Basically the above. Building a great fire and the thought came up.
In: 2
Think of it this way:
Eyes and the cells that they are composed of are small. There isn’t enough room in them to have an element that could be simulated by long wavelengths, like an antenna. They need to be compromised of a mechanism where excited elections from the incoming light are detected. But humans are frail, if the light is too high a wavelength it’ll tear us apart because the electrons would be completely liberated, destroying our cells too quickly. So there’s a range of light that’s good for sensing using tiny sensors and that doesn’t kill us. We evolved under the sun, so our bodies are strong enough to handle (mostly) the wavelengths that the sun emits.
Fires are hot. They’re hot enough to excite electrons, generating photons. Those photons have enough energy to excite electrons. If fires weren’t hot enough to do that they wouldn’t be fires. If they were hot enough for their light to destroy our bodies then they would be explosions, not fires, since all that energy would heat up everything too fast.
So fires were very likely to be visible to us. As others have pointed out, they emit a lot of invisible infrared light. But since a fire is heating any solid matter in it, that means that it will emit blackbody radiation, which means it will be a spread of different wavelengths, increasing the likelihood that our sensing range will be tickled. Fires that don’t have any hot solid particles in them are more likely to be invisible, but it depends on the particulars.
Latest Answers