Microwaves Heat Unevenly Because of Standing Waves
A microwave oven fills its cavity with electromagnetic waves that reflect off the metal walls and form a standing-wave pattern with fixed hot and cold spots — the rotating turntable exists specifically to move food through both, since a microwave without one would leave the same spots over- and under-cooked every time. Denser or thicker parts of food also absorb energy more slowly than thin parts, which is why stirring or rotating food partway through, and letting it rest a minute after, both meaningfully even out the final temperature.
Sources & methodology: These tips draw on established food-science references —
Harold McGee's food-science writing, America's Test Kitchen /
Cook's Illustrated testing, Serious Eats'
technique reporting, USDA food safety guidance,
and peer-reviewed food-safety research (including UC Davis
cutting-board studies) — not reworded recipe-blog consensus.