Category: WAVE–PARTICLE DUALITY

If all matter has wave-like properties, why is it that we don’t observe quantum effects in our daily lives? Consider, for example, the de Broglie wavelength of a 0.15-kg baseball batted at 30 m/s: At that wavelength, a baseball would need to interact with objects smaller than subatomic particles to show quantum effects. In summary,…

Electrons are still very small particles, so the question arises as to whether quantum weirdness extends to larger objects. The experimental answer is yes! In 1988, Austrian physicist Anton Zeilinger performed the basic interference experiment with neutrons.29 In 1991, Carnal and Mlynek did the same with helium atoms.30 In 1999, Markus Arndt, Anton Zeilinger, and co-workers31 at the…

Systems to observe single-electron interference have been built by other groups, and a committed experimenter‡ who would like to build such a device should study the excellent papers written by these research groups. This will help you to gain an understanding of how they overcame some of the difficult technical challenges involved. Even with today’s technology,…

De Broglie’s critics argued that the results from electron-diffraction experiments may indicate an undulating interaction between electrons, so these experiments didn’t decisively prove that electrons are waves when studied by diffraction. Definitive proof would still have to wait until technology advanced to make it possible to conduct the double-slit experiment with individual electrons. In one of his…

Experimental confirmation of de Broglie’s formula came in 1927, when G. P. Thomson at the University of Aberdeen and C. J. Davisson with L. H. Germer at Bell Labs observed diffraction—a typical wave-like behavior—from an electron beam. Unlike photons, electrons have a rest mass, and are thus perceived as “solid” particles. Electrons are negatively charged…

Even in the light of the Compton Effect, critics of the early single-photon interference experiments dismissed the importance of the observation by noting that a photon doesn’t have mass. Through some fancy hand-waving, they argued that the low-light interference could be caused through splitting and recombining the light quanta’s wavefront. Decisive proof would come when…

So, yet again, what is the answer? Is light a wave, or is light a stream of particles? Well, actually it’s neither (or both). Light apparently is something different altogether, but it behaves as a wave when the experiment is designed to reveal its wave-like properties, while it behaves as a particle when the experiment is designed to show…

A regular TV camera wouldn’t be able to detect anything at the low-photon flux we need to ensure only one photon passes the slits at a time. An “image-intensifier tube”—like those used by soldiers to see at night—is needed to make the image visible to a conventional camera element (e.g., a CCD camera). In our…

Taylor exposed photographic plates for up to 3 months to obtain interference patterns using his very weak light source. Today, we can conduct the same experiment within a few minutes, using the setup shown in the block diagram of Figure 90. The basic idea remains the same—to illuminate the double slit with a very weak beam.…

So light is a particle, right? But wait! What about diffraction and interference? Didn’t Foucault show that the speed of light in air and water needed to explain diffraction disagree with experimental data if we assume that light is a stream of particles (chapter 1, Figure 7)? And isn’t interference supposed to be the obvious signature…