Particle physics is the branch of physics that looks at the elementary constituents of matter. At the level of atoms and sub-atomic particles, objects behave very differently compared with large objects we see around us every day. Quantum theory is an attempt to describe the behaviour of matter and energy at this sub atomic scale. Particle Physics also deals with very fast particles, moving at speeds close to the speed of light.

Quantum and nuclear physics
a) Photons: photon model to explain observable phenomena, evidence supporting the photon model
b) Particles: evidence supporting the quantum model for particles, a study of particle diffraction would provide suitable depth of treatment

Scottish Curriculum

Physics Higher Potentially relevant to module: Particles and Waves (sub-atomic physics and waves. study of particle physics and waves, with wave-particle duality as a linking theme.)


Why is quantum physics important?

What is quantum physics?

The theory of relativity describes the behaviour of large everyday objects in the world around us. However this theory alone is not enough to describe things at a very small scale. At the level of atoms and sub-atomic particles objects behave very differently and quantum theory is an attempt to describe the behaviour of matter and energy at this sub atomic scale.

Experiments with particles in the early 1900s provided some very confusing results. One of the conclusions drawn from these experiments is that small particles such as photons and electrons can behave either like a wave or like a particle under different circumstances.

Particles can be subject to interference and diffraction like light waves. However the act of observing a particle causes it to be detected as a particle in a specific location and not a wave.


Schrodinger created the analogy of his famous imaginary cat. A cat is in a closed box with a sealed deadly poison. At some point the seal will be broken and the poison released into the box, which will kill the cat. At any one time it is impossible to say if the cat is alive or dead without looking in the box and observing the cat. As soon as the box is opened the state of the cat is determined. In quantum theory if a particle is placed in the box, the particle can be in any number of places in the box but its position is not definite until the "box" is opened and the particle "observed".

Scientists now have theories that relate quantum theory with the theory of relativity. But this still doesn't explain everything. One theory that attempts to explain quantum and particle physics is string theory, which proposes that particles are more like tiny strings that only look like particles because they are so small. Theories like this may allow us to answer fundamental questions about the universe and the world we live in that so far cannot be explained.


Why is this important?


The implications of quantum theory are wide ranging. Quantum mechanics has explained the structure of the atom and the structure of the nucleus. Without knowing the structure of the atom, most of the physics and chemistry that we know today wouldn't have been possible. Quantum theory predicted the existence of antimatter, and explains radioactivity.

Many applications resulting from quantum theory are in use today, and its applications in the future are potentially infinite.

The theory of lasers was first outlined in 1917 in a paper "On the Quantum Theory of Radiation" by Albert Einstein, and the first functional lasers were built in the 1950s. Quantum theory also explains the photoelectric effect, whereby electons are emitted from matter as a result of absorbing energy from light - this occurs in human vision, and has practical applications in digital cameras. Quantum physics is also used in night vision goggles and 'scanning tunnelling microscopes' (which create images of surfaces where individual atoms can be seen).

A couple of applications in development that might have greater use in the future include:

  • Quantum entanglement is a phenomenon where two particles are quantumly linked to each other regardless of how far apart they are. Disturbing one of the particles also disturbs the other. This principle has been used to encrypt information as any attempt to intercept one of the particles will disturb the other, which can then be detected.
  • Quantum computing uses the property that quantum particles can exist in multiple states at the same time so can be used to carry out many calculations in parallel. Currently, very small quantum computers have been created, but at present there are technical difficulties involved in building bigger systems.

To find out more about quantum computing, download the video here, which relates to an exhibit at the Summer Science Exhibition 2011.