Is the universe infinite or finite?

[firedragon]

Well if it's finite that would suggest a boundary.

The problem is the boundary itself. Something like that would require a dimension. How big? How thick? What lays beyond a boundary?

I view a finite universe as being contained by boundaries but the boundaries themselves cannot be finite for the same reasons.

What about time? Beginning, End?

 

[Twilight Hue]

What about time? Beginning, End?

There's never been a start point for time, neither an end point either. At least as far as I'm aware.

Time is just a yardstick as i see it. . A tool for measuring.

 

[firedragon]

There's never been a start point for time, neither an end point either. At least as far as I'm aware.

Time is just a yardstick as i see it. . A tool for measuring.

Thanks.

 

[Meow Mix]

Astrophysics grad student here.

The answer is, of course, that we don't have enough information; but we have good reason to think a few different things.

For instance, given inflation, it is likely there is an infinite universe. Why? Because inflation decays, but it doesn't decay uniformly. You'll end up with pockets of universe that are isotropic and homogeneous like the universe that we see (where inflation has decayed), but elsewhere inflation rapidly dominates. This goes on literally forever because in QFT it's what Paul Davies would call a free lunch (every positive balanced by a negative, so energy is conserved).

Given measurements of BAO (baryon acoustic oscillations) as measured by WMAP and more precisely by Planck, we've been able to constrain a few things that make inflation look pretty likely (and at least rule out a few other things, namely from the polarization of the cosmic microwave background; rules out some brane world ideas for instance).

Long story short, we end up with a pocket cosmos that appears finite from inside, but has a definable boundary (this would still be larger than the visible universe, since we detect almost no curvature whatsoever, itself evidence for inflation). Outside that boundary would be an infinite other number of cosmos-bubbles.

Thanks to QFT (quantum field theory, sorry, trying to avoid too many acronyms here), the interaction at the boundary with inflation fields can also have some effects on the physics within the boundary that I'm honestly not familiar with on a technical level (I work more with constraining dark energy than with inflation period).

 

[Meow Mix]

I guess I forgot to vote. That’s done now.

 

[gnostic]

I am talking about this universe. If you wish, the multiverse "idea" could be discussed in a new thread.

I think @Polymath257 is trying to provide you some theoretical examples of cosmological models that the universe could be infinite, with Multiverse being one of them.

Other theoretical model of infinite universe is the Cyclical Universe model or the Oscillating Universe model, which is sometimes called the Big Bounce. The cyclical model proposed that the universe goes through alternating series of Big Bang (expansion) and Big Crunch (contraction, back to singularity), sort of like birth, death, rebirth, an endless cycle.

Currently, we don’t have the technology of seeing beyond the surface of last scattering - the oldest observable residual radiation that you would known as the Cosmic Microwave Background Radiation (CMBR). So we cannot see earlier generations of Universe BEFORE this current Big Bang.

Likewise, we have no technology to observe other universes.

Multiverse, Cyclical Universe, and other alternative theoretical models, are only mathematically conceived, not observable, nor testable, at this stage.

Eternal universe is also another theoretical that are not observable, nor testable.

So the questions of universe being infinite or finite, remained an open question, and we really don’t know which one or if any is true.

As to the Big Bang theory, it is a theory about this Observable Universe, stopping the Planck Epoch, with the age of the Observable Universe being 13.79 billion years old, with observable diameter of 93 billion light years.

But I must remind you that these numbers only referred to the “Observable Universe”, but the entire universe, which cannot see, could be much bigger than the known diameter of 93 billion light years.

My point about the Big Bang theory is that it doesn’t attempt to explain anything before and beyond the Planck Epoch.

It would seem that the universe have finite past, according to BB model, but the universe expansion could be infinite, depending on the topology of the universe, eg universe ‘s shape is flat.

 

[firedragon]

I think @Polymath257 is trying to provide you some theoretical examples of cosmological models that the universe could be infinite, with Multiverse being one of them.

Other theoretical model of infinite universe is the Cyclical Universe model or the Oscillating Universe model, which is sometimes called the Big Bounce. The cyclical model proposed that the universe goes through alternating series of Big Bang (expansion) and Big Crunch (contraction, back to singularity), sort of like birth, death, rebirth, an endless cycle.

Currently, we don’t have the technology of seeing beyond the surface of last scattering - the oldest observable residual radiation that you would known as the Cosmic Microwave Background Radiation (CMBR). So we cannot see earlier generations of Universe BEFORE this current Big Bang.

Likewise, we have no technology to observe other universes.

Multiverse, Cyclical Universe, and other alternative theoretical models, are only mathematically conceived, not observable, nor testable, at this stage.

Eternal universe is also another theoretical that are not observable, nor testable.

So the questions of universe being infinite or finite, remained an open question, and we really don’t know which one or if any is true.

As to the Big Bang theory, it is a theory about this Observable Universe, stopping the Planck Epoch, with the age of the Observable Universe being 13.79 billion years old, with observable diameter of 93 billion light years.

But I must remind you that these numbers only referred to the “Observable Universe”, but the entire universe, which cannot see, could be much bigger than the known diameter of 93 billion light years.

My point about the Big Bang theory is that it doesn’t attempt to explain anything before and beyond the Planck Epoch.

It would seem that the universe have finite past, according to BB model, but the universe expansion could be infinite, depending on the topology of the universe, eg universe ‘s shape is flat.

Thanks.

You said the expansion could be infinite. But does that mean the universe does not have an r as in the hot Big Bang model etc? Is that what you are implying?

 

[Polymath257]

Thanks.

You said the expansion could be infinite. But does that mean the universe does not have an r as in the hot Big Bang model etc? Is that what you are implying?

No. The r (also seen as a(t) ) is a scale factor, not the radius. The universe can be infinite and r also finite. The hot BB model proposes an expansion factor, not a radius.

 

[Polymath257]

It is an easy answer.
If there was a Big Bang, a singularity spread out matter from one single point, such as particles being flung from a spinning disk.
It would mean that this matter will spread out into space in a spherical model, and will continue to travel away from its central point.
This means that no matter when, even billions of years from now, that sphere will only grow larger and less dense.

Sorry, but this is simply wrong. It is NOT how space and time are described by the BB model. In particular, we do NOT have expansion 'out of a point'. The expansion is of all space.

This is the Big Bang model contained within the laws of ennergy conservation.
If not the above, which renders a finite universe, then matter appeared throughout the universe, everywhere at once, and the Big Bang model never happened.

And that is also incorrect. The BB model definitely allows for a spatially infinite universe that 'appears' at a specific moment of time.

In that case, we will not have any clues whether the universe has a boundry, and it might be infinite, and finite.

In any case, I believe the universe to be finite due to the observable nature demonstrates that everything we know so far, has boundries.

There are no boundaries observed. There is a limit to what we can observe because the universe has only a finite age, but there are no boundaries in that.

 

[firedragon]

No. The r (also seen as a(t) ) is a scale factor, not the radius. The universe can be infinite and r also finite. The hot BB model proposes an expansion factor, not a radius.

I am no expert on this for sure, but the Hot Big Bang model has time and radius/temparature as axis's, the radius is expanding at a critical rate to avoid collapsing, which is the second unexplained phenomena of the HBB model.

 

[gnostic]

Thanks.

You said the expansion could be infinite. But does that mean the universe does not have an r as in the hot Big Bang model etc? Is that what you are implying?

As I said, what we can currently observe of the Observable Universe is finite - and I stressed the word “Observable” - BUT the rest of the universe that we cannot observe (with our current technology) might be many times larger than the Observable Universe, it could be infinitely larger, we just don’t know.

You need to remember that the Big Bang theory only focused on the evolution of this Observable Universe.

 

[Dan From Smithville]

If the universe is finite, what lies beyond the boundary?

Turtles.

 

[TransmutingSoul]

This question comes out of curiosity to find the arguments of those who make both sides of the word "or". If this is a false dichotomy I would like to hear the other options to this as well.

In a Provisional translation of a Tablet by Abdu’l-Baha it offers this;

"....Thus the suns of the praise of the one true God moved resplendent in a vast, infinite space, capable neither of being defined by limits nor contained within the compass of signs and allusions. All praise be to Him Who was its Author and Creator, Who spread it out, and adorned it with countless lamps and never-fading luminaries: 'None knoweth the hosts of thy Lord save Him' (Qur'an, 74:31)."

So we would have to look at the Arabic, or Persian used, but it is saying creation is not defined by limits and this is applicable to all the worlds of God.

In that tablet it offers another tradition about the expanse of creation and reading this, all we can know is in but One of those lamps.

"... The Dawning Places of Unity, the Daysprings of Singleness and the Suns of Holiness are also sanctified beyond the bounds of number, and the luminous spiritual worlds are exalted above limits and restrictions. In like manner the worlds of bodily existence the mind of no man can reckon nor the understanding of the learned comprehend. Consider the following well-known tradition and examine its meanings indicative of the vastness of the cosmos and its awesome limitless expanse: 'God, exalted be He, fashioned one hundred thousand, thousand lamps and suspended the Throne, the earth, the heavens and whatsoever is between them, even Heaven and Hell -- all of these in a single lamp. And only God knows what is in the rest of the lamps.' The fact that philosophers and sages have posited limits and restrictions for such matters is to be explained by the limitations of people~s minds and perceptions and the blindness of the followers of allusions, whose natures and intellects have been rendered dull and inanimate by the interposition of many veils."

Great hey

Regards Tony

 

[firedragon]

In a Provisional translation of a Tablet by Abdu’l-Baha it offers this;

"....Thus the suns of the praise of the one true God moved resplendent in a vast, infinite space, capable neither of being defined by limits nor contained within the compass of signs and allusions. All praise be to Him Who was its Author and Creator, Who spread it out, and adorned it with countless lamps and never-fading luminaries: 'None knoweth the hosts of thy Lord save Him' (Qur'an, 74:31)."

So we would have to look at the Arabic, or Persian used, but it is saying creation is not defined by limits and this is applicable to all the worlds of God.

In that tablet it offers another tradition about the expanse of creation and reading this, all we can know is in but One of those lamps.

"... The Dawning Places of Unity, the Daysprings of Singleness and the Suns of Holiness are also sanctified beyond the bounds of number, and the luminous spiritual worlds are exalted above limits and restrictions. In like manner the worlds of bodily existence the mind of no man can reckon nor the understanding of the learned comprehend. Consider the following well-known tradition and examine its meanings indicative of the vastness of the cosmos and its awesome limitless expanse: 'God, exalted be He, fashioned one hundred thousand, thousand lamps and suspended the Throne, the earth, the heavens and whatsoever is between them, even Heaven and Hell -- all of these in a single lamp. And only God knows what is in the rest of the lamps.' The fact that philosophers and sages have posited limits and restrictions for such matters is to be explained by the limitations of people~s minds and perceptions and the blindness of the followers of allusions, whose natures and intellects have been rendered dull and inanimate by the interposition of many veils."

Great hey

Regards Tony

Does t answer the OP Tony.

 

[TransmutingSoul]

Does t answer the OP Tony.

Well it did, I would have not given a reply if I think it did not, as the question asked was, is the Universe infinite of finite, with two answers provided. The reply I gave offered it is infinite, so it was answered. So Maybe not in your frame of reference though?

It seems that seems to be the way you always respond to my answers, Tony that is not applicable to the topic?

Regards Tony

 

[firedragon]

Well it did, I would have not given a reply if I think it did not, as the question asked was, is the Universe infinite of finite, with two answers provided. The reply I gave offered it is infinite, so it was answered. So Maybe not in your frame of reference though?

It seems that seems to be the way you always respond to my answers, Tony that is not applicable to the topic?

Regards Tony

Actually, it's not applicable to the topic.

 

[TransmutingSoul]

Actually, it's not applicable to the topic.

Oh dear.

 

[firedragon]

Oh dear.

I was just kidding this time Tony.

 

[Polymath257]

I am no expert on this for sure, but the Hot Big Bang model has time and radius/temparature as axis's, the radius is expanding at a critical rate to avoid collapsing, which is the second unexplained phenomena of the HBB model.

That is incorrect. The Hot Big Bang model has an *expansion factor* that is growing at a critical rate. The temperature is inversely dependent on that expansion factor.

That expansion factor can be regarded as a radius *if* space is positively curved, but not if it is flat or negatively curved. For the critical rate of expansion, space is flat.

No need to be an 'expert', just read some legitimate books on the subject. I can give recommendations, but they all require some significant math.

 

[firedragon]

That is incorrect. The Hot Big Bang model has an *expansion factor* that is growing at a critical rate. The temperature is inversely dependent on that expansion factor.

That expansion factor can be regarded as a radius *if* space is positively curved, but not if it is flat or negatively curved. For the critical rate of expansion, space is flat.

No need to be an 'expert', just read some legitimate books on the subject. I can give recommendations, but they all require some significant math.

So if the radius is expanding I dont know how that is "incorrect". Also I dont understand if the so called "expansion factor" exists and the radius is expanding at a critical rate, the universe is infinite.