Finite versus infinite universe

[snas (Stuart)]

I've been reading about various possible universes. One question that seems to come up frequently is, is the Universe finite or infinite? As I am not an astrophysicist, I may be missing something here. But, it seems to me that if the BB occurred when a "singularity" containing all of what now makes up the Universe suddenly underwent a period of massive, rapid expansion, then surely the original singularity had an edge,a boundary. If so, it was finite. So how would a growing universe get from a finite singularity on day one of the new Universe, to an infinite state. Surely a finite thing cannot become infinite.

Stuart

[CraigS]

Originally Posted by snas

I've been reading about various possible universes. One question that seems to come up frequently is, is the Universe finite or infinite? As I am not an astrophysicist, I may be missing something here. But, it seems to me that if the BB occurred when a "singularity" containing all of what now makes up the Universe suddenly underwent a period of massive, rapid expansion, then surely the original singularity had an edge,a boundary. If so, it was finite. So how would a growing universe get from a finite singularity on day one of the new Universe, to an infinite state. Surely a finite thing cannot become infinite.

Stuart

Oh boy .. tough question .. one for a mathematician to answer ..

The way out of the dilemma is to envisage the 'singularity' as having no boundaries and is infinitely small to start with. 'Infinitely small' is the same as 'infinite' … ie: infinite ...

A 'point' in geometry, has zero dimensions and thus has no boundaries because it has no dimensions to establish any boundaries - same thing.

Did that confuse you ?

Cheers
PS: I'm happy to side-step this one .. (I think what I've said is valid, though .. this is how I think of it) . Cheers (I tried, at least).

[bartman (Bart)]

One thing I have learned whilst pondering the same question you have Stuart, is that we are not yet able to comprehend the concept of "infinite".
The scientists ( all types) and We are trying to understand and make sense of how the BB eventuated.
Experiments, VLT's ,Satellites of all sorts, LHC's etc etc are all being used to make 'sense' of the why, where, when, what and how of the universe as we know it.
I'm sure once 'we' figure that out, your ( and mine!!!!!!)question can be answered!!!!!!
Edge or no Edge ....it's HUGEhttp://www.iceinspace.com.au/forum/....eyepopping.gif
Huge as in the recent VLT's discovery of the furtherest ( newest) galaxy as per post: http://www.iceinspace.com.au/forum/s...ad.php?t=67249 .
"It has taken 13.1 billion years, travelling at 300,000 kilometres (186,000 miles) per second, for this smudge of infant light to arrive.

[Max Vondel (Peter)]

The Universe is observably "finite" and I believe "finite" beond too
Also this string theory 10^500 Universes is absolute Cr#p!
A poor way to explain very fine tuning..................
There are many other interesting ways to get fine tuning without creating all these extra universes! What ever happened to "the simplest solution is best"?

[bartman (Bart)]

Originally Posted by Max Vondel

What ever happened to "the simplest solution is best"?

Is that a quote from the movie Contact?:

Ellie Arroway: Occam's razor. You ever heard of it?
Palmer Joss: Hack-em's Razor. Sounds like some slasher movie.
Ellie Arroway: No, Occam's Razor is a basic scientific principle and it says: All things being equal, the simplest explanation tends to be the right one.
Ellie Arroway: So what's more likely? That an all-powerful, mysterious God created the Universe, and decided not to give any proof of his existence? Or, that He simply doesn't exist at all, and that we created Him, so that we wouldn't have to feel so small and alone?
[Ellie challenges Palmer to prove the existence of God]
Palmer Joss: Did you love your father?
Ellie Arroway: What?
Palmer Joss: Your dad. Did you love him?
Ellie Arroway: Yes, very much.
Palmer Joss: Prove it.

[avandonk]

Are we talking about infinite bounded Universes or infinite unbounded Universes.

Infinity or it's concept is a really difficult conundrum.

It has troubled better thinkers than you or me.

I will dig up a very good video on just this.

Bert

[Barrykgerdes]

Its time we accepted the fact that infinity means infinity. Just the same as the answer to life, the universe and everything is 42.

Barry

[bartman (Bart)]

All I'm saying is we - us humans- cannot fathom the term infinite/unbounded universe(s).
Even if we say " yes I understand that the universe has no end" we still - in the back of our mind- wonder what is beyond the """""end""""".
Tis a coniption at best!
bartman

[sjastro]

Originally Posted by snas

I've been reading about various possible universes. One question that seems to come up frequently is, is the Universe finite or infinite? As I am not an astrophysicist, I may be missing something here. But, it seems to me that if the BB occurred when a "singularity" containing all of what now makes up the Universe suddenly underwent a period of massive, rapid expansion, then surely the original singularity had an edge,a boundary. If so, it was finite. So how would a growing universe get from a finite singularity on day one of the new Universe, to an infinite state. Surely a finite thing cannot become infinite.

Stuart

Stuart,

Mathematically the visible Universe is finite, the entire Universe is infinite. This is based on the visible Universe being flat or having a zero curvature. We know nothing beyond the boundaries of the visible Universe so an infinite Universe is a speculation.

An analogy which puts a physical perspective on the concept of infinity and how it relates to a flat visible Universe, is to think of the entire Universe as being a sphere. Our visible Universe is an area on the surface of the sphere.

If the radius of the sphere is small we can discern that the surface has a definite curvature. Increase the radius and the surface appears flatter.
Mathematically there is a relationship between radius and curvature, increasing the radius reduces the curvature of the surface.

When the radius becomes infinitely large, the curvature is zero and the surface of the sphere is flat.

With regards to the singularity it's one of those unfortunate timings that the science of Cosmology predated Quantum Mechanics. The singularity is an artefact of assuming that the laws of physics (in this case General Relativity) extends all the way down to the smallest scales.

In the very early history of the Universe, the Universe was small enough to obey the laws of Quantum Mechanics instead of General Relativity.
Singularities don't exist in Quantum Mechanics as space time is "smeared".

Regards

Steven

[Steffen]

Originally Posted by avandonk

Are we talking about infinite bounded Universes or infinite unbounded Universes.

Isn't "infinite bounded" a contradiction in terms?

Infinity or it's concept is a really difficult conundrum.

Yet, if you think about it, a finite universe is actually harder to swallow. As soon as you postulate it's finite (implying a boundary) you can't help but ask yourself "what's on the other side of that boundary?", which whatever it is must be part of the universe as well (the universe being "everything"). It is quite possible that all the "stuff" is huddled together in some corner of the infinite void but there is simply no way one could imagine a bounded void.

Cheers
Steffen.

[snas (Stuart)]

All very interesting points of view, and since I'm better at desexing dogs and cats than I am at getting my head around infinite bounded and infinite unbounded universes, I'll have to be happy with the thoughts you've all put forward and not try and decide who is right or wrong, if anyone is even right or wrong.
Craig, I see your point about the unbounded singularity. I guess it's a bit like saying, how thick is a line, given that a line is one dimensional it cannot have thickness, only length. I see two different types of boundary though, one being a fence or wall, a physical obstruction to going any further; the other being the boundary of "there is no fence, but this is the last star, keep going past here and there is nothing more to see." Perhaps a better description of what I am trying to say there is to go back to Alroy Downs, cattle station on the Barkly Tableland where I jackarooed in 1986. We had about 30 000 cattle on 9 000km^2. Most of these cattle were in fenced in paddocks. They lived in a finite universe. The southern end of the station was unfenced. There were cattle there but they could have walked all the way to Adelaide if the chose to (and could find water and grass on the way). But the lack of water past a certain point is what kept them "in". So these cattle lived in a universe with no physical fence boundary; there boundary was described by that point where you could keep going, but there were no more cattle. There was further "space" out there but this space was effectively a void. I doubt that our infinite universe is like that. If it is infinite then it surely must be similar everywhere to what we see around us.
Dang, my brain hurts.
Max, I agree. In my field the same applies, simplest solution is often the best and most likely.
Bert, I like a lot of the ideas you put forward. Bring on the video.
Steven, I fully understand that the curvature of a golf ball is greater than that of a beach ball. But I'm not even going to try to understand how we measure the curvature of space. None the less I do now get what they are talking about when they talk about flat or curved universes.
Thanks all
Stuart
maybe life was simpler when we were mustering cattle on Alroy!

[CraigS]

Hi Stuart;

Infinity is a tough concept, (probably one of the toughest .. as everyone says), but I think that the concept of 'nothing' has to be considered alongside of it.

According to the thinking, (and that’s what this is all about.. the theory follows on from the initial thought concepts and it isn't necessarily the 'truth'), the Big Bang didn't expand into anything. It expanded into nothing. The ‘thing’ it started from, (at the small end), was also infinite and dimensionless and therefore infinitely dense with energy. Infinite and dimensionless at the small end … expanding into infinite and dimensionless (and nothing), at the big end.

Eventually, (fairly quickly), it then brought into existence, the 'something' - all that we see.

In your example, I notice you're still seeking to describe the boundaries. Let ‘em go and the problem disappears. That’s the trick to all of this. Focussing on the boundaries just brings the problem back. Its only a thought exercise. Following ‘the rules’ and abandoning the boundaries, leads to an appreciation of the profound logic of what follows, and is very cool (IMHO).

It really doesn’t matter whether its true or not ..

Hope this helps.



Cheers & Regards.

[Steffen]

Originally Posted by CraigS

but I think that the concept of 'nothing' has to be considered alongside of it.

I reckon a lot of people who got into astronomy are very familiar with the concept of "nothing" from watching their bank balances

Cheers
Steffen.

[CraigS]

Originally Posted by Steffen

I reckon a lot of people who got into astronomy are very familiar with the concept of "nothing" from watching their bank balances

Cheers
Steffen.

Even that's not 'nothing'.

.. and that's coming from personal experience!



Cheers

[mswhin63 (Malcolm)]

Originally Posted by Steffen

I reckon a lot of people who got into astronomy are very familiar with the concept of "nothing" from watching their bank balances

Cheers
Steffen.

[snas (Stuart)]

So Craig, if I have to get used to the idea of no boundaries in the Universe, does that mean I've got to go back up to Alroy Downs and cut down all the fences so the cattle are then living in a boundary-less universe.
(See my previous post in this thread if that all sounds a bit weird)
Stuart

[CraigS]

Originally Posted by snas

So Craig, if I have to get used to the idea of no boundaries in the Universe, does that mean I've got to go back up to Alroy Downs and cut down all the fences so the cattle are then living in a boundary-less universe.
(See my previous post in this thread if that all sounds a bit weird)
Stuart

I'm not so sure I'm up with your thinking about the cattle but what is the need for the boundary fence, if they truly live in an unbounded universe ? As you have mentioned, there are other things which stop them. Whilst I don't think like cows/bulls, their boundaries seem to be limited by where they think they can roam .. and their will to survive (ie: proximity to water/food).

We can remove the thought boundaries, if we try.
Survival ? … Well ..?.. hmm .. dunno ..

The cosmological principle is usually stated formally as: 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is 'knowable' and is 'playing fair' with scientists.

Not the best of formal quotes but you can kind of get where they're coming from. No voids beyond your 'last star' boundary (a thought barrier), everything the same … we see just a sample.

Cheers
PS: Now my brain hurts … give me a beer !! Cheers

[avandonk]

Here is a very good BBC doco that tries to explain the unexplanable

Part one of ten

http://www.youtube.com/watch?v=Cw-zNRNcF90

Well worth a careful look!


Bert

[CraigS]

Great documentary, Bert !

I just watched part one and I'm hooked !!

I might launch another thread in the Books & Media forum .. folk there would be really interested in this.

Thanks.
Cheers

[avandonk]

Yes Craig all these blokes were all over the Physics and Maths that I with great difficulty finally partially understood after studying this at RMIT from 1968 on.

Bert