Positronium

Science continues to find that homeopathy doesn't work. I know homeopathy has sincere adherents who don't think about scientific evidence in the same way as the rest of us. I admire those people who are constantly in debate with them and I'm glad my own area of science is a long way away from this sort of topic. So I was quite taken aback to come across this account of positronium homeopathy.

Positronium is a sort of an atom but a very exotic one, with only a fleeting existence. Like an atom of hydrogen it consists of two elementary particles with equal and opposite electric charges. Like an atom of hydrogen one of these particles is an electron, familiar (as far as any subatomic particle is "familiar") as a constituent of the atoms around us. Unlike a hydrogen atom the positively charged particle is a positron. A positron has the same mass as an electron but a positive, rather than a negative charge. It is the electron's antimatter counterpart, a sort of evil twin. When an electron and a positron come together they cancel one another out (the word used is "annihilate") and the mass of both particles is converted into energy, in the form of light, according to Einstein's most famous relation E = mc².

Antimatter sounds like something out of science fiction (and one of its most famous occurrences must certainly be in the propulsion unit of the Starship Enterprise). Nonetheless it exists. The first discovery of a positively charged electron was in 1932 by the American scientist Carl Anderson. Now they are put to work every day in our hospitals (know somebody who's had a PET scan? Guess what the "P" in "PET" stands for).

Natural processes produce positrons, as do events in man-made particle accelerators. My own interest focuses on the energetic events of solar flares, in which positrons are sometimes produced. Once they exist, positrons don't hang around for very long. There's usually an electron for them to annihilate with. But before annihilating, for a ten-millionth of a second or less, the positron and the electron orbit one another as an atom of positronium. I like to think of them in a sort of dance, eyeball to eyeball, each recognising in the other its equal, its opposite and its imminent extinction. Finally they annihilate one another, producing a spectrum line in gamma-rays that we can detect and learn from.

Composed only of two very simple objects, the positronium atom gives very precise tests of the quantum theory of electromagnetism, so it has been studied in great detail in the laboratory. It lets us test very precisely elements of our basic understanding of the world.

Matter and anti-matter can both exist but there is more matter than anti-matter. If there were equal amounts of both, they would have annihilated each other very early in the history of the Universe. The Universe would be filled with light but there wouldn't be atoms and molecules i.e. ourselves. So the question, "why is there more matter than anti-matter" is a fundamental question about the Universe.

After all this I'm both sad and a bit cross to discover talk of "positronium homeopathy". In its yin-and-yang components, its brief existence, its annihilation, and the matter-antimatter asymmetry at which it hints, positronium is a very beautiful and exotic aspect of the physical world. There's more than enough real, deep beauty and weirdness there without making up a lazy, unsubstantiated fairy story.

Open Studies Astronomy bulletin

A few times a year I send out a wee email bulletin for people who come to some of our courses (let me know if you'd like to get these). The aim is to let them know - or remind them - of Glasgow University Open Studies Astronomy and Physics courses and day schools, and to highlight other interesting events in the Glasgow area. Here's the latest:

1. IMMINENT

   I've only just heard that the Scottish Dark Sky Observatory is hosting a visit from the science writer Stuart Clark, TOMORROW, 10 May. Stuart Clark is an excellent writer on Astronomy and Physics topics ("The Sun Kings"; "The Sky's Dark Labyrinth"; regular pieces in the Guardian). You may also have seen him interviewed by Philomena Cunk on the subject of "time" on Charlie Brooker's Weekly Wipe - clearly a man who doesn't take himself too seriously. I haven't heard him speak but I've heard good things. See http://www.scottishdarkskyobservatory.co.uk/events/dr-stuart-clark-lecture-and-stargazing/

2. The Institute of Physics are now hosting a series of talks here in Glasgow, aimed at a very broad audience. The titles so far have been really interesting, to my eye, including both pure and applied topics. The next of these will be given on Thursday 15 May, 19.00 in the Kelvin Building here in the University, by Dr Stuart Reid from the University of the West of Scotland: "Giving stem cells a good nano-kicking". More details at http://www.astro.gla.ac.uk/users/martin/ioplect/
3. Glasgow City of Science has a new website to showcase the city as a leading international destination for scientific discovery and innovation. Their words: "A diverse range of influential, partner organisations with local, national and international reach have come together through the Glasgow City of Science initiative to leverage our scientific potential as a major driver of sustainable economic development and to demonstrate the importance of communicating science as part of the region’s wider heritage and culture." So the City of Science project is about industry and companies, but also education and outreach. You'll find lots of interesting events on their Events page, and you might like to subscribe to their e-bulletin.
4. We ourselves have a couple of Astronomy events in the summer programme:

   Astronomy when the skies are bright, ideas and activities to stay involved with the wider universe even although it's difficult to see in Scotland in the summer. Douglas Cooper, Andrew Conway and myself; Saturday 24 May, 10.00 - 15.00

   Weighing the Earth on Schiehallion, Perthshire, recalling Nevil Maskelyne's fundamental experiment to determine the mass of the Earth, and taking a day to actually visit the mountain. With Andrew Conway, who in 2005 was involved in an attempt to repeat this experiment with modern equipment. Evening of 18 June and all day 21 June.