"THE universe is not only queerer than we suppose, but queerer than we can suppose," as geneticist J. B. S. Haldane once remarked. In recent decades, physicists have done their best to prove Haldane wrong, by supposing some very queer universes indeed.
Their speculations may seem fantastical, but they are well motivated. Physics poses some formidable questions that we are so far unable to answer. Why is the universe dominated by matter not antimatter? Why does our universe appear to be "fine-tuned" with just the right properties to give rise to galaxies, stars, planets, life and physicists?
The existing edifice of physics, built upon the twin foundations of general relativity and quantum mechanics, is clearly in need of renovation. We have been waiting for years for cracks to appear that might tell us how to go about it. But up to now, nature has remained stubbornly unmoved.