Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A finite dodecahedral Universe

13.10.2003


A franco-american quintet of cosmologists conducted by Jean-Pierre Luminet, from Paris Observatory (LUTH), has proposed an original explanation to account for a surprising detail observed in the Cosmic Microwave Background (CMB) recently mapped by the NASA satellite WMAP. According to the team, who published their study in the 9 october 2003 issue of "Nature", an intriguing discrepancy in the background luminous texture of the Universe can indeed be explained by a very specific global shape of space (its "topology"). The Universe could be wrapped around, a little bit like a "soccer ball", the volume of which would represent only 80% of the observable Universe! According to the leading cosmologist George Ellis, from Cape Town University (South Africa), who comments this letter in the "News & Views" of the same issue: "If confirmed, it is a major discovery about the nature of the Universe".



Primordial fluctuations

Cosmologists study the topology of space by analyzing in great details the temperature fluctuations of the fossil Cosmic Microwave Background [note a]. The standard cosmological model describes the Universe as a flat infinite space in eternal, accelerated expansion under the effect of a repulsive "dark energy". The data collected by the NASA satellite WMAP (Wilkinson Microwave Anisotropy Probe), which has recently produced a high resolution map of the CMB, allowed to check the validity of such an expansion model. Temperature fluctuations on small and mean scales (i.e. concerning regions of the sky of relatively modest size) are compatible with the infinite flat space hypothesis. However, on angular scales larger than 60°, the observed correlations are notably weaker that those predicted by the standard model. Thus the scientists are looking for an alternative.


CMB temperature anisotropies essentially result from density fluctuations of the primordial Universe : a photon coming from a denser region will loose a fraction of its energy to compete against gravity, and will reach us cooler. On the contrary, photons emitted from less dense regions will be received hotter. The density fluctuations result from the superposition of acoustic waves which propagated in the primordial plasma - see previous AlphaGalileo press releases "Vibrations of the cosmic drumhead" (6 jan 03) and "A small spherical Universe?" (12 nov 01).

The franco-american team of scientists has recently developed complex theoretical models to reproduce the amplitude of such fluctuations, which can be considered as vibrations of the Universe itself. In particular, they simulated high resolution CMB maps for various space topologies and were able to compare their results with real WMAP data. Depending on the underlying topology, the distribution of the fluctuations differs. For instance, in an infinite "flat" (Euclidean) space, all wavelengths are allowed, and fluctuations must be present at all scales.

Cosmic Harmonics

Like acoustic waves, the CMB temperature fluctuations can be decomposed into a sum of spherical harmonics [note b]. The first observable harmonics is the quadrupole (whose wavenumer is l=2). WMAP has observed a value of the quadrupole 7 times weaker than expected in a flat infinite Universe. The probability that such a discrepancy occurs by chance has been estimated to 0.2% only. The octopole (whose wavenumber is l=3) is also weaker (72%) than the expected value. For larger wavenumbers up to l=900 (which correspond to temperature fluctuations at small angular scales), observations are remarkably consistent with the standard cosmological model.

The unusually low quadrupole value means that long wavelengths are missing, may be because space is not big enough to sustain them. Such a situation may be compared to a vibraring string fixed at its two extremities, for which the maximum wavelength of an oscillation is twice the string length. A natural explanation of such a phenomenon relies on a model of finite space whose size constrains the wavelengths below a maximum value. The proposed space is the Poincaré dodecahedral space [note c].

The associated power spectrum, namely the repartition of fluctuations as a function of their wavelengths corresponding to the Poincaré dodecahedral space, strongly depends on the value of the mass-energy density parameter [note d]. There is a small interval of values within which the spectral fit is good, and in agreement with the value of the density parameter deduced from WMAP data (1.02 plus or minus 0.02). The result is quite remarkable because the Poincaré space has no degree of freedom. By contrast, a 3-dimensional torus, constructed by gluing together the opposite faces of a cube and which constitutes a possible topology for a finite Euclidean space, may be deformed into any parallelepiped : therefore its geometrical construction depends on 6 degrees of freedom.

The Poincaré Dodecahedral Space accounts for the low value of the quadrupole as observed by WMAP in the fluctuation spectrum, and provides a good value of the octopole. To be confirmed, such a "soccer-ball" model of space must satisfy two experimental tests :

1) A finer analysis of WMAP data, or new data from the future European satellite "Planck Surveyor" (scheduled 2007), will be able to determine the value of the energy density parameter with a precision of 1%. A value lower than 1.01 will discard the Poincaré space as a model for cosmic space, whereas a value greater than 1.01 will confirm its cosmological pertinence.

2) If space has a non trivial topology, there must be particular correlations in the CMB, namely pairs of correlated circles along which temperature fluctuations should be the same. The Poincaré Dodecahedral Space model predicts 6 pairs of circles with an angular radius of 35°. The model is therefore an ideal candidate to test the method of "matched circles" originally devised by the American astrophysicists N. Cornish, D. Spergel and G. Starkman
Notes

[a] The Cosmic Background Radiation, also called Fossil Radiation, is the relics of the radiation emitted soon after the Big Bang (about 400 000 years later), when matter and radiation decoupled. The tiny temperature irregularities of such a radiation allow to measure the density fluctuations of the matter present at this epoch, such fluctuations being the seeds of all galaxies and galaxy clusters.

[b] The temperature fluctuations of the Cosmic Background Radiation may be decomposed into a sum of spherical harmonics , much like the sound produced by a music instrument may be decomposed into ordinary harmonics. The "fundamental" fixes the height of the note (as for instance a 440 hertz acoustic frequency fixes the "A" of the pitch), whereas the relative amplitudes of each harmonics determine the tone quality (such as the A played by a piano differs from the A played by a harpsichord). Concerning the relic radiation, the relative amplitudes of each spherical harmonics determine the power spectrum, which is a signature of the geometry of space and of the physical conditions which prevailed at the time of CMB emission.

[c] Poincaré space may be represented by a dodecahedron (a regular polyhedron with 12 pentagonal faces) whose opposite faces are glued after a 36° twist ; such a space is positively curved, and is a multiply connected variant of the hypersphere, with a volume 120 times smaller. A rocket going out of the dodecahedron by crossing a given face immediately re-enters by the opposite face. Propagation of light rays is such that any observer whose line-of-sight intercepts one face has the illusion to see inside a copy of his own dodecahedron (since his line-of-sight re-enters the original dodecahedron from the opposite side).

[d] The mass-energy density parameter characterizes the contents (matter and all forms of energy) of the Universe. The curvature of space depends on the value of this parameter, usually denoted Omega. If Omega is greater than 1, then space curvature is positive and geometry is spherical; if Omega is smaller than 1 the curvature is negative and the geometry is hyperbolic; eventually Omega is strictly equal to 1 and space is "flat" (Euclidean geometry).

Jean-Pierre Luminet | alfa
Further information:
http://luth2.obspm.fr/Compress/oct03_lum.en.html

More articles from Physics and Astronomy:

nachricht From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison

nachricht Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

From rocks in Colorado, evidence of a 'chaotic solar system'

23.02.2017 | Physics and Astronomy

'Quartz' crystals at the Earth's core power its magnetic field

23.02.2017 | Earth Sciences

Antimicrobial substances identified in Komodo dragon blood

23.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>