We propose a mechanism by which an asymmetric nanostructure can passively generate a net propulsive force under atmospheric pressure. As a concrete and intuitive realization, consider a double-slit wall comprising two nanoslits each of width a and a single-slit wall containing one nanoslit of width 2a, placed facing each other and connected as a rigid unit with a separation of order the mean free path of the gas, under atmospheric pressure. Because the total slit width is equal on both sides, the number of gas molecules incident on the slits of each wall per unit time is equal. However, owing to the difference in quantum diffraction patterns between the two aperture configurations, the number of gas molecules per unit time that enter from the double-slit side and exit through the single-slit side without collision differs from the number that transmit in the reverse direction without collision. As a result, the balance of atmospheric pressure on the two walls is broken, and the structure acquires a net propulsive force. The present mechanism is described, in essence, solely by the Schrodinger equation and geometric boundary conditions. Moreover, no physical principle can be identified that would suppress the generation of this propulsive force. We have carried out a quantitative evaluation based on Fresnel analysis and confirmed the computational existence of the thrust. However, the de Broglie wavelength of air molecules at standard temperature and pressure is approximately 0. 002nm —- small compared to technologically achievable nanoslit widthsof a few nanometres—so that the quantum diffraction effect per molecule is not large. In the quantitative evaluation above, the effective propulsive force was found to be of order 10^−5 relative to atmospheric pressure. Experimental verification of whether the propulsive force is indeed generated remains necessary. Should the generation of this propulsive force be confirmed, the propulsion mechanism would operate without combustion, electrical input, or moving parts. Proceeding on this assumption, we have explored a configuration in which the enormous number of air molecules impinging on the nanostructure per unit time under atmospheric pressure is exploited, with the cumulative effect combined with device integration yielding a practically effective thrust. In the present work, we arrive at a new configuration based on edge diffraction. Despite maximising the diffraction effect, this configuration is in principle realisable using current microscale manufacturing processes, making large-scale integration straightforward. This represents a major advance that can resolve the fabrication challenges of the earlier approach, and should make experimental verification feasible. The mechanism is applicable to any assembly of nanoscale elements—including asymmetric nanopores, arrays of nanorods or nanowires, clusters of nanoparticles, or any other configuration of scatterers. The connection between sub-assembliesmay be achieved by rigid mechanical coupling or by various other interactions. The assembly may comprise three or more sub-assemblies. Atmospheric pressure, sustained at planetary scale by solar energy, provides an inexhaustible passive molecular reservoir. The present mechanism originates solely from the geometric asymmetry of the nanostructure. If the generation of a propulsive force is confirmed, the mechanism would impose no constraints on material composition and would operate at any altitude within the atmosphere where pressure is sustained. The present framework further suggests that naturally occurring asymmetric structures—from biological ion channels to crystal lattices—may be subject to, or constrained by, asymmetric momentum fluxes under ambient pressure, offering new perspectives on passive transport in biological systems and structural stability in condensed matter. Quantitative verification via computation of the propulsive force in the edge-diffraction configuration and its experimental measurement, together with the formulation of the propulsive force from first principles, remain essential next steps. Note: A patent application has been filed for the edge-diffraction-based passive propulsion device and method described in this paper (Japanese Patent Application No. 2026-079977).
Ryohei Komurasaki (Mon,) studied this question.