Dr Hannah Fry travels down the fastest zip wire in the world to learn more about Newton's ideas on gravity. His discoveries revealed the movement of the planets was regular and predictable. James Clerk Maxwell unified the ideas of electricity and magnetism, and explained what light was. As if that wasn't enough, he also predicted the existence of radio waves. His tools of the trade were nothing more than pure mathematics. All strong evidence for maths being discovered.
But in the 19th century, maths is turned on its head when new types of geometry are invented. No longer is the kind of geometry we learned in school the final say on the subject. If maths is more like a game, albeit a complicated one, where we can change the rules, surely this points to maths being something we invent - a product of the human mind. To try and answer this question, Hannah travels to Halle in Germany on the trail of perhaps one of the greatest mathematicians of the 20th century, Georg Cantor. He showed that infinity, far from being infinitely big, actually comes in different sizes, some bigger than others. This increasingly weird world is feeling more and more like something we've invented. But if that's the case, why is maths so uncannily good at predicting the world around us? Invented or discovered, this question just got a lot harder to answer.

Far from land, where few of us ever venture, is the ocean beyond the boundary of any country. Largely ungoverned, wild, and lawless. Venture into the deep, dark and desolate oceans that are home to an abundance of beautiful - and downright strange - creatures.

Bob Clewell's helicopter crew comes under intense fire in one of the final operations of the war. Joe Galloway returns to Vietnam and in Washington, D.C., Barry Romo throws down his medals in protest. The last American troops return home and POW wife Anne Purcell awaits word of her husband's fate. The fall of Saigon brings the unification of Vietnam.

'It's really about terror and intimidation and people basically fighting for survival and often committing extraordinary violence in order to protect themselves or to stay safe. It's kind of like the weak dog in the pack. If others spot weakness, they're gonna pounce on you for a couple of reasons. You pounce on that guy, that gives you a little more status. So, I had to ask myself, are you gonna be a victim? No, I ain't gonna be a victim. Well, that really only left me one choice in my mind. That means I gotta be the victimizer. At some point, for some reason, might be legitimate, might not be, someone's gonna test you.. Even if you lose, you're gonna have to stand up for yourself. '
'A guy comes over, and it's your day to get your package, and he tries to take your package from you that your people sent you, if you let him do it, there's gonna be 10 other dudes, oh, yeah, he let that guy take his package, I'm gonna go get his TV, right down the line until somebody's after your ass. But if you stand up that first time and they see you'll stand up for yourself, even if you lose, people will respect that. Oh, don't mess with him. There's easier prey. Why do you have to go and get that guy and get a couple lumps for it when he can go get that guy's stuff over there, don't cost you nothing. It usually only has to happen once or twice but just as importantly that you didn't go to the man for help... you're gonna be all right.'

'Every show is different. When the lights go down that's 30,000 people's lives colliding... for that one moment. Everyone that's there working or watching is there for that moment. It's when you're all kind of in agreement about what you're all doing at that time... so it's a wonderful feeling of togetherness and possibility Then I start getting real adrenaline... and start doing 'Rocky' shadow boxing and all that kind of stuff.
So I get as excited as anyone else. And I still get that excitement when I go and see anyone else's concert. I love that moment. And then it's about trying to hold that energy for an hour and a half... because it can go if you're not careful Whilst it might not be perceived as cool to be really enthused by the fact that people show up to hear your music... we don't really give a f***, we really love that and it's exciting, you know?'

Privately, he was humble, almost shy, and fiercely patriotic, donating millions to his native Brazil and contemplating a life beyond motor-racing. Yet he is struck down in his prime on the blackest weekend in the history of the sport, watched live on television by 300 million people. Years on he is revered in Formula One as the greatest motor racing driver of all time - and in Brazil as a Saint.