Not much in science is more of a mind-bender than thinking about the size and fate of the known universe (except for quantum mechanics and string theory, which also has a lot to do with the size and fate of the universe, albeit on the opposite end of the size spectrum). When we first developed theories about the universe, the model which resulted depicted all of space as static and unchanging, infinite in depth in any direction. Then Einstein posited general relativity and suddenly a whole host of universes were theoretically possible: static, dynamic, infinite, and finite.

For those of you who sometimes wonder why string theory can be one of the most talked about scientific ideas of our day without a whisper of evidence backing it up—admit, there are a few of you out there—there's a very interesting and not too complex article in the new issue of Physics World. The piece reviews some of the history and progress of past scientific theories, and why considering only the big ideas that can be backed by some experimental proof isn't a good thing for advancing our understanding of the universe. The simplified conclusion: At this point, string theory is the only real candidate capable of pulling together gravity and quantum physics, so we might as well stick with it.—Gregory Mone