How do we know where a sound is coming from? Another chance to hear this ear-opening episode, exploring a question from CrowdScience listener Chiletso. One day, he heard his son bounce a ball and instantly knew the direction it was travelling. How? Anand Jagatia sets out to discover what makes left, right, up and down sound so different. First, he gets blindfolded, so Alan Archer-Boyd, former auditory scientist and lead engineer at BBC R&D, can put his sound localisation skills to the test. It turns out that having two ears and pinnae, those flappy bits of cartilage on the side of your hea ..read more

Today there are over eight billion people on Earth. That’s an awe-inspiring figure… but how does it compare to the vast numbers who came before us? Listener Alpha wants to know how many people have ever existed, so CrowdScience sets out to do a historical headcount. The Population Research Bureau in the USA estimated this number back in the 90s, and have been updating their calculations ever since. Demographer Toshiko Kaneda explains how their model works, the assumptions it makes – and the huge uncertainties around the number it comes out with. We first need a date for when ‘humans’ first beg ..read more

We spend a lot of our time thinking about climate change, but listener Paul has a question that isn’t usually part of the conversation. He wants to know whether a hotter atmosphere will affect how often volcanoes erupt, or make them more explosive when they do. CrowdScience travels to New Zealand to search for answers, exploring volcanic craters and discovering traditional Maori knowledge about volcanoes. Contributors: Geoff Kilgour, Volcanologist, Geological and Nuclear Sciences Taupo, New Zealand Heather Handley, Volcanologist, University of Twente, The Netherlands Pouroto Ngaropo, Historian ..read more

Many of us have habits that calm us down in times of stress. Things we find deeply comforting, like sucking our thumb or biting our nails. We might not even be aware we’re doing them, but they play a fundamental role in helping us regulate our emotions. Our question this week comes from CrowdScience listener and nail-biter, Ash. He wants to know where these habits come from. And since his pet dog is also a nail-biter: do we share these traits with other animals? Recently, a video of a mouse cleaning up a man’s shed took the internet by storm. Was this a house-proud mouse, or was it the animal ..read more

Crowd Science listener Maik wants to know what the BMI is and what his BMI score says about his body. He trains dogs for a living and wonders if, like different breeds of dog, we simply have different body types? Marnie Chesterton comes up with some answers, talking to doctors about how the BMI is used and misused in clinical practice, and looks at some alternative methods for measuring our body composition. She also sits down with philosopher Kate Manne to discuss the realities of living in a fat-phobic world. We hear from Tonga in the South Pacific, where high BMI scores have labelled the co ..read more

CrowdScience listener Gregory wants to know what affects the way we see the colours of the world. He was looking at a blue summer sky with a friend and they got to wondering whether they both see the same colour blue. So what does influence our vision of the colours that surround us? Could eye colour have anything to do with it? And can we ever really know if your blue sky is the same as mine? Caroline Steel comes up with some answers, talking to colour scientists about their research into the multiple factors that enable us to see in multi colours, from the intricate biology of our eye to the ..read more

Storing your data in ‘the cloud’ might sound like an ethereal, intangible place, but it’s actually a physical location - a data centre. CrowdScience listener Art is worried about how much energy and water data centres are consuming. He’s from Ireland, where data centres are gobbling up almost 20% of the national electricity supply and that’s growing, fast. So how much energy and water are data centres using globally? And how can they become more sustainable? To answer Art’s question CrowdScience heads to chilly western Norway to visit a data centre hidden deep within a mountain, that’s said to ..read more

Why do humans have wisdom teeth if so many of them get removed soon after they appear? Wisdom teeth, the third molars in the back of our mouths, are so called because they normally appear in late teenage, early adulthood – the time in life we supposedly have learned some wisdom. But around 25% of people don’t develop all four. Of those that do emerge, it is not uncommon for them to appear at nasty angles, jutting into the tooth next door causing potentially dangerous infections and pain. Because of this, for decades many people have them surgically removed. Listener Khaleel was preparing to ha ..read more

When the first person set the very first clock, how did they know what time to set it to? This question, from listener Chris in the UK, sends CrowdScience off on a quest into the history of timekeeping. From sundials to water clocks, from uneven hours to precision seconds determined by the vibration of an atom, we examine how we came to measure time. We visit possibly the oldest working mechanical clock in the world to discover how its time was originally set; and hear how the time we go by today is not quite the same as it was in the past. Will all this be enough to solve Chris' question, or ..read more

In 2011, CrowdScience listener Amanda survived the devastating earthquake in Christchurch, New Zealand. It arrived unannounced - as all earthquakes do - leaving her with no time to prepare a response. So Amanda wants to know whether science will ever be able to give us advance warning of quakes. To explore her question CrowdScience heads to New Zealand to meet listener Amanda, as well as the brains behind the country’s earthquake forecasting models. We dig in a field for thousand-year-old tectonic clues that could help us understand when the next earthquake might strike. But even if we could g ..read more