Source: http://www.technolog...og/arxiv/26709/
These guys now say they've trapped 309 antihydrogen atoms for up to 1000 seconds. That's an increase in trapping time of four orders of magnitude, comparable to what's possible with good old ordinary matter.

The news is significant because it makes possible a new set of experiments that should answer some important questions.

Most important of these is whether ordinary gravity attracts or repels antimatter. In other words, does antihydrogen fall up or down?

The realization that we don't know whether antimatter would fall up or down was my Holy Shit moment of the day. So there are understandable basic questions open in physics after all...

Who wants to bet on the answer?
[/quote]A simple thought experiment shows anti-matter is affected the regular way by gravity otherwise energy wouldn't be conserved. e.g Put an atom of H next to one of anti-H and figure out what might happen if gravity was opposite.

The long term storage of significant amounts of antihydrogen should soon settle the question of whether antimatter falls up or down

That's just so sad. So, so sad.

Here's a better one to play with, though: An antiparticle is essentially the same as a normal particle moving backwards in time.
[/quote]

I think it is reasonable to wonder from whose perspective it would fall down. From our perspective, would an anti-particle appear to be affected negatively by gravity because it is moving backwards in time from our perspective? Not so much falling up as un-falling down.

Antimatter still has positive mass so it should be affected by gravity the same as normal matter.

The question is: How do you know that? Before I stumbled across that article, I suppose I was implicitly thinking more or less what you and others here in this thread wrote. Then again, has anybody ever actually checked this in an experiment? From the little I know about what type of observations have been made about antimatter, and judging from the article (as bad as it is), the answer is: apparently not.

Physicists have their models, which make certain predictions about what would happen. But those are just models. Mind you, I don't really expect antimatter to fall up. Still, the fact that this has yet to be verified in an experiment is fascinating. I am a bit surprised about the (faux?) cool attitude towards this here.

The question is: How do you know that?

Because antimatter is defined as having positive mass. And even as early as Newton we had proof that objects with positive mass gravitate towards each other. Therefore we have proof that antimatter gravitates towards other massive objects and not away from them.

EDIT: P.S. we also have proof anti-matter exists as defined. See matter antimatter collisions where the rest mass of both particles is converted additively (as opposed to subtractively) into energy.

[quote name='Prefect' timestamp='1304465577' post='4806172']The question is: How do you know that?

Because antimatter is defined as having positive mass. And even as early as Newton we had proof that objects with positive mass gravitate towards each other. Therefore we have proof that antimatter gravitates towards other massive objects and not away from them.
[/quote]
but from which particle's reference point does it gravitate towards stuff?

[quote name='forsandifs' timestamp='1304465868' post='4806174']
[quote name='Prefect' timestamp='1304465577' post='4806172']The question is: How do you know that?

Because antimatter is defined as having positive mass. And even as early as Newton we had proof that objects with positive mass gravitate towards each other. Therefore we have proof that antimatter gravitates towards other massive objects and not away from them.
[/quote]
but from which particle's reference point does it gravitate towards stuff?
[/quote]
Both. Gravity's a two sided effect, remember?

Are they going to gravitate to each other?

Forgive me, it's been awhile since I've actually looked at this stuff.

Are they going to gravitate to each other?

The real question is: Why not? They both have positive masses. And positive masses exert a gravitational force towards each other.

[quote name='way2lazy2care' timestamp='1304469324' post='4806198']
[quote name='forsandifs' timestamp='1304465868' post='4806174']
[quote name='Prefect' timestamp='1304465577' post='4806172']The question is: How do you know that?

Because antimatter is defined as having positive mass. And even as early as Newton we had proof that objects with positive mass gravitate towards each other. Therefore we have proof that antimatter gravitates towards other massive objects and not away from them.
[/quote]
but from which particle's reference point does it gravitate towards stuff?
[/quote]
Both. Gravity's a two sided effect, remember?
[/quote]

Not when the two things are going opposite directions in time.

Not when the two things are going opposite directions in time.

Jean Claude Van Dam's excellent Timecopping ensures that this is not an issue.