The Universe is inhomogeneous. Does it matter?

Interesting piece by Buchert et al. about the role of inhomogeneities in cosmology….


Yes! The biggest problem in cosmology—the apparent acceleration of the expansion of the Universe and the nature of dark energy—has stimulated a debate about “backreaction”, namely the effect of inhomogeneities in matter and geometry on the average evolution of the Universe. Our recent paper aims to close a chapter of that debate, to encourage exciting new research in the future.

Although matter in the Universe was extremely uniform when the cosmic microwave background radiation formed, since then gravitational instability led to

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2 Responses to “The Universe is inhomogeneous. Does it matter?”

  1. At the recent Texas Symposium in Geneva, there was an entire session on this topic. Suffice it to say a) that the comment box is too small to contain even truly marvelous proofs (in other words, the topic is rather complex and doesn’t lend itself to sound-bite discussion) and b) the jury is still out. There is an ongoing debate about the importance of this effect. Buchert is one of the key players in one of the camps, as are the other illustrious authors of the paper.

    Note, however, the “loaded statement”: The biggest problem in cosmology—the apparent acceleration of the expansion of the Universe and the nature of dark energy. Says who? One might just as well say that since 1920s cosmology explains everything we know about cosmology with regard to the classical cosmological tests, then, if anything, it is amazing that we haven’t uncovered evidence of something really different.

    Some people, like Ellis, seem to be concerned mainly with making sure that our conclusions follow from our assumptions in a well defined way. My impression is that, while he is often perceived as a devil’s advocate, he actually has no axe to grind, except the search for truth. Other people have an a priori hatred of the cosmological constant and try all sorts of bizarre stuff which has no other motivation whatsoever. There is a whole range of positions in-between.

    My guess is that while back reaction certainly exists at some level, even taking it completely into account would not radically change our view of cosmology.

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