Matter/antimatter, mass questions

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In summary, according to this source, antimatter has 1 extra matter baryon for every billion antimatter particles. This means that all of the antimatter currently in the universe is photons. Additionally, it is unclear what the rest mass of photons is, as it is different depending on how you look at them. It is also unclear what happened to the rest mass of normal matter after the big bang. However, it is clear that the expansion of the universe cooled everything down, causing the mass to be lost over time.
  • #1
Dav333
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I heard for every (think it was) billion antimatter there was 1 extra matter.

Does this mean before the annihilation after the big bang the universe was billions of times more heavy? So all that antimatter is now photons zipping around the universe?

Other question.
If there is all the matter & energy ever created, then why do particles pop in & out from the vacuum & annihilate each other? Looking for a simple answer if possible as wikipedia is over my head.
 
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  • #2
The total mass, including energy, was the same. Annihilation converts mass to energy (E=mc2).
 
  • #3
There is no global energy conservation rule, and during the energy-dominated era, the BB photons lost energy, and their energy per photon was on average proportional to t-1/2. At a microsecond, when baryon pair production was stopping, there were ~a billion photons per excess matter baryon, and the average photon energy was roughly the same as the baryon energy (~1000 MeV). Now there is the same ~billion ratio, but the average photon energy is well below 0.01 eV. Also the photon energy is now decreasing more rapidly than t-1/2.
 
  • #4
mathman said:
The total mass, including energy, was the same. Annihilation converts mass to energy (E=mc2).
This is incorrect. BillSaltLake has it right.
 
  • #5
Correct, energy is not conserved. However, you can isolate small flat region where it is conserved. In the case energy was the same after the annihilation.

What had happened to the rest mass is much more complicated story. Photons don't have rest mass, other particles (say, protons) have it, but it is not clear what is it. If we look at photon at whole it is one story, if we look at it as bound quark system we get different number, if we go back to hot vacuum without Higgs condensate we get the 3rd number - probably 0.
 
  • #6
Dmitry67 said:
Correct, energy is not conserved. However, you can isolate small flat region where it is conserved. In the case energy was the same after the annihilation.

What had happened to the rest mass is much more complicated story. Photons don't have rest mass, other particles (say, protons) have it, but it is not clear what is it. If we look at photon at whole it is one story, if we look at it as bound quark system we get different number, if we go back to hot vacuum without Higgs condensate we get the 3rd number - probably 0.
Well, at the time that there was a lot of anti-matter around, the rest mass was pretty much irrelevant. The particles themselves typically had a lot more kinetic energy than rest mass energy (this is why there was lots of anti-matter still around: if your particle has a lot more kinetic energy than rest mass energy, then collisions will often produce new matter/anti-matter pairs, to replace the ones that annihilate). The expansion cooled the universe until the typical kinetic energy became much smaller than the rest mass energy, and so the normal matter condensed out of the matter/anti-matter mix.

The result of this condensation is that the rest mass energy in the field in question got dumped into radiation. For example, when the temperature dropped much below the mass of the proton, anti-protons disappeared and their energy became radiation. Same thing happened when the temperature dropped much below the mass of the electron.

So you've sort of got two effects going on. Local interactions always conserve energy, in a sense. But globally the expansion was cooling everything down, meaning the universe lost energy as it expanded.
 
  • #7
My point was that the annihilation process does not result in any loss of total mass plus energy. The effect of expansion is another matter.
 
  • #8
mathman said:
My point was that the annihilation process does not result in any loss of total mass plus energy. The effect of expansion is another matter.
Ah, okay, good point.
 

1. What is the difference between matter and antimatter?

Matter and antimatter are essentially the same, except for their opposite electrical charges. Matter is made up of particles with a positive electrical charge, such as protons, and particles with a negative charge, such as electrons. Antimatter, on the other hand, is made up of particles with the opposite charge, such as antiprotons and positrons.

2. How is antimatter created?

Antimatter can be created through high-energy collisions between particles, such as in particle accelerators. It can also be produced through natural processes, such as radioactive decay.

3. Why is antimatter important in understanding the universe?

Antimatter plays an important role in understanding the Big Bang and the origins of the universe. According to the Big Bang theory, equal amounts of matter and antimatter were created in the early universe. However, as the universe expanded and cooled, matter and antimatter annihilated each other, leaving behind a small amount of matter to form the universe we know today.

4. Can matter and antimatter coexist?

No, matter and antimatter cannot coexist for long periods of time. When they come into contact, they annihilate each other, converting their mass into energy. This is why antimatter is difficult to study and contain.

5. What are the potential applications of antimatter?

Antimatter has potential applications in medicine, such as in cancer treatment, as well as in space travel. Antimatter engines could potentially provide a more efficient and powerful source of energy for spacecraft. However, the technology and resources needed to produce and contain antimatter are currently limited, making these applications difficult to achieve.

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