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Does Antimatter Fall Up?

Soulskill posted about a year and a half ago | from the where's-scotty-when-you-need-him dept.

Science 255

New submitter Doug Otto sends word that researchers working on the ALPHA experiment at CERN are trying to figure out whether antimatter interacts with gravity in the same way that normal matter does. The ALPHA experiment wasn't designed to test for this, but they realized part of it — an antihydrogen trap — is suitable to collect some data. Their preliminary results: uncertain, but they can't rule it out. From the article: "Antihydrogen provides a particularly useful means of testing gravitational effects on antimatter, as it's electrically neutral. Gravity is by far the weakest force in nature, so it's very easy for its effects to be swamped by other interactions. Even with neutral particles or atoms, the antimatter must be moving slowly enough to perform measurements. And slow rates of motion increase the likelihood of encountering matter particles, leading to mutual annihilation and an end to the experiment. However, it's a challenge to maintain any antihydrogen long enough to perform meaningful experiments on it, regardless of its speed. ... The authors of the current study realized that [antiatoms trapped in ALPHA] eventually escaped or were released from this magnetic trap. At that point, they were momentarily in free-fall, experiencing no force other than gravity. The detectors on the outside of ALPHA could then determine if the antihydrogen was rising or falling under gravity's influence, and whether the magnitude of the force was equivalent to the effect on matter."

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Maybe our universe is a 'matter bubble' (3, Interesting)

Anonymous Coward | about a year and a half ago | (#43595239)

Maybe our universe is a 'matter bubble' in a 'sea of anti-matter'. WE are the anti-matter.

To us, our normal matter is so common but that's only because we're sitting right smack in the middle of it. That would explain the repelling forces and show why dark matter could exist outside the bounds of the observable universe.

Re:Maybe our universe is a 'matter bubble' (1)

jimmetry (1801872) | about a year and a half ago | (#43595263)

Think of the nucleus as a shadow.

Re:Maybe our universe is a 'matter bubble' (5, Funny)

Anonymous Coward | about a year and a half ago | (#43595305)

First, consider a spherical cow.

Re:Maybe our universe is a 'matter bubble' (0)

Anonymous Coward | about a year and a half ago | (#43595593)

So what you're saying is its anti-matter so its moving towards it's anti-gravity.

Re:Maybe our universe is a 'matter bubble' (2)

egcagrac0 (1410377) | about a year and a half ago | (#43595601)

I'm only able to think of an even number of spherical cows, you insensitive clod!

Re:Maybe our universe is a 'matter bubble' (5, Funny)

femtobyte (710429) | about a year and a half ago | (#43595917)

OK, then consider the minimum supersymmetric extension of the spherical cow model [wikipedia.org] , in which all spherical cows have supersymmetric 'scow' partners. In practice, this should allow to work out similar results to the unpaired spherical cow model in the low energy cow scattering regime, while preserving the cow-pairing symmetry that you prefer.

Re:Maybe our universe is a 'matter bubble' (2)

tmosley (996283) | about a year and a half ago | (#43595939)

If antimatter falls up, does that mean it has negative mass?

If you make a ship out of something with negative mass, can you go faster than the speed of light without infinite energy input?

I'm not familiar with the equation describing the mass of an object as it moves faster. Could someone who is plug in a mass of zero, or negative mass and see what happens?

Also, is there a method for changing matter into antimatter? If so, one might be able to develop a tech that allows lightspeed acceleration and deceleration using antimatter and matter as fuel, and changing their ratios to bridge the asymptote.

Re:Maybe our universe is a 'matter bubble' (0)

Anonymous Coward | about a year and a half ago | (#43596353)

does that mean it has negative mass?

In reality, no, but I'm sure that some physicist somewhere will say "wow, if we just call antimass negative, a whole lot of equations get simpler" at which point it will have negative mass for the purposes of textbooks.

Re:Maybe our universe is a 'matter bubble' (0)

Anonymous Coward | about a year and a half ago | (#43596371)

You would still have mass, inside the ship. If you exceeded the speed of light, you'd blow up and take the ship with you in a blaze of matter/antimatter glory.

Re:Maybe our universe is a 'matter bubble' (2)

Brucelet (1857158) | about a year and a half ago | (#43595797)

Maybe any number of crazy things happen beyond our cosmological horizon. We'll never see them so it's not relevant. The observable universe is matter-dominated.

Re:Maybe our universe is a 'matter bubble' (1)

scheme (19778) | about a year and a half ago | (#43595815)

Then we should see a very bright border as matter and anti-matter annihilate on the edges. As far as I know, that doesn't exist so being a bubble of matter in anti-matter doesn't seem likely.

Re:Maybe our universe is a 'matter bubble' (1)

Calydor (739835) | about a year and a half ago | (#43595827)

Force field. *nod* We are the same experiment to the outer universe as the one described in the summary, caught in the equivalent of a magnetic trap.

Re:Maybe our universe is a 'matter bubble' (0)

Anonymous Coward | about a year and a half ago | (#43595843)

That depends on how far away that border is and how old the universe is.

Re:Maybe our universe is a 'matter bubble' (1)

tmosley (996283) | about a year and a half ago | (#43595975)

How fast is the universe expanding, and how big is it? We might have just not seen it yet.

Pretty scary thought, that the universe is doomed to destruction by a wall of arbitrarily energetic photons traveling inward from its edges.

Re:Maybe our universe is a 'matter bubble' (1)

Gindjurra (2884923) | about a year and a half ago | (#43596143)

Not necessarily. If antimatter falls up, it would imply a repulsion effect between normal mass and antimatter mass. If we are a matter bubble we wouldn't be floating in antimatter, we'd likely be repelling it with a gap between it and us.

Lets do an experiment (0)

PPH (736903) | about a year and a half ago | (#43595261)

Whoops! [slashdot.org]

What am I missing? (1)

The Living Fractal (162153) | about a year and a half ago | (#43595301)

If they have created hydrogen atoms already, why wouldn't they just check to see if those atoms fall to the bottom of the container, or float to the top? I would guess these atoms are stored in a vacuum, so buoyancy isn't a concern.

Re:What am I missing? (3, Informative)

Electricity Likes Me (1098643) | about a year and a half ago | (#43595343)

The problem is there's something like a 1000. Total.

Actually measuring them accurately is a challenge, although no one in the physics community really expects the answer to be "they fall up" at this point. It would be a huge upset if they did.

Re:What am I missing? (1)

The Living Fractal (162153) | about a year and a half ago | (#43595351)

Ah so just getting the detectors in place. Thanks.

Re:What am I missing? (2, Informative)

Anonymous Coward | about a year and a half ago | (#43595497)

No, hydrogen atoms in a vacuum are going to be more effected by nearby weak magnetic fields then by gravity. And even more so by what direction they where traveling. So you'd first need to slow them down which is hard to do when all you can use is magnetic force. Of course you could try to accurately measure there trajectory at two or more points and then figure out how gravity effected the atom. But it's hard to get real good measurements of atomic trajectories with strong magnetic fields. If we could make enough of and contain them; a simple balance scale would do.

Re:What am I missing? (1)

CanHasDIY (1672858) | about a year and a half ago | (#43595377)

... no one in the physics community really expects the answer to be "they fall up" at this point. It would be a huge upset if they did.

To the physicists, maybe.

For the rest of us... SUPERPOWERS!!!

Re:What am I missing? (5, Funny)

Shimbo (100005) | about a year and a half ago | (#43595397)

Actually measuring them accurately is a challenge, although no one in the physics community really expects the answer to be "they fall up" at this point. It would be a huge upset if they did.

There's a (possibly apocryphal) story about a physics professor. Whenever he dropped his chalk, writing equations on the board, he would look upwards. When one of the students finally asked him why he did this, he replied, "If one day it fell upwards, I wouldn't want to miss it."

Re:What am I missing? (1)

ygtai (1330807) | about a year and a half ago | (#43596073)

Depending on the professor's figure and the exact condition when this happens, he might need to look downwards or gradually upwards. Training in FPS helps.

Re:What am I missing? (3, Interesting)

ndogg (158021) | about a year and a half ago | (#43595531)

It would be a huge upset if they did.

Actually, I'm pretty sure a lot of them would have the opposite reactions. When the Higgs Boson was finally found, a lot of physicists were actually disappointed because it meant there wasn't really much in the way of new physics to be discovered.

Re: What am I missing? (4, Insightful)

ceoyoyo (59147) | about a year and a half ago | (#43595579)

Scientists like upsets. They wouldn't BE upset, it would be an upset.

Re:What am I missing? (1)

harrkev (623093) | about a year and a half ago | (#43596129)

Well, in all fairness, nobody was really sure about the Higgs. A lot of people were hoping, but nobody was willing to bet the farm on the mass (or even the existence of the Higgs).

Now, gravity on, the other hand, is a completely different aniamal.

IANAP (I am not a physicist), but the way that I understand it is that gravity is simply following a straight line in curved space-time. So, a straight line is a straight line for both matter and anti-matter. If anti-matter flies up, then that totally blows the "straight-line" theory away. While I am sure that an "anti-gravity" discovery would make more than a few careers and hundreds of papers, nobody is seriously expecting that to happen. This seems to be just another "Yup, relativity still works" type of experiment.

Re:What am I missing? (1)

Goaway (82658) | about a year and a half ago | (#43596197)

That is "upset" as a noun, not an adjective.

Re:What am I missing? (0)

Anonymous Coward | about a year and a half ago | (#43596367)

If gravity is backwards for antiparticles, then gravity would no longer be a function of (just) mass.

There would be a FUCKTON of new physics to be discovered.

Re:What am I missing? (0)

Anonymous Coward | about a year and a half ago | (#43595771)

See, I think they should fall up. Antiparticles are predicted by the negative energy solutions of the Dirac equation. I can only imagine that it makes sense that if E = mc^2, then surely, a negative energy results in a negative mass.

The question is, are we talking about gravitational mass, or inertial mass? What if, in reality, an antiparticle actually has the same charge, hypercharge and so forth as it's "normal" particle, but it's negative inertial mass just means all forces cause it to accelerate in the opposite direction that the force is applied? How can we tell the difference?

Re:What am I missing? (2)

Guy Harris (3803) | about a year and a half ago | (#43595859)

See, I think they should fall up. Antiparticles are predicted by the negative energy solutions of the Dirac equation.

But they still have positive energy. (Think of them as "holes" in a sea of negative-energy electrons; kick an electron out of that sea and you get a positive-energy negatively-charged electron and a positive-energy positively-charged "hole", i.e . a positron.)

Re:What am I missing? (1)

ron_ivi (607351) | about a year and a half ago | (#43596173)

And if they did fall up, wouldn't that contradict the idea that gravity is indistinguishable from being stuck inside an accelerating elevator?

Re:What am I missing? (1)

Hentes (2461350) | about a year and a half ago | (#43595429)

If I understand it right, they also wanted to check whether the gravity of antimatter is a fraction of the gravity of normal matter. So they needed some other force to measure gravity against.

Re:What am I missing? (0)

Anonymous Coward | about a year and a half ago | (#43595445)

If you put a normal gas in a container, it doesn't fall up or down. It expands to fill the space. The same would be true of antimatter gas, whether it responds normally to gravity or not. Even if there were a whole mole of atoms, it seems like you would have to cool them to a liquid before you could tell whether they fall up or down, unless it's possible to detect the tiny pressure difference between the top and bottom of the container without touching the antiatoms.

Re:What am I missing? (2, Informative)

Anonymous Coward | about a year and a half ago | (#43595677)

When you put a "normal" gas in a container, room temperature imparts speeds on the atoms that would take several kilometers to reach the top of a parabolic trajectory assuming no other interaction with container walls or other gas molecules. In a distance of one meter the difference of speeds would only be about 40 ppm at best for such molecules, and the mean free path is much shorter.

If you put any gas though into a container such that the mean free path is longer than the distance it takes for significant action of gravity, it will not fill the container. This can be done by some combination of slowing the molecules down (making it colder) so it takes less time for a significant change in velocity, or making a container large enough and the pressure low enough that they have room to travel without interaction.

Re:What am I missing? (1)

Alex Belits (437) | about a year and a half ago | (#43596017)

Gas fills up the whole container, however pressure on top and bottom parts of the container will still show the difference produced by gravity, so total force the gas applies to the container is directed down, and equal to the mass of gas multiplied by free fall acceleration (well, an integral over the volume of gas if we have uneven gravity, however on Earth surface it's negligible).

Re:What am I missing? (4, Insightful)

Charliemopps (1157495) | about a year and a half ago | (#43595893)

Because these are individual atoms. Very hard to detect unless they are clumped together as a mass... as in the millions. The only way to know their position is to force them to be where you want them via a magnetic field... etc... which ruins your chances of measuring any gravitational effect which is unfathomably tiny at atomic scales. You could make a whole pile of them (very difficult indeed) so it would act more like classical matter... the problem there is that by the time you had that much, when it hit the bottom of your container you'd find out just exactly what e=mc2 is all about and likely need to start looking for a new research facility.

Re:What am I missing? (1)

joe_frisch (1366229) | about a year and a half ago | (#43596263)

Its difficult because for a single atom gravity is very weak. Small magnetic or electric fields (or field gradients) can interact with the magnetic field, or electric dipole moment of the atom. Also the atoms are moving inside of the trap. The speed of their motion depends on temperature: (at room temperature it is > 1 kilometer/second). I assume they cool the anti-hydrogen, but the atoms may still be moving so quickly that gravitational effects are not very large.

The answer is... (-1, Troll)

Princeofcups (150855) | about a year and a half ago | (#43595309)

No. Can we move on to real news now.

Re:The answer is... (2)

Hentes (2461350) | about a year and a half ago | (#43595393)

And now we have proof of that. Most science isn't groundbreaking, but that doesn't make this experiment less important.

Re:The answer is... (0)

Anonymous Coward | about a year and a half ago | (#43595493)

And now we have proof of that. Most science isn't groundbreaking, but that doesn't make this experiment less important.

They don't quite have proof yet, but hat's okay, the goal of this experiment is to measure the ionization levels of anti-hydrogen. The anti-gravity test is a side show.

Re:The answer is... (4, Interesting)

lgw (121541) | about a year and a half ago | (#43595435)

It's easy to assume answers, but measurements separate science from philosophy.

Re:The answer is... (1)

Anonymous Coward | about a year and a half ago | (#43595755)

I disagree with that. For instance, game theory as applied to the study of effective ethics, is well within the realm of philosophy AND science. Never forget, as many mathematicians do, that all logic including the logical system known as mathematics are all parts of just one branch of philosophy.

Re:The answer is... (0)

Anonymous Coward | about a year and a half ago | (#43596027)

For instance, game theory as applied to the study of effective ethics, is well within the realm of philosophy AND science.

No, it's in the realm of philosophy (with a few nods towards mathematical rigor to provide a facade of credibility beyond standard armchair philosophical wanking).

I must be stupid (1)

MightyMartian (840721) | about a year and a half ago | (#43595331)

Obviously there must be some credence to this idea for such an experiment to take place, but since my understanding is that gravity is an inherent effect of mass warping space, wouldn't anti-matter possess mass in the same way that matter does, so why would gravity act differently?

Just asking. Not trying to claim anything.

Re:I must be stupid (5, Insightful)

Electricity Likes Me (1098643) | about a year and a half ago | (#43595373)

Obviously there must be some credence to this idea for such an experiment to take place, but since my understanding is that gravity is an inherent effect of mass warping space, wouldn't anti-matter possess mass in the same way that matter does, so why would gravity act differently?

Just asking. Not trying to claim anything.

Inertial mass and gravitational mass are observed - for normal matter - to be exactly equivalent. There's no actual reason they should be though, since they're the product of very different interactions - it's perfectly logical to have something which "weighs" a 1000kg when experiencing electromagnetic acceleration, and only 10kg when experiencing gravitational acceleration.

For normal matter, this is the case. For antimatter it's presumed but not actually tested, and therein lies the rub. Even a slight deviation would be huge - and have big implications for the question of why the universe has so much matter in the first place.

Re:I must be stupid (0)

Anonymous Coward | about a year and a half ago | (#43595491)

it's perfectly logical to have something which "weighs" a 1000kg when experiencing electromagnetic acceleration, and only 10kg when experiencing gravitational acceleration

How would you tell the difference between 'having 100x the inertia against EM fields' from just having 1% of the charge?

Re:I must be stupid (5, Informative)

Immerman (2627577) | about a year and a half ago | (#43595709)

Looking at just the object's reaction to EM fields, you couldn't. But you could also observe its effects on charged bodies of known mass and charge, which would provide you with enough data to deduce the reality.

Incidentally, it's not a question of "inetia agains X fields" - it's simply that there are two quantities we call mass - inertial mass, which resists acceleration by *any* force, and gravitational mass, which creates and reacts to a gravitational field ("gravitational charge"). There are theoretical reasons why inertial mass will be constant regardles of the nature of the force, but no accepted explanation for why gravitational and inertial mass maintain a fixed ratio in all observed phenomena.It is *presumed* that antimatter has positive gravitational mass because the existence of negative g-mass particles would have some really wierd consequences, the possibility of perpetually accelerating machines not the least of them. A positive g-mass with a different ratio to inertial mass would be unexplained by current theory, but wouldn't really break things - we still don't actually have a very good theory as to the source of gravitaional mass effects.

Re:I must be stupid (1)

Sique (173459) | about a year and a half ago | (#43595723)

By measuring the charge?

Re:I must be stupid (0)

Anonymous Coward | about a year and a half ago | (#43595943)

The latter case would produce 1% of the electric field and hence less force on other particles?

Re:I must be stupid (1)

emt377 (610337) | about a year and a half ago | (#43595769)

Inertial mass and gravitational mass are observed - for normal matter - to be exactly equivalent. There's no actual reason they should be though, since they're the product of very different interactions - it's perfectly logical to have something which "weighs" a 1000kg when experiencing electromagnetic acceleration, and only 10kg when experiencing gravitational acceleration.

The discussion is about mass, not weight. Weighing something is a very indirect way to determine mass; but regardless, it's about mass, not weight. If it were about weighing schemes a term other than mass would have been used.

Re:I must be stupid (2)

Stormy Dragon (800799) | about a year and a half ago | (#43595933)

Inertial Mass comes from Newton's second law:

F = m_i * a

That is, inertial mass determines how much an object will be accelerated by a particular force.

Gravitational Mass comed from Newton's law of graviation:

F = G * m_g1 * mg2 / r ^2

That is, the magnitude of the gravitational forces between two objects.

The question is whether the two definitions of mass are interchangable (e.g. does m_i = m_g1?). That appears to be the case for normal matter, which we can tell because all objects accelrate at the same rate in a given gravitational field regardless of mass. But it doesn't have to be the case.

Re:I must be stupid (3, Informative)

BitterOak (537666) | about a year and a half ago | (#43596191)

Inertial mass and gravitational mass are observed - for normal matter - to be exactly equivalent. There's no actual reason they should be though, since they're the product of very different interactions

Well, if you believe General Relativity, they darn well better be equivalent. In fact, Einstein took the Equivalence Principle as one if his starting points when developing GR. If the Equivalence Principle fails (which it must if anti-matter falls up), then they will have disproven Einstein's theory, which would be very big news, indeed.

Re:I must be stupid (2)

Antony T Curtis (89990) | about a year and a half ago | (#43595389)

Well... There are two conjectures which need to be tested.

1. Are anti-particles just like normal particles except with their direction of time reversed?
2. Do anti-particles have negative energy?

If they are the "travelling backwards in time", then gravity would be repulsive.

Re:I must be stupid (1)

Anonymous Coward | about a year and a half ago | (#43595695)

>If they are the "travelling backwards in time", then gravity would be repulsive.

No.

Acceleration is (d/dt) (d/dt) position.
Which is exactly the same as (d/d(-t)) (d/d(-t)) position

If you play a movie of our solar system backwards, Earth appears to move on the same ellipse only in a different direction. It still appears to be fallling into the sun.

Re:I must be stupid (2)

Em Adespoton (792954) | about a year and a half ago | (#43595547)

If they changed the definition of antimatter to "has an anti-higgs-boson-field" such that the matter actually has an inverse affect on the universe, that might cause it to have "anti-mass" which would warp the anti-space referenced by the anti-field. However, this is not how we have traditionally defined anti-matter; the original definition was actually due to the fact that the universe has significantly less mass than it should, and "anti-matter" was hypothesized as an explanation. So by definition, anti-matter in the traditional sense has, and is attracted by mass just like matter. Otherwise, we've still got that glaring "mass of the universe" issue.

Of course, I guess it could be that the original hypothesis was looking at it all wrong, and it's not that we're missing mass, just that there's a bunch of anti-mass that's brought us right out the other side... which makes what we're measuring the actual anomoly.

Re:I must be stupid (4, Informative)

Guy Harris (3803) | about a year and a half ago | (#43595773)

However, this is not how we have traditionally defined anti-matter; the original definition was actually due to the fact that the universe has significantly less mass than it should, and "anti-matter" was hypothesized as an explanation.

Actually, the original modern definition of anti-matter was "Dirac's relativistic equation for the wave function of the electron had negative energy states as well as positive energy states, which was a bit weird, so it was proposed that all the negative energy states were filled, and if you knocked an electron out of one of the low-energy states, a "hole" would be left behind, and that hole behaved like an electron, except that it has a positive charge". It was later seen in the real world (particles moved in a magnetic field as if they had the mass of an electron and a +1 electrical charge). See, for example, the Wikipedia article about the positron [wikipedia.org] .

Re:I must be stupid (1)

Anonymous Coward | about a year and a half ago | (#43595817)

No, antiparticles are predicted by the negative energy solutions of the Dirac equation. I think you're confusing antimatter with dark matter, and "the universe has significantly less mass than it should" with "the universe appears to have more mass if we measure the rate of rotation of galaxies than if we measure the amount of starlight and extrapolate".

Re:I must be stupid (1)

Em Adespoton (792954) | about a year and a half ago | (#43596049)

I stand corrected; you are absolutely right. And the various conclusions can be extrapolated from your concise response :)

I should pare back my parallel processing a few notches.

Re:I must be stupid (1)

PhamNguyen (2695929) | about a year and a half ago | (#43595689)

All theory says that anti-matter should behave like matter becasue both kinds of matter have positive energy (hence the release of energy when they annihilate). Negative energy is harder to produce than anti-matter, and it is possible that there are fundamental limits to its production. Negative energy would produce anti-gravity (at least I think, given my rudimentary knowledge of GR). As "Electricity Likes Me" said in his/her reply, it is *possible* that contrary to what is expected, anti-matter floats up in spite of having positive energy

Re:I must be stupid (1)

SEE (7681) | about a year and a half ago | (#43595985)

since my understanding is that gravity is an inherent effect of mass warping space, wouldn't anti-matter possess mass in the same way that matter does, so why would gravity act differently?

It's expected that gravity would work normally. However, we don't know that until we see antimatter fall.

Moreover, if it didn't fall just like matter, that would be important information for constructing a new theory (which, since we still have GR and QM contradicting each other, we know we need).

Re:I must be stupid (1)

joe_frisch (1366229) | about a year and a half ago | (#43596299)

In general relativity, gravity is a warping of space and EVERYTHING falls at exactly the same speed. This has been tested to very high accuracy in a variety of experiments. (see eotvos experiment)

There are other theories of gravity where this doesn't necessarily need to be true and antimatter and matter might fall at different rates. The eotvos type experiments have indirectly tested this since there is some amount of virtual antimatter in normal objects (from quantum fluctuations), but a direct measurement would be a nice demonstration.

This is one of those experiments were people are pretty sure of the answer, but getting a different result would be very important to physics.

H goes up, anti H goes up, unless anti-N is presnt (-1)

Anonymous Coward | about a year and a half ago | (#43595387)

3 questions.

1. Hydrogen rises in gravity because it is less dense than air(mostly Nitrogen), So if there was no air/vacuum then hydrogen would fall towards the earth.?
2. So then would anti hydrogen only go down if there was anti-matter-air (mostly anti-nitrogen) around as well.
3. Can someone explain the theory to me? This hurts my head. I wish they used non heavier than air molecules, then gravity would work again in my mind. ;)

Re:H goes up, anti H goes up, unless anti-N is pre (0)

Anonymous Coward | about a year and a half ago | (#43595545)

1. Yes, hydrogen would fall towards the earth in a vacuum... sort of. Hydrogen atoms have a very high kinetic energy at room temperature, to the extent that the more energetic ones achieve escape velocity at a noticeable rate. So if you released a bunch of hydrogen around an Earth-sized planet with no atmosphere, it would be attracted to the planet, forming a tenuous atmosphere, but in time it would dissipate. If you try this experiment around Jupiter, the hydrogen will stick around basically indefinitely. In fact, nature has already tried the experiment -- Jupiter has a lot of hydrogen in its atmosphere.

So basically, hydrogen is affected by gravity in the same way as any other gas is.

2. According to standard physics, anti-hydrogen should behave exactly like regular hydrogen. That is, it should be attracted to the earth. If you have a gigantic container of anti-nitrogen at atmospheric pressure and put in an anti-balloon of anti-hydrogen at atmospheric pressure, the balloon would go up, just like a regular balloon in the regular atmosphere.

If the alternative hypothesis is right, and Earth's gravity repels antimatter, then the anti-hydrogen balloon would go down instead, but this is very unlikely to be the case.

In any case, the experiment will be performed in a vacuum, where hydrogen would behave just like any other material (and probably, so will anti-hydrogen).

3. Which theory?

Re:H goes up, anti H goes up, unless anti-N is pre (4, Informative)

Jappus (1177563) | about a year and a half ago | (#43595561)

3 questions.

1. Hydrogen rises in gravity because it is less dense than air(mostly Nitrogen), So if there was no air/vacuum then hydrogen would fall towards the earth.?

I can't say anything to the other two questions, but this question is easily answered by something my high school physics teacher said to me. It has stayed with me since then as it is as eye-opening as it is obvious (in hindsight):

"The first mistake is to assume that helium rises. The truth is that it falls down towards the earth just like any other object. The reason for what you see is much simpler: It does not rise; it's just that everything else simply falls harder." (Freely translated from memory and German)

Helium only rises over the air, because regular air has the stronger draw to be below it. This explains why, in the absence of gravity; there is no lift. In the absence of a pull, the air has no impulse to displace the helium.

More generally, the same is true for liquid mixtures like oil/water. In gravity, the oil will rise above the water. In (close-to-)zero gravity, the oil and water will separate but stay where they are. That is because the water can't displace the oil without gravity pulling it more strongly down.

The same is true for solids. In meteorites with too little gravity, no submersion of the "heavier" elements like iron happen. This is why Earth has an iron core, but iron-rich asteroids have it distributed all over their volume.

Re:H goes up, anti H goes up, unless anti-N is pre (1)

rasmusbr (2186518) | about a year and a half ago | (#43596043)

3 questions.

1. Hydrogen rises in gravity because it is less dense than air(mostly Nitrogen), So if there was no air/vacuum then hydrogen would fall towards the earth.?

I can't say anything to the other two questions, but this question is easily answered by something my high school physics teacher said to me. It has stayed with me since then as it is as eye-opening as it is obvious (in hindsight):

"The first mistake is to assume that helium rises. The truth is that it falls down towards the earth just like any other object. The reason for what you see is much simpler: It does not rise; it's just that everything else simply falls harder." (Freely translated from memory and German)

Helium only rises over the air, because regular air has the stronger draw to be below it. This explains why, in the absence of gravity; there is no lift. In the absence of a pull, the air has no impulse to displace the helium.

More generally, the same is true for liquid mixtures like oil/water. In gravity, the oil will rise above the water. In (close-to-)zero gravity, the oil and water will separate but stay where they are. That is because the water can't displace the oil without gravity pulling it more strongly down.

The same is true for solids. In meteorites with too little gravity, no submersion of the "heavier" elements like iron happen. This is why Earth has an iron core, but iron-rich asteroids have it distributed all over their volume.

That is true for a container (e.g. a balloon*) filled with helium. AFAIK it would also be true for individual helium atoms if the temperature was 0 Kelvin. They would basically fall like little rocks.

In reality the Earth is actually warm enough and light enough that unconfined helium atoms frequently reach escape velocity and fly away into space. They do this often enough that a cloud of helium will never settle on top of the atmosphere like oil on top of water. It will just diffuse into space. There is no particular reason why a helium atom would want to travel upwards, except in the big scheme of every direction is basically upwards so once an atom has moved a good distance it will have moved up and away from Earth.

All of this hold for hydrogen molecules too, except my understanding is that hydrogen will usually react with oxygen in the atmosphere and form water on the way up, and water molecules are too heavy to escape the Earth at a noticeable rate.

*Assuming it's an indestructible balloon that doesn't pop at altitude, of course.

Re:H goes up, anti H goes up, unless anti-N is pre (1)

Immerman (2627577) | about a year and a half ago | (#43595931)

1) Not exactly.. In the absense of other forces all known objects/particles will accelerate towards each other due to gravity. Hydrogen rises for the same reason a boat floats in water - buoyancy. Denser things (like water or air) fall "harder" and push less-dense things (like boats or hydrogen) out of the way. When you release a piece of wood underwater it doesn't fall up, it gets lifted up by the denser surrounding water which experiences a larger gravitational force per unit volume. It's basically an energy game - gravitational potential energy in a constant field equals mass*gravitational acceleration*height. Imagine a chunk of wood and an equal-volume "chunk" of water next to it. At the same height the water will have more energy than the wood because it has more mass. If the wood is pushed downward the water will be pushed upwards since there's a finite volume to be occupied at that depth. As a result the wood will have lost some gravitational potential energy, and the water will have gained some; however, since the water is more massive it will have actually have gained more energy than the wood has lost. The effect is similar to pushing a ball up a hill - you've created a gravitational energy "battery" which will discharge itself as soon as you remove the forces holding things in position.

2. No. The effect of gravity will be the same regardless of surrounding particles. If anti-H has positive gravitational mass it will fall down unless displaced by something more massive. It's best to do such experiments in vacuum simply because it eliminates the "noise" of interparticle interactions.

AntiGravity (0)

Anonymous Coward | about a year and a half ago | (#43595401)

So now all we need to do is create a container of anti hydrogen and surround it with an electrical barrier to have our floating cars =)

Re:AntiGravity (1)

Naatach (574111) | about a year and a half ago | (#43595515)

So now all we need to do is create a container of anti hydrogen and surround it with an electrical barrier to have our floating cars =)

That annihilate a few city blocks when two cars collide.

Re: AntiGravity (1)

ceoyoyo (59147) | about a year and a half ago | (#43595685)

More than that. I don't have an envelope handy, but a couple thousand pounds of antimatter annihilating would probably make the planet a rather poor place to live.

Re: AntiGravity (4, Informative)

Brucelet (1857158) | about a year and a half ago | (#43596021)

You'd of course need enough antimatter to balance the weight of the car. Let's call it 1500 kg of antimatter per car. Multiply by 2 for two cars and by 2 again for the mass of normal matter gives 6000 kg total being annihilated. That has an energy equivalent of 5*10^20 joules, which per wikipedia [wikipedia.org] was the total world energy consumption in 2010. This is also equivalent to about 10^5 megatons of TNT or 2000 Tsar Bombas.

Re:AntiGravity (1)

Immerman (2627577) | about a year and a half ago | (#43595945)

And believe it or not that would actually be one of the *least* interesting implications of particles with negative gravitational mass.

Does Antimatter Fall Up? (1)

93 Escort Wagon (326346) | about a year and a half ago | (#43595437)

Is it black?

Does it live under water?

Most important question... (1)

HellKnite (266374) | about a year and a half ago | (#43595495)

If antimatter interacts with gravity in such a way that it "falls" up or pushes against the force like magnetic fields pushing against each other, does this mean that antimatter would make anti-gravity platforms possible?

I'm a science plebe who watches/reads too much sci-fi, this was the first thing that came to my mind.

Re:Most important question... (1)

habig (12787) | about a year and a half ago | (#43595549)

Sure, in principle.

However, a thorny engineering problem would be stopping the tons of antimatter holding up the platform from interacting with the normal matter around it. If it did, *boom*. That's the way you can get 100% of the "E" out of the "m" in E=mc^2.

Re:Most important question... (1)

ericloewe (2129490) | about a year and a half ago | (#43595557)

Assuming it "falls up", it'd be a heck of an engineering challenge to a) produce enough antimatter, b) trap it safely and c) keep it trapped safely.

It'd be easier to use hydrogen balloons. Not to mention safer.

Re: Most important question... (1)

smaddox (928261) | about a year and a half ago | (#43595671)

In principal, yes... as long as you don't mind the platform spontaneously detonating and vaporizing the earth when the containment field fails.

Re:Most important question... (0)

Anonymous Coward | about a year and a half ago | (#43595733)

The trick is keeping the antimatter where it is without the whole system coming apart.

Analogy: Take three magnets, all stuck together. Rotate the middle one to reverse its poles. Notice that you need to keep applying constant force or everything will fall apart.

Without constant force applied, the anti-grav system would shoot off into some random direction into space.

Re:Most important question... (1)

Immerman (2627577) | about a year and a half ago | (#43596059)

Absolutely. Of course a tiny floating 100kg platform would require 100kg of antimatter, and I wouldn't want to be anywhere nearby if your EM-containment field failed. If it were a solid chunk of anitmatter it probably wouldn't be *too* bad - a small surface explosion when it contacted the platform followed by a hail of antimatter meteors falling upwards while blasting out gamma rays from air-molecule collisions. A tank of anti-H though, that would mix very quickly and release all the energy at once - and a single kg of antimatter would annihilate with only slightly less energy than the 27,000kg Tsar Bomb - the largest thermonuclear weapon ever detonated. I wouldn't want to see what a gamma ray burst 100 times as large would do to the surrounding area. The secondary explosion of expanding plasma alone would likely dwarf the Tsar.

If it does fall up (1)

Sla$hPot (1189603) | about a year and a half ago | (#43595519)

Then all we just need a ton of it to cancel out the weight of, lets say a car.
It will be like the Blade Runner movie with cars, floating around in the sky, whizzing past each other.
But not too close. Because that would set of one gigantic chain reaction of sympathetic mass annihilations, blowing earth out of its orbit around the sun.

E.E. "Doc" Smith got it right (4, Funny)

idontgno (624372) | about a year and a half ago | (#43595551)

Negative matter DOES react to tractor beams in reverse, being repelled by the nominally attractive force.

Can anyone explain what it would mean? (1)

ndogg (158021) | about a year and a half ago | (#43595565)

I'd love it if we found out that antimatter falls upwards, but I'd be even more interested if anyone could conjecture on what that would mean.

Could that mean that antimatter warps space in the opposite direction as matter so that it has a repelling affect?

Re:Can anyone explain what it would mean? (0)

Anonymous Coward | about a year and a half ago | (#43596345)

Antimatter falling upwards potentially implies faster than light travel. Which means it's incredibly unlikely.

E=mc^2 (1)

q.kontinuum (676242) | about a year and a half ago | (#43595569)

Assuming floating up meant it to have negative mass, antimatter would have negative energy and therefore matter and antimatter with congruent weight would annihilate without any visible energy-output.

Re:E=mc^2 (3, Interesting)

iggymanz (596061) | about a year and a half ago | (#43595761)

we already know antimatter doesn't have "negative mass" in that sense, it responds with expected inertia to acceleration by electromagnetic forces. we already know the yield of annhilation too (relativistic mass is positive). question is just of response to gravitational field of normal matter, which way the force vector points.

Re:E=mc^2 (0)

Anonymous Coward | about a year and a half ago | (#43595865)

This experiment is of value, as it would add another nail in the coffin of the old theory that Antimatter is regular matter traveling backwards through time. From the perspective of the hydrogen atom traveling backwards in time it would be falling down, whereas we would see the particle falling upwards. If antimatter falls down, that along with other recent experiments would pretty much eliminate the backwards time traveling theory.

Re:E=mc^2 (1)

osu-neko (2604) | about a year and a half ago | (#43595949)

No, that doesn't mean it has negative mass. If antimatter does fall up, antimatter with negative mass would fall down.

Answer: No (1)

Anonymous Coward | about a year and a half ago | (#43595577)

No, it almost certainly doesn't. There's no theoretical indication, even non Einsteinian gravity theories, that indicates it would. But heck, we've never tested it, and we can test it, so why not? Maybe it does and everyone was all wrong and we'll have to think of all new stuff. It almost certainly won't happen, but almost certainly isn't a good enough reason not to try.

Photons fall down (1)

tepples (727027) | about a year and a half ago | (#43595599)

As I wrote in a comment to the submission [slashdot.org] : Photons fall down. Is there such thing as an "anti-photon"?

Re:Photons fall down (3, Interesting)

iggymanz (596061) | about a year and a half ago | (#43595665)

yes, but the photon is its own antiparticle

two photons interacting with sufficient energy can produce a pair of fermions

http://en.wikipedia.org/wiki/Two-photon_physics [wikipedia.org]

Re:Photons fall down (0)

Anonymous Coward | about a year and a half ago | (#43595679)

Photons are their own anti-particle.

Anyway, GR says that gravity is nothing more than the curvature of spacetime. Everything experiences the same gravitational acceleration for the same reason that everything experiences the same centrifugal and Coriolis acceleration.

Re:Photons fall down (0)

Anonymous Coward | about a year and a half ago | (#43595697)

Yes. It is called a photon.

But your point remains valid.

Why would it? (0)

Anonymous Coward | about a year and a half ago | (#43595619)

I see no reason to even think they would. Gravitation is dependent upon mass of and distance between objects. Particles have the same mass as their anti-particle equivalents.

This research sounds like a massive waste of money.

Re:Why would it? (2)

osu-neko (2604) | about a year and a half ago | (#43595997)

I see no reason to even think they would. Gravitation is dependent upon mass of and distance between objects.

That's not entirely accurate, but regardless, you're just (mis)stating current theory. Which we have good reason to believe is, at the very least, incomplete.

Particles have the same mass as their anti-particle equivalents.

This research sounds like a massive waste of money.

Assuming you prefer philosophy, yes. However, scientists believe in actually experimentally verifying our assumptions, rather than just assuming and never bothering to check.

Some Background... (0)

Anonymous Coward | about a year and a half ago | (#43595741)

Some background on antimatter antigravity from the Tikalon blog [tikalon.com] .

Background info (4, Interesting)

AdamHaun (43173) | about a year and a half ago | (#43595783)

The Usenet Physics FAQ [ucr.edu] has some background information [ucr.edu] on the theory behind this question. It's 14 years old but still worth reading. One interesting bit:

Based on what we currently know, we would expect that the only significant force acting on a piece of falling antimatter is gravity; by the equivalence principle, this should make antimatter fall with the same acceleration as ordinary matter. However, some theories predict new, as yet unseen forces: these forces would make antimatter fall differently than matter. But in these theories, antimatter always falls slightly faster than matter; antimatter never falls up. This is because the only force that would treat matter and antimatter differently would be a vector force (mediated by the hypothetical gravivector boson). Vector forces (like electromagnetism) repel likes and attract opposites, so a gravivector force would pull antimatter down toward the matter-dominated Earth, while giving matter a slight upward push.

Background (5, Informative)

Okian Warrior (537106) | about a year and a half ago | (#43595897)

The question of whether anti-matter experiences anti-gravity goes back as far as I can personally remember (1970's) and probably some decades before that.

For most of the past 300 years in physics, experiment has led theory. We measure something, it leads to a theory, and then experiments are done to check the theory. Examples abound of theories that explain previous observations, and also predict something new - probably the most famous is relativity predicting the precession of Mars, but there are lots of others. (Newton predicting elliptical orbits based on the inverse square law of gravity comes to mind.)

Since about 1970 the situation is reversed - theory has led experiment. We have a satchel of theories which attempt to explain questions in physics which have no discriminatory evidence. Theories such as "Super Symmetry", "Loop Quantum Gravity", and "String Theory". I'm reading a book right now [amazon.com] which claims 10^500 different string theories (yes, that's 10 with 500 zeroes after it), and lamenting the fact that few of these actually make testable predictions.

Relativity predicts that anti-matter should have positive gravity, but this has never been tested.

Until recently, the only antimatter we had access to has been charged particles: anti-protons and anti-electrons. Measuring the gravitational force on a charged particle is nigh impossible because the EM force is so large (relative to the gravitational force) that any EM effects swamp the readings. You can't just see if the particle falls in the container, because it's essentially impossible to shield a container well enough. It's like trying to measure the mass of a cork floating in a tornado.

Anti-hydrogen would work, but until recently we had none to test. Antiparticles tend to have high velocities when produced - they have to escape their anti-nemesis which is also produced - so they have to be slowed down enough to "pair" to make the neutral antimatter particle.

The vacuum used for the experiments has a big effect also. Depending on the level of vacuum used, any particle has a "mean free path [wikipedia.org] " before it will impinge on another particle. You have to get your anti-particles to slow down, form antimatter, and conduct the experiment before another particle comes in and annihilates it. This requires insanely good vacuum which is both hard to achieve and highly expensive.

The ALPHA [web.cern.ch] experiment at CERN now produces antimatter, so the referenced paper asks the question: what is the ratio "F" between the inertial mass and the gravitational mass of antihydrogen? For normal matter it's 1 and for "antigravity matter" it would be -1.

The paper reports that they have measurements within specific confidence levels that F < 110 almost certainly, and F < 75 at the 95% confidence level.

If the experiments outlined in the paper are continued (and perhaps refined), over time they can statistically narrow the results and ultimately settle the question by experiment.

I think that this would be a good thing, it would confirm (or contradict) by experiment something that is predicted by theory.

Correction: s/Mars/Mercury/ (3, Interesting)

Okian Warrior (537106) | about a year and a half ago | (#43596257)

Mental typo: typed "Mars" when I meant to say "Mercury". Relativity predicted the precession of Mercury.

Re:Background (1)

joe_frisch (1366229) | about a year and a half ago | (#43596325)

Don't equivelence principal experiments test this due to virtual anti-matter in normal matter? Maybe there isn't enough sensitivity?

A direct test is certainly nicer.

An important thing to understand (1)

MetricT (128876) | about a year and a half ago | (#43596007)

If antimatter is gravitationally repulsed by matter, then it could help explain dark matter. Instead of requiring a huge expansion of the Standard Model, it may simply be that the vacuum is gravitationally polarized.

http://arxiv.org/pdf/1106.0847.pdf [arxiv.org]

(I'm a big fan of Hajdukovic. Whether he's right or wrong, he asks fascination questions).

The consequences of falling up (0)

Anonymous Coward | about a year and a half ago | (#43596137)

Imagine you have a sealed super insulated magic box filled with energy that can be partially converted upon command to (anti)matter via pair production and later back to energy again.

The box is suspended over a cliff on a white dwarf by spring and left to free fall. The spring harvests some energy from the falling box and some is lost to friction and other resistance.

At the bottom of the cliff box produces matter anti-matter pairs reducing its effective gravitational mass. This allows spring to overcome gravitational force holding the box down and reposition itself at the top of the cliff where pairs are converted back into energy and the process begins all over again. You then run to the patent office and secure your patent for the worlds first working propetual motion generator. Not bloodly likely if you ask me.

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