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If a tree falls in a forest and no one is there to hear it, does it make a sound? Perhaps not, some say.

And if someone is there to hear it? If you think that means it obviously did make a sound, you might need to revise that opinion.

We have found a new paradox in quantum mechanics – one of our two most fundamental scientific theories, together with Einstein’s theory of relativity – that throws doubt on some common-sense ideas about physical reality.

Take a look at these three statements:

  1. When someone observes an event happening, it really happened.

  2. It is possible to make free choices, or at least, statistically random choices.

  3. A choice made in one place can’t instantly affect a distant event. (Physicists call this “locality”.)

These are all intuitive ideas, and widely believed even by physicists. But our research, published in Nature Physics, shows they cannot all be true – or quantum mechanics itself must break down at some level.


This is the strongest result yet in a long series of discoveries in quantum mechanics that have upended our ideas about reality. To understand why it’s so important, let’s look at this history.

To read more, click here.