What is Cosmic Microwave Background Radiation?
Why is CMB radiation important in studying the early universe right after the Big Bang?
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| Image source- Wikipedia- CMBR |
Radiation left over from the Big Bang. That is what they call it. Cosmic Microwave Background Radiation or CMBR in short. I know what you're thinking. Radiation from the Big Bang? But that was like 14 billion years ago!! Even if there WAS some sort of radiation from the Big Bang, what was the "source" of this cosmic radiation?
And out of all the regions of wavelengths, why is it in the microwave region of the spectrum?
To answer these questions, we're about to take a small tour all the way back to the Big Bang.
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| Image by WikiImages- Pixabay |
The Big Bang hypothesis suggests that our universe was initially extremely hot and dense, from which, it gradually continued to cool down and expand, a process that's now been going on for about 14 billion years.
After about a few hundred thousand years after the Big Bang, the universe was cool enough for the first hydrogen atoms to form from free electrons and protons, which further evolved into heavier elements like carbon and iron, and then to the formation of clumps of gaseous clouds to stars, stars systems, galaxies and so on.
Origin of the CMBR
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| Light getting redirected by ionized plasma- Wikipedia |
During the initial phase of the Big Bang, while the universe was still too hot and dense for elementary particles to even fuse and exist, our universe was glowing in high temperatures (several thousand degrees), with gaseous ions or free electrons, including photons (light) filling the empty space of our emerging universe. But because they were in fast motion that came with high temperatures, they had a thermal spectrum associated with them.
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| Image source- Igor Pefteiv- Unsplash |
At this stage, our universe is filled with the free electrons or ions, which we collectively call 'plasma'. But the photons which were also spread out in the universe, were being scattered off by the pool of free electrons, whenever they hit each other. In a way, the light (which is an electromagnetic radiation) was being redirected or emitted by these subatomic particles up until 370,000 years after the Big Bang. After the universe came down to about 3000K, the free electrons and protons combined to form the first neutral atoms and molecular structures, which we call the epoch of recombination. At this point, the existing light (photons) can no longer be emitted of by ionic particles, and thus light was finally travelling without any collisions or re-emissions.
The CMBR is the light that was being scattered or emitted by those free electrons, just before the formation of the first neutral atoms, which was marked as the final flash of all the ionized plasma pool of the early universe. That final light radiation is what we call the cosmic microwave background and it is distributed almost uniformly across our universe. Technically, we can say that the CMBR is the oldest yet mind-blowing evidence for the early universe, nearly 400,000 years after the Big Bang.
Thermal spectrum of CMBR
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| Image source- Gontran Isnard- Unsplash |
Even though it was released as light radiation, we know it as a type of microwave radiation. This is because as the universe expanded for another billions of years, the light radiation got more red-shifted (shifting to the red region of the visible region of the spectrum), and again shifted to the infrared region of the spectrum, which is the reason why empty space is utter black. And it doesn't end there, the radiation again red-shifts to the microwave region of the spectrum, growing more fainter than ever. If we point any radio telescope to the sky, it'll definitely catch glimpse of a faint microwave radiation, which is the CMBR. And the expansion of the universe didn't just shift its type of radiation but also the temperature of the CMB, to as low as 2.7K. The thermal spectrum of the CMB also matches that of a Blackbody spectrum, that is associated with blackbody radiation in thermodynamics.
For more on CMBR, click the link below :
For more on CMBR, click the link below to watch a detailed video by PBS Space Time :
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