How does a microwave oven heat food?

A microwave heats food by sending invisible microwaves through it. The waves push water molecules to turn rapidly, and their motion passes energy through the food as heat. A device called a magnetron makes the waves, while the oven’s metal walls keep them bouncing inside.

The heating pattern is patchy because waves overlap strongly in some places and weakly in others. The turntable carries dinner through these different zones, but stirring and resting still help. That stubborn cold middle is physics at work, not a personal failure by whoever reheated the pasta.