Chris - You work on the concept of parallel universes...
Michio - People have often wondered whether there is a carbon copy of us elsewhere that's leading a different life. This idea was often laughed at, but this doesn't happen at physics conferences anymore! Advancing space technology has provided us with baby pictures of the universe. The data from these are consistent with a rapidly expanding universe, but there is nothing in those photos to say that the big bang couldn't happen again. Our universe is like a bubble and we are trapped on the surface of it. As the universe expands, the bubble just gets bigger.
We might not be the only bubble in the universe: there might be lots of them. When we look in the kitchen sink, we can see that bubbles can sometimes cut in half. In space, a black hole could cause this same effect. Once space has been sucked into a black hole, it might get blown out the other end as a white hole. From the side of the white hole, it looks just like a big bang. This means that there might be another universe being born on the other side of every black hole in our universe. A probe called LISA will be sent up into space and should detect the initial vibrations of the birth of the universe. LISA should also tell us which big bang theory is the best. Hopefully the answer will be that we were born of a mother universe, and we might be giving birth to others.
The membranes of these different universe bubbles might be very close to each other. Gravity can jump between the membranes but objects don't, so that's why we don't bump into things in parallel universes. The fact that gravity can jump between them means that we can detect other universes floating just above us. This is what the Hubble Space Telescope has done with dark matter: what it has seen could be the gravitational outline of the dark matter of a parallel universe.
The benefit of knowing about parallel universes is that it provides a possible escape from our universe. Our universe bubble is getting bigger and bigger and one day might explode. With enough energy, it would be possible to heat up space to levels similar to that of the big bang. This amount of energy would make space unstable and new bubbles to be formed. From there, we could go into another universe. It is just like Alice and the Looking Glass.