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Comment by SeveredCross | Hacker News Reader

Possibly with something like 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).

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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.

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.

If they can be trapped using photons for this long, I guess they don't react?

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.

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>.

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.

I don't fully understand your analogy. How exactly is that situation "backwards in time" if it still is moving forwards? Where could I find more info on this?

Actually, it sounds like you got it perfectly. There is legitimately a way in which he's going "backwards", it's just not the way you would naturally think of if I just told you he's going "backwards". The backwards-through-time thing is one way of reading the math, but it doesn't mean what you think if you just read what the English says. Antimatter is way less interesting than "backwards in time" can make it sound. It's interesting, but not "kill your grandfather before your father is born" sort of interesting, just "fun particle physics" interesting.

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.

Go read Feynman's QED.

> 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!

I do not understand:

- I think all photons fall down in a gravitational field.

- you claim photons are their own antiparticle.

Hence, antiphotons fall down in a gravitational field. How then would antimatter fall upwards ~because~ it is the antiparticle of matter? Am I wrong in 'knowing' that all light bends the same under gravity?

Best as I can tell I don't think we disagree. You are saying that antimatter should react the same way with respect to gravity as matter does right? Then I agree. I do not think antimatter will be found to fall up or be repelled.

You are right. I must have mixed up two replies.

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