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In the science fiction novel Quarantine, Greg Egan imagines a universe where interactions with human observers collapse quantum wavefunctions. Aliens, unable to collapse wavefunctions, tire of being slaughtered by these collapses. In response they erect an impenetrable shield around the solar system, protecting the rest of the universe from human interference and locking humanity into a starless Bubble. When confronting scientific realism and the quantum, many philosophers try to do the theoretical counterpart of this fictional practical strategy. Quantum mechanics is beset with many hard-to-resolve interpretational challenges. Philosophers—appealing to decoherence and coarse-graining—try to put these in a Bubble and hope that they can go about their philosophizing as before. Chapter 4 aims to burst this Bubble, and then explores ways of eliminating quantum underdetermination, showing that such attempts lead to philosophical gridlock.

Despite the overwhelming successes of modern physics, there are questions that remain to be answered and these are considered in the final chapter. The interpretation of quantum mechanics is discussed, including the EPR paradox, the Aspect experiments and quantum entanglement. Next, the question of whether particles are really point-like and the possibility of an alternative description in terms of solitons is considered. The Skyrmion and the Standard Model sphaleron are described. Unexplained features of the universe, such as the matter–antimatter asymmetry, the existence of dark matter and the even more mysterious dark energy, are discussed. There is also a critique of the loose ends of the Standard Model and the need for a quantum theory of gravity. The chapter concludes with a look beyond the Standard Model at the arguments and evidence in favour of Grand Unified Theories and ultimately string theory.

The purpose of the present chapter is to respond to a thread of recent criticism against one candidate framework for interpreting quantum theories, a framework introduced and defended by David Albert and Barry Loewer: wave function realism, a framework for interpreting the ontology of quantum theories according to which what appears to be a nonseparable metaphysics ofentangled objects acting instantaneously across spatial distances is a manifestation of a more fundamental separable and local metaphysics in higher dimensions. Thechapterconsiders strategies for extending the wave function realist interpretation of quantum mechanics to the case of relativistic quantum theories, responding to arguments that this cannot be done.

The unresolved problem of the physical interpretation of quantum theory is laid out, and comments on existing attempts to solve it are given. The chapter then discusses ways in which the quantum picture of physical reality may or may not have something to offer to our understanding of human identity and divine action. It is unknown whether the physical expression of human identity relies on the more subtle features of quantum states. If it does, then it may be physically impossible to make copies of personal beings such as humans, and it may be invalid to invoke a reductionist model of brain function. However, this remains unknown and it is premature to make extensive claims. The same applies to the question of divine action. But quantum physics offers many positive lessons in truth-seeking, technology, humility, living with unanswered questions, and in enlarging our theological imagination.

We may think that the lack of time travellers from the future is evidence that time travel is physically impossible. This is the ‘Tourist Paradox’. After the chapter introduces the paradox, and discusses some of the extant solutions, it argues that the best solution is that—given Ludovicianism—we should never expect there to be time travellers, no matter how high the objective chance of people travelling in time. The chapter argues that the upshot is that we are rationally obligated to avoid conducting any experiment that, even accidentally, brings about time travel. It ends by sketching how that might bear on how we conduct contemporary high-energy experiments.