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December 01 2016

Archimedes
19:32
0078 340c 500

Emergent Gravity and the Dark Universe
by Erik Verlinde
arxiv.org/abs/1611.02269 (8 Nov 2016)


Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional `dark' gravitational force describing the `elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a0 = c H0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Tags: science
Reposted byscience science

November 29 2016

Archimedes
01:37
Saturn and Melancholia Dance of Death
(terminus 15 Sep 2017, 13:07 GMT)
Tags: science
Reposted byastronomygrouplimonlego-rojono-longer-koreretaliateRacuchalexandersmith8805abstractLoopscocciuellasevekStonerrsaysomethingfreedanceelchupacabraRekrut-Kstraycataperturev2pxjabolmaxkogsshallowxalmetafnordAndiyoungandstupiddrseilzugNaitliszreloveutionghalbadiousMeeresbrautthrill-killerporannyLuukkatentacleguydowyjscia

November 28 2016

Archimedes
17:03
3455 b923 500
Einstein - Ehrenfest - de Sitter
Eddington - Lorentz   (26 Sep 1923)
The critical geometry of a thermal big bang
by Niayesh Afshordi & Joao Magueijo
arxiv.org/abs/1603.03312, vs.2 (8 Nov 2016)


We explore the space of scalar-tensor theories containing two non-conformal metrics, and find a discontinuity pointing to a “critical” cosmological solution. Due to the different maximal speeds of propagation for matter and gravity, the cosmological fluctuations start off inside the horizon even without inflation, and will more naturally have a thermal origin (since there is never vacuum domination). The critical model makes an unambiguous, non-tuned prediction for the spectral index of the scalar fluctuations: nS = 0.96478(64). Considering also that no gravitational waves are produced, we have unveiled the most predictive model on offer. The model has a simple geometrical interpretation as a probe 3-brane embedded in an EAdS2 × E3 geometry.
Tags: science
Reposted bysciencemozgmnienieboli1Najadapandorcia

October 30 2016

Archimedes
13:36
3D print your own baby universe

(D L Clements, S Sato, A Portela Fonseca: "Cosmic sculpture: a new way to visualise the cosmic microwave background", European Journal of Physics, dx.doi.org/10.1088/0143-0807/38/1/015601, 28 Oct 2016)
Tags: science
Reposted byastronomygroupp856

October 29 2016

Archimedes
12:34
Headquarters of the Mathematical Association of America (18th Street, Washington, D.C.) with Type 5 pentagonal tiling in the entrance hall.
Tags: science
Reposted byweirdscenesinsidethegoldmineFlypngeometrykuroinekochrisankinyouammushusofiasgruetzemetafnordmarbearbollabollaandrewmylesirmelinanimareskmassivejackadremdicoJuNeonlubicyronisstraycatpesymistalevuneaperturenicapicellaikarishillenyahawakLuukkadevloqueAronarabusdafilkogsyubabamfmfmfjanInteMrCoffeoskibarricadefinkreghkrzyskkartoNikkovlSpinNE555manticoreAndikoszkapuck152fadenbgaf
Archimedes
10:19
28 Oct 2016: Grand opening of the "Höschen" bar (Dunckerstraße 9, 10437 Berlin) with Type 15 pentagonal tiling in the restroom.

(Casey Mann, Jennifer McLoud-Mann, David Von Derau: "Convex pentagons that admit i-block transitive tilings", arxiv.org/abs/1510.01186, 5 Oct 2015)
Reposted bygeometryberlinsofiasmushup856JuNeon

October 21 2016

Archimedes
15:21
Tags: untagged
Reposted byowlssmirekstraycatznuhYggrykartoNikMeeresbrautmetafnordprefectmushubagheraNemesis86MeeresbrautcittentacleguyJosette

October 20 2016

Archimedes
10:56
Mysterious Cosmic Objects Erupting in X-rays Discovered
(NASA: Chandra, 19 Oct 2016)
Tags: science
Reposted byastronomygroupDevaelisah
Archimedes
10:52

(ESA, 20 October 2016)  Essential data from the ExoMars Schiaparelli lander sent to its mothership Trace Gas Orbiter during the module’s descent to the Red Planet’s surface yesterday has been downlinked to Earth and is currently being analysed by experts.

Early indications from both the radio signals captured by the Giant Metrewave Radio Telescope (GMRT), an experimental telescope array located near Pune, India, and from orbit by ESA’s Mars Express, suggested the module had successfully completed most steps of its 6-minute descent through the martian atmosphere. This included the deceleration through the atmosphere, and the parachute and heat shield deployment, for example.

But the signals recorded by both Pune and Mars Express stopped shortly before the module was expected to touchdown on the surface. Discrepancies between the two data sets are being analysed by experts at ESA’s space operations centre in Darmstadt, Germany.

The detailed telemetry recorded by the Trace Gas Orbiter was needed to better understand the situation. At the same time as Schiaparelli’s descent, the orbiter was performing a crucial ‘Mars Orbit Insertion’ manoeuvre – which it completed successfully. These important data were recorded from Schiaparelli and beamed back to Earth in the early hours of Thursday morning.

The data have been partially analysed and confirm that the entry and descent stages occurred as expected, with events diverging from what was expected after the ejection of the back heat shield and parachute. This ejection itself appears to have occurred earlier than expected, but analysis is not yet complete.

The thrusters were confirmed to have been briefly activated although it seems likely that they switched off sooner than expected, at an altitude that is still to be determined.
Tags: science

October 16 2016

Archimedes
19:30
8026 de9c 500

Discovery of peculiar periodic spectral modulations in a small fraction of solar type stars
by Ermanno F. Borra & Eric Trottier
https://arxiv.org/abs/1610.03031 (10 Oct 2016)


A Fourier transform analysis of 2.5 million spectra in the Sloan Digital Sky Survey was carried out to detect periodic spectral modulations. Signals having the same period were found in only 234 stars overwhelmingly in the F2 to K1 spectral range. The signals cannot be caused by instrumental or data analysis effects because they are present in only a very small fraction of stars within a narrow spectral range and because signal to noise ratio considerations predict that the signal should mostly be detected in the brightest objects, while this is not the case. We consider several possibilities, such as rotational transitions in molecules, rapid pulsations, Fourier transform of spectral lines and signals generated by Extraterrestrial Intelligence (ETI). They cannot be generated by molecules or rapid pulsations. It is highly unlikely that they come from the Fourier transform of spectral lines because too many strong lines located at nearly periodic frequencies are needed. Finally we consider the possibility, predicted in a previous published paper, that the signals are caused by light pulses generated by Extraterrestrial Intelligence to makes us aware of their existence. We find that the detected signals have exactly the shape of an ETI signal predicted in the previous publication and are therefore in agreement with this hypothesis. The fact that they are only found in a very small fraction of stars within a narrow spectral range centered near the spectral type of the sun is also in agreement with the ETI hypothesis. However, at this stage, this hypothesis needs to be confirmed with further work. Although unlikely, there is also a possibility that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars.
Tags: science
Reposted byastronomygroupbesenpaket

October 13 2016

Archimedes
18:14

"The Evolution fo Galaxy Number Denisty at Z < 8 and its Implications"
, by Christopher J. Conselice, Aaron Wilkinson, et al. (preprint 9 Oct 2016)

The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z ∼ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies, more massive than M∗ = 10^6 M⊙ , decreases as φT ∼ t ^−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M∗ > 10^7 M⊙ . By using the M∗ = 10^6 M⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0 × 10^12 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.
Tags: science
Reposted byastronomygroupp-093-reade-gruppe

September 21 2016

Archimedes
22:56
Virtually unwrapped En-Gedi scroll

(W.B. Seales, C.S. Parker et al.  "From damage to discovery via virtual unwrapping: Reading the scroll from En-Gedi", Science Advances, DOI: 10.1126/sciadv.1601247, 21 Sep 2016)
Reposted byBlue-sing Blue-sing

September 12 2016

Archimedes
17:27

September 09 2016

Archimedes
00:27
Bennu
Tags: science
Reposted byastronomygroup astronomygroup

September 05 2016

Archimedes
19:42
Philae found! (ESA, 5 Sept 2016)
Tags: science
Reposted byastronomygroupjalokim0Kladderadatschriotyouambesensofiaspaketbugienordernzerocool911namelessczinok

August 26 2016

Archimedes
09:19
2171 fced 500

A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44
by Pieter van Dokkum, Roberto Abraham, et al.
http://arxiv.org/abs/1606.06291v1 (20 Jun 2016)


Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these Ultra Diffuse Galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of 47 km/s, which implies a dynamical mass of M_dyn=0.7x10^10 M_sun within its deprojected half-light radius of r_1/2=4.6 kpc. The mass-to-light ratio is M/L=48 M_sun/L_sun, and the dark matter fraction is 98 percent within the half-light radius. The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0.4" seeing we infer that Dragonfly 44 has 94 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are "failed" galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r=4.6 kpc to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ~10^12 M_sun, similar to the mass of the Milky Way. The existence of nearly-dark objects with this mass was unexpected, as galaxy formation was thought to be maximally-efficient in this regime.

(Scientists Discover Massive Galaxy Made of 99.99 Percent Dark Matter)
Tags: science
Reposted bybesenbollabolla

August 25 2016

Archimedes
10:34
Joe Biden: "Peace For Our Time"
"The settlement of the Syrian problem, which has now been achieved is, in my view, only the prelude to a larger settlement in which all Near East may find peace. This morning I had another talk with the Turkish President, Herr Erdoğan, ... I believe it is peace for our time. We thank you from the bottom of our hearts. Go home and get a nice quiet sleep."

"America has been offered a choice between war and shame. She has chosen shame, and will get war." (Winston Churchill)
Tags: politics

August 12 2016

Archimedes
18:46

"The signal"
by "Pale Red Dot - A search for Earth-like planets around Proxima Centaury"

"So while we are convinced there is a signal in the Doppler measurements of Proxima, previous data do not allow to confirm its presence and clarify its origin. The long term variability of Proxima spoiled our attempts to combine data from previous observations so we needed a dedicated campaign. Combination of UVES and HARPS data at different cadences suggest that the star is showing a smoothly varying Doppler signal. Since the UVES survey set an upper limit between 2-3 Earth masses and if the signal is not activity induced, it must correspond to a planet smaller than that (between 1-2 Earth masses). The signal might well be caused by stellar activity, which should be quasi-periodic as opposed to the strict periodicity of the orbital motion of a putative planet. [...]"
Tags: science
Reposted byastronomygroupp856

August 11 2016

Archimedes
07:32
Leaving the EU...

Long-term persistence

by Luigi Guiso, Paola Sapienza, Luigi Zingales
Journal of the European Economic Association. doi:10.1111/jeea.12177 (Jul 2016)


We study whether a positive historical shock can generate long-term persistence in development. We show that Italian cities that achieved self-government in the Middle Ages have a higher level of civic capital today than similar cities in the same area that did not. The size of this effect increases with the length of the period of independence and its intensity. This effect persists even after accounting for the fact that cities did not become independent randomly. We conjecture that the Middle-Age experience of self-government fostered self-efficacy beliefs—beliefs in one's own ability to complete tasks and reach goals—and this positive attitude, transmitted across generations, enhances civic capital today. Consistently, we find that fifth-graders in former free city-states exhibit stronger self-efficacy beliefs and that these beliefs are correlated with a higher level of civic capital.
Tags: politics

August 10 2016

Archimedes
00:32
7955 9e60 500
Explaining disappearing stars... (KH 15D)
Tags: science
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