Interstellar matter

The electromagnetic spectrum

This week I found myself in the pub with a group of astrophysicists – from undergraduate to head of department level. It’s funny to hear people talking casually about interstellar matter almost as an aside, as something they just know about. It left me wishing that I knew more about what happens beyond the earth, and about the building blocks of the universe.

I was asking the physicists about their methods; how do they observe things? How are new things discovered? They told me about some of their methods: spectroscopy involves measuring the emission of electromagnetic radiation from matter, morphology involves looking at the shape of bodies or collections of matter. You can test the chemistry of molecules in a lab by staging reactions on a small scale and measuring emissions, or you can observe stars and galaxies at a distance using telescopes to collect data on electromagnetic emissions and morphology. Observation is combined with mathematical modelling from the (sometimes sparse) data that has been collected.

Two things in particular struck me from peoples responses.

1) There seems to be a distinct split in physics between being an observer and being a theorist. Apparently very few people are both – you either work on the mathematics and the modelling, or you work on observation and data collection. Recently I listened to an old episode of ‘In Our Time’ on optics and in this episode they guests were talking about the separate paths of practice and theory in the development of lenses. Lenses were being made (e.g. for glasses) by artisans, whilst separately philosophers and mathematicians were writing treatises on optics without actually practically testing any of their theories. The programme suggested that it was really only with the enlightenment and the work of Galileo and Kepler that these two separate paths came together. Of course now theorists and observers work closely in the same university department, but I was surprised that this split endures.

2) Interpreting data beyond our visual capabilities can become second nature, like speaking a foreign language. Talking a bit about the large telescopes used to collect data, I asked whether they actually go and look through the telescopes (they do sometimes) or if data was collected and disseminated to different researchers (this is also often true). As a layperson I tend to think of telescopes in terms of magnification – visually observing distant planets. But although some observation is visual – looking at shape and colour – when considering the whole electromagnetic spectrum, most data is outside our visual range, so researchers receive it in numerical form. I asked whether, over time, interpreting this data becomes as straightforward as the visual interpretation that we all do habitually every day. One of the group suggested it’s like learning a foreign language – eventually you can think in this language.

I also had a discussion about how ideas progress and, from this meeting at least, it seemed that a theory often comes first (although in truth the process must be recursive). Then it’s a case of testing whether observed data supports that theory. Some of the Phd students present explained that when they want ‘telescope time’ they have to make a case to book this with a coherent proposal about what they are looking for. I also talked to one person a bit about the meeting point of process, of day to day work and its minutiae with the ambition of astrophysics to explain the universe – the bigger picture of discovery. Interestingly he said that, if you think too much about the big picture you will miss a lot of the detail. I can imagine trying to have both in mind at once, but one at the forefront of your mind and the other hovering in the background.