Look at this picture.

Does any part of it surprise you? Look more closely.

Now? Try crossing your eyes.

Do you see a boy’s name?

I spell “Peter” with two e’s, but “Piotr” and “Pyotr” appear as authors’ names in papers’ headers. Finding “Petr” in a paper shouldn’t have startled me. But how often does “Gretchen” or “Amadeus” materialize in an equation?

When I was little, my reading list included *Eye Spy*, *Where’s Waldo?*, and *Puzzle Castle*. The books teach children to pay attention, notice details, and evaluate ambiguities.

That’s what physicists do. The first time I saw the picture above, I saw a variation on “Peter.” I was reading (when do I not?) about the intersection of quantum information and thermodynamics. The authors were discussing heat and algebra, not saints or boys who picked pecks of pickled peppers. So I looked more closely.

Each letter resolved into part of a story about a physical system. The *P* represents a projector. A *projector* is a mathematical object that narrows one’s focus to a particular space, as blinders on a horse do. The *E* tells us which space to focus on: a space associated with an amount *E* of energy, like a country associated with a GDP of $500 billion.

Some of the energy *E* belongs to a heat reservoir. We know so because “reservoir” begins with *r*, and *R* appears in the picture. A *heat reservoir* is a system, like a colossal bathtub, whose temperature remains constant. The Greek letter , pronounced “tau,” represents the reservoir’s state. The reservoir occupies an *equilibrium *state: The bath’s large-scale properties—its average energy, volume, etc.—remain constant. Never mind about jacuzzis.

Piecing together the letters, we interpret the picture as follows: Imagine a vast, constant-temperature bathtub (*R*). Suppose we shut the tap long enough ago that the water in the tub has calmed (). Suppose the tub neighbors a smaller system—say, a glass of Perrier.^{*} Imagine measuring how much energy the bath-and-Perrier composite contains (*P*). Our measurement device reports the number *E*.

Quite a story to pack into five letters. Didn’t Peter deserve a second glance?

The equation’s right-hand side forms another story. I haven’t seen Peters on that side, nor Poseidons nor Gallahads. But look closely, and you *will* find a story.

*The images above appear in “Fundamental limitations for quantum and nanoscale thermodynamics,” published by Michał Horodecki and Jonathan Oppenheim in Nature Communications in 2013.*

^{*}Experts: The ρ_{S} that appears in the first two images represents the smaller system. The tensor product represents the reservoir-and-smaller-system composite.

I have put the letters of my alma mater USC into a recent paper to denote a unitary interaction between a system and closed timelike curve qubits:

Click to access 1306.1795.pdf

Go Trojans! 🙂

Petr is the Czech spelling of the name. For example, Petr Hořava (who co-authored some well-known paper with Witten) wears this first name.