Where are we

[Alien 13]

The current thinking is that the earth is at the center of the observable universe but where would it be in the universe as a whole, its obviously not near the center with third  or higher generation stars close by so is it a third the way or maybe half or near the edge or perhaps only a millionth of the way.

Alan

[Floater]

To paraphrase Bob Dylan, 'I'll let you be at the centre of my universe if I can be at the centre of yours'.

Keep thinking and wondering, Alan. ?

[D4N]

Ah but remember the old galaxies that we view in those wonderful Hubble images may not even be there any more, that light is billions of years old so the galaxies there will have evolved by now and may look a lot more like what we see near to us.

[DRT]

32 minutes ago, Alien 13 said:

The current thinking is that the earth is at the center of the observable universe but where would it be in the universe as a whole, its obviously not near the center with third  or higher generation stars close by so is it a third the way or maybe half or near the edge or perhaps only a millionth of the way.

Alan

Assuming the universe is of infinite size, everywhere in the universe is at the centre of the observable universe, and if it is infinite it has no centre.

This Talisker is excellent

 

[D4N]

Hmm it's not infinite, just unbounded.  The universe may well have a central point but finding it when there is no way to find the edges is going to be tricky!

[DRT]

14 minutes ago, D4N said:

Hmm it's not infinite, just unbounded.  The universe may well have a central point but finding it when there is no way to find the edges is going to be tricky!

Interesting. My statement was intentionally phrased as an assumption while yours reads as a statement of fact.

What evidence do we have that it is unbounded and not infinite?

And why would the space outside the unbounded part that holds all the matter not be part of the universe, and is that empty space infinite or unbounded?

[SilverAstro]

Do we need to define some terms first ?

Eg. :-

until recently the observable universe was limited by the CMB, when light ( EM ) became free to cross the universe at the time of last scattering. But now we are beginning to have the capability via gravity waves of observing before that event ( approx 300,000y after the BB).   Is that what you mean by the ref to 3rd and 4th gen stars ?

but, we can call the observable universe that which Einstein permits, that is, the universe that can communicate (and viceversa) with us. Because of expansion of the universe there is now much that is too far away, there has not been enough time for the light or anything else, not any other information,  to reach us from there.  So we have no way of knowing what is beyond, and thus no way of knowing where we are in relation to anything else anywhere else beyond.

It would seem that the universe is going to continue to expand so we will never be able to measure what is there and where beyond !

We will ( or do I mean may ? it is late at night !) be able to measure the shape of space ( bound / unbound etc. ) beyond because we will be able to assume that it is the same shape as the bit we can observe and thus measure.

I dunno, tis all beyond my pay grade !

 

[johnfosteruk]

Surely we are far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy. 

That's all you're going to get out of me, the last thread on this boggled my mind (Or was it the whisky?)

Pass the Laphroaig! 

 

[SilverAstro]

1 minute ago, johnfosteruk said:

Pass the Laphroaig! 

and that is something else that expands beyond all comprehension, the tax we have to pay on it

 

[johnfosteruk]

1 minute ago, SilverAstro said:

and that is something else that expands beyond all comprehension, the tax we have to pay on it

 

Criminal isn't it. I thought essentials/necessities were supposed to not be taxed..

[SilverAstro]

1 hour ago, johnfosteruk said:

Criminal isn't it. I thought essentials/necessities were supposed to not be taxed..

I think this is where we go to the other subforum ?

[johnfosteruk]

11 minutes ago, SilverAstro said:

I think this is where we go to the other subforum ?

Indeed.. Back on topic

3 hours ago, D4N said:

Hmm it's not infinite, just unbounded.  The universe may well have a central point but finding it when there is no way to find the edges is going to be tricky!

I still can't quite get my head around the unbounded/bounded lark but what I do understand is that we have the cmb/observable universe limit so surely if we can't see beyond that how do we know what lies beyond that and therefore how can we decide seemingly arbitrarily that its either finite or infinite? 

Assuming my reasoning is sound therefore we don't know whether there's a centre unless we can somehow see beyond that limit, which we can't. As far as I know. Further is this not what SilverAstro has already said? Almost. 

Please correct me at will. 

[SilverAstro]

24 minutes ago, johnfosteruk said:

I still can't quite get my head around the unbounded/bounded lark

 the cmb/observable universe limit so surely if we can't see beyond

Please correct me at will. 

In reverse order :

or even goodwill hunting ! ( gerrit?!)

see my previous on cmb ( ElectroMagnetic observable) vs. gravity wave  ( and, in addition neutrino flux, but that is summat else for another day)

There was a period of inflation that put most of the universe beyond our ken, that I think is the bit that Alien is trying stir ? and if you believe E=MC^2 etc it will remain beyond our ken, (unless everything goes into reverse. )

( I wish this editor wouldnt keep assigning two new lines to each cr ! I could get over it and compose this in standard english in another editor but then I would have to shoot you )

The cmb happened after inflation and defines our EM horizon.

 

so to your top, no me neiver, but neither can the talking heads on BBC4, so we can consider ourselves free here to humbly talk and explore our mutual undrestanding, cos it is well said that on the interweb there is no better way of getting an answer than to post a wrong-un ! [ To badly get Lord Denning out of context :- Be ye ever so high, be ye not high enough here to sort it ! ]

 

[cloudsweeper]

12 hours ago, DRT said:

Interesting. My statement was intentionally phrased as an assumption while yours reads as a statement of fact.

What evidence do we have that it is unbounded and not infinite?

And why would the space outside the unbounded part that holds all the matter not be part of the universe, and is that empty space infinite or unbounded?

By my (limited) understanding, there is no space outside.  Space is that which is expanding since it began with a "singularity" - it's meaningless to speak of space (or anything) beyond that.  I think.

As for Alan's original point, the Earth must be the centre of the observable universe, since that's where we do (most of) our observing from.

And is it not true that on a very, very large scale, the universe is homogeneous, and would look the same wherever you observed from?

Doug (with mind starting to boggle).

 

[SilverAstro]

I think that is true for the classical BB, no space outside, - until we start boggling over multiverses, M-branes &etc, where are all those supposed to exist ?