46 research outputs found
Space-time in light of Karolyhazy uncertainty relation
General relativity and quantum mechanics provide a natural explanation for
the existence of dark energy with its observed value and predict its dynamics.
Dark energy proves to be necessary for the existence of space-time itself and
determines the rate of its stability.Comment: 5 pages, Two misprints are correcte
Random versus holographic fluctuations of the background metric. II. Note on the dark energies arising due to microstructure of space-time
Over the last few years a certain class of dark-energy models decaying
inversely proportional to the square of the horizon distance emerged on the
basis either of Heisenberg uncertainty relations or of the uncertainty relation
between the four-volume and the cosmological constant. The very nature of these
dark energies is understood to be the same, namely it is the energy of
background space/metric fluctuations. Putting together these uncertainty
relations one finds that the model of random fluctuations of the background
metric is favored over the holographic one.Comment: 3 page
Gravitationally-Induced Quantum Superpopsition Reduction with Large Extra Dimensions
A gravity-driven mechanism (``objective reduction'') proposed to explain
quantum state reduction is analyzed in light of the possible existence of large
extra dimensions in the ADD scenario. By calculating order-of-magnitude
estimates for nucleon superpositions, it is shown that if the mechanism at
question is correct, constraints may be placed on the number and size of extra
dimensions. Hence, measurement of superposition collapse times ({\it e.g.}
through diffraction or reflection experiments) could represent a new probe of
extra dimensions. The influence of a time-dependent gravitational constant on
the gravity-driven collapse scheme with and without the presence of extra
dimensions is also discussed.Comment: 22 pp; 1 postscript figure Expanded version of previous submission To
appear in Phys Rev
Testing Gravity-Driven Collapse of the Wavefunction via Cosmogenic Neutrinos
It is pointed out that the Diosi-Penrose ansatz for gravity-induced quantum
state reduction can be tested by observing oscillations in the flavor ratios of
neutrinos originated at cosmological distances. Since such a test would be
almost free of environmental decoherence, testing the ansatz by means of a next
generation neutrino detector such as IceCube would be much cleaner than by
experiments proposed so far involving superpositions of macroscopic systems.
The proposed microscopic test would also examine the universality of
superposition principle at unprecedented cosmological scales.Comment: 4 pages; RevTeX4; Essentially the version published in PR
Tests of Basic Quantum Mechanics in Oscillation Experiments
According to standard quantum theory, the time evolution operator of a
quantum system is independent of the state of the system. One can, however,
consider systems in which this is not the case: the evolution operator may
depend on the density operator itself. The presence of such modifications of
quantum theory can be tested in long baseline oscillation experiments.Comment: 8 pages, LaTeX; no macros neede
Decoherence of Macroscopic Closed Systems within Newtonian Quantum Gravity
A theory recently proposed by the author aims to explain decoherence and the
thermodynamical behaviour of closed systems within a conservative, unitary,
framework for quantum gravity by assuming that the operators tied to the
gravitational degrees of freedom are unobservable and equating physical entropy
with matter-gravity entanglement entropy. Here we obtain preliminary results on
the extent of decoherence this theory predicts. We treat first a static state
which, if one were to ignore quantum gravitational effects, would be a quantum
superposition of two spatially displaced states of a single classically well
describable ball of uniform mass density in empty space. Estimating the quantum
gravitational effects on this system within a simple Newtonian approximation,
we obtain formulae which predict e.g. that as long as the mass of the ball is
considerably larger than the Planck mass, such a would-be-coherent static
superposition will actually be decohered whenever the separation of the centres
of mass of the two ball-states excedes a small fraction (which decreases as the
mass of the ball increases) of the ball radius. We then obtain a formula for
the quantum gravitational correction to the would-be-pure density matrix of a
non-relativistic many-body Schroedinger wave function and argue that this
formula predicts decoherence between configurations which differ (at least) in
the "relocation" of a cluster of particles of Planck mass. We estimate the
entropy of some simple model closed systems, finding a tendency for it to
increase with "matter-clumping" suggestive of a link with existing
phenomenological discussions of cosmological entropy increase.Comment: 11 pages, plain TeX, no figures. Accepted for publication as a
"Letter to the Editor" in "Classical and Quantum Gravity
Quantum Superposition of Massive Objects and Collapse Models
We analyze the requirements to test some of the most paradigmatic collapse
models with a protocol that prepares quantum superpositions of massive objects.
This consists of coherently expanding the wave function of a
ground-state-cooled mechanical resonator, performing a squared position
measurement that acts as a double slit, and observing interference after
further evolution. The analysis is performed in a general framework and takes
into account only unavoidable sources of decoherence: blackbody radiation and
scattering of environmental particles. We also discuss the limitations imposed
by the experimental implementation of this protocol using cavity quantum
optomechanics with levitating dielectric nanospheres.Comment: 19 pages, 17 figure
Prima Facie Questions in Quantum Gravity
The long history of the study of quantum gravity has thrown up a complex web
of ideas and approaches. The aim of this article is to unravel this web a
little by analysing some of the {\em prima facie\/} questions that can be asked
of almost any approach to quantum gravity and whose answers assist in
classifying the different schemes. Particular emphasis is placed on (i) the
role of background conceptual and technical structure; (ii) the role of
spacetime diffeomorphisms; and (iii) the problem of time.Comment: 20,IC/TP/0
On Di\'osi-Penrose criterion of gravity-induced quantum collapse
It is shown that the Di\'osi-Penrose criterion of gravity-induced quantum
collapse may be inconsistent with the discreteness of space-time, which is
generally considered as an indispensable element in a complete theory of
quantum gravity. Moreover, the analysis also suggests that the discreteness of
space-time may result in rapider collapse of the superposition of energy
eigenstates than required by the Di\'osi-Penrose criterion.Comment: 5 pages, no figure