Measuring methane from cows: the April 2021 issue of Physics World is now out


How infrared spectrometers and frequency combs are measuring methane emissions from cattle, plus super-efficient solar cells and a century of nuclear isomers

“Consider a spherical cow” is probably the start of a joke about the abstractions of theoretical physicists. But in the real world, cows are no laughing matter.

That’s because when they chomp on grass and straw, cows produce methane, which they belch out. And while that might be pleasant for the cow, it’s not great for the environment given that methane is a potent greenhouse gas.

Studying bovine emissions and trying to reduce the amount of methane they emit is therefore a clever, short-term solution to climate change.

But the tricky bit is measuring how much methane cows produce in the first place – especially from a herd of them.

As Michael Allen explains in the cover feature of the April 2021 issue of Physics World magazine, physicists have turned to drones carry spectrometers and even “frequency combs” – sensitive, laser-based systems that bagged a Nobel prize.

If you’re a member of the Institute of Physics, you can read the whole of Physics World magazine every month via our digital apps for iOSAndroid and Web browsers. Let us know what you think about the issue on TwitterFacebook or by e-mailing us at

For the record, here’s a run-down of what else is in the issue.

• Pulled paper slows hunt for Majorana – Physicists remain convinced that the elusive Majorana particle will be found, despite the retraction of a paper claiming its discovery, as Alexander Hellemans reports

• China powers ahead in neutrino physics – Ling Xin examines the legacy of the recently closed Daya Bay Reactor Neutrino Experiment on neutrino physics, US–China collaborations and future neutrino facilities

• Changing bad exam habits – Paolo Elias says that the COVID-19 pandemic offers the chance to revamp how we assess physics students at school and college

• A decade of success – James McKenzie celebrates some of the firms that have won business innovation awards from the Institute of Physics over the last 10 years

• Crisis in a lockdown – Robert P Crease describes how news of a radiation leak at a US neutron facility was handled in today’s online, networked and locked-down world

• Battling bovine belching – Cutting methane production from livestock is considered vital to climate change mitigation, with lots of research focusing on how animals breed and are fed. But physicists are playing their part too by developing ways to measure the emissions from cattle, using techniques such as spectroscopic analysis and aerial sampling, as Michael Allen discovers

• A century of nuclear isomers – One hundred years after “nuclear isomers” were first discovered, Philip Walker and Zsolt Podolyák pick five examples of these long-lived, excited nuclear states to show why they are so important in medical physics and beyond

• Solar superpower – Multi-layered solar cells stand on the brink of 50% efficiency, but the practical benefits of such high-efficiency cells are more likely to be realized in space than on Earth, as Richard Stevenson explains

• Mission to Mars – Andrew Glester reviews Dream Big: How to Reach for Your Stars by Abigail Harrison

• The surprises essential to life – David Appell reviews Seven Pillars of Science: the Incredible Lightness of Ice, and Other Scientific Surprises by John Gribbin

• Living in a materials world – Materials scientist Arnab Basu, head of radiation-detection technology developer Kromek, talks to Tushna Commissariat about founding a spin-off, the challenges of COVID-19 and looking to the future

• Ask me anything – Tim Gershon is a professor of physics at the University of Warwick, UK.

• Counting muons in schools – Andrew Ferguson on how lockdown didn’t stop him with his project to get school pupils into particle physics

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