Ultraviolet Catastrophe

We have all possibly heard about quantum physics but do we know when and how Physicists gave birth to it and to one of its most preponderant theory, the quantization of energy. It can be stipulated that quantum physics expanded the limitations of classical physics.

Well, it all started with Blackbody radiation.
A blackbody is an object capable of absorbing and emitting at all wavelengths in the electromagnetic spectrum uniformly. For example, the sun is a blackbody, having the ability to emit electromagnetic radiation at different wavelengths. A hot iron bar glowing is also a blackbody at it emits electromagnetic radiation in the visible light wavelength(the glow we see).




Let us now have a look at the ideal graph for blackbody radiation. (for now, neglect the curve for classical theory)

As it can be perceived from the graph on the right, the distribution of the curve depends on temperature and not on the material. As temperature increases, the peak of the graph shifts to the left and spectral radiance(the intensity of electromagnetic radiation) increases.
For low temperatures, mostly infrared radiation is emitted, but at very low intensity, as it can be seen from the graph.
For high temperatures, the intensity (spectral radiance) of electromagnetic radiation increases and the wavelength of the radiation decreases to that of visible light.
This is why at very high temperatures, metals glow and the intensity of radiation is greater for the yellow-orange color.

Well, this seems a pretty good explanation and is clearly true as it is in accordance with experimental results. But was this the case a century ago????

CRISIS
Back in time, the Physics that we are all familiar with, Classical physics, could not account for the graph distribution of the blackbody radiation, even though the distribution was experimentally right!!!
Let us indulge in a brief explanation:
In the 19th century, in order to explain blackbody radiation, scientists had to calculate what they called the energy density, being the total energy per unit volume. (and energy density is proportional to spectral radiance)
In the equation to calculate the energy density, there was a constant of proportionality,ρ(rho), known as the "density of states", which was relating the energy density to wavelength and temperature.
This density of states was derived from the Rayleigh-Jeans law and the equation is given below:
ρ=(8ㄫkT)/(λ^4)
This all sums up to this analogy:
Intensity∝Energy density∝ density of states∝(1/λ^4)
Meaning that the intensity is inversely proportional to the wavelength right?
And hence as wavelength decreases, the intensity should shift to the left and increase till infinity!!!!(because of the wavelength being at an exponent of 4), and hence, it was clear that the Rayleigh-Jean law was unsuccessful at small wavelength.

Succinctly, if the temperature of a blackbody was to be increased by a huge amount, intensity should increase and the wavelength of the electromagnetic radiation will decrease to that of the Ultraviolet wavelength and so we should be blasted by high-intensity ultraviolet radiation, meaning that when opening an oven which has been heated for long, we should be irradiated by Ultraviolet radiation.
But this is not the case.
This was how classical physics approached the matter and it was deemed totally inappropriate as the theory did not match with experimental data.
This notion of ultraviolet radiation blast was coined the "Ultraviolet Catastrophe."

SOLUTION
In science, if a theory does not match with a certain observation, the theory must be revised or discarded.
In 1900, Max Planck, a German Physicist, to account for the experimental observations, he proposed that electromagnetic radiation cannot just take any energy and that their energy is limited to certain discrete values, which he called the "quantum levels." This was the first concept of quantization of energy and Planck also developed the Plank's constant,h, which is generally accepted as 6.626х10^-34 Js.
It can be seen from the diagram on the left that energy is quantized according to the value of n(the quantum number)
Then after this, he devised a new formula for the quantized energy levels:
E=nhf,
where n can be any non-decimal integer(1,2,3....) and also known as quantum numbers
,h being the Planks constant and f the frequency.

Due to the involvement of integers, it can be clearly viewed that energies will be restricted to certain discrete values. On a macroscopic level, for example, to us, energy appears continuous but on a nanoscopic level, energy is quantized and appears as only as discrete values.
This seems a hard fact, but back in time, this also strained the credulity of scientists but they had to accept it because it solved the Ultraviolet Catastrophe and later on, more theories and principles were built on that.

And finally, Plank's idea of quantization of energy only to solve the UV Catastrophe gave birth to what we know as Quantum Physics.
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