The Knowledge: How to Rebuild our World from Scratch: 3. Dr Lewis Dartnell, astrobiologist and author of

"While Feynman's sentence is all good and true, it isn't particularly useful in an immediate pragmatic sense. I wrote a book recently which was intended as a guidebook for rebooting civilisation after an apocalypse, looking at the key technologies and central scientific principles that underpin our lives – the behind-the-scenes fundamentals that we all just take for granted today – and what enabled society to progress through the centuries of history. I argue how the greatest invention of history is the scientific method itself – the knowledge-generation machinery that we have been using for over 350 years now to come to understand how the world works. So if you could preserve only one single sentence, I would push for: 'The natural world is not governed by whimsical gods, but is essentially mechanical and can therefore be understood and then predicted by people, using careful observation, experimentation, and measurement, and importantly by testing your explanations to try to refute them.' It's this reiterative process of refinement that sets science apart from any other system for explaining how the world works.

"There are other tips that could help with immediate survival. Diarrhoeal disease kills millions of people every year – all preventable by simple means. One method recommended by the World Health Organisation in developing nations for low-tech treatment of drinking water is called SODIS, or solar disinfection. All you need to do is pour your suspect water into a plastic bottle and leave it in the sun. Ultraviolet rays in sunlight pass straight through and kill any germs. So you can come back to your bottle a day or two later and know that the water you put to your lips isn't going to kill you."