According to our best theories of physics, the fundamental building blocks of matter are not particles, but continuous fluid-like substances known as 'quantum fields'. David Tong explains what we know about these fields, and how they fit into our understanding of the Universe. Watch the Q&A here: https://www.youtube.com/watch?v=QUMeKDlgKmk Subscribe for regular science videos: http://bit.ly/RiSubscRibe David Tong is a professor of theoretical physics at Cambridge University, specialising in quantum field theory. The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter