Aristotle observed this phenomenon more than 2300 years ago: if you want to cool water quickly, you need to put it in the sun in the beginning. Although this counter intuitive phenomenon has often been mentioned in the past hundreds of years, it was not published as a scientific result until the 1960s. In 1963, Erasto Mpemba, a Tanzanian boy, heated the water to a high temperature to sterilize the equipment while making ice cream. Once while he was doing this, he noticed that hot water freezes faster than warm water. Later, he wrote a report on the phenomenon, becoming the first to describe the counter intuitive effect. This effect was later known as the mpamba effect. Since then, this effect has become the subject of experimental research, and also a controversial issue. Because in physics, the cooling process is not as simple as imagined; in addition, the complexity of water makes the freezing of water a very difficult process to control, making it difficult for scientists to reproduce this effect in the laboratory. Therefore, for a long time, scientists have no unified answer to the causes of this phenomenon, how to define this phenomenon, and whether it really exists. < p > < p > recently, Avinash Kumar and John bechhoefer, two physicists from Simon Fraser University, Canada By using some tiny glass beads instead of water molecules, we have developed a method to show the mpanbar effect in a controllable environment. It is proved that when two systems with different initial temperatures are cooled to the same temperature, the system with higher initial temperature can use shorter time than the system with lower temperature. The results were published in the August 5, 2020 issue of the journal Nature. In the past, the definition of mpanba effect was vague. In the new study, the researchers defined the mpanbar effect with three temperatures: th (initial temperature of high-temperature system), tw (initial temperature of low-temperature system), and TC (heat bath temperature), where th & gt; TW & gt; TC. Under such a definition, they demonstrated for the first time that the cooling time from th to TC is shorter than that from TW to TC under a fully controllable setting. < / P > < p > in the experiment, they used small glass beads with a diameter of only 1.5 microns to represent water molecules. Then, by setting parameters, thousands of small glass beads are put into a beaker as a hot bath under different conditions. When each glass bead falls, they use optical tweezers to apply force on the glass bead; at the same time, the glass bead is cooled in a hot bath during the process. From the movement of the glass bead under the corresponding force, the researchers can calculate the effective temperature of the glass bead. < / P > < p > to further investigate how the system cools, the researchers tracked the movement of glass beads over time. They measured the cooling time from th or TW to TC and found that under some settings, glass beads with an initial temperature of th cool much faster than those with an initial temperature of tw. For example, under a special setting, it takes only 2 ms to cool from th to TC, while it takes more than 10 times to cool down from TW to TC. < / P > < p > this phenomenon seems unreasonable because it is assumed that th is first cooled to TW during the cooling process from th to TC, which means that it needs more cooling time. However, why is this simple logic no longer valid in some special cases? The key to the problem of < / P > < p > may be whether the system is in thermal equilibrium (all parts of the system reach uniform temperature). For a system that does not reach thermal equilibrium, temperature can no longer be a feature to describe its behavior. In this case, the behavior of materials becomes extremely complex. When the glass beads are cooling, the system is not in thermal equilibrium. < / P > < p > such a system does not have a direct cooling path from hot to cold, but has multiple cooling paths, which makes some potential cooling shortcuts exist. For glass beads, a higher initial temperature may mean that they can be more easily rearranged into structures that match the target temperature. It’s like a hiker, whose initial position may be farther from the destination than others, but can get to the destination faster than others, because this further starting point can actually prevent him from climbing the most difficult mountain. According to the past research of some physicists, this shortcut may exist in the cooling process. Although we can not be completely sure that this is the cause of the mpamba effect. < p > < p > water is much more complex than we think. It can be still liquid at a temperature lower than freezing point, or the phenomenon that the higher the initial temperature, the faster the cooling. This water study uses a very simple setup to reproduce a complex effect of water. This setting may imply that the mpanba effect is not only present in glass beads or water, but also more likely to be widespread in nature. The researchers hope that the model built in the experiment may also be used for other unknown purposes.