27. Big Bang

Rave went back to the earth to be sage for his life as a sage in the Himalayas.

Elena and Jane went to him to gain the knowledge of being rulers of the heavens.

"So we will begin our lessons from today about the universe, it will help you understand yourself, and what help you should do and what not!"

Elena and Jane sat in front of him, and he began his lessons-

The Big Bang Theory is the leading explanation of how the universe began. At its simplest, it says the universe as we know it started with an infinitely hot, infinitely dense singularity, then inflated over the next 13.8 billion years to the cosmos that we know today.

Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.

While the majority of the astronomical community accepts the theory, some theorists have alternative explanations besides the Big Bang — such as eternal inflation or an oscillating universe.

The phrase "Big Bang Theory" has been popular among astrophysicists for decades!

Eternal inflation is a hypothetical inflationary universe model, which is itself an outgrowth or extension of the Big Bang theory.

According to eternal inflation, the inflationary phase of the universe's expansion lasts forever throughout most of the universe. Because the regions expand exponentially rapidly, most of the volume of the universe at any given time is inflating. Eternal inflation, therefore, produces a hypothetically infinite multiverse, in which only an insignificant fractal volume ends inflation.

"Eternal inflation and its implications", state that under reasonable assumptions "Although inflation is generically eternal into the future, it is not eternal into the past."

New inflation does not produce a perfectly symmetric universe due to quantum fluctuations during inflation. The fluctuations cause the energy and matter density to be different at different points in space.

Quantum fluctuations in the hypothetical inflation field produce changes in the rate of expansion that is responsible for eternal inflation. Those regions with a higher rate of inflation expand faster and dominate the universe, despite the natural tendency of inflation to end in other regions. This allows inflation to continue forever, to produce future-eternal inflation. As a simplified example, suppose that during inflation, the natural decay rate of the inflaton field is slow compared to the effect of quantum fluctuation. When a mini-universe inflates and "self-reproduces" into, say, twenty causally-disconnected mini-universes of equal size to the original mini-universe, perhaps nine of the new mini-universes will have a larger, rather than smaller, average inflaton field value than the original mini-universe because they inflated from regions of the original mini-universe where quantum fluctuation pushed the inflaton value up more than the slow inflation decay rate brought the inflaton value down. Originally there was one mini-universe with a given inflaton value; now there are nine mini-universes that have a slightly larger inflaton value. (Of course, there are also eleven mini-universes where the inflaton value is slightly lower than it originally was.) Each mini-universe with the larger inflaton field value restarts a similar round of approximate self-reproduction within itself. (The mini-universes with lower inflation values may also reproduce unless their inflation value is small enough that the region drops out of inflation and ceases self-reproduction.) This process continues indefinitely; nine high-inflaton mini-universes might become 81, then 729... Thus, there is eternal inflation.

The Oscillating Universe Theory is a cosmological model that combines both the Big Bang and the Big Crunch as part of a cyclical event. That is, if this theory holds, then the Universe in which we live exists between a Big Bang and a Big Crunch.

In other words, our universe can be the first of a possible series of universes or it can be the nth universe in the series.

As we know, in the Big Bang Theory, the Universe is believed to be expanding from a very hot, very dense, and very small entity. If we extrapolate back to the moment of the Big Bang, we can reach a point of singularity characterized by infinitely high energy and density, as well as zero volume.

This description would only mean one thing – all the laws of physics will be thrown out of the window. This is understandably unacceptable to physicists. To make matters worse, some cosmologists even believe that the Universe will eventually reach a maximum point of expansion and that once this happens, it will then collapse into itself.

This will essentially lead to the same conditions as when we extrapolate back to the moment of the Big Bang. To remedy this dilemma, some scientists are proposing that perhaps the Universe will not reach the point of singularity after all.

Instead, because of repulsive forces brought about by quantum effects of gravity, the Universe will bounce back to an expanding one. An expansion (Big Bang) following a collapse (Big Crunch) such as this is aptly called a Big Bounce. The bounce marks the end of the previous universe and the beginning of the next.

The probability of a Big Bounce, or even a Big Crunch for that matter, is however becoming negligible. Recent researches show that Universe will continue expanding and will most likely end in what is known as a Big Freeze or Heat Death.

There is however one mysterious entity whose deeper understanding may change the possibilities. This entity, known as dark energy, is believed to be responsible for pushing the galaxies farther apart and subsequently the universe's accelerated expansion. Unless its actual properties are very dissimilar from what it is showing now, we may have to shelve the Oscillating Universe Theory.