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Antihydrogen Trapped For 1000 Seconds (technologyreview.com)
230 points by eduardoflores on May 2, 2011 | hide | past | web | favorite | 105 comments

By the way, there's something I've been wondering about for a long time. I read somewhere that there are no antiphotons and antimatter emits light just the same as normal matter. So, I assume that there's no way to tell whether a photon was emitted by antimatter or by matter.

Therefore, how do we know distant galaxies aren't made of antimatter ?

Maybe there's an obvious answer, but as far as I know, the only thing we can know about these galaxies, we know because of the radiation they emit.

Empty space isn't completely empty, even between galaxies. There are traces of gas, almost entirely Hydrogen, between galaxies. If there were entire galaxies made of anti-matter then the areas where their clouds of inter-galactic anti-gas contacted normal inter-galactic gas would be rife with emissions due to annihilations. The amount of matter should be enough to be detectable even at tremendous distances.

I've wondered this myself. An explanation I have heard from a physisicist is: if there were regions of the universe where antimatter is dominant, the boundaries where they border normal matter space would be extremely bright from the annihilation reactions. Apparently even very thin interstellar gas would generate a lot of energy in matter/antimatter annihilations.

I think the way that is usually phrased is that "photons are their own antiparticles".

Rgd "anti matter galaxies", we do detect particle cosmic rays on earth that originate from outer space (outside the solar system), though I don't know either whether they might originate from as far as other galaxies.

However, gravity is weak compared to the other forces, so galaxies can be expected to eject fast moving matter in addition to radiation (just like our sun).

So, given my meagre understanding of physics, I wouldn't expect to have seen anti-matter galaxies without also seeing gamma radiation fields spanning the space between a matter and an antimatter galaxy as particles annihilate each other.

If antimatter are repulsed by gravity, they might be in the outer shell of the universe being pushed further away. If antimatter also repulsed among themselves (??), then they won't have a chance to come together to create antimatter star.

Most people believe antimatter attract just like matter, so it's a moot point.

I am nothing short of _astounded_ that we don't know if anti-matter "falls up".

Well, the point of science is that we don't know until we observe it. So it shouldn't be that astounding since we've had a ridiculously hard time getting large amounts of neutral antimatter (everything before was charged, so EM affects overwhelmed gravitational). The consensus seems to be that antimatter will behave 'normally'. but we haven't seen it yet. Also, it turns out that certain frameworks where anti-matter is repelled by matter gravity doesn't violate anything else that hasn't already been violated (for example, CP and CPT symmetry have already be observed to be broken). And thus the uncertainty.

Hold on, where are you getting the CPT-symmetry violation from? This paper http://arxiv.org/abs/0801.0287v4 has a collection of experimental results hinting at that but the conclusion does not as yet seem to be very strong.

I've never heard anyone argue that it would react any differently to gravity than normal matter. After all, the only difference is the electrical charge of the particles. They have the same mass.

I think the "falling up" argument comes from the conception that antimatter is the time-reverse of matter.

Of course, regular old hydrogen "falls up", being lighter than air. :) I guess if gravity is truly reversed for antihydrogen, it would fall up even faster. But I highly doubt it's actually gravitationally repulsive.

The simple solution is to let it fall in a vacuum, which seems to be what they're doing in this case.

Or perhaps must be affected by antigravity the way matter is by gravity. Assuming antigravity exists. Whether that's correct at all I don't know, but that's the logic being used.

So if it "reacts the opposite" to gravity, what does that mean?

I would see no reason for Newton's law to not hold true around our scale, so repelling means F=Gm1m2/r^2 which only makes sense if one of the masses is actually negative. Just the thought of it looks like fun.

I thought this was a settled question, but I guess it's never been tested... so it's just consensus opinion, not verified fact.

I am also surprised.

$100 says antimatter is also attracted by gravity. Anything else would be too cool for school.

I'm with you on this one. If antimatter was just backwards everything then there'd be large conspicuous clusters of the stuff all over the cosmos because ordinary matter would be repelling it instead of annihilating it.

While there does seem to be a lot of dark matter out there, if it were actually antimatter and had opposite gravity to normal matter one would imagine there would be a huge discrepancy between cosmologists' models and observation. The high-end supercomputer simulations and regressions cosmologists employ have good predictive power, even though we lack a full explanation for the phenomena we can observe. Cosmologists deal with such far-out concepts to begin with (by definition) that it's not as if they'd be averse to a concept like antigravity if it had predictive utility.

toys idly with desk magnets while thinking about it

Then again, given that photons are massless maybe there could be such a thing as a gravitational dipole...


We know two things about dark matter: - It doesn't interact electromagnetically. - It does interact gravitationally and produces extra gravitational attraction beyond the electromagnetically interacting matter we know about. - It is dispersed throughout galaxies.

The first property rules out baryonic antimatter as dark matter, since that would interact electromagnetically. The last two properties rule out anything that has a repulsive gravitational interaction as dark matter.

>We know two things about dark matter:

while we don't know whether it exists at all. Whatever phenomena are explained by DM are also easy explained by molecular hydrogen (i.e H2) which is almost not detectable. [The hydrogen we know about in the space is atomic - H, and there should be orders of magnitude more of molecular one than atomic when you have atomic at such interstellar space conditions]

We know that dark matter cannot be baryonic matter (atoms) for two reasons. First, models of the big bang that have been confirmed by experiment closely bound the total amount of baryonic matter in the Universe. Second, dark matter doesn't seem to behave the same way that baryonic matter behaves (normal matter clumps, dark matter doesn't appear to do so).

>...models of the big bang that have been confirmed by experiment ...

to put it mildly, it is a very overreaching statement.

>Second, dark matter doesn't seem to behave the same way that baryonic matter behaves (normal matter clumps, dark matter doesn't appear to do so).

double whammy - we couldn't observe dark matter and we couldn't observe its clumps.

Or consider it another way - while it supposedly have gravitational attraction, and have no other strong interactions known, we somehow should suppose that its non-clumping, ie. gaseous/cloudy/spread-around state is still a normal thing.

Fuck it, you're on. $100. I want to believe ...

Doesn't look like your odds are good (consensus atm is there's no theoretical basis): http://www.reddit.com/r/askscience/comments/h28sd/is_there_a...

Well, let's see what the data says. I confess I want the universe to surprise and confound. I want the theories to be wrong, I want reality to be stranger than fiction. That would be awesome!

Or I am wrong, in which case I'll happily pay out[1]. I'm a layman, as if that wasn't obvious, and it will be a much-needed physics lesson. Win-win.

[1] If in Australia, payout will take the form of alcohol credits at an establishment of winner's choosing. Hey, I want to learn from my superiors :) If not, a crisp USD$100 note will be posted to any mailing address in the world, to be supplied.

I want the theories to be wrong too, it's just that I'm a sceptic in this case simply because of the utter awesomness that would be the result.

I will happily spend more than $100 just on delivery if that is required to make a payout in liquor (local Swedish flavors) across the world. Crisp paper is fully acceptable as well :)

Doubt we will ever settle this though... I have painfully little faith in scientific breakthroughs.

Well, it would be really cool and confounding if gravity made antimatter move sideways. But I don't think that's likely.

Indeed, considering that there are 360 degrees of sideways. Which one? :)

That reddit post (and admittedly it is just a reddit post) actually says the opposite: there is no theoretical basis for antimatter not to behave exactly like regular matter in the presence of a gravitational field.

The null hypothesis (and, in the absence of any strong evidence to the contrary, the stronger hypothesis) is that antimatter and matter respond to gravity in exactly the same way.

That's what I said. The person making the bet is betting on attraction, so the response was betting on repulsion, and I responded to the latter.

Won't it have it's own flavor of gravity? As in a force that attracts matter together and a force that attracts anti matter together?

It is actually great that they're doing this experiment 'cos if it turned out in a way that contradicted theory (which I think says "antimatter falls") then we might have to re-examine a whole lot of things!

For example, if antimatter rises, there ought to be a statistical preference for black holes to emit antimatter.

One of the posters on that site said CPT violation would be another great thing to check. Hell yeah!

If it is proven that that anti-matter is repelled by gravity does that mean hover-boards will become a reality in our lifetimes? What are some of the potential practical applications?

Given that antimatter explodes violently when put into contact with regular matter, I kind of hope that's not how they go about achieving this. A kid who forgets to recharge his board, allowing the magnetic fields to collapse, could do a considerable amount of damage.

> I kind of hope that's not how they go about achieving this

Don't worry. The design is impractical anyway - regulating the "anti-mass" would be extremely difficult. Just when you got it balanced, the kid would drink a glass of water and the board would sink into the ground.

Due caution would indeed be advisable when selling these gadgets, though. A matter-antimatter collision of 50kg would be equivalent to about 2.1 gigatons of TNT, or about 400 times more powerful than the most powerful hydogen bomb ever developed, so it would indeed caused a "considerable amount of damage".

> The design is impractical anyway

Nah, you just need a miniature collider inside the board, manufacturing more anti-matter as necessary.

And obviously, it would be powered by annihilating matter/antimatter together, via a small Mr. Fusion at the back.

They could just use a compressed-air ballast tank. That would certainly be simpler than a miniature collider, and the explosion risk isn't that bad compared to the rest of the device.


So you're saying that this has fantastic military applications? Interesting...

The military don't like antimatter weapons because they are fail-dangerous. They require active stabilisation.

If a nuke fails, nothing happens. If antimatter containment fails, your entire arsenal of antimatter weapons go up at once.

For a similar reason, nitroglycerin is strangely unpopular for both civilian and military purposes.

Interesting, so you are suggesting some sort of gun that creates antimatter in a remote location. That's a great idea!

A weapon that could create antimatter at a remote location would be a particle accelerator. One that could create non-trivial amounts of antimatter would cause far more damage from its direct consequences than from antimatter. By factors of millions or billions.

It would be heinously expensive and would require the kind of energy input that only gigawatt-grade nuclear power plants could provide. Rather than using a complicated, failure prone and inefficient way to transform nuclear fission into destruction, it would be simpler and more effective to lob a nuke with the same amount of uranium or plutonium.

Hence, for your day-to-day megadeath needs, thermonuclear weapons will remain the tool of choice for the foreseeable future.

Unless we could convince the enemy to use that weapon!

I guess thermonuclear weapons are cheaper, though...

To build either nukes or particle accelerators you need physicists, who are the kind of non-team-players likely to point out that nukes would work better.

So .. you don't read much sci-fi, do you?

Not to mention that it would take a LOT of mass to balance out the weight of the board and the person riding it.

Not saying that it's as feasible as normal engine, but when you ride a bike you pretty much fill it with matter that explodes violently when ignited. Then you ignite small parts of it to make the bike move...

We may still see some normal devices which use antimatter in one way or another.

Meaningful amounts of Mater + antimatter produces extreme amounts of radiation, and takes ridiculous amounts of energy to produce.

To put things into perspective, 1kg (~2.2lb) of antimater + 1kg of matter = 2* (9×10^16 J/kg) of energy, TNT = 4.2×10^6 J/kg so that works out to 42,000,000,000 kg of TNT or a 100 mega ton bomb which is larger than the largest H bomb ever tested.

PS: The other issue is unlike gas which is fairly stable, any sort of containment failure = detonation.

No. I am not a physicist, but my understanding is that certain devices that have been proposed for use in space manipulation devices (e.g. wormholes, alcubierre drive), require either a form of matter that has reverse gravity or thousands of times the available energy of the known universe.

http://en.wikipedia.org/wiki/Worm_hole#Traversable_wormholes http://en.wikipedia.org/wiki/Alcubierre_drive

>thousands of times the available energy of the known universe.

the pieces of Universe that is more than 13B light years from us are moving with speed faster than light relative to us. The machinery behind it is space expansion. And by definition that is using energy less or equal to the universe's energy. So that is the start. The Alcubierre drive is the idea of how to use the same principle on much smaller scale. It is very doubtful that it would require more energy than moving the whole galaxies [which, let me repeat, are moving faster than light relative to us and to each other]

Antimatter is not going to help you there. You need exotic matter of the negative mass kind. which are not thought to exist.

>> which are not thought to exist

which have been observed a few times in colliders

Citation needed. Matter with negative mass would be big news.

"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?

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).

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.

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.

> 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!

So who is bootstrapping the first startup right now to make hoverboards?

Assuming 1kg of antimatter can be used to hover 1kg of matter and that your hoverboard could carry 80kg, should it's containment fail, it would detonate with the force of 3.4 gigatons of tnt. That's roughly equivalent with the entire present nuclear arsenal of the united states, and would cause 3rd degree burns out of direct thermal radiation over 300 kilometers away.

So, umm, no.

Antimatter is definitely ridiculously dangerous stuff in macro quantities.

Though strictly speaking, from a bomb-building point of view, it would be very difficult to design a weapon where matter-antimatter mixing happened more or less completely and simultaneously. Otherwise you "merely" have a series of uncontrolled multi-megatonne explosions in an increasingly large area, instead of a single multi-gigatonne explosion.

That "increasingly large area" would fall entirely inside the fireball (and likely within a few-meter radius), and the detonation would basically indistinguishable from it all going off in one go.

Disintegrating the device is a serious problem for nuclear bombs, because when they break themselves up, they leave otherwise good material unused. For an antimatter bomb, splashing the AM uncontrollably would, if anything, speed up the initiation. (After the AM and the normal matter around it is ionized, the particles home for the closest thing to annihilate with. AM basically does all the work of the weapons designer for him.)

Hmm, how about using two nukes to create light pressure from the two ends of initially split charge of hydrogen and anti-matter hydrogen? Or, however challenging by itself - creating spherical cavity in the hydrogen bomb to push normal matter to antimatter in the cavity for awhile.

You'll need a lot of bootstrapping for hoverboards. (teehee)

Antimatter torpedo is more profitable. Funding shouldn't be a problem since it's defense related.

Ooooh, if antimatter is repelled by gravity, that means that cavorite actually is antimatter, and therefore possible? I've always thought that cavorite is the cleverest Science Fiction device ever imagined...

This is super exciting. One day when I'm wealthier than God I'm going to donate some money to the guys who are trying to find him.

For those of us that don't know anything about it, can someone explain the significance of this achievement?

From the article:

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

One reason they would like to know if antimatter is repelled by gravity is that it could explain why the Universe is expanding at an accelerating rate.[1]

[1]: http://www.physorg.com/news/2011-04-antimatter-gravity-unive...

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

Would this mean that if I am "holding onto" a chunk of antimatter heaver than myself I will fall up into space?

Well, technically, it wouldn't be possible for a chunk of antimatter to be heavier than you.

But yeah, one theory is that if you hold one that's more massive than you are, its repulsion would overpower your attraction, and bang, zoom, straight to the moon!

it should be repelled by moon's gravity back to earth - recursion... =))

Not unless it's in a tube, and it would quickly reach an equilibrium anyway.

Unless he starts using his legs for extra propulsion!

In a vacuum?

Could be against the sides of the tube..

Well played, sir.

Surely there is a reason NASA trains underwater. ;)

If you were holding onto a chunk of antimatter you would probably be missing a hand.

1 megaton nuke is about 4000 TeraJoules of energy.

10g of antimatter yields about 10^15 Joules - i.e. 1 PetaJoule, or the equivalent of a 2+ Megaton nuke.

If you were holding onto a chunk of antimatter large enough to hold onto you'd be missing half of London.

Not sure if that conclusion is right. It probably wouldn't result in an explosion and the energy output would probably be in the form of light. Regardless, I'm going with Stephen Hawking on this one: "If you ever meet your anti-self, don't shake hands!"

"It probably wouldn't result in an explosion and the energy output would probably be in the form of light."

That's what nukes do too. Turns out that dumping absurd amounts of light (various parts of the spectrum, but certainly including visible) into the surrounding area absurdly fast tends to fuck stuff up pretty good.

Yeah, a lot of the power output from a nuclear explosion is in gamma rays, and even air is opaque enough to gamma rays that the energy deposition heats it up to way incandescent temperatures. That's what the fireball of a nuclear explosion is: incandescent air.

Funny that I actually managed to get the maths wrong. 4000 TeraJoules is 4 PetaJoules, i.e. 10g of antimatter is actually a 0.25 Megaton nuke. Still packs some serious punch, but I totally fail at arithmetic, it seems.

Not if you're holding onto it using a magnetic field, or any other method that doesn't involve direct contact.

Is there any conceivable way to make such a system fail-safe?

Nothing is fail-safe.

I think you misunderstand what the term means. For example, the control rods in some nuclear reactor designs are held up out of the core by electromagnets. Thus even in the event of complete power failure, the rods fall naturally, stopping the reaction. Since failure results in a safe state, this is referred to as a "fail-safe" system.

By contrast, if you were holding a lump of antimatter contained by an electromagnetic field, a power failure would result is the antimatter escaping confinement and annihilating with your body, releasing an unimaginably large amount of energy nearly instantly. This is what you might call a "fail-deadly" system, because a failure results in a decidedly unsafe state.

The first paragraphs at Wikipedia may help to understand the significance http://en.wikipedia.org/wiki/Antimatter


Previously it was "38 antiatoms for just 172 milliseconds".

Four orders of magnitude implies the previous best was 0.1 seconds.

They called it the greatest discovery in human history.

The civilizations of the galaxy call it... MASS EFFECT.

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