# Matter and antimatter

1. Dec 10, 2013

### us40

Hello,
There is a problem like why universe end up with more matter than anti matter but is it not possible that matter and antimatter does not have enough time to meet and annihilate because of inflationary epoch because of exponential expansion of space time????

2. Dec 10, 2013

### dauto

No, that doesn't work. You wouldn't produce the observed excess that way.

3. Dec 10, 2013

### mathman

Matter-antimatter pairs are created together. They would be all mixed together right after the big bang, so they couldn't separate fast enough.

4. Dec 10, 2013

### Chronos

5. Dec 10, 2013

### PAllen

The annihilation of electrons and positrons produces a characteristic gamma ray energy. Even if matter and antimatter somehow became well separated, we should see many more gamma rays of this characteristic energy than we do if antimatter survived in quantity into the era when the universe became transparent to EM radiation. There are many other lines of evidence as well, but I find this one easy to understand.

6. Dec 11, 2013

### Chalnoth

Close to the end of inflation, there was effectively no matter at all around (or anti-matter). There was only the field that drove inflation. When that decayed, it produced a zoo of particles, with equal numbers of matter and anti-matter particles. How that equal number of matter and anti-matter particles then evolved to the imbalance we see today is the issue at hand.

Anyway, here's the Wikipedia article on the subject:
https://en.wikipedia.org/wiki/Baryogenesis

7. Dec 11, 2013

### PAllen

I thought OP was asking how do we know that there is an imbalance today? If there is no imbalance, there is no problem. That is not immediately obvious, and as recently as circa 1960 there were Nobel winning physicists who weren't convinced we knew there was an imbalance. Today, I don't think there is any serious astrophysicist with any doubt about the imbalance.

8. Dec 11, 2013

### Chalnoth

Right. But he seemed to be attempting to claim that cosmic inflation would have separated the matter-dominated and anti-matter-dominated regions. This doesn't work for the reasons I mentioned.

9. Dec 12, 2013

### Naty1

In the article linked to by Chronos:

What's the bold face part all about? Never heard about such processes.....Edit: Any relation to vacuum energy??

10. Dec 12, 2013

### Chronos

Bear in mind it is believed that only about 1 particle in a billion survived the wild +/- pair annihilation frenzy of the early universe.

11. Dec 12, 2013

### PAllen

This is an interesting question. QFT is not an area I know very well, but I had only heard of neutrino oscillation, not, e.g. muons oscillating to anti-muons millions of times per second. I am definitely interested in the explanation of this statement from someone more knowledgeable in this area. Since the statement is in a CERN public document I assume it has some reasonable justification.

12. Dec 13, 2013

### George Jones

Staff Emeritus
13. Dec 13, 2013

### Chalnoth

Muons are charged particles. I'm pretty certain that charged particles cannot oscillate into their anti-particles. Neutrally-charged particles, however, can. I believe the earliest-discovered example of this was the $K^0$ meson (aka. the neutral kaon).

14. Dec 13, 2013

### PAllen

The misleading thing about the CERN press release referenced early in this thread is that there was was no indication that only some particles oscillate to their anti-particles, and of those, only a few do at the referenced rate of millions of times per second. They went from completely general discussion of antimatter to a specific situation without clarification. The CERN notes that George Jones linked were perfectly clear.

15. Dec 13, 2013

### mathman

The Cern article mentions B0 specifically and says there are a few others. Most particles do not oscillate with antiparticles.

16. Dec 13, 2013

### PAllen

17. Dec 13, 2013

### Chalnoth

That's really too bad. I didn't look at that press release.

18. Dec 31, 2013

### M. Bachmeier

I'm a novice, but how much of our perceived knowledge of particle / antiparticle annihilation based upon statistical estimation? Statistical inference may apply to our current state, but did it apply to the early development of matter with respect to space and time with respect to expansion of space?

Our we missing something grand? Is there a Rosetta Stone? Are there antiparticles in large quantities within our universe?

19. Jan 1, 2014

### Chalnoth

Statistics is an application of mathematics. It always applies.

20. Jan 9, 2014

### M. Bachmeier

Would you be surprise if our Maths failed to be the ultimate answer?

I'm sure the Romans felt their methods sound and without question, however, the lack of a zero did make some operations difficult and others impossible.