**** Energy

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 lots of crime in Nottingham”; neither  “it” nor “there” should really be needed but English likes 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.

After my talk in Dublin last Friday, somebody in the audience asked me what I thought about Dark Energy. There’s some discussion in the comments after my post on that too.

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 means and would rather it wasn’t there.  Most people think the resulting model is inelegant or even ugly.

In other words, it’s an expletive…

8 Responses to “**** Energy”

  1. Hey, where are comments more likely to be read, here or on Facebook? And why aren’t they consolidated?

    • telescoper Says:


      Well I have a lot more readers on here than I have friends on facebook (or anywhere else for that matter). It would be good to make the comments appear on facebook too, but I don’t know how to do that even if it is possible.


  2. Anton Garrett Says:


    Why have cosmologists proposed dark energy, rather than suppose that dark matter is hot instead of cold, please?

    When somebody says “It takes two to tango” I’ve often felt like asking: “What takes two to tango?”

    The short book “Rhyme’s Reason” by John Hollander follows in Pope’s footsteps, by explaining sonnet form in a sonnet and likewise for other forms of poetry.


  3. Anton Garrett Says:

    PS Swearing and using foul language were not the same thing in old English usage, certainly at the time the King James bible was translated. The former has come to mean the latter, but its original meaning is preserved in the phrase “to swear an oath” as witnesses are required to do in court – hence “uttering oaths” as another euphemism for foul language.

  4. telescoper Says:


    In the early 80s people used to favour hot dark matter because there was an experimental suggestion that neutrinos had a mass of order 30eV. If that had turned out to be true then the expected number density of relic neutrinos would be enough to make a flat Universe. These would be “hot” dark matter.

    Unfortunately, hot dark matter is very difficult to form into small structures. The particles stream freely on scales of many megaparsecs, much bigger than galaxies. The way galaxies form in a hot dark matter Universe has to be by fragmenting out of larger structures. This picture doesn’t account for observed galaxy properties as well as if the dark matter is cold, i.e. much more massive particles that don’t move about so much and are easier to persuade to form small clumps. We now know that neutrinos do have mass but it is very small, so their contribution to the overall budget is quite well constrained but small.

    In any case hot dark matter isn’t anything like dark energy. The equation of state of cold dark matter is p=0 which is what relativists call “dust”; basically it has zero thermal velocity. Hot dark matter has an equation of state of the form p=rho/3 (where c=1); relativistic matter behaves just like radiation. Dark energy is much wackier than this. Its equation of state is p=-rho, at least in the simplest form. More generally it could be something more complicated which has negative pressure. This means that that the strong energy condition is violated (rho + 3p)0.

    We have four basic observations to explain: (i) the clustering of large scale structure; (ii) the flatness of space (from CMB); (iii) the apparent acceleration of the Universe from supernovae; and (iv) the age of the oldest stars. Dark matter can account for (i) and (ii), but not (iii) and (iv).
    That’s why the expletive is needed.


  5. Anton Garrett Says:

    In other words, hot dark matter 1980s-style simply meant seriously massive neutrinos whizzing around at relativistic speeds. I’m grateful for the clarification, but couldn’t 30eV neutrinos have been ruled out at the time because they would have *over*corrected the then solar neutrino problem?

    I hate the idea of giving up positive definiteness of energy. It is an axiom of the Hawking-Penrose singularity theorems (perhaps the greatest work of each??) which is the only truly rigorous theoretical proof we have of the Big Bang based on General Relativity.


  6. telescoper Says:

    Neutrino oscillations constrain the difference in mass-squared across the neutrino generations. You could, at least in theory, have three equal mass neutrinos that didn’t mix at all…

    The strong energy condition is an important axiom, but there’s no proof that it’s right. It’s also violated in inflationary cosmology. Violating the strong energy condition is also a way of avoiding a cosmological singularity.

  7. Anton Garrett Says:

    Many thanks for the neutrino explanation Peter. I dislike negative energy because we don’t see it in terrestrial experiments, and the precedent for having the same physics out there as down here is pretty good – Newton thereby unified the theory of falling apples with the earth’s orbit round the sun, healing a longstanding breach due to classical Greek notions that the heavens were perfect and the earth was not. I positively like the aesthetics of the Big Bang from a singularity – you can’t get a more basic start than from a point. (I also like it on theological grounds as it’s the first scientific theory to say that the universe had a beginning, just like the first line of the Judaeo-Christian bible says; I regret that some of my kin in faith argue against the Big Bang on grounds of timing while ignoring this more fundamental accord.) As for inflation – and consequently negative energy – needed to explain a flat universe, I would hope that the flat universe will fall out of a future theory as naturally as spin-1/2 falls out of the Dirac equation. I hope some people are looking for such a theory.


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