# Research

## The Constructor Theory of Probability

###### Authors:

Chiara Marletto

###### Journal:

Proceedings of the Royal Society A, Volume 472, issue 2192

###### Date:

17 August 2016

###### DOI:

10.1098/rspa.2015.0883

###### Affiliations:

Oxford

#### Abstract

Unitary quantum theory, having no Born Rule, is non-probabilistic – hence the notorious problem of reconciling it with the unpredictability and appearance of stochasticity in quantum measurements. By generalising and improving upon the so-called ‘decision-theoretic approach’ (Deutsch, 1999; Wallace, 2003, 2007, 2012), I shall recast that problem in the recently proposed constructor theory of information – where quantum theory is represented as one of a class of ‘superinformation theories’, which are non-probabilistic theories conforming to certain constructor-theoretic conditions. I characterise the unpredictability of measurement outcomes exactly in constructor theory, showing that it necessarily arises in superinformation theories because of the impossibility of cloning certain sets of states. Then I explain how the appearance of stochasticity in (finitely many) repeated measurements arises under superinformation theories. Specifically, I establish sufficient conditions for a superinformation theory to inform decisions (made under it) as if it were probabilistic, via a Deutsch-Wallace-type argument. In my version, some of that argument’s assumptions, previously construed as merely decision-theoretic, follow from physical properties expressed by constructor-theoretic principles.

#### Relevant Talks

### David Deutsch on Physics without Probability, June 2015 in Oxford

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