Theoretical Astrophysics-An Introduction

Chapter 1

There have been multiple ways we have proved the possibility of the Big Bang and how the universe began, this started in the 1920s by Georges Lemaître, a Belgian Cosmologist and Catholic Priest, who wrote a paper on this theory which was published in 1931, the only problem with this was there was no evidence to support it.

However in the 1960s, a faint signal detected across the universe called Cosmic Microwave Background Radiation was discovered by accident, and if this is to exist, it is very strong evidence for the existence of the Big Bang too because this radiation is so old it has the information to what happened during the Big Bang, this links to the flatness problem and the horizon problem.

The horizon problem states that two identical points in outer space look exactly alike, but are millions of light years away from each other, stating the fact that there are different regions in space that have different thermal conditions, meaning it isn't the same everywhere. This is a big problem for the way that we interpret the Big Bang on a model because these photons have not had time to reach the entire universe as a whole from the opposite direction of where they came from.

This shows that there are patches of the universe that are denser than others; these patches will only keep getting denser and denser until they eventually collapse in on themselves, creating galaxies and stars and black holes. This is evidence against the Big Bang Theory and is currently being researched with the Hubble Volume Simulation, which created the first-ever image of the cosmic web. This is further discussed in a documentary called Life Of A Universe by Professor Brian Cox and Dr. Neil Degrasse Tyson who study the theories of our universe in depth.

The Flatness Problem shows that the maps we have of our universe look flat, which means it suggests the reason behind this is because it is only a small fraction of what we can see.

For example, if you look down at the ground now, it curved or is it flat?

It looks flat because it is only a small piece of the Earth, but when we look at the Earth as a whole, we see that it is round. If we have maps of our universe that show it is billions of light-years in diameter and it looks flat, then how big is the universe altogether? It would be too big for even our strongest telescopes and most intelligent simulations to show.

This is a big problem for how we interpret the Big Bang because it suggests that the density of the universe was already so strong that it should have recollapsed by now, and has reached critical density, but there is so much evidence already that shows that the universe is always expanding.

The most popular evidence of why the universe is always expanding is called Inflation.

Inflation began at approximately 10-38 of a second after the Big Bang, however, astrophysics have proven this wrong. This is because they cannot predict the cause of inflation and thus cannot pinpoint the exact time it occurred.

However, it could not have occurred before this time as the Cosmic Microwave Background because it was said to have occurred during the time of a fundamental break in the forces of nature, before 10-38 seconds, the electromagnetic force and the weak nuclear force acted in a stable, normal way under the extreme temperatures.

After this time, these forces broke apart suddenly and this was shown to have been affected by inflation and expanded the universe by an unmeasurable level.

This information links to the Inflationary Multiverse which suggests that when our universe comes to an end, it won't all end at once. This is also linking to the Horizon Problem because our universe is on such a large scale, it will only start to collapse when it reaches critical mass in patches.

Empty space will be more likely to collapse first as it is less dense, and our galaxies will slowly begin to collapse too. This will take place millions of years after the Earth dies when the Sun reaches its critical mass, and either burns the Earth as it turns into a red giant, or it could collapse too and deprive the Earth of heat.

However, in some studies of black holes and dark matter, there have been many studies that show empty space has the most energy, predicting wormholes which will be talked about in more depth soon.

So, looking at this evidence for and against the Big Bang Theory, should we believe this is how our universe was created? Or was there a much more powerful force out there that created this instead, that could also be the cause of our end and not just our beginning?