Metaphors and analogies: scientists’ friends or foes?

Metaphors are like men. If you take them
seriously the joke's on you.

The girls were about a year old and I was working from home. As I was reading yet another referee report that came with the preamble “we regret to inform you...,” I watched Gloria trying to push a square block through a round hole. We were really trying the same thing, I thought.

Decoding metaphors and using analogies is a prototypical right-brain task, a pattern finding that helps us get a grip on new situations quickly and that sheds new light on the familiar. Metaphors and analogies are omnipresent in literature and the arts, in humor and also in education. And popular science writing is full of it.

But relying on metaphors is like traveling to a new country and then heading to Starbucks. The very reason to do it is also what limits the experience. It’s familiar and easy to understand, but it prevents us from learning something new. This is why I have a love-hate relationship with Starbucks and other metaphors.

Love: Analogies and metaphors build on existing knowledge and thus help us to understand something quickly and intuitively.

Hate: This intuition is eventually always misleading. If a metaphor were exact, it wouldn’t be a metaphor.

And while in writing, art, and humor most of us are easily able to tell when an analogy ceases to work, in science it isn’t always so obvious.

When it comes to physics I can most often tell when an analogy fails to capture the actual science. But in other areas of science this sometimes is not clear to me. There are for example these artistic images that frequently accompany popular science accounts of new drugs or cancer treatments. You know, the ones with the molecules that fit like keys into locks of other molecules, or that cut through molecular bonds. I am reasonably sure that these explanations suggest a clarity of the underlying mechanism and structure that most often doesn’t quite exist in the actual data. But how much of it is science and how much of it is art is difficult for me to tell.

In a recent Nature comment “Mind the metaphor”, Eleonore Pauwels made a similar point:

“[I]n the late 1990s, computer scientists, physicists and engineers were fuelled by the idea that they might be able to direct cells in the same way that people program computers. In the laboratory, researchers started to use computing and engineering metaphors –switches, oscillators and logic gates, for instance – both to guide the design of synthetic constructs and to understand how natural systems function. Almost immediately, scientists were confronted with the uncertainties and constraints of engineering in the cellular context. Engineering concepts and metaphors could serve only as an inspiration...

Scientists using metaphors among themselves are often aware of, and even careful to point out, the subtleties that could be misconstrued. Problems tend to arise when metaphors are used outside the laboratory...

Faced with explaining the messy complexity and uncertainty of science to the public, it is understandable that scientists reach for metaphors. But [this] sends a message to policy-makers and laypeople that scientists can already make biological systems that are reliable and controllable. It widens rather than closes the gap between scientific realities and the expectations of policy-makers and the public.”

The same problem exists in physics, though at least in the area I work in there aren’t all that many implications for public policy. But I’ve seen it over and over again that people take analogies too seriously and start trying to build arguments on them. Suddenly a rubber sheet isn’t just an analogy for space-time, but it is space-time. The universe is an inflating balloon, the Higgs particle is a rumor, and entangled particles are shoes in parcels.

Except that, well, they’re not. The universe isn’t a clockwork and it’s not a drum either; the brain isn’t a computer, black holes are not cannibals and indeed not even black.

The main reason we use mathematics for scientific theories is that it’s a particularly clean way of thinking, uncluttered from what the right brain wants to associate. An electron isn’t a spinning top, it’s an element of a Hilbert space that transforms under the spinor representation of the Lorentz-group. There is really no metaphor that’ll do equally well. Feynman diagrams seem to be particularly prone to misinterpretation as many people believe they depict physical particles, while they are actually a handy short-notation for lengthy integrals.

But my uneasiness with metaphors and imagery goes beyond the communication issue.

If you spend some time with a set of equations, pushing them back and forth, you’ll come to understand how the mathematical relationships play together. But they’re not like anything. They are what they are and have to be understood on their own terms*.

Thus, as much as I value metaphors for the intuition that can serve as a guide to new ideas, I also mistrust them. We learn much more from the failure of metaphors than from their success.

I admired Gloria for her persistence in trying to push the square block through the round hole. Then Lara took the piece out of Gloria’s hand, opened the lid of the bucket and put the block in. Problem solved. If only it were so easy with my papers…

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*That is unless you are onto a theory that is truly equivalent (‘dual’) to some other theory.