Prize proves chemist was not so crazy

Some great scientific discoveries are the culmination of vast amounts of work carried out over long periods of time by many different people.

Others are truly "Eureka" moments which come out of the blue.

The work for which this year's Nobel Prize in Chemistry was awarded was an example of the latter.

On the morning of April 8, 1982, the Israeli chemist Dan Shechtman wrote "10-fold???" in his notebook.

Little did he know this annotation would lead to a Nobel Prize 29 years later for "the discovery of quasicrystals".

As (hopefully) every schoolkid knows, all matter can be classified into one of three phases: solid, liquid or gas.

Solids are distinguished by the fact that their constituent atoms are fixed firmly in place and, in contrast to those in liquids and gases, cannot move about freely.

We can further subdivide solids into two groups, crystalline and amorphous, depending on whether or not the atoms (or ions) in the solid form ordered, repeating patterns in three dimensions.

Examples of amorphous solids are soot and glass - in both of these substances, there is no such order of the atoms.

Common household substances such as sodium chloride (salt) and sucrose (sugar) are crystalline and the regular arrangement of atoms and ions leads to beautifully-shaped crystals with which I'm sure you are familiar.

It's the arrangement of the atoms/ions in three dimensions within the solid that is the important aspect of today's missive, and while it's a difficult thing to explain, the best analogy is tiling the floor, a two-dimensional problem.

If you want to cover your floor completely, there are only certain shapes of tiles you can use.

Rectangles are fine, as are equilateral triangles and squares.

We say these have 2-fold, 3-fold- and 4-fold symmetry, respectively, because when you rotate them about their centre point, they will become indistinguishable twice, three times and four times during each 360deg rotation.

Somewhat surprisingly, regular hexagons also work; these have 6-fold symmetry.

Before 1982, it was believed shapes having these symmetries were the only ones which could fill two-dimensional, and by extension, three-dimensional space - you can't tile a floor completely using regular pentagons (5-fold symmetry), because there will always be gaps.

And this is where Shechtman's "10-fold ???" annotation comes in.

Using a technique called electron diffraction, he discovered a crystalline substance that apparently exhibited 10-fold symmetry, something so out of line with the accepted wisdom of the time that he was asked to leave the research group in which he was working when he reported his results.

He was also pilloried by the scientific establishment, with one of his fiercest critics being the Nobel Laureate Linus Pauling.

The first time he tried to publish this result, the manuscript was rejected and it took more than two years to get the work into print.

Eventually, however, Shechtman was shown to be correct, and examples of crystalline substances with 5-fold, 8-fold, 12-fold and 18-fold symmetry are now known.

Crystalline substances displaying these unusual symmetries are called quasicrystals, because while they display short-range symmetry, there is no long-range repetition of the pattern, a situation once thought impossible.

Indeed, thanks to Shechtman's discovery, the scientific definition of a crystal was changed in 1992 to incorporate quasicrystals.

Shechtman's vindication is an object lesson in the way science works.

No matter how crazy a result may initially appear, when it is shown to be reproducible by other workers, it can itself end up being accepted wisdom.

Heck, it might even just lead to a Nobel Prize.

- Dr Blackman is an associate professor in the chemistry department at the University of Otago