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- Principle of relativity for quantum theory

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PIRSA Number:

12110073

In

a generic quantum experiment we have a given set of devices analyzing some

physical property of a system. To each device involved in the experiment we

associate a set of random outcomes corresponding to the possible values of the

variable analyzed by the device. Devices have apertures that permit physical

systems to pass through them. Each aperture is labelled as "input" or

"output" depending on whether it is assumed that the aperture lets

the system go inside or outside the device. Assuming a particular input/output

structure for the devices involved in a generic experiment is equivalent to

assume a particular causal structure for the space-time events constituted by

the outcomes happening on devices. The joint probability distribution of these

outcomes is usually predicted assuming an absolutely defined input/output

structure of devices. This means that all observers of the experiment agree on

whether an aperture is labelled as "input" or "output". In

this talk we show that the mathematical formalism of quantum theory permits to

predict the joint probability distribution of outcomes in a generic experiment

in such a way that the input/output structure is indeed relative to an

observer. This means that two observers of the same experiment can predict the

joint probability distribution of outcomes assuming different input/output

labels for the apertures. Since input/output structure is the causal structure

of the space-time events constituting the outcomes involved in the experiment

we conclude that in quantum theory, the causal structure of events may not be

regarded as absolute but rather as relative to the observer. We finally point

out that properly extending this concept to the cosmological domain could shed

light on the problem of dark energy.

©2012 Perimeter Institute for Theoretical Physics