[Show abstract][Hide abstract] ABSTRACT: To investigate the possibility that intrinsic gravitational decoherence can
be theoretically demonstrated within canonical quantum gravity, we develop a
model of a self-gravitating interferometer. We search for evidence in the
resulting interference pattern that would indicate coherence is fundamentally
limited due to general relativistic effects. To eliminate the occurence of
gravitational waves, we work in spherical symmetry, and construct the "beam" of
the interferometer out of WKB states for an infinitesimally thin shell of
matter. For internal consistency, we encode information about the beam optics
within the dynamics of the shell itself, by arranging an ideal fluid on the
surface of the shell with an equation of state that enforces beam-splitting and
reflections. We then determine sufficient conditions for (interferometric)
coherence to be fully present even after general relativistic corrections are
introduced, test whether or not they can be satisfied, and remark on the
implications of the results.
Physical Review D 07/2014; 90(4). · 4.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is argued that Hawking radiation has indeed been measured and shown to
posses a thermal spectrum, as predicted. This contention is based on three
separate legs. The first is that the essential physics of the Hawking process
for black holes can be modelled in other physical systems. The second is the
white hole horizons are the time inverse of black hole horizons, and thus the
physics of both is the same. The third is that the quantum emission, which is
the Hawking process, is completely determined by measurements of the classical
parameters of a linear physical system. The experiment conducted in 2010
fulfills all of these requirements, and is thus a true measurement of Hawking
Foundations of Physics 01/2014; 44(5). · 1.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A variety of historical coordinates in which the Schwarzschild metric is
regular over the whole of the extended spacetime are compared and the
hypersurfaces of constant coordinate are graphically presented. While the
Kruscal form (one of the later forms) is probably the simplest, each of the
others has some interesting features.
[Show abstract][Hide abstract] ABSTRACT: Inspired by the condensed matter analogues of black holes (a.k.a. dumb
holes), we study Hawking radiation in the presence of a modified dispersion
relation which becomes super-luminal at large wave-numbers. In the usual
stationary coordinates $(t,x)$, one can describe the asymptotic evolution of
the wave-packets in WKB, but this WKB approximation breaks down in the vicinity
of the horizon, thereby allowing for a mixing between initial and final
creation and annihilation operators. Thus, one might be tempted to identify
this point where WKB breaks down with the moment of particle creation. However,
using different coordinates $(\tau,U)$, we find that one can evolve the waves
so that WKB in these coordinates is valid throughout this transition region --
which contradicts the above identification of the breakdown of WKB as the cause
of the radiation. Instead, our analysis suggests that the tearing apart of the
waves into two different asymptotic regions (inside and outside the horizon) is
the major ingredient of Hawking radiation.
[Show abstract][Hide abstract] ABSTRACT: There is an analogy between the propagation of fields on a curved spacetime
and shallow water waves in an open channel flow. By placing a streamlined
obstacle into an open channel flow we create a region of high velocity over the
obstacle that can include wave horizons. Long (shallow water) waves propagating
upstream towards this region are blocked and converted into short (deep water)
waves. This is the analogue of the stimulated Hawking emission by a white hole
(the time inverse of a black hole). The measurements of amplitudes of the
converted waves demonstrate that they appear in pairs and are classically
correlated; the spectra of the conversion process is described by a
Boltzmann-distribution; and the Boltzmann-distribution is determined by the
determined by the change in flow across the white hole horizon.
[Show abstract][Hide abstract] ABSTRACT: The temperature of an oscillator coupled to the vacuum state of a heat bath via Ohmic coupling is non-zero, as measured by the reduced density matrix of the oscillator. This study shows that the actual temperature, as measured by a thermometer, is still zero (or, in the thermal state of the bath, the temperature of the bath). The decoherence temperature is due to 'false-decoherence', with a correlation between the oscillator and the heat bath causing the decoherence, but the heat baths state dragged along with the state of the oscillator.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 09/2012; 370(1975):4460-8. · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: That decoherence can take place in the presence of energy conservation seems to be a poorly known fact. That lack of knowledge has, for example, bedevilled the discussion of the 'black hole information' problem. I present a simple model that illustrates such energy-free decoherence.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 09/2012; 370(1975):4454-9. · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The equations for waves on the surface of an irrotational incompressible
fluid are derived in the coordinates of the velocity potential/stream function.
The low frequency shallow water approximation for these waves is derived for a
varying bottom topography. Most importantly, the conserved norm for the surface
waves is derived, important for quantisation of these waves and their use in
analog models for black holes.
[Show abstract][Hide abstract] ABSTRACT: One of the most striking examples for the production of particles out of the
quantum vacuum due to external conditions is cosmological particle creation,
which is caused by the expansion or contraction of the Universe. Already in
1939, Schr\"odinger understood that the cosmic evolution could lead to a mixing
of positive and negative frequencies and that this "would mean production or
annihilation of matter, merely by the expansion". Later this phenomenon was
derived via more modern techniques of quantum field theory in curved
space-times by Parker (who apparently was not aware of Schr\"odinger's work)
and subsequently has been studied in numerous publications. Even though
cosmological particle creation typically occurs on extremely large length
scales, it is one of the very few examples for such fundamental effects where
we actually may have observational evidence: According to the inflationary
model of cosmology, the seeds for the anisotropies in the cosmic microwave
background (CMB) and basically all large scale structures stem from this
effect. In this Chapter, we shall provide a brief discussion of this phenomenon
and sketch a possibility for an experimental realization via an analogue in the
[Show abstract][Hide abstract] ABSTRACT: Belgiorno et al have reported on experiments aiming at the detection of (the
analogue of) Hawking radiation using laser filaments [F. Belgiorno et al, Phys.
Rev. Lett. 105, 203901 (2010)]. They sent intense focused Bessel pulses into a
non-linear dielectric medium in order to change its refractive index via the
Kerr effect and saw creation of photons orthogonal to the direction of travel
of the pluses. Since the refractive index change in the pulse generated a
"phase horizon" (where the phase velocity of these photons equals the pulse
speed), they concluded that they observed the analogue of Hawking radiation. We
study this scenario in a model with a phase horizon and a phase velocity very
similar to that of their experiment and find that the effective metric does not
quite correspond to a black hole. The photons created in this model are not due
to the analogue of black hole evaporation but have more similarities to
cosmological particle creation. Nevertheless, even this effect cannot explain
the observations -- unless the pulse has significant small scale structure in
both the longitudinal and transverse dimensions.
Physical review D: Particles and fields 02/2012; 86(6).
[Show abstract][Hide abstract] ABSTRACT: The slinky, released from rest hanging under its own weight, falls in a
peculiar manner. The bottom stays at rest until a wave hits it from above. Two
cases - one unphysical one where the slinky is able to pass through itself, and
the other where the coils of the slinky collide creating a shock wave
travelling down the slinky are analysed. In the former case, the bottom begins
to move much later than in the latter.
[Show abstract][Hide abstract] ABSTRACT: The loss of coherence of a quantum system coupled to a heat bath as expressed
by the reduced density matrix is shown to lead to the miss-characterization of
some systems as being incoherent when they are not. The spin boson problem and
the harmonic oscillator with massive scalar field heat baths are given as
examples of reduced incoherent density matrices which nevertheless still
represent perfectly coherent systems.
[Show abstract][Hide abstract] ABSTRACT: The quantum noise in a linear amplifier is shown to be thermal noise. The
theory of linear amplifiers is applied first to the simplest, single or double
oscillator model of an amplifier, and then to linear model of an amplifier with
continuous fields and input and outputs. Finally it is shown that the thermal
noise emitted by black holes first demonstrated by Hawking, and of dumb holes
(sonic and other analogs to black holes), arises from the same analysis as for
linear amplifiers. The amplifier noise of black holes acting as amplifiers on
the quantum fields living in the spacetime surrounding the black hole is the
radiation discovered by Hawking. For any amplifier, that quantum noise is
completely characterized by the attributes of the system regarded as a
classical amplifier, and arises out of those classical amplification factors
and the commutation relations of quantum mechanics.
[Show abstract][Hide abstract] ABSTRACT: We summarize the results of a calculation (B. Losic and W.G. Unruh. Phys. Rev. D, 72, 123510 (2005).) of cosmological back reactions about a slowly rolling background space-time. In particular, we evaluate the effect of the superhorizon second-order corrections on the (superhorizon) inhomogeneous modes of the linearized fluctuations. Their physical significance is quantified by studying their effective equation of state, where the isotropic pressure and energy density at second order are defined in terms of the averaged eigenvalues associated with timelike (spacelike) eigenvectors of a total stress energy for the metric and matter fluctuations. Given a well-defined gauge fixing at second order, we find that the higher order corrections may dominate those of the linear terms and, furthermore, that this result holds for other reasonable gauge-fixing procedures. Our work suggests that for many parameters of slow-roll inflation, the second-order effects may dominate over the first-order effects for the super-Hubble evolution. We also find that the contribution to the equation of state due to the back reactions is that of a negative cosmological constant in this coordinate gauge, confirming earlier work.PACS Nos.: 31.15.Pf, 31.30.Jv, 32.10.Hq
Canadian Journal of Physics 02/2011; 84:599-605. · 0.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. To address this issue experimentally, we utilize the analogy between the propagation of fields around black holes and surface waves on moving water. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include surface wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep-water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.
[Show abstract][Hide abstract] ABSTRACT: Inspired by the condensed-matter analogues of black holes, we study the quantum correlations across the event horizon reflecting the entanglement between the outgoing particles of the Hawking radiation and their in-falling partners. For a perfectly covariant theory, the total correlation is conserved in time and piles up arbitrary close to the horizon in the past, where it merges into the singularity of the vacuum two-point function at the light cone. After modifying the dispersion relation (i.e., breaking Lorentz invariance) for large $k$, on the other hand, the light cone is smeared out and the entanglement is not conserved but actually created in a given rate per unit time. Comment: 5 pages RevTeX, 1 figure
[Show abstract][Hide abstract] ABSTRACT: Minkowski’s conception of spacetime has had a large impact on our interpretation of quantum theory. Time in quantum mechanics
plays a a role in the interpretation distinct from space, in contrast with the apparent unity of space and time encapsulate
in the notion of spacetime. It clearly ruled out any quantum mechanics and showed that quantum field theory was the only possible
consistent theory. And within quantum field theory, it also rules out the realistic interpretation of the wave function. Fortunately,
it is not incompatible with all approaches to quantum theory. Whether or not it is compatible with quantum theory once the
metric, the structure which defines the causal structure of the primitive notion of the manifold, is still an open question.
Minkowski spacetime-Quantum mechanics-Schroedinger representation-Heisenberg
[Show abstract][Hide abstract] ABSTRACT: We analyze the necessary and sufficient conditions for the occurrence of superradiance. Starting with a wave equation we examine the possibility of superradiance in terms of an effective potential and boundary conditions. In particular, we show that the existence of an ergoregion is not sufficient; an appropriate boundary condition, e.g. only ingoing group velocity waves at an event horizon, is also crucial. After applying our scheme to the standard examples of superradiance, we show that analogue models of gravity without an event horizon do not necessarily exhibit superradiance. Particularly, we show that the superradiant phenomenon is absent in purely rotating inviscid fluids with vorticity. We argue that there should be a catalogue of superradiant systems that can be found by focusing on the necessary and sufficient conditions outlined below.
Physical review D: Particles and fields 12/2009; 80(12).
[Show abstract][Hide abstract] ABSTRACT: We present a gauge-invariant argument that a nonlocal measure of second-order metric and matter perturbations dominates that of linear fluctuations in its effect on the gravitational field in "slow-rolling" spacetimes.