B Did the Big Bang follow multiple bangs? How did matter come to collide?

[jbriggs444]

I guess my post and phinds' reply are invisible unless I'm logged in. I'm replying to the latter.

I linked to CERN's page, where it says, at the top: "All matter in the universe was formed in one explosive event 13.7 billion years ago – the Big Bang".

One definition of an "explosion" is simply a 'rapid expansion'.

I read the whole. Thanks for your self-correction. I'll check the website page at home.

That article (https://home.cern/science/physics/early-universe) is pop sci. The headline sentence: you quote above is simply incorrect. It is a story for children.

To be fair, it is about as good as one can get in 18 words.

 

[Nick Levinson]

I don't think I'm qualified to tell CERN that. They don't seem to classify the page that way, so it's not like I should have avoided it.

Even explanations for children can be accurate, albeit often not also deep.

 

[jbriggs444]

I don't think I'm qualified to tell CERN that. They don't seem to classify the page that way, so it's not like I should have avoided it.

Even explanations for children can be accurate, albeit often not also deep.

Nobody is asking you to tell CERN that their page is bad. We're asking you to take it for what it is -- pop sci. Not a scholarly article. And not textbook material. Not suitable reference material for use here.

 

[phinds]

I don't think I'm qualified to tell CERN that. They don't seem to classify the page that way, so it's not like I should have avoided it.

Until you know enough to be able to distinguish between actual science and pop-sci presentations (even by reputable sources) you are going to have a hard time learning science. For example, perfectly reputable and knowledgeable scientists will make statements on pop-sci TV shows that they KNOW are gross over-simplifications and are statements that would get them laughed out of the room at any meeting of actual scientists. Why do they do that? In order to interest people in science, and because pop-sci presentations by their very nature do not have / make the time to do in-depth discussions, which would anyway likely involve actual math with is anathema to them.

You should mostly assume that unless it's from a textbook or from a refereed journal, it's pop-sci. Statements by folks here on PF are not guaranteed to be right but I can assure you that they are WAY more likely to be correct than pop-sci presentations, and you should get used to that.

 

[Ibix]

A singularity is a geometric description once it includes volume and density unless readers are intent on destroying even the concept of volume as geometry.

My understanding is that singularities are not part of the manifold, so it's somewhat questionable whether they are geometric objects or not. And, as has been pointed out before on this thread, the presence of singularities in the maths does not imply the presence of singularities in reality. Indeed, the usual interpretation of the singularity is that the model is telling us it doesn't work in regimes "near" the singularity.

If infinite density/zero volume is considered a valid geometric principle then so is its obverse - infinite volume/zero density which effectively is a self-defeating elaboration of the description of 'nothing'.

I am at a total loss to understand what you are trying to convey here. If infinity exists, so must zero? Or something like that?

They can also tell me what longitude meridian the North pole is in - all of thems or none of them ?.

That's the point of a singularity. The model you are using doesn't work there. At the pole you can fix that by using a different coordinate system. In GR, we don't know how to fix it yet.

And you still aren't defining anything. You are just pasting in quotations about the history of astronomy and making vague pronouncements.

 

[PeterDonis]

A singularity can contain a whole lot of things

No, it can't. A singularity can't "contain" anything since it's not part of the manifold at all.

 

[DaveC426913]

No, it can't. A singularity can't "contain" anything since it's not part of the manifold at all.

OK, I was sloppy.

Oriel was suggesting a singularity** is "nothing".

The singularity at the centre of a black hole is beyond our current physics, yet the mass of the BH is in there and is felt outside the BH.

So that's not nothing; it's simply physics we can't model yet.

** there may be a nuance here, between 'Big Bang singularity' and 'BH singularity' that has slipped through the cracks.

(*see sig line)

 

[PeterDonis]

Oriel was suggesting a singularity** is "nothing".

I'm not sure his suggestions were even that coherent. But in any case, he is no longer posting and his posts do not require any further response.

The singularity at the centre of a black hole is beyond our current physics, yet the mass of the BH is in there

No, it isn't. The mass of the black hole is a geometric property of the spacetime. It is not located at any particular place.

Furthermore, the singularity (both inside a black hole and at the beginning of idealized FRW models in cosmology) is not a "place". It's spacelike, so it's a moment of time. So it's not the kind of thing mass, or anything else, can be located at.

it's simply physics we can't model yet

This is pretty much the current mainstream opinion, yes. But it should not be confused with other statements about singularities that are misconceptions, which I have tried to clear up.

 

[Nick Levinson]

@phinds:

Yes, but I don't have a TV and (Covid-19 era aside) I read books by scientists, not just science writers. A book that's 200-300 pages tends to have more depth than a 30-minute TV show. A book is for a more selective audience. TV is for the millions, averaged.

A trap is in judging the quality of a source by its conclusions. Sometimes, yes, choosing what we agree with can be informative. But better to rely on agreement with starting points and logic; but that's more difficult.

Math is anathema to most lay readers, so editors counsel scientists away from it, too often for my taste.

Undergraduate and graduate texts tend not to be available in public libraries. One librarian said if they buy them they tend to get questioned by management, apparently because school libraries get them, so it would be duplicative. I think they're also more expensive and perhaps get stolen more. Interlibrary loan can get them but with more limited renewals; and my local library won't spend more than $15 to borrow an ILL book, so nothing can come from Harvard etc.

 

[shjacks45]

I blame string theory. Something happened in the 6 dimensions we can't see.

 

[shjacks45]

@phinds:

Yes, but I don't have a TV and (Covid-19 era aside) I read books by scientists, not just science writers. A book that's 200-300 pages tends to have more depth than a 30-minute TV show. A book is for a more selective audience. TV is for the millions, averaged.

A trap is in judging the quality of a source by its conclusions. Sometimes, yes, choosing what we agree with can be informative. But better to rely on agreement with starting points and logic; but that's more difficult.

Math is anathema to most lay readers, so editors counsel scientists away from it, too often for my taste.

Undergraduate and graduate texts tend not to be available in public libraries. One librarian said if they buy them they tend to get questioned by management, apparently because school libraries get them, so it would be duplicative. I think they're also more expensive and perhaps get stolen more. Interlibrary loan can get them but with more limited renewals; and my local library won't spend more than $15 to borrow an ILL book, so nothing can come from Harvard etc.

Feyneman Lecture Notes on Physics is one of the best. I believe its a free download from an archive.

 

[shjacks45]

Hang on.

A singularity can contain a whole lot of things in large amounts. Mass for example. That's not nothing.

And it's not the same thing as infinite.

No. It is the equation that defines the the singularity that includes the mass. Take a neutron, it has a location as a point. The point is defined by the neuton's wave function and interacts at action potential, based on that wavefunction, with other particles. Most atoms have an interaction area with neutrons by a few barns (an area measure), but 10Boron is 9000 barns and 157Gadolinium is 254,000 barns. Mass whose representation is gravity, but gravity is not a force, it is a field. It is the efect of mass warping space-time. We assume that mass pre-blackhole collapsed in a singularity. But the only thing we can observe is effects in the event horizon. Any conjectures as to the effects of a black hole is to the other 6 dimensions of string theory?

 

[PeterDonis]

Take a neutron, it has a location as a point. The point is defined by the neuton's wave function

This is not correct. The neutron's wave function does not define a single point location for the neutron; such a wave function, while it can be modeled mathematically, is not physically realizable. A physically realizable wave function will define a wave packet, which does not define a single location.

 

[Nick Levinson]

@phinds:

Thank you for the links. The authorship is sound. They state more than I can absorb anytime soon, but that's fine, and there's not much that authors can do about it, intellectually. Simply making them briefer leads to more questions. An unexplained term can be looked up. While I hesitate to read science publications older than 10 years unless I know enough of what's newer to recognize what's out of date, maybe space sciences can tolerate a longer period; 10 is somewhat arbitrary on my part.

If you have time to update your page: The page needing Java won't work anymore in many well-known browsers, but the rest of the page is interesting, so may be citable without the Java. A dead link can be replaced with one to the Wayback Machine (archive.org) if you don't mind that the author no longer maintains the page; this applies to the 2-page URL and to the primer.

@Motore: Re my last post being smiley-marked for skepticism: I wish I knew what you're skeptical about; then I could respond.