The Duration of the Big Bang: Exploding Myths and Misconceptions

[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.