Analogue Simulation in Modern Physics

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Many of the predictions of modern theoretical physics are extremely difficult to test. For example, Hawking's famous prediction that black holes radiate at a characteristic temperature. Since the temperature of `Hawking radiation' is very low, it is not (even in principle) detectable via observational astronomy. Furthermore, is is unlikely that we will ever be able to construct black holes here on earth. The lack of an in principle means for direct experimental testing of predictions such as Hawking radiation pose a challenge to conventional scientific methodologies. This challenge is taken up by techniques of `analogue simulation' wherein an accessible `source' system is used to simulate phenomena that are difficult or impossible to test directly within a `target' system. Analogue simulation in modern physics comes in two forms depending upon the type of source and target system: `quantum simulation' and `analogue gravity simulation'. In quantum simulation both source and target systems are typically within the domain of finite dimensional quantum theory. A simple example is where an array of ions (i.e. charged atoms) is controlled via magnetic fields such that they collectively simulate a ferromagnetic material (such as an iron bar magnet). Quantum simulations are potentially very powerful tools for gaining new insights into quantum systems that are hard to manipulate, for example relativistic quantum systems, nano-materials and quantum optical systems. In analogue gravity simulations, condensed matter systems, like fluids, are typically used to simulate gravitational systems, such as black holes or early universe cosmology. Analogue gravity simulations are potentially very powerful tools for gaining new insights into phenomena that are deemed impossible to test directly, such as Hawking radiation. This is a project in the philosophy of science within which we will evaluate the methodological, epistemological and metaphysical foundations of analogue simulation with the goal of providing analytic tools of direct use to scientists, philosophers of science, and science funding decision makers. We answer questions such as: What kind of evidence can analogue simulations provide?; What do analogue simulations have in common with computer simulations and experiments?; What is the scientific and economic value of analogue simulation? We propose that analogue simulation can be understood as a form of `Ersatz' experimentation, involving the `programming' of a physical system such that it can be used to `simulate' another physical system. In general terms, evidence gained from experiments on a particular system is only of real value to the extent to which we have justification for generalising it to a class of relevantly similar `target' systems. Such justificatory arguments are called `external validation' of an experiment. One of the key ideas explored in this project is conditions for external validation of analogue simulations. For example, we aim to examine the conditions in which the analogue simulation of Hawking radiation via condensed matter systems can be externally validated: i.e. when we can genuinely learn about black holes by doing experiments on the analogues.