Ever since the modern time, we are always trying to figure out the birth and beginning of universe. We have a great theory which tells us about the beginning of universe – The big bang theory. However this theory was not so perfect. There were still some problems which were unsolved. What a physicist do? He solves such problems.

Finally in 1980, A MIT physicist, Alan Guth proposed an amazing theory which solved these great problems. He proposed that our universe might have gone through the period of cosmic inflation where it expanded very fast, much faster than light, that you can’t even imagine. This theory of cosmic inflation solved three main problems:

Horizon Problem

The flatness problem and

The monopole problem

In this article we are going to discuss the first two problems of universe.

Horizon Problem

Our universe is very vast. We don’t know how much vast it is. But we know how much big our observable universe is. It’s something 90 billion light years in diameter. It’s called observable universe because our telescopes can see only up to that. No! It’s called observable universe because Light, radiation and signals from outside of it cannot reach to us because they would not have much time since the age of our universe is 13.7 billion years.

We can observe the boundary (horizon) of our observable universe. So, what we observed is that the universe is same in opposite direction even at horizon. Even the Microwave Background radiation (radiation from big bang explosion) is same at these two points of horizon in opposite directions. No matter where we look in space, the temperature of the background radiation does not deviates more than a thousandth of a degree.

This is the problem, because the speed of light is the fundamental limitation of speed in the universe. Nothing can exceed it. So radiation can only travel from horizon to center of our observable universe. So how it can be same even at the horizon in opposite direction?

But Guth realized that inflation was the key to explain this problem. He reasoned that our observable universe was probably a tiny part in the original fireball at big bang. Inflation suddenly expanded this tiny part of uniform matter by a factor of, much faster than the speed of light, so that the visible universe today is remarkably uniform. So the reason why the night sky and the microwave radiation is so uniform is that the visible universe was once a tiny but uniform part of the original fireball that suddenly inflated to become the universe.

Flatness Problem

There was another problem with the standard model of big bang. It was problem of flatness of universe.

Flatness of universe, what? The universe is flat? Yes. But first let’s understand the meaning of flat in the concept of universe. There are three possible shapes of universe –

Closed Universe like spherical ball.

Open universe but curved.

Flat universe like a sheet.

The First one – closed universe – suggests the shape of universe to be closed spherical. It means that if you choose one direction in space and start travelling in straight line, you will reach the same position from where you started. Just like Earth is spherical, take one direction and start moving. After the complete journey round the earth you will reach the position from where you started.

The second one – open but curved universe suggests the shape of universe to be curved. It means that if you travel in straight line in one direction, you would not reach the same point but your path would be curved as the space-time or universe is.

The third one – flat universe – suggests the universe is completely flat. If you travel in one direction in straight line, the path would be straight only. Or In other words flat universe is where the Euclid’s geometry is valid.

The value of omega, matter density of universe, determines such shape of universe. (I am not going to explain this omega; you can read about it here if you want). If it is less than 1, the universe is curved. If it is greater than 1, universe is closed and if it is equals to 1, universe is flat.

According to the current data, the universe was found to be close to flat. But for the universe to be flat (omega=1), chances were one in a hundred trillion. This can’t be simply possible. There should be some miracle, which caused it.

To Guth, the answer was obvious. The universe simply inflated by such a remarkable degree that it flattened the universe. Like a person concluding that Earth is flat because he cannot see the horizon, astronomers concluded that Omega is around 1 because inflation flattened the universe.

So, finally we have got a good theory on the beginning of universe. After this, one more theory was published related to inflation, you can say the new version of Guth’s inflation theory which takes us to multiverse, parallel universe and even gives the solution of big question – where did the universe come from or how it was created – The universe from nothing.