the primordial vacuum had a constant intrinsic negative spacetime curvature, meaning that it has to expand exponentially (de Sitter spacetime).

How much more lucky can the universe be? " de Sitter was born" to give it "expanding exponentially space-time", which was

constant! Can I ask: How does fit the "inflation" in this "constance"?

I don't think that de Sitter had anything to do to influence the universe. :-( The universe is a "fact" that we study; not "influence".

Some things can never be observed directly - just their influences are observable and that's what science is really about

Which means that, since we

observe is influence every Christmas morning, with our kids, Santa Claus as always been "scientifically" accepted and we didn't realize it. I don't like this "what science is really about" argument at all. It applies to anything.

Add to that the radiation, baryonic and dark matter's positive spacetime curvature that balances out de Sitter's spatial part, and you have a spatially flat, expanding universe.

Exactly! Simply because matter " curves" positively space-time, says the interpretation of Einstein/Newton bad mixture. It took a long time before the universe realized that it was Euclidian; way later than the birth of Euclid. In fact, it had to wait for de Sitter and Newton + Einstein, to be born.

I'm almost convince that the observer "creates" the "observation". In reality, we can specify that the "observer" creates is "interpretation" of the observation.

Now, we have a negatively curved space-time "created" by de Sitter, with the added "insertion" of positively curved space-time of "creators" Einstein/Newton,

which sums up to Planck satellite observation of a

balanced "flat" expanding universe (not space-time, mind you), that we "interpret"

as "needed". So, since expansion is

accelerating, that

balanced "flat" expanding universe as

a negatively curved expanding "expansion". Then we accept that

space is "flat" but

space-time is negatively curved. Which means that when matter/radiation

was more important than "vacuum energy", the space was still "flat" but

space-time was balanced "positively" curved .

So today we have a "curved"

space-time with a "flat"

space, because of the negatively curved space-time (de Sitter). Which, consequently, means that

space is "flat" but "

time" is curved.

Finally we have answered the question:

Is the universe a sphere, hyperbolic or flat? The answer is:

it's all three depending of the epoch we're talking about. Science cannot be "satisfying for everybody" more than that, can't it? Which explains

perfectly the actual "consensus" in the scientific "college". And furthermore, it cannot be more

clear and logical than this; thank you.

As a matter of fact, we can even conclude that "critical density" was always = 1 for space; but not = 1 for time. Which, evidently, explain the different epochs. CQFD.

But, again, scientists say: "we haven't found

all the answers explaining perfectly all of this; we are still searching" (I'm beginning to think they should ask J. K. Rowling for answers).

The cosmological constant is the simplest and most limited in scope (of the three) and has been pinned down with reasonable accuracy by observation.

You're talking here of the "inobservable"

dark energy (cosmological constant); aren't you?

Science is a serious study; someday, scientists will perceive it this way. I hope.

Maybe, then, they will realize that our actual technology is

way far ahead of previous ones and they will accept

to put aside all previous interpretations and start all over with

cleared eyes to "interpret" the lasts observations; instead of trying

to fit it to past interpretations given by less precise observations.

By the way, you are right: CMB is observed

exclusively in the micro-wave spectrum. This is the exact answer I was arguing for. Thank you.