What an astonishing book. Seth Lloyd, a quantum bit wrangler at MIT, proves that not only is the universe really a computer, but the universe is a computer we can program! He is not the first to see the world this way, but he is the first to translate this mathematical intuition into plain English. Lloyd is at the forefront of a revolution in science that says everything that exists (atoms, energy, space) is just bits of information. As the new mantra goes: all its are bits! The beauty of this book, and Lloyd’s heroic achievement, is to transform that utterly mind-boggling view into a reasonable idea that anyone can begin to understand. A programmable universe is a scientific idea whose time will come in future decades, but you can read it here first.
Ultimately, information and energy play complementary roles in the universe: Energy makes physical systems do things. Information tells them what to do.
Such a quantum computation would constitute a complete description of nature, and so would be indistinguishable from nature. Thus, at bottom, the universe can be thought of as a performing a quantum computation. Likewise, because the behavior of elementary particles can be mapped directly onto the behavior of qubits interacting via logic operations, a simulation of the universe on a quantum computer is indistinguishable from the universe itself.
The conventional view is that the universe is nothing but elementary particles. That is true, but it is equally true that the universe is nothing buts bits — or rather, nothing but qubits. Mindful that if it walks like a duck and quacks like a duck then it’s a duck, form this point on we’ll adopt the position that since the universe registers and processes information like a quantum computer and is observationally indistinguishable from a quantum computer, then it is a quantum computer.