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Comment by ncmncm | Hacker News Reader

I love articles like this.

Different branches of science have different relationships with their unknowns. Cosmologists will forever revile anybody who mentions something they don't know, if it conflicts with something they like to think they do know. But biologists are always eager to talk about things nobody knows about biology.

The public would be much better served by carefully curated lists of what doesn't fit, illustrating the boundaries of understanding, than by overconfident descriptions of (e.g.) the first .001 seconds of the universe's existence.

I just found out that inflation necessarily predates big bang, but nobody can guess by how much.

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> inflation necessarily predates big bang

A tangent, but how can anything pre-date the big bang? Time itself is supposed to have been created at that point. Did you mean inflation necessarily follows a big bang?

No. There is a (IIUC, recently floated, and non mainstream) theory that inflation did in fact precede the big bang. No, I don't understand how that's possible, or even a meaningful statement.

There was an article on it here on HN, almost certainly within the last month. I don't recall more.

One of the theories is that inflationary cosmology leads to inflationary cosmology: where one universe's big bang's inflation leads to pockets of inflation that can extend beyond the universe they came from -- effectively creating their own universe. Then a big bang extends from that, which repeats into their own inflationary systems, which repeats into their own system, etc. It's a theory from the 80s IIRC.

Inflationary cosmology[1] is mostly accepted in its basic form

[1] https://en.wikipedia.org/wiki/Inflation_(cosmology)

Right; that has inflation beginning after the big bang.

I think "the big bang" has a problem of changing meaning. Here's my understanding:

- Naïve extrapolation of GR backwards in time results in a singularity at a finite point in time. Call that the big bang singularity (at t = 0)

- Using current accepted theory, we're able to simulate what was going on at t > 10^-32 or so. Before this, the implied densities and temperature are beyond what our theories can handle and we're less confident about how we got to that point (with an excess of baryons, smooth distribution of energy and matter, and the other parameters that obtain in our current universe).

- Inflation is one of the favored explanations for what happened before, but it doesn't address its own cause ("what happened before inflation?"). There's a theory of "eternal inflation" (local regions that have stopped inflating surrounded by regions that are still inflating), which explains the fine-tuning problem (each region that has stopped inflating can have its own fine structure etc). This is less accepted, maybe this is what you're thinking of?

- There's a push to redefine "the big bang" as all the stuff we can explain with current physics, i.e. as starting after inflation (but still using t=0 at the big bang singularity everyone's pretty sure doesn't actually exist). Or maybe it's been like that for a while and it's just pop science that perpetuates the big bang = singularity idea. Like how relativistic mass has fallen out of favor as a concept.

"Surprise: the Big Bang isn’t the beginning of the universe anymore". Ethan Siegel, Starts with a Bang.

https://news.ycombinator.com/item?id=28851641

I can't tell whether this is just, "Actually having started with the Big Bang implies a singularity, which isn't allowed, so let's assume it wasn't a singularity and take what we get then."

> Time itself is supposed to have been created at that point

Our space-time began at the big bang. Even decades ago, Stephen Hawking was talking about it like "Since events before the big bang can have no observational consequences, we might as well leave them out of our discussion and simply say that time began at the big bang."

No observational consequences means t=0 is zero though - if no events from before then can have carried through consequences, then they might as well have not happened - certainly no information about them can ever be recovered.

You are making a very strong assertion that something did carry through - what are you basing that on?

You're also making a pretty big claim about whether a universe makes noise if no dimension is around to articulate it.

My claim is current provable cosmology. What's yours based on?

I didn't make any claim.

> then they might as well have not happened

"Might as well not" is different from "Did not". That's all I, and Mr Hawking, are saying. In fact, your first sentence is literally just a paraphrase of my quote from Hawking.

> You are making a very strong assertion that something did carry through

No, I most certainly did not.

All I said is, there could have been something, or could have not been. I did not say something did happen prior to the big bang, just that it is wrong to say that it could not have.

>> events before the big bang can have no observational consequences

There are people working to disprove this. There is a concept floating around that the CMB might contain evidence of something from before the BB. If our universe came into existence within some other universe, then arrangements of large gravitational objects in that universe may have some impact on the early formation of our 'pocket' universe.

It's not known that there was a single point in time that was the start of our universe. Our current models can pretty reliably calculate the history of the universe back to a specific point, which would be 10^-32 seconds after this big bang point in time, but those models don't work earlier than that.

You could do some extrapolation on the expansion of the universe and just say that yes, there was a point zero, 10^-32 seconds before the earliest point in time that our models can understand, and that's where everything started from a singularity. But then we are still left with a short period of time at the start, where some physics happened that we don't have a working model for.

So since an extrapolated expansion of the universe from a singularity doesn't work in our currently understood models (at least not in the very earliest part of that timeline), is it not then plausible that something other than that expansion from a singularity could have happened during this early unknown period of time?

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