WE LIVE in a world of color mostly invisible to us.
We now know that light is a wave. To be more specific, light is an electromagnetic wave, that is, it is a disturbance in the electromagnetic field analogous to the way waves in the beach are disturbances in water.
Like all waves, light can also have different wavelengths. The wave can be long, it can be short, or it can be anywhere in between.
Recall the colors of the rainbow. Of them, red has the longest wavelength. Violet, at the opposite end, has the shortest wavelength. The other colors that we see have wavelengths between red and violet. Color, therefore, is just a way for your brain to know the wavelength of the light your eyes are detecting.
Our brains can also perceive combinations of wavelengths. When your eyes detect a combination of long (red) and intermediate (green) wavelength light, your brain goes, “Oh that’s yellow.” When it’s a combination of intermediate (green) and short (blue or violet) wavelength light, your brain says, “Ah that’s blue-green or cyan.”
When your eyes detect long (red) and short (blue) wavelength light, but not intermediate ones, it says, “Now that’s pink!” Pink is not on the spectrum from red to violet. It’s not one of the colors of the rainbow. It’s just a way for your brain to say, “The eyes are not detecting any green light.”
When your eyes detect all the colors of the rainbow, your brain perceives the combination as white light. When your eyes are not detecting any of those colors, your brain perceives black or, in some contexts, darkness.
But darkness is not the absence of light. That’s because there are so many different kinds of light our eyes can never detect. We can be in what we feel as total darkness and still be drowned in a flood of invisible light.
Remember when I said that red is just light with long wavelength? Well, you can stretch that wavelength a bit longer to get infrared. We humans and many other animals glow in infrared! The hotter we get (such as when we have a fever), the brighter we glow in this color. But this color, this redder than red, is invisible to us. When we enter a dark room, we shine this light into the room without our knowing.
There are animals, such as some species of snakes, which can see this light. That means they can see us in the darkness.
But you can stretch the wavelength even longer to get microwaves, the waves we use to cook our food in microwave ovens.
Microwaves are also the kind of light in which the entire universe glows. The afterglow of the Big Bang is in microwaves. If your eyes could detect microwaves, you’d see this afterglow permeating the entire sky at night. If you could see microwaves, the night sky would not be total darkness punctured here and there by the light of stars. Instead, it will be a sea of this dim afterglow of the universe’s violent birth.
Longer still than microwaves are waves of radio, the very same kind of invisible light we use in the communication technology with the same name. It’s also the same kind of waves we use to transmit TV. Right now, as you reading this, you are basking in the glow of radio waves carrying the voices and images of thousands of TV and radio stations. But you see and hear none of them, unless you turn on a TV or radio.
Radio waves have the longest wavelength and can stretch the entire length of the known universe.
Now let’s go the other way. If you squish violet light a little bit, it suddenly becomes the invisible ultraviolet light that we have to protect our skins from. Some insects such as bees can see in UV.
Shorter still than UV are X-rays. Because of their short wavelength, X-rays can easily pierce through our flesh, allowing doctors to use them to see underneath our skins.
Squish X-rays even further and you get gamma rays, which can have wavelengths so short they are less than the size of an atom. If your eyes could see gamma rays, the night sky will be lit by the glow of the most violent explosions in the galaxy, from the explosive simultaneous birth of millions of stars to black holes sucking up neighboring stars.
If you stretch all the kinds of light from radio (longest wavelength) to gamma rays (shortest wavelength) along the length of the Philippines from Batanes to Tawi-Tawi, the part that we see (ROYGBIV) will occupy the space the size of a cell somewhere in Visayas.
How fantastic is it that science can make us “see” what our eyes never can?
Pecier Decierdo is resident physicist and astronomer of The Mind Museum.