Does Antimatter Fall Up Or Down? 480
KentuckyFC writes "There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field. We've never been able to make enough of the stuff to do the experiment. But at the European particle physics laboratory at CERN, where scientists have been refining the technique for making antihydrogen, researchers are designing an experiment called AEGIS that will finally settle the matter. The idea is simple — fire a beam of antihydrogen atoms and watch which way they fall — but the details are fiendish (abstract). The answer should help solve a number of important conundrums such as why there is so little antimatter in our part of the universe and what the value of the cosmological constant is."
Confused (Score:5, Funny)
Or will it settle (or unsettle) the anti-matter?
Re:Confused (Score:5, Interesting)
Gravity affects matter and antimatter the same way because gravity is not a charged property and a matter particle has the same mass as its antiparticle.
So the above is no longer believed to be true?
Re:Confused (Score:5, Insightful)
Re:Confused (Score:5, Insightful)
Re:Confused (Score:5, Informative)
Re: (Score:3)
Re:Confused (Score:5, Funny)
Re: (Score:3, Funny)
|It works|
Re: (Score:3, Funny)
No. I'm a chemist, and it doesn't help much to add more electrons to doubt.
Re: (Score:3, Insightful)
If the 2 possible outcomes are polar opposites, and it goes one way and not the other. I'd say "removes all doubt" is a fair statement. Note I didn't use the word "prove", more like doubt in the legal prosecution sense.
But now were just arguing semantics. Oh wait, this is /. never mind.
Re: (Score:3, Informative)
If the 2 possible outcomes are polar opposites, and it goes one way and not the other. I'd say "removes all doubt" is a fair statement. Note I didn't use the word "prove", more like doubt in the legal prosecution sense.
To get pedantic about it:
the experiment only shows that, under a certain set of conditions, antimatter behaves a certain way.
You've only removed all doubt if you expect every single possible type of antimatter to behave the same as antihydrogen.
You can extrapolate from the observed behavior, but as we've seen time and time again, there are plenty of edge cases & fringe behaviors that are completely unanticipated.
Re: (Score:3, Informative)
Re:Confused (Score:5, Interesting)
Why is there so much matter around, and no anti-matter? Perhaps because they repel each other? There is some evidence that nearby galaxies are made of matter and not anti-matter, but the universe is very big, and time could be effected differently by anti-matter gravity (speeding up). Why are galaxy clusters accelerating in their separation from each other? Could anti-matter still be present somewhere, causing the acceleration? Why is matter in the universe so clumped together, and not more uniformly spread out? Could there be clumps of antimatter between the clumps of matter?
Evidence suggests that there simply is no anti-matter left in the universe, but it's fun to speculate upon implications of anti-matter falling up.
Re: (Score:3, Interesting)
Re:Confused (Score:4, Informative)
Re: (Score:3, Insightful)
If you left any of these orbs near each other in space then they would exert a significant gravitational pull on each other and would both be
Re: (Score:3, Informative)
Re:Confused (Score:5, Informative)
Holes are a virtual particle with no mass, whereas anti-matter has mass. Electrons actually exist, but holes are simply a place where an electron can fit. Take the example of a helium balloon in a car: if you slam on the breaks, it flies to the back of the car because all the air is rushing forward, and the balloon's relative vacuum gets pushed backward. A hole behaves similarly. Antimatter, on the other hand, has mass just like its matter counterpart and therefore isn't directly comparable to a hole.
Re: (Score:3, Insightful)
Next time you've got a balloon, put it in the car and give this experiment a try. When you have a helium-filled balloon in the car, it reacts opposite to the way most other things in the car react. When you slam on the brakes, a ball on the floorboard will roll forward, but the balloon will float backward.
Re: (Score:3, Interesting)
In this view it would be quite natural that antimatter is 'falling' upwards.
In addition it would explain why we don't see antimatter in our universe: The antimatter universe simply evolved into the other (negative) direction of the timeline.
On the other hand - matter and antimatter as just another manifestation of energy - it should
Re:Confused (Score:5, Interesting)
If we maintain that causality only travels in the forward direction (not an unreasonable assumption to make), then you could actually solve this problem by saying the antiproton was, from its own frame of reference, annihilated, at the same time that it was created from your frame of reference, and vice versa.
Even more interestingly, when you consider that we travel through spacetime at the speed of light, you can think of the creation of a PP- pair as an antiproton "bouncing in time" off a burst of energy, one that is exactly equal in magnitude to the energy required to reverse the direction of a proton traveling at the speed of light.
Then, when you consider a recently-generated PP- pair that re-self-annihilates, releasing their combined energy, you can think of the same "bounce" in reverse, at which point, you have a single proton bouncing around in a game of nanoscopic temporal ping-pong!
Re:Confused (Score:4, Interesting)
>traveled backwards in time, then we would see it before we did the experiments that create it. However, in the
>lab, we create antimatter and it is still present after we create it. This would not be true if it traveled
>backwards in time. Just think about what you are saying. Not at all dear anonymous coward!
You may or may not have to check Feynmans precious books here, - he's going to explain it to you very well.
In short: When we 'create' antimatter - from the perspective of the antimatter this is the point of time of its annihilation (because for the antimatter time is running backwards)
When antimatter gets annihilated by the contact with ordinary matter (lateron in our timeframe) from the perspective of the antimatter this is the moment of creation of the antimatter.
I know it's not easy in the first place, but if you give it a few moments of thought it's logical and natural.
And it's been an accepted theory in physics for many years.
Re: (Score:3, Funny)
Shouldn't we instead be asking how it will fall?
What if it falls on an imaginary axis and ends up travelling in time or to a parallel universe?
I hate "news" like this. (Score:2, Insightful)
Unless they're trying to drum up interest for funding...
Re:I hate "news" like this. (Score:4, Insightful)
Re:I hate "news" like this. (Score:5, Insightful)
Re: (Score:3, Interesting)
Re:I hate "news" like this. (Score:4, Insightful)
Re:I hate "news" like this. (Score:5, Funny)
Nobody doesn't like Molten Boron!
Re:I hate "news" like this. (Score:5, Funny)
Layne
Gravitons (Score:2)
Re:Gravitons and Graviolis (Score:3, Funny)
Professor: And the microwave radiation, combined with the gravitons and graviolis from the supernova, blasted us through time itself.
Re:Gravitons (Score:5, Interesting)
The gravitational field as a scalar field surperposed on a flat space-time is just another way of describing gravitation - the curved geometry of general relativity is a better model, although it is more difficult to get a handle on. Perhaps it would be worth trying to tackle the other forces in the same way, as geometry in some sort of space-time. Perhaps we can even derive quantum mechanics as a special case of such a model; mathematics has certainly come a long way since the time of Einstein and Bohr, and it isn't unreasonable to hope that we are now approaching a situation where we can solve those old problems, that neither had the tools for.
What gravitons? (Score:4, Interesting)
Are they? Ever seen evidence of one? Gravitons are a purely theoretical construction and, worse of all, one that does not work. While you can construct a quantum field theory of gravity it does not work to arbitrary energies. You have to impose a cut-off threshold and since there is no valid reason for doing so the theory is broken...hence all the theoretical activity trying to reconcile GR and Quantum mechanics.
You mean a vector field since gravity has direction, rather than the Tensor field of GR.
Re:Gravitons (Score:5, Interesting)
Re: (Score:3, Insightful)
And why would people do anything about a model that gives ridiculous accuracy on fundamental particle-physics experiments? It works. You need to learn to deal with it, not the other way around.
Why? That's the wrong attitude; the real question is "Why not?"
Yes, for practical purposes QM is fine - but it is not enough for understanding. It's like the difference between engineering and science; engineers are good and worthy people, but their focus is practical: the construction of things, the application of knowledge to a practical purpose. The focus of the scientist is on the unknown, the unanswered questions; the practicality of things is not foremost in their mind, they speculate and grope in th
Re:Gravitons (Score:4, Interesting)
Re:Gravitons (Score:5, Informative)
It will fall down (Score:5, Informative)
Re: (Score:2, Interesting)
Re:It will fall down (Score:5, Insightful)
Because our understanding of physics is so consistent that it is a waste of time to test the cornercases of our theories *cough*quantum gravity*cough*dark matter*cough*dark energy*cough*
Re:It will fall down (Score:5, Informative)
There also is some direct evidence that if you have differences they are not due to gravity:
Reference e.g.:
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/antimatter_fall.html
"The only direct experimental result on antimatter and gravity comes from Supernova 1987A. This supernova in the Large Magellanic Cloud emitted both neutrinos and antineutrinos, some of which were eventually detected on Earth. Those neutrinos and antineutrinos took 160,000 years to reach Earth, and while travelling were bent from a "straight line" path by the gravity from our own galaxy. The bending with gravity changed the time needed to reach Earth by about 5 months, yet both the neutrinos and the antineutrinos reached Earth at roughly the same time (within the same 12 second interval). This shows that the neutrinos and antineutrinos "fell" similarly, to a very high level of precision (about 1 part in a million). [4] and [5] provide some background information on this."
Re:It will fall down (Score:4, Insightful)
Re:It will fall down (Score:5, Funny)
Why not? This is where I get my IP legal advice!
Re: (Score:3, Interesting)
Re:It will fall down (Score:5, Informative)
Re:It will fall down (Score:5, Funny)
Re: (Score:3, Informative)
According to GR, gravity is the curvature of Space-Time. As the anti-matter moves through space it has to follow this curvature. If it does not, that means GR is wrong (which may be the case, but I doubt this experiment will disprove GR).
Except that regular hydrogen falls up. Since the average velocity of its molecules is above the escape velocity of Earth, hydrogen tends to move away from Earth. If anti-hydrogen has similar velocities, it should also rise.
That is not "bringing it up as a related issue".
the AC who posted that esacape velocity has nothing to do with hydrogen rising
He did not say anything of the sort. You misunderstood that. He said:
bollocks. having a faster-than-escape velocity doesn't make things fall upwards. it merely means they don't come down fast enough to hit the earth
He was essentially pointing out that you were confusing unrelated issues in your original post.
Re:It will fall down (Score:5, Informative)
Re: (Score:2)
Re:It will fall down (Score:5, Informative)
1) That determines the rate of effusion. Molecules don't just go straight up. They bounce around. What actually happens in reality is that the force holding those molecules to the earth isn't actually enough to force it to happen. But the upward movement is going to happen slowly. You can still measure the effect that gravity has while this upward movement happens.
2) Also because it has to do with effusion, a *beam* of antiparticles in a vaccuum won't be affected by it. They're not going to bounce around and have effusion effects happen; it's going to be more like a batting practice machine - balls come out and curve, and are done the moment they hit something. This is obviously what they're going to do since antimatter is quickly eliminated in the presence of matter.
3) Even if that was a problem, it's not actually a problem at all temperatures and pressures. If you wanted to do an experiment where *normal* hydrogen didn't rise, just lower the temperature.
Re:It will fall down (Score:4, Insightful)
And do you honestly think that these physicists are going to be so stupid as to not do their antimatter experiments in a vacuum? That's about the only conditions where you could measure the rate of fall of individual atoms.
Re:It will fall down (Score:4, Insightful)
TFA questions whether anti-matter will be attracted (mass-> <-mass), or whether it will be repulsed (mass<- ->mass) by gravity.
Hydrogen is attracted rather than repulsed by earth's gravitational pull. Whether the earth's gravity well is deep enough to keep hydrogen captive is a separate topic. Having enough energy to escape earth does not mean that it is repulsed by earth's gravity. The Space Shuttle has enough energy in its fuel tanks to reach escape velocity, and there is no doubt that is is attracted, not repulsed, by earth's gravity.
Hot air is still attracted by earth's gravity. However, its higher energy state forces it to occupy a larger volume at a given ambient pressure, which makes its density lower than the surrounding cooler air. Hot air doesn't defy gravity by rising; cool air pushes the hot air up because it is denser.
Re:It will fall down (Score:5, Funny)
Re: (Score:3, Informative)
I suppose you have an alternative that is also consistent with all the observed instances of gravitation and meets your personal criteria for not being 'bunk'? Would you care to enlighten us? Why the heck is this drivel +1 Insightful anyway?
Re:It will fall down (Score:5, Interesting)
But how does antimatter react to curved spacetime (could it 'roll uphill')...
That's what the experiment in the article is testing. Does antimatter react the same way to an external gravitational field as normal matter, or oppositely?
It'd be Big News if it turned out to be oppositely, though. General relativity describes gravitation in terms of space-time curvature; particles under the influence of gravity alone move along geodesics which only depend on their initial position and velocity. There isn't any way to accomodate different particles feeling gravitation differently in that framework. There are generalizations like Einstein-Cartan gravity to accomodate spin, but that just allows the connection to have an antisymmetric part, and doesn't change the fact that there's only one curvature for every particle to feel. The key axiom of GR is the equivalence principle, which states that, locally, there is no observable difference between gravity an accelerated reference frame. This requires that gravity accelerate every particle by the same amount, independent of any other particle-specific variables.
Put briefly, this has never been tested before, but it'd be a very big surprise if antimatter behaved any differently from normal matter, and would throw most current theories of gravitation out the window. It'd be like a modern-day Michelson-Morley experiment.
and how does antimatter (with mass) curve spacetime? (could it 'outdent' rather than 'indent' it)
That's a different question, and one that would be far more difficult to test. You'd need to gain a few dozen orders of magnitude of precision in measuring these things, or assemble a macroscopic chunk of antimatter somehow.
It'd also be a big surprise for a different reason. This is essentially treating antimatter as having negative mass [wikipedia.org] and thus producing a repulsive gravitational effect. There's no deep reason why this would be mathematically inconsistent with GR, although it would have wacky consequences like perhaps the possibility of stable wormholes and FTL. In technical terms, it violates the weak energy condition. It's also unlikely for a different reason: conservation of momentum in GR requires inertial mass and gravitational mass to be equal, so for antimatter to produce a repulsive gravitational field like this would also require it to have negative intertial mass. It would respond oppositely to ordinary, non-gravitational forces, a positronium atom would have *negative* net mass (the electron and positron masses cancel, and the binding energy makes it negative), and a whole host of other consequences that would be readily observable but haven't been seen. Further, in quantum field theory having negative mass particles would create problems with vacuum stability.
So, both of these are possible in the sense that the experiment hasn't been done yet, so we don't know for sure they aren't true, but either one would invalidate huge swaths of physics and definitely qualify as Big News.
Re: (Score:3, Interesting)
negative mass also implies negative energy according to E=mc^2. I guess that will have to change as well. I want to see how that plays out with nuclear reactions.
That would be how we know it isn't true. Antimatter is already well known to have positive inertial mass/energy.
Obvious? (Score:5, Funny)
I wish it fell upwards (Score:3, Interesting)
Re:I wish it fell upwards (Score:5, Insightful)
Not necessarily - Merely opening that particular conceptual door would lead to a massive influx of funding and revisited anomalous past results.
Interesting thing about experimentation, even the most honest of researchers tends to throw away "bad" results (in the sense of not publishing them, not in the academically-dishonest sense of omitting them from the data). If the scientific community suddenly accepted the possibility of spooky-effect-X, you can bet that dozens or even hundreds of research groups would dredge up their past efforts to see if effect-X explains their results.
Case in point, l'Acedemie des Sciences and meteorites. Up to the turn of the 19th century, only idiots would dare claim that rocks could fall from space... Until the scientific community decided they could, at which point a huge body of past evidence appeared practically overnight supporting the existance of such falling objects.
Re:I wish it fell upwards (Score:5, Funny)
Re:I wish it fell upwards (Score:5, Funny)
I heard God banned him for 3,000 years.
Electromagvitational ? (Score:2)
I'm under the impression Electromagnetic fields & Gravitational fields function similarly or the same.
I'm thinking of a field situated like the simultanious implosion of a uranium or plutonium bomb, with these antimatter things trapped in the center.
What if on one point of the field the magnetic strength was weakened, perhaps by touching it with another magnetic field, while on the oppisite end the strength was increas
And I didn't even know ... (Score:2)
it had mass just like anything else, and is therefore affected by gravity just like any other particle with mass.
Wouldn't "falling up" mean that antimatter has negative mass ? And if so, how does this comply with energy/mass conservation laws ?
Re: (Score:2)
Re:And I didn't even know ... (Score:4, Insightful)
If light is affected normally by gravity... (Score:2, Informative)
Re:If light is affected normally by gravity... (Score:5, Insightful)
If it behaves exactly as predicted, you can make another mark and continue. If not, you've found something potentially very important.
Re:If light is affected normally by gravity... (Score:5, Insightful)
I mean, we see water falling off edges of waterfalls etc. Why should the edge of the world be any different?
And regardless of how good human intuition is (Score:4, Insightful)
Through this process, we come to understand the natural world, and come to be fairly certain that our understanding is correct. Math and theoretical work is great, but actually testing those theories is what makes science what it is.
So even if we are 99.999999% certain that our calculations are solid and anti-matter does something, we still need to test it. There are plenty of things that we've been certain about that, when we tested it, turned out not to be the case.
Re: (Score:3, Insightful)
Re: (Score:2, Informative)
Re: (Score:3, Insightful)
This is a Black Swan problem
Theory : All Swans are White
Proof : every swan I see is white, every swan
Problem : Australia was then discovered along with the black swan.....
The cosmological constant, (Score:4, Funny)
Re: (Score:3, Informative)
Then Hubble found the universe was expanding so Einstein took it out again
Then the inflational big bang model and observations that the current expansion of the universe was accelerating seemed to require it again
This is why experiments need to be done
Re:The cosmological constant, (Score:5, Funny)
I saw a paper in the Journal of Irreproducible Results advancing the theory that the age of the universe is a nonlinear function of time.
They plotted on a graph the age people (or rather, western civilization) thought that the age of the universe was at various points in history--when the 19th century geologists said it had to be at least hundreds of thousands of years old, when the 20th century astronomers said that it had to be even older than that-- and plotted the points on a graph. They formed a smooth curve demonstrating (I think) a geometric increase.
So their theory was that, assuming all the age-of-the-universe estimates were correct, that means the beginning of the universe is moving backwards in time, away from us. In 1000ad, the universe really was 6000 years old, and now it really is 14.5 billion years old, and in another century, it will probably be in the trillions of years old
(I love the Journal of Irreproducible Results!)
So Guinness is the anti-anti-matter? (Score:2)
But how does this help explain why our area of space has so little anti-matter? If this was true then it would mean we are at the bottom of the universe, as opposed to what; or is the current thinking that anti-matter is not effected by gravity and this experiment would provide that it is?
Re: (Score:2)
Like many other posters, my "physical intuition" (indoctrination in GR) tells me that this is most unlikely, but it would have tremendous consequences for cosmology.
Oooh... I can answer this one! (Score:5, Funny)
Re:Oooh... I can answer this one! (Score:5, Funny)
But what if it turns out it falls sideways?
Re:Oooh... I can answer this one! (Score:5, Funny)
Ah, so little imagination... (Score:5, Funny)
Antimatter falls strange.
Re: (Score:3, Funny)
Antimatter powered airships, hurrah! (Score:5, Funny)
Just a few technical details to sort out, first :-)
...and, of course, if your antimatter-powered airship crashes, the phrase "Oh, the Humanity!" is going to be even more applicable. Maybe without the "the".
Tested at SLAC with positrons years ago (Score:5, Interesting)
Yes, anti-matter does fall down just like matter.
I Bet (Score:3, Funny)
No Loopholes in General Relativity (Score:5, Informative)
Uh, no there are not. Gravity (or geometry, same thing in the theory) depends on mass energy in General Relativity. Stuff (with mass energy) follows the metric (the local geodesic). Even photons (which are their own anti-particles) follow the geodesic - and that has certainly been tested. Equivalence principle tests also show that different sorts of nuclear matter (including neutrons) individually follow the geodesic. Anti-matter certainly has mass energy, and (with matter) can be converted to photons and is no different in the theory. In other words [springerlink.com] "there is only one type of geodesics and there are no antigeodesics for antimatter."
The original article talks about "flavors" of General Relativity. Ain't so such beasties. Period. If you go to the real original article [arxiv.org], you find a proposal for a 1% test of the equivalence principle for antimatter, and no such claims of flavors. Now, the equivalence principle has been tested to better than parts per trillion, and part of the mass energy in ordinary matter is made up of antimatter (in virtual particle pairs), so (based on the experimental evidence) I would claim that this test will be negative and is not actually that interesting as new physics. (The articles say that these older tests are "model dependent," but they are not model dependent enough to matter for this.)
That doesn't mean that this shouldn't be done (everything should be tested in physics, and different tests are always useful), but the prediction of General Relativity is clear : if anti-matter has anti-gravity, then General Relativity is wrong. The experimental evidence is also clear : this isn't going to be accurate enough to matter. Will make for some good public relations, though.
Re: (Score:3, Informative)
we conclude that the Principle of Equivalence between particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10-9,
Just a little bit better than 1%.
What about the third option? (Score:3, Interesting)
No. (Score:4, Informative)
"Anti-matter" is not the opposite of matter. It is matter with opposite charge or other opposite properties. Mass has no opposite. It is there, or it isn't. (Or it is and then it isn't and then it is and then it isn't, on the level of quantum fluctuations of the gravitational field.)
And no, a hole isn't "anti-matter". It's merely a void in the surrounding matter. It rises because of a principle known as "buoyancy" which is really the gross action of the matter surrounding it causing pressure differentials as a function of distance from the CM. As long as the surrounding matter can flow, it can fill any displacement of the void, and the mass will tend to move down rather than up, and the void will therefore appear to tend to move up rather than down.
And no, hot-air balloons don't rise because of the heat, they rise because they make the air in the balloon less dense than the air outside the balloon. How they do it is not relevant. A rigid balloon and a vacuum pump would work, too.
Re: (Score:2)
Re: (Score:2)
Re: (Score:3, Funny)
Re: (Score:2)
Re: (Score:2)
I think the reason you can't measure the hydrogen is because there's not enough. It falls out before you can get enough to tell what its velocity is. Keep in mind that hydrogen is very light and won't fall downwards because of gravity. Instead, you have to measure the curvature of its path to try to see which way it's accelerat
Re: (Score:3, Informative)
There's an anti-photon ... it's the photon. There's anti-versions of several other particles (antineutrino, antiquarks, antineutron, etc).
Re: (Score:3, Insightful)
Re: (Score:3, Informative)
First of all they are using anti-hydrogen for two reasons. First of, gravity is proprotional to mass and positrons have a mass of 0.5MeV while protons have a mass of a GeV or so. Thats a difference in mass of a factor of 2000. The second reason is that the electromagnetism is many many many orders of magnitude stronger than gravity, the EM coupling constant is around 1/137 while gravities coupling constant is around 1/ (1.2x10^{19}). So unless the object is electrically neutra
Re: (Score:3, Funny)
This also explains why cats and babies act so weird. Down where they live they're practically swimming in a sea of anti-hydrogen.
Re: (Score:3, Informative)
On contact with organic tissues (or pretty much anything else), it will disapear in a burst of highly energetic photons (think gamma rays). So, depending on the dose (approx. ng to kg), it can range from totally harmess to skin burn to radiation poisonning to strategic-grade nuclear explosion.
"Does it have the potential for a destructive chain reaction?"
No, the reaction does not create new antimatter, and the potential energy of the created antimatter is only a