How Many People Can Live On Planet Earth

Ice is one of the strangest, most beguiling and mesmerising substances in the world. Full of contradictions, it is transparent yet it can glow with colour, it is powerful enough to shatter rock but it can melt in the blink of an eye. It takes many shapes, from the fleeting beauty of a snowflake to the multi-million tonne vastness of a glacier and the eeriness of the ice fountains of far-flung moons. Science writer Dr Gabrielle Walker has been obsessed with ice ever since she first set foot on Arctic sea ice. In this programme she searches out some of the secrets hidden deep within the ice crystal to try to discover how something so ephemeral has the power to sculpt landscapes, to preserve our past and inform our future.

There is a strange and mysterious world that surrounds us, a world largely hidden from our senses. The quest to explain the true nature of reality is one of the great scientific detective stories. Clues have been pieced together from deep within the atom, from the event horizon of black holes, and from the far reaches of the cosmos. It may be that that we are part of a cosmic hologram, projected from the edge of the universe. Or that we exist in an infinity of parallel worlds. Your reality may never look quite the same again.