Exhibit blog

Richard Lim kindly took a picture of me with the resonator. Thank you Richard. He sent it to a colleague at New Scientist who said “What’s Alan Titchmarch doing at the Royal Society?” Can you see the resemblance?

Further reading

  • Podesta, M. et al. 2013 A low uncertainty measurement of the Boltzmann constant. Accepted for publication in Metrologia

Everything around us is made of atoms, and they are constantly in motion. This energy of motion is called heat and the temperature of an object is related to the average speed of motion. Because everything is made of jiggling atoms, measuring temperature accurately is important in all branches of science, engineering and medicine.

See the scientists explain the science behind their exhibit in the video above

The current definition of the unit of temperature chooses one temperature, the temperature of the triple point of water (273.16 K or 0.01 °C), as the standard temperature. All other temperature measurements are really a statement of how much hotter or colder something is compared with this standard temperature.

In future we hope to change this definition so that temperature (in kelvin or degrees Celsius) is defined directly in terms of the energy of moving atoms.

How it works

The speed of sound in a gas is directly related to the average speed of molecular motion, so by measuring the speed of sound in a gas at 0.01 °C, we could work out how much energy of motion molecules (in joules) have at this temperature (in kelvin).

We made our measurement inside an expensive copper resonator and it took us 5 years! But along the way we found out we could also make useful measurements by timing pulses of sound along tubes or even directly through the air.

We hope our work will improve temperature measurements in all kinds of places such as the high atmosphere or hostile environments.

Lead Image: Triple Point of Water Cell