Penultimate Author

Quantum mechanics often conflicts with everyday assumptions. Entanglement, for example, defies the idea that two objects cannot physically interact with one another at a distance. Physicists have tried to resolve this by abandoning the idea of 'locality' in their theories. But as Markus Aspelmeyer from the University of Vienna in Austria and his colleagues reveal on page 871, this is not enough and certain aspects of realism — which holds that reality exists independently of observers — must also be cast aside.

Why is quantum physics so difficult for most people to understand?

Because classical concepts cannot be used to explain quantum phenomena.

What attracts people to the field?

We want to find out why quantum theory works so perfectly and yet cannot be understood by the intuitive concepts of the other physical theories. There are observable phenomena that cannot be explained by our current 'world view'. Isn't that attractive?

What is the difference between reality in normal life and from a quantum perspective?

People observe outcomes and believe each observed event can be fully explained by the properties of the system and independently of the observation. In this case, things have 'real' properties. This conclusion is wrong for the quantum world. Quantum physics does not tell us how nature is, only what we can say about nature. And we can only make statements about probabilities for outcomes.

What consequences do your findings have for the development of quantum theory?

I don't know. But anybody formulating a non-local hidden-variable theory will have to specify their exact idea of realism.

What are the largest and smallest systems to which your research can be applied?

In principle, quantum theory does not stop at massive objects. Quantum behaviour has been demonstrated for massive objects up to the size of macromolecules. It would be interesting to extend this work to even larger masses and sizes.

Did your studies in philosophy help your understanding of quantum mechanics?

I think they made me more sensitive to the underlying structures and assumptions of theories. You need to know the preconditions under which you are able to make statements about the physical world and observations in the physical world.

Is every quantum mechanic a philosopher?

I think so. But not many would admit it.