Let's talk about a true saviour in the history of mankind.
Mr. Percy Spencer. Circa 1946, he created the "Radarange".
Mr. Microwave. Welcome to the world.
The moment Percy created the Microwave, life got easier. What a Saint. I checked, he unfortunately wasn't canonized.
The Microwave's main pairt, the Magnetron tube, shakes the molecules of water that is inside every piece of food. That single shake of a water molecule happens 2.5 billion times a second. When they shake, it causes friction between the water molecules. With friction, comes heat.
Shake it hard girl, I need my 6 day old pizza nuked back to life!!!