We feel it every moment of our lives but for physicists, gravity is the longest running unsolved mystery of the universe. Why do all objects that have mass pull on one another? Cutting-edge theories are proposing unexpected answers.
The classical physics that we encounter in our everyday, macroscopic world is very different from the quantum physics that governs systems on a much smaller scale (like atoms).
Horizon looks at dark energy - the mysterious force that is unexpectedly causing the universe's expansion to speed up. The effects of dark energy were discovered in 1998 but physicists still don't know what it is. Worse, its very existence calls into question Albert Einstein's general theory of relativity - the cornerstone of modern physics. The hunt for the identity of dark energy is on. Experiments on earth and in space generate data that might provide a clue, but there are also hopes that another Einstein might emerge - someone who can write a new theory explaining the mystery of the dark energy.
A sword made of pure light that can cut through anything, the lightsaber is a truly awesome weapon. But it's not just a science fiction fantasy, Dr Michio Kaku reveals how we could one day build a real working lightsaber.
This two-part scientific detective tale tells the story of a remarkable group of pioneers who wanted to reach the ultimate extreme: absolute zero, a place so cold that the physical world as we know it doesn't exist, electricity flows without resistance, fluids defy gravity and the speed of light can be reduced to 38 miles per hour. Each film features a strange cast of eccentric characters, including: Clarence Birds Eye; Frederic 'Ice King' Tudor, who founded an empire harvesting ice; and James Dewar, who almost drove himself crazy by trying to liquefy hydrogen. Absolute zero became the Holy Grail of temperature physicists and is considered the gateway to many new technologies, such as nano-construction, neurological networks and quantum computing. The possibilities, it seems, are limitless. Part 2: Race for Absolute Zero Focuses on the fierce rivalry that took place in the laboratories in Britain, Holland, France and Poland as they sought the ultimate extreme of cold. The program will follow the extraordinary discoveries of superconductivity and superfluidity and the attempt to produce a new form of matter that Albert Einstein predicted would exist within a few billionths of degrees above absolute zero.