Geoff Watts investigates the latest thinking about our brain power in old age.

He meets researchers who argue that society has overly negative views of the mental abilities of the elderly - a dismal and fatalistic outlook which is not backed up by recent discoveries and theories.

Geoff talks to Professor Lorraine Tyler who leads a large study in Cambridge (CamCAN) which is comparing cognition and brain structure and function in 700 people aged between 18 and 88 years old.

He also meets scientists and participants involved in an unique study of cognition and ageing at the University of Edinburgh. It has traced hundreds of people who were given a nationwide intelligence test as children in 1932 and 1947. Since the year 2000, the study has been retesting their intelligence and mental agility in their 70s to 90s. The Lothian Birth Cohort study is revealing what we all might do in life to keep our minds fast and sharp well into old age.

One new and controversial idea holds that cognitive decline is in fact a myth. A team in Germany, led by Michael Ramscar, argues that older people perform less well in intelligence and memory tests because they know so much more than younger subjects and not because their brains are deteriorating. Simply put, their larger stores of accumulated knowledge slow their performance. Their brains take longer to retrieve the answers from their richer memory stores.

Producer: Andrew Luck-Baker.

Most traffic accidents are caused by human error. Engineers are designing vehicles with built in sensors that send messages to other cars, trucks, bikes and even pedestrians, to prevent collisions happening. The idea is to make the vehicles react to whatever's going on faster than the human drivers.

Jack Stewart drives around the university town of Ann Arbor, in Michigan, in some of the many vehicles that are fitted with experimental devices in the world's largest connected vehicles project. He finds out how the system works from researchers at UMTRI, the University of Michigan's Transportation Research Institute, and Kirk Steudle, Director, Michigan Department of Transportation.

Jack has a ride in Google's driverless car which has no steering wheel and no pedals. Google's Chris Urmson explains the company's approach to autonomous vehicles.

Jack visits Stanford University's driverless car project where Professor Chris Gerdes shows him Shelley, an automated Audi that races around a track at speed as well as a human driver. Chris is collaborating with a philosopher to explore some of the difficult questions around autonomous vehicles, such as who's liable if there's an accident. Is it the human or the car?

Are you a lark or an owl? Are you at your best in the morning or the evening? Linda Geddes meets the scientists who are exploring the differences between larks and owls. At the University of Surrey's Sleep Research Centre she talks to its director, Professor Derk-Jan Dijk, and finds out her own chronotype by filling in a questionnaire.

Linda discovers why we have circadian rhythms and why they don't all run at the same rate. Dr Louis Ptacek from the University of California, San Francisco, explains his investigation of the genes of families whose members get up very early in the morning and of those who get up very late.

She finds out why our sleep patterns change as we age - teenagers really aren't good at getting up in the morning. Professor Mary Carskadon from Brown University explains that although some schools have experimented with a later start there is no plan to put this into universal practice.

Linda talks to Professor Til Roenneberg from Ludwig-Maximilians-University Munich about his concept of social jetlag. And she hears about research trying to reduce the exhaustion often suffered by shift workers. Dr Steve Lockley of Harvard University tells her about using blue light to improve the wellbeing of people with medical conditions.

Geoengineering is a controversial approach to dealing with climate change. Gaia Vince explores putting chemicals in the stratosphere to stop solar energy reaching the earth.

When volcanoes erupt they put sulphur in the stratosphere. The particles reflect solar rays back into space and the planet cools down. Scientists are suggesting that it could be possible to put sulphur into the stratosphere using specialised aircraft or a very long pipe. But if this was implemented there could be impacts on rainfall and the ozone layer.

Another idea is to spray seawater to whiten clouds that would reflect more energy away from the earth.

Gaia Vince talks to the researchers who are considering solar radiation management. She also hears from social scientists who are finding out what the public think about the idea and who are asking who should make decisions about implementing this way of cooling the planet.

3.5 billion people are alive today because of a single chemical process. The Haber-Bosch process takes Nitrogen from the air and makes ammonia, from which synthetic fertilizers allow farmers to feed our massive population.

Ammonia is a source of highly reactive nitrogen, suitable not just for fertilizer but also as an ingredient in bomb making and thousands of other applications.

Now we make around 100 million tonnes of ammonia annually, and spread most of it on our fields.

But this is a very inefficient way to use what amounts to 1-2% of the planet's energy needs. Only around 20% of fertilizer made ends up in our food.

Prof. Andrea Sella explores some of the alternative ways we might make fertilizer.

Legumes, such as peas and beans, allow certain cells in their roots to become infected by a specific type of bacteria. In return, these bacteria provide them with their own fertilizer.

Could we infect the plants we want to grow for food - such as cereals - in a similar way to cut down the climatic and environmental impact of Haber-Bosch?

Quentin Cooper takes a look at the new materials that can mend themselves. Researchers are currently developing bacteria in concrete which, once awakened, excrete lime to fill any cracks. In South America you can choose a car paint that heals its own scratches. And there are even gold atoms which can migrate to mend tiny breaks in jet turbine blades.

Engineers normally design things so the likelihood of breaking is minimised. But by embracing the inevitability of breakage, a new class of materials which can mend cracks and fissures before you can see them may extend the lives of our cars, engines, buildings and aeroplanes far beyond current capability.

We like to think that we are in control of our lives, of what we do, think and feel. But, as Geoff Watts discovers, scientists are now revealing that this is just an illusion.

A simple magic trick reveals just how limited our conscious awareness of the world is, and how easy it is to fool us.

So if our conscious brain can cope with so little, what is responsible for the rest? Science is starting to reveal the crucial role of a silent partner inside our heads, that we are completely unaware of - our unconscious.

In this programme, Geoff enlists the help of not just brain scientists, but a conjuror and a musician to reveal the pivotal role the unconscious plays in pretty much everything we do, think and feel. This new-found knowledge is enabling scientists to harness its powers for both medical and military benefit.

What is it about the microbes in our guts that can have such an impact on our lives?

The human gut has around 100 trillion bacterial cells from up to 1,000 different species. Every person's microbiota (the body's bacterial make-up) is different as a result of the effects of diet and lifestyle, and the childhood source of bacteria.

Scientists are learning more and more about the importance of these bacteria, as well as the viruses, fungi and other microbes that live in our gastrointestinal tracts. Without them, our digestion, immune system and overall health would be compromised.

Adam Hart talks to researchers who are discovering how important a balanced and robust gut microflora is for our health. And he asks how this can be maintained and what happens when things go wrong.

The hormone oxytocin is involved in mother and baby bonding and in creating trust. Linda Geddes finds out if taking oxytocin can help people with autism become more sociable.

Larry Young, Professor in the Department of Psychiatry at Emory University in Atlanta, talks about the work in voles that demonstrated the role of oxytocin in pair bonding.

Professor Markus Heinrichs of Freiburg University in Germany tells Linda Geddes about doing the first research on oxytocin in human subjects. He was one of the authors of an influential paper on the hormone and trust, published in Nature in 2005.

As journalists for New Scientist, Linda and her husband, Nic, invited one of the other authors of that paper, Professor Paul Zak of Claremont Graduate University in California, to carry out an oxytocin experiment at their wedding.

At Cambridge University, Dr Bonnie Auyeung, is currently carrying out studies to find out if giving the hormone to adults with autism can improve their social skills.

And Professor Jennifer Bartz, from McGill University in Canada, explains how some research suggests that oxytocin doesn't always make people be more trusting and loving. She says the outcome depends on your previous relationship with the person.

Tracey Logan goes underground to find out how Crossrail is using the latest engineering techniques to create 26 miles of tunnels below London's tube network, sewers and foundations and through its erratic, sometimes unpredictable geology. She finds out about the latest science being used in Europe's biggest engineering project.

London sits on a varied geology of deposits of fine-grained sand, flint gravel beds, mottled clay, shelly beds which are sometimes mixed with pockets of water. This sheer variety has presented a challenge to London's tunnel engineers since the early 1800s.

Tracey goes on board one of the huge, 150 metre long, 1000 tonne tunnel boring machines as it makes its way beneath London's Oxford Street. At depths of up to 40 metres it can negotiate London's complex geology with incredible precision and can instantly adjust the pressure it applies at the cutting head to ensure there is no ground movement above.

Its precision engineering means it also follows a route which avoids the many existing foundations, sewers, and the tube network, sometimes travelling just centimetres past the London underground tunnels.

Tracey also finds out how unexploded ordnance from World War II still has to be carefully accounted for while digging beneath the capital.

The tunnel boring machines operate nearly 24 hours a day, 365 days a year and so even has an onboard kitchen and bathroom facilities for the 20 or so operators who make up its 'tunnel gang'.