The Cosmic Microwave Background
How the cosmos began is such an enigmatic idea, that even the most brilliant of minds cannot imagine it in full. You probably heard that the fastest thing in our cosmos is light, and nothing can travel faster. Light travels at around 3x108 m/s or 7.5 times around the equator in one second. However, light is simply not fast enough in the vast expanse of the Universe. For context, it takes light 4.3 years to reach our closest neighboring star system "Alpha Centauri". Even more fascinating, is that when light from Alpha Centauri reaches Earth, it shows Alpha Centauri 4.3 years ago. This phenomenon makes sense because the light that left Alpha Centauri kept traveling and remained unchanged since. This means that the further you delve into the cosmos, the further you look back in time. This gave rise to trace back the origins of our universe
How was the Cosmic Microwave Background Formed:
When the Big Bang occurred 13.8 billion years ago, it shot out beams of plasma, particles (electrons, protons, and neutrons), and photons (a packet of light that behaves both as a particle and a wave). As the temperature of the universe was above C ° C, the electrons were unable to bond with the protons to form elements like Hydrogen as it was too hot. Instead, they were free and interacted with the photons blocking photons and keeping them from traveling large distances. As light is made of photons the universe back then was opaque, like looking through fog. However, after more than 380,000 years the universe started to expand and its temperature slowly dropped to 3000 K. This caused electrons and protons to bond together to form the first atoms like Hydrogen. Due to the absence of free electrons, these photons were no longer kept from traveling into the vast universe. As these loose strings of photons traveled through space, the expansion of the Universe redshifted the photon's wavelengths as well as decreased its temperature to the 2.7 K we have in deep space today. This is what we see when we look into our night skies. The Cosmic glow in the background of our Universe is nothing but the long-lost photons from the era of the Big Bang.
Discovering the Cosmic Microwave Background:
In 1964, American physicist Arno Allan and radio astronomer Robert Woodrow discovered the Cosmic Microwave Background (CMB). While working with the Holmdel Horn Antenna (fig:1.2), they received uniform disturbances from the Sky. It later turned out that these disturbances could be traced back to the CMB. Since then, NASA's COBE mission in 1989 structured the first CMB Map. The most precise map was structured by ESA's Planck Observatory in 2013. It discovered 2 major facts, first, the radiation was only 2.736 Kelvin or 2.736°C above absolute zero. This meant its radiation was prominent in the microwave spectrum and therefore not visible to our naked eyes. Secondly, it determined that these Microwaves were formed 380,000 years after the Big Bang. This meant that the Cosmic Microwave Background is the furthest we ever looked into our visible universe at around 40 billion light years away from the source, reaching as far as 13.7 billion years back in time. (The difference in distance is due to the expansion of the universe.)
Why is the Cosmic Microwave Background important:
The earliest benefit Cosmic Microwave Background provided was evidence to back up the Big Bang Theory. The alternative idea of Steady State theory was majorly adopted due to its alignment with how the universe made matter to stay in an equilibrium density, which allowed galaxies and other bodies to be formed. It also made time infinite, which suggests the universe had no beginning, making questions such as," How did the universe begin?" simple to answer. It existed forever. However, the discovery of the CMB suggested other ideas are more prominent over the Steady State theory and leaning towards the Big Bang Theory, of a point of creation of the cosmos. With this, today the Big Bang Theory is the most widely accepted theory of how our universe began, all thanks to the Cosmic Microwave Background.
With more research and development into the CMB, more precise CMB maps came into existence. As written above, the most precise map was laid down by the ESA's Planck observatory, in 2013. The figure beside shows the thermal imaging of the CMB. The higher the temperature the higher the gradient of red and the cooler the bluer the gradient. This "Fossil Radiation", which remains as a remnant of the early universe, provides details of the universe's unequal temperature distribution and the quite prominent "Cold Spots" in the center. These spots are approximately 140mK cooler than the average radiation temperature. The most significant cold spot is located near the constellation of Eridanus.
Conclusion:
In conclusion the Cosmic Microwave Background (CMB) is the magnificent burst of photons out into the static universe around 380,000 years after the Big Bang. These photons, since then, have traveled over 40 billion light years to reach our humble planet. However, along its journey, the radiation red-shifted, causing it to divert into the microwave spectrum, invisible to our naked eyes. The accidental discovery of the CMB in 1964, through the Holmdel Horn Antenna, marked the start of a new era of discovery in our universe. Since then, multiple observatory satellites such as WMAP from NASA and Planck from ESA have traced down thermal maps of these Cosmic Radiations. As we investigate further, we find new fundamental ideas arise from these simple bursts of photons, these sparks of light that brighten up our night sky as we look into, "The Baby Picture of the Universe" from back home.
Sources:
“Determining the Hubble-Lemaitre Parameter with the Simons Observatory: Kavli Institute for Particle Astrophysics and Cosmology (KIPAC).” Determining the Hubble-Lemaitre Parameter with the Simons Observatory | Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), 14 Mar. 2019, kipac.stanford.edu/highlights/determining-hubble-lemaitre-parameter-simons-observatory.
(Robert Trembley, 16 June 2023, https://www.vaticanobservatory.org/sacred-space-astronomy/historic-holmdel-horn-site-saved/ )
“How far away is the cosmic microwave background”(Nick Smith, May 2nd 2022, https://www.astronomy.com/science/ask-astro-how-far-away-is-the-cosmic-microwave-background/ )
“Cosmic Microwave Background.” Wikipedia, Wikimedia Foundation, 13 Nov. 2023, en.wikipedia.org/wiki/Cosmic_microwave_background.
“CMB Cold Spot.” Wikipedia, Wikimedia Foundation, 24 Nov. 2023, en.wikipedia.org/wiki/CMB_cold_spot#:~:text=The%20radius%20of%20the%20%22cold,direction%20of%20the%20constellation%20Eridanus.
“Planck and the Cosmic Microwave Background”(ESA, https://www.esa.int/Science_Exploration/Space_Science/Planck/Planck_and_the_cosmic_microwave_background#:~:text=The%20cosmic%20microwave%20background%20(or,)%20and%20photons%20(light). )
Howell, Elizabeth, and Daisy Dobrijevic. “What Is the Cosmic Microwave Background?” Space.Com, Space, 28 Jan. 2022, www.space.com/33892-cosmic-microwave-background.html.