The Steady-State Theory suggests that the universe's expansion happened due to the continuous bubbling of hydrogen atoms from an empty space at the rate of 3 hydrogen atoms per cubic meter million years.This theory was first put forward in 1948 by British scientists Sir Hermann Bondi and Sir Fred Hoyle. Hoyle compares this theory to a river to where "it may appear unchanging, but there is plenty of movement and change under the sufrace."

The Steady-State Universe

The braneworld theory states that in order for the universe to have survived, it would have had to create relatively small "black holes". Moreover, this theory can be experimented upon.This theory suggests that we are in a three dimensional membrane that exist inside the bulk or the higher dimensional space.In the case of the Randall-Sundrum model, such tests could involve measuring the gravitational waves that are emitted by the black holes thus linking one brane to another.

The Braneworld Theory

The Big Splat also known as the Ekpyrotic Theory, was thought of by cosmologists Neil Turok and Paul Steinhardt who believe that eventually a brane would collide with another and through the collision there will be enough energy to create a whole new universe.The term "ekpyrotic" came from the word ekpyrosis which means conflagration in Greek.

The Ekpyrotic Theory

This theory comes from the philosophers. It questions that if all of the information about the universe are input into our brains via our sense and other scientific instruments, who's to say that this isn't all just some cleverly constructed illusion?This is a great argument for the existence of the universe however there is no way that it could be proved true or false

Simulation Theory

The Big Bang to this day, remains to be a fan favorite of many scientists and with that theory comes two key observations: the expansion of the universe, and the cosmic wave background.The CMB is thought to be the leftover radiation from the occurence of the Big Bang. The CMB cannot be seen with the naked eye however, its radiation is most visible in the microwave part of the electromagnetic spectrum.

The Cosmic Microwave Background (CMB)

The laws of physics hold a handful of fundamental constants that determine the strength of gravity, electromagnetism and subatomic forces. However, these numbers could have any possible value and with any value that gets displaced, the universe would be entirely different.This argument make some people believe that the Universe allows for creatures like us to come into existence with it and that is proof enough in itself.

Self-Centered Anthropic Theory

The theory of eternal inflation was proposed by Paul Steinhardt. This theory suggests that there are other bubbles of universes that are constantly popping up in other parts of the inflationary sea, therefore comprising a "multiverse".

Eternal Inflation

The Holographic Universe denotes the idea that the three-dimensional universe that we are used to could actually be a fundamental two-dimensional space.So how it works is that there couble be a distant two-dimensional surface that contains the data that is needed to fully describe our world and therefore is projected to appear in 3D.This was researched by the University of Southampton in the UK and the findings showed consistency with the observed pattern of the CMB fluctuations.

The Holographic Universe

Gravity is the only force in physics that affects matter on humongously large scales however it can't, on its own, explain certain astronomical observations. There are two options that we could forego with: unseen dark matter - that provides for the missing gravity, or to replace our theory of gravity into the Modified Newtonian Dynamics (MOND) that proposes a modification of Newton's laws in order to accounr for the observed properties of galaxies.

Dark Matter and Modified Newtonian Dynamics

The universe may only exist in three dimensions but we can also visualize it having a fourth in the form of time, so to speak, the universe may exist in four-dimensional space-time.This idea was proposed by Stefano Liberati from the International School for Advanced Studies and Luca Maccione of Ludwig Maximilian University. This theory argues that the 4-D universe is made up of microscopic particles that are on a deeper level or reality that our instruments cannot reach yet.

Four-Dimensional Space-Time

Why is the universe the way it is? Over the years, scientists have explored many ways to explain the cosmos, leading to some crazy-sounding ideas…