Long-running series in which readers answer other readers’ questions on the subject, from trivial fantasies to deep scientific and philosophical concepts

Last modified on Sunday, October 24, 2021 09.01 EDT

For decades, I have been working hard to study how to make "negative microwave" work, this kind of equipment can quickly cool food or beverages and other items without pre-filling already cold things. I understand many reasons why this is almost impossible, but is it actually impossible? Maybe quantum physics can do this mysteriously. George Stewart

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I believe that the most promising way to quickly cool food or drinks is to put the plates/cups/glasses in a box that can be evacuated. The resulting increase in water evaporation will take away heat. Advantages: no chemical pollution, no large magnetic field, etc., no need to store gas under pressure. Disadvantages: Depending on the low pressure applied, evaporation may cause the part to be cooled to explode, and the beverage may boil and overflow, which means that the pressure drop should be limited for safety reasons. This method is inefficient for dry food. Alternative: The plate/cup/glass can be placed in a volume that allows the compressed air from the storage bottle to expand. Just like the cooling of a carbon dioxide fire extinguisher, the expanding gas (which should be ambient air for safety reasons) will be very cold. Disadvantages: Cooling will be achieved by rapid airflow, which may be inconvenient if you want to put food on a plate or put liquid in a cup. The large thermal gradients involved can cause damage to meals or plates (especially in the case of icing). Need to reserve pressurized ambient air. Perhaps the safest way is still to wait for the food to cool "naturally" while talking to a good person. Michael Bremer

The rapid cooler is the equipment you need. There is no quantum physics: it is a kind of super refrigerator. European restaurants require the use of rapid coolers, but they are not uncommon in private homes. I am Italian and my husband bought one recently. When he cooks too much lasagna, he will use a rapid cooler to cool down quickly to prevent the growth of bacteria. Food will be kept longer and safer, and when you reheat it, it will taste much better. Valeria Andreoli

Just put the food in the liquid helium. It is used to cool the hospital MRI scanner. Guess, I would say that every time you use it in your home kitchen, it costs about £50, so if you think it's worth it, this is your answer. Terry Eaton

Microwaves use microwaves to collide with water molecules to heat food, excite electrons and make them heat food and beverages. This energy needs to be removed in some way to de-excite the electrons. In quantum mechanics, this can be achieved by increasing the wavelength of electronic vibrations, making them less vigorous, so it is theoretically possible. However, as we all know, heat will naturally change from warm to cool. According to the second law of thermodynamics, warm things will cool to ambient temperature. So, I think the question is: if the time arrow determines that things will cool naturally anyway, what is the point of creating negative microwaves? Elvis

Thanks to Robert Boyle, this has been known since the 17th century. Keep the pressure constant and reduce the pressure; the temperature drops. Increase the pressure, the temperature rises. But it takes a lot of energy to do it. Kevin Aston

For many years, I have been trying to solve this idea. Tinkering in the garden shed has not produced any results. Once you solve this problem, maybe you can help me complete another project of mine, the dark flashlight, which projects a "no light" field. David Sorgen

Of course, this is possible, but microwave ovens cannot be used. Instead, the liquid pressurized gas released into the vacuum cooling chamber is used. As the gas volume increases, this will create a very cold environment. Google "the coldest place in the universe" and you will find that it is a rapidly expanding gas cloud with a lower temperature than other parts of the universe. When you refill the lighter with butane gas, you can feel the effect. The filling bottle will become very cold. OJ Nordhagen, Norway

I am a nuclear scientist and have a PhD in physics. Since you have been working hard to solve this problem, I think you have done some research yourself, so if I repeat what you have learned, please forgive me. Microwaves heat food because electromagnetic radiation interacts with water molecules in the food. This wavelength interacts with the different vibration modes of the molecules in the food, and the energy from the microwave excites the molecules and makes them vibrate faster. This will heat up the food. It particularly interacts with hydrogen bonds, such as hydrocarbons in water and oil.

In order to cool, we must extract heat from food. This is a bit tricky and generates heat as a by-product. One method is laser. Negative temperature has been generated in the laboratory, but it will not produce cold objects as you would like. A more feasible method is to use cold liquid and remove heat, just like a powerful refrigerator. Perhaps it is enough to spray nitrogen quickly at extremely cold temperatures. In my work, we use low temperature, if we can use negative microwave equipment to indirectly cool objects, we would like to know! Rose brown

Various methods can be used to ensure that the surface of the food/object radiates heat and receives the least incoming heat (for example, cooling the wall of the metal container in which it is located to near absolute zero.) These will quickly cool the surface of the object ("flash freeze" "). However, there is no — and it is impossible — to cool the inside of an object, other than by conducting heat to the outside. Microwaves send electromagnetic energy into the interior, but there is no such thing as negative energy (except in strange circumstances). Martin Melish

No, the reason is simple, because of the second law of thermodynamics. This is the only physical process that is fundamentally asymmetric (in this universe anyway), so it is usually considered the definition of the arrow of time. It basically shows that entropy (disorder) always increases in an isolated system. Heating increases entropy, and you are dealing with the natural trends of the universe, so this is easy-put any energy (for example, microwaves) into anything and it will only become more entropy without any further work. On the other hand, cooling means putting more order (reducing entropy) into the system, working in the opposite direction that the universe wants to go as defined by thermodynamics, so it requires a lot of extra work (and therefore energy) to reduce entropy (ie Cooling) increase (heating) by the same degree. Did you feed the fish

If you put energy into something, no matter what you do, it will not become colder. As far as I know, the working principle of the refrigerator is to allow the energy in the air in the box to act on certain materials in the refrigerator, thereby cooling the air inside. In general, the surrounding air is warmer than when the refrigerator is not turned on; if you leave the door open (a bad idea), it will not cool the room. So even in this case, although you put energy into the device and it is cooling something, in general, the refrigerator is heating something.

However, if you can reverse the time, you only need to use ordinary microwave equipment. You put the hot food in the microwave, wait until the microwave leaves the food in the surrounding equipment, and then take out the cold food. Somewhat rational

I'm sure that about 30 years ago, they had a device on Thresher's contraband, and you can ask them to put your bottle in it to cool down quickly. If I remember correctly, it swayed a lot in the process. I sometimes wonder what happened to these machines and why there is no modern equivalent. Hot burrito

The idea of ​​using fluorescence to cool materials under light excitation was first proposed in the 1920s and then theoretically verified by Landau in 1946. As expected by George Stewart, it relies on the principles of quantum mechanics: if a laser is used to drive electrons to an excited state with non-equilibrium occupancy, then the electrons can absorb phonons (the wave-like structure that carries heat in the material vibrates) and then emits Higher-energy photons (fluorescence) relax to a low-energy state. This leads to a net heat loss of the material, called "anti-Stokes fluorescence": for a better description (and an example of cooling macroscopic objects from room temperature to -182C), see here.

However, if this cooling process is to exceed the usual heating effect caused by electromagnetic wave absorption, the irradiated material must have extremely high quantum efficiency. This means that the electrons must accurately follow the correct sequence of excitation, absorption, and emission, rather than absorbing energy from the laser through non-radiative dissipation. So far, I believe that only ultra-high purity glass containing rare earth ions can finally prove this point. (In the past decade, scientists have claimed that similar laser cooling has been achieved in certain semiconductors and perovskites, but these experiments have not been replicated and are still controversial.) So I am worried about any attempt to cool gazpacho with laser The person may be disappointed. furry_marmot

I think the answer here is counterintuitive. Instead of recruiting the best and most dedicated talents in academia and industry to study solutions to this problem, you also need to gather a group of incompetent former science students who have been expelled from the university. In this way, the team will definitely reach zero, so it will be absolutely successful. No owls