As the temperature of a cooling object decreases as it relaxes to thermal equilibrium, it is intuitively assumed that a hot object should take longer to cool than a warm one. Yet, some 2,300 years ago, Aristotle observed that "to cool hot water quickly, begin by putting it in the sun"1,2. In the 1960s, this counterintuitive phenomenon was rediscovered as the statement that "hot water can freeze faster than cold water" and has become known as the Mpemba effect3; it has since been the subject of much experimental investigation4-8 and some controversy8,9. Although many specific mechanisms have been proposed6,7,10-16, no general consensus exists as to the underlying cause. Here we demonstrate the Mpemba effect in a controlled setting-the thermal quench of a colloidal system immersed in water, which serves as a heat bath. Our results are reproducible and agree quantitatively with calculations based on a recently proposed theoretical framework17. By carefully choosing parameters, we observe cooling that is exponentially faster than that observed using typical parameters, in accord with the recently predicted strong Mpemba effect18. Our experiments outline the generic conditions needed to accelerate heat removal and relaxation to thermal equilibrium and support the idea that the Mpemba effect is not simply a scientific curiosity concerning how water freezes into ice-one of the many anomalous features of water19-but rather the prototype for a wide range of anomalous relaxation phenomena of broad technological importance.

中文翻译：

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在胶体系统中以指数方式快速冷却

随着冷却物体的温度随着它松弛到热平衡而降低，直观地假设热物体应该比温暖物体需要更长的时间来冷却。然而，大约 2,300 年前，亚里士多德观察到“要快速冷却热水，首先将其放在阳光下”1,2。在 1960 年代，这种违反直觉的现象被重新发现，因为“热水比冷水结冰的速度更快”，并被称为 Mpemba 效应 3；从那时起，它就成为了许多实验研究 4-8 和一些争议 8,9 的主题。尽管已经提出了许多具体机制6,7,10-16，但对于根本原因尚无普遍共识。在这里，我们展示了在受控设置中的 Mpemba 效应 - 浸入水中的胶体系统的热淬火，用作热浴。我们的结果是可重复的，并且与基于最近提出的理论框架的计算在数量上一致。通过仔细选择参数，我们观察到冷却速度比使用典型参数观察到的要快，这与最近预测的强 Mpemba 效应一致。我们的实验概述了加速散热和弛豫达到热平衡所需的一般条件，并支持这样一种观点，即 Mpemba 效应不仅仅是关于水如何冻结成冰的科学好奇心——水的许多异常特征之一——而是原型用于具有广泛技术重要性的各种异常松弛现象。根据最近预测的强 Mpemba 效应，我们观察到冷却速度比使用典型参数观察到的速度快得多。我们的实验概述了加速散热和松弛达到热平衡所需的一般条件，并支持这样一种观点，即 Mpemba 效应不仅仅是关于水如何冻结成冰的科学好奇心——水的许多异常特征之一——而是原型用于具有广泛技术重要性的各种异常松弛现象。根据最近预测的强 Mpemba 效应，我们观察到冷却速度比使用典型参数观察到的速度快得多。我们的实验概述了加速散热和松弛达到热平衡所需的一般条件，并支持这样一种观点，即 Mpemba 效应不仅仅是关于水如何冻结成冰的科学好奇心——水的许多异常特征之一——而是原型用于具有广泛技术重要性的各种异常松弛现象。