Far out cosmology: new view of Big Bang (Introduction)

by David Turell , Saturday, August 27, 2022, 18:45 (817 days ago) @ David Turell

The cosmic inflationary period cnfuses the issue:

https://bigthink.com/starts-with-a-bang/big-bang-meaning/?utm_source=mailchimp&utm_...

"The idea that the Universe had a beginning, or a "day without a yesterday" as it was originally known, goes all the way back to Georges Lemaître in 1927. Although it's still a defensible position to state that the Universe likely had a beginning, that stage of our cosmic history has very little to do with the "hot Big Bang" that describes our early Universe. Although many laypersons (and even a minority of professionals) still cling to the idea that the Big Bang means "the very beginning of it all," that definition is decades out of date. Here's how to get caught up.

***

"Originally, the idea was that the Universe itself, not just the matter within it, had emerged from a state of non-being in the finite past. And that idea, as wild as it sounds, was an inevitable but difficult-to-accept consequence of the new theory of gravity put forth by Einstein back in 1915: General Relativity.

***

"If we were to extrapolate backward in time, the Universe would have been in a hotter, denser, more radiation-dominated state. Gamow leveraged this fact to make three great, generic predictions about the young Universe.

"At some point, the Universe’s radiation was hot enough so that every neutral atom would have been ionized by a quantum of radiation, and that this leftover bath of radiation should still persist today at only a few degrees above absolute zero.

"At some even earlier point, it would have been too hot to even form stable atomic nuclei, and so an early stage of nuclear fusion should have occurred, where an initial mix of protons-and-neutrons should have fused together to create an initial set of atomic nuclei: an abundance of elements that predates the formation of atoms.

"And finally, this means that there would be some point in the Universe’s history, after atoms had formed, where gravitation pulled this matter together into clumps, leading to the formation of stars and galaxies for the first time.

***

"The Big Bang, as verified by our observations, accurately and precisely describes the emergence of our Universe, as we see it, from a hot, dense, almost-perfectly uniform early stage.

"But what about the “beginning of time?” What about the original idea of a singularity, and an arbitrarily hot, dense state from which space and time themselves could have first emerged?

"But at the absolute earliest times, this picture breaks down. There was a new idea — proposed and developed in the 1980s — known as cosmological inflation, that made a slew of predictions that contrasted with those that arose from the idea of a singularity at the start of the hot Big Bang. In particular, inflation predicted [a series of facts]:

"On all of these accounts, the inflationary picture has succeeded in ways that the hot Big Bang, without inflation, has not.

***

"Now, there are many reasons to believe that the inflationary state wasn’t one that was eternal to the past, that there might have been a pre-inflationary state that gave rise to inflation, and that, whatever that pre-inflationary state was, perhaps it did have a beginning.

***

"Whether there was a singular, ultimate beginning to all of existence or not, it no longer has anything to do with the hot Big Bang that describes our Universe from the moment that:

"...inflation ended, the hot Big Bang occurred, the Universe became filled with matter and radiation and more, and it began expanding, cooling, and gravitating, eventually leading to the present day.

"There are still a minority of astronomers, astrophysicists and cosmologists who use “the Big Bang” to refer to this theorized beginning and emergence of time-and-space, but not only is that not a foregone conclusion anymore, but it doesn’t have anything to do with the hot Big Bang that gave rise to our Universe. The original definition of the Big Bang has now changed, just as our understanding of the Universe has changed."

Comment: this means the hot inflationary period is all we can see of a beginning for this universe. We can assume a start but it is hidden. The idea of singularity is Newtonian and in light of General Relativity cannot be applied. This is what Guth means by 'past incomplete'.