My column in Sunday's Boston Globe is on a popular topic here at Language Log Plaza: the multitudinous metaphors spun to explain the Higgs boson discovery to a non-scientific audience. Metaphors noted by Mark Liberman in his two posts on the subject (from divine wraiths to smoking ducks) make cameos in the column as well, and I dig a bit deeper into the history of describing the Higgs field as "cosmic molasses."
As I mention in the column, the earliest example of the molasses metaphor I was able to find is in a book review by Dennis Flanagan in the March 1990 issue of Bulletin of the Atomic Scientists. The review is of From Quarks to the Cosmos by Leon Lederman (he of "God particle" fame) and David Schramm. Flanagan writes:
What From Quarks to the Cosmos suggests is that the Higgs field would act as a kind of universal molasses through which other fields would have to force their way.
What Americans call molasses is usually called treacle on the other side of the pond, and this is the term that British writers on the Higgs beat have favored. In 1991, Colin A. Ronan wrote the following in his book The Natural History of the Universe:
In our present-day, comparatively low-energy universe, the Higgs field is present everywhere and couples to the weak field. It acts like treacle, making the W and Z particles sluggish, and giving them a large effective mass. Photons are unaffected.
Both molasses and treacle make appearances in the locus classicus for the metaphor: an article by an American physicist in a British magazine, namely Frank Wilczek's "Masses and Molasses" (New Scientist, Apr. 10, 1999). As Wilczek told me for the Globe column, his original title for the piece was the rhythmically appealing "Cosmic Molasses for Particle Masses." His editors nixed that and also inserted treacle in the subheading: "Is space filled with a cosmic treacle whose stickiness gives particles their mass?" Fortunately, Wilczek's "cosmic molasses" survived in the main text:
It would be easier, then, to understand an imaginary world with only massless particles, forever whizzing around at the speed of light. But we know that in our world particles do have mass. So to get from that ideal world to ours, we need some kind of cosmic molasses that fills all space and slows down these massless speed demons. But if this molasses is everywhere, why can't we see it?
A few years after Wilczek popularized the molasses metaphor, another physicist noted its flaws. In his 2003 book The Fabric of the Cosmos: Space, Time, and the Texture of Reality, Brian Greene presents the metaphor but explains all the ways that it fails. First, if particles are supposed to be ping pong balls (or pearls, or what have you) slogging through the molasses, you can’t actually pull them out as you would the analogical equivalents, since the Higgs field fills all of space. Second, while molasses resists all motion, the Higgs field resists only accelerated motion. Third, the molasses metaphor only applies to fundamental particles like electrons and quarks, which garner all their mass from the "drag" of the Higgs field, while other forces come into play in composite particles.
Despite these flies in the ointment, the "cosmic molasses" metaphor has been the most popular one used to describe the workings of the Higgs mechanism over the past decade. For a roundup of other common analogical examples, check out J. Bryan Lowder's piece for Slate. While these metaphors can be useful in moderation, I keep thinking about an interview with Richard Feynman (available on YouTube here) in which he refuses to explain magnetism in terms of more familiar analogies:
I can't explain that attraction in terms of anything else that's familiar to you. For example, if we said the magnets attract like as if rubber bands, I would be cheating you. Because they're not connected by rubber bands. I'd soon be in trouble. And secondly, if you were curious enough, you'd ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces, which are the very things that I'm trying to use the rubber bands to explain. So I have cheated very badly, you see. So I am not going to be able to give you an answer to why magnets attract each other except to tell you that they do. And to tell you that that's one of the elements in the world – there are electrical forces, magnetic forces, gravitational forces, and others, and those are some of the parts. If you were a student, I could go further. I could tell you that the magnetic forces are related to the electrical forces very intimately, that the relationship between the gravity forces and electrical forces remains unknown, and so on. But I really can't do a good job, any job, of explaining magnetic force in terms of something else you're more familiar with, because I don't understand it in terms of anything else that you're more familiar with. (transcript)
[Update: As noted by Andy Averill in the comments below, Lawrence Krauss says here that he first used the molasses metaphor 25 years ago. This would predate 1990, though I have yet to see printed evidence for the claim.]