Evaporation by light, time dilation, & adventurous fish | Last Week in Science (28 Apr 2024)


Light can evaporate water

Water changes from liquid to gaseous state, which is the water vapour, in the presence of heat. A group of scientists at MIT have made a startling discovery that even visible light can cause evaporation of water. 

In a study that was conducted last year, evaporation due to light was shown to happen from the surface of hydrogels - gels that were soaked in water. Water molecules are bound to each other in the liquid state. For water to become gaseous the molecules need to come apart. This phenomenon was named - 'photomolecular effect' wherein, photons of light cause molecules of water to separate. 

In a recent study, it has now been shown that for evaporation to happen via light no special surface is needed. Light could evaporate water from all the surfaces - be it a plane surface of a water body like sea or ocean or a curved surface of a water drop as inside a cloud. They also found that the evaporation was affected by the wavelength or the color of the light, the angle of incidence i.e., the angle at which it touches the water surface and polarization of light. The maximum evaporation occurs in the presence of the green light and at an incident angle of 45 degrees. Although, they could explain how the angle of incidence and polarization could provide energy to water molecules to evaporate but could not explain the difference because of the color.

This discovery has opened up applications like desalination of water and industrial drying of materials using light.

Slowing down time?

It is thought that since human body does not have any special organ to perceive time, the brain relies on the sensory information that it receives and experiences. Haven't we all thought that time has slowed down when sad or in pain? It is not just our emotions that affect how we perceive or understand the speed of time but our visual system also has an effect of its own.

In a recent study, scientists wanted to see whether the size, clutter (like filled with a lot objects and details), and memorability (something that is memorable) can affect the understanding of the speed of time. They showed different images - like an empty room or a closet filled with clothes - for one second each to 52 participants and asked them to note the time as 'long' or 'short' depending on what they thought for how long the image was shown. The participants thought that larger and less cluttered images were shown for a longer duration. For example image of an empty room was thought to be shown for a longer duration as compared to a closet full of clothes.

The scientists found that the brain is able to take in the details of a larger and less cluttered image and is able to process it quickly. This fast processing by the brain makes the time slow down for the person. While if an image is smaller or having a lot of objects or details then it is difficult and more time consuming for the brain to process and take in the details. Since the brain is not able to quickly process the information time seems to have passed fast as the details could not be taken in. Imagine you are standing and a car shoots past you at 150 km/h and another one at 20 km/h. You will be able to remember the color and number of the one that was moving slowly. So, the brain makes you think that you may have seen the image for a short duration and so the brain could not take in all the details of a complex scene or image.

The images that were processed quickly were also found to be more memorable i.e., could be remembered in detail by the participants even the next day. We know that images seen for longer are easy to remember. And  it seems now that we remember those images or scenes that were thought to have been seen for a long time.

Reference: Your perception of time is skewed by what you see

Adventurous fish of Africa

There exists a family of fish called cichlid that has 240 different species. The variety in the shape, size, form, habitat, and food sources vary a lot. Some fish eat plants, some eat eggs, insects or other fish. Some fish are as small as a paper clip and some are a meter long. This diversity has made it possible for the fish to inhabit all the possible regions of the 32,000 square km area of Lake Tanganyika in Africa. These different regions of the lake include stony and sandy floors to regions that are covered by plants. One of the fish even lives inside snail shells. The scientists have been intrigued by the evolution of cichlid fish into so many different types of species.

The role of environment has been known to explain the differences seen between species of a same family, but the cichlid fish seem to have evolved into diverse species despite being in the same environment. Behaviour is another factor that is thought to drive evolution but it has not been tested yet which made the scientists at University of Basel to study the behaviour of 57 different species of cichlid fish. 

They created artificial ponds, introduced the fish and observed their behaviour in this new environment. The movement of the fish inside the pond was tracked. Some fish explored the entire pond in a few minutes while others did not move much. 

Fish are known to move and explore a new environment cautiously. And yet some of the cichlid fish appeared to be fearless. The scientists even identified a gene that may be responsible for making these fish fearless. These findings made them conclude that it would have been the 'adventurous and fearless' behaviour of cichlid fish ancestors that would have let them explore the entire Lake Tanganyika.

Reference: A gene mutation turned these fish into intrepid explorers

Editing by Ashish Gourav