Wednesday, 29 June 2011

Particle physics, units, and old age drinkers

Internal view of a very technical looking cylinder
I have asked a number of my regular readers/commenters if they'd like to write something. Actually, it was more like, "Please, could you write a blog post? I've got nothing to say and I don't want to lose all my readers."

Here is the first contribution, from old friend and intermittent blog commenter 'CERNoise', who, as the name suggests, works at CERN, the site of the Large Hadron Collider (LHC). We went to university (the first time) together, where she distinguished herself by being extremely good at physics, and playing the violin, while I distinguished myself by being extremely bad at engineering, and learning to ride a unicycle.
We particle physicists have invented some strange units over the years, to describe the very small things we study. My favourite unit actually mixes up the very small and the very big. It is the megaparsec-picobarn, and it describes the volume of space that is typically swept out by a cosmic ray particle charging about the universe at close to the speed of light. A megaparsec is about the right size to measure the distances between galaxies, and a picobarn is the cross-sectional area that says how likely the cosmic ray is to interact if it happens to meet another cosmic ray going in the other direction.

Here's a blog entry about barns and LHC records by my friend Jon.
[Ed: I love the ways that scientists demonstrate that they have a sense of humour. Jon's blog post reports that a barn is a unit of area. It was supposed to be something big and easy to hit (as in 'barn door')]
Multiplying a very long distance by a really tiny area, it turns out that a megaparsec-picobarn is still a rather small volume. If I managed to look up the conversion factors properly, it comes out as:

0.000 000 000 003 cubic centimetres.

The UK press is always reporting on warnings to limit the number of units we drink, and they are talking about a unit of volume too, in this case ten cubic centimetres of alcohol, but then mixed up in a small glass of wine, or a larger glass of beer, or maybe even part of an exotic cocktail.

I was at a workshop in Germany in January, and I was trying to work out how many units (of alcohol) were in each bottle of the very nice local beer we were knocking back. None of the other physicists from around the world seemed to come from countries with such well publicised guidelines. They would have been even more shocked to read the latest recommendations that by the time we hit 65 we're shouldn't drink more than 1.5 units a day.

Another ten thousand billion megaparsec-picobarns of your best ale please landlord!

1 comment:

A Heron's View said...

That is very interesting. I have just this to say: unless of course you like using lots of 000's behind the decimal point you could have determined the cubic content in Millimeters instead.

From my personal experience at being 68.5 years young, the new recommended limit is a viable target to achieve on a annual basis, especially when saved up for special occasions :)