Conner Dailey Physics graduate student, hobby photographer

A Quantum Mechanical Anecdote

Classical Mechanics

At the beginning of the 1900’s, many important aspects of physics had been well developed. The best theories up to and around that date are referred to today as classical mechanics. Many scientists in this era erroneously considered physics to be relatively complete, and part of the reason for this was the lack of proper tools to investigate physics at the scales needed to see effects from the theories in modern physics 1.

Once technology progressed enough to give physicists the tools to investigate individual particles, they discovered mind-bending properties. It is recognized as a huge paradigm shift in science, and I will try to explain just what confused the scientists of that day.

Weird Quantum Properties

I like to think that at heart, physicists are just kids on a playground, experimenting with toys. Before the 1900’s, one of their favorite games was “Wall-Ball”, a simple game that involves throwing a rubber ball repeatedly at a wall. As the good scientists they are, they recorded the “rules” that seem to govern the game:

  • If one throws the ball at the wall, it bounces back always
  • If one throws the ball over the wall, it continues over the wall always

They had played this game for so long that it seemed that these rules were very concrete. Soon after 1900, they were given new tools that allowed them to play with smaller and smaller balls. Eventually, one scientist suggests that they instead try to play the game with an electron, one of the smallest “balls” known. Excited to play with this new toy, they begin throwing it at the wall just like before.

At first, things seem normal, until one of them throws the ball directly at the wall, and it disappears. After some investigation, it seems the ball has gone directly through the wall. Confused, they keep playing. After a while, another peculiar thing happens, one of them throws the ball far over the wall and it bounces directly back at them! After many iterations, they establish some new rules of the game:

  • If one throws the ball at the wall
    • Most of the time it bounces back
    • Sometimes it goes though the wall entirely
  • If one throws the ball over the wall
    • Most of the time it goes over
    • Sometimes it bounces back off of seemingly thin air

Clearly, the previous rules no longer apply in this electron game, and their strategy must be modified accordingly.

This behavior is referred to in literature as quantum tunneling, and is one of the many features of quantum mechanics that challenges a “classical” intuition. I think this short story is a great way to introduce the weird nature of quantum mechanics to those who might not understand physics jargon.


  1. Agar, J. “Science in the 20th Century and Beyond.” United Kingdom: Wiley, 2012.