Renowned physicist Michio Kaku embarks on a journey to put the earth's 4.6 billion years of age into context. With a human lifetime seeming so short set against the backdrop of the 4.6 billion year old earth, Kaku wonders about his place, and that of the human race, within earth's epic lifespan.

Historian Ruth Goodman and archaeologists Peter Ginn and Tom Pinfold turn the clock back as they learn how to build a medieval castle using the tools, techniques and materials available in the 13th century. Although Britain has some of the finest remaining castles of the medieval period, many of their secrets have been lost to time. Peter and Tom set to work straight away, learning the skills of the medieval stonemasons to construct a beautiful spiral staircase. After digging stone out of the quarry, they take it to the tracing floor, where every stone is marked out using the most closely guarded knowledge of the medieval castle builders: geometry. Then each step is hand-carved, a three-day task, before being winched into place using the treadmill-powered crane.

Tony Robinson takes on the worst jobs from 43 AD to 400 AD. What do you do to get a piece of crust? Tony Robinson presents some of the worst jobs ever from various historical periods in England, ranging from the dark ages through the Victorian era. Season one focuses on historical periods, while season two combines places, social status and periods of time (for example, rural, urban, maritime, etc.). From the channel 4 website: "The history we are taught usually features the lives and times of the great and the good, of the haves but not the have-nots. However, the monarchs, aristocrats and magnates could not have existed without the battalions of minions who performed the tasks that were beneath their masters and mistresses."

Hawking poses the ultimate of ultimate questions: Why does the universe exist and why does it follow rules and laws? Finding out leads to the very deepest of secrets, to the one principle that's at the heart of everything in the cosmos -- string theory.