We are living through a revolution that is bigger than the world wide web. The technology we are all using every day is beginning to share our data gadget to gadget, storing and analysing unimaginable amounts of data. The use of our data now known as big data will change our world in ways unimaginable. Liz Bonnin looks at how big data monitors Rolls Royce jet engines dozens of times a second wherever they are in the world, and how that same system of analytics can automatically detect secondary brain injury in intensive care units. Jem Stansfield creates a low-tech computer and storage system with hacksaw blades and magnets. And with the government about to allow private companies access to our medical data, Maggie Philbin examines the dark side of big data: privacy. Just how much information on each and every one of us is out there, and how easy is it to find?