The last episode in the series examines how humans perceive and experience time, investigating the internal body clock which tells people when to eat, drink, sleep and relax. The importance of accurately measuring time is explored in relation to human evolution, and there's a debate about whether mankind will ever be able to travel between past, present and future.
Dame Sally Davies talks to Brian Cox about her interest in antibiotic resistance and admiration of Alexander Fleming and Howard Florey for their development of penicillin.
We are all at the mercy of the Sun. Its glowing disc sustains nearly all life on Earth. But the Sun also holds a dark secret: someday, our aging, expanding star will bathe the Earth in a fiery holocaust. Everything we know will turn to hot, bubbling, plasma.