Scientists at MIT discovered it. It is a new phenomenon in the most fundamental of physical processes. Light evaporates water without heat. This ‘photomolecular effect’ could be important for understanding climate change. Also to improve some industrial processes, they say.
Light does this by hitting the surface of the water where air and water meet. It can break up water molecules and make them float in the air. This causes evaporation in the absence of any heat source.
Implications
This surprising new discovery could have a wide range of important implications. It would explain mysterious measurements made over the years about how sunlight affects clouds. And lead to new ways of designing industrial processes. For example, desalination with solar energy or drying of materials.
The effect must occur widely in nature. Everywhere, from clouds to fogs and ocean surfaces, soils and plants. MIT reports this in a statement.
It occurs on any water surface exposed to light. Either a flat surface like a body of water or a curved surface like a drop of vapor from a cloud. The team worked to prove its existence with as many different lines of evidence as possible. There was one key indicator. When water began to evaporate from a test container under visible light, the air temperature measured above the water surface cooled and then stabilized. It means that thermal energy was not the driving force behind the effect.
Color effect
The evaporation effect varied depending on the angle of the light, the exact color of the light, and its polarization. The effect is strongest when light hits the water surface at a 45-degree angle. It peaks with the green light. Interestingly, it is the color in which the water is most transparent and therefore interacts the least.
Light evaporates water without heat. But they still cannot explain the color dependence. This will require further studies. They have called it the photomolecular effect, by analogy with the photoelectric effect discovered by Heinrich Hertz in 1887 and finally explained by Albert Einstein in 1905. It was one of the first demonstrations that light also has particle characteristics. It had important implications in physics and led to a wide variety of applications, including LEDs.
