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Sean M. Carroll
California Institute of Technology
  1. Self-Locating Uncertainty and the Origin of Probability in Everettian Quantum Mechanics.Charles T. Sebens & Sean M. Carroll - 2016 - British Journal for the Philosophy of Science (1):axw004.
    A longstanding issue in attempts to understand the Everett (Many-Worlds) approach to quantum mechanics is the origin of the Born rule: why is the probability given by the square of the amplitude? Following Vaidman, we note that observers are in a position of self-locating uncertainty during the period between the branches of the wave function splitting via decoherence and the observer registering the outcome of the measurement. In this period it is tempting to regard each branch as equiprobable, but we (...)
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    Mad-Dog Everettianism: Quantum Mechanics at Its Most Minimal.Sean M. Carroll & Ashmeet Singh - 2019 - In Anthony Aguirre, Brendan Foster & Zeeya Merali (eds.), What is Fundamental? Springer Verlag. pp. 95-104.
    To the best of our current understanding, quantum mechanics is part of the most fundamental picture of the universe. It is natural to ask how pure and minimal this fundamental quantum description can be. The simplest quantum ontology is that of the Everett or Many-Worlds interpretation, based on a vector in Hilbert space and a Hamiltonian. Typically one also relies on some classical structure, such as space and local configuration variables within it, which then gets promoted to an algebra of (...)
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  3. Beyond Falsifiability: Normal Science in a Multiverse.Sean M. Carroll - 2019 - In Richard Dawid, Radin Dardashti & Karim Thebault (eds.), Epistemology of Fundamental Physics: Why Trust a Theory? Cambridge, UK: Cambridge University Press.
    Cosmological models that invoke a multiverse - a collection of unobservable regions of space where conditions are very different from the region around us - are controversial, on the grounds that unobservable phenomena shouldn't play a crucial role in legitimate scientific theories. I argue that the way we evaluate multiverse models is precisely the same as the way we evaluate any other models, on the basis of abduction, Bayesian inference, and empirical success. There is no scientifically respectable way to do (...)
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  4. In What Sense Is the Early Universe Fine-Tuned?Sean M. Carroll - forthcoming - In Barry Loewer, Brad Weslake & Eric Winsberg (eds.), Time's Arrows and the Probability Structure of the World. Harvard University Press.
    It is commonplace in discussions of modern cosmology to assert that the early universe began in a special state. Conventionally, cosmologists characterize this fine-tuning in terms of the horizon and flatness problems. I argue that the fine-tuning is real, but these problems aren't the best way to think about it: causal disconnection of separated regions isn't the real problem, and flatness isn't a problem at all. Fine-tuning is better understood in terms of a measure on the space of trajectories: given (...)
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  5. Many Worlds, the Born Rule, and Self-Locating Uncertainty.Sean M. Carroll & Charles T. Sebens - 2014 - In Daniele C. Struppa & Jeffrey M. Tollaksen (eds.), Quantum Theory: A Two-Time Success Story. Springer. pp. 157-169.
    We provide a derivation of the Born Rule in the context of the Everett (Many-Worlds) approach to quantum mechanics. Our argument is based on the idea of self-locating uncertainty: in the period between the wave function branching via decoherence and an observer registering the outcome of the measurement, that observer can know the state of the universe precisely without knowing which branch they are on. We show that there is a uniquely rational way to apportion credence in such cases, which (...)
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  6. Why Boltzmann Brains Are Bad.Sean M. Carroll - forthcoming - In Shamik Dasgupta & Brad Weslake (eds.), Current Controversies in Philosophy of Science. Routledge.
    Some modern cosmological models predict the appearance of Boltzmann Brains: observers who randomly fluctuate out of a thermal bath rather than naturally evolving from a low-entropy Big Bang. A theory in which most observers are of the Boltzmann Brain type is generally thought to be unacceptable, although opinions differ. I argue that such theories are indeed unacceptable: the real problem is with fluctuations into observers who are locally identical to ordinary observers, and their existence cannot be swept under the rug (...)
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  7.  50
    Spacetime and Geometry: An Introduction to General Relativity.Sean M. Carroll - 2003 - San Francisco, USA: Pearson.
    Graduate-level textbook in general relativity.
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  8. Why Is There Something, Rather Than Nothing?Sean M. Carroll - forthcoming - In Eleanor Knox & Alastair Wilson (eds.), Routledge Companion to the Philosophy of Physics.
    It seems natural to ask why the universe exists at all. Modern physics suggests that the universe can exist all by itself as a self-contained system, without anything external to create or sustain it. But there might not be an absolute answer to why it exists. I argue that any attempt to account for the existence of something rather than nothing must ultimately bottom out in a set of brute facts; the universe simply is, without ultimate cause or explanation.
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  9.  39
    De Sitter Space Without Dynamical Quantum Fluctuations.Kimberly K. Boddy, Sean M. Carroll & Jason Pollack - 2016 - Foundations of Physics 46 (6):702-735.
    We argue that, under certain plausible assumptions, de Sitter space settles into a quiescent vacuum in which there are no dynamical quantum fluctuations. Such fluctuations require either an evolving microstate, or time-dependent histories of out-of-equilibrium recording devices, which we argue are absent in stationary states. For a massive scalar field in a fixed de Sitter background, the cosmic no-hair theorem implies that the state of the patch approaches the vacuum, where there are no fluctuations. We argue that an analogous conclusion (...)
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  10. Does the Universe Need God?Sean M. Carroll - 2012 - In J. B. Stump & Alan G. Padgett (eds.), The Blackwell Companion to Science and Christianity. Wiley-Blackwell. pp. 185-197.
    I ask whether what we know about the universe from modern physics and cosmology, including fine-tuning, provides compelling evidence for the existence of God, and answer largely in the negative.
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    Energy Non-Conservation in Quantum Mechanics.Sean M. Carroll & Jackie Lodman - manuscript
    We study the conservation of energy, or lack thereof, when measurements are performed in quantum mechanics. The expectation value of the Hamiltonian of a system can clearly change when wave functions collapse in accordance with the standard textbook (Copenhagen) treatment of quantum measurement, but one might imagine that the change in energy is compensated by the measuring apparatus or environment. We show that this is not true; the change in the energy of a state after measurement can be arbitrarily large, (...)
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    Quantum Mereology: Factorizing Hilbert Space Into Subsystems with Quasi-Classical Dynamics.Sean M. Carroll & Ashmeet Singh - manuscript
    We study the question of how to decompose Hilbert space into a preferred tensor-product factorization without any pre-existing structure other than a Hamiltonian operator, in particular the case of a bipartite decomposition into "system" and "environment." Such a decomposition can be defined by looking for subsystems that exhibit quasi-classical behavior. The correct decomposition is one in which pointer states of the system are relatively robust against environmental monitoring (their entanglement with the environment does not continually and dramatically increase) and remain (...)
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  13. Reality as a Vector in Hilbert Space.Sean M. Carroll -
    I defend the extremist position that the fundamental ontology of the world consists of a vector in Hilbert space evolving according to the Schrödinger equation. The laws of physics are determined solely by the energy eigenspectrum of the Hamiltonian. The structure of our observed world, including space and fields living within it, should arise as a higher-level emergent description. I sketch how this might come about, although much work remains to be done.
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  14. Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime.Sean M. Carroll - 2019 - New York, USA: Dutton.
    A non-technical introduction to quantum mechanics, the Everett interpretation, and the emergence of spacetime.
     
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  15. The Quantum Field Theory on Which the Everyday World Supervenes.Sean M. Carroll - manuscript
    Effective Field Theory (EFT) is the successful paradigm underlying modern theoretical physics, including the "Core Theory" of the Standard Model of particle physics plus Einstein's general relativity. I will argue that EFT grants us a unique insight: each EFT model comes with a built-in specification of its domain of applicability. Hence, once a model is tested within some domain (of energies and interaction strengths), we can be confident that it will continue to be accurate within that domain. Currently, the Core (...)
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