## The Essence of Cosmology is Statistics

I’m grateful to Licia Verde for sending this picture of me in action at last week’s conference in Castiglioncello.

The quote is one I use quite regularly, as the source is quite surprising. It is by George McVittie and appears in the Preface to the Proceedings of the Third Bekeley Symposium on Mathematical Statistics and Probability, which took place in 1956. It is surprising for two reasons. One is that McVittie is more strongly associated with theoretical cosmology than with statistics. In fact I have one of his books, the first edition of which was published in 1937:

There’s a bit in the book about observational cosmology, but basically it’s wall-to-wall Christoffel symbols!

The other surprising thing is that way back in 1956 there was precious little statistical information relevant to cosmology anyway, a far cry from the situation today with our plethora of maps and galaxy surveys. What he was saying though was that statistics is all about making inferences based on partial or incomplete data. Given that the subject of cosmology is the entire Universe, it is obvious we will never have *complete* data (i.e. we will never know everything). Hence cosmology is essentially statistical. This is true of other fields too, but in cosmology it is taken to an extreme. George McVittie passed away in 1988, so didn’t really live long enough to see this statement fulfilled, but it certainly has been over the last couple of decades!

P.S. Although he spent much of his working life in the East End of London (at Queen Mary College), George McVittie should not be confused with the even more famous, or rather infamous, Jack McVitie.

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September 8, 2015 at 2:56 pm

“One is that McVittie is more strongly associated with theoretical cosmology than with statistics.”In the old days, there were only two-and-one-half facts in cosmology, as Peter Scheuer told Malcolm Longair. (In the early 1990s, Longair, in a piece in the sorely missed

QJRAS, noted that there were then 9 facts. Now, there are thousands at least, depending on how one counts.) Sparse data indeed. In his wonderfulCosmologybook, Bondi muses on the problems of doing statistics with one object in the sample.These days, “cosmology is a data-driven science”, and very much work in the field is statistical in nature.

A related quote is by Paul Schechter: “Surveys are the lifeblood of astronomy”.

September 8, 2015 at 3:03 pm

“There’s a bit in the book about observational cosmology, but basically it’s wall-to-wall Christoffel symbols!”Somehow, I missed the fact that Steven Weinberg published a cosmology textbook a few years ago (

nota new edition of his classicGravitation and Cosmology: Principles and Applications of the General Theory of Relativityfrom 1972). Has anyone here read it? Seen it?Weinberg is one of the few people to have done important work both in particle physics (for which he is better known) and in cosmology (excluding the early-universe–cosmology types, who do a bit of both, of course).

September 8, 2015 at 5:30 pm

Yes, not only have I seen it I have also written a review of it for Science:

https://telescoper.wordpress.com/2008/09/19/nice-work-if-you-can-get-it/

September 9, 2015 at 7:19 am

Does the “nice work if you can get it” refer to Weinberg’s book (which, strangely, I have never seen) or to your paywalled review? 🙂

September 9, 2015 at 10:07 am

I recently read Weinberg’s

To Explain the World: The Discovery of Modern Science. I had read hisThe First Three Minutesdecades ago (borrowed from a library) andDreams of a Final Theorywhich I bought when it was new in hardback. These are close to his actual work, of course. As he himself notes, he is not a historian, but I think that this is a good history-of-science book, and brings some new insights even to people familiar with the material. I have since got hisLake Views: This World and the Universewhich I also like though, as a collection of previously published essays (though updated and with prescripts (is that a word?) and postscripts), it is something of a mixed bag (with respect to themes, not to quality).He is actually a good writer as well, up there with other active scientists who write (or wrote) well, such as Barrow, Sagan, and so on.

I haven’t read his

Gravitation and Cosmologyfrom cover to cover, but have checked it out (pun, as always, intended) in libraries a few times (and even exchanged a few emails with Weinberg when tracking down a typo regarding sign conventions* insomeprintings of the book, this prompted by a strangeApJpaper by F. Curt Michel, but I digress).Can anyone else comment on any of his other books, technical or popular?

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*This is rather tricky in GR, where one person’s typo is another person’s differing sign convention. The table in MTW is a good resource in this regard.