Everything is a particle. And everything is a wave. Light? It’s a wave but it is also made of tiny packets of energy known as photons that behave like particles. Electrons? They behave as both particles and waves. This duality has been known about for almost a century, when Louis-Victor de Broglie claimed that all matter had a wave-like nature. And he really meant all matter. Even you have a specific wavelength.
The most renowned experiment used to prove this is called the double-slit experiment. It is easy to assemble to show that light is a wave. If you cut two slits in a piece of cardboard and put a flashlight behind it, a beautiful diffraction pattern forms on the other side.
This double-slit diffraction also happens with electrons and atoms, and one might wonder how big we can go. New research shows that we can go pretty big. Using a complex experiment, they were able to demonstrate the particle-wave duality of a molecule with 2,000 atoms. These are the heaviest objects to date for which this has been possible. The achievement is reported in Nature Physics.
This high-mass molecule is said to be in superposition. For all intents and purposes, this means that the molecule goes through multiple places at once. They are delocalized and for this reason, we see them behave like waves. If you are feeling like “Woah!” or "WTF?", don’t worry that is perfectly normal when talking about quantum mechanics.
“Every molecule is in a superposition of possible positions. This is what we abbreviate by 'being in two places at once'. Hot as they are, no two molecules would ever interfere. It is the superposition and interference of paths,” the team stated in a Q&A press release.
The results from the experiment were three years in the making, using particular organic molecules and a setup known as a Talbot-Lau interferometer. The wavelength scale is the inverse of the mass so as the mass grows bigger, the wavelength grows smaller, making it more and more difficult to test the interference.
But pushing this boundary is important to gain new insight into quantum mechanics and produce a new understanding of its limits in explaining reality.
“Quantum physics has been around for 100 years and has been confirmed to be the valid theory of the inanimate nature (excluding gravity) throughout all tests,” the authors write. “However, if quantum objects can be in superposition of two different energies, two positions, two velocities and directions, why don't we see this in our daily lives?”
They point to both simple and complex answers for it, but to confirm we will have to go even bigger yet.