John Preskill, while talking about taking a quantum mechanics class with the late John Wheeler, mentions this story:
Later, at a student-faculty lunch, Wheeler seemed troubled. He had been asked to explain the essence of quantum mechanics in five words or less, and was stumped. Frank Calaprice, a nuclear physicist within earshot, interjected helpfully, “What we expect to measure?” I was silent.
The question was absurd. It was fascinating. I still think about it. I can’t answer it.
This idea–explain quantum mechanics in five words–has captured the imagination of people. In the the blog comments, a number of people chime in with their thoughts:
- “Nature’s way of reasoning.” - Michael Nielsen
- "Non-commutative Probability Theory." - Steve Flammia
- "Unitary evolution, projective measurement." - Graeme Smith
My attempt at non-technical answer is: Quantum mechanics is nature's casino.
Sean Carroll, via Michael Nielsen, picked up on the idea and posted this Twitter challenge:
Explain quantum mechanics in 5 words or less? A task for Twitter if ever there was one. #5wordqm
— Sean Carroll (@seanmcarroll) July 9, 2012
My attempt: "Reality is greater than measurement." #5wordqm
— Sean Carroll (@seanmcarroll) July 9, 2012
Which has led to a flood of tweets trying to summarize quantum mechanics. Here are my favourites so far:
All knowledge is precisely uncertain.#5wordQM
— C. G. P. Grey (@cgpgrey) July 10, 2012
A tale of two slits. empiricalzeal.com/2011/06/10/why… #5wordQM
— Aatish Bhatia (@EmpiricalZeal) July 9, 2012
Schrodginger walks into an h-bar.#5wordqm
— Zach Weiner (@ZachWeiner) July 9, 2012
"Unperformed experiments have no results" #5wordqm #AsherPeres
— Blake Stacey (@blakestacey) July 9, 2012
Everything not forbidden is mandatory. RT @seanmcarroll: Explain quantum mechanics in 5 words or less? #5wordqm
— Chad Orzel (@orzelc) July 9, 2012
We are inflated vacuum fluctuations. #5wordqm en.wikipedia.org/wiki/Inflation… @seanmcarroll
— Jasper Palfree (@wellcaffeinated) July 10, 2012
All possibilities contribute to amplitude #5wordQM
— minutephysics (@minutephysics) July 9, 2012
How would you explain quantum mechanics in five words or less?