Monday, September 03, 2007

Not Dark Energy

The speculation called "dark energy" is subject of more questions in NEW SCIENTIST, Swiss cheese universe challenges dark energy.

"Dark energy may not be needed to explain why the expansion of space appears to be speeding up. If our universe is like Swiss cheese on large scales – with dense regions of matter and holes with little or no matter – it could at least partly mimic the effects of dark energy, suggests a controversial new model of the universe."

As nige has noted, if the Universe is not homogeneous different regions will appear to expand at different rates. If your telescope looked in a direction of lower expansion, the Universe would appear to be accelerating. This adds to many anisotropies seen in the Cosmic Microwave Background. Though this model is very preliminary, physicists Sabino Matarrese and Rocky Kolb have published online On cosmological observables in a swiss cheese universe.

Back in March, NEW SCIENTIST published Is dark energy an illusion?

"The quickening pace of our universe's expansion may not be driven by a mysterious force called dark energy after all, but paradoxically, by the collapse of matter in small regions of space."

Just last week A Hole In the Universe indicated that the Universe is not quite homogeneous, and a cosmology including "dark energy" may be all wrong. The proposed Supernova Acceleration Probe would survey only 15 square degrees of sky before ending its service life. The whole sky has an area of 41,253 square degrees! If SNAP looked at the wrong part of an inhomogeneous sky, it could give researchers the wrong value of cosmic acceleration. Then again, disciples of "dark energy" may already have the wrong idea.

Lawrence Krauss said that supernova data "naively implied that the Universe is accelerating." The inferrence of cosmic acceleration relies on a daisy chain of assumptions, including homogeneity. It especially relies on assumption of a constant speed of light. SNAP/JDEM is subject to a review whose results will be announced Wednesday. With all the outstanding questions about its basic science, it is hard to see how SNAP can supersede projects like Constellation-X.

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3 Comments:

Anonymous Anonymous said...

Ernst Fischer in arXiv:0708.3577v1 [astro-ph], "An Equilibrium Balance of the Universe" offers an alternate cosmology that also does not require the presence of mysterious 'dark energy/matter' - or any 'new physics'.I would be interested in reading comments on Fisher's suggestion.

8:01 AM  
Anonymous Anonymous said...

Marra, Kolb, Matarrese, and Riotto say in astro-ph 0708.3622
"... we built a swiss-cheese model ... where the cheese consists of the usual Friedmann-Robertson-Walker (FRW) solution and the holes are constructed out of a Lemaitre-Tolman-Bondi (LTB) solution ... placing the observer in the cheese and having the observer look through the swiss-cheese holes ... the evolution of the inhomogeneities bends the photon path compared to the FRW case. Therefore, inhomogeneities will be able (at least partly) to mimic the effects of dark energy ...".

Their general idea seems similar to the two-phase structure of my model
Minkowski (constant-c) like their FRW cheese where we material beings live
and
Segal-type conformal (varying-c) like their LTB holes that make up most of the volume of our universe.
It would be interesting to do detailed calculations like theirs with the conformal (varying c) metric used by Segal.

Tony Smith

11:11 AM  
Blogger alex kaplan said...

If the universe is not homogeneous,and principle of cosmology is wrong,general relativity should be combined with the theory of complexity,which is immpossible

7:05 PM  

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