Christmas is a time of mysteries so we thought we'll give you the chance to put your favourite mystery to the experts. Pick a question in the poll on the right — after Christmas we'll answer the most popular question in articles and podcasts based on interviews with physicists and mathematicians who really know about these things.

We've already done this once before. The question that won was "what is time?" Find our answers here!

This project is a collaboration between Plus and FQXi, an organisation that supports and disseminates research on questions at the foundations of physics and cosmology.