One tablespoon? Is that all? Depends on the recipe, I guess. But does anyone know exactly how much one tablespoon actually is? The answer, which I found out at the weekend, demonstrates exactly why the world needs physicists.
According to the instructions with my wife’s new breadmaker, an Australian tablespoon is different from a New Zealand tablespoon. Like the dollar, the Aussie tablespoon is 20% bigger than its kiwi counterpart. It strikes me that this is an utterly stupid state of affairs. How is anyone supposed to get recipes right when you need to know whether the instructions originate in NZ (like the Pavlova) or Oz (like, the, err, any suggestions?)? Fortunately, physicists have come to the rescue, saving the world from manifold culinary disasters, or at least they would if people like Ramsay, Oliver and the Edmonds cookbook could be bothered to listen.
The Systeme International (S.I.) set of units provides a world-wide standard on measurements. Amongst other things, it says exactly how much a kilogram is, and how much a litre is. Now, these definitions might not be all that useful for cooking; for example the litre is defined as a thousandth part of a cubical volume of side 1/299792458 times the distance light travels in a second. (The second, incidentally, being the time it takes for 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.) True, most people don’t have caesium clocks and lasers in their kitchen cupboards, but the point is that there is a fundamental agreement on what a volume, mass etc. measurement actually is. In some high precision applications, it becomes very important to get it very precise. In fact, ‘measurement’ is so important that it has its own branch of science – called metrology.
Unfortunately, this doesn’t detract from the human factor. In 1999, the Mars Climate Orbiter crashed gracefully into the red planet, because one group of team members had been doing their measurements in kilometres (as approved by S.I.), while another had been doing so in miles. And no-one noticed until it was too late. The really shameful part is that a fair proportion of them would have been physicists. Using miles? How could they?