#331 What is the opposite of white?

What is the opposite of white? Either black or transparent.

Let’s look at what colors are, what white is, and what black and transparent are.

Colors appear when an object reflects a certain wavelength of light. Light is energy that is flying through space, called electromagnetic radiation. There are many different types of light and they differ by their wavelength. The light with the smallest wavelength is called a Gamma ray. It has a wavelength of about 0.0000000001 mm. Light with the longest wavelength is a radio wave. It has a wavelength of about 1 km. Light that we can see is a very narrow band in the middle and it falls between ultraviolet, infrared and microwaves. We can see radiation with a wavelength between 380 nanometers and 700 nanometers.

The colors we can see happen because certain objects absorb some wavelengths of radiation and reflect others. Objects reflect or absorb many different types of radiation, but we can only detect that narrow band in the middle. Some animals can detect light that we cannot. Mosquitoes, snakes, and some bats can see some infrared light. Hedgehogs, dogs, and cats can see some ultraviolet light. We obviously haven’t evolved to see light either side of the visible spectrum. The reason for this is that seeing infrared would require big sensitive detectors in our eyes because those wavelengths are very low energy. We would need more energy to maintain a system like that and there is not enough benefit for us to need it. Snakes use it to hunt warm blooded animals in complete darkness, so they gain a benefit from it. On the other side, ultraviolet rays have a lot more energy than the visible spectrum and they would be very damaging to our eyes. Animals that can see UV light gain a benefit from it that we wouldn’t and they don’t live as long as us so the damage to their eyes isn’t a problem.

When the electromagnetic wave hits the object, the energy of the light makes the molecules in the object vibrate. Some of the energy will stay in the object (absorbed) and some of the energy will be sent back the way it came (reflected). A rose is red, for example, because it absorbs every wavelength of light except for about 700 nm, which is reflected. The reflected wavelengths hit the photoreceptors in our eyes. The photoreceptors send a different signal to the brain, depending on the number of photons that they absorb. The shorter the wavelength, the more photons they will absorb. This signal goes to the brain where our brains tell us that the rose is red.

So, what is white? There are two answers to this question because real white and the white that we see are different. In physics, something that is pure white equally reflects every color of the light spectrum and doesn’t absorb anything. All of the wavelengths are reflected back equally. The white that we see isn’t always pure white. Our brain plays a trick on us and uses its white balance on colors. In the morning, Light coming from the sun has more of a blue hue in the morning and more of an orange hue in the evening. If you wear a white T-shirt, it will be a pale blue in the morning and a pale orange in the evening. However, our brains white balance and we see the same white throughout the day. If you take photos of the same T-shirt at different times of the day, you will be able to see the different shades, but our brain alters it for us.

So, if white is when every wavelength of light is equally reflected, what is the opposite of white? The automatic answer is black. Black occurs when every wavelength of light is absorbed. Because light is energy, when an object is black and absorbs all of the light, it gets hot. It is very difficult to get “true black” here on Earth because even black objects will reflect some light. There are a couple of materials that can absorb 97.5% of light, but even that is not complete black.

However, if the opposite of white is something that doesn’t reflect all wavelengths of visible light equally, then transparent objects must also be the opposite of white. Materials like clear glass and clean water don’t reflect any light. When light hits the glass, the molecules in the glass vibrate with the extra energy, but they pass the energy through the glass and it emerges from the other side unchanged. This makes the object transparent. However, just as with black, it is very difficult to make something that is completely transparent.

So, what is the opposite of white? White appears when all of the light is reflected equally, so the opposite could either be black, where the light is all absorbed, or transparent, where the light is neither reflected or absorbed. And this is what I learned today.

Sources

https://astronomy.swin.edu.au/cosmos/e/electromagnetic+spectrum#:~:text=The%20electromagnetic%20spectrum%20(EMS)%20is,3%20%C3%97103%20Hz.

https://science.nasa.gov/ems/09_visiblelight

https://socratic.org/questions/when-a-red-filtered-light-is-shown-on-a-red-flower-why-does-the-leaves-look-blac

https://education.nationalgeographic.org/resource/infrared-vision

https://www.pa.uky.edu/~sciworks/light/preview/color4aa.htm