A news item today about BOSS (yet another observational cosmology survey) gives me an excuse to recycle an idea from an old post.
The phrase expletive deleted was made popular at the time of Watergate after the release of the expurgated tapes made by Richard Nixon in the Oval Office when he was President of the United States of America. These showed that, as well as been a complete crook, he was practically unable to speak a single sentence without including a swear word.
Nowadays the word expletive is generally taken to mean an oath or exclamation, particularly if it is obscene, but that’s not quite what it really means. Derived from the latin verb explere (“to fill out”) from which the past participle is expletus, the meaning of the word in the context of English grammar is “something added to a phrase or sentence that isn’t strictly needed for the grammatical sense”. An expletive is added either to fill a syntactical role or, in a poem, simply to make a line fit some metrical rule.
Examples of the former can be found in constructions like “It takes two to Tango” or “There is a lot of crime in Nottingham”; neither “it” nor “there” should really be needed but English just seems to like to have something before the verb.
The second kind of use is illustrated wonderfully by Alexander Pope in his Essay on Criticism, which is a kind of guide to what to avoid in writing poetry. It’s a tour de force for its perceptiveness and humour. The following excerpt is pricelessly apt
These equal syllables alone require,
Tho’ oft the open vowels tire;
While expletives their feeble aid do join;
And ten low words oft creep in one dull line
Here the expletive is “do”, and it is cleverly incorporated in the line talking about expletives, adding the syllable needed to fit with a strict pentameter. Apparently, poets often used this construction before Pope attacked it but it quickly fell from favour afterwards.
His other prosodic targets are the “open vowels” which means initial vowels that produce an ugly glottal sound, such as in “oft” (especially ugly when following “Tho”). The last line is brilliant too, showing how using only monosyllabic “low” words makes for a line that plods along tediously just like it says.
It’s amazing how much Pope managed to fit into this poem, given the restrictions imposed by the closed couplet structure he adopted. Each idea is compressed into a unit of twenty syllables, two lines of ten syllables with a rhyme at the end of each. This is such an impressive exercise in word-play that it reminds me a lot of the skill showed by the best cryptic crossword setters. Needless to say I’m no more successful at writing poetry than I am at setting crossword clues.
Anyway, what’s all this got to do with cosmology?
Well, I was reminded of it when I attended the 2012 Gerald Whitrow Lecture by Andrew Liddle last Friday at the Royal Astronomical Society, during which he talked, amongst other things, about Dark Energy.
The Dark Energy is an ingredient added to the standard model of cosmology to reconcile observations of a flat Universe with a matter density that seems too low to account for it.
Other than that it makes the cosmological metric work out satisfactorily (geddit?), we don’t understand what Dark Energy really is or why there is as much of it. Indeed, many of us would rather it wasn’t there at all, because we think the resulting model is inelegant or even ugly, and are trying to think of other cosmological models that do not require its introduction.
In other words, Dark Energy is an expletive (though not one that’s been deleted).
Incidentally, one of the things Andrew said in his talk – and I agree with him 100% – is that in some sense we already know enough about dark energy from observations that we know we don’t understand it at all from a theoretical point of view. Bigger and better surveys, such as Euclid, producing more and more data will characterize its properties with greater statistical accuracy, but they won’t on their own solve the Dark Energy puzzle. For that we need better theoretical understanding.
My own view is that the problem of the vacuum energy is of the same character as the ultraviolet catastrophe that ushered in the era of quantum physics: a big problem that needs a big solution. What I mean by that is that it’s not something that can be resolved by tinkering with the existing theoretical framework. Something much more radical is needed.
In the Dark 