Why do some objects glow when the temperature is high enough?

Objects move with temperature (at the atomic level) and bounce off each other. These collisions effectively convert thermal energy into radiant energy. In life, we will meet some objects that glow when heated, and we also know clearly that some luminous objects are very hot. But why? Why do some objects glow when the temperature is high enough? To be precise, anything above absolute zero will glow, but in most cases, light is invisible to the naked eye. Objects above absolute zero will glow.

Now back to the atomic world, the same thing will happen. When they interact, some will fly out, and when some of them exist in the form of photons, we can see them glow. This energy can also explain why fire can feel its warmth without contact, because heat "radiates" to our bodies (at least mainly). Then why can't our eyes see all the heat? There is a simple reason. We can't see radio waves or many other things. We can only see a small part of "light" that may exist in the universe. The transition from temperature to particle motion is regular. The (thermal) velocity of a particle is proportional to the square root of its temperature.

In a substance (such as hot iron), the particles in the metal are influenced by potential energy, which causes them to gather together. Subsequently, the particles thermally oscillate due to temperature changes and remain at this energy level, and they must be accelerated because they oscillate. When charged particles accelerate, they radiate outward. The wavelength of this light is related to the magnitude of acceleration, which (in our example) is related to temperature. So the color of hot objects can actually tell us the temperature. Similarly, if we know the temperature, we can also know what color it is (of course, it doesn't reflect sunlight). This equation is called Wayne's law. Therefore, only when the object is hot enough and the wavelength is within our visual range (380 nm -780 nm) can we see it.

However, why can humans only see light with a wavelength between 380 nm and 780 nm? This has something to do with our sun, which has been emitting radiation and bringing energy to the earth. Evolution took advantage of this and gained some favorable factors. Finally, since the problem is extended to this level (evolution), we will consider the sun, which warms the earth through radiation and brings vitality to everything. We can recognize the photon interaction of the sun in some areas of the earth, so our eyes are very sensitive to it. When an object enters a specific temperature (or energy state) and is about the same distance from the sun, our eyes can see them. Hot objects will shine on our naked eyes, isn't this a bit like warning us: don't touch! It's very hot!