How Humans Act as Waves (In Quantum Physics)

“Is it a wave or a particle?” is a simple question with a complex answer, one that can change depending on how the question is asked. If you pass a beam of light through two slits, light is a wave. But if you pass that same beam through a conducting plate of metal, it will act like a particle. This is all to say that light, also known as photons, illustrates the dual nature of reality.

Even more, this phenomenon isn’t just restricted to light. We see this is in all quantum particles, such as electrons, protons, and neutrons, and even in large collections of atoms. Even human beings act like quantum waves.

The debate over whether light behaves as a wave or a particle began in the 17th century with Isaac Newton and Christian Huygens, a Dutch scientist. Newton believed in the “corpuscular” theory of light: that light acts as a particle—in straight lines, refracting, reflecting, and carrying momentum just as any other kind of material would. Huygens, opposingly, believed in the wave theory of light, which includes interference and diffraction. Interference is when two waves meet, while diffraction is when a light is spread out as a result of passing through a narrow aperture.

Thomas Young noticed a wavelike pattern associated with light in the 18th century. It was an alternating pattern of constructive and destructive interference. Scientists derived a form of charge-free radiation: an electromagnetic wave that travels at the speed of light. As a result, Einstein was able to devise and establish the special theory of relativity; the wave nature of light was a fundamental reality of the universe.

Light behaves as a quantum particle in a number of ways. Its energy is quantized into individual packets called photons, each containing a specific amount of energy. It is also possible to create and send individual photons through any experimental apparatus devised. When all synthesized together, the most mind-bending demonstration of quantum “weirdness” of all is the result: even molecules with as many as 2,000 atoms have demonstrated to display wavelike properties.

For human beings, with about 1028 atoms present in each of us, the quantum wavelength associated with a fully formed human is large enough to have physical meaning. In most real particles, including humans, only two things determine the wavelength: rest mass and the speed it’s moving at.

There are two things you can do to coax matter particles into behaving as waves. One, reduce the mass of the particles into as small a value as possible, resulting in larger wavelengths, or two, reduce the speed of the particles you’re dealing with, meaning less momentum, larger wavelengths, and larger-scale quantum behaviors.

This opens up to a fascinating new area of technology: atomic optics. We could use slow-moving atomic beams to observe nanoscale structures without disrupting them in the ways that high-energy photons would. As of 2020, there is an entire sub-field of condensed matter physics devoted to ultracold atoms and the study and application of their wave behavior.

One of those is atomic optics, a research field that becomes even more powerful when combined with microscopic atom-optical elements on the surface. The development of cold atoms can be used for experiments such as high-resolution spectroscopy, atom lithography, atom microscopy, atomic fountains, and cold atoms in confined space.

Many technological breakthroughs have been and will continue to be laid by these scientific foundations. The closer we get to absolute zero—the lowest temperature that is theoretically possible—the more the field of atomic optics and nano-optics will advance. At this temperature, the velocity of particles slows to nearly zero, which can cause a “superposition of states.” Different momenta permit the atoms to separate spatially and then be manipulated to fly along different trajectories. And maybe, someday, we will be able to measure quantum effects for entire humans, even if little is known about it now.