Are coin tosses really random?

The probability of a coin landing either heads or tails is supposedly 50/50.  

26th August 2014
Are coin tosses really random? (iStock)

Asked by: Simon Ridley, Penzance

While a coin toss is regarded as random, it spins in a predictable way. In 2008, a team from the Technical University of Łódź, Poland, analysed the mechanics of a coin tumbling in the air. The theory revealed that the coin’s behaviour is predictable – until it strikes the floor. Then ‘chaotic’ behaviour sets in, with small differences producing radically different outcomes.

This suggests that coin tosses caught in mid-air may have a slight bias, a possibility investigated by Persi Diaconis of Stanford University. He found that caught coins have a slight tendency to end up in the same state as they were when initially tossed. The bias is, however, incredibly slight.

So the outcome of tossing a coin can indeed be seen as random – whether it’s caught in mid-air, or allowed to bounce.


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