The CMB was emitted when our universe condensed from a plasma to a gas. This phase change happens at around 3000K (about 5000 degrees Fahrenheit). Since then, our universe has expanded around a thousandfold, which in turn has cooled the CMB by a factor of about a thousand, leading to the current temperature of around 3K.HarryWertM said:In other words, when did the big bang cool down to 3 degrees? Like 13.7 billion years ago, or in recent millenia? If it only cooled that much near current time - which is what I understood - then the CMB must be "coming from" the space right around the Milky way - which is not what I understood.
Or not. If the universe is infinite, no rapid early expansion is necessary.Chalnoth said:The rapid early expansion of our universe has caused the light to take this long for it to reach us.
Infinite or not, rapid expansion is very much required for light that starts out around 48 million light years away to take 13.7 billion light years to get here.bapowell said:Or not. If the universe is infinite, no rapid early expansion is necessary.
Scientists use a variety of methods to determine the age of the CMB (Cosmic Microwave Background). One way is by measuring the radiation from the CMB and determining its temperature. The temperature of the CMB decreases over time, so by calculating its current temperature, we can estimate its age. This method has been used to determine that the CMB is approximately 13.8 billion years old.
The CMB is a remnant of the Big Bang, which is the event that is believed to have created the universe. As the universe expanded and cooled down after the Big Bang, the leftover radiation from this event became the CMB. Therefore, the age of the CMB is closely linked to the age of the universe and the time since the Big Bang.
After the Big Bang, the universe was extremely hot and dense, with temperatures reaching billions of degrees. As the universe expanded, the temperature gradually decreased. At around 400,000 years after the Big Bang, the temperature had cooled enough for atoms to form, which allowed the radiation from the Big Bang to travel freely and become the CMB. Since then, the CMB has continued to cool down due to the expansion of the universe.
There is a wealth of evidence that supports the theory of the Big Bang and the age of the CMB. One key piece of evidence is the redshift of galaxies, which can be observed in the light spectrum and indicates that the universe is expanding. Other evidence includes the abundance of light elements in the universe, the large-scale structure of the universe, and the uniformity of the CMB temperature in all directions.
No, the CMB and the age of the universe are closely related and cannot have different ages. The CMB is the oldest light in the universe, and its age corresponds to the time since the Big Bang. If the CMB had a different age, it would mean that the universe would have had to exist before the Big Bang, which goes against current scientific understanding.