Question

1. What is the cosmic microwave background (CMB)?
2. What significant event after the Big Bang is related to the appearance of the CMB, and when did that event happen?
3. Was the CMB always radiating in the microwave part of the spectrum?
4. What is cosmic inflation, and what are the problems that inflation resolves?
5. What is Olber's paradox, and what is its resolution?

Answer 1

WHAT IS COSMIC MICROWAVE BACKGROUND RADIATION? (CMB)

It all starts from the end of the Big Bang which happened almost 13.8 billion years ago! The heat radiation which was emitted out in the time of Big Bang still prevails in space. They are called as the Cosmic wave Microwave Background (CMB) Radiations and as the name mentions the spectrum of the CMB lies in the microwave region and hence not visible to our naked eyes.The temperature of these radiations are now low as 2.7 Kelvin!!

The CMB was so intense during the time of Big Bang which was almost 275 million degrees and as time passed the intensity of radiation due to the huge spread over space. All these would give a clear picture I hope.

APPEARENCE OF CMB AND THEIR SPECTRUM:

We can measure the CMB far into the future as the "microwave " portion falls into the radio portion of the spectrum as the photon densities drops with advent in time. The radiation will be still there as long as we have more sensitive telescopes to detect it. The CMB was emitted when the whole universe was almost 380,000 years old and it was not microwaves when emitted, it was infrared, with portions of it as hot enough and visible to the human eyes.

Well, there is a much bigger picture and research happening on this. Scientists abserve these CMB and by studying them they were able to study the large scale structure and bodies. They also helped in studying the origin of our galaxy. Talking about the recent articles, CMB is giving idea about the Dark matter and Dark energy which are assumed to be the driving forces pushing the universe forward.

COSMIC INFLATIONS AND THE MODEL THAT SOLVED THE PROBLEM:

The discovery of gravitational waves in the echo of the Big Bang lends support to the inflation model of the cosmologgy

The inflation model was proposed by Alan Guth n 1980 as one way to explain two problems in cosmology - the horizon problem and flatness problem. The horizon problem is that the areas of the universe saperated by vast distances have identical physical properties such as temperature, but, since the exchange of information is limited by the speed of light, this should be impossible, as regions on opposites sides of the universe have not been in causal contact with another during the universe's life time.

The flatness problem is similar isuue lacking to the lack of explanation as to why the universe appears to be nearly flat on a large scale - i.e.e why the density of matter and energy appears to be precisely fine-tuned so that the universe neither rapidly collapse back on itself shortly after the big bang expands so quickly that the galaxies are unable to form.

In the inflationary model, the extremely rapid expansions of the very early universe flattens out any large scale inhomogeneties in temperature and density, quickly creating a large cosmos out of a much smaller one that was previously casually connected.

Guth's model also explains the origins of the large scale structure of the universe - before inflation there are quantum fluctuations in the very early universe, which then get magnified to macroscopic size and became the sites where galaxies, clusters of galaxies form.

No physical mechanism capable driving inflation is currently known.

OLBER'S PARADOX:

Olber's Paradaox states that in an infinite universe every line of straight will end on a star. Such brightness is independent of distance (moving a star further away makes it smaller and reduces its flux but not its surface brightness).

Since the speed of light is finite, we are only able to see as far as light had time to travel (the age of universe). Since the universe is approximately 13.8 billion years old, the radius of the visible universe is 13.8 billion light years which is much smaller than the line of sight. Most line of sights will leave the visible universe without reaching any stars.

The size of our visible universe, which is related to it's age, is too small to have a star at each point in the night sky. Any starlight outside the universe has not had time to reach us leaving the portions of the sky dark. These dark portions indicate that the light is emitted from stars at distances greater than the radius of our visible universe. This means that universe has a finite age providing further evidence for the Big Bang!