
The Big Bang Theory is the number one explanation for how the universe began 13.8 billion years ago. Though it’s far the main explanation, several theorists have come up with alternative ideas or extensions to the Big Bang Theory. We discover a number of these theories in the detailed infographic below.
To look into how the universe came into existence, we first want to ask what exactly is it? The term “observable universe“ refers to the entirety that we are able to see, consistent with NASA.
Due to the relationship among distance and speed of light, scientists can peer at a region of space that light 13.8 billion light-years away that means we are able to look 13.8 billion light-years in each direction. But it is not that simple. Due to the expansion of the universe, recent precisely place the diameter of the observable universe sphere more than 90 billion light-years, consistent with Forbes.

Big Bang Theory Assumptions
Scientists make 3 assumptions about the universe based on theories and observations:
1. The laws of physics are universal and do not change with time or location in space.
2. The universe is homogenous, or kind of the same in each direction (though not always all the time).
3. Humans do not examine the universe from a privileged location which includes its very center.
When implemented to Einstein’s equations, they shows that the universe has numerous properties:
1. The universe is expanding.
2. The universe emerged from a hot, dense state at a few endless time in the past.
3. The lightest elements, hydrogen and helium had been created in the first moments.
4. A history of microwave radiation fills the whole universe.
Big Bang Alternatives
If any of those simple assumptions are wrong, the Big Bang Theory would not give an explanation for all of the properties of this universe. This results in some theorists asking “is it possible the Big Bang never happened?”
One alternative theory is the Steady State universe. An early rival to the Big Bang theory, Steady State posits the continuous creation of matter all through the universe to explain its apparent expansion, consistent with NASA Cosmic Times. This kind of universe would be infinite, without a beginning or end. However, a mountain of proof discovered since the mid-1960s shows that this theory isn’t correct.
Another alternative is the Eternal Inflation theory. After the Big Bang, the universe expanded quickly during a short period referred to as inflation. The Eternal Inflation theory posits that inflation never stopped and has been happening for an infinite period of time. Somewhere, even now, new universes are getting into existence in a huge complex referred to as the multiverse. Those many universes ought to have different physical laws.
The Oscillating model of the universe concerned an infinite series of Big Bangs, accompanied by Big Crunches that restarted the cycle, endlessly. The modern cyclic model includes colliding “branes” (a “membrane” within a higher-dimensional volume referred to as the “bulk”).
Implications discovered in quantum gravity & string theory tantalizingly shows a universe that is, in reality, not anything like the way it appears to human observers. It can be a flat hologram projected onto the surface of a sphere, for example. Or it is able to be a totally digital simulation running on a huge computer.