MadSci Network: Engineering

Re: Is it possible to make the reverse of a microwave?

Date: Tue Jun 12 22:50:11 2001
Posted By: Edward Peterson, Staff, Chemical Engineering, S&B Engineers and Constructors
Area of science: Engineering
ID: 991779168.Eg


The answer to your question has been asked by a lot of different people 
with advanced degrees in science and engineering.  There are several 
different answers to your question.  I will try to answer what I BELIEVE 
you want to know.

First, you have seen that a microwave oven heats objects without any 
apparent application of heat.  There are no flames or glowing cooking 
elements, as you would see on a gas or electric stove.  The result of 
something heating in a microwave oven is caused by forcing microwaves, a 
form of energy found in sunlight and many other sources, into a box that 
contains something that can absorb these microwaves.  Materials such as 
water, meat (protein), fats, carbohydrates, granular metal, carbon, house 
bricks, and such absorn the energy very well.  The energy penetrates 
millimeters to several centimeters into the material, depending upon its 
properties (dielectric behavior).  Once inside the material, the energy 
converts to molecular motion and some chemical bond distortion.  This 
increase in motion and disorder creates heat.

To reverse the effect of a microwave, we would have to be able to REDUCE 
molecular motion by application of a form of energy.  If we cool the air 
around an object, its molecular motion is reduced, but only because the 
average heat in the objects surroundings is lower, allowing the object to 
lose heat.  If we apply a vacuum to a wet object, the object cools due to 
the liquids instability at that pressure, and its resulting evaporation, 
which is a cooling process.  Still, we have not done the opposite of a 
microwave oven, although we have cooled instead of heated.

There is a special case where we can cause the opposite of microwave 
heating, although it is only useful on a few different materials.  Let me 

Hydrogen is normally a gas.  It is so hard to liquify that it becomes a 
liquid at just a few degrees above absolute zero.  Water liquifies at 373 
degrees (Centigrade type) above abolute zero, and freezes at 273 degrees 
above absolute zero, so you can imagine how cold hydrogen must get to 
become a liquid.  A few degrees cooler, I THINK (I did not look this up), 
at about 4 degrees Kelvin, hydrogen can become a solid.  How do we cool 
the solid hydrogen down any further?  What refrigeration process will work?

Many years ago, some bright scientists decided that since heat is the 
measure of disorder, that anything that forces order on a system will cool 
it down.  Hydrogen (see your periodic chart) is a metal.  Because it is a 
metal, it can react to magnetic fields.  They imposed a powerful magnetic 
field on a small sample of very cold hydrogen and discovered that the 
temperature of the hydrogen dropped to a few tenths, then a few 
hundredths, then a few thousandths of a degree above absolute zero!  The 
ordering of the hydrogen molecules, which were already highly ordered, was 
improved in a volumetric manner.  Since microwave heat materials by 
imposing disorder in a volumetric manner, these act in an opposite manner.

Unfortunately, a huge amount of energy was required to cool a very small 
sample of hydrogen just a few degrees.  As a practical source of 
volumetric cooling, magnetic fields do not qualify, but from a scientific 
standpoint, they are very interesting.

If you would like to discuss this further, email me at

Edward Peterson, PhD, P.E.

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