Facts happen at every interaction, but they are not absolute: they are relative to the systems involved in the interaction. Stable facts are those whose relativity can effectively be ignored. In this work, we describe how stable facts emerge in a world of relative facts and discuss their respective roles in connecting quantum theory and the world. The distinction between relative and stable facts resolves the difficulties pointed out by the no-go theorem of Frauchiger and Renner, and is consistent with (...) the experimental violation of the Local Friendliness inequalities of Bong et al.. Basing the ontology of the theory on relative facts clarifies the role of decoherence in bringing about the classical world and solves the apparent incompatibility between the ‘linear evolution’ and ‘projection’ postulates. (shrink)

Landauer's Principle asserts that there is an unavoidable cost in thermodynamic entropy creation when data is erased. It is usually derived from incorrect assumptions, most notably, that erasure must compress the phase space of a memory device or that thermodynamic entropy arises from the probabilistic uncertainty of random data. Recent work seeks to prove Landauer’s Principle without using these assumptions. I show that the processes assumed in the proof, and in the thermodynamics of computation more generally, can be combined to (...) produce devices that both violate the second law and erase data without entropy cost, indicating an inconsistency in the theoretical system. Worse, the standard repertoire of processes selectively neglects thermal fluctuations. Concrete proposals for how we might measure dissipationlessly and expand single molecule gases reversibly are shown to be fatally disrupted by fluctuations. Reversible, isothermal processes on molecular scales are shown to be disrupted by fluctuations that can only be overcome by introducing entropy creating, dissipative processes. (shrink)

According to Bohmian mechanics, we see the particle, not the pilot wave. But to make predictions we need to know the wave. How do we learn about the wave to make predictions, if we only see the particle? I show that the puzzle can be solved, but only thanks to decoherence.

In a famous passage drawing implications from determinism, Laplace introduced the image an intelligence who knew the positions and momenta of all of the particles of which the universe is composed, and asserted that in a deterministic universe such an intelligence would be able to predict everything that happens over its entire history. It is not, however, difficult to establish the physical possibility of a counterpredictive device, i.e., a device designed to act counter to any revealed prediction of its behavior. (...) What would happen if a Laplacean intelligence were put into communication with such a device and forced to reveal its prediction of what the device would do on some occasion? On the one hand, it seems that the Laplacean Intelligence should be able to predict the device's behavior. On the other hand, it seems like that device should be able to act counter to the prediction. An examination of the puzzle leads to clarification of what determinism does entail, with some insights about various other things along the way. (shrink)