Did the Universe ever Has Beginning?

Image Source : nasa.gov

We've all heard this theory of Big Bang, the commonly well-accepted theory of how universe began, where universe was once only zero volume of space , and then Bang! the universe exploded spreading matters all over the place and keep on expanding ever since right?...

Well that's the big bang model which is commonly perceived among general public, but unfortunately not quite right. Big bang is simply the rapid expansion of existing super hot and dense space. We never really know how it all begin at the first place.

The universe began, scientists believe, with every speck of its energy jammed into a very tiny point. This extremely dense point exploded with unimaginable force, creating matter and propelling it outward to make the billions of galaxies of our vast universe. Astrophysicists dubbed this titanic explosion the Big Bang.

- Quoted from exploration.edu

If we don't know how big bang happen, then how do scientist think it happened?

The expanding universe is among the clue that Big Bang did happen, if universe keep on expanding larger and larger then it is a common sense that at some point in the past universe started from very small volume of space, by imagining the rewinding back of time the universe would smaller and smaller.

It is also the case that astronomer do observe light emitted from distant galaxy and it appears that other galaxies moving further away from our galaxy through the concept of Doppler effect, where the further away an object become, the more the light is seen as 'shifted' towards the red part of the spectrum and the closer object become the more blue it is then astronomer know whether or not those galaxy moves further away or move closer to us by looking at the wave spectrum of color.

Cosmic Micowave Background is also the clue that support Big Bang Theory

Astronomers believe these microwaves, whose temperature is about -270 degrees Celsius, are the remnants of the extremely high-temperature radiation produced by the Big Bang. Another clue reference is that Astronomer found that the universe contains about 74 percent hydrogen and 26 percent helium by mass, the two lightest elements. All the other heavier elements -- including elements common on earth, such as carbon and oxygen - make up just a tiny trace of all matter. So how does this prove anything about the Big Bang? Using theoretical calculations, these abundances could only have been made in a universe that began in a very hot, dense state, and then quickly cooled and expanded which consistent with all other existing clues. This is exactly the kind of universe that the Big Bang theory predicts.

and so..it is the very nature that universe began with inflation or the so-called ever expanding of space time continuum

Since it was hypothesized back in the 1980s, inflation has been tested in a variety of ways against the alternative: a universe that began from a singularity. When we stack up the scorecard, we find the following:

1. Inflation reproduces all of the successes of the hot Big Bang; there’s nothing that the hot Big Bang accounts for that inflation can’t also account for.

2. Inflation offers successful explanations for the puzzles that we simply have to say “initial conditions” for in the hot Big Bang.

3. Of the predictions where inflation and a hot Big Bang without inflation differ, four of them have been tested to sufficient precision to discriminate between the two. On those four fronts, inflation is 4-for-4, while the hot Big Bang is 0-for-4.

But things get really interesting when we try to rewind back the time into the initial condition of universe where we would expect the "singularity" a point of space and time with zero volume at all.

Due to its exponential nature, even if you run the clock back an infinite amount of time, space will only approach infinitesimal sizes and infinite temperatures and densities, it will never reach it, This means, rather than inevitably leading to a singularity, inflation absolutely cannot get you to one by itself.

Quoted reference from : bigthink.com

But in an inflationary scenario (yellow), we never reach a singularity, where space goes to a singular state; instead, it can only get arbitrarily small in the past, while time continues to go backwards forever. Only the last minuscule fraction of a second, from the end of inflation, imprints itself on our observable universe today. (Credit: E. Siegel)

So we're not confident as to how universe begin, however with lots of reference, we think that it may be the case that singularity is not exists and it still be the case that Big Bang do occured at some point of time but it wasn’t begin with what we think it supposed to be. However for some of you another question may arise what about the Black Hole

Does Black Hole has Singularity?

This is a consequential question, because if black hole could have a singularity then why cannot the big bang has one?

The concept of singularity is supposedly no man's land meaning it may not really exists in real world phenomenom, even in black hole when a star collapsed and get squeezed down into very small dense pack of space due to the gravitional collapse, it doesn't get into the infinitely small volume like how singularity concept tell us.

As matter squishes down under the immense gravitational weight of a collapsing star, it meets resistance. The discreteness of space-time prevents matter from reaching anything smaller than the Planck length (around 1.68 times 10^-35 meters). All the material that has ever fallen into the black hole gets compressed into a ball not much bigger than this. Perfectly microscopic, but definitely not infinitely tiny.

Quoted from : space.com

So it is most likely that Black Hole doesn't have the singularity we're all thinking about, instead there is theory that black hole can take us to the other universe or other side of our universe but those theories remain unproven whatsoever.

No Boundary Universe Proposal by Stephen Hawking,

James Hartle & Thomas Hertog

Image Source : Quanta Magazine Infographic

The bottom image shows the conventional big bang singularity model in which universe began at certain singularity point of universe and has been inflated from there point ever since, however in the No Boundary Proposal (NBP) by Stephen Hawking, James Hartle & Thomas Hertog, the universe didn't start from a singular point of space but rather it began from a shuttlecock like geometry beginning and there are reason for that..

The NBP proposal take account quantum mechanic for the beginning of the universe, in quantum mechanics particles can behave like a wave or a particles which is very complex concept derived from the Path Integral Formulation of Quantum Mechanics provided by Richard Feynman replacing the classical notion of a single, unique trajectory of partile for a system, with a sum over all possible trajectories.

The likeliest outcomes of a particle collision, Feynman found that you could sum up all possible paths that the colliding particles could take, weighting straightforward paths more than convoluted ones in the sum. Calculating this “path integral” gives you the wave function: a probability distribution indicating the different possible states of the particles after the collision.

Quoted from : quantamagazine.org

So, based on Richard Feynman's method, Hawking and Hartle both express the wave function of the universe to descibe the likely states of universe, as the the sum of all possible ways it might have smoothly expanded from the beginning of universe, the hope from the wave function is to sum all possible "inflation universe" history.

According to the calculation a smooth bottomed universe would yield a huge, flat universe like the one we're living in and if based on the calculation for possible cosmic expansion history show that the likeliest outcome would be the universe different from ours than No Boundary Proposal fails.

The problem is that the path integral over all possible expansion histories is far too complicated to calculate exactly. Countless different shapes and sizes of universes are possible and up till now there are two possible expansion history thath potentially dominate the calculation among all of the possibilities of cosmic history.

One possibilities is the the No Boundary Proposal universe model and the other potentially dominant universe shape is nothing like reality. As it widens, the energy infusing it varies more and more extremely, creating enormous density differences from one place to the next that gravity steadily worsens.

Density variations form an inverted bell curve, where differences between regions approach not zero, but infinity. If this is the dominant model on the calculation then the No Boundary Proposal model may be wrong

@SoulE.Space