Small world, big physics

Find the magic formula and you can recreate the most exotic of cosmic objects in the humblest of settings, f inds Sophie Hebden

IN MANY an unassuming corner of the globe, you might come across an attic, shed or spare room with a table-top railway. To the uninitiated, these model train sets, with tiny figures standing at platforms and tracks fringed by green sponge bushes, represent a harmless, if peculiar, pastime. To the hobbyist, they are a serious affair – a labour of love, and a way to run a railway almost as if for real. This spirit of tinkering, of exploring and learning about the real world by making smaller-scale models of it, is also alive in the physics lab. Many desirable things lie beyond the practical reach of physicists: recreating the first moments of the universe, playing freely with high-energy particles, wandering the fringes of a black hole. And so on bench-tops across the world, you’ll see odd apparitions. Whether a black hole fashioned from water waves, or a Higgs boson sculpted from liquid helium, these  are “analogues” – lovingly crafted replicas  of physical systems that, primed in the right way, can be made to work just like the original. The hope is they might help overcome some of the practical and financial limitations of larger experiments, and themselves become an engine driving our understanding of the real world. The idea of doing physics without actually doing it is not new. Purely hypothetical thought experiments have long been used to investigate the consequences – or perhaps absurdities – of physical theories, from ancient Greek times right up to these modern days of relativity and quantum theory. In recent years, powerful computers have given a new way to simulate physical processes, as they roam through lines of code to explore the mathematics that underlies a phenomenon.