How big is a 'shedload'? Let's ask the nuclear physicists

Josie Ford Feedback is New Scientist’s popular sideways look at the latest science and technology news. You can submit items you believe may amuse readers to Feedback by emailing feedback@newscientist.com A load of sheds In a previous instalment of our ongoing crusade to identify the weirdest units of measurement in the world (7 March), Feedback made a throwaway remark. At the end of an extended bit about using polar bears as a unit of snow mass, we quoted reader Steve Tees, who wondered quite how big the titular shed was in the term “shedload”, as in ” ‘shedload of xxxx’ causing tailbacks on various motorways”. Email after email has come charging into our inbox ever since. If only there were a word we could use to convey the concept of an inordinate quantity of something. Advertisement Two readers independently offer a possible etymology for the word. Bryn Glover and John Newton have both made the same connection with motorway accidents: “The lorry had obviously shed its load”. F. Ian Lamb suggests we should consider a “shedload” to be “an endogenous relative scaling (ERS) unit”. This means that one person’s perception of big may differ from someone else’s, depending on past experience. For instance, for a person living in poverty, £1000 might be a shedload, but a billionaire might drop the same sum just to eat in a fancy restaurant. “I am sure there must be other units with these properties,” says Ian. Readers can send any examples of ERS units to the usual address. But maybe the solution lies in some fairly fundamental physics. William Croydon writes to tell us that shed is a unit that has been used in nuclear physics. This may take a little explaining. In particle physics, researchers spend a lot of time shooting infinitesimal particles at each other and seeing what happens if they collide. Consequently, they needed a label for very small cross-sectional areas. Hence the unit “barn”, which, as William explains, is 100 square femtometres, or 10 -28 square metres. This is the approximate cross-sectional area of the nucleus of a uranium atom, which, of course, is what you are trying to hit if you want to set off a nuclear reaction. Apparently, this ridiculously small area is, in nuclear physics speak, the equivalent of the broad side of a barn in terms of being easy to hit. William adds that, in the past, “the smaller ‘shed’ was also used”, but he confesses to being “hazy” on quite how much smaller it is. Feedback looked online and discovered two smaller derivates of the barn. The first, defined as 1 millionth (10 -6 ) of a barn, is apparently called an outhouse. The far tinier yoctobarn, defined as 10 -24 of a barn, is a shed. Feedback isn’t sure what the physicists were thinking when they decided that a shed would be orders of magnitude smaller than an outhouse. Regardless, William is clearly right when he says that even a very large load of sheds indeed would be “too small to cause problems on a motorway”. Finally, Tony Lewis offers a solutio