Galaxies

[Vraith]

V - can you just spin out a quick explanation of the difference between the visible and observable universe.

Maybe. It's weird. But....
The visible is a hard ruler/measure, the observable isn't.
Say you've got a piece of fishing line that's a foot long.
And a piece of elastic that is a foot long.
So, you've got this itty-bitty hare, and it starts running along the fishing line as you pull it taut.
And an itty-bitty tortoise running down the elastic while you pull it taut.
The fishing line STAYS 1 foot long.
The elastic STRETCHES [[and if you pull it fast enough, your tortoise, while "running" slower races past the hare.]]
The fishing line is how visible is [usually] meant/measured. The universe is 15 years old, so we can see exactly [and only] 15 light-years in any direction [a 30 diameter sphere] And that's true in one sense.
The elastic is what is actually happening in the universe as space expands, [[the elastic gets longer]] that's observable.
That's about the best I can do, I think...cuz it's weird.
[[[though there's so much science-ish media out there...not always cossistent...but phys.org and other places similar always make the distinction.]]]

Sky, what's beyond that could be an infinite number of other universes scattered loosely around [and constantly being born] in a hyper-velocity inflating void

[peter]

Yes - it sort of stretches the mind getting around it, but I think I see where it's coming from. Interesting to consider how measuring a foot rule inside the universe from a position outside the universe would differ from the same measurement taken from inside. Have a feeling that the observed measurements (if indeed it were possible to take them and they didn't fail in a sort of "position or velocity, but not both" way) would have to be different, but my mind is not elastic enough to work out how.

[Vraith]

Yes - it sort of stretches the mind getting around it, but I think I see where it's coming from.

Yea...sorta think see. Agreed.
Like---a fun/odd thing if the math/description/observations are roughly correct:::
BECAUSE of that....
Every instant, SOME things we've never seen before come into viewing range...
BUT some things we have [or at least could have, if looking] move into "never be able to see again" range.
Some things are constrained by gravity that we'll always be able to see them [ at least till everything dies].
Some things we never could see, and never will see...and that stuff is almost definitely enormously and perhaps infinitely larger than all the stuff we can, did and ever will see.

In case you're wondering, the rough calculation I've seen is that everything we will ever see, even potentially, is roughly two and a half times more than what we've seen so far.

And then there's this thing...I wonder if anyone has talked about it? I bet they have someones/where I just haven't seen it...I'll call it the "calculable" universe.
Like this: suppose you can see and measure in excruciatingly fine detail a thing that is 1 mile away.
Given all one knows about how the physical works, AND given arbitrarily accurate measurements of all the observations of that thing 1 mile away,
how far away would a place with a, or several, or many, DIFFERENT "rules"/physics have to be from that thing, but still have SOME connection/influence?
[[if it's a totally calm, still day on the ocean where you are, and you can see a boat a mile away that looks EXACTLY as calm/still/sunny/etc....how far away must a hurricane, or tidal wave, or a waterfall at the edge swarmed by dragons, be for us to have no idea at all?
Between that boat and that storm...that's what I'd call the "calculable" universe. Similar, I think, but not quite identical, to "observable."

[peter]

That one is out on a limb beyond where my mind will stretch V!

Science writer John Gribben once wrote that in thinking about the red shift observed when looking at galaxies we should not think of the galaxies moving apart so much as the space between them stretching in the way that dots on the surface of a balloon would do so as it was inflated. OK - but where does it stop......or indeed does it stop. I mean, there is space between the nucleus and electrons in an atom; is this stretching too along with the space between galaxies? If so are not every day size bodies not 'inflating' along with the galaxies, such that actual measurements of distance are always the same because relatively, everything stays the same distance apart (ie the length of the ruler increases at the same rate as the thing being measured). If this isn't the case, why not? In what way (and it would have to be fundamental) would inflating space be different from the non-inflating space of more mundane distances. Something is wrong here (in my understanding no doubt).

And is extra space being created by the expansion - is the universe actually getting bigger -if so and at what rate (can a rate even be given with no external yardstick to make the measurement against). Is extra matter created in the expanding universe to keep it's density stable or does it get ever more rarified and diaphanous until it simply "poof" (like Kyza Soza), dissapears into nothing?

Sorry V - the more I think about it, the more the questions flood in. They're not for answering unless you spot some really glaring mistake in my understanding which I'd be gratified if you'd correct!

[Skyweir]

I think thats brilliantly exciting Pete .. that the act of expansion and contraction might give rise to new space, universes etc.

And I understand far less than you dear friend. To my mind you have arguably unwittingly stumbled on a stroke of genius

Following your introduced logic the universe and fathomless space around it is expanding AND contracting.

Maybe blackholes that are caused by whatever they cause are part of the expansion and the cause of some of the contraction?

Ive truly no clue .. but it sounds good to me.

[peter]

That's the trouble with science Sky - it's all damn questions and no bloody answers! I think one thing about me is I've always had to fight for the understandings that seem to come to others so easily, so tend to finish up with explanations that can be expressed relatively simply in layman's terms.

[Skyweir]

Works for me at my age

I know Im waaay out of my depth here .. what I dont know could fill multiple universes

Its an interesting journey isnt it?

[Vraith]

should not think of the galaxies moving apart so much as the space between them stretching

OK - but where does it stop......or indeed does it stop.

I mean, there is space between the nucleus and electrons in an atom; is this stretching too along with the space between galaxies?

If so are not every day size bodies not 'inflating' along with the galaxies, such that actual measurements of distance are always the same because relatively,

Is extra matter created in the expanding universe to keep it's density stable or does it get ever more rarified and diaphanous

Some stuff, within the limits of my brain---
Yea, space is stretching, but not everywhere...other things, mostly mass/gravity local curvature hold things together, are stronger than the expansion pressure....so atoms aren't being expanded, and on the large scale, our local group of galaxies aren't speeding away...Andromeda, I believe is coming closer, on a collision course....which would be cool to live long enough to see.

The "everything is expanding, including our rulers, so we can't tell" is fun. But it doesn't work. There are a lot of reasons, including our ruler [light] DOES change...and we can tell. That's what red-shift and blue shift ARE in a measuring sense---noticeable changes in our ruler.
[[a physical thing I think would make such immediately noticeable...distance grows at a rate...area grows as the SQUARE, volume grows as the CUBE. EVERYTHING would go all fuckity [mass and density and curvature change with those too, remember] if that were the case.

I'm not sure if new matter comes into being in new space except in tiny amounts...but those tiny amounts might add up??? That's a lot of huge-number math among other things to get at.
BUT---the base, inherent energy of "empty space"---THAT density remains constant. In many interps, that's the CAUSE of expansion, and that's what dark energy "is."
I"ve seen claims that 1) the expansion was lower, and sped up about 8 billion years ago. 2) that something might happen to flip it's "sign" and make it reverse. 3) that it might change/fluctuate in other ways. Don't know enough about any of those to have even a hint of why/how/if they work.

[Skyweir]

Makes sense that the universes are in a constant state of flux, expanding contracting, creating high pressure, high gravity areas offset by low gravity, low press areas elsewhere.

[peter]

Got a feeling that the net energy of the universe is always zero - that every time a bit of extra mass or whatever is squeezed out here, it is equaled and opposited by some anti equivalent elsewhere. Beyond this I'm thinking that the stuff we are dipping into is 'out there' at the front edge of where the theoreticians are scribbling, so its no surprise we struggle to be a handle on it - I expect they do too.

[Vraith]

Got a feeling that the net energy of the universe is always zero

Bizarrely, [for normal intuition/expectation] that is an essential part [and maybe the causal part] of the EXPANSION.
A positive net would [according to almost everyone] guarantee a "Big Crunch"

As far as I've seen, no one talks about a net-negative universe...I've begun to suspect that's cuz no theory of such has ever been found that allows any universe at all...but that's just an assumption from absence.

[Skyweir]

Amen to that .. it makes sense that the universe is zero net