How light can vaporize water without the need for heat

🌈 Abstract

The article discusses a new discovery by researchers at MIT that light can cause water to evaporate, in addition to heat. This "photomolecular effect" could have significant implications for understanding cloud formation, climate change, and industrial processes like solar desalination.

🙋 Q&A

[01] The Newfound Phenomenon

1. What is the newfound phenomenon discovered by the researchers?

• The researchers have discovered that light, in addition to heat, can cause water to evaporate. This "photomolecular effect" occurs when light strikes the water's surface, breaking water molecules away and causing them to float into the air.

2. How did the researchers demonstrate the existence of this effect?

• The researchers conducted 14 different types of tests and measurements to establish that water was indeed evaporating due to light alone, and not due to heat. Key indicators included:
  • The air temperature above the water's surface cooled down and leveled off as the water began to evaporate, showing that thermal energy was not the driving force.
  • The evaporation effect varied depending on the angle, color, and polarization of the light, even though water hardly absorbs light at those wavelengths.

3. What physical mechanism do the researchers propose to explain the effect?

• The researchers have proposed that the photons of light can impart a net force on water molecules at the water surface, sufficient to knock them loose from the body of water. However, they cannot yet account for the color dependence of the effect, which requires further study.

4. How does this newfound effect compare to the photoelectric effect discovered earlier?

• The researchers have drawn an analogy between the photomolecular effect and the photoelectric effect discovered by Heinrich Hertz and explained by Albert Einstein. Just as the photoelectric effect liberates electrons from atoms in response to light, the photomolecular effect shows that photons can liberate entire water molecules from a liquid surface.

[02] Implications and Applications

1. How could this discovery help explain a longstanding mystery in climate science?

• Measurements have shown that clouds absorb more sunlight than conventional physics can account for. The additional evaporation caused by the photomolecular effect could help explain this discrepancy, which has been a subject of debate.

2. What are some potential practical applications of this discovery?

• The effect could lead to new ways of designing industrial processes such as solar-powered desalination or drying of materials. The researchers have already been approached by companies interested in harnessing the effect for applications like evaporating syrup and drying paper.

3. What are the next steps for the researchers in further studying and applying this discovery?

• The researchers say the experiments needed to demonstrate and quantify the effect are very time-consuming, as there are many variables to explore, from understanding water itself to extending the effect to other materials, liquids, and solids.