5 ms·

"The ALPHA team now plans to cool a small lump of antihydrogen ..." How do you cool something at this scale? And how about when it can't collide with any norma

"The ALPHA team now plans to cool a small lump of antihydrogen ..." How do you cool something at this scale? And how about when it can't collide with any normal matter?

SeveredCross 16y ago
Possibly with something like http://en.wikipedia.org/wiki/Laser_cooling http://en.wikipedia.org/wiki/Laser_cooling, where you're not actually striking it with matter, but only with photons, though I don't know if photons react with antimatter (I presume not, but I am not a particle physicist).
- sp332 16y ago
  Of course they interact with photons. Photons are how electric and magnetic fields are propagated. So if they can be contained by an electromagnetic trap, they interact with photons.
  - SeveredCross 16y ago
    I think I should've been more specific—I know that the two interact, but I wasn't sure if they /react/. That is, would collision between photons and antimatter produce the same sort of decay as matter-antimatter collision. Some research suggests that it indeed would.
    - BoppreH 16y ago
      If they can be trapped using photons for this long, I guess they don't react?
- Dn_Ab 16y ago
  Antimatter is just matter moving backwards in time, so it interacts with photons (which by the way, is its own antiparticle). This is one line of reasoning which strongly suggests antimatter should fall down not up in a gravitionational field. although iirc Dark matter is something does not interact with light.
  - zoul 16y ago
    > Antimatter is just matter moving backwards in time That could finally put an end to the chicken-egg problem. There was an anti-matter chicken in the first egg and it had moved back in time to lay its own egg after it hatched!
  - mikle 16y ago
    Seriously, matter moving backwards in time? This is amazing. I never had a reason to learn more about antimatter until now. Thanks <off to wikipedia>.
    - Dn_Ab 16y ago
      Well, in the same manner that a cow is spherical. :) I use it to motivate that antimatter is not so different from matter and not this exotic thing.
    - jerf 16y ago
      I think people may be overselling this a bit. It is true that antimatter bears certain resemblances to matter traveling "backwards in time" when the math is examined, but the mental images conjured up by a plain-English reading of that phrase are almost entirely wrong. It's not like you tap the antimatter and the motion goes backward in time. I hate using metaphors, but it's somewhat more like you have a guy walking forward on the road, but if you hit him violently enough he'll end up turned around, walking back-first but in the same direction. Yeah, he's walking backwards through time! ime! ime! ime! but it's not like you can actually send messages backwards or anything; give him a message and he's still walking in the positive-time direction. There's a lot of cancellation of the negative term that goes on and he's still dancing to the tune of the same arrow-of-time as the rest of us. I'm pretty pessimistic that antimatter will be repulsed by gravity, because you would suddenly have a term that would have to appear for the potential energy of the now-flipped gravity field. It makes much more sense for it to be affected normally. It's an interesting question that we might as well look at, on the off chance that the science will be wrong (which is when it advances, after all), but I wouldn't hold your breath.
      - 16y ago

"The ALPHA team now plans to cool a small lump of antihydrogen ..." How do you cool something at this scale? And how about when it can't collide with any normal matter?

SeveredCross 16y ago

Possibly with something like http://en.wikipedia.org/wiki/Laser_cooling http://en.wikipedia.org/wiki/Laser_cooling, where you're not actually striking it with matter, but only with photons, though I don't know if photons react with antimatter (I presume not, but I am not a particle physicist).

sp332 16y ago
Of course they interact with photons. Photons are how electric and magnetic fields are propagated. So if they can be contained by an electromagnetic trap, they interact with photons.
- SeveredCross 16y ago
  I think I should've been more specific—I know that the two interact, but I wasn't sure if they /react/. That is, would collision between photons and antimatter produce the same sort of decay as matter-antimatter collision. Some research suggests that it indeed would.
  - BoppreH 16y ago
    If they can be trapped using photons for this long, I guess they don't react?
Dn_Ab 16y ago
Antimatter is just matter moving backwards in time, so it interacts with photons (which by the way, is its own antiparticle). This is one line of reasoning which strongly suggests antimatter should fall down not up in a gravitionational field. although iirc Dark matter is something does not interact with light.
- zoul 16y ago
  > Antimatter is just matter moving backwards in time That could finally put an end to the chicken-egg problem. There was an anti-matter chicken in the first egg and it had moved back in time to lay its own egg after it hatched!
- mikle 16y ago
  Seriously, matter moving backwards in time? This is amazing. I never had a reason to learn more about antimatter until now. Thanks <off to wikipedia>.
  - Dn_Ab 16y ago
    Well, in the same manner that a cow is spherical. :) I use it to motivate that antimatter is not so different from matter and not this exotic thing.
  - jerf 16y ago
    I think people may be overselling this a bit. It is true that antimatter bears certain resemblances to matter traveling "backwards in time" when the math is examined, but the mental images conjured up by a plain-English reading of that phrase are almost entirely wrong. It's not like you tap the antimatter and the motion goes backward in time. I hate using metaphors, but it's somewhat more like you have a guy walking forward on the road, but if you hit him violently enough he'll end up turned around, walking back-first but in the same direction. Yeah, he's walking backwards through time! ime! ime! ime! but it's not like you can actually send messages backwards or anything; give him a message and he's still walking in the positive-time direction. There's a lot of cancellation of the negative term that goes on and he's still dancing to the tune of the same arrow-of-time as the rest of us. I'm pretty pessimistic that antimatter will be repulsed by gravity, because you would suddenly have a term that would have to appear for the potential energy of the now-flipped gravity field. It makes much more sense for it to be affected normally. It's an interesting question that we might as well look at, on the off chance that the science will be wrong (which is when it advances, after all), but I wouldn't hold your breath.
    - 16y ago