Is there genuinely good evidence that the universe could have been eternal/infinite into the past?

[We Never Know]

For those theories that allow for an infinite amount of time, the Big Bang was one phase transition, possibly among many (even infinitely many). Alternatively, it is a single 'budding off' of a region of 'different expansion'.

Out of the many, which do you prefer?
In the end one is only right.

 

[Polymath257]

If there were no beginning point, why would we see any stars in the sky?
The universe is expanding. Everything is becoming farther apart -- and the rate of expansion is increasing. If you run the observed expansion backwards, it a comes to a single point ~14 billion years ago.

Yes, that is the classical description produced by general relativity. The problem is that this changes when quantum mechanics is merged into the calculations. The problem is that we have several candidates for a quantum theory of gravity, but not enough evidence to tell which is correct.

If the universe had begun twenty or thirty billion years ago, would there be any stars still close enough to see?
If the universe were eternal, and had been expanding forever, we'd surely see nothing when we looked up at night.

Be careful. In those versions that allow for an infinite time, the Big Bang was one of many times we see such an expansion (combined with production of matter).

 

[Polymath257]

Out of the many, which do you prefer?
In the end one is only right.

I am content not making a decision until the data is in.

 

[We Never Know]

I am content not making a decision until the data is in.

But yet in your posts you seem to prefer some over others without knowing.

 

[Polymath257]

I'm not sure we can comprehend infinity, we as humans, tend to need a beginning and an end. Perhaps, that is the man made part of the whole thing.

It takes some training, but it is expected of every undergraduate math major to know the basics of how infinite sets work.

Many aspects are initially counterintuitive, but that only means the intuition needs to change to accommodate the facts.

 

[We Never Know]

It takes some training, but it is expected of every undergraduate math major to know the basics of how infinite sets work.

Many aspects are initially counterintuitive, but that only means the intuition needs to change to accommodate the facts.

Have your ever experienced infinity or anything that was infinite?
How would you know?

 

[Polymath257]

But yet in your posts you seem to prefer some over others without knowing.

The evidence at this point doesn't break out of general relativity, which has time beginning with matter at the Big Bang.

But we know that quantum mechanics will be relevant at some point. We just don't know how. There are speculations, but all could well be wrong.

When QM is merged with GR, it is possible that time remains finite into the past. It is also possible it can be extended infinitely into the past.

I have noticed that there are a LOT of bad arguments on all sides of this issue. And a lot of misunderstandings of what it would even mean if time were either finite or infinite.

In some ways I like the 'neatness' of a spatially finite and temporally finite universe. In other ways, I like the diversity allowed in a multiverse with many different regions each experiencing their own version of the Big Bang. And, in other ways, I like the symmetry of having a previous contraction phase before the current expansion phase.

Which is correct (if any)? I have no idea.

 

[Polymath257]

Have your ever experienced infinity or anything that was infinite?
How would you know?

The set of natural numbers is infinite. The set of real numbers is infinite and is a 'larger' infinite size than the size of the set of natural numbers. I deal with these sets a matter of course, every day.

As for 'experiencing' infinity. That gets into questions of what it means to experience mathematics and other rather thorny issues.

 

[We Never Know]

The evidence at this point doesn't break out of general relativity, which has time beginning with matter at the Big Bang.

But we know that quantum mechanics will be relevant at some point. We just don't know how. There are speculations, but all could well be wrong.

When QM is merged with GR, it is possible that time remains finite into the past. It is also possible it can be extended infinitely into the past.

I have noticed that there are a LOT of bad arguments on all sides of this issue. And a lot of misunderstandings of what it would even mean if time were either finite or infinite.

In some ways I like the 'neatness' of a spatially finite and temporally finite universe. In other ways, I like the diversity allowed in a multiverse with many different regions each experiencing their own version of the Big Bang. And, in other ways, I like the symmetry of having a previous contraction phase before the current expansion phase.

Which is correct (if any)? I have no idea.

"But we know that quantum mechanics will be relevant at some point. We just don't know how. There are speculations, but all could well be wrong.

When QM is merged with GR, it is possible that time remains finite into the past. It is also possible it can be extended infinitely into the past."

So its a either or neither. So the honest answer is we really don't know.
If we really don't know how can anyone argue either is true or not true?

 

[We Never Know]

The set of natural numbers is infinite. The set of real numbers is infinite and is a 'larger' infinite size than the size of the set of natural numbers. I deal with these sets a matter of course, every day.


As for 'experiencing' infinity. That gets into questions of what it means to experience mathematics and other rather thorny issues.

Aren't numbers man made?

 

[Polymath257]

Aren't numbers man made?

Not just. Other animals also have a number concept.

But math is a type of language.

 

[We Never Know]

Not just. Other animals also have a number concept.

But math is a type of language.

What others species use numbers and/or math? And are aware of it?

 

[Polymath257]

"But we know that quantum mechanics will be relevant at some point. We just don't know how. There are speculations, but all could well be wrong.

When QM is merged with GR, it is possible that time remains finite into the past. It is also possible it can be extended infinitely into the past."

So its a either or neither. So the honest answer is we really don't know.
If we really don't know how can anyone argue either is true or not true?

We are all waiting for relevant evidence.

 

[Polymath257]

What others species use numbers and/or math? And are aware of it?

I don't know how to test awareness in the absence of language.

Several other species are able to distinguish numbers up to 7 or so.

 

[Magical Wand]

In some ways I like the 'neatness' of a spatially finite and temporally finite universe. In other ways, I like the diversity allowed in a multiverse with many different regions each experiencing their own version of the Big Bang. And, in other ways, I like the symmetry of having a previous contraction phase before the current expansion phase.

Which is correct (if any)? I have no idea.

A model of a (single) contraction phase (empty of baryonic matter) prior to the expansion is my favorite. It is very simple and elegant. I also think it is compatible with (future) eternal inflation, so the inflationary multiverse goes well with this idea.

 

[gnostic]

I've heard experts claim that there are models that show that an infinite past universe is possible, is that so?

Yes, there are other models, BUT your subject heading says “good evidence”.

So the only real evidence we really have points to the Expanding Universe Model, which is what loosely called from the 1920s, but was later more popularly referred to as the “Big Bang theory” since 1949.

Since the late 1990s, the Big Bang theory was expanded to include the Dark Energy denoted by Greek letter lambda and Cold Dark Matter (CDM), so the new name for the Big Bang theory is “ΛCDM model” (Lambda-CDM model).

Anyway, @epronovost is correct, the Observable Universe points to universe being UNDER 14 billion years old.

Ther other models but they are not science yet, because there are no good evidence for these alternative models. The only reasons why these models are not thrown out as garbages, is because these models provide mathematical solutions - meaning equations - that are still theoretically possible, but without scientific evidence.

Equations are good and useful tools in physics, but maths are not evidence.

Science needs “evidence”, not equations, evidence to test and either verify or refute any model.

Those “models” you talked about are only “proposed” models, not scientific models.

Anyway, there are no “good evidence” that points to eternal universe. Actually there are no evidence at all.

 

[gnostic]

@Jos , I like to extend what I mean by what I wrote below:

Anyway, there are no “good evidence” that points to eternal universe. Actually there are no evidence at all.

What I meant that we can currently observe diameter of 96 billion light years.

That’s what astrophysicists called the “Observable Universe”.

We cannot observe beyond the Observable Universe, so no observations, no evidence can be obtained or gathered the observational limits, therefore “we don’t know” if the universe is infinite, nor we cannot know if the universe is eternal.

So far the other alternative models, that trying to explain the universe (beyond the Observable Universe) being eternal or infinite or eternal, or that there are multiple universes (eg Multiverse), are just speculations.

Sure, these alternative models could be right, but they could ell be wrong, and right now they are limited by what we can currently observed.

So I think it is foolish to think one of these alternative models being right when don’t even have new information, new data and new evidence to work with that can support their views.

The only these models have going for them are some mathematical equations and mathematical solutions, but maths are not physical evidence, so their alternative models are just speculative at best.

 

[gnostic]

A model of a (single) contraction phase (empty of baryonic matter) prior to the expansion is my favorite. It is very simple and elegant. I also think it is compatible with (future) eternal inflation, so the inflationary multiverse goes well with this idea.

Except as I have pointed out to Jos, there are no evidence gathered beyond the Observable Universe, therefore the Multiverse of inflationary sort or otherwise, are just speculative at best.

Sure the Multiverse haven’t being refuted yet, but it also haven’t been verified too. So the question of Multiverse being science, remained unresolved.

I am willing to wait for resolutions of any alternative models (not just Multiverse, I am talking about all alternatives to the bb cosmology), but I am not going to side with them, until they have some things more concrete than “possible” abstract mathematical solutions.

 

[Magical Wand]

Except as I have pointed out to Jos, there are no evidence gathered beyond the Observable Universe, therefore the Multiverse of inflationary sort or otherwise, are just speculative at best.

Sure the Multiverse haven’t being refuted yet, but it also haven’t been verified too. So the question of Multiverse being science, remained unresolved.

I am willing to wait for resolutions of any alternative models (not just Multiverse, I am talking about all alternatives to the bb cosmology), but I am not going to side with them, until they have some things more concrete than “possible” abstract mathematical solutions.

I've already responded to your claims here.

 

[gnostic]

I've already responded to your claims here.

Yes, I know, in the other thread.

I simply don’t accept thing to be true, when the matter of fact, Multiverse remained unresolved. I don’t like to take sides on something that may not exist.

I will only accept Multiverse if we have more conclusive evidence to verify it being true and being probable. And I don’t think we at that stage...yet...quite possibly never.

What you have quoted from Guth, Barrau and Vilenkin, are only “possibilities” that statistical data may be linked to Inflationary Multiverse, not verification of it being “probable”.

You do understand the differences between possibilities and probabilities, don’t you?

Possible links to Multiverse, isn’t definitive - it might be true, but it might well be wrong. There are just not enough information to make informed decisions about Multiverse’s status.