2023-04-18 12:00:06
For more than two hundred years, thanks to Young’s famous physics experiment, we have known that, if the light projected on a screen passes through two slits drilled in an obstacle, we observe bands without light and bands that are very bright. Whereas, if there was only one slit, we would have an almost uniform illumination of the surface.
Through this experiment, Thomas Young, in 1801, highlighted the wave nature of light, which behaves through these slits like water through an obstacle: behind each of the two holes, waves propagate and interfere with each other. , forming an alternation of deep hollows (analogous to the absence of light) or on the contrary high bumps (analogous to a strong luminosity).
Later, others will prove that this wave nature also inhabits each particle – electron, atom, molecule… – therefore capable of passing through two holes at the same time.
Twice through the same open door
English physicists have just shown, on April 3, in Nature Physics, that another strange thing can happen. Light is able to pass through two time slots at once. That is to say, it passes through a shutter which opens twice in succession, as if, by taking two photos very quickly, the second was influenced by the first and vice versa… If the light were a person, it would pass through the same open door twice.
As “shutters”, the researchers actually used a mirror reflecting infrared light, invisible to the naked eye. The mirror is masked, then unmasked, then masked again and re-masked. All this in record time of less than a picosecond, or one billionth of a millisecond.
The result on the screen is not the superposition of two independent reflections of light. It is indeed the interference between two waves generated by a single signal reflected at two different times by the mirror that appears.
More specifically, physicists have observed, by analyzing the colors that make up the light obtained, the appearance of a real rainbow (but invisible to the naked eye), equivalent to the succession of hollows and bumps of Young’s experience. If there was only a mirror, this firework would not exist.
No temporal paradox in this story, but always the wave side in the light. “In fact, the wave lasts long enough to be reflected twice”says Romain Tirole, doctoral student of the team at Imperial College London.
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