How do we prepare for the distant future? Helen Keen meets the people who try to.

If our tech society continues then we can leave data for future generations in huge, mundane quantities, detailing our every tweet and Facebook 'like'. But how long could this information be stored? And if society as we know it ends, will our achievements vanish with it? How do we plan for and protect those who will be our distant descendants and yet may have hopes, fears, languages, beliefs, even religions that we simply cannot predict? What if anything can we, should we, pass on?