5 Summary of Week 3

Quantum theory has greatly improved our understanding of the world of atoms and subatomic particles. Nevertheless, it poses conceptual challenges which question our intuitive understanding of the structure of space and matter. It turns out that our minds, trained by the observable world around us, aren’t well suited to understanding how an electron can behave like a particle and a wave simultaneously. We must therefore carefully observe and develop explanatory theories for why things in the subatomic world behave very differently to our naive intuition.

Our current understanding of quantum theory severely limits what we can know about systems at the subatomic scale. Heisenberg’s uncertainty principle shows that we cannot pin down the location of anything too precisely without increasing the uncertainty of its other measured quantities. In particular, there is a limit as to how precisely we can know both the position and momentum of a particle. Measuring one property of a quantum system automatically affects others – and this can extend even over large distances. Einstein called this phenomenon the ‘spooky action at a distance’. The effect of measurements on a quantum system may be exploited in secure quantum communication, where any eavesdropping would be detectable.

Going further into smaller and smaller distances, the Planck length may well prove to be the ultimate limit beyond which we cannot gain any information.

Now you’ll be moving from the very small to the very large, as next week looks at our knowledge of the universe.

You can now move on to Week 4 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .