Have you ever been invited to multiple cool events on the same night? Wished you could go to all of them but knew you had to pick one and live with the choice? Well if you were an electron you might just be able to attend them all at once or maybe none of them at all. Who knows! Unless you were observed. Then we would know. WE WOULD KNOW. Sound like I’m talking gibberish? You’re right I am because in this edition of Mind Blown I tackle THE COPENHAGEN INTERPRETATION. (Cue trippy orchestral sci-fi theme)
What is the Copenhagen Interpretation? Good question, glad you asked. The Copenhagen Interpretation emerged as an outgrowth of Heisenberg’s Uncertainty Principle, which states that you can observe an electron’s position or its momentum but by observing one you make it impossible to know the other, and Bohr’s Principle of Complementarity, which states that that objects have complementary properties which cannot be measured accurately at the same time.
Together Bohr and Heisenberg (who had worked together at Copenhagen University in the 1920’s hence the name) formulated the beginnings of what would become the Copenhagen Interpretation which basically says that electrons exist in both a particle and wave state. Before the system is observed the electron exists as a wave covering all possible locations but once it is observed it collapses into a particle state that indicates only one of the possible outcomes. Trippy right?
This is best illustrated by the Double Slit experiment which comes standard with just about every university level physics class. In this experiment a focused light source (think laser) illuminates a wall/plate/solid piece of whatever with two parallel slits in it. The light passing through the slits is observed on a screen behind the wall. The light produces bright and dark bands on the screen, consistent with the concept of light as a wave and not a particle. But the light is absorbed by the screen at specific points consistent with the light acting as individual particles. To add to the mind-blowingness if you place detectors at the slits you’ll find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave). Boom. Light acts as both a particle and a wave. Like a boss.
The Copenhagen interpretation gave rise to another famous (thought) experiment concerning a certain physicist’s cat in a box. While you may have heard Schrodinger’s Cat mentioned in a pop culture reference or as a throw away joke from one of your nerdier friends you may not know what the actual exercise is so I’ll walk you through it now. Imagine a cat in a box. It doesn’t matter what kind of cat. Persian, Abyssinian, Korat whatever breed of cat you can think of imagine it in a box. Also in the box (and secured against interfurence {see what I did there}) would be a bit of radioactive material and a Geiger counter. The Geiger counter would be designed so that when it sensed the decay of the radioactive material, it triggered a hammer which was poised to break a flask containing hydrocyanic acid, which, when released, would kill the cat. Now seal up the box. Is the cat alive or dead? You won’t know until you open up the box again thus the cat is both alive and dead until you do. Schrodinger actually meant the exercise as a critique of the absurdity of the Copenhagen Interpretation but it took on a life of its own and came to be the go to way to explain the concept of Superposition, the probability cloud that exists before a particle is observed.
Okay well I hope this served as a suitable introduction to The Copenhagen Interpretation. Obliviously much more has been written on the topic by fellows much smarter than I am but I thought it was mind blowing enough a topic to give you a bit of a teaser. ‘Till next time. Science!