What did Planck do?
Planck studied a black body and saw.
If Michelson/ Morley quantum of light, which moves
with constant speed c=1, fells into black body and
doesnt come back when the radiations/ thermodynamics
death of Universe must come.
Therefore, in order to save the Universe from death,
Planck decided that the Michelson/ Morley quantum
of light must radiate from the black body by quantum of
light. This quantum of light is an energy quanta.
Why?
Because the quantum of light come from black body.
Max Laue called it as The Kirchhoff 's vacuum.
On my opinion the thermal equilibrium of black body,
The Kirchhoff 's vacuum is a real model of Vacuum: T=0K.
And Vacuum itself, as QT says, is the Homogeneous Space
of the lowest ( the background ) level of Energy.
Therefore, quantum of light must be an energy quanta.
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Our education.
I n the schools books is written that black coal or soot
is good example of a black body. But astrophysicists
use the laws of black body to understand the Universe.
And the Universe doesnt covered with black coal or soot.
Our Universe as whole is Vacuum.
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P.S.
In physics, a black body is an idealized object that absorbs all
electromagnetic radiation that falls on it. No electromagnetic
radiation passes through it and none is reflected. Because no light
(visible electromagnetic radiation) is reflected or transmitted,
the object appears black when it is cold. However, a black body
emits a temperature-dependent spectrum of light. This thermal radiation
from a black body is termed black-body radiation
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In astronomy, objects such as stars are frequently regarded as
Black bodies, though this is often a poor approximation.
An almost perfect black-body spectrum is exhibited by the
cosmic microwave background radiation. Hawking radiation
is the hypothetical black-body radiation emitted by black holes.
http://en.wikipedia.org/wiki/Black_body
http://en.wikipedia.org/wiki/Thermal_radiation
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