Article The Big Bang doesn’t mean what it used to (updated version, Sept 2025)

[C C]

https://bigthink.com/starts-with-a-bang/...ng-meaning

KEY POINTS: 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still cling to the idea that the Big Bang means “the very beginning of it all,” that definition is decades out of date.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...

EXCERPT: . . . 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 [cosmic] inflation, and that, whatever that pre-inflationary state was, perhaps it did have a beginning. There are theorems that have been proven and loopholes discovered to those theorems, some of which have been closed and some of which remain open, and this remains an active and exciting area of research.

But one thing is for certain. 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, 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. If you’re still behind, that’s ok; the best time to catch up is always right now... (MORE - missing details)

Surprise: There was a universe before the Big Bang ... https://youtu.be/o6g8W6BaF_I

https://www.youtube-nocookie.com/embed/o6g8W6BaF_I

[Syne]

And that's why people should specify the "hot Big Bang." Because the expansion of our universe started at the inflationary period. That makes the slower, hot expansion only a different phase of the same expansion.

This redefining is just an attempt to avoid or deny the universe having a beginning.

[C C]

And the next(?) day...

The strongest evidence for a Universe before the Big Bang
https://bigthink.com/starts-with-a-bang/...e-big-bang

KEY POINTS: For many decades, people conflated the hot Big Bang, describing the early Universe, with a singularity: that this “Big Bang” was the birth of space and time. However, in the early 1980s, a new theory called cosmic inflation came along, suggesting that before the hot Big Bang, the Universe behaved very differently, pushing any hypothetical singularity unobservably far back. Earlier this century, some very strong evidence arrived showing that there was a Universe before the Big Bang, demonstrating that the Big Bang wasn’t truly the start of it all... (MORE - details)