Dyson (2013 Int. J. Phys. 28 1330041) argued that the extraordinarily large number of gravitons in a gravitational wave makes them impossible to be resolved as individual particles. While true, it is shown in this paper that a LIGO interferometric detector also undergoes frequent and discrete quantum interactions with an incident gravitational wave, in such a way as to allow the exchange of energy and momentum between the wave and the detector. This opens the door to another way of finding gravitons. The most basic form of an interaction is the first order Fermi acceleration (deceleration) of a laser photon as it is reflected by a test mass mirror oscillating in the gravitational wave, resulting in a frequency blueshift (redshift) of the photon depending on whether the mirror is advancing towards (receding from) the photon before the reflection. If e.g. a blueshift occurred, wave energy is absorbed and the oscillation will be damped. It is suggested that such energy exchanging interactions are responsible for the observed radiation reaction noise of LIGO (although the more common way of calculating the same amplitude for this noise is based on momentum considerations). Most importantly, in each interaction the detector absorbs or emits wave energy in amounts far smaller than the standard graviton energy (h) over bar omega where omega is the angular frequency of the gravitational wave. This sets a very tight upper limit on the quantization of the wave energy, viz. it must be at least approximate to 10(11) times below (h) over bar omega, independently of the value of omega itself.

A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying B/P > 2 x 10(16) G s(-1) (1G =3D 1 statvolt cm(-1)) as the source, is proposed. When the parallel component E-parallel to of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5% of the critical field E-c =3D m(e)(2) c(3) (e(SIC)), in strength, the field can readily decay via the Schwinger mechanism into electron-positron pairs, the back reaction of which causes E-parallel to to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies. less than or similar to 1 GHz where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over a timescale approximate to a few x 10(-3) s, the duration of a fast radio burst. Owing to the circumstellar environment of a young magnetar, however, the less than or similar to 1 GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of approximate to 1 GHz and above are on a par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.

It has long been known that a uniform distribution of matter cannot produce a Poisson distribution of density fluctuations on very large scales 1/k > ct by the motion of discrete particles over timescale t. The constraint is part of what is sometimes referred to as the Zel'dovich bound. We investigate in this paper the transport of energy by the propagation of waves emanating incoherently from a regular and infinite lattice of oscillators, each having the same finite amount of energy reserve initially. The model we employ does not involve the expansion of the Universe; indeed there is no need to do so, because although the scales of interest are all deeply sub-horizon the size of regions over which perturbations are evaluated do far exceed ct, where t is the time elapsed since a uniform array of oscillators started to emit energy by radiation (it is assumed that t greatly exceeds the duration of emission). We find that to lowest order, when only wave fields proportional to 1/r are included, there is exact compensation between the energy loss of the oscillators and the energy emitted into space, which means P(0) =3D 0 for the power spectrum of density fluctuations on the largest scales. This is consistent with the Zel'dovich bound; it proves that the model employed is causal, has finite support, and energy is strictly conserved. To the next order when near fields proportional to r(-2) are included, however, P(0) settles at late times to a positive value that depends only on time, as t(-2) (the same applies to an excess (non-conserving) energy term). We further observe that the behavior is peculiar to near fields. Even though this effect may give the impression of superluminal energy transport, there is no violation of causality because the two-point function vanishes completely for r > t if the emission of each oscillator is sharply truncated beyond some duration. The result calls to question any need of enlisting cosmic inflation to seed large scale density perturbations in the early Universe.

As an extension of the ideas of Hanbury-Brown and Twiss, a method is proposed to eliminate the phase noise of white chaotic light in the regime where it is dominant, and to measure the much smaller Poisson fluctuations from which the incoming flux can be reconstructed. The best effect is achieved when the timing resolution is finer than the inverse bandwidth of the spectral filter. There may be applications to radio astronomy at the phase noise dominated frequencies of 1-10 GHz, in terms of potentially increasing the sensitivity of telescopes by an order of magnitude.

For each photon wave packet of extragalactic light, the dispersion by line-of-sight intergalactic plasma causes an increase in the envelope width and a chirp (drift) in the carrier frequency. It is shown that for continuous emission of many temporally overlapping wave packets with random epoch phases such as quasars in the radio band, this in turn leads to quasi-periodic variations in the intensity of the arriving light on timescales between the coherence time (defined as the reciprocal of the bandwidth of frequency selection, taken here as of order 0.01 GHz for radio observations) and the stretched envelope, with most of the fluctuation power on the latter scale which is typically in the millisecond range for intergalactic dispersion. Thus, by monitoring quasar light curves on such short scales, it should be possible to determine the line-of-sight plasma column along the many directions and distances to the various quasars, affording one a three-dimensional picture of the ionized baryons in the near universe.

For each photon wave packet of extragalactic light, the dispersion by line-of-sight intergalactic plasma causes an increase in the envelope width and a chirp (drift) in the carrier frequency. It is shown that for continuous emission of many temporally overlapping wave packets with random epoch phases such as quasars in the radio band, this in turn leads to quasi-periodic variations in the intensity of the arriving light on timescales between the coherence time (defined as the reciprocal of the bandwidth of frequency selection, taken here as of order 0.01 GHz for radio observations) and the stretched envelope, with most of the fluctuation power on the latter scale which is typically in the millisecond range for intergalactic dispersion. Thus, by monitoring quasar light curves on such short scales, it should be possible to determine the line-of-sight plasma column along the many directions and distances to the various quasars, affording one a three-dimensional picture of the ionized baryons in the near universe.

In some versions of the theory of inflation, it is assumed that before inflation began the universe was in a Friedmann-Robertson-Walker stage, with the energy density dominated by massless particles. The origin of the nearly scale-invariant density perturbations is quantum fluctuations in the inflaton field. Here we point out that under those conditions there would necessarily also be large thermally induced density perturbations. It is asserted that inflation would smooth out any pre-existing perturbations. However, that argument relies on linear perturbation theory of the scalar modes, which would be rendered invalid because of the non-negligibility of the vector and tensor modes when the perturbation in the total density becomes large. Under those circumstances, the original proof that inflation would have the desired smoothing effect no longer applies, i.e. for the theory to be robust an alternative (and hitherto unavailable) demonstration of the smoothing that takes account of these non-linear terms is necessary.

The "missing baryons" of the near universe are believed to be principally in a partially ionized state. Although passing electromagnetic waves are dispersed by the plasma, the effect has hitherto not been utilized as a means of detection because it is generally believed that a successful observation requires the background source to be highly variable, i.e., the class of sources that could potentially deliver a verdict is limited. We argue in two stages that this condition is not necessary. First, by modeling the fluctuations on macroscopic scales as interference between wave packets, we show that, in accordance with the ideas advanced by Einstein in 1917, both the behavior of photons as bosons (i.e., the intensity variance has contributions from Poisson and phase noise) and the van-Cittert-Zernike theorem are a consequence of wave-particle duality. Nevertheless, we then point out that, in general, the variance on some macroscopic timescale tau consists of (1) a main contributing term alpha 1/tau, plus (2) a small negative term. alpha 1/t(2) due to the finite size of the wave packets. If the radiation passes through a dispersive medium, this size will be enlarged well beyond its vacuum minimum value of Delta t approximate to 1/Delta nu leading to a more negative (2) term (while (1) remains unchanged), and hence a suppression of the variance wrt the vacuum scenario. The phenomenon, which is typically at a few parts in 10(5) level, enables one to measure cosmological dispersion in principle. Signal-to-noise estimates, along with systematic issues and how to overcome them, will be presented.

The "missing baryons" of the near universe are believed to be principally in a partially ionized state. Although passing electromagnetic waves are dispersed by the plasma, the effect has hitherto not been utilized as a means of detection because it is generally believed that a successful observation requires the background source to be highly variable, i.e., the class of sources that could potentially deliver a verdict is limited. We argue in two stages that this condition is not necessary. First, by modeling the fluctuations on macroscopic scales as interference between wave packets, we show that, in accordance with the ideas advanced by Einstein in 1917, both the behavior of photons as bosons (i.e., the intensity variance has contributions from Poisson and phase noise) and the van-Cittert-Zernike theorem are a consequence of wave-particle duality. Nevertheless, we then point out that, in general, the variance on some macroscopic timescale tau consists of (1) a main contributing term alpha 1/tau, plus (2) a small negative term. alpha 1/t(2) due to the finite size of the wave packets. If the radiation passes through a dispersive medium, this size will be enlarged well beyond its vacuum minimum value of Delta t approximate to 1/Delta nu leading to a more negative (2) term (while (1) remains unchanged), and hence a suppression of the variance wrt the vacuum scenario. The phenomenon, which is typically at a few parts in 10(5) level, enables one to measure cosmological dispersion in principle. Signal-to-noise estimates, along with systematic issues and how to overcome them, will be presented.

The phenomenon of cosmic shear, or distortion of images of distant sources unaccompanied by magnification, is an effective way of probing the content and state of the foreground universe, because light rays do not have to pass through matter clumps in order to be sheared. It is shown that the delay in the arrival times between two simultaneously emitted photons that appear to be arriving from a pair of images of a strongly lensed cosmological source contains not only information about the Hubble constant, but also the long-range gravitational effect of galactic-scale mass clumps located away from the light paths in question. This is therefore also a method of detecting shear. Data on time delays among a sample of strongly lensed sources can provide crucial information about whether extra dynamics beyond gravity and dark energy are responsible for the global flatness of space. If the standard Lambda CDM model is correct, there should be a large dispersion in the value of H-0 as inferred from the delay data by (the usual procedure of) ignoring the shear from all other mass clumps except the strong lens itself. The fact that there has not been any report of a significant deviation from the h = 0.7 mark during any of the H-0 determinations by this technique may already be pointing to the absence of the random effect discussed here.

Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demonstrate that the evolution of a cluster's cooling core, in terms of its density, temperature, and magnetic field strength, inevitably enables the plasma electrons there to quickly become Cerenkov loss dominated, with emission at the radio frequency of less than or similar to 350 Hz, and with a rate considerably exceeding free-free continuum and line emission. However, the same does not apply to the plasmas at the cluster ' s outskirts, which lacks such radiation. Owing to its low frequency, the radiation cannot escape, but because over the relevant scale size of a Cerenkov wavelength the energy of an electron in the gas cannot follow the Boltzmann distribution to the requisite precision to ensure reabsorption always occurs faster than stimulated emission, the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh-Taylor instability, at a rate determined by the outermost radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at approximate to 2 M circle dot year(-1), consistent with observational inference. Thus, the process appears to provide a natural solution to the longstanding problem of "cooling flow" in clusters; at least it offers another line of defense against cooling and collapse should gas heating by AGN feedback be inadequate in some clusters.

There has recently been some interest in the prospect of detecting ionized intergalactic baryons by examining the properties of incoherent light from background cosmological sources, namely quasars. Although the paper by Lieu et al. proposed a way forward, it was refuted by the later theoretical work of Hirata & McQuinn and the observational study of Hales et al. In this paper we investigate in detail the manner in which incoherent radiation passes through a dispersive medium both from the frameworks of classical and quantum electrodynamics, leading us to conclude that the premise of Lieu et al. would only work if the pulses involved are genuinely classical ones containing many photons per pulse; unfortunately, each photon must not be treated as a pulse that is susceptible to dispersive broadening. We are nevertheless able to change the tone of the paper at this juncture by pointing out that because current technology allows one to measure the phase of individual modes of radio waves from a distant source, the most reliable way of obtaining irrefutable evidence of dispersion, namely via the detection of its unique signature of a quadratic spectral phase, may well be already accessible. We demonstrate how this technique is only applied to measure the column density of the ionized intergalactic medium.

The observational and theoretical status of the search for missing cosmological baryons is summarized, with a discussion of some indirect methods of detection. The thermal interpretation of the cluster soft X-ray and EUV excess phenomenon is examined in the context of emission filaments, which are the higher density part of the warm hot intergalactic medium (WHIM) residing at the outskirt of clusters. We derived an analytic radial profile of the soft excess surface brightness using a simple filament model, which provided us a means of observationally constraining the WHIM parameters, especially the total mass budget of warm gas associated with a cluster. We then pointed out a new scenario for soft excess emission, viz., a cluster that can strongly lens the soft X-rays from background WHIM knots. If, as seems quite likely, the missing baryons are mostly in the WHIM halos of galaxy groups, the lensing probability will be quite high (similar to 10%). This way of accounting for at least part of a cluster's soft excess may also explain the absence of O VII absorption at the redshift of the cluster.

We specifically study one aspect of foreground primordial matter density perturbations: the relative gravitational time delay between a pair of light paths converging toward an observer and originating from two points on the last scattering surface separated by the physical scale of an acoustic oscillation. It is found that time delay biases the size of acoustic oscillations systematically toward smaller angles, or larger harmonic numbers l; that is, the mean geometry as revealed by light from the cosmic microwave background becomes that of an open universe if Omega = 1. Since the effect is second-order, its standard deviation delta l/l similar to (delta Phi)(2), where (delta Phi)(2) similar to 10(-9) is the normalization of the primordial matter spectrum P(k), the consequence is too numerically feeble to warrant a reinterpretation of WMAP data. If, however, this normalization were increased to delta Phi greater than or similar to 0.01, which is still well within the perturbation limit, the shift in the positions of the acoustic peaks would be substantial enough to implicate inflationary Lambda CDM cosmology. Thus, Omega is not the only parameter (and, by deduction, inflation cannot be the only mechanism) of relevance to the understanding of observed large-scale geometry. The physics that explains why delta Phi is so small also plays a crucial role, but since this is a separate issue, independent of inflation, might it be less artificial to look for an alternative solution to the flatness problem altogether?