Physics

The Double-Slit Experiment: Wave-Particle Duality Made Visible

Richard Feynman called the double-slit experiment „a phenomenon which is impossible to explain in any classical way, and which has in it the heart of quantum mechanics.“ The experiment demonstrates that individual particles — electrons, photons, even molecules — produce an interference pattern when passing through two slits, as if each particle interferes with itself. The pattern vanishes when „which-path“ information is obtained.

The video below shows the famous Hitachi/Tonomura experiment (1989) — single electrons fired one at a time through a biprism. Each electron arrives as a discrete dot; over time, the dots build up the characteristic interference fringes. This experiment was voted „the most beautiful experiment in physics“ by Physics World readers in 2002.

Key Papers and References

• Tonomura, A. et al. „Demonstration of single-electron buildup of an interference pattern.“ American Journal of Physics 57 (1989): 117–120.
• Bach, R. et al. „Controlled double-slit electron diffraction.“ New J. Phys. 15 (2013): 033018. arXiv:1210.6243
• Frabboni, S. et al. „The Young-Feynman two-slits experiment with single electrons.“ arXiv:0706.2057
• Arndt, M. et al. „Wave-particle duality of C60 molecules.“ Nature 401 (1999): 680–682.
• Nairz, O. et al. „Quantum interference experiments with large molecules.“ American Journal of Physics 71 (2003): 319–325. arXiv:quant-ph/0208023
• Schlosshauer, M. „Decoherence, the measurement problem, and interpretations of quantum mechanics.“ arXiv:quant-ph/0312059
• Hitachi R&D — Double-slit experiment

Tomáš Mančal — A Reflection on Two Paths to Quantum Mechanics

The lecture explores two routes to fully-fledged quantum mechanics, whose centenary — 1925 and 1926 — we are celebrating. It compares Heisenberg’s modus operandi, rooted in the extension of Hamilton-Jacobi mechanics and a philosophically motivated renunciation of the concept of state, with Schrödinger’s path, which also proceeds via a limit — in this case the eikonal equation — towards a generalised wave equation and the introduction of the concept of state in an entirely new context.

The lecture reveals the naturalness of the transition: in the classical limit, almost everything was already in place — save for the paradigmatic leap that the quantum conception demands. It traces both the technical dimension of the passage and the broader theme of how history is treated in physics (and ultimately in every discipline) — internal myth versus the history of historians. Everything unfolds with technical richness on one hand and philosophical, even paradoxical, depth on the other.