What would happen to our carbon emissions if we all went vegan? Astrophysicist, Sarah Bridle tells Jim Al-Khalili why she switched her attention from galaxies to food. A rising star in the study of extra-galactic astronomy, Sarah was a driving force behind one of the most ambitious astronomy projects of recent times, the Dark Energy Survey of the universe. A few years ago, she started trying to calculate the carbon emissions from different foods so that she could make more informed choices about what she was eating in terms of the impact they were having on climate change. Before long, she was adapting the statistical tools and techniques she had developed to study dark matter and dark energy, to quantify the carbon cost of different foods and lobby government to make food labels indicating carbon cost of foods compulsory. Producer: Anna Buckley