Your Editorial 'Parallel worlds galore', celebrating the fiftieth anniversary of the multiverse hypothesis (Nature 448, 1; doi:10.1038/448001a 2007), was a timely and stimulating reminder that the interaction of science and fiction sometimes leads to facts, or at least to scientific implications. But in your two News Features on the topic (Nature 448, 15–17 and 18–21; 2007), I wonder why chemistry was largely ignored, as this discipline offers excellent scientific platforms for science-fiction narrative. Likewise, fiction holds lessons for chemistry.

Chemists have always wondered whether life in a parallel universe could actually be based on atoms other than carbon. Perhaps that thinking inspired Lewis Carroll's Alice to call into question whether milk could be different in the universe behind the mirror in Through the Looking Glass.

Although Kurt Vonnegut's Galapagos is quoted as a great example of science fiction in biology, his 1963 novel Cat's Cradle has lessons for science. Here, the protagonist, Felix Hoenikker, creates a solid form of water called ice-nine — a narrative probably influenced by the work of Nobel laureate Irving Langmuir. At least 12 forms of ice have now been reported, including ice IX — though this is unlike the fictional ice-nine. Cat's Cradle also inspired interest in what seemed to be an extraordinary form of water with anomalous properties, known as 'polywater'. This Russian discovery may have had its roots in papers published during the late 1920s on the vapour pressure of water and other liquids in small capillaries (see, for example, J. L. Shereshefsky J. Am. Chem. Soc. 50, 2966–2980 and 2980–2985; 1928). But the research caused much excitement when it was presented in the West in 1966, and it became widely accepted until proved, a few years later, to be fallacious.

It seems appropriate, therefore, to consider chemistry as a tool for uncovering facts that either inspire or imitate fiction. What is really astonishing, to a chemist, about a parallel world coexisting with our own is not its existence in itself, but rather the matter we could find there.