Quantum mechanics has brought about many surprising results since its inception in the early 1900s. One of the most intriguing and counter-intuitive is the phenomenon of particle wave duality. This means that subatomic particles (like electrons) can exhibit both wave-like and particle-like behavior, depending on the experiment being performed.
Particle wave duality is often explained using the famous double slit experiment. In this setup, a beam of particles (say, electrons) is fired at a screen with two slits in it. If we observe where the particles hit the screen, we find that they create two bright fringes separated by a dark region in between (this is called an interference pattern). However, if we instead observe which slit each particle went through, we find that each particle behaves like it went through just one slit! How can this be?
The key lies in understanding that subatomic particles are not really “particles” in the traditional sense of the word. They are more accurately described as “quantum objects” which occupy a fuzzy state somewhere between being a true particle and a true wave. The amount of “waviness” vs “particle-ness” depends on how you measure them. In the double slit experiment, if you try to determine which slit each electron went through, you force it to become more “particle-like” and it will behave accordingly. However, if you simply observe where it hits the screen without trying to determine which slit it went through, then you allow it to remain more “wave-like” and it will produce an interference pattern.
Of course, this leads to all sorts of strange consequences when applied to other quantum objects like atoms or molecules. For example, because they can exist as either waves or particles depending on how they are measured/observed, does that mean that subatomic particles can be in multiple places at once? The answer appears to be yes! This bizarre behavior may seem contradictory but it actually makes perfect sense when viewed from a purely mathematical standpoint – something we will explore further in another article.