Matter and Antimatter?

[Jay-qu]

In fact there is a constant creation of particles, and anti particles, and that annihilate all the time.

 

Is this not the reason that blackholes are said to 'evapourate'? a pair of particles created on the event horizen go in different directions and one gets sucked in the other doesnt...something like that

[lindagarrette]

There's actually more matter than antimatter because the universe isn't perfectly symmetrical.

And in a vaccum, even though it is considered as "empty space", it is not. In fact there is a constant creation of particles, and anti particles, and that annihilate all the time.

I don't thinik antiparticles are being created naturally anymore. That era ended a tiny fraction of a second after the BB, when the universe was about the size of a basketball (or football). Right?

[CraigD]

I don't thinik antiparticles are being created naturally anymore. That era ended a tiny fraction of a second after the BB, when the universe was about the size of a basketball (or football). Right?

No, antiparticles are created naturally all the time and in substantial numbers, mostly during radioactive decay. The total mass of this antimatter is miniscule, however, and unless something extraordinary occurs, annihilates with an ordinary particle almost immediately.

 

If you’ve ever had a PET scan, the gamma photons from antimatter annihilation of positrons emitted from radioflourine injected into your veins just before the procedure are what it’s measuring. Although this radioflourine is artificially manufactured, similar processes occur naturally.

 

The “virtual pair production” Aki describes is a different process. In this case, any photon can be thought of as splitting into equivalent-energy antiparticles, then annihilating back into the original. It’s “virtual”, because, not being measured, in some sense it didn’t really happen, plus some quantum weirdness reasons. “Virtually” produced antiparticle pairs can become “actual” – that is, actually be measured – when they’re prevented from annihilating. The intense gravity of something like a black hole can do this – Hawking radiation.

 

Something related – the Casimir effect - can be measured by physically restricting empty space – vacuum – so that virtual pair production can’t occur.

[Qfwfq]

The asymmetry is only due to weak interactions.

 

In fact there is a constant creation of particles, and anti particles, and that annihilate all the time.

Only virtually!

[lindagarrette]

No, antiparticles are created naturally all the time and in substantial numbers, mostly during radioactive decay. The total mass of this antimatter is miniscule, however, and unless something extraordinary occurs, annihilates with an ordinary particle almost immediately.

 

I am still researching this but it seems to me Baryogenesis, not radioactive decay generates antiparticles. You may be right about black holes being a source, however, as there may be enough energy in that vicinity for baryogenesis to occur. Elsewere, we would surely see explosions going on all the time as antimatter and matter collide.

[Erasmus00]

I am still researching this but it seems to me Baryogenesis, not radioactive decay generates antiparticles. You may be right about black holes being a source, however, as there may be enough energy in that vicinity for baryogenesis to occur. Elsewere, we would surely see explosions going on all the time as antimatter and matter collide.

 

Consider the nuclear decay 7Be4 -> 7Li3 + positron. Also consider that cosmic rays striking the atmosphere produce positron/electron pairs. (Carl Anderson's discovery of this in 1932 earned him a nobel prize). Antimatter is created all the time, it's just very short lived.

-Will

[CraigD]

…Elsewere, we would surely see explosions going on all the time as antimatter and matter collide.

Such explosions do occur all the time – they’re just very tiny. (thought very useful)

 

The wikipedia article “Positron emission tomography” has a good description of the workings of a PET scanner.

 

I know of no experimental verification of matter/antimatter annihilation occurring outside particle accelerators or PET scanners, but reason that, since the radioisotopes used in the PET scanning procedure occur in small quantities naturally, such events must occur. Experimental evidence of which I’m simply unaware may well exist.