How we are in a matter dominated universe (without antimatter annihilation)

[brooknorton1]

Assuming the situation where there is an infinite inflation stream, from which bubble universes are appearing in locally slowed regions. There could be many many such bubble universes and so very rare occurrences in some bubbles can sometimes happen.

Also assumed, as is often postulated, that the seed (prior to the local inflation) of a bubble universe has quantum fluxuations creating areas of higher and lower densities of the "seed" material prior to inflation. When the local inflation happens, these regions of various densities are greatly expanded into large areas of various densities of matter and antimatter.

I'm wondering, given the random nature of the initial quantum fluxuations, if there could be extraordinary areas of high density that, after inflation, maintain a higher density of matter or antimatter. Total matter and antimatter are created in equal part, but there could be large areas dominated by matter or antimatter. An area of local matter density could be very large in volume, perhaps as large as our visible universe. In that case, beyond the observable universe horizon there would be other areas of higher antimatter density, so that the total bubble universe would have equal matter and antimatter.

Nearly all regions of all bubble universes would have equal matter and antimatter in relative close proximity and those areas would self-annihilate, leaving no matter or antimatter. We would live, of course, only in a region of a bubble universe that had an extraordinary random distribution of mostly matter.

It seems like this scenario fits the bubble universe model and also fits our observations of our visible universe, dominated by matter.

 

[PeterDonis]

We would live, of course, only in a region of a bubble universe that had an extraordinary random distribution of mostly matter.

But we don't. Our observable universe contains, IIRC, about ten billion photons for every baryon. That means the excess of matter over antimatter in our early universe was about one part in ten billion, since the ten billion photons per baryon were produced by annihilation of baryons and antibaryons.

 

[brooknorton1]

So initially the random distribution of matter and antimatter in our visible universe was nearly equal, with a slightly higher amount of matter than antimatter. The balance of antimatter residing within our bubble but beyond our visible horizon.

 

[PeterDonis]

So initially the random distribution of matter and antimatter in our visible universe was nearly equal, with a slightly higher amount of matter than antimatter.

The slightly higher amount of matter vs. antimatter could be due to random distribution, or it could be due to an asymmetry in the physical laws involved that we don't yet understand.

The balance of antimatter residing within our bubble but beyond our visible horizon.

No. At least, we have no reason to think that is the case. We expect that the rest of our "bubble" started out with the same distribution as the part we can see.

 

[brooknorton1]

We know that within regions in our visible universe that matter density varies, so there is not perfect homogeneity. It would just be an extrapolation to say that matter densities vary on a larger scale. Compared to our total bubble volume, our visible volume might be a very very tiny fraction. An initial inflationary random density distribution could make "tiny" areas like our visible universe, slightly more or less dense than neighboring areas beyond what we can see.

 

[PeterDonis]

We know that within regions in our visible universe that matter density varies

That's because of gravitational clumping over billions of years. It doesn't mean there was that much variation just after the end of inflation and the formation of our "bubble". There wasn't.

Indeed, there was still only one part in 100,000 variation at the time the CMBR was formed, several hundred thousand years after the end of inflation. We know that because that's the level of variation in temperature in the CMBR.

It would just be an extrapolation

No, it wouldn't. It would be a misinterpretation of what we see. See above.

 

[brooknorton1]

If you could help me here - how do you get those quotes to reply to like "brooknorton1 said"...

You say "That's because of gravitational clumping over billions of years. It doesn't mean there was that much variation just after the end of inflation and the formation of our "bubble". There wasn't."

But there was SOME variation right from the beginning. Once, in principle, that density variations are possible, it is just a matter of time until a quantum variation is large enough to cause a matter/antimatter imbalance to an area large enough to fit our visible universe in.

The CMBR is just for our visible universe. If you could see the CMBR for our entire bubble, there could very well be significant non-homogeneities.

 

[PeterDonis]

how do you get those quotes

The quickest way is to highlight what you want to quote and click the "Reply" button that pops up; that will automatically put the quote into the window for a new post.

 

[PeterDonis]

there was SOME variation right from the beginning

A very, very tiny amount, yes. But you are talking about density variations. That's not the same as variations in the proportion of matter vs. antimatter. Those are two different things.

it is just a matter of time until a quantum variation is large enough to cause a matter/antimatter imbalance to an area large enough to fit our visible universe in.

What is your basis for this claim? If you think it is just obvious, no, it isn't.

 

[brooknorton1]

I don't know enough to know what the current thinking is on the largest theoretically possible quantum noise in the pre-inflation seed. It seems for quantum random phenomenon, I hear that a quantum event is extremely likely to fall into a most likely range, but that the tail of probabilities not rule out highly unusual occurrences, like all the air molecules randomly moving all to a corner of the room, suffocating the occupants. But, as you point out, in our visible universe, there nearly was equal matter and antimatter, matter just barely winning out. So I'm just saying maybe the next part of the universe adjacent to our visible part has slightly more antimatter.

I doesn't seem like a typical region in our bubble would have EXACTLY equal matter and antimatter. And if not EXACT, then, after the mutual annihilation, the resulting left over matter or antimatter would form a matter or antimatter dominated region. So long as the matter/antimatter balance was equal for the entire bubble, we might expect matter/antimatter dominance in different regions.

 

[PeterDonis]

I doesn't seem like a typical region in our bubble would have EXACTLY equal matter and antimatter

Remember that what happens at the end of inflation is that energy density gets transferred from the inflaton field (which transitions from false vacuum to true vacuum, giving up energy) to the Standard Model fields. The Standard Model fields start out in their vacuum states, and our expectation is that when those fields are in their vacuum states and energy is pumped into them, the energy goes into particle-antiparticle pairs. That requires that matter and antimatter are exactly equal at the instant when the pairs are created.

Once the pairs are created, there will be some time period during which the temperature is high enough that, even if pairs annihilate each other, new pairs will be created just as fast. During that time period, random fluctuations can cause slight excesses of particles over antiparticles in some places, and antiparticles over particles in others. Also, if there is any asymmetry in the physical laws that allows reactions to take place that create an excess of matter over antimatter, those could take place during this period.

The advantage of the second process over the first is that it would be taking place everywhere, so it would naturally produce an excess of matter everywhere. Whereas the first process requires us to believe that random fluctuations could entirely empty our observable universe of antimatter, which is much more unlikely.

The disadvantage of the second process, of course, is that there is no such asymmetry in our best current model of the laws of physics. But of course our current model is not complete.

 

[brooknorton1]

That description helped. Assuming that the particle and its antiparticle are created in close proximity, after inflation, it seems we should have near total annihilation, with just a few stray atoms and anti-atoms here and there, but we see a lot of matter. I can now better appreciate the mystery of matter dominance.

 

[Orodruin]

When the local inflation happens, these regions of various densities are greatly expanded into large areas of various densities of matter and antimatter.

This is incorrect. Inflation expands regions of the universe into what is essentially complete voids without any matter whatsoever. Anything that may have existed before inflation is diluted into essential nothingness, leaving essentially only the inflaton field. The decay of the inflaton field then repopulates the matter sector of the model through a process called reheating.

During that time period, random fluctuations can cause slight excesses of particles over antiparticles in some places, and antiparticles over particles in others. Also, if there is any asymmetry in the physical laws that allows reactions to take place that create an excess of matter over antimatter, those could take place during this period.

Random fluctuations near the end of inflation cannot generally be the reason for the matter-antimatter asymmetry as that would defeat one of the benefits of inflation (explaining why causally disconnected regions display similar properties). You would end up with matter or antimatter excesses in different parts of the observable universe.

The physics properties required to generate the asymmetry are well known, ie, the Sakharov conditions, and include not only an asymmetry in the physics itself, but also a deviation from thermal equilibrium in the evolution of the Universe.

The disadvantage of the second process, of course, is that there is no such asymmetry in our best current model of the laws of physics. But of course our current model is not complete.

The Sakharov conditions are satisfied in the Standard Model so we indeed know physics that fulfill the requirements. The issue is that the asymmetry is not large enough to produce the observed matter excess by several orders of magnitude.

 

[Vanadium 50]

You would end up with matter or antimatter excesses in different parts of the observable universe.

You do, but that is not observationally a problem. You can have regions a few 100 MPc in size of alternating matter and antimatter, and the annihilation radiation kind of gets lost in the diffuse x-ray background. This was one of the motivations for AMS.

AMS has been very slow in publishing, but my understanding from rumors is that they see anti-He3 and anti-tritons but no anti-iron. That will probably push these limits out, just not as far as had they seen no anti-nuclei.

I absolutely agree that separated regions of matter and antimatter would be theoretically problematic.