7.30pm to 8.30pm BST, Thursday 22 May
This event has already taken place
Maybe an asteroid hit Earth. Perhaps a nuclear war reduced our cities to radioactive rubble. Or an avian flu killed almost everyone on Earth. However it happened, the world as we know it is over and we must start again.
So how do we set about rebuilding our world from scratch? How do you grow food and make clothes? Or generate energy and develop medicines? On 8 May, Lewis Dartnell helped us, as the survivors, reconnect with the basic skills and knowledge which our lives and world depend upon.
For those of you who missed it, you now have your chance to watch his talk online and ask him your questions during this live twitter chat.
New to Twitter? To join in this Twitter chat, you will need to register for a (free) twitter account.
Read this handy Beginners' Guide to Twitter to help you get started.
Once you have an account, and know the general rules, you can follow the conversation by searching for the hashtag #RiChat or clicking on this hashtag in someone's tweet. If you include this hashtag in each of your tweets, it will appear along with the others in the conversation. We and Lewis Dartnell will then see it and answer your questions or respond to your comments, using the same hashtag.
Benefit from free and better than half-price tickets, special offers and access to the CHRISTMAS LECTURES ticket ballot.