Scientists genuinely don't know what most of our universe is made of. The atoms we're made from only make up four per cent. The rest is dark matter and dark energy (for 'dark', read 'don't know'). The Large Hadron Collider at CERN has been upgraded. When it's switched on in March 2015, its collisions will have twice the energy they did before. The hope is that scientists will discover the identity of dark matter in the debris. The stakes are high - because if dark matter fails to show itself, it might mean that physics itself needs a rethink.
Hannah is going the other way by asking whether everything could, in fact, be smaller. But going smaller turns out not to be much safer... First, we shrink the Earth to half its size - it starts well with lower gravity enabling us to do incredible acrobatics, but things gradually turn nasty as everyone gets altitude sickness - even at sea level. Then we visit Professor Daniel Lathrop's incredible laboratory, where he has built a model Earth that allows us to investigate the other effects of shrinking the planet to half size. The results aren't good - with a weaker magnetic field we would lose our atmosphere and eventually become a barren, lifeless rock like Mars. In our next thought experiment, we shrink people to find out what life is like if you are just 5mm tall. We find out why small creatures have superpowers that seem to defy the laws of physics, meet Jyoti Amge, the world's smallest woman, and with the help of Dr Diana Van Heemst and thousands of baseball players reveal why short people have longer lives. Lastly, the Sun gets as small as a sun can be. We visit the fusion reactor at the Joint European Torus to find out why stars have to be a minimum size or fusion won't happen. And if our Sun were that small? Plants would turn from green to black, and Earth would probably resemble a giant, frozen eyeball. Which all goes to show that size really does matter.
Meet Nikola Tesla, the genius engineer and tireless inventor whose technology revolutionized the electrical age of the 20th century. Although eclipsed in fame by Edison and Marconi, it was Tesla's vision that paved the way for today's wireless world. His fertile but undisciplined imagination was the source of his genius but also his downfall, as the image of Tesla as a "mad scientist" came to overshadow his reputation as a brilliant innovator.