by Sunshine Chen ’23
Have you ever turned your TV or radio to an undefined channel and only heard white noise? 1% of what you are listening to is the noise of the universe from 13.7 billion years ago. You are witnessing the history of the universe and evidence for the Big Bang theory—cosmic background radiation (CBR). If you look out into space, you might expect nothing. In reality, instead of nothing, you would find static. The static that exists in every single point in the universe is cosmic background radiation.
On October 8th, the 2019 Nobel prize for physics was awarded to James Peebles, who successfully predicted cosmic background radiation in the 1960s and used the radiation to calculate the structure and composition of the universe.
Why is space orange and what is CBR?
In the very beginning, about 380,000 years after the Big Bang, the universe was the color of beige. It was a mushy soup of extremely hot and dense particles. Everything was squished so tightly together with so much energy that even atoms were unable to form. Like every object in the universe, the “cosmic latte” also released thermal radiation. The photons that carried small packets of thermal radiation bounced around like ping-pong balls between the mush of particles. While all of this was happening, space was expanding. The process of inflation thinned and cooled the soup of plasma.
After the universe cooled down enough, atoms finally formed. The thermal radiation that was created at the very beginning could now move without colliding into other particles and being absorbed. As the universe expanded, the thermal radiation redshifted* from the orange to red to black and eventually to the cosmic background radiation.
Red-shifting is much like the Doppler effect but for electromagnetic radiation. You experience the Doppler effect when an ambulance drives towards and then past you. At the very beginning, the sound from the car is very high-pitched but as it speeds away from you, the sound waves are stretched and you hear a low-pitched sound. This also happens on the electromagnetic spectrum with light. When an object in the sky is moving away from you, it redshifts (the waves are stretched out). When an object is moving towards you, it blue-shifts (the waves are more compressed). Hubble used redshift to prove the expansion of the universe. If space is always expanding, then everything is moving away and red-shifting.
Why did scientists kill pigeons and how was CBR discovered?
Surprisingly, the discovery of CBR was an accident. In the 1960s, a group of scientists led by Robert Dicke at Princeton university predicted the existence of cosmic background radiation. At that time, James Peebles was also working on Dicke’s team. In 1965, Arno Penzias and Robert Wilson, who later received the 1978 Nobel Physics prize, was working in Bell Telephone Laboratories. The scientists were trying to use the giant radio in the laboratory to capture sound from outer space. However, they found that no matter where they pointed the telescope, there were always static background noises coming from space. The group tried to eliminate the background noise by cleaning the radio disk and killing pigeons to stop them from excreting on the disk, but nothing worked and the static remained. At a loss, they conveyed their frustration to a local scientist who then reached out to Dicke at Princeton University. Dicke and his team eventually confirmed that the static in the background was cosmic background radiation.
What is the significance of CBR?
The discovery of the CBR was the most direct evidence of the Big Bang theory. The CBR’s thermal radiation graph exactly matched the predicted wavelength and radiation that scientists calculated using Wien’s displacement law. The CBR’s temperature of 2.725 Kelvin also matched redshift predictions.
By studying CBR—which is the leftover heat from the Big Bang—we can also learn a lot more about how the universe was created. James Peeble used tiny fluctuations/variations in the CBR to show how matter clumped together in specific parts of the universe. CBR helped scientists model the shape, structure, age, temperature, and density of the universe.
Keyton, David. “Three Scientists Share 2019 Nobel Prize in Physics.” Time, Time, 8 Oct. 2019, https://time.com/5694931/2019-nobel-prize-physics-universe-cosmos/.
Howell, Elizabeth. “Cosmic Microwave Background: Remnant of the Big Bang.” Space.com, Space, 24 Aug. 2018, https://www.space.com/33892-cosmic-microwave-background.html.
“WMAP Big Bang CMB Test.” NASA, NASA, https://map.gsfc.nasa.gov/universe/bb_tests_cmb.html.
“What Is the Cosmic Microwave Background Radiation?” Scientific American, 1 Nov. 2004, https://www.scientificamerican.com/article/what-is-the-cosmic-microw/.
“Cosmic Microwave Background: COSMOS.” Centre for Astrophysics and Supercomputing, http://astronomy.swin.edu.au/cosmos/C/Cosmic Microwave Background.
Geach, James, and Royal Society University Research Fellow. “Nobel Prize in Physics: James Peebles, Master of the Universe, Shares Award.” The Conversation, 10 Oct. 2019, http://theconversation.com/nobel-prize-in-physics-james-peebles-master-of-the-universe-shares-award-124916.