The Duration of the Big Bang: Exploding Myths and Misconceptions

[OCR]

If the Big Bang had happened at different times in different parts of the universe, that would not be the case.

Huh ?

 

[PeterDonis]

Then I am not seeing how it is a remnant of the Big Bang.

It's a remnant of the process that started with the Big Bang, and it gives us information about that process, including how it started. See further comments below.

From what I understand the B.B. produced a universe that was huge in less than a second.

Define "huge". Usually the various phases of the process are described in terms of the density or temperature, not the "size of the universe" (which is something of a misnomer in any case, since according to our current best model the universe is spatially infinite).

it sounds to me that some believe the CMB was created by recombination and that recombination occurred as much as 378,000 years after the B.B.

This isn't something that "some believe"; it's part of the standard model of cosmology. But, as I said above, recombination is part of the process that started with the Big Bang, and the CMB, by giving us information about recombination--when it happened and how evenly it happened everywhere in the universe--gives us information about the process that led to it. Once again: if the Big Bang had happened at different times in different parts of the universe, then recombination would have happened at different times in different parts of the universe, and the CMB would not have the same redshift and other characteristics in all directions.

That would mean that the cause of the CMB was already distributed in every direction and so it would not be subject to red shift resulting from the expansion of the B.B. itself.

I don't understand what you mean by this.

It took hundreds of thousands of years for the first, simplest element, -hydrogen, -to form.

No, it took hundreds of thousands of years for atoms of hydrogen to form--in other words, for the universe to become cool enough that, when electrons combined with nuclei to form atoms, the atoms didn't immediately get blasted apart again by radiation. But hydrogen nuclei were formed in the first few minutes after the Big Bang, along with the nuclei of a few other light elements. (Protons, btw, are hydrogen-1 nuclei; but nuclei of hydrogen-2/deuterium, helium-3, helium-4, and lithium-7 were also formed in the first few minutes.)

 

[PeterDonis]

Huh ?

I'm responding to Dave Eagan's question, "how do we know the Big Bang happened everywhere at once?" In order to respond to that, I have to consider the possibility that it didn't, and show how that would lead to predictions that are contrary to our observations.

 

[Dave Eagan]

Let's review my original question. I asked how we know that the B.B. "happened everywhere at once", and the answer given was that the CMB is uniform in all directions with no red shift.

Peter, you said

the CMB was produced a few hundred thousand years after the Big Bang

Before that, however (if I have it right), nucleosynthesis, which happened just minutes after the B.B., created atomic nuclei (protons). About 378,000 years later those nuclei became bound to electrons, forming hydrogen atoms.

You also said that recombination is part of the process that started with the Big Bang. Ummm, well, of course it is, as is everything else. So I don't find that adding to my understanding yet.

I assume that since such processes as electrons changing their position around nuclei and bonding with protons to form atoms involves a release of energy, that it may be this bonding that produced the CMB. Could it be that I'm right?

If the CMB originated almost 400,000 years after the B.B. and it originated when electrons became bound to protons to form hydrogen atoms, by then the universe had expanded how many lightyears? I don't have that info handy but the number was significant, and so at that point the generation of radiation from the event of electrons bonding to protons would have happened "everywhere at once" it would seem since the universe was already so large. Plus, radiation generated by one electron bonding to one proton would be an event in a point in space in an instant of time. Hence there would be no red shift since the source is not continually emitting radiation as it moves.

Realize that I came here to get answers from people who know this stuff much better than I do, and the best way I can find to get you to understand my question (since I'm not up to speed on correct terminology) is to express what I can imagine to be "reasonable explanations" so that you can correct my errors and assumptions. This would, I hope, help you to avoid answering a question I didn't ask due to a misunderstanding of where my confusion lies.

Thanks.

 

[phinds]

To address a few of your points:

... then the universe had expanded how many lightyears?

This is not a meaningful question. The universe does not expand by lightyears, it expands at a rate. Things move apart and if you can identify two objects, then it is valid to ask how many lightyears apart they have moved.

... it would seem since the universe was already so large.

Size is not necessarily meaningful since it may have been infinite to start and thus infinite at every point in time since then.

Plus, radiation generated by one electron bonding to one proton would be an event in a point in space in an instant of time. Hence there would be no red shift since the source is not continually emitting radiation as it moves.

This is a misunderstanding. Of course there would be red shift. Ref shift due to cosmological expansion has nothing to do with the movement of the source after a photon is emitted, it has to do with the fact that the space through which the photon travels is expanding.

 

[Dave Eagan]

Well, I'm reading elsewhere and finding that I'm getting more confused. It seems what I'm reading contradicts itself and the explanations aren't chronologically sequenced.

This doesn’t make sense to me... http://cosmictimes.gsfc.nasa.gov/online_edition/1993Cosmic/inflation.html
“Inflation Theory explains . . . that shortly after the Big Bang, the universe expanded tremendously in a very short amount of time. This expansion grew the size of the universe from submicroscopic to the size of a golf ball in 10-35 seconds. Thus, regions once in contact with each other are now far apart in the universe.”

An inch and a half? But wait! There's more ...

“As space expanded, the universe cooled and matter formed, and then protons and neutrons formed.”

Pardon me, but matter is protons and neutrons . . . and electrons, etc. So what’s this “and then” business? Cart before the horse?

Once again, the source of the CMB is recombination? In layman's terms, the CMB is the energy released when atoms are formed from free charged protons and electrons? If so, the energy released from one such event would be identical to the energy released from every such event. So I'm having trouble being excited or surprised by the fact that the CMB is uniform.

 

[Dave Eagan]

"Ref shift due to cosmological expansion has nothing to do with the movement of the source after a photon is emitted, it has to do with the fact that the space through which the photon travels is expanding."

And yet red shift is an effect of movement of an object away from the observer.

 

[phinds]

To address just one of your questions:

An inch and a half?

Yes. That's the observable universe. You need to familiarize yourself with
o the term "universe"
o the term "observable universe"
o the fact that many people say "universe" when they mean "observable universe", which leads to confusion

 

[phinds]

And yet red shift is an effect of movement of an object away from the observer.

Only in the sense that recession is a form of objects moving away from each other, but this is not proper motion. You need to study the difference between recession and proper motion. Google "metric expansion"

 

[OCR]

In order to respond to that, I have to consider the possibility that it didn't, and show how that would lead to predictions that are contrary to our observations.

Gotcha... carry on.

 

[Drakkith]

“As space expanded, the universe cooled and matter formed, and then protons and neutrons formed.”

Pardon me, but matter is protons and neutrons . . . and electrons, etc. So what’s this “and then” business? Cart before the horse?

I believe they are using the term matter to mean high-mass exotic particles such as several different types of quarks, mesons, and other particles that have very short lifetimes and decay very quickly. When the universe was very young, it was so hot that these particles were being created and destroyed all the time. One the temperature dropped past a certain critical point they could no longer be created, so the number of existing high-mass particles quickly dropped to essentially zero via decay. Part of this decay process led to the creation of lower-mass particles such as protons, neutrons, and electrons which cannot decay since they have nothing to decay into (assuming the neutrons are bound to the protons. If not, they decay to protons in about fifteen minutes).

Once again, the source of the CMB is recombination? In layman's terms, the CMB is the energy released when atoms are formed from free charged protons and electrons? If so, the energy released from one such event would be identical to the energy released from every such event. So I'm having trouble being excited or surprised by the fact that the CMB is uniform.

If the CMB were purely the result of recombination, then the CMB would be just a few discrete wavelengths corresponding to the energy levels of the hydrogen atom. Instead, the CMB is a broad-spectrum signal between about 0.3 to 630 GHz created by the thermal motion of the plasma at the time of recombination. What recombination did was to suddenly turn the universe transparent to most EM radiation, allowing this thermal radiation to begin traversing the universe instead of being absorbed right after emission.

http://hypertextbook.com/facts/2004/HeatherFriedberg.shtml

 

[PeterDonis]

Before that, however (if I have it right), nucleosynthesis, which happened just minutes after the B.B., created atomic nuclei (protons).

Protons were created earlier, when the temperature became low enough for quarks to form bound states (protons and neutrons). What happened during nucleosynthesis was that protons and neutrons combined into light nuclei--hydrogen-2 (deuterium), helium-3, helium-4, and lithium-7.

I assume that since such processes as electrons changing their position around nuclei and bonding with protons to form atoms involves a release of energy, that it may be this bonding that produced the CMB.

No. The radiation that makes up the CMB was already there before recombination; but it could not travel freely, because the matter in the universe was plasma (i.e., electrons and nuclei not bound into atoms). So the radiation was constantly being absorbed and re-emitted by free electrons and nuclei, making the universe effectively opaque. But after recombination, with the electrons and nuclei bound into atoms, the radiation that already existed could now travel freely, without being absorbed and re-emitted; in other words, the universe became transparent to radiation. That radiation, redshifted by a factor of about 1000, is what we now see as the CMB.

If the CMB originated almost 400,000 years after the B.B. and it originated when electrons became bound to protons to form hydrogen atoms, by then the universe had expanded how many lightyears?

As I said before, the "size of the universe" is not a good way to think of it. A better way is to think of the density or temperature of the universe. The temperature of the universe was a few thousand degrees at the time of recombination. I'd have to look up what density that corresponds to.

at that point the generation of radiation from the event of electrons bonding to protons would have happened "everywhere at once" it would seem since the universe was already so large.

The size of the universe is not what makes us think that recombination happened everywhere at once; it is perfectly possible in principle for it to have happened at different times in different parts of the universe. The reason we think it happened everywhere at once is that the redshift of the CMB is the same in all directions, and that redshift tells us when recombination happened. Physically, this makes sense because, as far as we can tell, the universe was the same temperature everywhere, and temperature determines when recombination happens.

radiation generated by one electron bonding to one proton would be an event in a point in space in an instant of time.

Yes.

Hence there would be no red shift since the source is not continually emitting radiation as it moves.

No. The redshift we observe is not determined by the motion of the source; it's determined by how much the universe has expanded since the source emitted the light, which is determined by how much time has passed. Pop science treatments often talk of the redshift as being due to the Doppler effect, but this is not really correct; it's an approximation that only works for objects that are close enough to us (and hence emitted the light we are seeing recently enough) for the redshift-distance relation to be linear. This approximation certainly does not work for the CMB.

 

[PeterDonis]

An inch and a half?

As phinds says, that is the size of the observable universe, not the entire universe.

Pardon me, but matter is protons and neutrons . . .

To a cosmologist, "matter" means "anything that isn't radiation". More precisely, "matter" means "anything with nonzero rest mass", and "radiation" means "anything with zero rest mass". "Matter" is certainly not limited to protons and neutrons (and electrons).

In layman's terms, the CMB is the energy released when atoms are formed from free charged protons and electrons?

No. See my previous post and Drakkith's post. However, it's worth noting that, even if the CMB were composed entirely of radiation released by recombination, your logic would not be correct:

If so, the energy released from one such event would be identical to the energy released from every such event.

But the events could still have happened at different times, which would mean we would observe the radiation from them redshifted by different amounts.

 

[nikkkom]

This doesn’t make sense to me... http://cosmictimes.gsfc.nasa.gov/online_edition/1993Cosmic/inflation.html
“Inflation Theory explains . . . that shortly after the Big Bang, the universe expanded tremendously in a very short amount of time. This expansion grew the size of the universe from submicroscopic to the size of a golf ball in 10-35 seconds. Thus, regions once in contact with each other are now far apart in the universe.”

An inch and a half?

You are right about being confused by "shortly after the Big Bang, the universe expanded tremendously" part - because it is wrong. There is no single inflation theory, there are many such theories. And they all basically take "ordinary" BB theory (one where everything expands from initial singularity), then clip away first ~10e-32 seconds of this model and replace it with a different scenario. The duration of this "different scenario" varies among different inflation theories. In some, it is infinitely long (see, for example, https://en.wikipedia.org/wiki/Eternal_inflation). Therefore, it's possible that there was no such thing as "shortly after the Big Bang".

Regarding "An inch and a half". Yes, why not? The entire currently visible spherical observable part of the Universe is theorized to be about "an inch and a half" at some very early point.

What's important to know to understand the model, this "inch and a half" ball was rapidly expanding. In fact, its surface was receding from the center at many times speed of light. So, if a neutrino was emitted by some reaction on this surface in the direction of the center of the ball, it would fly to the center at (very nearly) speed of light, but would be swept away by the expansion, so for several billions of years the distance from this neutrino to the center would be *increasing*. But the neutrino will be reaching locations which recede from center with smaller and smaller apparent velocity. Eventually, it would reach locations which recede slower than light. Then this neutrino will start decreasing its distance to the center of the ball. And 13.7 billion years after it was emitted, it can finally reach the center.

 

[Dave Eagan]

Thanks to everyone for taking time to explain all this. I really appreciate it. You've covered concepts I knew nothing about. I never considered myself an amateur cosmologist or anything close to it but I have some interest in things scientific. You have all given me many things to research and study. Thank you.

By the way, Drakkith posted a link which I went to and read. I found it . . . umm . . . --surprising. You see, I inquired once about the "explosion" of the Big Bang and was instructed sternly that there was no explosion, but an expansion. To think in terms of an explosion would be incorrect and lead to a risk of incorrect conclusions. That distinction was burned into my brain. Never speak of the BB as "an explosion".

And yet that link says:

"The Cosmic Microwave Background (CMB) is the isotropic, electromagnetic radiation which resulted from the explosion of the universe between 15 and 18 billion years ago. This theory, accepted by many but not all, is called The Big Bang theory. The Big Bang was the explosion of the universe from the extremely small, dense, and hot conditions of the early universe. " http://hypertextbook.com/facts/2004/HeatherFriedberg.shtml

No wonder I get confused.

Cheers

 

[Drakkith]

By the way, Drakkith posted a link which I went to and read. I found it . . . umm . . . --surprising. You see, I inquired once about the "explosion" of the Big Bang and was instructed sternly that there was no explosion, but an expansion. To think in terms of an explosion would be incorrect and lead to a risk of incorrect conclusions. That distinction was burned into my brain. Never speak of the BB as "an explosion".

Indeed. It's unfortunate that many sources describe the big bang as an explosion. But no worries. What we decide to call it is less important than what the theory and math describe. Let the former encourage you to learn the latter.