• Question: What is quantum mechanics and what are it's applications? Or is it a purely theoretical study?

    Asked by AnswerME123 to Anna, George, Jodi, Rob, Stefan on 17 Nov 2014.
    • Photo: Stefan Lines

      Stefan Lines answered on 17 Nov 2014:

      Quantum Mechanics is an extremely complex and diverse area of Science that tends to deal with Physics on very small scales. It has many applications, including quantum computers, cryptography… and is also an integral part of devices such as lasers and electron microscopes. Quantum physics can also be seen on a large (macroscopic) scales in super-fluids (frictionless fluids – climbs up walls!). It is very much not just a purely theoretical study 🙂

    • Photo: Anna Scaife

      Anna Scaife answered on 17 Nov 2014:

      That’s a big question! Quantum mechanics is the study of very small systems, like individual particles. When you look at the smallest components of matter they behave quite differently to large complex systems. If you’re dealing with large systems, then we say you are doing “classical” mechanics.

      It gets its name from the fact that on those small scales many quantities that we regard as continuous classically – such as energy – are actually observed to exist in discrete units (i.e. quanta), and objects which we would classically describe as individual units can be just as well represented as continuous waves – such as elementary particles. So on very small scales we can’t divide the world into either discrete or continuous, things have a dual nature.

      The limit between a classical and a quantum system is around about 100 interacting atoms, i.e. something larger than that can can be treated as a single classical system but something smaller should be treated as a quantum system. For example, if you had a tank of gas then you could treat the behaviour of the gas in the tank as a whole classically, but if you wanted to understand each of the gas molecules then you’d treat it quantum mechanically (unless they were super big molecules with more than 100 atoms).

      Quantum mechanics has more applications than you’d think, for example:

      Atomic clocks use the signal emitted when atoms in crystals move between discrete energy levels. They’re used as a precise time standard in many things, including GPS navigation.

      Lasers rely on a similar process – the particular discrete energy transition in an atom. The colour/power of a laser depends on the type of atom and the particular transition.

      Transistors are a type of amplifier ubiquitous in all modern electronics. The principle behind them is based on the fact that electrons in an atom have discrete energy levels and therefore move in different orbits around the nucleus depending on that energy level. The conductivity of a material depends on the electron orbits, and this understanding of conductivity allowed the transistor to be designed.

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