Physical Review A reports a recent "experimental observation of simultaneous wave and particle behavior in a narrowband single-photon wave packet." This is also covered in a more accessible form in Science News. The experiment is a variation on the delayed choice model that submits a photon to being observed (measured) after it has already been through a double beam splitter setup. This essentially is a way of forcing the photon to behave first as a particle (by passing it through a beam splitter) and then after having made that "choice" having it behave like a wave again, as predicted by quantum physics. The recent experiment takes this one step further by first stretching out a single photon so that it takes a small but measurable period of time to pass through the second beam splitter. With the splitter in place, the photon acts like a wave. With it removed while the photon is still passing through it, the photon manifests as a particle. The very same photon during one single act of observation -- in two parts -- is both particle and wave. This does not violate quantum physics but, as a scientist quoted by Science News suggests: "‘Wave’ and ‘particle’ are just words. In quantum physics, those words are imprecise at best."
This beautifully done experiment offers a window into the nature of not only light but the universe. As noted before, at the speed of light, time does not exist. Therefore, every photon is everywhere it will ever be at the same instant. The speed of light measures the degree of departure of our existence as mass affected by gravity from that cosmic external moment in which light exists. When we measure light we seek to capture in time that which exists without time. Wave and particle are the way we perceive its timeless nature as we move at our own pace through time and space.
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