A Melted Candy Bar Changed the World: The Accidental Invention of the Microwave Oven

This article is written for general informational purposes only. Historical facts have been cross-verified across multiple open-access sources. Some anecdotes — including the exact type of candy bar — lack primary documentation and are noted as legendary accounts. Results and interpretations may vary depending on the source consulted.

📋 Table of Contents

1. Overview — The Man Behind the Oven
2. The Discovery — What Really Melted in His Pocket
3. The Chain of Experiments — Popcorn to Exploding Egg
4. The Radarange — A Refrigerator-Sized Revolution
5. Percy Spencer — The $2 Inventor
6. Frequently Asked Questions
7. References & Further Reading

🎯 Overview — The Man Behind the Oven

Reheating leftovers takes 90 seconds today. That convenience traces back to a single moment in a Massachusetts research lab in 1945 — when a radar engineer reached into his pocket and found a melted candy bar he hadn't eaten yet.

The engineer was Percy LaBaron Spencer (1894–1970), a self-taught prodigy at defense contractor Raytheon. He left school after fifth grade, taught himself calculus and trigonometry at night, and eventually held over 300 patents — making him one of America's most prolific inventors despite never earning a formal degree.

1945

Candy bar incident & patent filed

1947

Radarange commercially launched

1967

First affordable home model

1997

90% of U.S. homes owned one

🍫 The Discovery — What Really Melted in His Pocket

On an otherwise unremarkable day in 1945, Spencer was working near an active magnetron — the high-frequency microwave-generating device used in radar systems. When he reached into his pocket, he found his candy bar had melted completely. The lab temperature was perfectly normal.

✅ Fact Check

The candy bar's identity: Multiple sources, including History.com and the University of Maine Library, specifically name it as a Payday bar (peanuts and caramel — not chocolate). However, no verified primary source exists, and Wikipedia classifies the account as legendary. "Chocolate bar" is a common but imprecise description.

Most people would have shrugged it off. Spencer didn't. Decades of magnetron expertise told him exactly what had happened: the microwaves had agitated the water molecules inside the candy bar, generating heat from within. Not from the outside in — from the inside out.

This wasn't just a curiosity. It was an entirely new principle of cooking. Microwaves pass straight through glass, plastic, and paper, but cause water molecules to vibrate billions of times per second. That friction creates heat — directly inside the food.

🔬 The Chain of Experiments — Popcorn to Exploding Egg

Needing to confirm his hypothesis, Spencer ran a rapid sequence of tests.

• 🍿 The Popcorn Test
  He held kernels of corn in front of the magnetron. Within seconds, popcorn was flying across the lab. It was, quite literally, the world's first microwave popcorn.
• 🥚 The Egg Test
  He placed an egg inside a kettle and aimed microwaves at it. Pressure built rapidly inside the shell — and the egg exploded, directly into the face of a curious colleague who had leaned in to watch. (Confirmed by Smithsonian Lemelson Center and Wikipedia.)

✅ Fact Check

The original Korean article simply said the egg "exploded." Both Smithsonian and Wikipedia add that it exploded into a colleague's face — a detail that makes the story more vivid and accurate. Placing a whole egg in a microwave remains dangerous today and should never be attempted.

📡 The Radarange — A Refrigerator-Sized Revolution

Spencer and Raytheon moved quickly. They encased a magnetron in a metal box, filed a patent on October 8, 1945 (granted January 24, 1950), and in 1947 introduced the world's first commercial microwave oven — named Radarange, a portmanteau chosen through an employee naming contest.

📊 Radarange Specs (1947)

Height	~5 ft 11 in (1.8 m) — taller than most adults
Weight	750 lbs (340 kg) — water-cooled system included
Power	3,000 W — 3× a modern home microwave
Price	$5,000 → ~$52,000–$73,000 in today's money

✅ Fact Check

The original text described the price as equivalent to "tens of millions of won" — a significant understatement. Per Wikipedia, the APS, and History.com, $5,000 in 1947 equals roughly $52,000–$73,000 today. Early adopters were limited to hotels, ocean liners, and restaurants. The first countertop home model ($495) arrived in 1967 via Amana, a Raytheon subsidiary.

Miniaturization was relentless. By 1975, microwave ovens outsold gas ranges in the United States for the first time. By 1997, 90% of American homes had one — cementing it as one of the fastest-adopted kitchen appliances in history.

👨‍🔬 Percy Spencer — The $2 Inventor

Spencer's personal story rivals his invention in drama. Orphaned at 18 months, abandoned by his mother, he was raised by relatives in rural Maine. He left school at 12 to work in a textile mill and later taught himself trigonometry, calculus, chemistry, and physics — entirely on his own — during whatever hours the mill left him.

After a stint in the Navy, he joined Raytheon and eventually rose to Senior Vice President. He earned 300+ patents. And for the invention that fundamentally changed how humanity feeds itself, Raytheon paid him the standard employee inventor bonus:

$2

"An educated scientist knows many things that won't work. Percy doesn't know what can't be done."
— MIT scientist, as reported in Reader's Digest, 1958

❓ Frequently Asked Questions

Will a whole egg really explode in a microwave?

Yes. A microwave rapidly heats water molecules inside food. A whole egg in its shell creates a sealed pressure chamber — internal pressure builds until the shell fails explosively. Spencer's colleague experienced this firsthand in 1945. Never microwave a whole egg in its shell.

Why doesn't the container get hot?

Microwaves pass straight through materials like glass, ceramic, and microwave-safe plastic without interacting with them. They only interact with polar molecules — primarily water. So the container stays cool while the food heats. (Metal is different: it reflects microwaves and can cause arcing.)

Did Percy Spencer get rich from his invention?

No. Under Raytheon's standard policy, employee inventors received a flat $2 bonus. He was promoted to Senior Vice President and widely respected within the company, but received no royalties. Spencer was posthumously inducted into the National Inventors Hall of Fame in 1999.

Is it true Percy Spencer had no formal education?

Correct. He left school after fifth grade. Everything he knew — trigonometry, calculus, physics, chemistry — he taught himself. He is frequently cited as one of the most striking examples of self-directed learning producing world-class expertise.

📎 References & Further Reading

All links below are freely accessible as of 2025. No paywall. No login required.

📖 Wikipedia — Percy Spencer 📖 Wikipedia — Microwave Oven 📰 History.com — Who Invented the Microwave Oven? 🔬 MIT Technology Review — Melted Chocolate to Microwave (1999) 🏛️ Smithsonian Lemelson Center — Percy Spencer Biography ⚛️ American Physical Society — 1945: First Patent for the Microwave 🎓 University of Maine Libraries — Percy Spencer Research Guide 🗞️ New England Historical Society — Percy Spencer Melts a Chocolate Bar 🏅 Lemelson-MIT — Percy Spencer 📅 HISTORY — First Patent Filed for the Microwave (Oct 8, 1945)

Accidental Discoveries Series #7 · Fact-Checked · 10 Open-Access Sources Verified
© Written for informational purposes. Please credit this source if referencing.