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In our online poll to find out what Plus readers would most like to know about the Universe, you told us that you'd like to find out what happened before the Big Bang. We took the question to the renowned cosmologist John D. Barrow, Professor of Mathematical Sciences at the University of Cambridge, and here is his answer. The Universe is an infinitely self-perpetuating foam of bubbles, it seems. This podcast accompanies the article What happened before the Big Bang? and is part of our celebration of the International Year of Astronomy 2009.