The simplest of instruments can often illustrate the most profound of scientific concepts. This spectroscope consists of nothing more than a glass prism and cardboard with a slit cut in it. A normal incandescent light globe produces a rainbow of colours whilst a low energy fluorescent discharge lamp produces discrete narrow lines. The rainbow of colours illustrate how a hot object radiates continuously over a range of wavelengths. The narrow lines from the fluorescent lamp are a graphic demonstration that electrons can only occupy discrete energy levels. To explain these two observations and the difference between them requires classical electromagnetism, phonons, atomic physics and quantum mechanics. Those pretty bars of colour from the fluorescent lamp are a simple lounge room proof that we live in a quantum universe - of course fully understanding that quantum universe requires a big brain and some rather more sophisticated lab equipment!

Our lead story in this issue is about the changing rate of expansion of the universe. The results that underpin this work were gathered using some of the world’s most sophisticated telescopes, but to illustrate that the universe really is expanding you only need your eyes and a line of reasoning developed by the nineteenth century German astronomer Heinrich Wilhelm Olbers. Olbers argued that if the universe was infinite and filled with an infinite number of stars and if it had been around for ever then which ever way one looked into the sky one would be looking at a star. In this case the whole night sky should be blazing bright not black. The answer to this paradox is that the universe is not static, it’s expanding.

In the nineteenth century, the notion of an expanding universe wasn’t acceptable to conventional wisdom and Olbers concluded that the dark sky was caused by interstellar dust obscuring distant skylight. Although interstellar dust does exist, if there were enough of it to absorb that much light, and the universe were static, the dust would become so hot it would radiate light itself. With no disrespect to Olbers, this illustrates the classic trap of becoming too wedded to one’s expectations to see where the evidence is truly leading you.

My favourite simple demonstration of a profound scientific concept is illustrating the quantum nature of the universe with a prism and a couple of light bulbs. The prism and a cardboard slit are used to make a rudimentary spectrometer. If you use this to examine a normal incandescent light bulb, you should see a continuous rainbow of emission (following the Stefan–Boltzmann black body radiation law.)

But a fluorescent light (such as one of the new low energy lamps) emits only in narrow lines of certain colours. The explanation is that atoms in the excited gas within the fluorescent light only emit energy at set wavelengths. This in turn is because the orbitals of their electrons are only allowed to occupy certain quantum states. If there was no quantum physics the electrons would slowly wind down towards the nucleus radiating multiwavelength electromagnetic waves as any moving charge on the macroscopic scale does.

This is the cool thing about science, you don’t have to just accept what you’re told. You can test many of its theories for your self using the simplest of equipment, and logical reasoning. All you have to do is keep asking why? And be sure to follow your observations rather than your expectations.

Dr Tim Wetherell - ScienceWise Editor