“Anyone who is not shocked by quantum theory has not understood it.” Since Niels Bohr said this many years ago, quantum mechanics has only been getting more shocking. We now realise that it’s not really telling us that “weird” things happen out of sight, on the tiniest level, in the atomic world. Rather, we can now see that everything is quantum: our everyday world is simply what quantum becomes at the human scale. But if quantum mechanics is right, what seems obvious and right in our everyday world is built on foundations that don’t seems obvious or right – or even possible. The writer Philip Ball was formerly an editor at Nature.