Paul Younger, Rankine Professor of Energy Engineering at the University of Glasgow, in conversation with Jim al-Khalili in front of an audience at the Free Thinking Festival at Sage Gateshead.

Paul Younger's future career was inspired by the hills around him near the River Tyne. From a background in geology he now carries out research into, as he says, "keeping the lights on and keeping homes and businesses warm whilst de-carbonising our energy systems."

He spent many years at the University of Newcastle, where he built up his expertise in the relationship between water and rocks. He has advised on how to clean up the highly polluted water left in mines after they are closed - from the North East to Bolivia.

His knowledge of the rocks beneath our feet has lead him to investigating how we might use more geothermal energy in the future. Paul Younger tells Jim al-Khalili about the experimental holes that have been drilled in County Durham and central Newcastle, and explains why these projects are now mothballed. And Professor Younger also talks about his research into other unconventional ways of generating energy - such as turning coal deep underground into gas.