Updated: Mar 6, 2022
Our ideas of transparent, translucent, and opaque aren’t real but relational.
Imagine a star that peaks in microwave. To us, the residents of Earth, it would look like a small red star. Planets around that star would respond to its properties. If it has trees, they would develop the ability to work with microwave radiations. If it has animals, their eyes would adapt to microwave. Their visible spectrum would be totally different from ours.
Their categories of transparent, translucent, opaque would include different things than ours. Microwaves are transparent to us but would be opaque to them. Space would look translucent to opaque because they would see the cosmic microwave background everywhere. Perhaps, everything would be translucent-opaque because the CMB is omnipresent. But they would be able to see far off things on their planet because microwave frequencies bend more.
Imagine how we would look like if we were adapted to a planet full of Xrays. Human bodies would become translucent. Clothes would become transparent. We would have to wear different fabrics. At the same time, we wouldn’t be able to see as far as we do on Earth because Xrays scatter more. It would make a lot of things translucent that are transparent on Earth.
Some people wrongly marvel how the Sun so miraculously peaks in green. They think there must be a God who made it exactly compatible with the human eye. But that’s an egocentric world view. The Sun and Earth are both far older than humans. Plants, animals, and humans have evolved to adapt to them, not the other way round. The species that did not evolve to see what we call “visible lights” either failed to survive or survives in the dark.