How to make water boil until it freezes

Professor Leif stepped up to the podium and gave a lecture to the freshmen on the stage. After a brief introduction, Professor Leif suddenly asked the question, "How do you get water to boil until it freezes?"

　　This question made the students in the audience look at each other. Boiling water until it freezes? This is completely impossible. Not to mention that they are highly talented students who have been admitted to prestigious universities, as long as they have a little bit of general knowledge of physics, they all know that the temperature needed to boil water is 100 ℃, and the temperature needed to freeze is 0 ℃, which are completely two extremes, how can it be achieved?

　　Seeing the students shaking their heads repeatedly, Professor Leif smiled and instructed his assistant to put an apparatus chamber with transparent glass on the podium. Professor Leif filled a beaker with a glass of tap water and put the beaker into the apparatus chamber. Then, Professor Leif asked his assistant to make some settings on the apparatus cabin, and in a short time, the students saw the tap water boiling in the beaker through the transparent glass. And in the assistant's continuous operation, the water in the beaker also maintained a continuous boiling state. However, the students were stunned by the next scene: the tumbling water in the beaker was not moving - it was frozen!

　　The students were in an uproar. Professor Leif smiled and said, "We all know that the normal boiling point of water is 100°C at standard atmospheric pressure. In other words, the boiling point of water depends on two things: temperature and air pressure. We only considered the temperature, but ignored the condition of air pressure. This is a pressure chamber, put the water into the pressure chamber, while using the pump to reduce the air pressure. In this way, the boiling point of water will also be lowered. So, although we see the water boiling, its temperature is very low, continue to lower the air pressure, the water will continue to boil, but the temperature has actually dropped below 0 ℃, so it is normal to freeze."

　　After hearing Professor Leif's words, the students were enlightened and nodded their heads. Professor Leif went on to say, "But there is a prerequisite here to throw the traditional creed out of the window. Otherwise, I'm afraid I'll just have to assume, as I did at the beginning, that it's an impossible thing to do. And this is one of the most important qualities that we must have to do physics research. Always remember that anything is possible."

　　This was the first physics class for students at MIT, where Professor Leff is the president, Raphael Leff.