Publications (91)123.76 Total impact
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ABSTRACT: Crystals, as quantum objects typically much larger than their lattice spacing, are counterexamples to a frequent prejudice that quantum effects should not be pronounced at macroscopic distances. We propose that the Einstein theory of gravity only describes a fluid phase and that a phase transition of crystallization can occur under extreme conditions such as those inside the black hole. Such a crystal phase with lattice spacing of the order of the Planck length offers a natural mechanism for pronounced quantumgravity effects at distances much larger than the Planck length. A resolution of the black hole information paradox is proposed, according to which all information is stored in a crystalphase remnant with size and mass much above the Planck scale.  [Show abstract] [Hide abstract]
ABSTRACT: We propose a new nonholographic formulation of AdS/CFT correspondence, according to which quantum gravity on AdS and its dual nongravitational field theory both live in the same number D of dimensions. The field theory, however, appears (D1)dimensional because the interactions do not propagate in one of the dimensions. The Ddimensional action for the field theory can be identified with the sum over (D1)dimensional actions with all possible values $\Lambda$ of the UV cutoff, so that the extra hidden dimension can be identified with $\Lambda$. Since there are no interactions in the extra dimension, most of the practical results of standard holographic AdS/CFT correspondence transcribe to nonholographic AdS/CFT without any changes. However, the implications on blackhole entropy change significantly. The maximal blackhole entropy now scales with volume, while the BekensteinHawking entropy is interpreted as the minimal possible blackhole entropy. In this way, the nonholographic AdS/CFT correspondence offers a simple resolution of the blackhole information paradox, consistent with a recently proposed gravitational crystal.  [Show abstract] [Hide abstract]
ABSTRACT: The possibility of quantum interference of a composite object with many internal degrees of freedom is studied, such that the internal degrees play a role of an internal environment. In particular, if the internal degrees have a capacity for an irreversible record of whichpath information, then the internalenvironment induced decoherence prevents external experimentalists from observing interference. Interference can be observed only if the interfering object is sufficiently isolated from the external environment, so that the object cannot record whichpath information. Extrapolation to a hypothetical interference experiment with a conscious object implies that being a Schrödinger cat would be like being an ordinary cat living in a box without any information about the world external to the box.  [Show abstract] [Hide abstract]
ABSTRACT: Crystals, as quantum objects typically much larger than their lattice spacing, are a counterexample to a frequent prejudice that quantum effects should not be pronounced at macroscopic distances. We propose that the Einstein theory of gravity only describes a fluid phase and that a phase transition of crystallization can occur under extreme conditions such as those inside the black hole. Such a crystal phase with lattice spacing of the order of the Planck length offers a natural mechanism for pronounced quantumgravity effects at distances much larger than the Planck length. A resolution of the blackhole information paradox is proposed, according to which all information is stored in a crystalphase remnant with size and mass much above the Planck scale.  [Show abstract] [Hide abstract]
ABSTRACT: An argument by Banks, Susskind and Peskin (BSP), according to which violation of unitarity would violate either locality or energymomentum conservation, is widely believed to be a strong argument against nonunitarity of Hawking radiation. We find that the whole BSP argument rests on the crucial assumption that the Hamiltonian is not highly degenerate, and point out that this assumption is not satisfied for systems with many degrees of freedom. Using Lindblad equation, we show that high degeneracy of the Hamiltonian allows local nonunitary evolution without violating energymomentum conservation. Moreover, since energymomentum is the source of gravity, we argue that energymomentum is necessarily conserved for a large class of nonunitary systems with gravity. Finally, we explicitly calculate the Lindblad operators for nonunitary Hawking radiation and show that they conserve energymomentum.  [Show abstract] [Hide abstract]
ABSTRACT: An argument by Banks, Susskind and Peskin (BSP), according to which violation of unitarity would violate either locality or energymomentum conservation, is widely believed to be a strong argument against nonunitarity of Hawking radiation. We find that the whole BSP argument rests on the crucial assumption that the Hamiltonian is not highly degenerate, and point out that this assumption is wrong. Using Lindblad equation, we show that high degeneracy of the Hamiltonian allows local nonunitary evolution without violating energymomentum conservation. Moreover, since energymomentum is the source of gravity, we argue that energymomentum is necessarily conserved for a large class of nonunitary systems with gravity. Finally, we explicitly calculate the Lindblad operators for nonunitary Hawking radiation and show that they conserve energymomentum.  [Show abstract] [Hide abstract]
ABSTRACT: In the usual formulation of quantum theory, time is a global classical evolution parameter, not a local quantum observable. On the other hand, both canonical quantum gravity (which lacks fundamental timeevolution parameter) and the principle of spacetime covariance (which insists that time should be treated on an equal footing with space) suggest that quantum theory should be slightly reformulated, in a manner that promotes time to a local observable. Such a reformulated quantum theory is unitary in a more general sense than the usual quantum theory. In particular, this promotes the nonunitary Hawking radiation to a unitary phenomenon, which avoids the blackhole information paradox.  [Show abstract] [Hide abstract]
ABSTRACT: In the literature one often finds the claim that there is no such thing as an energymomentum tensor for the gravitational field, and consequently, that the total energymomentum conservation can only be defined in terms of a gravitational energymomentum pseudotensor. I make a trivial observation that such a conclusion can be avoided by relaxing the assumption that gravitational energymomentum tensor should only depend on first derivatives of the metric. With such a relaxation, the Einstein equation directly leads to the result that gravitational energymomentum tensor is essentially the Einstein tensor.  [Show abstract] [Hide abstract]
ABSTRACT: In the usual formulation of quantum theory, time is a global classical evolution parameter, not a local quantum observable. On the other hand, both canonical quantum gravity (which lacks fundamental timeevolution parameter) and the principle of spacetime covariance (which insists that time should be treated on an equal footing with space) suggest that quantum theory should be slightly reformulated, in a manner that promotes time to a local observable. Such a reformulated quantum theory is unitary in a more general sense than the usual quantum theory. In particular, this promotes the nonunitary Hawking radiation to a unitary phenomenon, which avoids the blackhole information paradox.  [Show abstract] [Hide abstract]
ABSTRACT: The possibility of quantum interference of a composite object with many internal degrees of freedom is studied, such that the internal degrees play a role of an internal environment. In particular, if the internal degrees have a capacity for an irreversible record of whichpath information, then the internalenvironment induced decoherence prevents external experimentalists from observing interference. Interference can be observed only if the interfering object is sufficiently isolated from the external environment, so that the object cannot record whichpath information. Extrapolation to a hypothetical interference experiment with a conscious object implies that being a Schrodinger cat would be like being an ordinary cat living in a box without any information about the world external to the box.  [Show abstract] [Hide abstract]
ABSTRACT: We present evidence that quantum Zeno effect, otherwise working only for microscopic systems, may also work for large black holes (BH's). The expectation that a BH geometry should behave classically at time intervals larger than the Planck time tPltPl indicates that the quantum process of measurement of classical degrees of freedom takes time of the order of tPltPl. Since BH has only a few classical degrees of freedom, such a fast measurement makes a macroscopic BH strongly susceptible to the quantum Zeno effect, which repeatedly collapses the quantum state to the initial one, the state before the creation of Hawking quanta. By this mechanism, Hawking radiation from a BH of mass M is strongly suppressed by a factor of the order of mPl/MmPl/M.  [Show abstract] [Hide abstract]
ABSTRACT: In the textbook proofs of the Lorentz covariance of the Dirac equation, one treats the wave function as a spinor and gamma matrices as scalars, leading to a quite complicated formalism with several pedagogic drawbacks. As an alternative, I propose to teach the Dirac equation and its Lorentz covariance by using a much simpler, but physically equivalent formalism, in which these drawbacks do not appear. In this alternative formalism, the wave function transforms as a scalar and gamma matrices as components of a vector, such that the standard physically relevant bilinear combinations do not change their transformation properties. The alternative formalism allows also a natural construction of some additional nonstandard bilinear combinations with welldefined transformation properties.  [Show abstract] [Hide abstract]
ABSTRACT: We present evidence that quantum Zeno effect, otherwise working only for microscopic systems, may also work for large black holes (BH's). The expectation that a BH geometry should behave classically at time intervals larger than the Planck time t_Pl indicates that the quantum process of measurement of classical degrees of freedom takes time of the order of t_Pl. Since BH has only a few classical degrees of freedom, such a fast measurement makes a macroscopic BH strongly susceptible to the quantum Zeno effect, which repeatedly collapses the quantum state to the initial one, the state before the creation of Hawking quanta. By this mechanism, Hawking radiation from a BH of mass M is strongly suppressed by a factor of the order of m_Pl/M.  [Show abstract] [Hide abstract]
ABSTRACT: In the textbook proofs of Lorentz covariance of the Dirac equation, one treats the wave function as a spinor and gamma matrices as scalars, leading to a quite complicated formalism with several pedagogic drawbacks. As an alternative, I propose to teach Dirac equation and its Lorentz covariance by using a much simpler, but physically equivalent formalism, in which these drawbacks do not appear. In this alternative formalism, the wave function transforms as a scalar and gamma matrices as components of a vector, such that the standard physically relevant bilinear combinations do not change their transformation properties. The alternative formalism allows also a natural construction of some additional nonstandard bilinear combinations with welldefined transformation properties.  [Show abstract] [Hide abstract]
ABSTRACT: Bohmian mechanics can be generalized to a relativistic theory without preferred foliation, with a price of introducing a puzzling concept of spacetime probability conserved in a scalar time. We explain how analogous concept appears naturally in classical statistical mechanics of relativistic particles, with scalar time being identified with the proper time along particle trajectories. The conceptual understanding of relativistic Bohmian mechanics is significantly enriched by this classical insight. In particular, the analogy between classical and Bohmian mechanics suggests the interpretation of Bohmian scalar time as a quantum proper time different from the classical one, the two being related by a nonlocal scale factor calculated from the wave function. In many cases of practical interest, including the macroscopic measuring apparatus, the fundamental spacetime probability explains the more familiar space probability as an emergent approximate description. Requiring that the quantum proper time in the classical limit should reduce to the classical proper time, we propose that only massive particles have Bohmian trajectories. An analysis of the macroscopic measuring apparatus made up of massive particles restores agreement with the predictions of standard quantum theory. 
Article: Solipsistic hidden variables
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ABSTRACT: We argue that it is logically possible to have a sort of both reality and locality in quantum mechanics. To demonstrate this, we construct a new quantitative model of hidden variables (HV’s), dubbed solipsistic HV’s, that interpolates between the orthodox noHV interpretation and nonlocal Bohmian interpretation. In this model, the deterministic pointparticle trajectories are associated only with the essential degrees of freedom of the observer, and not with the observed objects. In contrast with Bohmian HV’s, nonlocality in solipsistic HV’s can be substantially reduced down to microscopic distances inside the observer. Even if such HV’s may look philosophically unappealing to many, the mere fact that they are logically possible deserves attention. 
Article: Closed Timelike Curves, Superluminal Signals, and “Free Will” in Universal Quantum Mechanics
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ABSTRACT: We explore some implications of the hypothesis that quantum mechanics (QM) is universal, i.e., that QM does not merely describe information accessible to observers, but that it also describes the observers themselves. From that point of view, “free will” (FW)–the ability of experimentalists to make free choices of initial conditions–is merely an illusion. As a consequence, by entangling a part of brain (responsible for the illusion of FW) with a distant particle, one may create nonlocal correlations that can be interpreted as superluminal signals. In addition, if FW is an illusion, then QM on a closed timelike curve can be made consistent even without the Deutch nonlinear consistency constraint.  [Show abstract] [Hide abstract]
ABSTRACT: It is often argued that measurable predictions of Bohmian mechanics cannot be distinguished from those of a theory with arbitrarily modified particle velocities satisfying the same equivariance equation. By considering the wave function of a closed system in a state with definite total energy, we argue that a distinction in measurable predictions is possible. Even though such a wave function is timeindependent, the conditional wave function for a subsystem depends on time through the timedependent particle trajectories not belonging to the subsystem. If these trajectories can be approximated by classical trajectories, then the conditional wave function can be approximated by a wave function which satisfies Schrodinger equation in a classical timedependent potential, which is in good agreement with observations. However, such an approximation cannot be justified for particle velocities significantly deviating from the Bohmian ones, implying that Bohmian velocities are observationally preferred.  [Show abstract] [Hide abstract]
ABSTRACT: In 1930, Einstein argued against the consistency of the time–energy uncertainty relation by discussing a thought experiment involving a measurement of the mass of the box which emitted a photon. Bohr seemingly prevailed over Einstein by arguing that Einstein's own general theory of relativity saves the consistency of quantum mechanics. We revisit this thought experiment from a modern point of view at a level suitable for an undergraduate readership and find that neither Einstein nor Bohr was correct. Instead, this thought experiment should be thought of as an early example of a system demonstrating nonlocal 'EPR' quantum correlations, five years before the famous Einstein–Podolsky–Rosen paper.  [Show abstract] [Hide abstract]
ABSTRACT: In classical relativistic mechanics, a "preferred" proper direction in spacetime for each particle is determined by the direction of its 4momentum. Analogously, for each quantum particle we find a local direction uniquely determined by the manyparticle wave function, which for each particle defines the proper foliation of spacetime. This can be used to formulate a relativisticcovariant version of Bohmian mechanics, with equivariant probability density on proper hypersurfaces.
Publication Stats
865  Citations  
123.76  Total Impact Points  
Top Journals
Institutions

19982015

Ruđer Bošković Institute
Zagrabia, Grad Zagreb, Croatia


20032005

Ruder Boskovic Institute
Zagrabia, Grad Zagreb, Croatia


20002005

Institute of Physics, Zagreb
Zagrabia, Grad Zagreb, Croatia
