LIGO’s new Gravitational Pulse – puzzling for Black-Hole interpretations

The four instances of the inspiral-merger pattern of a gravitation pulse from coalescing binary objects are over-interpreted and raise statistical questions.  The final ring-down is too weak to distinguish exotic ‘Black Hole’ mergers from neutron star mergers.  Why no identifications of the expected closer and smaller merger events?  The extraordinary claim to ‘primordial’ Black Holes is based on uncertain indications of spins.  

The LIGO team has registered a further gravitational wave pulse that shows the inspiral-merger pattern – diminishing wavelength with rising intensity (‘chirp’), then collapse to a low energy tail.  This characterises the coalescence of a pair of compact masses, mutually orbiting ever closer (and faster) as gravitational energy is shed, till they touch and merge. The size at the point of merging at is important, being the Schwarzschild radii for BHs (‘black holes’) but somewhat larger for neutron-star collapsars in general. Spin of the merging objects is a small complicating matter. The shape of the collapse-tail characterises the spin-states and type of coalescing objects.

Detector data (gray), and 90% confidence intervals for wave-forms reconstructed from the morphology-independent wavelet analysis (orange) and binary black hole (BBH) models (blue). “GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2”    B. P. Abbott et al. (LIGO Scientific and Virgo Collaboration) Phys. Rev. Lett. 118, 221101, 2017

The inspiral-merger-collapse signal was recorded both at Hanford and Livingston (Figure shows slight time shift) so it’s real. The LIGO team now use two models to fit the trail (‘Wavelets’ and ‘BBH’) and are able to fit fewer wavelengths (6 rather than ~10 of the discovery pulse).

This fourth detection of merging BHs (the third was only marginal) is close in inferred size (50M rather than the 60M combined mass of the discovery detection). Its post-merger signal has half the signal:noise, so again is too weak to discriminate between types of coalescing objects. This fourth example is inferred – from the energy in the gravitational pulse – to be twice as far away. With uncertainty due to the orbit inclination to the direction of view, the distances of the first three merger events would be similar, ~300-500Mpc.

Two examples of similar mass and one a little smaller is a surprising. BHs were expected to be smaller, ~1-3M, because of mass loss in star evolution, and similar to classical neutron stars. Stars lose mass throughout their lives so have to evolve without significant mass loss in order to leave a 30M BH. Larger stars may exist, having low metallicity or strong magnetisation.  LIGO is sensitive to 4-100M total mass so covers the expected small sizes. The  LIGO network for binary merger events probes to ~70 Mpc for 1.4+1.4 M, 300 Mpc for 10+10 M and 700 Mpc for 30+30 M mergers, showing bias to detecting larger more distant BH mergers (amplitude is inversely proportional to the distance). If the current detection is really twice as far (8 times the space volume) several examples comparable to the new one should be dropping out of the data already accumulated. So why only one?

Why also just one report of  a marginal detection of lower amplitude pulses?   The LIGO team try to match templates of the theoretical inspiral-merger-collapse profile to the noisy signals recorded in the two detectors. A multiplicity of templates covers unknown inclinations and spin states as well as mass ratios. The new signal was so strong as to be detected by eye – yet, where are the smaller events (smaller or more distant mergers)? BBH fitting shows a significant difference beyond 5 wavelengths pre-peak to ‘wavelet’ fitting (Figure above) which implies interpretations including inferences of spin are uncertain.

The LIGO team say there’s a “potentially” significant indication of counter spinning to the orbital spin, which would imply dynamical capture into a binary system rather than co-evolution of the binary pair. This leads them to suggest these ~30M⊙ objects are primordial BHs. Though these hypothetical objects are currently popular, having potential for being the hidden dark matter, this suggestion is problematic as they fail to show in gravitational lensing of light from distant quasars (Mediavilla et al., ApJ Letters 836(2), L18). With such doubts over BH-model fitting, it’s time other models of the compact objects are properly considered.

Merging via gravitational energy loss requires the binary components to be highly dense (neutron matter density) and close to a few times MG/c2 (the gravitational or Schwarzschild scale). The LIGO team should be open to non-BH interpretations. Neutron stars can no longer be excluded as too low in mass, as shell-collapsars can far exceed the supposed limit of 3M.

Posted in gravitation | Tagged , , , , , | Leave a comment

Fixing the Nobel prize for LIGO/gravitational-waves comes unstuck

They got the application in by the 31 January deadline, stimulated a lot of endorsements and swept up an array of other awards – Gruber Cosmology Prize, the Kavli Prize in Astrophysics, the Shaw Prize in Astronomy, Special Breakthrough Prize in Fundamental Physics. So why did they come unstuck?
Was it that the LIGO insiders tried to fix the 3 persons, when there were others thought to be equally or more deserving. Once there was lobbying for Barry Barish etc. to share the honours, the Nobel Committee would have delayed any decision to allow these others to be nominated before next year’s deadline.
Or was it that the LIGO group tried to claim too much, in their claim to detect black-holes? Black-holes are disputed, while just the detection of gravitational waves would surely have merited the prize, but then Barry Barish could well have displaced Kip Thorne from the chosen three.  Einstein’s supporters likewise claimed too much in seeking the Nobel for General Relativity, when observational tests were disputed/uncertain in 1916-1920, over the years when the Nobel was richly merited for Einstein’s well-attested Special Relativity (eg. mass-energy of relativistic electrons) [Aant Elzinga, Einstein’s Nobel Prize: A Glimpse Behind closed Doors, review in Brit. J. Hist.Sci. 41. 148-149, March 2008]
In the LIGO case, they knew ‘horizonless’ compact objects are theorised, which equally fit the gravitational wave signal of an inspiralling binary. They knew the tail of the signal showing the actual merging was below threshold, when that could indicate the type of object. Mixing in the claim for black-hole detection rather than just an inspiralling binary (for which Landau-Lifshitz have a prior claim) should in any case defer any Nobel prize for the LIGO discovery. The lesson is – leave the Nobel Committee free to make their assessments using independent scientists and to choose the precise terms and nobelists.

Posted in gravitation | Tagged , , , , , , | 3 Comments

Do details in LIGO’s signals distinguish ‘frozen stars’ from ‘black hole’ interpretations

R. J. Spivey argues that “Coincident down-chirps in GW150914 betray the absence of event  horizons”.  The LIGO discovery is said to confirm Einstein’s gravitation theory, yet Einstein (in 1939) gave mathematical grounds for dismissing the notion that black holes exist, points out Spivey.  His article uses secondary signals seen in both LIGO detectors (Fig. below)

Spivey Fig. 1: The gravitational wave spectrograms for the Hanford (top) and Livingston (bottom) Advanced LIGO detectors. Right column: the common secondary trace (down-chirp) deviating from the primary up-chirp suggests the ejection of mass against gravity of the merging binary system. Credit: LIGO-Virgo collaboration.

Spivey Fig. 1: The gravitational wave spectrograms over the 170ms (0.17 seconds) prior to merging for the Hanford (top) and Livingston (bottom) aLIGO detectors. Right column: the common secondary trace (down-chirp) deviating from the primary up-chirp suggests the ejection of mass against gravity of the merging binary system. Credit: LIGO-Virgo collaboration.

It’s well appreciated that close binaries of compact stellar objects (neutron stars) are strong sources of gravitational waves – the energy loss in the waves causes the orbits to spiral inwards until the objects are disrupted or merge.  The LIGO gravitational wave pulses show the predicted oscillating signal of directional beamed waves, increasing in frequency corresponding to the shrinking orbits.

The LIGO community was so taken with this ‘chirp’ of increasing frequency (curving upwards in the Fig.) and the finding that the mass associated with ‘chirp’ models is much bigger than normal stars (totals ~20 and 65 solar masses Ms in the two LIGO instances) that they failed to look at details in the spectrogram.  They largely embraced the claim that the objects must be fashionable ‘black holes’ rather than supermassive neutron stars or other extreme matter.   They’ve dismissed these as ‘exotic’ matter, whereas the ‘event horizon’ that delays mass accretion into black-holes for infinite time is the real ‘exotic’ physics.

The last stage of the LIGO signals, as the inspiralling objects touch and merge, would distinguish between models.  It’s expected that oscillations depend on a boundary or a ‘horizon’.  But this stage is lost in the signal noise, below the detection threshold.  Robin Spivey points out an earlier secondary signal – from 160ms, a ‘down-chirp’ of decreasing frequency – provides some evidence.  The spectral traces from the two detectors (at Hanford and Livingstone, Fig. above) would match ejection of a fraction of the matter with a launch radial velocity  ~ 0.04c.  (Other secondary spectral features are ‘noise’, differing in the two detectors.)

Was disruption not expected, associated with the violent inspiralling ?  Gigantic amounts of energy are emitted in gravitational waves, equivalent to 3 solar masses (3Msc2 in the larger case).  Calculations for a binary of unequal point-masses do find that the smaller mass can be expelled at high (sub-relativistic) speed.   Strong perturbations of extended bodies might well expel significant amounts of matter from their fringes.  Non-radial instabilities have been indicated in a model ‘gravastar’, implying asymmetric break-up.  On the other hand, disruption of a black-hole is inconceivable – is this why the LIGO community have overlooked the ‘down-chirp’ signal ?

Posted in gravitation | Tagged , , , , , | 1 Comment

Second Gravitational Wave signal – Coalescing binary components, not Black Holes

Following the February discovery, a second signal was found by the same LIGO team in the ‘noise’, by looking for a pulse of waves of increasing frequency in the two detectors.  This pulse is longer (~55 waves compared with ~10 previously) and the frequency change (‘chirp’) indicates binary components of smaller mass (total ~20M⊙ compared with ~60M⊙).

LIGO2-wave-in-noise2 Jun'16

The modelled wave train (in black) on the two detectors’ signals (red and blue)

The new LIGO paper again asserts coalescing Black-Holes is the only explanation, saying the masses are higher than the maximum for canonical neutron stars. The last stage ‘ringdown’ signal, which could distinguish the form of the merging object, is minor and well below detection threshold.

It retains this position as originally agreed by its thousand authors, despite some critical voices eg. in Physics World of 29th April  reporting Vitor Cardoso on the gravastar interpretation “Are ‘gravastars’ mimicking…“.  That it’s vital to detect the ringdown part of the signal is stressed by a leading expert Remo Ruffini (“What we can really infer from GW150914?“).  B. Sathyaprakash of Cardiff’s LIGO team admitted (to Physics World) “Our signal is consistent with both the formation of a black hole and a horizonless object – we just can’t tell.”  ‘Horizonless’ models of super-compact objects include gravastars and do not suffer from the infinite time dilution at black-hole horizons:

The new LIGO paper shows weakness in stating the only alternative binary components are neutron stars and not admitting to excluding the ‘exotic’ alternatives – lest people point out that Black Holes are ‘exotic’. It’s weak also in not admitting that the ‘ringdown’ signal of black-hole coalescence is below their detection threshold.

The statement in mid-May by Ruffini and colleagues thus remains unchallenged:

“… the signal around 150 Hz occurs just at the limit of the sensitivity of LIGO… not sufficient to determine the astrophysical nature of GW 150914, nor to assess that it was produced by a binary black-hole merger leading to a newly formed black-hole.”

NOTE  The topic ‘mentors’ of physicsforums didn’t like me questioning the Black-Hole interpretation. They first stopped an informative exchange on grounds of unpublished ‘personal speculation’. When I showed Cardoso (and others) had already published, they allowed the new thread, citing Physics World and Ruffini’s new paper on arXiv, but then blocked me from continuing the discussion.  It smells of a conspiracy to give LIGO prizes for discovering black-holes, when there’s no such ‘discovery’ – LIGO’s gravitational pulse indicated the spin-down and merging of two compact bodies in a binary system. Unexpectedly massive bodies indeed, at 10-30 times the Sun’s mass M⊙, something for theorists to explain.

Posted in gravitation | Tagged , , , , | Leave a comment

LIGO scientists row back on claim to detect black-holes from their gravitational signal

It is gradually coming out that LIGO’s main gravitational wave pulse could indicate various types of binary astrophysical systems, as we said on this blog in February. Cardoso et al 2016 point out (Phys Rev Lett. to come) there are compact objects that are not black holes, including gravastars of similar dimensions (~30 solar masses) which produce a similar main signal. The late part of the signal was below detection threshold, and that is needed to distinguish between astrophysical objects. In discussing this, Physics World quotes Prof Sathyaprakash from Cardiff’s LIGO team saying that “Our signal is consistent with both the formation of a black hole and a horizonless object – we just can’t tell.” Rather different from him in the Guardian of 11 Feb. “The fusion of two black holes created this event”. Now, Remo Ruffini (of the Rees-Ruffini-Wheeler textbook) co-authors an preprint (16 May 2016) saying: unfortunately the signal of the merging “occurs just at the limit of the sensitivity of LIGO (so is) not sufficient to determine the astrophysical nature of GW 150914, nor to assess that it was produced by a binary black-hole merger leading to a newly formed black-hole.”

Posted in gravitation | Tagged , , , , | 1 Comment

Gravitational wave event at last – success for Einstein, not black-holes

Detecting gravitational waves after decades of searching and developing more sensitive techniques is a great achievement, in technology as well as the accompanying analysis.

What a pity the research teams have sullied the discovery by conflating the detection of a very clear gravitational wave signal with their particular interpretation.  Doubtless the big signal over milliseconds implies very large condensed masses interacting cataclysmically, inferred to be over 25 solar masses. The event had to be relatively close to us in space to give a signal well above numerous extragalactic ones.  The teams apply their model for two ‘black holes’ merging, as if it’s the sole contending explanation. The model merging scale is the Schwarzschild radius MG/c2, not of point-like black holes. Megamassive condensed stars (largely of neutrons) are of this scale too.  The rapid merging two of them would generate a similar signal, if with differences in detail.  This was dismissed simply on the basis of the out-dated belief that neutron stars can be no bigger than 2 solar masses (Ms).

Einstein himself did not believe in Black Holes; physicists should at least accord him respect in allowing that this first clear gravitational wave event implies the sudden rebalancing of large condensed masses, probably a merging binary – to give his quadrapole emissions – and opens up a way to investigate such structures.  The big majority of the gravitational energy pulse comes out from the mutually orbiting stars (rapid, up to ~0.5c) as they become increasing close in last second before becoming one.  Open-minds are especially required when black-hole modelling uses a faulty metric, having a non-physical region beyond a ‘surface of separation’, which requires dodgy computational treatments.

The discovery kills off the notion that gravitational energy is non-localised. The observed pulse was tightly constrained in time, ~10ms scale.  The pulse moves through space with the speed of light, akin to electromagnetic waves, not through “space-time” as is confusingly said.  Both electromagnetic and gravitational equations have wave solutions to small perturbations – travelling waves that carry energy – as Einstein first predicted, though not dipole but of quadrupole order for gravitational waves.

The inference of large compact masses – neutron stars of tens of solar masses – is an indirect discovery of an unrecognised population of mega-stars that are indeed predicted from the Hilbert-Einstein equations of General Relativity.  These can be neutron stars above the so-called TOV size limit of 2.0Ms given by Cameron (1959); our modelling given at the recent Moscow PIRT conference (link here) finds higher mass ‘gravastar’ structures, ie. shell-stars of compact matter with centres dominated by hypergravitational fields.

Posted in gravitation | Tagged , , , , | 5 Comments

Gravitational collapse without black holes

The contemporary notion of black holes originates in Oppenheimer and Snyder’s 1939 article “On Continued Gravitational Contraction” (Phys. Rev. 56:455, 1939).  Later Roger Penrose (Phys. Rev. Lett. 14:57, 1965)  showed that the O&S metric gave rise to trapped surfaces, ie. regions of space from which no light rays can escape, and proved that within such surfaces black-hole formation is inevitable. But what if their metric is faulty?

Trevor Marshall’s challenging article uses differential geometry to show that a simple modification of the O&S metric, fully consistent with General Relativity, enables all radial light rays originating in the interior escape to the exterior. There is no trapped surface and no black hole; on the contrary there is a stable end state with finite density, contained within a sphere of Schwarzschild radius, contracting ever more slowly on itself over infinite time.

Such solutions may be seen as counter-intuitive if, above a certain density, “no force can countervail against gravity”.  Indeed, they require gravity to be repulsive in the extreme high regime, where its energy density is comparable to mass densities.  It therefore fits intuitively with the field interpretation of gravity.  On the other hand, the purely geometric interpretation based on the extreme form of the ‘Equivalence Principle’ has no light-ray connectivity, so is not consistent with causality. Is that not counter-intuitive?

Trevor Marshall’s full paper is in the December issue of Astrophys. Space Sci. (2012) 342:329–332.  DOI 10.1007/s10509-012-1170-y

Posted in gravitation | Tagged , , , , , , , , | 1 Comment

Higgs science in turmoil

New Scientist shines some realism into the Higgs-hype in reporting (by Slezak and Grossman, 14 July) from some of the scientists involved

“…beginning of the end of the standard model” (Georg Weiglein)
Rates of decay into pairs of other particles are different from predicted (especially the decay into photon pair), so that the Higgs could be a composite (Alex Pomarol), not a fundamental particle after all.

Higgs doesn’t cover photons which, being mass-less, are supposed to slip unhindered through the Higgs field. It tells us nothing about the neutrino, perhaps also mass-less. Nor does it cover the majority of matter in the galaxy – “dark matter”.

Rather than the discovery of the Higgs being a keystone, they now say the standard model doesn’t include gravity and gravitons and quote Steven Weinberg “it’s crucial to keep looking for a more comprehensive theory”.

Lisa Grossman changed her tune from only one week earlier (Let the Higgs games begin, New Scientist, 7th July) when she claimed the ‘standard’ “model is one of the most successful in physics” and wrote than knowing the Higgs’ mass should give us a theory explaining the varied masses of ‘fundamental’ particles, dark matter and gravity. A severe affliction of hope trumping reason, as spawned ‘Higgsteria‘.


Posted in fundamental particle physics, gravitation | Tagged , , , , , | 2 Comments

Self-bending wave packets – a counter-example to the photon model

Self-bending light-beams are predicted in a new PRL paper called Nondiffracting Accelerating Wave Packets of Maxwell’s Equations (April 2012)

Previously ‘Airy’ wave packet solutions had been found and demonstrated experimentally, but diffraction for finite angles of bending tend to destroy them.  ‘Airy’ plasmons propagating at an air-conductor interface do show self-healing properties and bend while retaining a beam-like form to a distance of 10-20 μm.

The new non-diffracting solutions of Maxwell’s equations are much superior, propagating in vacuo in a 90 degree arc in just 35μm.  The  ‘photon’ model of light has no counterpart to these exact vector-solutions of the full Maxwell equations.  This adds to the examples of photon-failures described earlier.

Posted in fundamental particle physics, quantum crisis | Tagged , , , , | Leave a comment

The Higgs after Einstein’s Unified Field Theory

After the Higgs  mania, in the cold light of 2012, let’s think back to the basic scepticism of reality-physicists for the current ‘standard model’ and string ‘theory’ – which is a string of conjectures without principles such as energy conservation. 

Einstein wrote in the 1931 Commemoration volume of essays, that Maxwell tried to find a mechanical model for light vibrations, but “the equations themselves were all that was essential” and “the field intensities… were elementary, not derivable from other simpler entities.” Since Maxwell, Physical Reality is viewed as “represented by continuous fields, governed by PDEs and not capable of any mechanical interpretation.”

“This change in the conception of Reality is the most profound and the most fruitful that physics has experienced since the time of Newton”, wrote Einstein, and that notwithstanding Quantum Mechanics, physicists will be brought back to “Maxwell’s programme” ie. “the description of Physical Reality by fields which satisfy without singularity a set of partial differential equations.”

Einstein however failed in his life-project to develop a ‘unified field theory’ covering all physical forces. So current models of Physical Reality still require massive ‘particles’ as well as the fields.

Whatever the outcome over the Higgs, the current ‘standard model’ cannot be the ultimate answer – it doesn’t include the gravitational field while its ‘photons’ are inadequate in modeling the e-m field.  Pretty secure as a basis for combatting Higgs mania and delusion!

Posted in fundamental particle physics, gravitation | Tagged , , , , , , , | Leave a comment

Crunch-time over Higgs

The ATLAS group at CERN claims to see a ‘hint’ of Higgs in their event statistics around energies of 125 GeV.

As fields and particles are viewed as complementary, why does the Higgs Field get little mention. Does the term “God field” lack punch? Does the particle “boson” grab you, while the “boson field” lacks umph?

The Higgs field – in the Standard Model – consists of two neutral and two charged component fields while the Higgs boson is the particle associated with it.

Proponents of the ‘standard model’ have long avoided the issue of the ‘graviton’, the particle supposed to be associated with the gravity field, but given little credibility by physicists. So are we not right to be highly sceptical of the ‘higgs’? Non-detection would be a blow to the ‘standard model’ community, so claims to detection are over-influenced by self-interest.

As detection implies a new higgs-energy field, let’s not forget it would make an interesting addition to the Einstein-Hilbert field equation.

Posted in fundamental particle physics, gravitation | Tagged , , , , , , | 1 Comment

Wave neutrinics – new territory of the neutrino

 Alice has a pot at Jim Al-Khalili’s rash promise…..

So neutrinos might – just might – go faster than light. Maybe some neutrinos go faster than some light – maybe. Let’s face it, we don’t really understand neutrinos as much as light. There’s an awful lot of them, and they might – just might – have a little bit of mass – or at least some of them might. 

Say the neutrino field (in all of its varieties) has zero mass, so it propagates at the speed of light. But what is that? The speed of light depends on its frequency, through the refractive index of the medium. Do you retort there is no medium – that the aether went out a hundred years ago? Well there is hardly empty space between Geneva and Gran Sasso.

Also, the full understanding (if that is what we have) of light propagation requires us to distinguish between ray optics and wave optics, even in “empty” space. To a very good approximation we work out how light paths are bent by the Sun’s gravity by applying Fermat’s Principle (ray optics) to the path length. One way of describing this latter calculation (see The Theory of Gravity by A. A. Logunov, 2001) is that the Riemann forward light cone is contained within the Minkowski causality cone. But there is a region of space-time between the two cones, and that region is where there is scope for different frequencies to behave differently.

Now throw in the new varieties of speed-of-light objects and, without needing to wander into any exotic new dimensions, you have some new physics. While holding firm to causality, I would not be sure that Jim Al-Khalili will not have to “eat his boxer shorts on live TV”.

Posted in astrobiology | Tagged , , , , , | 1 Comment

Neutrinos do Cherenkov, don’t they?

CERN theorists seem baffled, but it’s no surprise that standard physics predicts supraluminal (FtL) neutrinos to slow down via Cherenkov radiation analogous to FtL charged particles, although Cohen & Glashow call it bremstrahlung of electron-positron pairs. Cherenkov radiation is best depicted by analogy with the sonic boom of a supersonic projectile – a sonic boom in the electromagnetic field from a supersonic particle. Likewise, a FtL neutrino would generate a sonic boom in the gravitational field and slow down to ‘c’ (not lower as suggested).

Another argument (neutrino-reaction) is that light is slowed below ‘c’ due to transient electron-positron pairs – zeropoint vacuum fields – but neutrinos are not slowed. This forgets that the field energy has an equivalent gravitating mass (E/c2), which decreases ‘c’ below cvaccuum – FtL neutrinos slowed to ‘c’ by Cherenkov-type emission.

It seems physicists need reminding that the powerful Einstein-Hilbert gravitational field equation includes source terms from field-energy, both gravitational and electromagnetic. Depicting fields as particles – whether gravitons or photons – can readily mislead.

Posted in fundamental particle physics, gravitation | Tagged , , , , , , , | Leave a comment

Can we celebrate Defeat for the Photon by Maxwell-Planck theory?

Success for SPUC and Maxwell-Planck theory is reported in Wikipedia as

“experimental prediction of SED dubbed ‘spontaneous parametric up-conversion’ (SPUC) was tested in 2009 and 2010 with positive results.”   [consulted 1 Aug.2011]

The formulations of both the Chinese (2009) and Indian (2010) groups appear to fit well with our 2002 prediction and the technical description presented at the Bristol ABB conference.  The new studies show

## the cutting angle of the BBO crystal must be such as to avoid confusion with second harmonic generation (SHG)

## the need for a large (20 degree) conical angle, which contrasts with the very small angles used with Lithium Iodate in the earlier Italian experiments.

## the dependence on crystal thickness confirms exponential growth of the SPUC and SPDC signals.

## acknowledgement by the Chinese group that SPUC occurs as a consequence of interaction between the zeropoint (“quantum noise”) and the laser components.

Their reference to “early nonlinear optics” relates to the analysis in the 1960s, by people like Bloembergen and Kleinmann, as stressed in 2002.

These results underline the inadequacy of post-1960s nonlinear (that is Quantum) optics, whereby a laser “photon” converts into two lower-energy photons (SPDC).  Both groups confirm SPUC, that is the outgoing cone may contain components whose frequency is higher than the laser.  If the claims about excluding SHG are correct, the results give us grounds for celebrating the long-awaited confirmation of the 2002 prediction.

Posted in quantum crisis | Tagged , , , , , | Leave a comment

The Shell Collapsar established in GR

A consistent description is possible for gravitationally collapsed bodies in General Relativity, in which collapse stops before the object reaches its gravitational radius. Non-singular solutions exist with the density reaching a maximum close to the surface and then decreasing towards the centre. While such solutions have been calculated in specific cases, a recent study (Entropy journal, special issue on Black Hole thermodynamics) establishes the general conclusion from re-analysing the classic Oppenheimer-Snyder (OS) 1939 modelling of a dust star contracting under its self-gravity. ie. as a spherical distribution of non-interacting dust particles.

Though that article On Continued Gravitational Contraction implied support for a black-hole solution, this re-analysis shows that the final OS density distribution accords with gravastar and other shell model solutions. The parallel Oppenheimer-Volkoff (OV) study of 1939 used the equation of state for a neutron gas, but considered only stationary solutions of the field equations. Recently the OV equation of state was found to permit solutions with minimal rather than maximal central density, and now a similar topology is found for the OS dust collapsar, in which a uniform dust-ball starts with large radius and collapses to a shell at the gravitational radius with density decreasing monotonically towards the centre. The OS dust model gave the first exact, time-dependent solution of the field equations and was at one time considered central in black-hole theory. Regarded as a limiting case of OV, it indicates the possibility of neutron stars of unlimited mass with a similar shell topology, termed ‘horizonless’ as they lack the ‘event horizon’ of black-hole theory.

Posted in gravitation | Tagged , , , , , | Leave a comment

Gruber Prize for LIGO team’s gravitational waves

The 2016 Gruber Cosmology Prize of $500 000 award citation reads:

The Gruber Foundation proudly presents the 2016 Cosmology Prize to Rainer Weiss, Kip Thorne, Ronald Drever, and the entire LIGO team for pursuing a vision to observe the universe in gravitational waves, leading to a first detection that emanated from the collision of two black holes. 

This remarkable event provided the first glimpse into the stronggravity regime of Einstein’s theory of general relativity that governs the dynamics of black holes, giving direct evidence for their existence, and demonstrating that their nature is consistent with the predictions of general relativity.

The first detection of gravitational waves was a major technical achievement, but it’s the identification as from a collision of a pair of black-holes that’s given by Gruber as its cosmological significance.  If not black-holes, then would theoretician Kip Thorne still merit the prize?  The “first glimpse” into Einstein’s general relativity was of course gained from “pulsars”, rapidly-pulsing radio wave emitters which were quickly identified with neutron stars of highly compact neutron matter.  The collision of two such objects has long been predicted to give a mega-burst of gravitational radiation.

Science normally demands an observation is reproducible – waiting for further detections or even a spectrum  of wave sizes and periods would normally be required.  Moreover, a study back in 2002 established that the late-stage part of the wave pulse (‘ring-down’ modes) would be needed to provide strong evidence for black-holes [Abramowicz et al., Astron & Astrophys.] – the LIGO signal was not strong enough for this.  So the LIGO team fell back on saying neutron stars cannot be as big as 30 times the sun’s mass and ignoring possibilities of other condensed-matter astrophysical objects of similar size.

The cosmological significance of the LIGO detection was thus the first detection of compact objects of around 30 times the sun’s mass, spiralling in to touch each other and then coalescing in the way predicted by Landau and Lifshitz in the 1960s.  But condensed-matter objects generally, whether the ‘horizonless’ variety or exotic black-holes.  The analysis and computational methods (‘post Newtonian’ expansions) have been advanced since then, but as leading theorists have just shown (Ruffini et al.), the results are close to the Landau-Lifshitz modelling.   As long as the nature of the binary compact objects remains uncertain, there’s no living theoretician to share the prize with Weiss, Drever and the LIGO team.

Posted in gravitation | Tagged , , , , , | Leave a comment