Beginning/End of the World - Discussion

[Airbrush]

From what I heard from Stephen Hawking, Michio Kaku, Neil Tyson, and other popular scientists, there is never any mention of infinite matter coming out of the big bang. They always say the universe (observable universe) originated from a tiny region, not an infinite region. Until they can clarify how a universe with an infinite amount of matter can originate, I will prefer a finite universe (big bang).

Edited October 20, 2014 by Airbrush

[Strange]

From what I heard from Stephen Hawking, Michio Kaku, Neil Tyson, and other popular scientists, there is never any mention of infinite matter coming out of the big bang. They always say the universe (observable universe) originated from a tiny region, not an infinite region.

 

The observable universe is obviously finite. Beyond that, we don't know. And, equally obviously, the observable universe must have had a finite size in the early universe.

 

But, if the rest of the universe is infinite now, then it was probably infinite then. (There are models, which I am not familiar with, where a finite universe can become infinite.)

 

 

Until they can clarify how a universe with an infinite amount of matter can originate, I will prefer a finite universe (big bang).

 

As we don't even have a theory for how, or even if, a finite universe can originate there is nothing to prefer. (The big bang model says nothing about the origin of the universe and nothing about whether it is finite or infinite.)

[Airbrush]

 

The observable universe is obviously finite. Beyond that, we don't know. And, equally obviously, the observable universe must have had a finite size in the early universe.

 

But, if the rest of the universe is infinite now, then it was probably infinite then. (There are models, which I am not familiar with, where a finite universe can become infinite.)

 

 

As we don't even have a theory for how, or even if, a finite universe can originate there is nothing to prefer. (The big bang model says nothing about the origin of the universe and nothing about whether it is finite or infinite.)

 

 

A finite universe can NEVER become infinite. Even cosmic inflation, however much faster than light speed, was a finite rate.

 

The big bang model says the observable universe was smaller than a proton at an early moment, and it says nothing about what is beyond, as if there was nothing beyond the observable. There is no mention about how an infinite universe can originate in a big bang. This shows a clear preference for a finite universe.

Edited October 24, 2014 by Airbrush

[Strange]

A finite universe can NEVER become infinite.

 

I am assured by people who know about this stuff that there are models where a finite universe can become infinite. But, as I say, not something I know anything about.

 

The big bang model says the observable universe was smaller than a proton at an early moment, and it says nothing about what is beyond, as if there was nothing beyond the observable.

 

The standard assumption (the cosmological principle) is that the universe is pretty much the same beyond the observable universe.

 

There is no mention about how an infinite universe can originate in a big bang. This shows a clear preference for a finite universe.

 

The big bang model makes no distinction or preference for a finite or infinite universe. It works identically in either case.

[elfmotat]

A finite universe can NEVER become infinite.

That's certainly not true. Consider, for example, the metric:

 

[math]ds^2 = -dt^2 + f(t) dx^2[/math]

 

where f(t=0)=0, and f(t>0)>0. At t=0 all points are condensed into a singularity, and the space has zero length. However any time after t=0 the metric describes an unbounded (infinite) line. Also notice the similarity to the FLRW metric.

[Mordred]

Singularity in this case is when we can no longer describe the physics involved. Its not the same as a point like singularity. We do not know the size of the universe at the beginning we only know our Observable portion started at a point. Just an FYI

Edited October 24, 2014 by Mordred

[Airbrush]

That's certainly not true. Consider, for example, the metric:

 

[math]ds^2 = -dt^2 + f(t) dx^2[/math]

 

where f(t=0)=0, and f(t>0)>0. At t=0 all points are condensed into a singularity, and the space has zero length. However any time after t=0 the metric describes an unbounded (infinite) line. Also notice the similarity to the FLRW metric.

 

In the context of this discussion, that a finite universe can expand to an infinite size in less than 14 Billion years, please EXPLAIN how the finite volume/diameter expands so rapidly that the volume/diameter becomes infinite. Cosmic inflation is not an infinite rate. You seem to be discussing math formulas related to infinity and looks irrelevant to the subject. Please show how it is related to the subject.

Edited October 24, 2014 by Airbrush

[elfmotat]

 

In the context of this discussion, that a finite universe can expand to an infinite size in less than 14 Billion years, please EXPLAIN how the finite volume/diameter expands so rapidly that the volume/diameter becomes infinite. Cosmic inflation is not an infinite rate. You seem to be discussing math formulas related to infinity and looks irrelevant to the subject. Please show how it is related to the subject.

 

That equation is called a metric equation. In general relativity the geometry of spacetime is defined by the metric. "s" is a measure of distance, and I've given every point in space a label for its location, "x," and time, "t." I've defined the metric so that distances between points are time-dependent. At t=0, there is zero distance between every point in space. At t>0 there is finite distance between points, and there are an infinite set of points. I.e. the space goes from length=0 to length=infinity. The metric I provided is essentially the same as the FLRW metric (see here: http://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric ), which is what describes the expansion of the universe.

[Airbrush]

That is interesting elfmotat, but could you put that equation, which is beyond me, into common everyday English for those of us who are challenged?

 

I'm trying to imagine how something expands from finite to infinite with futility.

[elfmotat]

That is interesting elfmotat, but could you put that equation, which is beyond me, into common everyday English for those of us who are challenged?

 

I'm trying to imagine how something expands from finite to infinite with futility.

 

Basically all it says is that the distance between any two points in space varies over time. The function f(t) is what determines that distance. I've chosen the function f(t) such that f(0)=0. So at t=0, the distance between all points in space is zero. However after t=0 there will be nonzero distance between any two points because I've chosen f(t) so that it's positive after t=0. I don't know if it's something you can really visualize.

[Airbrush]

 

Basically all it says is that the distance between any two points in space varies over time. The function f(t) is what determines that distance. I've chosen the function f(t) such that f(0)=0. So at t=0, the distance between all points in space is zero. However after t=0 there will be nonzero distance between any two points because I've chosen f(t) so that it's positive after t=0. I don't know if it's something you can really visualize.

 

Does anyone else know what elfmotat is trying to say? Seems like his formula has nothing to do with a finite-sized universe accelerating its' expansion to such a degree that it becomes infinite in volume and diameter within 14 Billion years.

 

An infinite universe would have to be infinite at the moment of the big bang, right? All the talk about expansion and cosmic inflation is besides the point. All you are saying is the size is "positive" after t=0. How do you get infinite size in a finite time?

Edited October 25, 2014 by Airbrush

[Strange]

There seem to be two different things here.

 

One is that a universe can go from zero size to some non-zero size (as described by elfmotat's equation). That non-zero size can be infinite. Or it could be finite. It makes no real difference either way. (And it isn't clear that "zero sized" was ever a realistic description of our universe).

 

The other is whether a universe can go from being of finite but non-zero size to infinite. I used to believe the answer to that was no, but I have been told that there are solutions where that is possible.

[elfmotat]

 

Does anyone else know what elfmotat is trying to say? Seems like his formula has nothing to do with a finite-sized universe accelerating its' expansion to such a degree that it becomes infinite in volume and diameter within 14 Billion years.

 

An infinite universe would have to be infinite at the moment of the big bang, right? All the talk about expansion and cosmic inflation is besides the point. All you are saying is the size is "positive" after t=0. How do you get infinite size in a finite time?

 

I'm not really sure how to explain it any more simply than I already have. Like I said, I don't think it's something you can visualize. At t=0 every point is zero distance from every other point. At any time after that (even t=0.0000001), the distance between any two points isn't zero, and because there is a continuously infinite set of points the length of the space is infinite.

 

 

There seem to be two different things here.

 

One is that a universe can go from zero size to some non-zero size (as described by elfmotat's equation). That non-zero size can be infinite. Or it could be finite. It makes no real difference either way. (And it isn't clear that "zero sized" was ever a realistic description of our universe).

 

The other is whether a universe can go from being of finite but non-zero size to infinite. I used to believe the answer to that was no, but I have been told that there are solutions where that is possible.

 

AFAIK in all inflation models the whole universe is modeled to be infinite in size even at the big bang. When you hear talk of "the whole universe was really tiny," what they are referring to is the observable universe. Every point in the observable universe was scrunched very close together at the big bang. However the whole universe was still infinite, even at the big bang, and the observable universe was just a tiny patch.

 

I don't know whether you can go from a bounded to an unbounded universe. That's an interesting question though.

[Strange]

I don't think it's something you can visualize.

 

Maybe it is easier to think of it by "winding the clock back" so that points in space get closer and closer together. As you approach time 0, the distance between any two points will approach zero no matter how far apart they were originally.

 

 

However the whole universe was still infinite

 

I was under the impression that the topology could be such that the universe was finite in size although still unbounded.

[elfmotat]

 

Maybe it is easier to think of it by "winding the clock back" so that points in space get closer and closer together. As you approach time 0, the distance between any two points will approach zero no matter how far apart they were originally.

 

I was trying to visualize it like that, but the line immediately goes from being infinite to length zero with nothing intermediate. I couldn't get my brain to visualize that.

 

 

 

 

I was under the impression that the topology could be such that the universe was finite in size although still unbounded.

 

I was being sloppy with my language. I don't know if it can go from being closed to open or flat. I'm not sure how that would work.

Edited October 25, 2014 by elfmotat

[Mordred]

Universe geometry is constant a closed universe is always closed same with an open universe

[elfmotat]

Universe geometry is constant a closed universe is always closed same with an open universe

 

I agree that that's true in the FLRW metric, but I don't know whether it's true in general. If you have links to any related articles I'd be interested in reading them.

[Mordred]

Not sure I understand what you mean. In the FLRW metric k is the intrinsic curvature constant. This constant determines whether the universe is flat positive/negative curved. The value k is constant in time and location in a homogeneous and isotropic universe. The FLRW metrics is 100% compatible with the Einstein field equations. Even LQC has a constant curvature parameter. LCDM is based on more than just the FLRW metrics the model uses both EFE and FLRW as well as the ideal gas laws.

 

As the curvature affects lightpaths this is critical to get accurate a varying k would result in variations in our lightpaths to date none have been found mind you we cannot see beyond the dark ages prior to the CMB, however any observational evidence we have shows the observable universe as having the same curvature constant. Based on that and using the ideal gas laws as well our knowledge of particle physics and energy conservation laws we can develop the metrics to describe the universes evolution prior to the dark ages. Though there is obviosly contention this did allow us to develop the big bang nucleosynthesis that we later measured and found to be accurate in the predicted %s of hydrogen lithium etc. My signature has numerous articles in the curvature constant including several textbook styles. Overview to cosmology goes into detail on k however so does the other materials including the free textbook from Liddle. feel free to browse it.

 

To date after years of reading cosmology based papers I honestly cannot recall any papers or metrics that has a varying intrinsic curvature constant.

If I recall correctly outside of the textbooks I own "General Relativity" by Mathius Blau also states that an open universe will remain open and vise versa but I would have to re read the 998 pages to find the statement. Its also in my signature

[elfmotat]

Not sure I understand what you mean. In the FLRW metric k is the intrinsic curvature constant. This constant determines whether the universe is flat positive/negative curved. The value k is constant in time and location in a homogeneous and isotropic universe. The FLRW metrics is 100% compatible with the Einstein field equations. Even LQC has a constant curvature parameter. LCDM is based on more than just the FLRW metrics the model uses both EFE and FLRW as well as the ideal gas laws.

 

As the curvature affects lightpaths this is critical to get accurate a varying k would result in variations in our lightpaths to date none have been found mind you we cannot see beyond the dark ages prior to the CMB, however any observational evidence we have shows the observable universe as having the same curvature constant. Based on that and using the ideal gas laws as well our knowledge of particle physics and energy conservation laws we can develop the metrics to describe the universes evolution prior to the dark ages. Though there is obviosly contention this did allow us to develop the big bang nucleosynthesis that we later measured and found to be accurate in the predicted %s of hydrogen lithium etc. My signature has numerous articles in the curvature constant including several textbook styles. Overview to cosmology goes into detail on k however so does the other materials including the free textbook from Liddle. feel free to browse it.

 

To date after years of reading cosmology based papers I honestly cannot recall any papers or metrics that has a varying intrinsic curvature constant.

 

As I said, I'm aware that k is a constant in the FLRW metric. I'm wondering whether or not other solutions to the EFE's exist which have a parameter analogous to k, but are time-dependent.

Edited October 25, 2014 by elfmotat

[Mordred]

I've never encountered any to be honest and my database of articles I have is extensive. At least not that I've encountered in a homogeneous and isotropic based model. Still trying to learn ADS/CFT though. What I understand of LQC has a constant K though I am by no means an expert in the other metrics

Edited October 25, 2014 by Mordred

[elfmotat]

I've never encountered any to be honest and my database of articles I have is extensive.

 

Yeah, I kind of figured. That would be interesting though.

[Mordred]

Would probably throw LCDM out the window lol

[AthenasChosenOne]

1. Yes. It seems to be a very logical explanation.

2. Its valid not proven

3. No. I don't belive that the universe will ever end. I belive its infinate.

4. No beacuse of this ^