Yixuan C. 10 Grade
Cosmic Microwave Background

For those who own an old-fashioned analogue TV, a full screen of “snowflakes” on it is a common scene to see during channel-switching. Audiences normally take it as disturbed signals or transmission while scientists call it white noise. In fact, this noise is a reflection of the fundamental mystery of our universe, Cosmic Microwave Background Radiation (CMBR or simply as CMB). Approximately 1% of the “white noise” indeed is caused by CMB, according to modern scientists.

When we talk about modern physics or cosmology, it is always associated with a great name, Albert Einstein, and his Relativity Theory. Scientists have been looking for the origin of the cosmos since the very beginning of last century. Einstein first gave a bold prediction through his general relativity that the cosmos is in a course of inflation which is against mainstream assumption then that the whole universe was stable. This crazy idea laid the foundation for Big Bang Theory and later discovery of Cosmic Microwave Background (CMB).
In 1948, Einstein’s friend, George Gamow, together with his two students Ralph Alpher and Robert Herman jointly made another aggressive speculation that if the newly created Big Bang Theory was true, that is to say our universe stemmed from a tiny point, then the trace of that original explosion must have been left over in a form of microwave radiation at 5K (Kelvin, SI unit of temperature), which can be seen as the echo or the residual temperature of the Big Bang. Amazingly, this theoretical estimation of 5K is very close to today’s experimental detection at 2.7 K.
However, not until 1964, 15 years later after the first speculation of Cosmic Microwave Background in theory, did anyone have the luck to prove its existence. Two American scientists, Penzias and Wilson achieved the breakthrough at Bell Telephone Laboratories in New Jersey. In a radio communication experiment, they made their first measurement clearly showing the presence of the microwave background with their instrument having an excess 4.2K antenna temperature they could not either erase or account for. They even thought it might be the “pigeon droppings” on the antenna that ruined their experiment. After long-time confusion and consultation with other research teams, they finally awakened to the fact that it was exactly the Cosmic Microwave Background, the residual of Big Bang that many physicists had looked for. The 1978 Nobel Prize in Physics was rewarded to Penzias and Wilson for their discovery of the first light of our universe.

乔治·伽莫夫(George Gamow) 拉尔夫·阿尔弗(Ralph Alpher) 罗伯特·赫尔曼(Robert Herman)
(images from internet, all rights to original owner)
For the first 380,000 years or so after the Big Bang, the entire universe was a hot soup of particles and photons, too dense and opaque for light to travel through. As the cosmos expanded, it cooled and became transparent. During the so-called “Recombination” event at this phase, the joining of electrons to nuclei produced first Hydrogen atoms along with light that now could travel freely through the less soupy universe and even reach us 13.8billion years later. Light from “Recombination” was very energetic at about 3000 Kelvin, but it cooled off with the expanding universe, until it reached the microwave portion of the spectrum. This light corresponds to a temperature today of 2.7 Kelvin: (2.7º C above absolute zero, which now we call as Cosmic Microwave Background).
Cosmic Microwave Background has significant meaning since it’s the critical proof of big bang and the only media that carries the message of the very early universe right after the Big Bang. If we want to understand how our universe was created and what it is composed of, the answer lies in it.
The Discovery of the First Light -Cosmic Microwave Background (CMB)
- 1964, Penzias and Wilson achieved the breakthrough at Bell Telephone Laboratories in New Jersey.
- First measurement showing the presence of the microwave background with their instrument having an excess 4.2K antenna temperature.
- The 4.2K “noise ” eventually was confirmed as CMB, the residual of Big Bang.
- 1978 Nobel Prize in Physics
Through CMB study, scientists find that most of our universe is made up of Dark Energy, the mysterious force that drives the accelerating expansion of the universe. The next largest ingredient is Dark Matter, which only interacts with the rest of the universe through its gravity. On the contrary, Normal Matter, including all the visible stars, planets and galaxies, only makes up less than 5 percent of the total mass of the universe.
To further study the Cosmic Microwave Background, NASA and ESA (European Space Agency) have launched probes into space respectively since 1989, COBE, WMAP and Planck. Among them, Planck Surveyor was the latest one, launched in 2009, and performed a much more detailed measurement. The last released picture from Planck was in 2018 and it is sometimes called the panorama of the universe.
Significant Meaning of CMB
- Critical proof of Big Bang & the only media carrying the message of the early universe after Big Bang.
- Dark Energy: The mysterious force that drives the accelerating expansion of the universe.
- Dark Matter: The next largest ingredient, only interacts with the rest of the universe through gravity.
- Normal Matter: including all the visible stars, planets and galaxies, only makes up less than 5 percent of the total mass of the universe.
Physics advancement always follows the pattern: speculation, accidental discoveries and proof by experiment. This journey was, is and will be tough and even endless while human beings seek the ultimate truth of the universe. Today, China has also built super ground telescope FAST (Five-hundred-meter Aperture Spherical radio Telescope) in Guizhou and will launch space telescope CSST (China Space Station Telescope) in 2026 to join the effort to solve the mystery of the universe. We are so lucky to live in this era as we can reach for stars, and step on an adventure journey to the beginning of our universe.
References: