How is Nature so Sparkly and Shiny?
Have you ever looked at a shiny fish scale or the metallic flecks of colour in a peacocks majestic tail and wondered how nature could be so reflective?
Researchers from the University of Bristol in England think they have the answer, with what they call a “universal explanation” for all of the shiny colours in the natural world. They have published their findings in the Journal of the Royal Society.
In a previous study, the team found that very shiny silvery fish had scales that are made up of microscopic layers of crystals. Study lead, Dr Nicholas Roberts, explained at the time that it was possible that fish have evolved these layers in order to help conceal them from predators.
“These fish have found a way to maximise their reflectivity over all angles they are viewed from,” he said. “This helps the fish best match the light environment of the open ocean, making them less likely to be seen.”
But in the latest research, the team found that it was these same layers of crystals that reflect light in a bird’s shiny feathers, or in an insect’s wings, or even in a beetle’s metallic-looking shell.
But Dr Tom Jordan, another member of the team, pointed out that an important factor is that the crystals are not a uniform size, but, rather, have a range of different thickness. This means that different amounts of crystals are found in fish scales and butterfly wings, or bird feathers and beetle carapaces.
And the metallic effect is produced by something called the Anderson localisation. In the 1950s, Philip Anderson found that light cannot spread in a straight line in a cloudy substance – or disordered medium – such as a dirty crystal because the layers of crystal diverts the light. If there is too much diverted light (known as defects), the light waves can’t spread inside the cloudy disordered medium at all.
As a result, when light enters the medium, it moves around inside the layers of crystal, with the multiple waves all interfering with one another and is reflected back out. This produces a colourful metallic effect that is able to reflect more light than anything man-made.
The team said that it would be possible for humans to produce hyper-reflective surfaces by copying this effect. For example, reflectors could be manufactured to make LED lights more energy efficient.
“Disorder within both types means that it is the same optical property that causes the coloured and silver surfaces [to shine],” Dr Roberts explained. “This is why we find science exciting; [we can] look at nature to find things we haven’t even thought of.”