[Lewis Thomson (OP)]

Listener Richard is curious about finding the answer to this question,

"A microwave heats stuff by speeding up the electrons. Why can't we cool stuff by slowing down the electrons in a magnetic field?
Wouldn't it be great to have a Magnacooler next to the microwave, and be able to cool as quickly as you heat?"

Leave your answers in the comments below...

[Eternal Student]

Hi.

   First, I don't think it's all that useful to think about "speeding up electrons" as the method of heating food.

Microwaves cause water molecules in food to vibrate, producing heat that cooks the food.
   

[https://www.fda.gov/radiation-emitting-products/resources-you-radiation-emitting-products/microwave-oven-radiation]

    So, straight away, "slowing down electrons" won't really be a way to cool food down.   What you'd really want to do is slow down the movement of whole atom-sized and molecule-sized particles.
   
    Next, do you really want to use magnetic fields as your tool for the cooling, or are we free to suggest other things?

Best Wishes.

[evan_au]

The James Webb Space Telescope has to operate at very low temperatures (like 50 degrees on the Kelvin temperature scale).

There is a very big sunshade on one side. The telescope is on the other side, exposed to open space.
The Cosmic Microwave Background Radiation will effectively heat the telescope to 2.7K.
The telescope uses microwave radiation from the telescope itself to cool down from room temperature on Earth (around 300K) to around 30K. But this is a slow process that took a month or so.

The Mid Infra-Rad Instrument needed to get down to 7K, so they had to use a refrigerator mechanism to get the rest of the way.

See: https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html   and click on "Temperature Plots"

[paul cotter]

One could in theory, use the microwave energy from a magnetron to drive an absorbtion chiller. There are more efficient methods so there would be no point in doing this

[SeanB]

You can do so, though this is normally limited to very small volumes, where you use laser light that is just short of the wavelength that will stimulate emission of a photon, so that the higher energy atoms will eventually emit a photon, and then lose energy. About the only way to cool matter down to millikelvins, you rely on quantum effects to remove energy from the tiny volume of material, stripping it off a photon at a time. You can also do it with microwaves, just the materials you can cool are more limited, though the volume can be larger. This all takes place in a very high vacuum, well insulated so that you do not get stray energy leaking in. Not going to cool your food down, but works for physics experiments with Bose Einstein condensates, where you have matter acting like a massive single quantum particle.

[Rodneyhhernandez]

Of course we can, it's just that people haven't figured out where to use it until now. But the most effective way to cool something is in the freezer.