Information and entanglement-assisted communication from a manipulability account of causation
OLIMPIA LOMBARDI AND CRISTIAN LÓPEZ
CONICET, University of Buenos Aires (Argentina)
 
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The physical interpretation of the concept of information is very usual among physicists and communication engineers (Landauer 1996). According to this view, information is a physical item whose essential property consists in its capacity to be generated in one place and to be transmitted to another place. It can also be stored, accumulated and transformed from one form to another, like other physical quantities. In some cases, information is conceived as a physical magnitude with the same ontological status as energy (Stonier 1990): like energy, information needs a signal acting as its physical carrier, and can only be transferred through interactions.
In spite of its wide diffusion, this interpretation began to be challenged by the advent of “quantum” information. In fact, entanglement-assisted communication shows that, although mere correlation is not sufficient for communication, asking for a physical signal acting as a carrier of information from source to destination is a too strong requirement. The traditional physical view leads to hardly acceptable conclusions. An option is to accept artificial solutions as those of information flowing backwards in time (Penrose 1998, Josza 1998) or of quantum information hidden in classical bits (Deutsch and Hayden 2000). The other option is to accept that entanglement-assisted communication does not involve transmission of information at all. This situation faces the physical interpretation with a serious problem: does it mean that we must discard the physical interpretation?
We want to argue that, even in the case of entanglement-assisted communication, there is no need to discard the physical interpretation of information. For this purpose it is necessary to furnish the physical interpretation with some further ideas. In fact, we need to retain the idea of information as a physical magnitude without falling into a mere epistemic view of information, but without requiring a physical carrier for its transmission. What is needed, therefore, is to support the idea that what happens at the source of information causes what happens at the destination, but with a concept of causality that does not rely on physical interactions or space-time connections. We think that a manipulability account of causation works perfectly in this sense. Intuitively, any transmission of information produces a relationship between source and destination, and from the manipulability approach this relationship is causal because it is potentially exploitable for purposes of manipulation and control (Woodward 2003, 2013, Pearl 2009). The link between transmission of information and manipulability lies in the fact that there is transmission of information whenever we can change the informational content of the destination (effect) by manipulating the source (cause). Although still relying on physical actions, in this characterization of information transference nothing alludes to interactions or carrier signals.

References
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Jozsa, R. (1998). “Entanglement and Quantum Computation.” Pp. 369-79, in S. Huggett, L. Mason, K. P. Tod, S. T. Tsou, and N. M. J. Woodhouse (eds.), The Geometric Universe. Oxford: Oxford University Press.
Landauer, R. (1996). “The Physical Nature of Information.” Physics Letters A, 217: 188-193.
Pearl, J. (2009). Causality. New York: Cambridge University Press.
Penrose, R. (1998). “Quantum Computation, Entanglement and State Reduction.” Philosophical Transactions of the Royal Society of London A, 356: 1927-1939.
Stonier, T. (1990). Information and the Internal Structure of the Universe: An Exploration into Information Physics. New York-London: Springer.
Woodward, J. (2003). Making Things Happen: A Theory of Causal Explanation. Oxford: Oxford University Press.
Woodward, J. (2013). “Causation and Manipulability.” In E. N. Zalta (ed.), The Stanford Encyclopedia of Philosophy (Spring 2011 Edition), URL = <http://plato.stanford.edu/archives/win2013/entries/causation-mani/>.