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

[Nick Levinson]

TL;DR

The Big Bang theory did not preclude prior big bangs; still so? Must ejecta have traveled along radii from one center? If so, how could they collide later?

I understand that the Big Bang was an explosion from an extremely tiny mass with particles and quanta traveling away into empty space (anything out there at the instant of this bang being too far to hit yet). I also understand that some ejecta from the Big Bang have been colliding since then.

The mental image I have is of a sphere exploding once and so that every particle or quantum travels along a radius from the center of the original sphere. However, that would mean that the particles and quanta, once ejected, could never collide with each other.

But since they do, something's wrong with my mental image. What am I getting wrong? For example, were there multiple explosions over time? By analogy to an unlikely scale, could it be that the original mass was like a basketball that exploded producing golf balls with some golf balls exploding later so that quanta from one golf ball flew into quanta from another golf ball? Multiple explosions separated by time would support multiple centers for the radii of travel.

Or was some precollision travel nonradial? If, with a single-explosion model, not all radii used for travel had to be equidistant from each other, could gravitational effects have differed allowing unequal attraction between traveling particles? If so, do we have any idea what caused the unequal distribution of radii used as travel routes?

Or did the universe have something like a ceiling that some particles or quanta reached or approached with the ceiling-like structure causing them to bounce or otherwise be redirected back into the thus-bounded universe?

Or is the explanation for the collisions something else?

 

[phinds]

Must ejecta have traveled along radii from one center? If so, how could they collide later?

This is perhaps the most common misconception in science, promulgated by popular science presentation. There was no explosion from a central point. There is no center.

I understand that the Big Bang was an explosion from an extremely tiny mass with particles and quanta traveling away into empty space (anything out there at the instant of this bang being too far to hit yet).

Again, it is unfortunate that you "understand" this since it is totally wrong.

 

[diogenesNY]

Have a look at this:

http://pages.erau.edu/~reynodb2/LineweaverDavis_BigBang_SciAm_March05p36.pdf

same thing - another link - from Lineweaver's personal site

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdfIt is an article by Charles Lineweaver and Tamara Davis entitled 'Misconceptions About the Big Bang' and appeared in _Scientific American_ magazine. It is very lucid and readable and should not only answer your questions but give a pretty good thumbnail on the whole big bang subject from two exceedingly credible authors.

Lineweaver's Web Page: http://www.mso.anu.edu.au/~charley/

--diogenesNY

 

[Nick Levinson]

Describing the Big Bang as an explosion is not unreasonable (https://home.cern/science/physics/early-universe (as accessed 11-13-20)) albeit as an explosion of space itself and not of a object made of matter within space.

The SciAm article made good reading, clearer than some explanations I've seen, and useful in revising past teachings I had learned. I'm still not clear on what it is that space is expanding inside of (maybe there are two kinds of space and one encloses the other?), but that's for another time.

Analogies are popular, but maybe they're too easily misunderstood. The universe is often compared to a balloon, so, when it's said that the universe has no center, this seems to conflict with the idea of a balloon, which has a center, at least if we're perceiving three spatial dimensions (sometimes people talk of only two) and if it's spherical. A balloon shaped like a Dachshund I guess has a center although calculating its location might be a challenge, and it might be a line segment or an arc rather than a point.

Thank you.

 

[phinds]

The universe is often compared to a balloon, so, when it's said that the universe has no center, this seems to conflict with the idea of a balloon ..

Only by people who completely misunderstand the balloon analogy. I recommend the link in my signature

 

[phinds]

Describing the Big Bang as an explosion is not unreasonable

Actually, yes it is. An "explosion" is pretty much by definition something happens at a single point in space. The early universe could well have been infinite in extent but whatever size it was, it didn't have a center, so "explosion" is a very bad description and leads to obvious fallacies in thinking about the universe.

 

[DaveC426913]

Actually, yes it is. An "explosion" is pretty much by definition something happens at a single point in space.

Not to mention a litany of other ways "explosion" is a misleading mechanic.

For example: an explosion results in end-products following ballistic motion - i.e,: it is propulsive only occurring during the initial process, with no further impetus thereafter.

This leads to a lot of naive questions about how - with the extreme gravitational gradient during the BB - matter could have expanded at all. (i.e.: Q:"Why wouldn't all that "exploding" matter just collapse back on itself?")

 

[Bandersnatch]

For example: an explosion results in end-products following ballistic motion - i.e,: it is propulsive only occurring during the initial process, with no further impetus thereafter.

Ah, but this particular bit is a correct intuition for expansions without dark energy or in epochs when the effects of dark energy are negligible. In those cases, there's only the initial impetus followed by deceleration. Recollapse is possible if density of the universe is over critical, and the degree to which it exceeds critical density determines how early recollapse occurs. So the reason for why the early universe didn't collapse on itself is not there being some additional force pushing it apart - it's just that the density was not high enough.

 

[phinds]

So the reason for why the early universe didn't collapse on itself is not there being some additional force pushing it apart - it's just that the density was not high enough.

No, the energy density was irrelevant. What mattered was the UNIFORMITY of the matter throughout. There was no place that was more dense than any other (to any significant degree at all) so there was nowhere to collapse toward. The energy density could have been enormous and there still would have been no collapse.

 

[trees and plants]

Perhaps popular science books should be more helpful and not lead to wrong views? Because i know that it was a spacetime singularity at t=0 and a manifold could not be formed but i thought it was an explosion. So it was not or we do not know?

About the question the person who made the thread, how much work has been done to describe how after the Planck time our solar system and galaxies were formed?

 

[phinds]

... but i thought it was an explosion. So it was not or we do not know?

We know conclusively that it was not an explosion. An exposion implies a center and there was none. It also implies an outer edge to the "explosion" and there is none (that is, the universe has no edge). I recommend the link in my signature.

...how much work has been done to describe how after the Planck time our solar system and galaxies were formed?

THAT is exactly what the Big Bang Theory IS ... a description of the evolution of the universe AFTER the singularity (which, itself, is not part of the big bang theory). SO ... lots of work. That doesn't mean we have all the answers but scientists have been working on it for at least in all the decades Since Hubble's discovery of the expansion led to the understanding that everything was a lot closer together in the past.

 

[trees and plants]

We know conclusively that it was not an explosion. An exposion implies a center and there was none. It also implies an outer edge to the "explosion" and there is none (that is, the universe has no edge). I recommend the link in my signature.

THAT is exactly what the Big Bang Theory IS ... a description of the evolution of the universe AFTER the singularity (which, itself, is not part of the big bang theory). SO ... lots of work. That doesn't mean we have all the answers but scientists have been working on it for at least in all the decades Since Hubble's discovery of the expansion led to the understanding that everything was a lot closer together in the past.

Thank you very much about the link, now I corrected the wrong views i had about cosmology.

 

[trees and plants]

If i understand correctly, the coherent galaxies in the observable universe do not expand, but the space of the observable universe expands and galaxies which are close to the "boundary" of it are expanding?

 

[phinds]

If i understand correctly, the coherent galaxies in the observable universe do not expand, but the space of the observable universe expands and galaxies which are close to the "boundary" of it are expanding?

Galactic CLUSTERS do not expand, nor does anything smaller such as galaxies, stars, planets, you, me, atoms, etc.

Galaxies at the outer reaches of the observable universe act no differently than those anywhere else. As far as those galaxies are concerned, each of THEM is at the center of the observable universe.

 

[Bandersnatch]

No, the energy density was irrelevant. What mattered was the UNIFORMITY of the matter throughout. There was no place that was more dense than any other (to any significant degree at all) so there was nowhere to collapse toward. The energy density could have been enormous and there still would have been no collapse.

That's not correct. Look at how the critical energy density is defined in our universe.

 

[phinds]

That's not correct. Look at how the critical energy density is defined in our universe.

OK, but I though that the energy density of the very early universe was MUCH greater than the critical density but expansion prevented collapse.

I DO see that my argument that the lack of a place to contract TOWARDS is meaningful is incorrect. The contraction of the entire universe is not towards anything, it's just an overall contraction. Thanks for correcting my misunderstanding. I should have never made that mistake in my logic since I do know that the expansion is not towards anything (and thus contraction would not be towards anything)

 

[happyhacker]

Oh wouldn't it have been easier if Genesis had given a little more detail and not just 'without form or void'?
Really though it blows my mind.Reading diogenesNY reference seems to be saying 'abracadabra'! So what does it mean in terms of the appearance of matter?

 

[phinds]

Really though it blows my mind. How important is it?

How important is WHAT? All of modern cosmology?

 

[phinds]

Really though it blows my mind.Reading diogenesNY reference seems to be saying 'abracadabra'! So what does it mean in terms of the appearance of matter?

You went back and changed your question after I had already asked you about your question. Bad form here on PF to do that.

My question still stands. What is/was it that you were asking about the importance of?

 

[happyhacker]

You went back and changed your question after I had already asked you about your question. Bad form here on PF to do that.

My question still stands. What is/was it that you were asking about the importance of?

Oh, right. Apologies. Point taken. Did not know a reply came through in that short time.

 

[phinds]

Oh, right. Apologies. Point taken. Did not know a reply came through in that short time.

Yeah, we all get hit with that sometimes, particularly when composing a long response --- it will often happen that by the time you post, another post or posts has appeared before your post actually registers.

BUT ... you still haven't answered my question

 

[weirdoguy]

I'm still not clear on what it is that space is expanding inside of

It does not have to expand inside of anything, you just have to properly understand what expansion means in this context. And it means that distance between two gravitationally non-bound objects grows with (standard cosmic) time. No "creation of space" or other weird things you read in a lot of pop-sci sources.

 

[happyhacker]

It does not have to expand inside of anything, you just have to properly understand what expansion means in this context. And it means that distance between two gravitationally non-bound objects grows with (standard cosmic) time. No "creation of space" or other weird things you read in a lot of pop-sci sources.

Well I read it again and still confused (is the Big Bang a bad term?)! So are we saying that we need a point in time when everything we observe (e.g. in Space) suddenly came into existence or (inconceivable to us?) was it already there and we just need a time zero for some reason? I must be conceptually challenged here.

 

[phinds]

"Big Bang" was first stated as a derisory term by Fred Hoyle to describe a theory that he thought ridiculous. Unfortunately, the term caught on. Yes, it is a terrible term to use to describe something that was not an explosion in the normal sense.

The Big Bang theory says nothing whatsoever regarding the beginnings of the universe, it is simply a description of the evolution of the universe after the period of inflation (which itself is not a known fact but is generally considered to be true).

 

[jbriggs444]

Well I read it again and still confused (is the Big Bang a bad term?)! So are we saying that we need a point in time when everything we observe (e.g. in Space) suddenly came into existence or (inconceivable to us?) was it already there and we just need a time zero for some reason? I must be conceptually challenged here.

The Big Bang model does not extend to cover a "creation event" where the universe went from nothing to a singular point. Nor does it cover a transition from a singularity to a rapidly expanding hot, dense cloud.

In general, models of the sort we normally use (manifolds) do not include singularities as part of the manifold. Manifolds are based on open sets. Think of them like open intervals -- like the interval from 0 to 1, exclusive. The point 0 is not part of the interval. The transition from outside the interval to inside the interval is not part of the interval. Every event in space-time is surrounded by other events in space-time. No events are exactly at an edge.

In General Relativity, time itself is part of the geometry of the universe. Asking about what happened at a time before the creation of time is contradictory.

The Big Bang model actually starts well after the "time zero" for a hypothetical, extrapolated initial singularity. It starts in a hot, dense, rapidly expanding state and does not attempt to describe any creation event.

 

[DaveC426913]

As an astronomer (not an astrophysicist), a singularity is just an elaborate way to describe 'nothing'.

Infinite density/zero volume is just as valid as infinite volume/zero density therefore a 'singularity is a geometric non-starter. If the former is allowed within a geometric spectrum then so is the latter.

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.

 

[Bandersnatch]

OK, but I though that the energy density of the very early universe was MUCH greater than the critical density but expansion prevented collapse.

Critical density is a function of the expansion rate (H). The density of the early universe was of course much greater. But so was H, and hence so was the critical density. For a given universe, the critical density falls (or rises, if collapsing) in lock step with changing density as the universe expands. Just as (by analogy with ballistic motion) escape velocity becomes smaller as a thrown body climbs out of a gravity well.
But in both cases you only have to sample the state of the system at anyone time and find out whether the density is higher than critical, or the velocity is higher than escape V, to know whether the universe will recollapse/thrown body will fall back down. It can never* be the case that you throw a body with V<escape V, and it'll exceed escape V at some point in the trajectory. Just as it can never be the case that the universe was over critical density but then evolved into below critical density.

*with the usual caveats of unpowered throw, central fixed gravity field, etc.

 

[Nick Levinson]

@phinds: If it's unreasonable, did someone tell CERN? Evidently, a lot of this field is grounded in math and observation so that even the most reliable narrative explanations are one step removed from the fundamental knowledge and apparently are a bit less reliable than the math and the observations.

@phinds: Either the forum doesn't show me your signature or it does but without a link. Maybe you meant one found through your profile page, Inflation Balloon Analogy Misconceptions. I read it now and, although it's unsourced, I'm glad I read it and I see what you're saying. Being unsourced is an important caveat; there's been criticism on this forum of my reading pop sci even though I avoid it, and your article qualifies as that; it should cite sources or at least bibliograph a few key sources. One point: I've read that a fly landing on the middle of a 12"-long steel rod (thickness forgotten) held at the ends depresses the landing spot, and that's plausible, so it's plausible that, all else equal, an ant would have a similar effect on a house, albeit only if the house was solidly built and granted that determining whether all else is equal is likely beyond our technological capabilities. And, no, it cannot "overcome the forces that keep the house on its foundations", but breaking that bond requires more than the most motivated ant can deliver, whereas if all we want is for the ant to have "an effect", and can accept that an effect even if too tiny for us to measure is possible, the ant can have that and likely does.

@weirdoguy: I try to avoid pop sci and statements of the just-believe-this variety without a logical underpinning. Some explanations come from scholars. Even so, at the level of narratives, scholars sometimes disagree with each other, and that won't be resolved in 500 words.

 

[phinds]

@phinds: If it's unreasonable, did someone tell CERN?

I am QUITE confident that the scientists at CERN don't believe that the universe started with an explosion. If you think otherwise, I assure you you are misunderstanding something.

@phinds: Either the forum doesn't show me your signature or it does but without a link.

Hm ... maybe you have to hover the mouse over it. It IS pretty indistinct until you hover over it.

Maybe you meant one found through your profile page, Inflation Balloon Analogy Misconceptions.

Yes, that's the one

... your article ... should cite sources

It was written for PF with the express help of a number of PF mentors.

or at least bibliograph a few key sources.

I take it you didn't read the whole article and get to the bottom where there IS a short list of references. OOPS ... my bad. The ORIGINAL link, which points to my own website DOES have a list of references. Here: http://www.phinds.com/balloonanalogy/

 

[Nick Levinson]

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.