Best of Last Week: Speed of sound upper limit found, new solar panel design and machine washing COVID-19 masks

It was a good week for physics as a team with members from the Institute for High Pressure Physics in Troitsk, the University of Cambridge and Queen Mary University of London found the upper limit for the speed of sound. When moving through solid atomic hydrogen, sound traveled close to the theoretical fundamental limit. And amateur physicists Jussi Lindgren and Jukka Liukkonen devised a new interpretation of quantum mechanics that suggests reality does not depend on the person measuring it. Also, a team at the University of Maryland presented new mathematical tools to better understand simulations of hyperbolic spaces. They called them mind- and space-bending physics on a convenient chip.

In technology news, a combined team from the University of York and NOVA University of Lisbon unveiled a new solar panel design that could lead to wider use of renewable energy—the design is based on checkerboard lines that increased their ability to absorb light. And a team with members from the University of Sussex Business School and the International School of Management found that countries should prioritize support for renewables rather than nuclear power if they want to lower emissions rapidly and do it as cost-effectively as possible. Also, an international team of engineers demonstrated wearable sensors that could be printed directly on the skin without using heat. And a team with members from the Bretagne Atlantique Research Center and the French National Center for Scientific Research wondered whether explanations for data-based predictions actually increase user trust in AI.

In other news, a team at the University of Birmingham found that a deficiency of vitamin D increased the risk of COVID-19 in healthcare workers. And a team of mathematicians and computer scientists at Carnegie Mellon University solved a 90-year-old geometry problem called Keller's conjecture.

And finally, if you are like billions of others around the world still trying to protect yourself and your loved ones from being infected with the SARS-CoV-2 virus, you may want to check out the results of a study done by a team at UNSW Sydney: they found that cloth masks work, but only if you machine wash them after use.