96 replies to this topic

[Prefect]

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?

[kdmiller3]

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

(Exotic matter with negative mass should also fall down since gravity would push it away but it would react to the force backwards. While not as spectacular as antimatter, it would produce an...interesting result when it touched the ground.)

[Human Resource]

As kdmiller3 pointed out, you've mixed up two concepts... The concept of antimatter and that of exotic matter. Antimatter differentiates "only" in charge from it's matter twin... Their spin is actually the same, which is the reason why they can annihilate when they meet their matter counterpart, but to keep it simple... It's the difference in charge which enables annihilation, crossing into photons in the case of electron-positron contact, which is the simplest to digest. That's the "magic" of antimatter.

What you are referring to is exotic matter, a theoretical construct which allows for cute, but unobserved (and highly hypothetical) matter which has wild properties like negative mass or negative energy density... But when you start diverging in such theories, consider the "story" of the aether which had all sorts of magical properties, only to be shot down by Einstein. But also, it's worth noting that the aether, although incorrect is a great example how even the incorrect theories can point us in the right direction. That's the awesome self-optimization of science, willingness to see and rectify our mistakes and proceed onwards into new intellectual victories. Anyways, to keep it short, when you shove negative mass into relativistic equations, you get some nifty results which imply the possibility of wormholes. Still highly theoretical and very sketchy.

[Yann L]

But when you start diverging in such theories, consider the "story" of the aether which had all sorts of magical properties, only to be shot down by Einstein.

And to be 'resurrected' in the form of vacuum energy. Sometimes a wild idea may have some truth to it, but in a completely different way than originally thought.

Anyway, I think the article linked by the OP shows some symptoms of, let's call it 'popular creative journalism'. I was very surprised that it mentioned possible gravitational repulsion, which antimatter does most certainly not exhibit. Of course, as expected, the original CERN paper does not mention gravitational repulsion in any way. The main idea, apart from the obvious analysis of long term trapping, is to cool down the antimatter to a level where observations about the validity of the charge, parity and time reversal symmetries can be made.

[Promit]

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.

[Human Resource]

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.

That one originated with Feynman, right? It's funny actually, Feynman spent most of his life "making fun" of pure mathematicians (the story about oranges was particularly amusing)... And here he used the same idealistic mathematics which allow for physically untestable (technically and sensibly) situations by negating the variable of time and finding his dear antiparticles, in essence the same as their "normal" counterparts going "backwards in time". It's fun to think about it, but there's no way to test such a concept. But generally speaking, I loved Feynman's way of portraying physics, communicating his ideas... Such a brilliant man.

[taby]

To be perfectly clear, it was Einstein who killed the aether with special relativity, and it was he who resurrected it with general relativity. Zero point energy and quantum mechanics were totally irrelevant to Einstein's initial formulation of general relativity. This is in spite of the fact that it was Einstein himself who had discovered zero point energy three years beforehand.

But why were they irrelevant, you ask? Because a gravitational field consists of energy, even in the classical (e.g., non-quantum) theory of general relativity.

Additionally, there is solid evidence of matter-antimatter CP asymmetry. A CP asymmetry is tantamount to a T asymmetry. So, there is not quite a pure symmetry:
"Fermilab scientists find evidence for significant matter-antimatter asymmetry"
"CP asymmetry inplies T asymmetry"

[Human Resource]

I find it exhilarating that there are actually quite a few people on GameDev who are actually genuinely interested in physics and a lot of other fields in depth. My experience with a lot of people was that they only learned the superficial stuff, while rendering; the basics of linear algebra, lacking the true understanding necessary for... Intellectual pleasure, at least. But understanding of such concepts surely affects everything. The need to understand must keep you guys up at night, too. Always just a little bit more to learn and comprehend about the Universe we inhabit before getting a little bit of shuteye.

I must say, I'm impressed!

[taby]

Hey, let's not get carried away. I'm an utter crackpot, and no amount of knowledge with respect to physics will change that fact. I am convinced via my own numerological argument that the GZK cutoff (2.7 J or so) is related entirely to the mass and density of the Earth. Hence, I am a crackpot, and proud of it.

If you think I'm kidding around, or being facetious, then ask the operators of El Naschie Watch or The Reference Frame. I'm a crackpot dude, and these actual mathematicians/physicists will likely vouch for the fact that I'm very proud of it.

In other words, please don't ever again imply that I am an authority figure. Your doing so makes me almost as mad as when I see racist self-declared experts act like they know everything there is to know about predator-prey systems.

Cheers, and welcome to GD.net! Good timez. If you want to apologize, I'll be here waiting, reading my supersymmetric string theory books.

Edit: Given your lack of apology over the past 8 hours, I thought it would be fun to test if negative reputation is possible. Apparently not, since you're at 0, not -2. Lucky! So maybe you should go back to following your own sig -- STFU, listen, and stop spreading false information.

Edit: Oh noes, you rated me down! In case you haven't figured it out yet, this isn't a popularity contest for me. I feed off of your negative emotions.

[taby]

Dear pseudoanonymous US citizen who googled me at 12:36 yesterday... Please use proper capitalization, though I must commend you for at least spelling it right.

To the pseudoanonymous US citizen who googled me at 13:44 on April 26th, thanks for capitalizing it properly!

To the pseudoanonymous US citizen who googled me at 18:24 on April 25th, it's "Shawn", not "hawn".

You know who you are, and so do I. I mean, you don't spend thousands of hours teaching comp sci to people for free without earning a few favours. Don't fuck with me, and I won't fuck with you. OK?

On a much lighter note... this Tron: Legacy R3C0NF1GUR3D remix album is the cat's pajamas! Totally recommend it for anyone not sure of the power of electronic music. End of Line (Photek Remix) for the win!

Until more gravity threads come up... toodles!!

[d000hg]

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?

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.

[way2lazy2care]

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.

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.

[Prefect]

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.

[forsandifs]

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.

[way2lazy2care]

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.

but from which particle's reference point does it gravitate towards stuff?

[Promit]

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.

but from which particle's reference point does it gravitate towards stuff?

Both. Gravity's a two sided effect, remember?

[Alpha_ProgDes]

Are they going to gravitate to each other?

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

[owl]

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.

[way2lazy2care]

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.

but from which particle's reference point does it gravitate towards stuff?

Both. Gravity's a two sided effect, remember?

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

[Khaiy]

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.