8 ms·

Physicists investigate why matter and antimatter are not mirror images

91 points by dschuetz 8y ago

amelius 8y ago
Couldn't open the article. Do they mean literally mirror images (like geometrically mirrored in a plane)? This makes me wonder, in chemistry you have the concept of chirality. What would happen if you'd literally mirror a non-chiral molecule (down to the quark level)?
- consp 8y ago
  More in as: all properties (except for gravitational) are opposed to the other variant; e.g. charge, spin, parity but not mass. see the wiki entry for some information: https://en.wikipedia.org/wiki/Antimatter https://en.wikipedia.org/wiki/Antimatter
- cjg 8y ago
  The entire article addresses the question of whether antimatter "falls-up" or "falls-down". In other words, does gravity act in the normal way on antimatter, or is its action inverted?
  - dschuetz 8y ago
    That would mean that matter and anti-matter should generally slowly repel (due to the (anti-)gravity), but upon forceful collision they ultimately annihilate each other. That would mean that matter just touching anti-matter should not lead to annihilation of both.
- iand 8y ago
  They want to test whether antimatter falls up in a gravitational field.
  - foxes 8y ago
    Gravitational mass is not meant to be affected by charge / parity conjugation - so anti-matter `should` behave the same way in a gravitational field.
    - acqq 8y ago
      The article ends with: “Few really believe that antimatter falls up, because so much existing theory predicts it will not. But in 1887 existing theory predicted that the apparent speed of light would vary with the speed at which the observer was moving. When Albert Michelson and Edward Morley showed that it does not, they tore up the rule book of physics. It could happen again.”
- dschuetz 8y ago
  Sorry, I've posted an empty submission first, w/o the URL. This one above should work now, or this one: https://www.economist.com/science-and-technology/2018/09/22/physicists-investigate-why-matter-and-antimatter-are-not-mirror-images https://www.economist.com/science-and-technology/2018/09/22/... Mea Culpa
- cjg 8y ago
  Perhaps you can view this archived copy instead: http://archive.is/nEAjt http://archive.is/nEAjt
- evanb 8y ago
  There is a concept of chiral symmetry [0] in QCD---the symmetry whereby left and right handed quarks can be phase rotated independently. It is explicitly broken by quark masses, but the dominant effect is actually the dynamical breaking by the QCD vacuum [1]. However, as far as anyone knows, the chirality at the quark level has nothing to do with the chiral symmetry breaking apparent in eg. the organic molecules of life whereby one enantiomer is used and not the other. [0] https://en.wikipedia.org/wiki/Chirality_(physics)#Chiral_symmetry https://en.wikipedia.org/wiki/Chirality_(physics)#Chiral_sym... [1] https://en.wikipedia.org/wiki/Chiral_symmetry_breaking https://en.wikipedia.org/wiki/Chiral_symmetry_breaking
- MrEldritch 8y ago
  >Do they mean literally mirror images Almost! To be more specific, the laws of physics are CP-symmetric[1] - if you take any interaction involving matter and/or antimatter, and you swap all the positively charged particles with their negatively charged antiparticles and vice versa, and then you invert the coordinate system (swapping left-handed and right-handed chirality, aka "literally mirror image") it should now behave exactly the same. Basically, antimatter is matter with the charges reversed and the handedness mirrored. [1]techically it's only CPT symmetric - you're only guaranteed perfect symmetry under simultaneous reversal of charge, parity (handedness), and time. But almost all processes (anything mediated by gravity, electromagnetism, or - as far as we can tell - the strong nuclear force) are perfectly CP-symmetric; As far as we can tell, CP symmetry violation only shows up in rare scenarios involving the weak nuclear force, where some particles can take slightly longer to decay than their antiparticles.
  - amelius 8y ago
    Thanks! This makes me wonder, since we've obviously never actually mirrored any particle, is there any chance that charge will (ultimately) also turn out to be a geometric concept? (By analogy to magnetism, where changing the orientation of the current flips the polarity of the magnetic effect).
    - MrEldritch 8y ago
      Depending on what you mean by "geometric", maybe - there's been attempts at constructing theories where the electromagnetic field is also, like gravity, a product of spacetime geometry; these generally involve adding extra dimensions to give spacetime enough freedom to hold those behaviors, and then curling up the extra dimensions small enough to explain why we hadn't noticed them yet. (String theory is one of the distant descendants of these attempts.)
      - antidesitter 8y ago
        This is probably referring to https://en.wikipedia.org/wiki/Kaluza–Klein_theory https://en.wikipedia.org/wiki/Kaluza–Klein_theory.
stephengillie 8y ago
Article doesn't match title. They're studying gravity's pull on antimatter.
- gumby 8y ago
  Actually it does. The article intro starts with the fundamental question (why is there an apparent imbalance in the amount of matter/antimatter), then says that one experiment is this gravity one. It returns at the end to the point that the standard model doesn't predict a difference, but then again the standard model doesn't predict the mismatch either.
Aardwolf 8y ago
Is it possible that if they were, they would annihilate each other, so you couldn't live in an area where both are present, and so we are necessarily born in a place where there's much more of only one type? The antimatter might be outside of the observable universe, safely away from interacting with us for the foreseeable future.
- krastanov 8y ago
  Yup, this reasoning even has a name: the anthropic principle. However we still would like to know the underlying mechanism that led to the asymmetry.
  - posterboy 8y ago
    The principle is broader. In this specific example its application is actually reasonable.
  - fpoling 8y ago
    Anthropic principle by itself suggests a mechanism. We know that with probability one there is life that can ask questions about antimatter. Yet the only known explanation for the lack of antimatter is an extremely unlikely fluctuation. But then to solve this probability mismatch one can assume that there many universes separated either in time or space or coexisting via, say, some wonder of quantum mechanics. Only in very few universes the matter dominates just by random accident. Which in turn suggests to look for signs of those other universes.
- stephengillie 8y ago
  There was a short story about an antimatter alien who visited Earth. It shook hands with a human and both were annihilated.
  - Aardwolf 8y ago
    Wouldn't it already be annihilated by air particles though :)
realize 8y ago
I’ve always wondered about this, perhaps someone who understands this subject could explain. Say matter and antimatter were created in roughly equal proportions then some collided to create energy. Couldn’t then this energy coalesce back to regular matter through the mass-energy equivalence? E=mc^2? Repeat this a bit and you’d end up with more matter than antimatter. As I said, this is so simple there must be an easy argument against it but I’ve never heard the idea addressed.
- fahadkhan 8y ago
  I am not a physicist. But obvious question is why would the energy not coalesce back to equal matter and anti matter?
  - misnome 8y ago
    This is a good question! In reality, for this process they do: see https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production. But ignoring this and JBorrows (correct) comments on other properties to be conserved, we can ask: IF more matter is made (in some process) than anti-matter, then why? To explain this, we would need some sort of mechanism where matter was treated differently to antimatter in the laws of physics... and then you are back to the original question of looking for differences. Non-gravitationally, the general case of antimatter behaving differently to matter is covered by the concept of https://en.wikipedia.org/wiki/CP_violation https://en.wikipedia.org/wiki/CP_violation - we do know of cases where this is the case, but not strongly enough to explain what we observe in the universe - the article looks a little heavy but does have a section on the matter-antimatter imbalance that is a little easier to read.
- jcims 8y ago
  I had a similar thought but then wondered if the question would be why there's a bias in which type of matter condenses out of the energy. All this stuff is way over my head but it's fun to think about.
  - MrEldritch 8y ago
losvedir 8y ago
Interesting. I was just talking with a friend about that this weekend. He's working on another experiment, the Deep Underground Neutrino Experiment (DUNE) which is investigating this question, among others. They're shooting a neutrino beam from Fermi Lab in Chicago to a detector deep underground in South Dakota, allowing them to measure several characteristic parameters of these neutrinos. One of them, delta_cp, will give insight into the question of the matter-antimatter imbalance[0]. As just a lowly software developer, it's quite amazing to me to see what cutting edge physicists are up to. The engineering scale of these experiments is mind boggling. [0] 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_...
- nkrisc 8y ago
  Since you mentioned it I'll plug it (simply because I think it's cool): FermiLab has a lot of public events they host as well as various interesting lectures http://news.fnal.gov/newsroom/public-events/ http://news.fnal.gov/newsroom/public-events/ It's in Batavia, about an hour's drive outside Chicago.
  - breatheoften 8y ago
    Are there any good podcasts offering behind the scenes perspectives on experiments at this level?
madrocketsci 8y ago
Do we really know for sure that there is more matter than antimatter in the universe? All we collect from distant galaxies is light, which, as far as I know, interacts with antimatter in the exact same way as with matter. Do we see any gamma-ray producing zones in intergalactic space that might form the boundaries between "matter-zones" and "antimatter-zones"?
- wlesieutre 8y ago
  You're spot on with the gamma producing zones. We don't see any of those, and that's why we don't think any galaxies are made of antimatter. https://www.scientificamerican.com/article/how-do-we-know-that-dista/ https://www.scientificamerican.com/article/how-do-we-know-th...
  - phkahler 8y ago
    I thought there were signs of gamma radiation surrounding galaxies. Perhaps the gas filled void between galaxies is antimatter while the galaxies are matter. Perhaps antimatter is repelled by both types and regular matter is attracted to both types. This might lead to a gaseous cloud pushing things apart and clumps of regular matter. It would also allow some configurations to accelerate and violate conservation of momentum, so it doesn't seem likely. To me there are more questions than "does antimatter fall up?" There are 4 interactions to test.
  - vorg 8y ago
    If anti-matter falls "up" wrt ordinary matter, but still self-attracts, then there wouldn't be any gamma producing zones.
- deleted 8y ago
  [deleted]

91 points by dschuetz 8y ago

Couldn't open the article. Do they mean literally mirror images (like geometrically mirrored in a plane)? This makes me wonder, in chemistry you have the concept of chirality. What would happen if you'd literally mirror a non-chiral molecule (down to the quark level)?

consp 8y ago
More in as: all properties (except for gravitational) are opposed to the other variant; e.g. charge, spin, parity but not mass. see the wiki entry for some information: https://en.wikipedia.org/wiki/Antimatter https://en.wikipedia.org/wiki/Antimatter
cjg 8y ago
The entire article addresses the question of whether antimatter "falls-up" or "falls-down". In other words, does gravity act in the normal way on antimatter, or is its action inverted?
- dschuetz 8y ago
  That would mean that matter and anti-matter should generally slowly repel (due to the (anti-)gravity), but upon forceful collision they ultimately annihilate each other. That would mean that matter just touching anti-matter should not lead to annihilation of both.
iand 8y ago
They want to test whether antimatter falls up in a gravitational field.
- foxes 8y ago
  Gravitational mass is not meant to be affected by charge / parity conjugation - so anti-matter `should` behave the same way in a gravitational field.
  - acqq 8y ago
    The article ends with: “Few really believe that antimatter falls up, because so much existing theory predicts it will not. But in 1887 existing theory predicted that the apparent speed of light would vary with the speed at which the observer was moving. When Albert Michelson and Edward Morley showed that it does not, they tore up the rule book of physics. It could happen again.”
dschuetz 8y ago
Sorry, I've posted an empty submission first, w/o the URL. This one above should work now, or this one: https://www.economist.com/science-and-technology/2018/09/22/physicists-investigate-why-matter-and-antimatter-are-not-mirror-images https://www.economist.com/science-and-technology/2018/09/22/... Mea Culpa
cjg 8y ago
Perhaps you can view this archived copy instead: http://archive.is/nEAjt http://archive.is/nEAjt
evanb 8y ago
There is a concept of chiral symmetry [0] in QCD---the symmetry whereby left and right handed quarks can be phase rotated independently. It is explicitly broken by quark masses, but the dominant effect is actually the dynamical breaking by the QCD vacuum [1]. However, as far as anyone knows, the chirality at the quark level has nothing to do with the chiral symmetry breaking apparent in eg. the organic molecules of life whereby one enantiomer is used and not the other. [0] https://en.wikipedia.org/wiki/Chirality_(physics)#Chiral_symmetry https://en.wikipedia.org/wiki/Chirality_(physics)#Chiral_sym... [1] https://en.wikipedia.org/wiki/Chiral_symmetry_breaking https://en.wikipedia.org/wiki/Chiral_symmetry_breaking
MrEldritch 8y ago
>Do they mean literally mirror images Almost! To be more specific, the laws of physics are CP-symmetric[1] - if you take any interaction involving matter and/or antimatter, and you swap all the positively charged particles with their negatively charged antiparticles and vice versa, and then you invert the coordinate system (swapping left-handed and right-handed chirality, aka "literally mirror image") it should now behave exactly the same. Basically, antimatter is matter with the charges reversed and the handedness mirrored. [1]techically it's only CPT symmetric - you're only guaranteed perfect symmetry under simultaneous reversal of charge, parity (handedness), and time. But almost all processes (anything mediated by gravity, electromagnetism, or - as far as we can tell - the strong nuclear force) are perfectly CP-symmetric; As far as we can tell, CP symmetry violation only shows up in rare scenarios involving the weak nuclear force, where some particles can take slightly longer to decay than their antiparticles.
- amelius 8y ago
  Thanks! This makes me wonder, since we've obviously never actually mirrored any particle, is there any chance that charge will (ultimately) also turn out to be a geometric concept? (By analogy to magnetism, where changing the orientation of the current flips the polarity of the magnetic effect).
  - MrEldritch 8y ago
    Depending on what you mean by "geometric", maybe - there's been attempts at constructing theories where the electromagnetic field is also, like gravity, a product of spacetime geometry; these generally involve adding extra dimensions to give spacetime enough freedom to hold those behaviors, and then curling up the extra dimensions small enough to explain why we hadn't noticed them yet. (String theory is one of the distant descendants of these attempts.)
    - antidesitter 8y ago
      This is probably referring to https://en.wikipedia.org/wiki/Kaluza–Klein_theory https://en.wikipedia.org/wiki/Kaluza–Klein_theory.

stephengillie 8y ago

Article doesn't match title. They're studying gravity's pull on antimatter.

gumby 8y ago
Actually it does. The article intro starts with the fundamental question (why is there an apparent imbalance in the amount of matter/antimatter), then says that one experiment is this gravity one. It returns at the end to the point that the standard model doesn't predict a difference, but then again the standard model doesn't predict the mismatch either.

Aardwolf 8y ago

Is it possible that if they were, they would annihilate each other, so you couldn't live in an area where both are present, and so we are necessarily born in a place where there's much more of only one type? The antimatter might be outside of the observable universe, safely away from interacting with us for the foreseeable future.

krastanov 8y ago
Yup, this reasoning even has a name: the anthropic principle. However we still would like to know the underlying mechanism that led to the asymmetry.
- posterboy 8y ago
  The principle is broader. In this specific example its application is actually reasonable.
- fpoling 8y ago
  Anthropic principle by itself suggests a mechanism. We know that with probability one there is life that can ask questions about antimatter. Yet the only known explanation for the lack of antimatter is an extremely unlikely fluctuation. But then to solve this probability mismatch one can assume that there many universes separated either in time or space or coexisting via, say, some wonder of quantum mechanics. Only in very few universes the matter dominates just by random accident. Which in turn suggests to look for signs of those other universes.
stephengillie 8y ago
There was a short story about an antimatter alien who visited Earth. It shook hands with a human and both were annihilated.
- Aardwolf 8y ago
  Wouldn't it already be annihilated by air particles though :)

realize 8y ago

I’ve always wondered about this, perhaps someone who understands this subject could explain. Say matter and antimatter were created in roughly equal proportions then some collided to create energy. Couldn’t then this energy coalesce back to regular matter through the mass-energy equivalence? E=mc^2? Repeat this a bit and you’d end up with more matter than antimatter. As I said, this is so simple there must be an easy argument against it but I’ve never heard the idea addressed.

fahadkhan 8y ago
I am not a physicist. But obvious question is why would the energy not coalesce back to equal matter and anti matter?
- misnome 8y ago
  This is a good question! In reality, for this process they do: see https://en.wikipedia.org/wiki/Pair_production https://en.wikipedia.org/wiki/Pair_production. But ignoring this and JBorrows (correct) comments on other properties to be conserved, we can ask: IF more matter is made (in some process) than anti-matter, then why? To explain this, we would need some sort of mechanism where matter was treated differently to antimatter in the laws of physics... and then you are back to the original question of looking for differences. Non-gravitationally, the general case of antimatter behaving differently to matter is covered by the concept of https://en.wikipedia.org/wiki/CP_violation https://en.wikipedia.org/wiki/CP_violation - we do know of cases where this is the case, but not strongly enough to explain what we observe in the universe - the article looks a little heavy but does have a section on the matter-antimatter imbalance that is a little easier to read.
jcims 8y ago
I had a similar thought but then wondered if the question would be why there's a bias in which type of matter condenses out of the energy. All this stuff is way over my head but it's fun to think about.
- MrEldritch 8y ago

losvedir 8y ago

Interesting. I was just talking with a friend about that this weekend. He's working on another experiment, the Deep Underground Neutrino Experiment (DUNE) which is investigating this question, among others. They're shooting a neutrino beam from Fermi Lab in Chicago to a detector deep underground in South Dakota, allowing them to measure several characteristic parameters of these neutrinos. One of them, delta_cp, will give insight into the question of the matter-antimatter imbalance[0]. As just a lowly software developer, it's quite amazing to me to see what cutting edge physicists are up to. The engineering scale of these experiments is mind boggling. [0] 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_...

nkrisc 8y ago
Since you mentioned it I'll plug it (simply because I think it's cool): FermiLab has a lot of public events they host as well as various interesting lectures http://news.fnal.gov/newsroom/public-events/ http://news.fnal.gov/newsroom/public-events/ It's in Batavia, about an hour's drive outside Chicago.
- breatheoften 8y ago
  Are there any good podcasts offering behind the scenes perspectives on experiments at this level?

madrocketsci 8y ago

Do we really know for sure that there is more matter than antimatter in the universe? All we collect from distant galaxies is light, which, as far as I know, interacts with antimatter in the exact same way as with matter. Do we see any gamma-ray producing zones in intergalactic space that might form the boundaries between "matter-zones" and "antimatter-zones"?

wlesieutre 8y ago
You're spot on with the gamma producing zones. We don't see any of those, and that's why we don't think any galaxies are made of antimatter. https://www.scientificamerican.com/article/how-do-we-know-that-dista/ https://www.scientificamerican.com/article/how-do-we-know-th...
- phkahler 8y ago
  I thought there were signs of gamma radiation surrounding galaxies. Perhaps the gas filled void between galaxies is antimatter while the galaxies are matter. Perhaps antimatter is repelled by both types and regular matter is attracted to both types. This might lead to a gaseous cloud pushing things apart and clumps of regular matter. It would also allow some configurations to accelerate and violate conservation of momentum, so it doesn't seem likely. To me there are more questions than "does antimatter fall up?" There are 4 interactions to test.
- vorg 8y ago
  If anti-matter falls "up" wrt ordinary matter, but still self-attracts, then there wouldn't be any gamma producing zones.
deleted 8y ago
[deleted]