The shallow Yangtze river produced a smooth reflection of the setting autumn sun. Here, a few dozen kilometres north of Shanghai, one could barely perceive the giant metropolis nearby. Like so often in the early September days, an immovable heat dome rested over the river delta, heavy, as though its crushing presence had produced the flat terrain underneath.

Many families from the city were using the river to cool down after work, and the Yinghe family was no exception. The mother of the house, De, had enthusiastically left the Department of Pharmacology looking forward to some family time on the beach; while her boyfriend, Xing, could only reluctantly emerge from his pleasantly cool office at the Mathematics Department. He loved his kids, too, but he hated both the humidity and the lack of modern amenities this pristinely natural portion of the beach provided. Still, he buckled to the decision that was reached democratically by his girlfriend and kids.

Shanghai was incredibly pleasant to get around with its state-of-the-art public transit system, but foregoing the purchase of a mostly useless family car sometimes meant having to carry heavy bags of towels, sunshades, and other miscellanea all the way to the beach. Fortunately, the kids were as enthusiastic about enforcing their decision as they were about making it, so Xing was at least spared the literal burdens of this trip.

Xing and De had met at Jiao Tong university; she was attending his tutorial group on mathematics for natural scientists. Although outstanding in her own field, De had needed his help the most. Xing, four semesters ahead, was earning some cash teaching her class about calculus and deductive reasoning, and after she graduated a few years later, she returned the favour by teaching him about the wonders of human reproductive biology. The certificate for the course came in duplicate: Yang and Yue, twin boys and now age ten, were living proof that Xing had passed with flying colours; though not without receiving a forceful slap in the face after jokingly insinuating that De now had the perfect setup for a twin study.

The extra mischief the twins would enjoy causing by looking alike was offset by a sort of harmony which only that same symmetry could provide, currently materialising in the precious sight of them working on a little dam to back up some water from the river. It was backing up the water inside a narrow channel fed by the river proper. Right now, De had given up on trying to take pictures against the fading sun, and it was Xing’s turn to watch them, away from the textbooks and papers he packed to distract himself from the inauspicious number 44 that the thermometer kept producing.

Crouching over the shallow stretch of water that has been building up behind the dam, Xing was fascinated by an effect he had recently learned that linear mathematics could not explain: He dipped a little plastic shovel into the water which caused a soliton - A lone wave, expanding in both directions, travelling the entire length of the channel without losing any of its energy. His play was interrupted by Yang, who managed to cause another such soliton, but with a different shape and speed. It was about to reach Xing’s wave shortly before the dam, when something happened that seemed like witchcraft to the twins:

Instead of the heights adding up like normal, periodic water waves, soliton heights do not add linearly. When one soliton reaches another, their combined height can greatly exceed the sum of their individual heights. The result of this strange kind of addition was the unfortunate demise of the little dam they had just built, but due to Xing’s incessantly honed ability to eloquently explain what just happened, the evening miraculously remained without tears.

When the family finally came home in the last twilight, they had already forgotten about this neat little demonstration. Subconsciously though, it had irreversibly forged the future lifes of the twins: Yue, with a newfound respect for the hidden dangers of nature, was preoccupied to learn how to better protect his constructions and became an engineer; while Yang would become engrossed with more such otherworldly phenomena hiding in plain sight, and follow his father’s footsteps to also become a mathematician working on nonlinear phenomena.