Professor Jim Al-Khalili investigates the most accurate and yet perplexing scientific theory ever – quantum physics. At the beginning of the 20th century, scientists were led into the hidden workings of matter, into the sub-atomic building blocks of the world around us. They discovered phenomena unlike any encountered before – a realm where things can be in many places at once, where chance and probability call the shots and where reality appears to only truly exist when we observe it.