Antiparticles Question

[ParanoiA]

I've just started reading The Elegant Universe and I've run into the whole antiparticles thing again. What I don't understand and what never seems to be explained is: If every particle has a partner antiparticle upon which contact annihilates each other, then how can there be more matter than antimatter? Does something else also annihilate antimatter?

 

I've run into this before, so apparently I'm missing something.

[[Tycho?]]

You're not missing anything.

 

This is one of the fundamental questions in current physics. As far as we can tell, the universe is not biased towards matter or anti-matter. Yet, we observe everything being made of matter, and almost no anti-matter. This is very curious, and as far as I know nobody has offered a valid explanation for it.

[ParanoiA]

;306624']You're not missing anything.

 

This is one of the fundamental questions in current physics. As far as we can tell' date=' the universe is not biased towards matter or anti-matter. Yet, we observe everything being made of matter, and almost no anti-matter. This is very curious, and as far as I know nobody has offered a valid explanation for it.[/quote']

 

Which makes me wonder why we conclude that every particle has an antiparticle partner. I'm guessing the math suggests this?

 

Fascinating, nonetheless.

[[Tycho?]]

Which makes me wonder why we conclude that every particle has an antiparticle partner. I'm guessing the math suggests this?

 

Fascinating, nonetheless.

 

Well most if not all anti-matter particles can be observed directly, so they defaintely are not just mathematical constructs. Anti-matter is a very real thing, which is why the observed inequality is such a big question.

[ParanoiA]

;306627'']Well most if not all anti-matter particles can be observed directly, so they defaintely are not just mathematical constructs. Anti-matter is a very real thing, which is why the observed inequality is such a big question.

 

Actually, I meant why do we conclude the 1:1 ratio of particle / antiparticle since there is very little antimatter. I wondered if perhaps the math suggested this.

 

From what I understand, we can generate antimatter in small quantities - for quite the price I hear.

[Spyman]

Actually, I meant why do we conclude the 1:1 ratio of particle / antiparticle since there is very little antimatter. I wondered if perhaps the math suggested this.

AFAIK: When we create matter from energy it is created in the 1:1 ratio with a particle / antiparticle pair.

 

Quote of Diego Casadei: "We know from experimental high energy physics that whenever matter is created, an equal amount of antimatter is also created."

From what I understand, we can generate antimatter in small quantities - for quite the price I hear.

So when we generate a small quantity of antimatter, we also generate the same amount of normal matter.

[J.C.MacSwell]

Actually, I meant why do we conclude the 1:1 ratio of particle / antiparticle since there is very little antimatter. I wondered if perhaps the math suggested this.

 

From what I understand, we can generate antimatter in small quantities - for quite the price I hear.

 

I think we conclude otherwise, but wonder how it came about. AFAIK "every particle has an anti-particle" refers to the type of particle not the quantities, although any new production of one must be balanced by the other.

 

Isn't there also a small "flaw" in the conservation law that in theory biases matter over anti-matter?

[swansont]

I think we conclude otherwise, but wonder how it came about. AFAIK "every particle has an anti-particle" refers to the type of particle not the quantities, although any new production of one must be balanced by the other.

 

Isn't there also a small "flaw" in the conservation law that in theory biases matter over anti-matter?

 

 

CP symmetry has been observed to be violated in some decays, giving more matter than antimatter. However, the degree to which it is violated does not AFAIK account for the discrepancy. Whether this violation is greater at higher energies (which might imply that the imbalance was generated during the early stages of the universe) is another question to which I do not know the answer.

[swansont]

Actually, I meant why do we conclude the 1:1 ratio of particle / antiparticle since there is very little antimatter. I wondered if perhaps the math suggested this.

 

From what I understand, we can generate antimatter in small quantities - for quite the price I hear.

 

Symmetry and the implied conservation laws.

 

You are generating several antiparticles per minute, presumably for free, in your body. C-14 and K-40, naturally present, both beta-minus decay, yielding antineutrinos.

[ParanoiA]

Ok, that all makes sense. When matter is created (assuming from energy because where else would it come from?) an equal amount of antimatter is also created, thus concluding that at some point, all particles have (or had) antiparticle partners.

 

Cool. So, how do you create mass from energy? Or, at least, what's an example of that?

[ParanoiA]

CP symmetry has been observed to be violated in some decays, giving more matter than antimatter. However, the degree to which it is violated does not AFAIK account for the discrepancy. Whether this violation is greater at higher energies (which might imply that the imbalance was generated during the early stages of the universe) is another question to which I do not know the answer.

 

Interesting. I wonder if Greene will take a stab at that question in this book.

 

Also, would our universe be built and behave the same way if it was built on antimatter rather than matter?

[insane_alien]

antimatter is chemically indistinguishable from normal matter if you ignore the nasty effects of matter and antimatter colliding so yes the universe would be the same.

[J.C.MacSwell]

antimatter is chemically indistinguishable from normal matter if you ignore the nasty effects of matter and antimatter colliding so yes the universe would be the same.

 

Other than the CP conservation violation Swanton mentioned.

 

Forgot where I ready this but if you are off galavanting around the universe and meet your "twin", and he offers to shake your hand, if he offers the left hand don't shake it!

[Severian]

Bear in mind that some particles, like the photon, are their own antiparticles.

 

Most probably (in my opinion) the matter-antimatter asymmetry will be coming from neutrinos. If the right handed neutrino has a majorana mass (one of the possible ways of explaining why neutrinos have such low mass is the "see-saw mechanism" which requires this majorana term) then they can convert matter into antimatter. Basically the (chiral eigenstate) neutrino would be ints own antiparticle, so it could decay to particles (like and electron) or antiparticles (like a positron). This is lepton number violation, which is a form of matter-antimatter symmetry violation.

[ParanoiA]

Other than the CP conservation violation Swanton mentioned.

 

Forgot where I ready this but if you are off galavanting around the universe and meet your "twin", and he offers to shake your hand, if he offers the left hand don't shake it!

 

But I'm left handed...

[ParanoiA]

Bear in mind that some particles, like the photon, are their own antiparticles.

 

Most probably (in my opinion) the matter-antimatter asymmetry will be coming from neutrinos. If the right handed neutrino has a majorana mass (one of the possible ways of explaining why neutrinos have such low mass is the "see-saw mechanism" which requires this majorana term) then they can convert matter into antimatter. Basically the (chiral eigenstate) neutrino would be ints own antiparticle, so it could decay to particles (like and electron) or antiparticles (like a positron). This is lepton number violation, which is a form of matter-antimatter symmetry violation.

 

So, are you theorizing that lepton number violation could explain the bulk of matter-antimatter asymmetry?

 

I only understand about 20% of what you just said. Hopefully that number will come up as I read this thing.

[swansont]

Cool. So, how do you create mass from energy? Or, at least, what's an example of that?

 

 

A photon with at least 0.511 MeV of energy passes by a nucleus, and you get an electron/positron pair. (The nucleus needs to be there to conserve momentum). Happens all the time.

[Kyle]

Other than the CP conservation violation Swanton mentioned.

 

Forgot where I ready this but if you are off galavanting around the universe and meet your "twin", and he offers to shake your hand, if he offers the left hand don't shake it!

 

I think all the aliens and their planets are made of antimatter.

[swansont]

I think all the aliens and their planets are made of antimatter.

 

If this were the case, you'd expect there to be a dividing line between areas of matter and anitmatter. At the interface there should be a significant source of annihilation radiation, e.g. the .511 MeV gammas from electron-positron annihilation. This isn't observed.

[ParanoiA]

If this were the case, you'd expect there to be a dividing line between areas of matter and anitmatter. At the interface there should be a significant source of annihilation radiation, e.g. the .511 MeV gammas from electron-positron annihilation. This isn't observed.

 

I wonder if there are any sci-fi books using anti-matter as the explanation for some far away land or setting for a story. Seems irresistable.

[Spyman]

I think all the aliens and their planets are made of antimatter.[/quote']If this were the case, you'd expect there to be a dividing line between areas of matter and anitmatter. At the interface there should be a significant source of annihilation radiation, e.g. the .511 MeV gammas from electron-positron annihilation. This isn't observed.

Maybe because we have not observed any aliens and their planets yet...

[Kyle]

If this were the case, you'd expect there to be a dividing line between areas of matter and anitmatter. At the interface there should be a significant source of annihilation radiation, e.g. the .511 MeV gammas from electron-positron annihilation. This isn't observed.

If there are no interfaces then where is all the antimatter? Does the matter "zone" go on forever without any sign of antimatter?

[swansont]

If there are no interfaces then where is all the antimatter? Does the matter "zone" go on forever without any sign of antimatter?

 

That's apparently the case, and the asymmetry is not yet explained. The observed CP violations are not large enough (AFAIK) to account for the difference.

[[Tycho?]]

If there are no interfaces then where is all the antimatter? Does the matter "zone" go on forever without any sign of antimatter?

 

Yes, as far as anyone can tell, antimatter is not present in observable quantities in our universe. Which is puzzling.

[Spyman]

But assuming large zones of antimatter exist, there must be some boundary where antimatter atoms from the antimatter galaxies or stars will come into contact with normal atoms. In those regions a powerful flux of gamma rays would be produced. This has never been observed despite deployment of very sensitive instruments in space to detect them.

http://en.wikipedia.org/wiki/Antimatter

 

But the Universe is so HUGE.

 

The main disk of the Milky Way Galaxy is about 80,000 to 100,000 light years in diameter, about 250-300 thousand light years in circumference, and outside the Galactic core, about 1,000 light years in thickness.

http://en.wikipedia.org/wiki/Milky_Way

 

The Local Group is the group of galaxies that includes our galaxy, the Milky Way. The group comprises over 30 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. The galaxies of the Local Group cover a 10 million light-year diameter. The group resides in the Canes Venatici cloud in the Virgo Supercluster.

http://en.wikipedia.org/wiki/Local_Group

 

The diameter of the Supercluster is about 200 million light years; it contains about 100 groups and clusters of galaxies and is dominated by the Virgo cluster near its center. Our Local Group is located near the edge and is being drawn inward toward the Virgo cluster.

http://en.wikipedia.org/wiki/Virgo_Supercluster

 

Superclusters can range in size up to several 10^8 light years. No clusters of superclusters are known, but the existence of structures larger than superclusters is debated. Interspersed among superclusters are large voids of space in which few galaxies exist. Even though superclusters are the largest structures confirmed, the total number of superclusters leave possibilities for structural distribution; the total number of superclusters in the universe is believed to be close to 10 million.

http://en.wikipedia.org/wiki/Supercluster

 

With enormous large voids with very low matter density.

 

In astronomy, voids are the empty spaces between filaments, the largest-scale structures in the Universe that contain very few, or no, galaxies. Voids typically have a diameter of 11 to 150 Mpc; particularly large voids, defined by the absence of rich superclusters, are sometimes called supervoids.

http://en.wikipedia.org/wiki/Void_%28astronomy%29

 

Intergalactic space is the physical space between galaxies. Generally free of dust and debris, intergalactic space is very close to a vacuum. The average density of the Universe is less than one atom per cubic meter. The density of the Universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to extremely rarefied conditions in vast voids that have lower density than the Universe's average.

 

Surrounding and stretching between galaxies, there is a rarefied gas that is thought to possess a cosmic filamentary structure and that is slightly denser than the average density in the Universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen (i.e. a plasma) consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter). It reaches densities as high as 1000 times the average density of the Universe in rich clusters of galaxies.

http://en.wikipedia.org/wiki/Intergalactic_space

 

So it makes me wonder:

 

Can we really be sure, that there will be enought interactions, inside those "small" threads of filaments between Superclusters, with sufficient power to be detected from the very far edge of our observable part of the universe, with our "very sensitive instruments in space" ?

 

Somehow I have the impression, (from my human perspective), that: inside Milky Way - sure, inside our Local Group - problably, inside our Supercluster - maybe, between Virgo and other Superclusters - doubtfully, between Superclusters beyond Superclusters - not likely.

 

How far are we able to observe these gamma rays according to estimates and sensitivity ?