Smashing up guitars is a classic rock star activity, but how about drowning them? 7-year-old listener Cornelius has set CrowdScience a challenge: to find out what happens if you play a guitar underwater. Could this be the next avant-garde music sensation?

Host and amateur musician Caroline Steel tackles Cornelius’ question with the help of one increasingly soggy guitar. The UK’s National Physical Laboratory is our first port of call, with a guitar-sized water tank at the ready, and acoustic scientists Dr Freya Malcher and Ben Ford helping tackle our questions.

Since an acoustic guitar’s sound is amplified by its internal chamber, what happens as that chamber starts to fill with water? How about if the whole guitar - strings, body and all - is submerged? What difference does it make if our ears are listening above or below the water? And can special water-adapted microphones help us explore this unusual question, before our guitar disintegrates?

Our guitar then heads off on tour to Denmark, where the band Between Music have teased out questions just like these for their underwater music project, Aquasonic. We talk to violinist and Innovative Director Robert Karlsson, and singer Nanna Bech, who also plays a unique subaquatic instrument. With their help, we discover how to get the best out of a submerged guitar, and find out whether other instruments are better suited to the life aquatic. Presenter: Caroline Steel

Producers: Cathy Edwards and Florian Bohr

Editor: Ben Motley

National Physical Laboratory: Underwater Acoustics - https://www.npl.co.uk/research/underwater-acoustics

Between Music: Aquasonic - https://www.betweenmusic.dk/aquasonic

Photo – Caroline Steel and Nanna Bech in an Aquasonic aquarium playing a guitar. Copyright BBC.

Can we turn the world’s deserts green? CrowdScience listener Youcef is captivated by the idea of bringing water back to Earth’s driest landscapes. With sea levels rising and huge stretches of land drying out each year, he wonders whether redirecting seawater inland could offer a solution to both problems. Presenter Alex Lathbridge sets out to investigate starting with a kettle of salty water.

Alex speaks to scientists about how deserts form, and how human actions like overgrazing can tip a fragile grassland into a barren landscape. He learns how the brightness of bare sand affects local weather, reducing cloud formation and rainfall. Researcher Yan Li reveals how huge solar and wind farms could darken and roughen the Sahara’s surface enough to double its rainfall, potentially kickstarting a self-reinforcing cycle of vegetation and moisture.

But what about deserts where clouds already drift overhead? In the Atacama, one of the driest places on Earth, geographer Virginia Carter shows how fog harvesting nets can coax litres of fresh water from the air.

Alex also investigates desalination, where professor Chris Sansom is trying to harness solar power to remove the salt from seawater without burning vast amounts of fossil fuels. It is promising, but can it reduce the impact of rising sea levels? And what do you do with all the salt that’s left over?

Climate scientist Alan Condron proposes an even wilder idea: towing kilometre-sized icebergs from Antarctica to parched nations. His models show it might be possible, but the logistics verge on science fiction.

Finally, plant scientist Zinnia Gonzalez Carranza warns that greening deserts isn’t just about adding water. Introducing new species, even hardy ones like mesquite, can trigger ecological chaos and harm the very communities who depend on these landscapes.

Presenter: Alex Lathbridge Producer: Sam Baker Editor: Ben Motley

(Photo: Palm trees growing in cracked, parched earth and the sun rising behind them. Credit: Danymages/Getty Images)

When listener Sakura’s husband came home from his morning walk in Cambridgeshire, UK, he told her about a massive rainbow he’d seen. But when he showed her a picture, she didn’t think it was particularly large. So how big is a rainbow really? Are they always the same size? And if some are bigger than others, is there a limit?

To find the answers, presenter Marnie Chesterton meets independent rainbow expert Philip Laven in a pitch-black studio to simulate how a rainbow is formed. He demonstrates how they are created by sunlight, reflecting and refracting in millions of little water droplets.

But what does that mean for their size? Raymond Lee, retired professor from the US Naval academy, says that rainbows are not objects and don’t have a linear size, just a specific angular size that’s relative to the person seeing it. But Marnie doesn’t give up so easily – some rainbows still look bigger than others.

In her journey to discover other ways to size up a rainbow, Marnie hears from Australian aerial photographer Colin Leonhardt who stunned the world with a beautiful picture. Next, assistant professor Ping Wah Li from The Chinese University of Hong Kong explains why it’s possible to come across more than one rainbow at a time.

And finally, atmospheric scientist Harald Edens shares another way to consider size, as well as how much he struggles to explain the complexity of rainbows to his four-year old daughter.

Presenter: Marnie Chesterton

Producer: Florian Bohr

Editor: Ben Motley

Photo: Rainbow of Dreams - stock photo stock photo Credit: Laurent Fox via Getty Images)

Tears of joy, tears of sadness, tears of frustration or tears of pain - humans are thought to be the only animals that cry tears of emotion. CrowdScience listener Lizzy wants to know: why do we cry for emotional reasons? What is its evolutionary benefit? And why do some people cry more than others?

It turns out that humans cry three types of tear: basal, reflex and emotional. The first kind keeps our eyes nice and lubricated and the second flushes out irritants such as fumes from the pesky onion, but the reasons for emotional tears are a bit harder to pin down.

Using a specially designed tear collection kit, presenter Caroline Steel collects all three kinds of tears. With them safely stashed in tiny vials, she heads to the Netherlands, to Maurice Mikkers’ Imaginarium of Tears. Looking at her crystallised tears under a microscope will hopefully unveil a mystery or two.

Marie Bannier-Hélaouët, who grew tear glands for her PhD, explains how the nervous system processes our emotions into tears. But why should we cry for both happiness and sadness, and for so many other emotions in between? Ad Vingerhoets, Professor of Clinical Psychology at Tilburg University, suggests we cry for helplessness - our bodies do not know how to process such intensity of feeling.

But do these tears bring relief? Lauren Bylsma, Associate Professor of Psychiatry at the University of Pittsburgh, has been studying heart rates during crying episodes to find out. With her help, we also explore if women do in fact cry more than men, and why that might be.

Presenter: Caroline Steel

Producer: Eloise Stevens

Editor: Ben Motley

Photo: Fisheye woman having a cry - stock photo Credit: sdominick via Getty Images)

Tsunamis destroy buildings, habitats and danger to everything in its path on land. But how do they affect life under the water? That's what CrowdScience listener Alvyn wants to know, and presenter Anand Jagatia is searching beneath the waves for answers. Anand meets Professor Syamsidik who is learning about how tsuanami waves are formed to help protect against future disasters. He runs the Tsunami and Disaster Mitigation Research Center at Universitas Syiah Kuala, Indonesia. With him at this state-of-the-art lab is Dr David McGovern, expert in ocean and coastal modelling at London South Bank University. David tells Anand how the energy of a tsunami is spread across the entire water column. To explain the forces at play, Anand chats to Professor Emile Okal a seismologist from Northwestern University in the United States. Tsunami wave can move as fast as 800 kilometres an hour but, despite this, out at sea you might not notice it - but can the same be said for marine life? We follow the wave as it nears land and all that force is contracted and begins to show its might. Professor Suchana 'Apple' Chavanich from Chulalongkorn University, Thailand was one of the first people to swim off the Thai coast after the 2004 tsunami and remembers how coral reefs were battered. In Japan, after the 2011 Tohoku Earthquake and Tsunami as the water retracted it pulled with it tons and tons of debris into the water. The fishing communities of the Sanriku Coast lost almost everything, their equipment was destroyed and the water was heavily polluted. Anand meets Hiroshi Sato who set up the Sanriku Volunteer Divers, a team of people who dragged the debris out of the water. One of them was diver and journalist Bonnie Waycott who tells her story of witnesses the destruction first hand and trying to rescue the fishing industry with Hiroshi. Finally, we learnt that the effect of modern tsunamis carries far further than people might have imagined. On the west coast of the United States Professor Samuel Chan is an expert in invasive species at Oregon State University. He explains how modern infrastructure is contributing to some incredible migrations. Presenter: Anand Jagatia Producer: Tom Bonnett Editor: Ben Motley

Photo: USA, California, Sonoma County, Bodega Bay, tsunami evacuation panel - stock photo Credit: Brigitte MERLE via Getty Images)

In your final moments, they say, you may walk down a tunnel of light. You might rise above your body, watching the scene below before passing into another world. Perhaps you’ll be met by glowing figures, see your life flash before your eyes, or feel a deep, unearthly calm.

These are the stories of people who’ve reached the edge of death and returned. They’re not rare, nor random, and they have a name: near-death experiences.

CrowdScience listener Steven in Chile first heard of them during a CPR class and wondered, are they fictitious?

Psychologist Susan Blackmore once had an out-of-body experience as a student in Oxford, UK — floating above herself before soaring over the rooftops and dissolving into the universe. That single moment changed everything. She’s spent her career trying to understand what happened, and she believes such experiences are explainable.

At the University of Michigan in the US, neuroscientist Professor Jimo Borjigin has done what few have dared: record the dying brain in action. Her studies show that even after the heart stops, the brain can produce powerful surges of coordinated activity, bursts that might explain the lights, the tunnels, and the sense of peace. She believes near-death experiences could become one of science’s most intriguing scientific frontiers for research into consciousness.

At University College London in the UK, neuroscientist Dr Christopher Timmermann is exploring similar states using psychedelics, pushing the boundaries between self and oblivion to identify what induces a near-death experience and what we can learn about our consciousness along the way.

Near death experiences, a paranormal mystery or explainable phenomenon?

Presenter: Caroline Steel Producer: Harrison Lewis Editor: Ben Motley

(Photo: Gap in the wall - stock photo Credit: peterschreiber.media via Getty Images)

For some they’re the stuff of nightmares, but many of us can’t get enough of horror films. For Halloween, CrowdScience investigates the science of why we enjoy films that scare the living daylights out of us.

CrowdScience listener Maria from Taiwan is one of those people who would rather avoid frightening films, yet her husband loves them and is always trying to get her to watch with him. She wants to know why people like her husband are so drawn to horror films.

To try and find out, presenter Anand Jagatia travels to the Recreational Fear Lab in Aarhus, Denmark, which is dedicated to understanding why people frighten themselves for fun. He meets the research lab’s directors Mathias Clasen and Marc Andersen who explain how horror and recreational fear could help us cope better with uncertainty, bond with those we are frightened beside, and perhaps even have some physical health benefits. They also take Anand to a haunted house, called Dystopia, which has used the Recreational Fear Lab’s research to become as terrifying as possible.

And we hear from horror film music composer, Mark Korven, who creates tension and fear using an invention he calls ‘the apprehension engine’. He speaks to BBC Naturebang’s Becky Ripley who has been investigating sounds that scare us and their evolutionary origins.

Presenter: Anand Jagatia Producer: Jonathan Blackwell

(Photo: Couple watch horror movie with blanket to cover their heads. Credit: WC.GI via Getty Images)

We all know insects are important, but one CrowdScience listener worries that they don’t seem to have equal billing when it comes to human love and attention.

In Scotland’s capital Edinburgh, listener Ruth loves to sit and listen to the birds, the bees and the hoverflies as they go about their daily chores. And it’s got her wondering why bees and butterflies seem to get all the conservation efforts. What do we need to do to protect butterflies as less beautiful caterpillars, and ladybirds as less glamorous larvae? Are people even aware that insects exist in multiple stages of a lifecycle, and that around the world, insect populations are facing perilous levels of decline.

Presenter Alex Lathbridge is on a mission to identify the other unsung insect heroes. Along the way we meet Dr Caitlin Johnstone and Dr Nick Balfour at the Royal Botanic Gardens Edinburgh, who help listener Ruth find out about the lifestyles and lifecycles of hoverflies.

We meet the midge that pollinates cocoa crops in Ghana, as well as Dr Tonya Lander from Oxford University and Dr Acheampong Atta-Boateng from the University of Arizona who have been studying them. And Marc Vaez-Olivera from the company Polyfly introduces us to the billions of hoverflies helping to double avocado yields in Spain.

We also learn what we can all do to help keep insects in our gardens… even if that may involve sacrificing a cabbage or two.

Presenter: Alex Lathbridge

Producer: Marnie Chesterton

Editor: Ben Motley

(Photo: Caterpillar eating flowering plant with pink background - stock photo Credit: Raquel Lomas via Getty Images)

How would you record a special moment? Maybe you could take a photograph, film a little video, or record some audio. We have lots of ways of recording what life LOOKS and SOUNDS like, but is the same true for the other senses? What if you wanted to record the smells that greet you on entering your favourite restaurant? Or record the way your loved ones hand feels in yours?

These are the questions on the mind of listener Aravind, from California in the USA. He wants to know if there are any ways of recording and reproducing sensory experiences like taste and smell, or physical touch.

Anand Jagatia is on the case, and is smelling, tasting, and quite literally FEELING his way to the answer. From a multi-sensory movie experience in Valencia, Spain, to the fascinating history of the pioneers of ‘scented cinema’, through to the ground-breaking “haptic technology” which is enhancing the capabilities of our sense of touch. Both for us, and for the robots which do the jobs we don’t want to.

Presenter: Anand Jagatia

Producer: Emily Knight

Editor: Ben Motley

(Photo: Woman making ASMR sounds with microphone and perfume on yellow background, closeup - stock photo. Credit: Liudmila Chernetska via Getty Images)

Atoms are the building blocks of our world. Many have been around since right after the Big Bang created the universe nearly 14 billion years ago. And if life on Earth is made of atoms that are from all the way back then... will those atoms keep existing forever? That’s what CrowdScience Listener Rob in Australia would like to know.

Caroline Steel investigates the immortality of atoms by travelling to CERN, the world’s largest particle physics laboratory located along the border of France and Switzerland. There, theoretical physicist Matthew McCullough explains whether the smallest atoms can decay or survive the test of time.

Physicist Marco van Leeuwen from Nikhef, the National Particle Physics Laboratory in the Netherlands, gives Caroline a behind-the-scenes tour of the ALICE experiment and the Large Hadron Collider at CERN. She learns how atoms are smashed at incredibly high speeds, and whether that might spell the end of an atom.

And all life on earth is made up of atoms, but how does a collection of tiny particles become a living being? Astrobiologist Betül Kaçar from the University of Wisconsin, Madison, breaks down how life works from an atomic point of view.

Presenter: Caroline Steel

Producer: Imaan Moin

Editor: Ben Motley

(Photo: Hands cupping a glowing atom in the studio - stock photo. Credit: Paper Boat Creative via Getty Images)

Listener Jude in Canada wants to know why some animals are black and white. Why do zebras risk being so stripy? Why do pandas have such distinct marking? And do they have something in common? Presenter Caroline visits Pairi Daiza, a zoo in Belgium. Together with her guide for the day, Johan Vreys, she looks at these weird and wonderful animals up close. First, she visits three zebras having breakfast. Ecologist Martin How from the University of Bristol explains his ingenious experiment involving horses with zebra blankets. Next on the tour is the giant panda which, according to Prof Tim Caro from the University of Bristol, looks at the way it does to camouflage in snowy forests in China. But there are many more animals to see, and many more reasons to be monochrome, including the penguin and its tuxedo-like colouration. Hannah Rowland, senior lecturer at the University of Liverpool explains that it might have more than just a single function. It turns out, scientific answers aren’t always black and white.

Presenter: Caroline Steel Producer: Florian Bohr Editor: Ben Motley

(Photo: The zebra was running gracefully running in the green water. Credit: Surasak Suwanmake/Getty Images)