Cosmic Microwave Background Radiation: Proof For The Big Bang

1. Cosmic Microwave Background Radiation: Proof For The Big Bang Rachel Hanson Physics 211 Honors Option Penn State Brandywine

2. Abstract • The discovery of Cosmic Microwave Background Radiation (CMB) provided the necessary evidence for the scientific community to come to the consensus that the Big Bang model of the universe is the most accurate theory. I wanted to research this particular topic because it fascinates me that radiation that is billions of years old can still be measured and observed today. My goal in this research was to better understand what the CMB is, where it came from, and what its significance is.

3. Prediction & Discovery • Long before Cosmic Background Radiation was discovered, it was predicted. In 1948, George Gamow, a supporter of the Big Bang model of the universe, predicted that there should be some sort of radiation left over from the Big Bang. • It was also predicted that the remnant radiation would have a spectrum of a blackbody. This was proven later with COBE. • Gamow’s prediction was proven right when, in 1965, Arno Penzias and Robert Wilson accidentally discovered CMB when looking for signals from early communication satellites.

4. Cosmic Microwave Background (CMB) • CMB is radiation that was created at the time of the Big Bang and permeates all of space. • This radiation peaks in the microwave section of the spectrum. • Its current measured temperature is 2.725 +/- 0.002 degrees K (measured from absolute zero). • The CMB is nearly perfectlyisotropic (having the same intensity everywhere) although large scale anisotropies have been measured. • The CMB spectrum is the most precisely measured blackbody spectrum found in nature. Electromagnetic Spectrum

5. Blackbody Radiation • A blackbody is something that absorbs all radiation that it comes in contact with, so it reflects no light. Thus, it appears black when cold. • There is a specific spectrum (blackbody curve) that is characteristic of a blackbody This curve depends only on temperature. • Some examples of approximate blackbodies are an electric stove burner, the Earth, and the Sun. Examples of blackbody radiation curves. The peak of the curve indicates what type of radiation is being measured.

6. COBE & WAMP • COBE, short for Cosmic Background Explorer, was a satellite sent in to orbit by NASA from 1989 to 1996 to investigate the Cosmic Microwave Background. • Using its Differential Microwave Radiometer, COBE was able to measure large scale density fluctuations, or anisotropies, in the CMB. These fluctuations proved to be crucial to the Big Bang theory. • WAMP was a second mission launched by NASA in June 2001 to take more precise measurements of the anisotropies in the CMB. Cosmic Background Explorer (COBE)

7. The Big Bang & Recombination • CMB is radiation that was created during the initial explosion of the Big Bang. This radiation, however, did not begin filling the universe until approximately 300,000 years after the Big Bang. Because it was so hot before this time, the universe was made up of a plasma of electrons, protons, helium nuclei, and photons. At this time, the photons were easily scattered (absorbed and re-emitted) by the electrons and never got far. Once the universe expanded enough and cooled to around 3000 K, the electrons and protons were able to form hydrogen atoms. This process is known as recombination. Electron absorption and emission

8. Opaque vs. Transparent • Before recombination, photons could not get far, so the universe was opaque. After recombination occurred, photons were no longer being scattered by electrons because the electrons were now trapped in hydrogen atoms. The photons were finally able to travel off in every direction. This marks the time when the universe became transparent and CMB was born. Hydrogen atom

9. Post-Transparency & Expansion • Since the point of transparency, the original electromagnetic radiation (made up of photons) has been traveling in every direction. Because the universe is expanding and cooling, the original gamma radiation has red-shifted to longer wavelengths, and is now in the microwave region of the Electromagnetic Spectrum. • As the universe continues to expand, the CMB wavelength will continue to increase, eventually becomig radio radiation .

10. Anisotropies & Inflation • The CMB was originally thought to be completely isotropic. However, for such things as galaxies and galaxy clusters to form, there had to have been some density variation in the CMB initially. These crucial density variations were discovered using COBE. • Scientists believe that these tiny density fluctuations in the CMB were magnified by inflation, a period of rapid expansion just after the Big Bang. The differences in density were then amplified by gravity, which tends to pull matter toward denser regions. • Because of this amplification, it was possible for galaxies and galaxy clusters to form and, therefore, for us to exist. COBE Sky Map image of temperature anisotropies

11. Conclusions • CMB carries information about the nature of the universe at the time of recombination. • The density and temperature fluctuations in the CMB are very small irregularities which have grown to become the galaxies and clusters of galaxies we see today. • CMB provides very convincing evidence for the Big Bang model of the universe. • Without CMB, we would not exist.

12. References • Arny, Thomas T. “Cosmology.” Explorations: An Introduction to Astronomy. New York: McGraw-Hill, 2006. 505-528. • Frank, Adam. “How Te Big Bang Forged The First Elements.” Astronomy 35.10 (Oct. 2007): 32-38. ProQuest Multiple Databases. ProQuest. Vairo Lib. 26 Nov. 2007 <http://proquest.umi.com/‌login>. • Hinshaw, Gary. “WMAP Cosmology 101: Cosmic Microwave Background .” Tests of the Big Bang: The CMB. 12 Dec. 2005. NASA. 26 Nov. 2007 <http://map.gsfc.nasa.gov/‌m_uni/‌uni_101bbtest3.html>. • Nave, Carl R. “The 3K Cosmic Background Radiation.” HyperPhysics. 2006. 26 Nov. 2007 <http://hyperphysics.phy-astr.gsu.edu>. • Scott, Douglas, and Martin White. The Cosmic Microwave Background. Feb. 2000. 26 Nov. 2007 <http://www.astro.ubc.ca/‌people/‌scott/‌cmb_intro.html>. • Silk, Joseph. “Cosmic Microwave Background.” On The Shores of The Unknown. Cambridge: Cambridge University Press, 2005. 47-56. • Universe. Ed. Martin Rees. New York: DK Publishing, Inc., 2005. • Zeilik, Michael, and Stephen A Gregory. “Cosmology: The Big Bang & Beyond. Introductory Astronomy & Astrophysics. 4th ed. N.p.: Thomson Learning, Inc., 1998.