How do physicists know the universe is mostly normal matter not antimatter?

[Icebreaker]

I'm told that most of the observable universe is made up of "normal" matter. How did physicists come to this conclusion? There is no difference between matter and antimatter when observed.

 

[kenhcm]

This is the way I think and it might not be correct. The assignment of "matter" and "anti-matter" are arbitrary since we do not have a standard reference. We could simply call one of them "matter" and the other to be "anti-matter". This is similar in the situation to assign "left" and "right".


Kenneth

 

[Icebreaker]

We do, which is exactly why I'm puzzled by the claim that the observable universe is made up of one type, the one of which you and I are made. i.e. protons and electrons, as opposed to antiprotons and positrons.

 

[hellfire]

Take a look to: http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/baryogenesis.html

 

[Icebreaker]

So it's just "chances are." I thought there was a way to detect antimatter (other than annihilation) that I was not aware of.

 

[Chronos]

If there were large amounts of anti-matter in the universe, we would see enormous emissions of energy where they meet. Hellfire gave a link explaining that.

 

[ohwilleke]

This is the way I think and it might not be correct. The assignment of "matter" and "anti-matter" are arbitrary since we do not have a standard reference. We could simply call one of them "matter" and the other to be "anti-matter". This is similar in the situation to assign "left" and "right".


Kenneth

One could, but it is certainly sensible to name the kind of matter that makes up 99.99999% of what you obserb matter and the rest anti-matter. It saves a heckuvalot of typing.

 

[ohwilleke]

I'm told that most of the observable universe is made up of "normal" matter. How did physicists come to this conclusion? There is no difference between matter and antimatter when observed.

Because we would expect to see fireworks at a matter-anti-matter horizon which we don't see. A mixed matter-anti-matter system is unstable.

 

[Nereid]

So it's just "chances are." I thought there was a way to detect antimatter (other than annihilation) that I was not aware of.

Observing at a distance, I can't think of any way of detecting antimatter (other than annihilation), except (possibly) rather indirectly. Up close & personal, antimatter particles reveal their 'true colours' in several ways other than by annihilation (e.g. estimates of charge and mass -> clean distinctions); however, this isn't much help, as all it does is tell you there is little anti-matter in cosmic rays (and none, to speak of, where spacecraft have ventured).