Introduction to Cosmic Microwave Background (CMB)
There are many stories regarding how the universe or the world started off. One of the best examples is, according to the Bushongo tribe of central Africa, in the beginning, there was only darkness, water and the great God Bumba. One day Bumba, suffering from a stomach ache, threw out the sun!! The sun-dried up some of the water, leaving land. Similarly, he brought out the moon, planets, etc… This is one of the stories about how the universe was born.
13.8 billion years ago, when the universe formed, many mutations took place as a result of the big bang. The cosmic microwave background which is also abbreviated as CMB by cosmologists was actually found 40,000 years forth the Big Bang. The cosmic microwave background (or CMB) initially understood as just some leftover heat radiation from the Big Bang, or the time when the universe formed. The Cosmic Microwave Background radiation, or CMB radiation for short, is a just faint glow of light (Or radiation) that fills the universe, falling on Earth from every direction with nearly uniform intensity.
Cosmic Background:
As the theory goes, when the universe was formed it underwent a rapid increase in size, inflation and expansion. One of the interesting facts is that the universe is still expanding even today, and the expansion rate appears different depending on where you observe (in other words, it depends on the frame of reference), that is what relativity suggests to us. The cosmic microwave background represents the heat radiation left over from the Big Bang. It is the residual heat of creation i.e., the afterglow of the big bang, streaming through space these last 13.8 billion years like the heat radiation from a sun-warmed rock, reradiated at night.
When the universe was just a few minutes old, the surviving protons and neutrons recombined to form an atomic nucleus, mainly of what would become hydrogen and helium. The hydrogen and the helium that formed at a very early time in the universe are still charged, so fog remains impossible to see through. At this point, the foggy material is not unlike what we find inside a star, but of course, it fills the entire universe.
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After the heavy uncontrollable action of the few minutes of existence, the universe stays much the same for the few hundred thousand years, continuing to expand and cool down, the hot fog becoming steadily thinner, dimmer, and redded as the wavelengths of light are stretched by the expansion of the universe.
After 380,000 years, when the part of the universe that we will eventually observe from the earth has grown to be millions of light-years across the fog finally clears. Due to the electric charges of the electrons and the nuclei cancel each other out, the complete atoms are not charged so that now the photons can travel uninterrupted, which implies that the universe has slightly got transparent.
After this long wait for the fog clearance, what do we get to see? Only fading red wavelengths scattered in all directions, which becomes redder and dimmer as the expansion of space continues to stretch the wavelengths of photons. Finally, light radiation ceases to be visible in all directions. The photons from that last glow have been travelling and stretched into space and even steadily appeared to be redder and these photons are detected now as Cosmic Background radiation and they are still arriving on earth from every direction in the sky.
Cosmic Background Radiation:
Physics is a fascinating subject, and cosmology leaves everyone in awe by its own remarkable information regarding earth and the universe. One of the important things about the universe is the electromagnetic field. It is found in every dimension of the universe, the atoms are held together due to the effect of the electromagnetic field. Our entire living is functioning depending on the electromagnetic magnetic field, not only at the atomic level even living things such as human beings rely on the functioning of the electromagnetic field. As much as we go into the depth of the universe and space we find out so many fascinating things that will make us wonder about every action happening around us. Is not our universe mysterious!!
And in the course of seeking farther out into space, and deeper back in time, cosmologists have discovered some truly amazing things. One of the best discoveries is Cosmic background radiation. During the 1960s, astronomers became aware of microwave background radiation that was detectable in all directions of space and called it the Cosmic Microwave Background (CMB); the existence of this cosmic background radiation has helped to inform our understanding of how the Universe began.
We can't visualize the cosmic background radiation with our naked eye, but it is present everywhere in the universe. It is invisible to humans because of its low temperature, cosmic background radiation is so cold that it is just 2.725 degrees above absolute zero i.e., around minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius. This means its radiation is most visible in the microwave part of the electromagnetic spectrum, hence it is also known as the Cosmic microwave background radiation.
Cosmic Microwave Background Radiation:
So, what is cosmic microwave background radiation? What do we mean by cosmic microwave background radiation!
Very hot celestial objects ( objects present in space), such as stars are capable of generating visible light, which may travel a very long way before it strikes something. When we look at the stars at night, the light from the stars may have been travelling serenely through space for hundreds of years. The light from the star strikes your eye and jiggling electrons in your retina, turns into electricity, which is sent along the optic nerve to your brain and hence we can see the star!!
For thousands of years, human beings have been aspiring to understand the structure and nature of the Universe and seeking to determine its true extent. But, whereas ancient philosophers have believed that the world consisted of a disk, a ziggurat or a cube surrounded by many celestial oceans or some kind of ether (an organic substance), the turtle holding the universe and many more. Later the advancement of modern astronomy opened their eyes to new frontiers. By the 20th century, scientists and cosmologists have begun to understand just how vast (and maybe even unending) the Universe really is.
The universe is constantly expanding, inflating like a hot air balloon. This implies that the distant stars and galaxies are moving away from the earth. As a result of these transitions, it will stretch its light (light from the celestial bodies) as it travels through space towards us, the further it travels, the more it gets stretched. This stretching will make the objects appear red in colour, the more they travelled away they appear redder, and this effect is known as the redshift.
If the light travelled and red-shifted far enough, the light would no longer be visible and it would become very first infrared and then microwave radiation. This is how an extremely powerful light produced during the big bang and after around 13.8 billion years of travelling the light is detectable now and it is detected as a form of microwave coming from every dimension of space. This light is further named with a very powerful and grand title of Cosmic Microwave Background Radiation and it is nothing less than the afterglow of the big bang itself.
Did You Know:
The universe has no definite centre or edge, and every part of the cosmos is expanding regularly. That implies if we run the clock backwards, we can figure out exactly when everything was packed together 13.8 billion years ago (though it is impossible but according to cosmos theory it is a possibility). Because every place we can map in the universe on this date, it has occupied the same place 13.8 billion years ago. There wasn't a location for the Big Bang. Instead, it happened everywhere simultaneously in an enormous way.
Big Bang broadly refers to the theories of cosmic expansion and the hot early universe. However, sometimes even cosmologists will use the term to describe a moment in time when everything was packed into a single point. The problem is that we don’t have either observations or theory that describes that moment when the universe was formed, which is properly (if clumsily) called the initial singularity. The initial singularity is the starting point for the universe we observe (or assumed), but there might have been something that came before. Unlocking the mysteries of the universe is the most interesting part of cosmology.
FAQs on Cosmic Microwave Background
1. What is the Cosmic Microwave Background (CMB)?
The Cosmic Microwave Background (CMB) is the faint, residual radiation or afterglow from the Big Bang. This electromagnetic radiation fills the entire universe and is one of the most crucial pieces of evidence supporting the Big Bang theory. It originated approximately 380,000 years after the universe's formation when the cosmos cooled enough to become transparent to light for the first time.
2. Why is the Cosmic Microwave Background considered strong evidence for the Big Bang?
The CMB is considered strong evidence because it confirms a key prediction of the Big Bang model. The theory predicted that the early universe was extremely hot and dense, and as it expanded, it would cool, leaving behind a uniform glow of radiation. The CMB matches this prediction perfectly with two key characteristics:
- Its temperature is almost perfectly uniform in all directions.
- It has a near-perfect black-body radiation spectrum, which is exactly what a cooling, expanding universe would produce.
3. Why is the Cosmic Microwave Background so cold today?
Although the CMB was emitted when the universe was very hot (around 3,000 Kelvin), its temperature is now just 2.725 Kelvin above absolute zero. This dramatic cooling is a direct result of the continuous expansion of the universe. Over the last 13.8 billion years, this expansion has stretched the wavelengths of the CMB photons, causing them to lose energy and cool down significantly, shifting them into the microwave part of the spectrum.
4. Who discovered the Cosmic Microwave Background and how?
The Cosmic Microwave Background was discovered accidentally in 1965 by American radio astronomers Arno Penzias and Robert Wilson. While using a large radio antenna, they detected a persistent, low-level noise coming from every direction in the sky. After eliminating all possible sources of interference, they realised they had found the residual heat predicted by the Big Bang theory, a discovery for which they won the Nobel Prize in Physics.
5. Why can't we see what existed before the Cosmic Microwave Background?
We cannot see past the CMB because the early universe was opaque. For the first 380,000 years, the universe was a hot, dense plasma of protons and electrons. Light photons were constantly scattered by these free electrons, preventing them from travelling freely. The CMB represents the exact moment this 'fog' cleared—when the universe cooled enough for protons and electrons to combine into neutral hydrogen atoms (an event called recombination). This made the universe transparent, allowing light to travel unimpeded for the first time. Therefore, looking at the CMB is like looking at the surface of this primordial fog.
6. What is the importance of the tiny temperature fluctuations in the CMB?
The tiny temperature fluctuations, or anisotropies, in the CMB are incredibly important. While the CMB is almost perfectly uniform, these minuscule variations (about one part in 100,000) represent slight differences in density in the early universe. Over billions of years, gravity amplified these slightly denser regions, pulling in more matter. These fluctuations were the primordial seeds from which all large-scale structures, such as galaxies and galaxy clusters, eventually formed.
7. What are the main properties of the Cosmic Microwave Background radiation?
The main properties of the CMB that make it a cornerstone of modern cosmology are:
- Uniformity: It has a consistent temperature of about 2.725 K in every direction we look, indicating that the early universe was remarkably homogeneous.
- Black-body Spectrum: Its radiation follows a perfect black-body curve, which is the expected thermal signature of the universe's hot, early state.
- Anisotropies: It contains very small temperature variations that provide a snapshot of the density fluctuations that seeded the formation of cosmic structures.
