The prediction of the cosmic microwave background was predicted by Ralph Alpher in 1948 (Griswold, 2016). Alpher was a doctoral student of George A. Gamow (Griswold, 2016). Alpher was the first researcher to develop ideas based on radiation (Griswold, 2016). Evidence of the existence of the CMB was first discovered in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories (Griswold, 2016). The radiation was occurring as a wave of noise, and luckily researchers at Princeton University lead by Robert Dicke and Dave Wilkinson were doing research into the CMB and understood what the Bell Telephone Laboratories had discovered (Griswold, 2016). They realized that the cosmic microwave background had been found from the first set of researchers at the Bell Telephone Laboratories and released a combined study detailing the discovery (Griswold, 2016). The name of the theoretical curve that describes its intensity distribution vs. frequency/wave length is a black body (Wright, 2009). The blackbody spectrum is produced by an isothermal, opaque and non-reflecting object (Wright, 2009). The blackbody spectrum occurs by radiation that enters the cavity through the hole and it bounces off multiple walls before it returns to the outside, so even if the walls are only a little dark, the hole will look completely black (Wright, 2009). The thought of the CMB existed early on, but it took decades to prove it.
The CMB is invisible, but can be found everywhere throughout the universe (Griswold, 2016). It is very cold and only 2.725 degrees Celsius (Griswold, 2016). The CMB is often thought as a part of the left-over heat from the Big Bang (Griswold, 2016). The CMB occurred 13.7 billion years ago, happening only a few hundred thousand years after the Big Bang, before even stars or galaxies began to exist (Griswold, 2016). Studying the CMB allows researchers to study the conditions of the universe on a large scale, by understanding the properties of radiation (Griswold, 2016). It is implied that the universe at one point was smaller and hotter than it is now (Griswold, 2016). Observations show that the universe is expanding. The universe was very hot through its early history. (Griswold, 2016). When the universe was one hundredth of its present size for example, the cosmic microwave background was a hundred times hotter than it is now (Griswold, 2016). Over time the universe became cooler and protons and electrons were able to combine to form neutral hydrogen, occurring 400 000 years after the Big Bang, and the universe was only one elven hundredth of its present size (Griswold, 2016). The CMB provides evidence that the universe expands in relation to the Big Bang.
One of the three satellite missions that has been taken to measure the detailed properties of the CMB is known as the COBE satellite. COBE was launched on November 18, 1989 and was terminated on December 23, 1993 (“COBE,” 2016). The purpose of this mission was to collect exact measurements of the diffuse radiation over the entire celestial sphere (“COBE,” 2016). COBE was rotated at 1rpm around the axis of symmetry to control the errors in the anisotropy measurements and to allow observations of the light at multiple solar angles (“COBE,” 2016). With the orbit and spin-axis orientation established, the instruments performed a scan of the celestial sphere every six months (“COBE”, 2016). This satellite revolutionized the understanding of the early cosmos, as well as confirming the results of the Big Bang theory and eliminated many theories about the Big Bang (COBE, 2016). The next satellite was known as the Wilkinson Microwave Anisotropy Probe (WMAP). This satellite was launched by NASA Explorer on June 2001 to make measurements of cosmology, studying the entire universe (Griswold, 2017). The WMAP produced the new Standard model of Cosmology (Griswold, 2017). The third satellite is known as Planck, it is dedicated to measurements of the CMB anisotropies (“Planck 2015 results,” 2016). The Planck data is precise than any data from other CMB research (“Planck 2015 results,” 2016). The satellites have revolutionized research about the universe.
The term isotropic means that it is uniform (“Why do we study the CMB?” n.d.). The uniformity of the CMB refers to the evolution of the universe when it was much smaller and denser (“Why do we study the CMB?” n.d.). The most recent satellite launched to observe the CMB Planck, produced a first all-sky image of the CMB, new challenges of the origin and evolution of the cosmos (Tauber, 2013). The standard model of cosmology is described as homogenous and isotropic, and that the cosmic structure is the result of slow growth that occurred after the Big Bang (Tauber, 2013). The new images produced by Planck reflects the presences of differences in the CMB pattern, which might challenge the foundation of cosmology (Tauber, 2013). The most serious difference is a deficit in the signal at the large angular scales on the sky, which amounts to around 10 % weaker than a standard model would be (Tauber, 2013). With the new information from the Planck satellite the CMB does not support the notion of an isotropic universe, the cosmos is not isotropic on scales so large that extend beyond the horizon of the patch of the universe that we can access with observations (Tauber, 2013). The recent research done may not support the precision of the isotropic universe at the largest scales of study.