Question

In: Physics

As I hope is obvious to everyone reading this, the universe contains more matter than antimatter,...

As I hope is obvious to everyone reading this, the universe contains more matter than antimatter, presumably because of some slight asymmetry in the amounts of the two generated during the Big Bang. This raises the question of whether there are any processes short of the Big Bang that produce more matter than antimatter. That is, is there any known process where a particle collider (or whatever) would convert some energy into matter not through the production of particle-antiparticle pairs but through some process that produced more matter than antimatter? This doesn't need to be restricted to current accelerators-- if there's some mechanism for this that requires impractically high energies, but is based on solid theories (i.e., the Standard Model or straightforward extensions thereof), that would be interesting, too.

I'm fairly certain that the answer is "no," because I know that the matter-antimatter asymmetry is related to CP violation, and I also know that existing measurements of CP violation are not enough to explain the asymmetry. If there were a known way to slam protons together and make more quarks than antiquarks, I wouldn't expect this to still be a mystery. My particle physics knowledge is far from comprehensive, though, so it can't hurt to ask.

(I was briefly confused into thinking that there was such an experiment a while back, but it turned out to just be sloppiness about marking the antiquarks on the part of the people writing about it...)

(This is another question prompted by the book-in-progress, on relativity, this time a single word: I wrote that matter created from energy in particle physics experiments is "generally" in the form of particle-antiparticle pairs. Then I started wondering whether that qualifier was really needed, and thus this question.)

Solutions

Expert Solution

you misinterpret the statement that "the known sources of CP-violation are not enough to explain the matter-antimatter asymmetry in the Universe."

You seem to think that the statement means that the known CP-violating parameter (namely the CP-violating phase in the CKM matrix) and the processes based on it are qualitatively insufficient to produce matter-antimatter asymmetry. But they are just quantitatively insufficient. One simply doesn't get enough of the asymmetry - but qualitatively, the CKM phase would be enough.

However, there are additional conditions beyond the CP-violation that have (or had) to be satisfied for the Universe to produce matter-antimatter asymmetry. They're known as the Sakharov conditions:

CP-violation as well as C-violation
Violation of the conservation of the baryon number B (and/or lepton number L)
Evolution away from the thermal equilibrium.

All of these "violations" have be present simultaneously to produce quarks and antiquarks asymmetrically. If one of them is absent, the processes remain matter-antimatter symmetric.

As you can see, lab experiments may deviate from thermal equilibrium but all lab experiments we can perform conserve the baryon number B (as well as the lepton number L). That's why we can't imitate the matter-antimatter asymmetry in the lab.

The attempted "lab experiments" violating B are the proton decay experiments - those big reservoirs of pure water with sensitive detectors able to see every single proton decay. So far, none of them has been seen (even though the simplest grand unified theories predicted that the proton decay should have been observed rather quickly). For theoretical reasons, it still seems extremely likely that the proton is unstable (although its lifetime is longer than expected in the SU(5) GUT) and B is not conserved. Consequently, L is not conserved, either.

In particular, black holes radiate the Hawking radiation away and the composition of the Hawking radiation carries B=0 in average because the event horizon looks the same regardless of the value of B of the initial star that has collapsed into the black hole. This paragraph was meant to be a proof that locality implies that B has to be violated in quantum gravity (or earlier, e.g. in the GUT theory) as long as there are no gauge fields associated with B.

However, the combination B?L may be in principle conserved - it may be a generator of a grand unified group. However, this symmetry is probably broken because there are no long-range forces acting on this combined charge. So all these charges unrelated to gauge symmetries have to be violated (non-conserved) at some level; this reflects the wisdom that quantum gravity doesn't allow any global symmetries. Any symmetry is either explicitly broken by some effects or it is a gauge symmetry.


Related Solutions

Why is the luminous matter so much more compact than the dark matter?
Why is the luminous matter so much more compact than the dark matter?
I am a researcher interested in children’s reading. I feel children should be reading more as...
I am a researcher interested in children’s reading. I feel children should be reading more as they get older and feel generally interested in learning about current reading trends. I feel a good way to learn about the current reading trends to learn about their Accelerated Reader points. I feel older students are already reading more and should have more AR points than younger students. I predict that the older children will have more AR points than younger children. What...
Why does comparative advantage matter more than absolute advantage for trade?
Why does comparative advantage matter more than absolute advantage for trade?  Why does the production possibilities frontier bow out?  
A diet needs to be created that contains not less than 2146 calories, not more than...
A diet needs to be created that contains not less than 2146 calories, not more than 58 grams of protein, not less than 10 grams of carbohydrates and not less than 13 grams of fat. Also, the diet should haveminimal cost. In addition the diet should include at least 1 Units of fish and at least 1.2 cup of milk. The diet will consist of the six different foods: Bread, Milk, Cheese, Fish, Potato and Yogurt. The following table lists...
Everyone makes mistakes. Some are more costly than others. By cost, a negative or inappropriate post...
Everyone makes mistakes. Some are more costly than others. By cost, a negative or inappropriate post can cost someone his or her job. A company may lose sales or stock value. Search the Internet for an example of a social media mistake. Describe the situation. Summarize the consequences/outcome. Why do you think the outcome was fair/just? Do you think people should lose their jobs as a result of personal social media posts? Explain.
What are the major effects encountered by an electron traversing matter? more than one answer multiple...
What are the major effects encountered by an electron traversing matter? more than one answer multiple Coulomb scattering bremsstrahlung Compton scattering conversion into electron-positron pairs annihilation photoelectric effect energy loss by excitation and ionisation
A friend of yours is very nice but more patriotic than excited about reading books. At...
A friend of yours is very nice but more patriotic than excited about reading books. At a party with friends she says, “America’s health care system is by far the best in the world, and therefore our pregnant moms and newborn babies are the healthiest.” Based on what you read and watched in Unit 1, what might you say about at least two issues related to prenatal care, the birthing process, and the health of pregnant mothers and newborns that...
A researcher claims that more than 30 percent of students of WPU use reading glasses. A...
A researcher claims that more than 30 percent of students of WPU use reading glasses. A consumer agency wants to test this claim. The agency takes a random sample of 120 students and finds that 60 of them use reading glasses. If the agency conducts hypothesis testing, which would be the computed p-value for the test? 4.7 4.8 0.2 0.7 None of the above
A certain large shipment comes with a guarantee that it contains no more than 25% defective...
A certain large shipment comes with a guarantee that it contains no more than 25% defective items. If the proportion of items in the shipment is greater than 25%, the shipment may be returned. You draw a random sample of 12 items and test each one to determine whether it is defective. a. If in fact 25% of the items in the shipment are defective (so that the shipment is good, but just barely) what is the probability that 7...
A certain large shipment comes with a guarantee that it contains no more than 20% defective...
A certain large shipment comes with a guarantee that it contains no more than 20% defective items. If the proportion of items in the shipment is greater than 20%, the shipment may be returned. You draw a random sample of 10 items and test each one to determine whether it is defective.             If in fact 20% of the items in the shipment are defective (so that the shipment is good, but just barely) what is the probability that 7...
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT