A black body absorbs all electromagnetic radiation and its color is determined by its temperature. Blackbody radiation is important in quantum mechanics and is emitted by black holes. The emission spectrum of black-body radiation led to the discovery of quantized electromagnetic radiation and the development of quantum mechanics.
In physics, a black body is an object that absorbs all electromagnetic radiation, being purely non-reflective and opaque. Consequently, its color is dictated only by its temperature. Different temperatures cause the atoms to bounce at different intensities which correspond to the respective wavelengths of the electromagnetic radiation produced. Black bodies and the issues surrounding their radiation are particularly famous for their role in the formulation of quantum mechanics in the early 20th century.
Blackbody radiation is also sometimes called cavity radiation, because in a laboratory, the closest approximation to a blackbody is a small hole connected to a larger cavity. Because the incoming light has to bounce around the inside of the cavity multiple times to be reflected back out, during which time it is almost certain to be absorbed, the hole in the cavity closely matches the non-reflective criteria for black bodies. According to Gustav Kirchhoff, the physicist who introduced the terms “black body” and “black body radiation” in 1860, the spectrum emanating from the whole will depend only on the temperature of the cavity and not at all on the particular materials to be heated.
As a black body’s temperature increases, it emits electromagnetic radiation at higher intensities and shorter wavelengths. Around 1000 K (Kelvin, equal to Celsius but 0 is absolute zero, –273.15 °C), black body radiation is red, from 2000 K to 4000 K, the radiation is orange, then starts to turn white at temperatures above 4000 K, where all typical substances are in liquid form.
In the real world, the closest approximation to black-body radiation is the cosmic microwave background, the “echo” of the Big Bang. Black holes can be described as black bodies, and it was Stephen Hawking who discovered that they emit their own black-body radiation, which has been named Hawking radiation in his honor.
Attempts to characterize the emission spectrum of black-body radiation is what led scientists such as Planck and Einstein to suggest that electromagnetic radiation is quantized, which ultimately led to the revolution in quantum mechanics.
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