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If antimatter has an indistinguishable spectrum from regular matter, maybe there is more of it in the universe than we thought.
by Sir_Cmpwn 10y ago
If antimatter has an indistinguishable spectrum from regular matter, maybe there is more of it in the universe than we thought.
- danbruc 10y agoIf there were regions of antimatter in the universe, then there would be boundaries with regions of matter. And on those boundaries a lot of matter antimatter annihilation would happen, we would see those boundaries glow in energetic gamma light. We don't see something like that, therefore there are probably no large region of antimatter in the universe.
- Sir_Cmpwn 10y agoGotcha, makes sense. Are we sure the density of the intergalactic medium is high enough to make interactions between matter and antimatter produce light visible from long distances, though?
- danbruc 10y agoWe have bounds on the density near such boundaries and their distance from Earth above which they would become visible. [1] [1] https://en.wikipedia.org/wiki/Baryon_asymmetry#Regions_of_the_universe_where_antimatter_dominates https://en.wikipedia.org/wiki/Baryon_asymmetry#Regions_of_th...
- johnfn 10y agoIsn't space mostly empty? Aren't galaxies like millions of light years apart, and don't they collide only incredibly rarely? If some galaxies were antimatter and some matter, how would we know?
- danbruc 10y agoThe space between galaxies is not completely empty, there is still about one atom per cubic meter. Boundaries in outer space would stretch across billions of square light years, enough space to generate noticeable signals even at such low densities.
- hwillis 10y agoIt is the most energetic reaction possible. We can see the background radiation of the universe- hot objects give off heat, even when they are very, very cold. The universe glows like it's 3 degrees above absolute zero, and we can see it. Compared to that antimatter annihilation would look very bright indeed.
- danbruc 10y agoThe photons are much more energetic than the cosmic microwave background, the intensity could still be low enough to escape detection.
- lomnakkus 10y agoWatch this: https://www.ted.com/talks/david_deutsch_on_our_place_in_the_cosmos https://www.ted.com/talks/david_deutsch_on_our_place_in_the_...
- nol13 10y agoAny reason to suspect that these regions aren't just much larger than the observable universe?
- hwillis 10y agoThat question is a nonstarter, essentially. Physics is interested and concerned with why the observable universe has almost no antimatter, so asking "what if all the antimatter is outside the observable universe" doesn't actually answer the question.
- danbruc 10y agoOne could maybe argue that there has to be some fundamental asymmetry between matter and antimatter. If there were none, you have to find a good explanation why there was not the same amount of matter and antimatter right after the Big Bang and why therefore not all matter and antimatter just turned into photons leaving behind an empty universe. If on the other hand there is an asymmetry and matter is favored over antimatter, then the matter we see today would just be the difference left over after all the antimatter annihilated. In that case there seems to be no obvious reason why regions should form.
- gus_massa 10y agoIt's reasonable to suppose that if in one experiment you replace each particle by it's antiparticle you will get the same result. (Symmetry C) The problem is that this is not true in all experiments :( It's reasonable to suppose that if in one experiment you make a mirror image of all the part of the experiments, with the mirrored version of all the velocities and spin, you will get the same result. (Symmetry P) The problem is that this is not true in all experiments :( (I'll skip T symmetry.) For some technical reason it's more easy to expect that if you combine both symmetries and change all particles by the antiparticle and make a mirrored version, you will get the same result. (Symmetry CP) This is almost almost almost true. Not completely true, but it's difficult to make an experiment where the result is different. So, in some experiments the CP version is different from the original version. It is possible to measure this in a laboratory, and this is one possible explanation of the different of the amount of mater and antimatter around us, but no one is sure about the details. See https://en.wikipedia.org/wiki/CP_violation#CP_violation_and_the_matter.E2.80.93antimatter_imbalance https://en.wikipedia.org/wiki/CP_violation#CP_violation_and_...