I think zero energy with the cosmological constant allows matter to be created by the inflation but controlled by non-uniformity in perfect harmony; repulsive gravity drives inflation and according to Gunt it decays at t=10^-33 seconds after the big bang with the continuity of inflation faster then the metastable rate of decay. This is why thermodynamics is relevant viz., how new universes are apparently formed. I am unsure what you are suggesting though, Jorn, with the title and all...

Since we're talking cosmology, how can a universe that has expanded from a point explosion be anything other than a sphere, or at least spherish? How can a flat universe that started from a point 14,000,000,000 years ago be infinite?

And while we're on the subject, how can portions of the universe which were next to each other 14 billion years ago be more than 14 billion light-years apart now? I've looked up discussions of this and still can't figure it out.

My take, is that this type of Sci Fi is only mildly entertaining at best and doesn't even come close to the real thing, like The Twilight Zone. But it is a fun profession if someone is willing to fund it. Personally, I would rather the resources be spent on growing organic food for children.

Lacking anything interesting to present, and having lots of mouths to feed, science had become a never-ending series of fabricated stories.

how can a universe that has expanded from a point explosion be anything other than a sphere, — T Clark

It was not from a point but a volume of points. Or rather a volume of points changed their scale. They always had a size (and an energy density) from the start. Then that size expanded (and cooled).

And while we're on the subject, how can portions of the universe which were next to each other 14 billion years ago be more than 14 billion light-years apart now? — T Clark

If two of these "points" were to either side of us back then, they are now to either side of us today. So we all swell together.

Next question is "swelled into what?". We want to imagine a collection of swelling points as swelling within some further embedding space.

Imagine instead every point was some compacted tangle of thread. Expansion of the point is the thread being stretched out so that it takes up more room. Imagine a whole volume of such points untangling together and creating an expansion that is also now very sparsely occupied by any thread.

The Big Bang can only be understood if you see the way it is both an expansion and a cooling. So if you want some intuitive mental image, you have to supply an analogy that represent both parts of that "explosion".

... which, in turn, suggests that something is missing. — jorndoe

It doesn't feel like it makes a lot of sense talking about the initial conditions of the Big Bang as being either finite or infinite. Both alternatives feel metaphysically suspect. So something "beyond" these traditional choices may be needed.

What we know for sure is that the Big Bang did not start from just a single of Planck-scale point right at the beginning. And indeed, something like inflation is needed to guarantee that the initial region that "banged" was already humongously large.

But to then jump to that extent being "infinite" is a large assumption - if also a pretty natural one.

There are alternatives. The initial conditions could have been "infinite" yet finitely closed - like the surface of a sphere.

Or they could have been the opposite - open and "infinitely" finite in being utterly disconnected and hyperbolically curved at every point. So we might imagine a dust of points which are disconnected as they all curve away from each other with maximum energetic violence. They don't glue together to form a connected volume - a single actual space with shared dimensionality. And then the Big Bang is in fact the gluing together moment when the curvature (which physically would be the violent energy of the Planck density/temperature) started to connect and create a generalised flattening out.

Using the threads analogy, threads would start to connect to other threads and the whole "infinite" fabric would start to knit together and so share a common story concerning their stretching out and flattening out.

Perhaps something an established unification of relativity and quantum mechanics could shed light on? — jorndoe

Yep. That was what loop quantum gravity approaches were looking at. An emergent spacetime knit together out of the pure potential for a cooling~expanding interaction. We start with an "infinity" of points so hot that they can't even connect. Then everywhere there is a phase transition like water crystallising to ice. The points start to align everywhere, flattening out and tying together, to form our familiar cooling~expanding spacetime metric.

It was not from a point but a volume of points. Or rather a volume of points changed their scale. They always had a size (and an energy density) from the start. Then that size expanded (and cooled). — apokrisis

And you know this how?

This is what I mean, science has become simple story telling. Just make things up as required. Single point. Volume of points (what the heck is a volume of points?). Etc, etc., Etc. Everyone satisfied now that science has explained it?

And you know this how? — Rich

I was there. Saw it with my own eyes. Idiot.

what the heck is a volume of points? — Rich

A holographic quantum mind projection. Just without the "mind" part you like to add.

Exactly. Just story telling, subject to revision if someone around the camp fire asks a question. Spinning tales. And people get paid good money for conjuring up while ideas such as a "volume of points", that's contacting and cooling???? Contacting and cooling in what? Another universe?

Science fiction.

You sound like the kid who doesn't believe in Santa. And maybe you will never recover from the shock.

You sound like the parent trying to convince someone that Santa Clause is real. I suppose loop quantum gravity is suppose to give it the air of gravitas.

Whatever. If you want to be the eternal child, your choice.

I like good yarns, just don't care calling them science with the purpose of creating some high ground. A good yarn is just that. We'll call this the volume of points yarn. Science always had a story to tell, whether or not it is worth telling. Was this within .4 uncertainty?

I like good yarns, just don't care calling them science with the purpose of creating some high ground. A good yarn is just that. We'll call this the volume of points yarn. Science always had a story to tell, whether or not it is worth telling. Was this within .4 uncertainty? — Rich

This is a discussion of the most up-to-date consensus of the scientific community. Your beliefs, disbeliefs rather, are well known and you get plenty of opportunity to express them. That's a good thing. In this discussion you're just being disruptive and I wish you'd stop.

I l particularly love the .4 uncertainty part of it. I suppose everyone is suppose to kowtow to this nonsense. That is how it is perpetuated. That it comes from "science" is sad and a commentary on modern life.

I l particularly ove the .4 uncertainty part of it. I suppose everyone is suppose to kowtow to this nonsense. That is how it is perpetuated. — Rich

I'm a strong believer in people being able to have their say and I generally resist moderators getting involved, but I've flagged your post as harassment.

A strong believer in perpetuating nonsense.

But to then jump to that extent being "infinite" is a large assumption - if also a pretty natural one. — apokrisis

Thanks for your interesting response. When we say "infinite" do we mean infinite volume or infinite mass? Both? Or something else?

Thanks for the posts all.

I am unsure what you are suggesting though, Jorn, with the title and all... — TimeLine

It seems that, by current findings, big bang inflation + expansion does not account for the spatial extent of the universe.
Admittedly I haven't gone through the motions/calculations myself, but that was my thinking with the opening post.

how can portions of the universe which were next to each other 14 billion years ago be more than 14 billion light-years apart now? — T Clark

The light speed limit applies to mass, not to spatiotemporal geometry (while going by relativity).
So, big bang inflation + expansion itself has "carried" things apart at seemingly superluminal speeds, if you will.
(If that's what you meant.)

Anyway, the three references in the opening post taken together, seems to indicate that the big bang was sort of "localized" spatially.
Even if the spatial geometry is not quite flat, it's close enough to suggest a (much) larger extent than what might have come about over some 14 billion years.
Maybe you're up to par with the latest, @apokrisis?

When we say "infinite" do we mean infinite volume or infinite mass? Both? Or something else? — T Clark

It would be both. For those arguing for an actually infinite extent, it would be just as unexpanded at every point, and so just as maximally dense and hot at every point, hence just as massive or energetic in its "explosiveness".

But as I said, any such extrapolation from our rather classical view of the Universe - one in which distances and energies have some relative value - really becomes quite moot if we are talking about an initial conditions where there just is nothing for distance and energy to be relative too, as yet.

So the infinity of the initial conditions would have to be infinite in some more general sense that we aren't good at describing in classical terms. A theory of quantum gravity would probably help that ... if not rely on that kind of re-conceptualisation.

It seems that, by current findings, big bang inflation + expansion does not account for the spatial extent of the universe. — jorndoe

Inflation definitely does. But then inflation is hardly a proven story. And also inflation can produce as big a common starting point as you like. Just leave inflation running a few more ticks of the clock and you get exponentially more growth.

So inflation is a free parameter. You can just dial it up as much as you need.

Then the eternal inflation article you referenced is another story again. It presumes inflation keeps happening forever and keeps spawning an unlimited number of big bangs. Ours is just one infitesimal region of the inflation that has cooled and slowed enough to bud off. There would be an unlimited number of other similar universes being created.

So the eternal and infinite version of inflation depends on an inflation event that spawns an unlimited number of big bangs. Ordinary inflation says our Big Bang suddenly took off and inflated a split second after it was first born. It wasn’t born inflating, but then inflation came along to make the universe sufficiently big and ensure that any local wrinkles were smoothed out and make the whole thing look as if it started off as perfectly flat and thermalised as possible.

So either inflation is eternal and we are a spot that dropped out of its exponential rate expansion with no cooling, to be a Universe with a steady rate expansion and cooling. Or inflation kicked in just after the Big Bang for a split second, which would still be enough to stretch out and flatten spacetime as far as the eye could ever see.

It seems that, by current findings, big bang inflation + expansion does not account for the spatial extent of the universe. Admittedly I haven't gone through the motions/calculations myself, but that was my thinking with the opening post. — jorndoe

The idea in inflationary terms is that the total energy at the beginning was 0 where the negative contribution to the energy of the cosmic gravitational field - as in gravitational repulsion where the energy density produces these gravitational fields - cancels the energy of matter or the positive energy. Inflation thus becomes eternal because as mentioned earlier the matter is being created by the inflation but controlled by the non-uniformity. It would mean the pre-big bang would have been this singularity, where the big bang would occur and then inflation would drive exponential expansion and dark energy smooths the inflationary transition. There is no real answer as far as I know what the original value of omega actually is but inflation solves this problem as the universe is expanding faster and this exponential rate of expansion means that omega could be any number but that it will reach 1.

Einstein would agree that universe doesn't need to be Eucledean and why in general relativity cosmological constant can explain the flatness problem or the uniformity issue. Basically, if the universe is uniform or homogenous and cosmic microwave background is kind of proof of that, therein develops the geometric limitations and one of them is the flat universe. In general relativity, the flatness problem is calculated according to its mass density and critical mass density and this latter 'critical' or constant depends on universal inflation (that is, if the universe is flat (k=0) it is because inflation pushes omega to 1 (anything greater or smaller would make the universe curved or closed) and thus the curvature of the universe is being flattened by the expansion and this occurs a fraction of a moment after the big bang). The critical mass density makes the universe flat and the problem here is that pushing omega to 1 is actually unstable and it needs to be exactly 1 and even being off infinitesimally would mean that we would probably experience a crunch or infinity or basically there wouldnt be a universe, the conditions would not have allowed it.

The paper you have attached attempts to measure the universe as finite and this could be a problem with the big bang because it started with chaos and eventually smoothened that may contradict the second law. But, if we assume the big bang occurred as a ‘fluctuation’ and therefore an addition within one meta-system where there are a number of universes, this somehow resolves our problem (well, in a way). Have you heard about the possible reversibility of statistical thermodynamics with mirror universes where time can move both forward and backward? So cool.

how can a universe that has expanded from a point explosion be anything other than a sphere, — T Clark

It was not from a point but a volume of points. Or rather a volume of points changed their scale. They always had a size (and an energy density) from the start. Then that size expanded (and cooled). — apokrisis

Depending on the mass density, it could force omega > 1 and would therefore make the universe a closed system like a sphere or reduce omega < 1 and therefore the curvature would open and this is problematic viz., euclidean geometry. Flatness problem is when the geometry is a 1 exactly and perfectly between the two.

You will have to explain why your comment makes any difference to my comment.

Observation says the geometry is almost perfectly flat with just enough hyperbolic curvature to count against any gravitational collapse (and so any reheating of the universe and its contents).

Thus I don’t understand what you are getting at here.

How is it that you don't understand and yet claim that it is no different to your comment?

Huh? You do write weird. I asked what difference did your comment make. I did not say your comment was no different. So I was saying your comment was a non sequitur as far as I could see as it did not follow from mine in any useful or relevant fashion.

But if you think it did qualify my remarks in some meaningful fashion, could you explain in what way.

You say:

You will have to explain why your comment makes any difference to my comment. — apokrisis

And then:

I asked what difference did your comment make. I did not say your comment was no different. — apokrisis

And I write weird? I think you are intentionally being dramatic because if now, apparently, you claim that my comment was a non sequitur as far as you could see it, where, exactly? I think you just want all the glory or something, hence why you are trying to answer questions directed to me. Alright, if you want to be ungenerous, let's do this.

What we know for sure is that the Big Bang did not start from just a single of Planck-scale point right at the beginning. And indeed, something like inflation is needed to guarantee that the initial region that "banged" was already humongously large. — apokrisis

Since we're talking non sequiturs, what is this "humongously" large you are speaking of? What are you comparing it to, exactly? Your shape and size of the universe is the observable universe of 46gly from earth and just to help ameliorate your understanding, the singularity - whilst it does not reference a single planck point - is a physically impossible point that we use to explain how the universe came to be. So the assumption is that the early conditions were infinitely dense at the size of 10^-28cm (with energies at 10^16 GeV) and that would mean that anything larger or smaller would blow the universe apart or suck it away.

So the eternal and infinite version of inflation depends on an inflation event that spawns an unlimited number of big bangs. Ordinary inflation says our Big Bang suddenly took off and inflated a split second after it was first born. It wasn’t born inflating, but then inflation came along to make the universe sufficiently big and ensure that any local wrinkles were smoothed out and make the whole thing look as if it started off as perfectly flat and thermalised as possible. — apokrisis

What? First of all, inflation is pushing omega to 1 and the asymptotic curvature would therefore be flattened by the expansion, thus the curvature would equal 0 or at least be very close to 0 and this would cause infinite expansion. The symmetry between these points is explained by fluctuations in the anisotropy of the cosmic microwave background and so the universe is isotropic and homogenous; the best way to explain thermal equilibrium (actually the only as far as I know) is inflation.

I think you just want all the glory or something, hence why you are trying to answer questions directed to me. — TimeLine

My goodness. Is that what it is about? Hilarious.

Your shape and size of the universe is the observable universe of 46gly from earth and just to help ameliorate your understanding, the singularity - whilst it does not reference a single planck point - is a physically impossible point that we use to explain how the universe came to be. So the assumption is that the early conditions were infinitely dense at the size of 10^-28cm (with energies at 10^16 GeV) and that would mean that anything larger or smaller would blow the universe apart or suck it away — TimeLine

Who mentioned singularities? I didn’t. And what is the relevance of a length scale 100,000x the Planck length? I’m not following you at all. This is another series of irrelevancies.

What? First of all, inflation is pushing omega to 1 and the asymptotic curvature would therefore be flattened by the expansion, thus the curvature would equal 0 or at least be very close to 0 and this would cause infinite expansion. The symmetry between these points is explained by fluctuations in the anisotropy of the cosmic microwave background and so the universe is isotropic and homogenous; the best way to explain thermal equilibrium (actually the only as far as I know) is inflation. — TimeLine

Inflation doesn’t have to balance the kinetics of its expansion with its gravitational attraction. So an Omega balance is irrelevant. Inflation is about a scalar field that stays the same energy density while expanding exponentially. Repulsion dominates and gravity is simply impotent.

You are mixing up quite different things.

Who mention singularities? I didn’t. And what is the relevance of a length scale 100,000x the Planck length? I’m not following you at all. This is another series of irrelevancies. — apokrisis

To speak in your language, I mention singularities. Let's return back to the problem, shall we. What is this "humongously" large you are speaking of? What are you comparing it to, exactly?

Inflation doesn’t have to balance the kinetics of its expansion with its gravitational attraction. So an Omega balance is irrelevant. Inflation is about a scalar field that stays the same energy density while expanding exponentially. Repulsion dominates and gravity is simply impotent. — apokrisis

Omega is irrelevant? Friedman just rolled in his grave. >:O We are talking about the universe right and all start at Einstein-de Sitter points. I already know that inflation is about the physics of scalar fields and matter, the particles that make up the universe following the initial phase of inflation are the quantum representation of Higgs fields. The problem though is not that the emergence of elementary particle masses that contains both positive and negative contributions together with a constant value at every space time point, because that is only attempting to explain quantum density fluctuations in scalar fields as a source of temperature anisotropies in CMB radiation. It ends at the de-sitter dSn point. If inflation is pushing omega to 1 with omega being the mass density divided by critical mass density, it means a universe with 0 matter density and critical mass density in the cosmological constant; the expansion of the universe is accelerating and the vacuum energy of this empty space has a mass density (which would mean that it is not actually empty). So Omega is relevant.

Sorry. Your post is a torrent of incoherence. I can’t be arsed untangling it for you.

This might help you.

Whoah, you are a cranky one. But really, your posts on cosmology are a garbled mess. And being polite to you was clearly wasted breath.