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Asked by Eleanor to Jackie, Michele, Oliver, Vicky, Yelong on 9 Mar 2015.
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Oliver Brown answered on 9 Mar 2015:
Roughly speaking, it’s the theory of really small things!
The short story is that when considering extremely small objects like particles, single-atoms, or even slightly larger ones like crystals, or molecules the energy of the system can not simply have any value it likes. The energy is ‘quantised’, that is can only take on certain specific values.
This effect is lost in systems where very many quantum objects interact, so that’s why a single electron behaves in a quantum way, but a tennis ball (or a person!) does not. We call objects that behave in the ‘normal’ way as classical, and they follow the rules of classical mechanics. Quantum objects behave follow the rules of quantum mechanics, and the field of quantum theory is all about uncovering those rules, and investigating their consequences. One thing that’s still being investigated is where the dividing line between quantum and classical physics actually is!
The long story goes all the way back to the late 19th century when people first began investigating the properties of light, electricity, and atoms — many of the devices we take for granted today such as screens, mobile phones and computers rely on our understanding of quantum physics! I’m obviously biased, but I definitely think quantum theory is the most interesting part of physics 😉
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Jaclyn Bell answered on 16 Mar 2015:
I think Ollie has said it all really! Quantum theory is a theory used to explain the behaviour of matter and energy on an atomic and subatomic level. There are different interpretations of it and it is difficult to get your head around, but nowadays physicists have come to accept that quantum theory gives us accurate answers and so we don’t worry too much about whats actually going on. There is a minute physics episode on quantum mechanics you should watch here (I love minute physics!) https://www.youtube.com/watch?v=i1TVZIBj7UA
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