The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and the "dark" side of your custom observable universe might catch up with you, causing all sorts of havoc.
> We may not know the exact size at the start, but we know it was infinitesimally smaller than it is today. So the size of the initial universe isn't a big factor in the equations about how big it likely is today. Weather it started as a few centimeters across or a few thousand light years across, both are functionally zero compared to the current size.
Most things you're saying are correctly rooted except for what's beyond the observable universe. I'm not sure why the staunch belief that you can confidently claim this. To be clear, you aren't provably wrong - likewise not provably right either.
The replies to you are just fine, they represent a significant portion of the scientific community that says our universe is likely infinitely big and that, possibly, the big bang was infinitely small, yet still, still infinitely large. An infinite expanding into infinite still results not knowing what's out there.
PBS Space time talks about it in terms of "scale factor"[0] instead of absolute diameter.
Still, these are all debatable theories, so your take _could_ be valid, but generally, it points infinitely large.
It’s better to think of the Big Bang as describing a point in time rather than a point in space.
What do you mean by that last claim? Any observable region is bigger at later times than it is at earlier times. The reason all points always appear to be moving away from all other points is that that is in fact happening.
What's the significance of claiming that the size of the infinite plane never changes? It's just as true that if you start with the unit interval [0, 1] and let it evolve under the transformation f(x) = tx, the size of the interval will never change -- every interval calculated at any point in time will be in perfect 1:1 correspondence with the original (except at t=0). But this doesn't mean that the measured length of the interval at different times isn't changing; it is.
https://www.wolframalpha.com/input?i=plot+%28x%2Cy%29+%3D+%2...
f(x,y) = (c * x, c * y)
f(x,y) = c * (x,y)
f(P) = c * P
Our current knowledge is functionally zero in the grand scheme of things.
I uncovered this for myself when asking, "where is that point now?" and discovering it was never a point at all, space is expanding from all points simultaneously.
The unobserved universe is likely to be many orders of magnitude larger than the observed universe. It is possible that it is unimaginably larger.
Technically, it is possible that the unobserved universe is infinite, however whether that is a credible option depends on individual scientists informed intuitions. We simply have no experimental or theoretical evidence either way at this point.
So there is no estimate of how many galaxies there are in the universe in toto.
As has already been pointed out, our best current model of our universe is that it is spatially infinite. That means an infinite number of galaxies.
The finite galaxy numbers that astronomers give are for the observable universe.
> The size and shape of the observable universe also changes.
Not the way you are describing, no. The observable universe does increase in size as time goes on, because there is more time for light to travel so the light we see can come from objects further distant. Its shape, however, does not change.
A good reference is Davis & Lineweaver's 2003 paper:
https://arxiv.org/abs/astro-ph/0310808
> A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another.
I don't know where you're getting this from. What part of the universe you can observe from a given point does not depend on your state of motion.
> Accelerate quickly enough and the "dark" side of your custom observable universe might catch up with you, causing all sorts of havoc.
This is nonsense. The Unruh effect is (a) nothing like what you are describing, and (b) irrelevant to this discussion anyway, since the Unruh effect only applies to objects which have nonzero proper acceleration, which is not the case for any galaxies, stars, or planets in the universe.
That is correct. The only tenable answer to "where did the Big Bang take place" is "everywhere".
My understanding is that, at the largest scales, clusters of galaxies are organized along a series of gravitationally bound filaments, sometimes called the cosmic web.
So they aren't distributed like random noise, but more like a web. I have no reason to think this changes anything about calculating average densities, but it is notable that there's the general density but probably a significantly different density within that structure.
But for now we can't really say if the universe in its entirety has a finite size.
It seems like GWB is a superposition of infinite overlapping waves that would be impossible to single out and "unwind" in order to form a map.
And big bang neutrinos are very weak, which makes them undetectable. My assumption was we'd need a breakthrough in measurement sensitivity but is there more to it?
And that assumes the observable universe is homogeneous, which it isn't
It is now, but up until a few billion years ago, it wasn't, it was decreasing. Many of the objects we currently see are far enough away that the light we are now seeing from them was emitted while the universe's expansion was still decelerating.
> that assumes the observable universe is homogeneous, which it isn't
No, the models cosmologists use do not assume the universe is homogeneous period. They only assume it is homogeneous on average, on large distance scales (roughly scales larger than the size of the largest galaxy clusters).