Imagine yourself stood at a train station with instructions to count the number of people on the trains that pass. The trains that stop at the station allow you to achieve this; the non-stopping trains, however, present a near impossible task. The issue is time. As with any observation, a greater amount of time allows a more precise measurement.
This simple analogy is what drives the fast growing field of cold molecules.
A molecule becomes ‘cold’ when its temperature descends below 1 Kelvin and is classed as ‘ultra-cold’ when it gets to a thousandth of 1 Kelvin. At these temperatures, molecules start to move so slowly that they can be observed for unprecedented lengths of time with incredible precision.
As well as this, strange quantum-mechanical phenomena start to dictate the behaviour and interactions of the molecules. Many different methods exist to bring molecules to these low speeds and temperatures.
Returning to the trainspotting analogy, using a very steep hill or a bombardment of millions of tennis balls could bring the train to rest. Alternatively, some well-placed dynamite on a coupling between carriages could blow the train apart and force half of the train to rest, hopefully without damaging any of the passengers.
In fact, all of these methods are currently being developed at Durham University to bring new insights into our understanding of nature. In windowless rooms filled with lasers, stainless steel and endless lengths of wire, molecules are being cooled on a daily basis.
Quite recently the most accurate measurement of the energy needed to break a chemical bond was made in Durham and many more exciting discoveries are on the horizon here and around the world in the field of cold molecules.
Photograph: Wikimedia Commons