On the role of shear in cosmological averaging

Using the spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi dust solution, we study how the shear and the backreaction depend on the sharpness of the spatial transition between voids and walls and on the size of the voids. The voids considered here are regions with matter density Omega ~ 0 and expansion rate Ht ~ 1, while the walls are regions with matter density Omega ~ 1 and expansion rate Ht ~ 2/3. The results indicate that both the volume-average shear and the variance of the expansion rate grow proportional to the sharpness of the transition and diverge in the limit of a step function, but, for realistic-sized voids, are virtually independent of the size of the void. However, the backreaction, given by the difference of the variance and the shear, has a finite value in the step-function limit. By comparing the exact result for the backreaction to the case where the shear is neglected by treating the voids and walls as separate Friedmann-Robertson-Walker models, we find that the shear suppresses the backreaction by a factor of (r_0/t_0)^2, the squared ratio of the void size to the horizon size. This exemplifies the importance of using the exact solution for the interface between the regions of different expansion rates and densities. The suppression is justified to hold also for a network of compensated voids, but may not hold if the universe is dominated by uncompensated voids.Comment: 17 pages, 3 figure

On the role of shear in cosmological averaging II: large voids, non-empty voids and a network of different voids

We study the effect of shear on the cosmological backreaction in the context of matching voids and walls together using the exact inhomogeneous Lemaitre-Tolman-Bondi solution. Generalizing JCAP 1010 (2010) 021, we allow the size of the voids to be arbitrary and the densities of the voids and walls to vary in the range 0 < Omega_v < Omega_w < 1. We derive the exact analytic result for the backreaction and consider its series expansion in powers of the ratio of the void size to the horizon size, r_0/t_0. In addition, we deduce a very simple fitting formula for the backreaction with error less than 1% for voids up to sizes r_0 = t_0. We also construct an exact solution for a network of voids with different sizes and densities, leading to a non-zero relative variance of the expansion rate between the voids. While the leading order term of the backreaction for a single void-wall pair is of order (r_0/t_0)^2, the relative variance between the different voids in the network is found to be of order (r_0/t_0)^4 and thus very small for voids of the observed size. Furthermore, we show that even for very large voids, the backreaction is suppressed by an order of magnitude relative to the estimate obtained by treating the walls and voids as disjoint Friedmann solutions. Whether the suppression of the backreaction due to the shear is just a consequence of the restrictions of the used exact models, or a generic feature, has to be addressed with more sophisticated solutions.Comment: 19 pages, 5 figure

Vapaaehtoisuus- ja oikeudenmukaisuuskokemukset lähisuhdeväkivallan sovittelussa

Lähisuhdeväkivallan sovittelu on Suomessa ollut lakisääteistä vuodesta 2006, jota ennen sitä soviteltiin eri laajuudella Suomen eri osissa. Lähisuhdeväkivallan sovittelu on ollut alusta alkaen varsin kiistanalaista. Uhrin asemaa on sovittelussa pidetty huonona, hänen aitoa vapaaehtoisuuttaan on epäilty ja rikoksesta epäillyn on katsottu pääsevän sovittelussa liian vähällä. Toisaalta sovittelusta on saatu runsaasti hyviä kokemuksia ja osapuolia on ohjattu palveluiden piiriin. Kahdessa viimeisessä hallitusohjelmassa lähisuhdeväkivallan sovittelun asema on ollut selvittelyn kohteena. Tässä tutkielmassa tarkastellaan lähisuhdeväkivallan sovittelun osapuolten ja sovittelijoiden oikeudenmukaisuus- ja vapaaehtoisuuskokemuksia ja heidän kokemuksiaan sovittelun menettelytavoista. Vertailuryhmänä tutkimuksessa ovat muun väkivallan kuin lähisuhteessa tapahtuneen väkivallan sovittelun osapuolet ja sovittelijat. Tutkimus toteutettiin poikittaistutkimuksena kyselyllä, jonka kohteina olivat kolmen Etelä-Suomen sovittelutoimiston lähisuhdeväkivallan ja muun väkivallan sovittelun osapuolet ja sovittelijat noin 12 kuukauden aikana vuosina 2016–2017. Oikeudenmukaisuuskokemuksen mittari perustui Colquittin (2001) ja Gramatikovin ym. (2009) tuloksiin, vapaaehtoisuuden mittari itseohjautuvuusteorian ulkoisen kontrollin mittareihin ja sovittelun menettelytapojen mittari Alexanderin (2008) metamalliin. Kyselyä testasivat vapaaehtoiset sovittelijat ja sovittelutoimiston henkilökunta noin kahden kuukauden ajan. Kyselyn oltua käynnissä noin kaksi kuukautta havaittiin, että vastausprosentti on erittäin huono. Korjaustoimenpiteenä kyselyä lyhennettiin, mutta toimenpiteistä huolimatta vastausprosentti jäi selvästi tavoitetta alhaisemmaksi. Aineisto (n = 169) analysoitiin R-ohjelmistolla käyttäen muun muassa havainnollistavia kuvia, faktorianalyysiä, ei-parametrisiä testejä, lineaarista regressioanalyysia ja logistista regressioanalyysia. Aineiston perusteella osapuolet kokevat sovittelun oikeudenmukaisemmaksi kuin sovittelijat arvioivat. Osapuolet myös kokevat sovittelijan ohjaavan sovittelutapahtumaa voimakkaammin kuin sovittelijat arvioivat mutta osapuolet ovat tyytyväisempiä sovitteluun kokonaisuutena kuin sovittelijat arvioivat. Vapaaehtoisuus- ja oikeudenmukaisuuskokemuksissa ei ole eroa lähisuhdeväkivallan ja muun väkivallan sovittelussa. Fasilitoiva sovittelun menettelytapa vaikuttaa positiivisesti oikeudenmukaisuuskokemukseen lähisuhdeväkivaltatapauksissa mutta muun väkivallan sovittelussa sillä ei havaittu olevan merkitystä. Osapuolet ovat muutamaa poikkeusta lukuun ottamatta erittäin tyytyväisiä sovitteluun ja oikeudenmukaisuuskokemus on hyvin myönteinen. Vaikka osapuolet kokevat, että he osallistuvat sovitteluun vapaaehtoisina, he voivat kuitenkin kokea syyllisyyttä, elleivät hakisi sovintoa, tai he voivat epäillä kieltäytymisen aiheuttavan pahaa mieltä toiselle henkilölle. Aineisto tukee lähisuhdeväkivallan sovittelun jatkamista mutta osapuolten aitoon haluun ja kykyyn osallistua sovitteluun on syytä kiinnittää huomiota. Tutkielmassa annetaan joitakin suosituksia sovittelutoiminnan kehittämiseksi. Jatkotutkimus lähisuhdeväkivallan sovittelun osapuolten ja sovittelijoiden kokemuksesta ja sovittelun vaikuttavuudesta on tarpeellista. Tutkielmassa esitetään ehdotus jatkotutkimuksen tutkimusasetelmasta ja tutkimuksen menettelytavoista, jotta toiminnan kehittämisen pohjaksi saataisiin riittävän luotettavaa tietoa.The mediation of intimate partner violence (IPV) has been statutorily regulated in Finland since year 2006. Earlier IPV was mediated around Finland to different extents. The mediation of IPV has been very controversial from the very beginning. Status of victims has been considered bad, there have been doubts about her/his voluntariness and it has been seen that the suspect is too slightly affected. On the other hand there has been a lot good experiences of mediation and the parties have been instructed to further services. This thesis studies perceived justice and voluntariness in the mediation of IPV and perceived mediation procedures of mediation parties and mediators. As a control group in the study there were mediation parties and mediators of cases with other violence than IPV. The study was cross-sectional and the survey aimed to cover all parties and mediators of IPV and non-IPV violence mediation cases managed by three service providers in Finland during 12 months period. Measure of perceived justice was based on results by Colquitt (2001) and Gramatikov et al (2009), measure of voluntariness was based on self-regulation questionnaires of self-determination theory and measure of mediation procedure was based on the metamodel of Alexander (2008). The survey was tested by employees of mediation service providers and by voluntary mediators. After a short period it was found that the response rate is very low. As a corrective action the survey was truncated but despite survey simplification response rate did not achieve target level. Data (n = 169) was analysed with R software using illustrative figures, factor analysis, non-parametric test, linear regression analysis and logistic regression analysis. Based on study data mediation parties perceive mediation as more fair than mediators. Parties also perceive that mediators control more the process than mediators assess but parties are more satisfied with the mediation than mediators assess. There are no differences of perceived voluntariness and justice between IPV mediation and other violence than IPV mediation. Facilitative mediation style is in positive relation with perceived justice in IPV cases but in control group no relation was seen between the constructs. Almost all mediation parties are very satisfied with the mediation and their perceived justice is very positive. Even the parties see that they are voluntarily in mediation, they might feel guilty if they were not aiming to reconciliation, or they might think that their refusal to participate mediation could upset the other party. Study data supports that it’s reasonable to continue IPV mediation but attention should be drawn to the genuine desire and capacity of the parties to participate mediation. In the thesis there are some recommendations how to develop mediation activities. Further studies are needed to understand better IPV mediation effectiveness and how the parties and mediators perceive the mediation. In the thesis a study design is presented to get valid and reliable data for continuous development of IPV mediation activities

Hubble flow variance and the cosmic rest frame

We characterize the radial and angular variance of the Hubble flow in the COMPOSITE sample of 4534 galaxies, on scales in which much of the flow is in the nonlinear regime. With no cosmological assumptions other than the existence of a suitably averaged linear Hubble law, we find with decisive Bayesian evidence (ln B >> 5) that the Hubble constant averaged in independent spherical radial shells is closer to its asymptotic value when referred to the rest frame of the Local Group, rather than the standard rest frame of the Cosmic Microwave Background. An exception occurs for radial shells in the range 40/h-60/h Mpc. Angular averages reveal a dipole structure in the Hubble flow, whose amplitude changes markedly over the range 32/h-62/h Mpc. Whereas the LG frame dipole is initially constant and then decreases significantly, the CMB frame dipole initially decreases but then increases. The map of angular Hubble flow variation in the LG rest frame is found to coincide with that of the residual CMB temperature dipole, with correlation coefficient -0.92. These results are difficult to reconcile with the standard kinematic interpretation of the motion of the Local Group in response to the clustering dipole, but are consistent with a foreground non-kinematic anisotropy in the distance-redshift relation of 0.5% on scales up to 65/h Mpc. Effectively, the differential expansion of space produced by nearby nonlinear structures of local voids and denser walls and filaments cannot be reduced to a local boost. This hypothesis suggests a reinterpretation of bulk flows, which may potentially impact on calibration of supernovae distances, anomalies associated with large angles in the CMB anisotropy spectrum, and the dark flow inferred from the kinematic Sunyaev-Zel'dovich effect. It is consistent with recent studies that find evidence for a non-kinematic dipole in the distribution of distant radio sources.Comment: 37 pages, 9 tables, 13 figures; v2 adds extensive new analysis (including additional subsections, tables, figures); v3 adds a Monte Carlo analysis (with additional table, figure) which further tightens the statistical robustness of the dipole results; v4 adds further clarifications, small corrections, references and discussion of Planck satellite results; v5 typos fixed, matches published versio

Maailmankaikkeuden kiihtyvä laajeneminen kosmisten rakenteiden aiheuttamana ilmiönä

The cosmological observations of light from type Ia supernovae, the cosmic microwave background and the galaxy distribution seem to indicate that the expansion of the universe has accelerated during the latter half of its age. Within standard cosmology, this is ascribed to dark energy, a uniform fluid with large negative pressure that gives rise to repulsive gravity but also entails serious theoretical problems. Understanding the physical origin of the perceived accelerated expansion has been described as one of the greatest challenges in theoretical physics today. In this thesis, we discuss the possibility that, instead of dark energy, the acceleration would be caused by an effect of the nonlinear structure formation on light, ignored in the standard cosmology. A physical interpretation of the effect goes as follows: due to the clustering of the initially smooth matter with time as filaments of opaque galaxies, the regions where the detectable light travels get emptier and emptier relative to the average. As the developing voids begin to expand the faster the lower their matter density becomes, the expansion can then accelerate along our line of sight without local acceleration, potentially obviating the need for the mysterious dark energy. In addition to offering a natural physical interpretation to the acceleration, we have further shown that an inhomogeneous model is able to match the main cosmological observations without dark energy, resulting in a concordant picture of the universe with 90% dark matter, 10% baryonic matter and 15 billion years as the age of the universe. The model also provides a smart solution to the coincidence problem: if induced by the voids, the onset of the perceived acceleration naturally coincides with the formation of the voids. Additional future tests include quantitative predictions for angular deviations and a theoretical derivation of the model to reduce the required phenomenology. A spin-off of the research is a physical classification of the cosmic inhomogeneities according to how they could induce accelerated expansion along our line of sight. We have identified three physically distinct mechanisms: global acceleration due to spatial variations in the expansion rate, faster local expansion rate due to a large local void and biased light propagation through voids that expand faster than the average. A general conclusion is that the physical properties crucial to account for the perceived acceleration are the growth of the inhomogeneities and the inhomogeneities in the expansion rate. The existence of these properties in the real universe is supported by both observational data and theoretical calculations. However, better data and more sophisticated theoretical models are required to vindicate or disprove the conjecture that the inhomogeneities are responsible for the acceleration.Kosmologiset havainnot supernovista, kosmisesta mikroaaltotaustasta ja suuren mittakaavan galaksijakaumasta viittaavat avaruuden laajenemisen kiihtyneen suunnilleen maailmankaikkeuden iän jälkimmäisen puoliskon aikana. Yleisimmin kiihtyvyyden aiheuttajaksi on arveltu tasaisesti kaikkialle avaruuteen jakautunutta tuntematonta kenttää, jolla on suuri negatiivinen paine. Tämä nk. pimeä energia saa yleisen suhteellisuusteorian kenttäyhtälöiden mukaisesti painovoiman käyttäytymään repulsiivisesti, eli avaruuden laajenemisen kiihtymään. Havaintojen selittämisen ohella pimeä energia tuo kuitenkin mukanaan myös vakavia teoreettisia ongelmia, kuten selittämättömiä yhteensattumia ja kosmisten parametrien äärimmäisen tarkkaa hienosäätöä. Havaitun kiihtyvyyden fysikaalisen alkuperän ymmärtäminen onkin kenties eräs teoreettisen fysiikan tämän hetken suurimmista haasteista. Tässä työssä tarkastellaan sitä vaihtoehtoa, että kiihtyvyyden olisi pimeän energian sijaan aiheuttanut galaksirihmastojen ja suurten tyhjien alueiden muodostumisen vaikutus kosmologisista kohteista havaittavaan valoon. Tämän selityksen kannalta oleellisessa osassa ovat epälineaariset efektit, jotka jäävät huomiotta jos rakenteenmuodostusta kuvataan standardikosmologian tapaan lineaarisella häiriöteorialla. Esitämme ilmiölle seuraavanlaisen fysikaalisen tulkinnan: Koska varhaisessa maailmankaikkeudessa tasaisesti jakautunut aine keräytyy ajan myötä läpinäkymättömistä galakseista koostuviksi rihmastoiksi, havaittavan valon kulkemat alueet tulevat maailmankaikkeuden vanhetessa yhä tyhjemmiksi ja tyhjemmiksi. Näiden suurenevien tyhjien alueiden alkaessa laajeta keskiarvoon nähden sitä nopeammin mitä tyhjemmiksi ne tulevat, laajenemisnopeus voi kasvaa pitkin maailmankaikkeuden kehityshistorian halkovaa näkösädettämme ilman avaruuden laajenemisen kiihtymistä, tehden mahdollisesti oletuksen pimeän energian olemassaolosta tarpeettomaksi. Sen lisäksi, että esitetty selitys tarjoaa luonnollisen tulkinnan havaitulle kiihtyvyydelle, osoitamme että rakenteenmuodostuksen epälineaarisella tasolla huomioiva fenomenologinen malli sopii kosmologiseen havaintoaineistoon ilman pimeää energiaa myös kvantitatiivisella tasolla. Datasovituksen tuloksena saatavassa kosmologisessa mallissa maailmankaikkeuden ikä on 15 miljardia vuotta ja se sisältää 90% pimeää ainetta sekä 10% tavallista ainetta. Malli tarjoaa myös täsmäratkaisun yhteensattumaongelmaan: jos havaittu laajenemisen kiihtyminen aiheutuu tyhjistä alueista, kiihtyvyyden alkaminen luonnollisestikin osuu samaan aikaan tyhjien alueiden muodostumisen kanssa, kuten havaintojen mukaan näyttäisi tapahtuvan. Tulevaisuudessa suoritettavia lisätestejä ovat mm. mallin parametrien laskeminen teoriasta ja kvantitatiivisten ennusteiden laskeminen epäisotrooppisesta tyhjien alueiden jakaumasta aiheutuville kulmariippuvuuksille. Tutkimuksen sivutuotteena esitetään luokittelu kosmisten rakenteiden vaikutuksista sen perusteella, kuinka ne voivat aiheuttaa kiihtyvää laajenemista pitkin näkösädettämme. Olemme tunnistaneet kolme fysikaalisesti erillistä mekanismia: laajenemisen avaruudellisista vaihteluista aiheutuva maailmankaikkeuden keskimääräisen laajenemisnopeuden kasvu, suuren tyhjän alueen aiheuttama keskiarvoa nopeampi paikallinen laajeneminen, sekä havaitun valon kulku keskimääräistä nopeammin laajenevien tyhjien alueiden muodostaman verkoston läpi. Yleinen johtopäätös on se, että havaitun kiihtyvyyden selittämiseksi oleellisia ominaisuuksia ovat rakenteiden kasvu ja laajenemisnopeuden avaruudelliset vaihtelut. Näiden ominaisuuksien olemassaoloa maailmankaikkeudessamme tukevat havaintojen lisäksi myös teoreettiset laskelmat. Parempaa havaintoaineistoa ja kehittyneempiä teoreettisia malleja kuitenkin tarvitaan ratkaisemaan, onko esitetty otaksuma rakenteenmuodostuksesta kiihtyvyyden fysikaalisena alkuperänä oikeellinen. Rakenteiden vaikutus kosmologisiin havaintoihin on kiihtyvyyden alkuperästä riippumatta joka tapauksessa selvitettävä nykyistä tarkemmin, jotta tehtyjä havaintoja voidaan tulkita luotettavasti

Dark energy as a mirage

Motivated by the observed cosmic matter distribution, we present the following conjecture: due to the formation of voids and opaque structures, the average matter density on the path of the light from the well-observed objects changes from Omega_M ~ 1 in the homogeneous early universe to Omega_M ~ 0 in the clumpy late universe, so that the average expansion rate increases along our line of sight from EdS expansion Ht ~ 2/3 at high redshifts to free expansion Ht ~ 1 at low redshifts. To calculate the modified observable distance-redshift relations, we introduce a generalized Dyer-Roeder method that allows for two crucial physical properties of the universe: inhomogeneities in the expansion rate and the growth of the nonlinear structures. By treating the transition redshift to the void-dominated era as a free parameter, we find a phenomenological fit to the observations from the CMB anisotropy, the position of the baryon oscillation peak, the magnitude-redshift relations of type Ia supernovae, the local Hubble flow and the nucleosynthesis, resulting in a concordant model of the universe with 90% dark matter, 10% baryons, no dark energy, 15 Gyr as the age of the universe and a natural value for the transition redshift z_0=0.35. Unlike a large local void, the model respects the cosmological principle, further offering an explanation for the late onset of the perceived acceleration as a consequence of the forming nonlinear structures. Additional tests, such as quantitative predictions for angular deviations due to an anisotropic void distribution and a theoretical derivation of the model, can vindicate or falsify the interpretation that light propagation in voids is responsible for the perceived acceleration.Comment: 33 pages, 2 figs; v2: minor clarifications, results unchanged; v3: matches the version published in General Relativity and Gravitatio

Evaluating Factors Impacting Fallen Tree Detection from Airborne Laser Scanning Point Clouds

Fallen tree mapping provides valuable information regarding the ecological value of boreal forests. Airborne laser scanning (ALS) enables mapping fallen trees on a large scale. We compared the performance of line-detection-based individual fallen tree detection when using moderate point density ALS data (15 points/m2) and high-point-density unmanned aerial vehicle-based laser scanning (ULS) data (285 points/m2). Furthermore, we inspected the dataset and detection methodology-related factors impacting performance in each case. The results of this study showed that increasing the point density of the laser scanning dataset enables the detection of a larger proportion of fallen trees. However, based on our experiment, a line-detection-based fallen tree detection approach is sensitive to noise, thus generating a large number of false detections, especially with high-point-density data. Different types of filters, such as a simple height-based filter and machine-learning-based filters, can be used for reducing noise. However, using such filters is always a compromise, as in addition to reducing noise and thus false detections, they also reduce the number of true detections. Hence, a less noise-sensitive fallen tree detection method utilizing the finer details visible in high-density point clouds could be more suitable for high-point-density laser scanning data

The effect of inhomogeneous expansion on the supernova observations

We consider an inhomogeneous but spherically symmetric Lemaitre-Tolman-Bondi model to demonstrate that spatial variations of the expansion rate can have a significant effect on the cosmological supernova observations. A model with no dark energy but a local Hubble parameter about 15% larger than its global value fits the supernova data better than the homogeneous model with the cosmological constant. The goodness of the fit is not sensitive to inhomogeneities in the present-day matter density, and our best fit model has Omega_M ~ 0.3, in agreement with galaxy surveys. We also compute the averaged expansion rate, defined by the Buchert equations, of the best fit model and show explicitly that there is no average acceleration.Comment: minor corrections to match the version published in JCA