Do humans exhibit wave–particle duality?

After the discovery that light can behave as both a wave and a particle, French physicist Louis de Broglie took a bold step further. He suggested that duality should not be exclusive to light, whose particles, photons, were found to be massless. Instead, it should be a fundamental property of all particles, including those of matter such as electrons. Importantly, de Broglie’s hypothesis places no upper limit on mass. This raises a tantalizing question: do human bodies also exhibit the wave-particle duality?

Fig. 1. Every step you take echoes as a wave, too small to see, but never absent.

According to de Broglie, any moving particle has an associated wavelength. The relation between the wavelength λ and the particle's mass m, velocity v, and Planck’s constant h is given by:

In essence, this equation suggests that every moving object, from tiny electrons to macroscopic human bodies, has wave-like properties, with a wavelength inversely proportional to its mass and speed. waves. For example, an electron can exhibit a relatively large wavelength when moving slowly. A more massive molecule has a shorter wavelength. As mass increases to macroscopic scales, the associated wavelength becomes unimaginably small, far smaller than anything we can currently measure.

Do we exist as both waves and particles?

The greater the mass m and velocity v, the shorter the wavelength λ. For a typical person with a mass of 70 kg, moving at a leisurely speed of 1 m/s, the de Broglie equation assigns a wavelength on the order of the Planck length, a scale at which our current physical theories are no longer sufficient to describe reality fully. What does this say about our dual nature? Are we still waves, just as much as we are particles?

To observe wave-like behavior, physicists typically rely on setups such as Young's double-slit experiment. In such experiments, the slit width must be comparable to the wavelength of the particle being tested. Only under this condition do interference patterns, clear signatures of wave behavior, emerge.

For electrons, this requirement can be met, which is why their wave nature is experimentally observable. However, for an object as massive as a human, the required slit width would need to be unimaginably small, far beyond any scale accessible to current or foreseeable technology. In practice, this makes observing wave behavior in macroscopic objects effectively impossible.

So far, electrons, atoms, and even relatively large molecules have been tested and shown to produce interference patterns consistent with de Broglie’s predictions. However, the interpretation of these “matter waves” remains subtle. The prevailing view in quantum mechanics is that these waves do not represent physical ripples in space in the classical sense, but rather mathematical constructs that describe probabilities of measurement outcomes.

Macroscopic objects, by contrast, interact constantly with their environment. This suppresses quantum effects through processes such as quantum decoherence, making their behavior appear entirely classical. As a result, they do not exhibit observable wave-like properties, even though the underlying principles still apply.

While classical physics successfully describes the macroscopic world, the idea that we possess wave nature, even if fundamentally unobservable, remains deeply intriguing. The same principles govern all matter, regardless of scale. If every step we take is associated with a wavelength, then we are never truly separate from the quantum world. And perhaps that is the most remarkable insight of all. We are not exceptions to quantum reality, but quiet participants in it.