Why not an equal amount of matter and antimatter in the universe?

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Discussion Overview

The discussion revolves around the question of whether there could be an equal amount of matter and antimatter in the universe, exploring theoretical implications and the nature of the early universe. Participants consider concepts related to cosmology, inflation, and the cosmic microwave background, while also touching on the potential existence of antimatter regions beyond the observable universe.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the universe could have equal amounts of matter and antimatter, suggesting that our observable universe might simply be a region with more matter due to its lumpy nature.
  • Others argue that significant anisotropies in the matter-antimatter distribution would be required for this scenario to hold, which may not align with most inflation models.
  • There is a discussion about the definition of anisotropy and its implications for understanding the cosmic microwave background, with some participants noting that the observed anisotropies are quite small.
  • One participant mentions the concept of baryogenesis, which describes the imbalance of matter and antimatter in the early universe, referencing external resources for further reading.
  • Another participant suggests that if there were regions dominated by antimatter, there would likely be detectable signatures of matter-antimatter annihilation, which are not observed.
  • Some participants express uncertainty about their understanding and the complexity of the topic, indicating a desire to learn more and engage with advanced concepts.
  • There is a mention of the potential confusion between antimatter and dark matter, with clarifications provided regarding their definitions.

Areas of Agreement / Disagreement

Participants express a range of views on the matter-antimatter question, with no consensus reached. Some support the idea of equal amounts of matter and antimatter, while others challenge this notion based on current cosmological models and observations.

Contextual Notes

Limitations in the discussion include varying levels of understanding among participants regarding advanced concepts such as baryogenesis, anisotropy, and the implications of the cosmic microwave background. Some mathematical steps and definitions remain unresolved.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, particle physics, or anyone curious about the fundamental questions regarding the composition of the universe and the nature of matter and antimatter.

Mpcahn
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Couldn't there be an equal amount of matter and antimatter in the universe. While from what I've read there is little antimatter in the universe as we see it. Isn't it a leap to assume that the universe at the Big Bang had slightly more matter than antimatter? Isn't it just as likely that there still is the same amount of antimatter and matter in the universe, but the reason were here is the lumpy nature of the early universe had it so our little observable corner of it had more matter than antimatter and now matter is just about all we can see? Couldn't there be another corner of the universe beyond our observable horizon where there are galaxies made of antimatter and living beings who call it matter and wonder why there isn't more antimatter?

Just some food for thought.
 
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For this to be possible there would need to be significant anisotropies in the matter/anti-matter distribution pretty early on during inflation I believe, which I don't think is the case in most models. I don't know enough about inflation to say much more though.
 
Isn't "anisotropy" a property not a thing. Anisotropy being not uniform, isotropy being uniform? The microwave background looks quite anisotropic. Thanks for a more scientific sounding word for "lumpy." I'll do the math when I learn it. I'm about 3/4 of the way through Khan Academies maths sequence. What else do I need to learn to attempt to make a proof?
 
Maybe I'll ask some cosmologists.
 
Mpcahn said:
Isn't "anisotropy" a property not a thing. Anisotropy being not uniform, isotropy being uniform? The microwave background looks quite anisotropic.

Not sure what you are getting at. Yes I mean "not uniform". As for the microwave background, it only looks anisotropic in the pretty pictures people show of it because it has had the much larger isotropic component subtracted off. The temperature fluctuations are around 18 microKelvin, while the average temperature is 2.7 Kelvin. So the anisotropies are very very small (see https://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation#Features).

Mpcahn said:
I'm about 3/4 of the way through Khan Academies maths sequence. What else do I need to learn to attempt to make a proof?

A proof of how CMB anisotropies constrain your proposal? Really a very large amount I'm afraid. You'll probably need at least a masters in cosmology.
 
Yeah, sounds like a topic for a Ph.D. thesis. My guess would be a full time investment of about 4 years. And I guess "proof" wouldn't be the right word either. I'll keep chipping away at it in my spare time. I have too many ideas like this and my guess is most of them are wrong. But I'll get wiser learning which is and which isn't.
 
Actually could the mod's move this thread to the cosmology subforum? Didn't realize you had one until now.
 
I see they moved your thread.

What you are after in the matter antimatter question in regards to the universe is described by the particke physics term baryogenesis.

http://en.m.wikipedia.org/wiki/Baryogenesis

During the first moments of of the early universe matter and anti matter were balanced. For reasons covered on the wiki page an imbalance occurs favouring matter.

Coincidentally there is another related new thread.

https://www.physicsforums.com/showthread.php?t=692988
 
Last edited:
Mpcahn said:
Isn't "anisotropy" a property not a thing. Anisotropy being not uniform, isotropy being uniform? The microwave background looks quite anisotropic. Thanks for a more scientific sounding word for "lumpy." I'll do the math when I learn it. I'm about 3/4 of the way through Khan Academies maths sequence. What else do I need to learn to attempt to make a proof?


Isotrophy is no preferred direction. Anistrophy is the opposite.

Homogeneous is no preferred location one spot is the same as another.

both combined signify uniformity at needed size scales.
 
  • #10
Mordred said:
Isotrophy is no preferred direction. Anistrophy is the opposite.
Homogeneous is no preferred location one spot is the same as another. both combined signify uniformity at needed size scales.

Ahh yes, thanks, the homogeneity is important, I should have mentioned it.
 
  • #11
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  • #12
Thanks Mordred! I'll have to take some time to do the necessary research to understand this paper.
 
  • #13
Well if your looking for info on understanding that look at CP violations. Early particle QFT articles.

This resource may help it covers all the needed maths but it requires good math skills and some previous knowledge.

be forwarned it 889 pages long but it covers classical and quantum fields of a large variety.

CP violations is included.

http://arxiv.org/abs/hepth/9912205
 
  • #14
Mpcahn said:
Couldn't there be an equal amount of matter and antimatter in the universe. While from what I've read there is little antimatter in the universe as we see it. Isn't it a leap to assume that the universe at the Big Bang had slightly more matter than antimatter? Isn't it just as likely that there still is the same amount of antimatter and matter in the universe, but the reason were here is the lumpy nature of the early universe had it so our little observable corner of it had more matter than antimatter and now matter is just about all we can see? Couldn't there be another corner of the universe beyond our observable horizon where there are galaxies made of antimatter and living beings who call it matter and wonder why there isn't more antimatter?

Just some food for thought.

By anti-matter I assume you mean 'dark matter" which is not quantifiable by observation, but should be present by mathematical calculation. This could be due to the fact that we as humans can only perceive reality in three dimensions. What if the universe is not as it appears? If there are more (such as the multi-verse theory) dimensions, we would need a way to perceive and interpret those other dimensions...
 
  • #15
Just Steve said:
By anti-matter I assume you mean 'dark matter" which is not quantifiable by observation, but should be present by mathematical calculation. This could be due to the fact that we as humans can only perceive reality in three dimensions. What if the universe is not as it appears? If there are more (such as the multi-verse theory) dimensions, we would need a way to perceive and interpret those other dimensions...

I'm pretty sure he actually meant antimatter, i.e. matter in the form of antiparticles. You might want to take a look at http://en.wikipedia.org/wiki/Antiparticle
 
  • #16
If there had ever (after the appearance of the CMB) been a region of space dominated by antimatter, I believe there would also have been a boundary between that region and the one we occupy (which is matter dominated). At that boundary, I would expect there to be ongoing matter-antimatter annihilation which should leave a detectable signature in the form of gamma radiation. Since we see no such signature, I would conclude that there is no such boundary and therefore no antimatter region. (Although I could be wrong about this.)
 

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