The document discusses cosmic microwave background radiation (CMBR), which is the oldest electromagnetic wave in the universe produced after electrons and protons formed stable hydrogen atoms during the epoch of recombination post-Big Bang. It details the accidental discovery of CMBR in 1965 by Arno Penzias and Robert Wilson, along with Ralph Alpher's earlier theoretical predictions, leading to further advancements in mapping CMBR through missions like COBE, WMAP, and Planck. It explains that as the universe expanded, the high-frequency radiation cooled, eventually being detected in the microwave region of the electromagnetic spectrum.

1. Cosmic microwave background radiation
Presenter Name: Jagannatha Gardia College Roll no: BS20-P-066

2. Table of Content
Introduction
Historical Background
Electromagnetic Spectrum
Discovery
Developments on mapping the CMB
Applications
Conclusion
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3. Introduction
When you look at night sky using an optical telescope you’ll
see stars, galaxies using more powerful telescope you can see
more distant stars, nebulae, galaxies but mostly dark void as
if nothing is there.
But when using a radio telescope you’ll observe a certain
kind of noise, glow in that void region which permeates
through out the entire universe this glow is known as CMBR.
It is the oldest EMW in the universe.
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This Pho by Unknown Author is licensed under CC B

4. Historical
Background
How CMBR was created?

5. Recombination
In cosmology, recombination refers to the epoch
during which charged electrons and protons first
became bound to form electrically neutral hydrogen
atoms.
So according to the big bang model, in the beginning
the universe was extremely hot and dense as a result
the electron and proton couldn’t combine and form a
stable atom. The photon couldn’t travel further as it
collides with any electron and proton which scatter it
back hence the universe was opaque.
But as the universe cools down the recombination
between electrons and protons takes place and forms
the first ever stable atoms. Which leads the photon to
travel freely and hence universe became transparent
and CMBR forms.
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Before Recombination
After Recombination
Hydrogen Atom
Electron
Proton
Photon Scattering

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This Pho by Unknown Author is licensed
under CC BY-NC-N
At t = 380,000year the universe cooled to 4000K,cool enough to form atoms.
In the early time the CMBR was very hot in temperature and had high frequency. But as
the universe continued to expand its temperature decreased and wavelength increased.

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Electromagnetic Spectrum
It is the range of frequencies of electromagnetic radiation and their
respective wavelengths and photon energies.

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As the cosmos continued to cool, the photons that had been in the visible part of the spectrum in the
early period lost energy to the expanding universe and eventually slid down the spectrum, morphing
into infrared photons. Further the expansion continued and that infrared photons now lies in the
microwave region of EM spectrum, which is where we derive the name “cosmic microwave
background radiation”, or CMB for short.

9. Discovery of CMBR
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The Accidental Discovery !

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Robert Woodrow Wilson Anro Allan penzias Ralph Asher Alpher
American cosmologist Ralph Apher first predicted the CMB in 1948, when he was doing research
related to Big Bang. But the CMB was first found by accident. In 1965, two researchers with Bell
Telephone Laboratories (Arno Penzias and Robert Wilson) were creating a radio receiver and were
puzzled by the noise it was picking up. They soon realized the noise came uniformly from all over the
sky.
At the same time, a team at Princeton University (led by Robert Dicke) was trying to find the CMB.
Dicke's team got wind of the Bell experiment and realized the CMB had been found.
Both teams quickly published papers in the Astrophysical Journal in 1965, with Penzias and Wilson
talking about what they saw, and Dicke's team explaining what it means in the context of the universe.
(Later, Penzias and Wilson both received the 1978 Nobel Prize in physics).

11. Developments in
mapping the CMBR
Further advancement in science and technology leads to better understanding of CMBR.

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After its discovery there were many attempts on mapping of the CMBR as a outcome only a
portion of CMB was mapped. But as the technologies had advancement further level of mapping
were donned.
There are mainly 3 missions launched to map CMBR:
1) COBE(Cosmic background explorer) which launched in 1989 .
2) WMAP(Wilkinson Microwave Anisotropy Probe) which launched in June 2001.
3) Plank space telescope which was launched in 2009.
1.COBE 2.WMAP 3.PLANK SPACE TELESCOPE

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• Here we can see the different maps observed by different satellites, t
latest and most clear map that we have is taken by plank satellite.
• It clearly shows the temperature variations/fluctuations present in the
CMBR.
• Hence CMBR is anisotropic means it has a kind of patterns of low
density and high-density regions.
WMAP PLANK

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15. Summary
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16. Thank You
Presenter Name
Email Address
Website Address
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