What do mainstream cosmologists mean by Infinte universe ?

[HossamCFD]

What do mainstream cosmologists mean by "Infinte universe" ?

How can something that had a beginning in time (13.7 billion years ago) and expanded with a finite speed be infinite with no edges ?

I know that this is the implication of the LCDM, but still I find it very counter intuitive. I've always preferred to think of the universe as finite but curved with no boundaries (kind of 3d sphere with a curvature in a 4th dimension).

The only way that i can digest the flat infinite idea is that by "infinite" we mean that the outside is irrelevant and therefore it does not exist, at least within the realm of cosmology. And if there is no outside, then the universe is infinite.

is this an acceptable interpretation of the flat infinite idea ?

Thanks in advance

 

[Dmitry67]

How can something that had a beginning in time (13.7 billion years ago) and expanded with a finite speed be infinite with no edges ?

If Universe is finite now, it was always infinite
no transition from finite into infinite is possible.

You should, however, clarify what do you mean by 'expansion speed'.
Note that far parts of the universe recede from us much faster than light

 

[HossamCFD]

You should, however, clarify what do you mean by 'expansion speed'.
Note that far parts of the universe recede from us much faster than light

I know that distant parts of the universe recede from us faster than c. but this is still a finite speed, right ?

Are you suggesting that the big bang singularity was infinite as well ?

 

[Dmitry67]

Of course it was infinite (if Universe in infinite now)
Finite explosion in empty black void is a common misconception discussed here every month.

Regarding the speed, for objects too far from us (beyond cosmological horizon) it is not clear how to define a speed.

 

[dgtech]

What I find curious is how much "dark energy" is out there, if it is finite, then the expansions should stop, an infinite expansion would require an inflow of dark energy.

The mainstream view is of a FINITE universe, but it's only about the observable part, which logically is finite. And that finite universe is expanding... into the nothingness and will do so until it runs out of energy, and then will collapse, in one a few proposed scenarios.

However I can state the universe is infinite and there is not a single person in the world who can prove otherwise, not with a solid argument anyway. Truth is no one really knows, it is all theories and nothing more.

 

[Dmitry67]

What I find curious is how much "dark energy" is out there, if it is finite, then the expansions should stop, an infinite expansion would require an inflow of dark energy.

The mainstream view is of a FINITE universe, but it's only about the observable part, which logically is finite. And that finite universe is expanding... into the nothingness and will do so until it runs out of energy, and then will collapse, in one a few proposed scenarios.

Collection of misconceptions
1. There is no 'nothingness' where Universe expands
2. Mass and energy are not conserved contrary to what people believe (and it is a complicated subject), so the current amount of DE is irrelevant - it can increase in the future, it is not conserved. In the Big RIP scenario, for example, the more Universe expands, the more dense Dark Energy will be.
3. Collapse scenario is excluded based on the current observations

 

[dgtech]

So the universe is expanding into what?

I mean of the universe is everything there is, what is the type of medium it is expanding into? Or is space itself expanding through division, like an iterating fractal maybe? Or the universe is not expanding, but matter is contracting - that would produce a similar effect as expansion...

 

[Dmitry67]

Take infinite line from -INF to +INF
Mark positions of all integer numbers on that line: -1, 0, 1, 2, ...
Now multiply all distances by 10
The same points will be at -10, 0, 10, 20, ...

As you see, infinite object still can expand
Where did it expand into? The question does not make sense.

 

[dgtech]

numeral infinity and spatial infinity are different IMO

what you proposed is actually what I suggested as division, every 1 divides into 10, just like a fractal is able to generate more and more detail with each iteration... into infinity

but how is this mechanics applied to space? If the mainstream is right and it is dark energy that is pushing matter apart we have spatial expansion rather than spatial division

in other words, if dark energy is expanding the universe, then it must be expanding in some medium

if space is dividing/iterating into infinity - then there is a fractal principle to it, rather than dark energy

 

[Dmitry67]

what is a difference between numerical infinity and spatial infinity?
Space (Newtonian) is set R3.
Line is R1.
With a little imagination you can use the same logic for R3 (3D space)
What is a difference?

 

[HossamCFD]

Dmitry67, thanks for your answers,

I understand that the big bang was not an explosion in an empty void, simply because there was no outside, no space, nothing outside of the big bang. space originated inside the big bang.I also understand that the universe does not need an outer space to expand into. I don't share any of these common misconceptions. Yet, I've always heard references to the size of the universe at the moment of the Big Bang (like the universe was in the size of golf ball after a small fraction of a second from the B.B).

now my question is: what do you mean by "infinite" ? does it mean that nothing is outside of it (like in my first post in this thread) ? or do you really mean that the singularity happened in a very very big size and that these references to the size of the B.B that I hear all the time in the documentaries (Michio Kaku for instance) are wrong ?

thank you for your patience

 

[Dmitry67]

I am also thinking that you are trapped by some 'common sense reasoning concepts' when you are talking about spatial expansion vs spatial division

Intuitively, I understand what you are talking about, but physically, there is no difference if you think that space expands or you somehow 'insert' extra space in the middle.

 

[dgtech]

Dmitry67 - I get what you mean, but please examine the last 3 paragraphs of my last post, because I don't think your proposal reflects the mainstream view

if space is dividing, it is not due to dark energy, but some unknown universal principle, as far as I understand, dark energy is pushing things apart, it is not generating more space

what is the mechanics that generates more space?

 

[Dmitry67]

now my question is: what do you mean by "infinite" ? does it mean that nothing is outside of it (like in my first post in this thread) ? or do you really mean that the singularity happened in a very very big size and that these references to the size of the B.B that I hear all the time in the documentaries (Michio Kaku for instance) are wrong ?

The references about the size of the universe talk about the size of the VISIBLE universe.
If Universe is infinite, the Big Bang was also infinite. Not just very big, but truly infinite.

 

[Dmitry67]

if space is dividing, it is not due to dark energy, but some unknown universal principle, as far as I understand, dark energy is pushing things apart, it is not generating more space

I am explaining you mainstream view.
And it appears that you have your own theory.

Now simple question: how experimentally you can tell 2 cases: 'things are pushed apart by expansion' from 'something is generating more space between them'?

 

[HossamCFD]

The references about the size of the universe talk about the size of the VISIBLE universe.

Now I get it. I was confused by these references. Now it makes more sense indeed.


Thanks Dmitry67

 

[dgtech]

I am explaining you mainstream view.
And it appears that you have your own theory.

Now simple question: how experimentally you can tell 2 cases: 'things are pushed apart by expansion' from 'something is generating more space between them'?

We are talking strictly theoretically, cosmology is not a practical science yet ;)

Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction.

Take each Planck length^3 to be a structural unit of the spatial universe, that includes matter and all space around it. If something begins to push matter apart space between matter expands, or you have additional structural units "inserted"

I understand some mystery force pushing things apart, but I don't know where those extra units of space come form, or how do they come into being. Is there some information on how that can theoretically and logically happen?

The other version would be that those extra units of space already exist, so that matter can be pushed outwards along them. That however would mean there is some sort of medium of space excising prior to the big bang, along which the universe expands.

Or do we actually contract and thus we reach the next order of magnitude of the division of space or something, like going *-10 with each iteration of time or something? Some form of division like cells divide...

I can hardly accept the notion that prior to the big bang nothing excised, nor time or space. That would deprive the scenario of any cause for any form of bang, if it happened there was something that caused it. And I don't mean fancy string or M theories, but how do we do a model that is logical and most of all simple enough to work.

From what you say it appears that space just comes out of the nowhere, but still did not exist prior to the big bang, and that's confusing...

 

[Dmitry67]

At first, even if plank length might be minimum length, it is wrong to imagine space as if it is built from these tiny 'pixels'. I understand that it is natural in the era of computers to think about pixels/voxels, but this is wrong.

Space did not 'come out of the nowhere' in my scenario. To "come out from" is an event:

BEFORE: NOTHING
AFTER: SOMETHING

So implicitly it uses the notion of time, and this is incorrect because there was no time without our Universe. Example: take functions ln(x). It is not defined at x<=0. So:

How ln(x) can "come from nowhere" when x reaches 0?
Where it exists - in what media?

These questions make no sense. Like the same questions about the Big Bang.

 

[dgtech]

If there was no time prior to the big bang, wouldn't that mean it was all stationary, again, giving no possible cause of the big bang. Please don't tell me it didn't need a reason, in the universe everything happens for a reason ;)

Nothing cannot create something, it defies the laws of practical science, and IMO practical science has an edge over theoretical

The concept there was nothing prior to the big bang, and nothing caused it, and something was created out of nothing is a badly written fairy tale, it is not logical. It is a theory that disobeys the few laws of physics we KNOW to be legit ;) Like the of laws of thermodynamics