered wave particle duality in electrons?
Louis De Broglie
The solar system model of the atom was introduced by who?
Rutherford in 1911
What is the basic flaw with Rutherford's “classical” model of the atom?
The orbiting electron circles the nucleus and it should emit electromagnetic waves of an intensity increasing rapidly to infinity in a tiny fraction of a second, as it spirals inwards and plunges into the nucleus.
Niels Bohr solved the problem of the Rutherford atom model - how?
The Bohr model shows that the electrons in atoms are in orbits of differing energy around the nucleus (think of planets orbiting around the sun).
Bohr used the term energy levels (or shells) to describe these orbits of differing energy. He said that the energy of an electron is quantized, meaning electrons can have one energy level or another but nothing in between.
Which three important physicists tried to solve the problem of probability?
What did Schrodinger realise about wave mechanics?
He realised that the maths of classical physics could be adapted to the quantum world - this introduced the concept of wave function.
Max Born introduced the idea of the 'probability wave' - what was this?
The action of an electron being in a particular place depended on its wave function.
Heisenberg relied on what can be observed to predict the actions of particles - what conclusion did he reach?
You could measure the position of an electron or measure it's momentum but you could not determine both at the same time. The more precisely you measure one the more uncertainty there is of the other.
Heisenberg developed the uncertainty principle which underlies all of quantum theory - what is the uncertainty principle?
Everything that can be observed or measured are subject to unpredictable fluctuations. These fluctuations appear to be spontaneous events that cannot be predicted of explained.
What implications does the uncertainty principle have for science and religion?
Science has to admit that it cannot explain or predict everything (and never will) - this leaves the way open for the belief that God is still involved with creation and the universe does not run like a mechanical clock.
Laplace once said that he had no need to consider the hypothesis of God since science had discounted his need for existence. How does quantum mechanics change this?
Science would no longer agree with Laplace - there is still plenty of room for God in explaining the observations of science.
Heisenberg realised that uncertainty had a huge effect on everything - in what way?
He said that all of our understanding of reality was based on observations - but if things behave differently when we observe them, then how can we know what is really happening when no one is observing.
What we observe is not nature itself but only nature exposed to our method of questioning and observation.
Niels Bohr proposed the Copanhagan interpretation - what does this mean?
He proposed that an electron is both a wave and a particle (at the same time) until some act of measurement of observation forces it to be one or the other.
Who said "everything we regard as real is made of things that cannot be regarded as real"
What is superposition?
This claims that while we do not know what the state of an object is, it is actually in all possible states simultaineously - as long as we don't look to check.
Schrodingers Cat was a thought experiment to ridicule what?
The idea of superposition
It is known that superposition actually occurs at the subatomic level - because of observable effects. Electrons can be in multiple positions at once. What does this imply about the reality of nature as we can see it?
It is difficult for QM to prove or appreciate the effects of superposition on the larger observable level.
How can we know what is real when the moment we try to observe it, it changes or ceases to be?
Who said "God does not play dice" and why did he say it?
Albert Eistein - he did like the idea that he could not understand or predict science. He wanted to prove that everything could be "Newtonion" and deterministic again.