The pond behind the gym was not on any map of the school. It had been a fire reservoir once, then the groundskeeper's duck pond, then nothing. Lin Yuhang found it in his second week of senior year, looking for a quiet place to eat lunch. Duckweed sealed the surface like a green lid. A white pipe stuck out of the bank, dry and rusted, and a row of young willows leaned over the water as if listening.
体育馆后面那个池塘，不在学校的任何一张地图上。它曾经是消防蓄水池，后来成了园丁的鸭池，再后来什么也不是。林宇航在高三第二周发现了它，当时他想找个安静的地方吃午饭。浮萍像一只绿色的盖子封住了水面。岸边伸出一根白色的管子，干枯而生锈，一排小柳树朝水面倾着，像在倾听。
His science-fair project was about nutrients and algae. The idea had come from an article his teacher, Mr. Fang, had pinned to the lab door: small changes in a closed system can produce large, visible results. Yuhang needed a system small enough to observe, close enough to visit daily. The pond was perfect. He measured its width with a rope, drew a map, and photographed the same patch every morning for a week before touching anything.
他的科学展项目与营养物和藻类有关。这个想法来自方老师钉在实验室门上的一篇文章：封闭系统里的小变化，可能产生巨大而可见的结果。宇航需要一个足够小、便于观察，又足够近、可以每天去看的系统。那个池塘再合适不过。他用绳子量了宽度，画了地图，在动手之前，连续一周每天早上拍同一片水面。
Mr. Fang read the proposal twice and asked one question: 'What will you do if it works?' Yuhang said he would record it, then present the data at the fair. 'And after the fair?' Mr. Fang asked. Yuhang had no answer. He wrote the question in the margin of his notebook, underlined it, and went to prepare the solution anyway.
方老师把方案读了两遍，只问了一个问题：“如果它真的起作用，你打算怎么办？”宇航说他会记录下来，然后在科学展上展示数据。“那科学展之后呢？”方老师问。宇航答不上来。他把这个问题写在笔记本页边，画了下划线，然后还是去准备那瓶溶液了。
For nine days, nothing happened. Then the color changed. It began at the drain, a faint green cloud that spread by afternoon into something thick enough to hold the light. By the end of the second week the pond looked like a bowl of soup, and the smell reached the gym doors. The ducks left. Yuhang stood at the bank with his notebook, writing numbers that no longer felt like triumph.
头九天，什么也没发生。然后颜色变了。变化从排水口开始，先是一小团淡淡的绿雾，到下午便扩散成浓得能托住光的东西。第二周结束时，池塘看起来像一碗汤，气味一直飘到体育馆门口。鸭子走了。宇航拿着笔记本站在岸边，写下的数字再也不像胜利。
He tried to undo it. He dragged a net through the scum and filled three bags, which was like bailing a boat with a spoon. He asked Mr. Fang whether they could drain the pond. Mr. Fang said the outlet fed a stream that watered the vegetable plots, and draining it would simply move the problem downhill. 'You wanted a closed system,' he said, not unkindly. 'The pond disagrees.'
他试着挽回。他拖着网从浮沫里捞，装满了三个袋子，那感觉就像用勺子舀干一条船。他问方老师能不能把池塘抽干。方老师说，排水口连着一条浇灌菜地的小溪，抽干只会把问题挪到下游去。“你想要一个封闭系统，”他说，语气并不刻薄，“池塘不同意。”
That evening Yuhang read his own proposal again. Under 'expected outcomes' he had written, in careful handwriting, 'visible growth within two weeks.' He had been right. He crossed out the phrase so hard the pen tore the paper, then sat in the dark lab listening to the frogs that had not yet returned, and understood that the experiment had ended the moment he poured, and that everything after was not science but consequence.
那天傍晚，宇航又读了一遍自己的方案。在“预期结果”一栏，他用工整的字迹写着：“两周内出现可见增长。”他写对了。他把那句话划掉，用力到笔尖划破了纸，然后坐在黑下来的实验室里，听着还没有回来的蛙声。他明白，实验在他倒下去的那一刻就结束了，之后的一切不再是科学，而是后果。
The fair was in April. Yuhang's board had two halves. On the left, in neat panels, were the graphs he had planned: nutrient level, algae density, the clean curve rising. On the right, unadorned, was a photograph of the pond at its worst and a list of his repairs — the net, the bags, three Saturdays of dredging, the straw Mr. Fang had suggested, willow cuttings to shade the bank.
科学展在四月举行。宇航的展板分成两半。左边是整齐的图栏，贴着他原本计划展示的图表：营养物浓度、藻类密度、那条干净上升的曲线。右边没有任何装饰，只有一张池塘最糟时的照片，以及一份他的补救清单——网、袋子、三个星期六的清淤、方老师建议的稻草、为遮蔽岸边而插下的柳枝。
The judges stopped, as he had hoped. One of them, a woman from the water authority, asked what he would do differently. 'I would build a model first,' he said. 'A tank. Something I could empty.' She nodded and wrote nothing. He did not win. A boy with a solar cooker won, and Yuhang clapped until his palms hurt, and meant it.
评委们停了下来，正如他希望的那样。其中一位来自水务部门的女士问他，如果再做一次会有什么不同。“我会先做一个模型，”他说，“一个水槽。一个我能清空的东西。”她点点头，什么也没记。他没有获奖。一个做太阳能灶的男生得了第一，宇航一直鼓掌到掌心发疼，而且真心实意。
In June, the pond was still green at the edges, but the frogs had come back. Mr. Fang took him out at dusk to listen. 'The report is not the experiment,' he said. 'It is the part someone else can use.' Yuhang opened his notebook to the question in the margin. Under it, in newer ink, he wrote: 'Tell the truth, then stay.' The water held the last of the light. Neither of them spoke for a while.
到了六月，池塘边缘仍然泛绿，但青蛙回来了。方老师在黄昏时带他去听。“报告不是实验本身，”他说，“它是别人能用的那一部分。”宇航翻到笔记本上那个写在页边的问题。在它下面，他用更新的墨水写道：“说出真相，然后留下来。”水面盛着最后一点光。两人沉默了一会儿。