* Astronomy

Blobrana · L

RE: Space-time

Blobrana · L

Title: Goodness in the Axis of Evil
Authors: Rudolph E. Schild, Carl H. Gibson

An unexpected alignment of 2-4-8-16 cosmic microwave background spherical harmonic directions with the direction of a surprisingly large WMAP temperature minimum, a large radio galaxy void, and an unexpected alignment and handedness of galaxy spins have been observed. The alignments point to RA=202 degrees, delta = 25 degrees and are termed the "Axis of Evil". Already many authors have commented about how the AE impacts our understanding of how structure emerged in the Universe within the framework of Lamda-CDM, warm dark matter, string theory, and hydro-gravitational dynamics (HGD). The latter uniquely predicts the size scales of the voids and matter condensations, based upon estimates of fluid forces in the early phases of structure formation. Reported departures from simple Gaussian properties of the WMAP data favor two regimes of turbulent structure formation, and from these we make predictions of the nature of finer structure expected to be measured with the PLANCK spacecraft.
From HGD, friction has limited the expansion of superclusters to 30 Mpc but supervoids have expanded with the universe to 300 Mpc.

Read more (626kb, PDF)

Blobrana · L

Poincaré Dodecahedral Space (PDS) topology

Blobrana · L

RE: Space-time

Blobrana · L

Title: Towards observable signatures of other bubble universes II: Exact solutions for thin-wall bubble collisions
Authors: Anthony Aguirre, Matthew C Johnson
(Version v3)

We assess the effects of a collision between two vacuum bubbles in the thin-wall limit. After describing the outcome of a generic collision possessing the expected hyperbolic symmetry, we focus on collisions experienced by a bubble containing positive vacuum energy, which could in principle contain our observable universe. We provide criteria governing whether the post-collision domain wall accelerates towards or away from this "observation" bubble, and discuss the implications for observers located at various positions inside of the bubble. Then, we identify the class of solutions which have minimal impact on the interior of the observation bubble, and derive a simple formula for the energy density of a shell of radiation emitted from such a collision. In the context of a universe undergoing false vacuum eternal inflation, these solutions are perhaps the most promising candidates for collisions that could exist within our past light cone, and therefore in principle be observable.

Read more (455kb, PDF)

Blobrana · L

In an unusual logjam of contradictory claims, a revolutionary new model of the universe, as a soccer ball, arrives on astronomers' desks this morning at least slightly deflated.
In a paper being published today in the journal Nature, Dr. Jeffrey Weeks, an independent mathematician in Canton, N.Y., and his colleagues suggest, based on analysis of maps of the Big Bang, that space is a kind of 12-sided hall of mirrors, in which the illusion of infinity is created by looking out and seeing multiple copies of the same stars.
If the model is correct, it would rule out a popular theory of the Big Bang that asserts that our own observable universe is just a bubble among others in a realm of vastly larger extent.

"It means we can just about see the whole universe now" - Dr. Jeffrey Weeks.

But other astronomers, including a group led by Dr. David Spergel of Princeton, said a continuing analysis of the same data had probably already ruled out the soccer ball universe.

Read more

Most astronomers think that the universe is infinite, but recent measurements suggest that it could be finite and relatively small. Indeed, as Jean-Pierre Luminet describes, we could be living in an exotic universe shaped rather like a football

Read more

It seemed to have been kicked into touch, but now the notion of a "ball-shaped" universe is bouncing back, thanks to a look at the radiation left over from the big bang.

Read more

Blobrana · L

Plans to explore and understand the cosmic web - one of the biggest and most mysterious features of the universe - have been unveiled by scientists.
The sky appears as a vast darkness with spots of lights and clouds of dust, but astronomers have discovered that the stars and galaxies we can see are embedded in streams of light stretching between inky voids, forming a wispy invisible structure called "the cosmic web."
This "framework" for the universe contains visible matter that we are all familiar with but 80 per cent of it consists of dark matter, the matter that astronomers only know to be there because of its gravitational tug on nearby objects.
The structure, and how it glues the cosmos together, poses one of the next big challenges for astronomy. Scientists believe that a quantum leap in computing power and the development of powerful new telescopes will soon unravel the secrets of the web, which reaches right into our own cosmic back yard.
One puzzle, says Farbrizo Nicastro of the Harvard-Smithsonian Centre for Astrophysics and colleagues, is that predictions about the makeup of ordinary matter in the web are wrong.

Read more

Blobrana · L

Time may literally be running out - and could one day vanish altogether, according to a bizarre new theory.
The suggestion has been put forward to explain a cosmological mystery that has baffled scientists.
A decade ago, measurements of the light from distant exploding stars showed the universe to be expanding at an accelerating rate.
Physicists assumed that a kind of anti-gravitational force must be driving the galaxies apart, and gave it the name "dark energy".
However, to this day no-one has been able to say what dark energy is or where it comes from.
The new theory from Professor Jose Senovilla, at the University of the Basque Country in Bilbao, Spain, offers a radical alternative idea.
He believes there is no such thing as dark energy. Instead, he says we have been fooled into thinking the expansion of the universe is accelerating because time itself is slowing down.

Read more

-- Edited by Blobrana at 14:03, 2007-12-22

Blobrana · L

Title: When Worlds Collide
Authors: Spencer Chang, Matthew Kleban, Thomas S. Levi

We analyse the cosmological signatures visible to an observer in a Coleman-de Luccia bubble when another such bubble collides with it. We use a gluing procedure to generalise the results of Freivogel, Horowitz, and Shenker to the case of a general cosmological constant in each bubble and study the resulting spacetimes. The collision breaks the isotropy and homogeneity of the bubble universe and provides a cosmological "axis of evil" which can affect the cosmic microwave background in several unique and potentially detectable ways. Unlike more conventional perturbations to the inflationary initial state, these signatures can survive even relatively long periods of inflation. In addition, we find that for a given collision the observers in the bubble with smaller cosmological constant are safest from collisions with domain walls, possibly providing another anthropic selection principle for small positive vacuum energy.
Read more (32kb, PDF)

Blobrana · L

Shape of the universe