From particles to parsecs

Toby Friend considers how the development of astronomy and cosmology on the largest of scales, and particle physics on the very smallest; has often been intertwined

- Toby Friend

Аt a glance, physics can seem a radically unfocused discipline. In a single research department you'll find particle physicists investigating the smallest and most ubiquitous objects we know of, like quarks, leptons and bosons. But you'll also find astronomers (including astrophysicists and cosmologists) investigating the largest and most distant things that we know of, like galaxies, nebulae and black holes. No other science comes close to matching interests on such a range of scales. So why do both extremes count within the remit of doing physics?

One suggestion is that physicists are interested in the small and big, the near and far, just because they are interested in everything. At least that's what the many physicists trying to find a 'grand unifying theory of everything' might tell you. But the notion of everything' in this context can't really mean everything we might possibly want a scientific theory for. Physicists do not, for example, aspire to theorise about the zebra population of the Serengeti or about the rock strata in the Grand Canyon. Those phenomena are within the remit of ecology and geology, not physics.

The search by physicists for a theory of everything is really a quest for a theory of the behaviour of the constituents of everything. That explains the continuing interest by physicists in the ever smaller, but why do planets and stars remain of interest? The reason, I suggest, is that the investigation of the far away big stuff is often of benefit to our ability to theorise about the nearby small stuff, and vice versa.

A division of labour