David Deutsch is a really smart man who studies things called "quantum mechanics" and "computing". Quantum mechanics is like a secret code that tells us how tiny things like atoms and particles work, while computing is using computers to solve problems.
David is famous for a special kind of computing called "quantum computing". This is a different way of solving problems that uses the power of atoms and particles to do things much faster than normal computers can. It's kind of like having a really really fast and smart helper in your brain who can help you do things much quicker and easier.
David also believes that there are many different worlds out there, and each one is real and exists at the same time as ours. This idea is called the "multiverse" and it's kind of like having many different books in a library and each book tells a different story about what could happen in our world.
Overall, David Deutsch is a super smart person who studies cool things like quantum mechanics, computing, and the multiverse. His work helps us understand the world around us and solve problems faster and more efficiently.