Does anyone understand quantum mechanics?

One of the central characters in the film Watchmen is Dr Manhattan, a physicist turned superhero following an accident in his lab. Manhattan is able to teleport, see into the future and past, duplicate himself and much more. But what if the most superhuman of his powers was that of understanding quantum mechanics?

What is quantum mechanics?

Quantum mechanics is a relatively recent area of physics which studies the behaviour of the tiniest existing components of matter. Tiny they may be, but discoveries about these particles have turned our understanding of the world on its head.

What makes quantum physics awkward to get to grips with is that in many ways the workings of particles at a subatomic scale contradict everyday logic. ‘We are in an area which is very difficult to imagine because it’s so different from the macroscopic world we live in,’ explains Vlatko Vedral, professor of quantum information science at Leeds University. ‘So it’s very difficult to relate everyday objects we know to the behaviour of small objects.’

For the most part, classical physics is intuitive: whether or not you are aware of Newton’s laws, when you kick a ball common sense and everyday experience allow you to make a pretty good estimate of where it will go.

But imagine for a second that your football began to behave like an electron. In that case, quantum physics would tell you that it's impossible to know where your ball will land, and, come to think of it, if you look at it from the right angle it is actually a wave of energy rather than a physical object.

From equations to reality


Things really begin to get hairy when you pause to consider the wider implications of quantum mechanics. As everything around us is made up of these tiny constituents, how does their odd behaviour impact upon reality as we know it?

‘For all that we know, every quantum object - a particle of light, a particle of matter like an atom even a small molecule -  can simultaneously exist in different places at the same time,’ says Vedral. How such properties might translate into the reality we perceive with our human senses remains a mystery.

As a result, there is fiery debate amongst physicists on how to reconcile quantum mechanics with what we see around us on a day to day basis. ‘I would say most of us certainly agree up to a certain level what the predictions are, but as you scale it up then you really have a strong division in the community,’ comments Vedral.

‘We have something spectacularly successful when it comes to predictions, but somehow we find it very difficult to understand what these actually mean,’ he adds.

Philosophical musings aside, the fact remains that at a subatomic level, quantum mechanics just works, even if it sometimes seems to defy the human imagination.

Vedral takes the example of the structure of an atom: ‘For me it’s very difficult to tell you what an atom really is, because it’s now outside our visualisation - it’s difficult to draw it, to come up with a geometric image. But I can still use the correct mathematics to make predictions about what will happen if you move it, or shine a laser on it.’

This means that practical applications of quantum mechanics such as quantum computing or cryptography are likely to see the light of the day in the near future, even if gaining a complete understanding of quantum mechanics remains a distant dream.

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              25 Mar 2009

 

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