Absolutely – it’s all to do with probability. Pretty much any event or object in our lives has the power to generate coincidences. It’s just that we don’t notice the vast majority because they’re boring – like seeing two blue cars parked next to each other. But every so often, we think we’ve encountered an incredibly rare coincidence. What we’re forgetting is a basic rule of probability: that even rare events are sure to happen if given enough opportunities. It’s often hard even to estimate the number of these, and thus it’s impossible to gauge their true probability, leaving us feeling baffled and spooked.

But such estimates can be calculated for some coincidences. For example, probability theory shows there’s almost a 50:50 chance of at least two of the 23 players in any football match (including the ref) having the same birthday. Those chances increase dramatically if we’re willing to be a bit flexible about what counts as a coincidence. For instance, if we allow birthdays within a day of each other to count, then the chances of witnessing at least one coincidence among any two football teams soars to around 90 per cent. This example involves random, independent variables (i.e. players’ birthdays). If there’s something linking the variables, the chances of coincidences get a boost.

Take the bizarre case of The Wreck Of The Titan, a novel about how the world’s largest ocean liner sank when it hit an iceberg, resulting in many deaths because of a lack of lifeboats. Spookily, the book appeared 14 years before the real-life Titanic disaster of 1912. But there are reasons for the similarities: the threat of icebergs to giant liners and the provision of lifeboats were already concerns when this book was written. Moreover, such vast ships tend to be given grand names.

In short, many of the ‘coincidences’ in the novel aren’t independent, but are a direct consequence of its storyline.

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## Authors

Robert is a science writer and visiting professor of science at Aston University.