ward struyve | Rutgers, The State University of New Jersey (original) (raw)

Papers by ward struyve

The British Journal for the Philosophy of Science

There are two kinds of quantum fluctuations relevant to cosmology that we focus on in this articl... more There are two kinds of quantum fluctuations relevant to cosmology that we focus on in this article: those that form the seeds for structure formation in the early universe and those giving rise to Boltzmann brains in the late universe. First, structure formation requires slight inhomogeneities in the density of matter in the early universe, which then get amplified by the effect of gravity, leading to clumping of matter into stars and galaxies. According to inflation theory, quantum fluctuations form the seeds of these inhomogeneities. However, these quantum fluctuations are described by a quantum state which is homogeneous and isotropic, and this raises a problem, connected to the foundations of quantum theory, as the unitary evolution alone cannot break the symmetry of the quantum state. Second, Boltzmann brains are random agglomerates of particles that, by extreme coincidence, form functioning brains. Unlikely as these coincidences are, they seem to be predicted to occur in a quantum universe as vacuum fluctuations if the universe continues to exist for an infinite (or just very long) time, in fact to occur over and over, even forming the majority of all brains in the history of the universe. We provide a brief introduction to the Bohmian version of quantum theory and explain why in this version, Boltzmann brains, an undesirable kind of fluctuation, do not occur (or at least not often), while inhomogeneous seeds for structure formation, a desirable kind of fluctuation, do.

Scientific reports, Jan 15, 2017

Loop quantum gravity is believed to eliminate singularities such as the big bang and big crunch s... more Loop quantum gravity is believed to eliminate singularities such as the big bang and big crunch singularity. This belief is based on studies of so-called loop quantum cosmology which concerns symmetry-reduced models of quantum gravity. In this paper, the problem of singularities is analysed in the context of the Bohmian formulation of loop quantum cosmology. In this formulation there is an actual metric in addition to the wave function, which evolves stochastically (rather than deterministically as the case of the particle evolution in non-relativistic Bohmian mechanics). Thus a singularity occurs whenever this actual metric is singular. It is shown that in the loop quantum cosmology for a homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker space-time with arbitrary constant spatial curvature and cosmological constant, coupled to a massless homogeneous scalar field, a big bang or big crunch singularity is never obtained. This should be contrasted with the fact that in the ...

Eprint Arxiv Quant Ph 0506243, Jun 28, 2005

Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should... more Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should be able to distinguish between Standard Quantum Mechanics and Bohmian Mechanics. It is our aim to show that the claims made by Ghose, Golshani and Akhavan are unfounded.

Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should... more Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should be able to distinguish between Standard Quantum Mechanics and Bohmian Mechanics. It is our aim to show that the claims made by Ghose, Golshani and Akhavan are unfounded.

Metascience, 2010

While standard quantum theory is empirically extremely successful, it is a measurement theory, ma... more While standard quantum theory is empirically extremely successful, it is a measurement theory, making predictions about possible outcomes of measurements. Since the notion of measurement is rather ambiguous, it can not be regarded as a fundamental theory of nature. An alternative theory which is free of this problem and yet reproduces the predictions of standard quantum theory (at least when those are unambiguous) is the de Broglie-Bohm theory. This theory forms the subject of Riggs' book "Quantum Causality".

The Philosophy Of Cosmology, 2000

Astrophysics and Space Science Proceedings, 2016

There is a widespread belief that the classical small inhomogeneities which gave rise to all stru... more There is a widespread belief that the classical small inhomogeneities which gave rise to all structures in the Universe through gravitational instability originated from primordial quantum cosmological fluctuations. However, this transition from quantum to classical fluctuations is plagued with important conceptual issues, most of them related to the application of standard quantum theory to the Universe as a whole. In this paper, we show how these issues can easily be overcome in the framework of the de Broglie-Bohm quantum theory. This theory is an alternative to standard quantum theory that provides an objective description of physical reality, where rather ambiguous notions of measurement or observer play no fundamental role, and which can hence be applied to the Universe as a whole. In addition, it allows for a simple and unambiguous characterization of the classical limit.

Journal of Physics A: Mathematical and Theoretical, 2016

Richard Healey's talk was divided in two parts. In the first part he argued that we are not justi... more Richard Healey's talk was divided in two parts. In the first part he argued that we are not justified in believing that localized gauge potential properties are there, but we are in believing that holonomy properties are. In the second part, he conceded that the holonomy interpretation offers an incomplete local and causal account, but he maintained that the onus is on QM.

Quantum Studies: Mathematics and Foundations, 2015

The version of Bohmian mechanics in relativistic space-time that works best, the hypersurface Boh... more The version of Bohmian mechanics in relativistic space-time that works best, the hypersurface Bohm-Dirac model, assumes a preferred foliation of space-time into spacelike hypersurfaces (called the time foliation) as given. We consider here a degenerate case in which, contrary to the usual definition of a foliation, several leaves of the time foliation have a region in common. That is, if we think of the time foliation as a 1-parameter family of hypersurfaces, with the hypersurfaces moving towards the future as we increase the parameter, a degenerate time foliation is one for which a part of the hypersurface does not move as we increase the parameter. We show that the hypersurface Bohm-Dirac model still works in this situation; that is, we show that a Bohm-type law of motion can still be defined, and that the appropriate |ψ| 2 distribution is still equivariant with respect to this law.

Physical Review D, 2015

We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Rober... more We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Robertson-Walker model and investigate the question whether or not there are singularities, in the sense that the universe reaches zero volume. We find that for generic wave functions (i.e., nonclassical wave functions), there is a non-zero probability for a trajectory to be non-singular. This should be contrasted to the consistent histories approach for which it was recently shown by Craig and Singh that there is always a singularity. This result illustrates that the question of singularities depends much on which version of quantum theory one adopts. This was already pointed out by Pinto-Neto et al., albeit with a different Bohmian approach. Our current Bohmian approach agrees with the consistent histories approach by Craig and Singh for single-time histories, unlike the one studied earlier by Pinto-Neto et al. Although the trajectories are usually different in the two Bohmian approach, their qualitative behavior is the same for generic wave functions.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2007

We present a way to construct a pilot-wave model for quantum electrodynamics. The idea is to intr... more We present a way to construct a pilot-wave model for quantum electrodynamics. The idea is to introduce beables corresponding only to the bosonic degrees of freedom and not to the fermionic degrees of freedom of the quantum state. We show that this is sufficient to reproduce the quantum predictions. The beables will be field beables corresponding to the electromagnetic field and they will be introduced in a similar way to that of Bohm's model for the free electromagnetic field. Our approach is analogous to the situation in non-relativistic quantum theory, where Bell treated spin not as a beable but only as a property of the wavefunction. After presenting this model we also discuss a simple way for introducing additional beables that represent the fermionic degrees of freedom.

Journal of Physics A: Mathematical and Theoretical, 2014

Non-relativistic de Broglie-Bohm theory describes particles moving under the guidance of the wave... more Non-relativistic de Broglie-Bohm theory describes particles moving under the guidance of the wave function. In de Broglie's original formulation, the particle dynamics is given by a first-order differential equation. In Bohm's reformulation, it is given by Newton's law of motion with an extra potential that depends on the wave function-the quantum potential-together with a constraint on the possible velocities. It was recently argued, mainly by numerical simulations, that relaxing this velocity constraint leads to a physically untenable theory. We provide further evidence for this by showing that for various wave functions the particles tend to escape the wave packet. In particular, we show that for a central classical potential and bound energy eigenstates the particle motion is often unbounded. *

Annals of Physics, 2014

It was recently pointed out (and demonstrated experimentally) by Lundeen et al. that the wave fun... more It was recently pointed out (and demonstrated experimentally) by Lundeen et al. that the wave function of a particle (more precisely, the wave function possessed by each member of an ensemble of identically-prepared particles) can be "directly measured" using weak measurement. Here it is shown that if this same technique is applied, with appropriate post-selection, to one particle from a (perhaps entangled) multi-particle system, the result is precisely the so-called "conditional wave function" of Bohmian mechanics. Thus, a plausibly operationalist method for defining the wave function of a quantum mechanical sub-system corresponds to the natural definition of a subsystem wave function which Bohmian mechanics (uniquely) makes possible. Similarly, a weakmeasurement-based procedure for directly measuring a sub-system's density matrix should yield, under appropriate circumstances, the Bohmian "conditional density matrix" as opposed to the standard reduced density matrix. Experimental arrangements to demonstrate this behavior -and also thereby reveal the non-local dependence of sub-system state functions on distant interventions -are suggested and discussed.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013

In relativistic space-time, Bohmian theories can be formulated by introducing a privileged foliat... more In relativistic space-time, Bohmian theories can be formulated by introducing a privileged foliation of space-time. The introduction of such a foliation -as extra absolute space-time structure -would seem to imply a clear violation of Lorentz invariance, and thus a conflict with fundamental relativity. Here, we consider the possibility that, instead of positing it as extra structure, the required foliation could be covariantly determined by the wave function. We argue that this allows for the formulation of Bohmian theories that seem to qualify as fundamentally Lorentz invariant. We conclude with some discussion of whether or not they might also qualify as fundamentally relativistic.

Physical Review D, 2014

In a previous work we have exhibited a clear description of the quantum-to-classical transition o... more In a previous work we have exhibited a clear description of the quantum-to-classical transition of cosmological quantum fluctuations in the inflationary scenario using the de Broglie-Bohm quantum theory. These fluctuations are believed to seed the small inhomogeneities, which are then responsible for the formation of large scale structures. In this work we show that using the de Broglie-Bohm theory it is also possible to describe the quantum-to-classical transition of primordial perturbations which takes place around a bouncing phase, even if the latter is caused by quantum effects due to the quantization of the background geometry.

New Journal of Physics, 2010

The de Broglie-Bohm theory is about non-relativistic point-particles that move deterministically ... more The de Broglie-Bohm theory is about non-relativistic point-particles that move deterministically along trajectories. The theory reproduces the predictions of standard quantum theory, given that the distribution of particles over an ensemble of systems, all described by the same wavefunction ψ, equals the quantum equilibrium distribution |ψ| 2 . Numerical simulations by Valentini and Westman have illustrated that non-equilibrium particle distributions may relax to quantum equilibrium after some time. Here we consider non-equilibrium distributions and their relaxation properties for a particular class of trajectory theories, first studied in detail by Deotto and Ghirardi, that are empirically equivalent to the de Broglie-Bohm theory in quantum equilibrium. For the examples of such theories that we consider, we find a speed-up of the relaxation compared to the ordinary de Broglie-Bohm theory. Hence non-equilibrium predictions that depend strongly on relaxation properties, such as those studied recently by Valentini, may vary for different trajectory theories. As such these theories might be experimentally distinguishable.

Metascience, 2010

While standard quantum theory is empirically extremely successful, it is a measurement theory, ma... more While standard quantum theory is empirically extremely successful, it is a measurement theory, making predictions about possible outcomes of measurements. Since the notion of measurement is rather ambiguous, it can not be regarded as a fundamental theory of nature. An alternative theory which is free of this problem and yet reproduces the predictions of standard quantum theory (at least when those are unambiguous) is the de Broglie-Bohm theory. This theory forms the subject of Riggs' book "Quantum Causality".

The British Journal for the Philosophy of Science

There are two kinds of quantum fluctuations relevant to cosmology that we focus on in this articl... more There are two kinds of quantum fluctuations relevant to cosmology that we focus on in this article: those that form the seeds for structure formation in the early universe and those giving rise to Boltzmann brains in the late universe. First, structure formation requires slight inhomogeneities in the density of matter in the early universe, which then get amplified by the effect of gravity, leading to clumping of matter into stars and galaxies. According to inflation theory, quantum fluctuations form the seeds of these inhomogeneities. However, these quantum fluctuations are described by a quantum state which is homogeneous and isotropic, and this raises a problem, connected to the foundations of quantum theory, as the unitary evolution alone cannot break the symmetry of the quantum state. Second, Boltzmann brains are random agglomerates of particles that, by extreme coincidence, form functioning brains. Unlikely as these coincidences are, they seem to be predicted to occur in a quantum universe as vacuum fluctuations if the universe continues to exist for an infinite (or just very long) time, in fact to occur over and over, even forming the majority of all brains in the history of the universe. We provide a brief introduction to the Bohmian version of quantum theory and explain why in this version, Boltzmann brains, an undesirable kind of fluctuation, do not occur (or at least not often), while inhomogeneous seeds for structure formation, a desirable kind of fluctuation, do.

Scientific reports, Jan 15, 2017

Loop quantum gravity is believed to eliminate singularities such as the big bang and big crunch s... more Loop quantum gravity is believed to eliminate singularities such as the big bang and big crunch singularity. This belief is based on studies of so-called loop quantum cosmology which concerns symmetry-reduced models of quantum gravity. In this paper, the problem of singularities is analysed in the context of the Bohmian formulation of loop quantum cosmology. In this formulation there is an actual metric in addition to the wave function, which evolves stochastically (rather than deterministically as the case of the particle evolution in non-relativistic Bohmian mechanics). Thus a singularity occurs whenever this actual metric is singular. It is shown that in the loop quantum cosmology for a homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker space-time with arbitrary constant spatial curvature and cosmological constant, coupled to a massless homogeneous scalar field, a big bang or big crunch singularity is never obtained. This should be contrasted with the fact that in the ...

Eprint Arxiv Quant Ph 0506243, Jun 28, 2005

Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should... more Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should be able to distinguish between Standard Quantum Mechanics and Bohmian Mechanics. It is our aim to show that the claims made by Ghose, Golshani and Akhavan are unfounded.

Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should... more Recently Ghose [1-3] and Golshani and Akhavan [4-6] claimed to have found experiments that should be able to distinguish between Standard Quantum Mechanics and Bohmian Mechanics. It is our aim to show that the claims made by Ghose, Golshani and Akhavan are unfounded.

Metascience, 2010

While standard quantum theory is empirically extremely successful, it is a measurement theory, ma... more While standard quantum theory is empirically extremely successful, it is a measurement theory, making predictions about possible outcomes of measurements. Since the notion of measurement is rather ambiguous, it can not be regarded as a fundamental theory of nature. An alternative theory which is free of this problem and yet reproduces the predictions of standard quantum theory (at least when those are unambiguous) is the de Broglie-Bohm theory. This theory forms the subject of Riggs' book "Quantum Causality".

The Philosophy Of Cosmology, 2000

Astrophysics and Space Science Proceedings, 2016

There is a widespread belief that the classical small inhomogeneities which gave rise to all stru... more There is a widespread belief that the classical small inhomogeneities which gave rise to all structures in the Universe through gravitational instability originated from primordial quantum cosmological fluctuations. However, this transition from quantum to classical fluctuations is plagued with important conceptual issues, most of them related to the application of standard quantum theory to the Universe as a whole. In this paper, we show how these issues can easily be overcome in the framework of the de Broglie-Bohm quantum theory. This theory is an alternative to standard quantum theory that provides an objective description of physical reality, where rather ambiguous notions of measurement or observer play no fundamental role, and which can hence be applied to the Universe as a whole. In addition, it allows for a simple and unambiguous characterization of the classical limit.

Journal of Physics A: Mathematical and Theoretical, 2016

Richard Healey's talk was divided in two parts. In the first part he argued that we are not justi... more Richard Healey's talk was divided in two parts. In the first part he argued that we are not justified in believing that localized gauge potential properties are there, but we are in believing that holonomy properties are. In the second part, he conceded that the holonomy interpretation offers an incomplete local and causal account, but he maintained that the onus is on QM.

Quantum Studies: Mathematics and Foundations, 2015

The version of Bohmian mechanics in relativistic space-time that works best, the hypersurface Boh... more The version of Bohmian mechanics in relativistic space-time that works best, the hypersurface Bohm-Dirac model, assumes a preferred foliation of space-time into spacelike hypersurfaces (called the time foliation) as given. We consider here a degenerate case in which, contrary to the usual definition of a foliation, several leaves of the time foliation have a region in common. That is, if we think of the time foliation as a 1-parameter family of hypersurfaces, with the hypersurfaces moving towards the future as we increase the parameter, a degenerate time foliation is one for which a part of the hypersurface does not move as we increase the parameter. We show that the hypersurface Bohm-Dirac model still works in this situation; that is, we show that a Bohm-type law of motion can still be defined, and that the appropriate |ψ| 2 distribution is still equivariant with respect to this law.

Physical Review D, 2015

We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Rober... more We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Robertson-Walker model and investigate the question whether or not there are singularities, in the sense that the universe reaches zero volume. We find that for generic wave functions (i.e., nonclassical wave functions), there is a non-zero probability for a trajectory to be non-singular. This should be contrasted to the consistent histories approach for which it was recently shown by Craig and Singh that there is always a singularity. This result illustrates that the question of singularities depends much on which version of quantum theory one adopts. This was already pointed out by Pinto-Neto et al., albeit with a different Bohmian approach. Our current Bohmian approach agrees with the consistent histories approach by Craig and Singh for single-time histories, unlike the one studied earlier by Pinto-Neto et al. Although the trajectories are usually different in the two Bohmian approach, their qualitative behavior is the same for generic wave functions.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2007

We present a way to construct a pilot-wave model for quantum electrodynamics. The idea is to intr... more We present a way to construct a pilot-wave model for quantum electrodynamics. The idea is to introduce beables corresponding only to the bosonic degrees of freedom and not to the fermionic degrees of freedom of the quantum state. We show that this is sufficient to reproduce the quantum predictions. The beables will be field beables corresponding to the electromagnetic field and they will be introduced in a similar way to that of Bohm's model for the free electromagnetic field. Our approach is analogous to the situation in non-relativistic quantum theory, where Bell treated spin not as a beable but only as a property of the wavefunction. After presenting this model we also discuss a simple way for introducing additional beables that represent the fermionic degrees of freedom.

Journal of Physics A: Mathematical and Theoretical, 2014

Non-relativistic de Broglie-Bohm theory describes particles moving under the guidance of the wave... more Non-relativistic de Broglie-Bohm theory describes particles moving under the guidance of the wave function. In de Broglie's original formulation, the particle dynamics is given by a first-order differential equation. In Bohm's reformulation, it is given by Newton's law of motion with an extra potential that depends on the wave function-the quantum potential-together with a constraint on the possible velocities. It was recently argued, mainly by numerical simulations, that relaxing this velocity constraint leads to a physically untenable theory. We provide further evidence for this by showing that for various wave functions the particles tend to escape the wave packet. In particular, we show that for a central classical potential and bound energy eigenstates the particle motion is often unbounded. *

Annals of Physics, 2014

It was recently pointed out (and demonstrated experimentally) by Lundeen et al. that the wave fun... more It was recently pointed out (and demonstrated experimentally) by Lundeen et al. that the wave function of a particle (more precisely, the wave function possessed by each member of an ensemble of identically-prepared particles) can be "directly measured" using weak measurement. Here it is shown that if this same technique is applied, with appropriate post-selection, to one particle from a (perhaps entangled) multi-particle system, the result is precisely the so-called "conditional wave function" of Bohmian mechanics. Thus, a plausibly operationalist method for defining the wave function of a quantum mechanical sub-system corresponds to the natural definition of a subsystem wave function which Bohmian mechanics (uniquely) makes possible. Similarly, a weakmeasurement-based procedure for directly measuring a sub-system's density matrix should yield, under appropriate circumstances, the Bohmian "conditional density matrix" as opposed to the standard reduced density matrix. Experimental arrangements to demonstrate this behavior -and also thereby reveal the non-local dependence of sub-system state functions on distant interventions -are suggested and discussed.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013

In relativistic space-time, Bohmian theories can be formulated by introducing a privileged foliat... more In relativistic space-time, Bohmian theories can be formulated by introducing a privileged foliation of space-time. The introduction of such a foliation -as extra absolute space-time structure -would seem to imply a clear violation of Lorentz invariance, and thus a conflict with fundamental relativity. Here, we consider the possibility that, instead of positing it as extra structure, the required foliation could be covariantly determined by the wave function. We argue that this allows for the formulation of Bohmian theories that seem to qualify as fundamentally Lorentz invariant. We conclude with some discussion of whether or not they might also qualify as fundamentally relativistic.

Physical Review D, 2014

In a previous work we have exhibited a clear description of the quantum-to-classical transition o... more In a previous work we have exhibited a clear description of the quantum-to-classical transition of cosmological quantum fluctuations in the inflationary scenario using the de Broglie-Bohm quantum theory. These fluctuations are believed to seed the small inhomogeneities, which are then responsible for the formation of large scale structures. In this work we show that using the de Broglie-Bohm theory it is also possible to describe the quantum-to-classical transition of primordial perturbations which takes place around a bouncing phase, even if the latter is caused by quantum effects due to the quantization of the background geometry.

New Journal of Physics, 2010

The de Broglie-Bohm theory is about non-relativistic point-particles that move deterministically ... more The de Broglie-Bohm theory is about non-relativistic point-particles that move deterministically along trajectories. The theory reproduces the predictions of standard quantum theory, given that the distribution of particles over an ensemble of systems, all described by the same wavefunction ψ, equals the quantum equilibrium distribution |ψ| 2 . Numerical simulations by Valentini and Westman have illustrated that non-equilibrium particle distributions may relax to quantum equilibrium after some time. Here we consider non-equilibrium distributions and their relaxation properties for a particular class of trajectory theories, first studied in detail by Deotto and Ghirardi, that are empirically equivalent to the de Broglie-Bohm theory in quantum equilibrium. For the examples of such theories that we consider, we find a speed-up of the relaxation compared to the ordinary de Broglie-Bohm theory. Hence non-equilibrium predictions that depend strongly on relaxation properties, such as those studied recently by Valentini, may vary for different trajectory theories. As such these theories might be experimentally distinguishable.

Metascience, 2010

While standard quantum theory is empirically extremely successful, it is a measurement theory, ma... more While standard quantum theory is empirically extremely successful, it is a measurement theory, making predictions about possible outcomes of measurements. Since the notion of measurement is rather ambiguous, it can not be regarded as a fundamental theory of nature. An alternative theory which is free of this problem and yet reproduces the predictions of standard quantum theory (at least when those are unambiguous) is the de Broglie-Bohm theory. This theory forms the subject of Riggs' book "Quantum Causality".