Saturday, October 17, 2009
Universe or multiverse?
Recently there has been some peak of comments on the blogosphere about the multiverse, partially because of a new article by Linde and Vanchury titled How many universe are in the multiverse?.
But the battle against the multiverse, and it's buddy's, the anthropic principle and the string landscape are not new at all. Peter Woit is a championship of that cause. I have always considered P.W. as innocuous, and a source of information about string theory, even if he doesn't like it. Being he a mathematician, or at most a mathematical physicist it is not a lack of respect to his position in an university to not take seriously their objections to a branch of physics that he mostly doesn't understand.
But recently I am beginning to think that in fact he can be causing some damage. The problem I see is that he is so intended to criticise string theory that he only search the part that is good for his purposes without worrying of understanding the whole picture. Worse still, he can make believe that his biased view is the whole view. And that's very bad because it gives a very wrong perspective of what is being done in string theory, and in cosmology and high energy physics in general.
In particular what he says about multiverse, string landscape and similar topics is totally misleading. I am not saying that these are not conflictive areas. Only that what Woit says about them is not representative. To begin with one may realize that the existence of multiverses is, in some cases, inflation, mostly a consequence of already proved physicist with the only assumption of some special issues on he potential of the inflaton. Also, if one trust string theory, the multiverses would rise as a consequence of a saltatory cosmological constant. In fact that two scenarios are similar in spirit, although very different in the details.
If a reader of this blog would want to get a much better idea I would recommend him the reading of the book presented at the beginning of this entry. IT is edited by Bernard Card, who also makes a presentation chapter and thematic one, "the anthropic principle revisited". The firs chapter gives an overview of the rest of the book and explains the many meanings of the term "multiverse" that are treated.
The book itself is bases in a series of conferences partially supported by the templeton foundation. The list of participants includes a list of very prominent physicist such as S. Weinberg, S. Hawkings, L. Susskind,A. Linde, P. Davies, R. Kallosh and a long etc. The list of topics is also very broad, covering many of the variants of the multiverse idea and why it raises in nowadays physics research.
I only have read a few (six) part of the articles and I am alternating them with other articles about inflation in string theory, supersymmetry breaking and general literature about the cosmological constant. My idea is that probably there are better alternatives for the apparent existence of an accelerated universe (and in general, possibly, for some fine tunning problems) but that it would be stupid not to read (at least a part of) what appears in that book if ones is concerned about it.