Modern theoretical physics is shot with paradoxes. No matter how far scientists dig into their experimental data, no matter how subtle their measurements or sophisticated their mathematics, the exact shape and nature of being just refuses to hang together in a logical, consistent form. Objects shift inexplicably from particles to waves and back again, space keeps buckling into impossible dimensions, time runs forwards backwards. Worst of all, the very act of observation seems to create, bringing existence out of what was previously no more than a cloud of possibilities. The author introduces the non-scientist reader to a new concept that is increasingly attracting the interest of his fellow physicists and may, despite its unsettling oddness, offer solutions to the most worrying paradoxes. It is the idea that instead of one world or universe, there is in fact an infinity of worlds or universes - interwoven, alternating, yet each of them different from the next.