Some of the comments above are informed and interesting; others belong in the "Crank Science" Topic (which see). But quite a few (in no particular order) are just annoying. Please, folks, you are entitled to any opinion you choose; but if you want others to read your opinion and take it seriously, you need to do your homework and make sure you at least know a little of what you are talking about. Read up on the history of elementary particle physics, from the Greeks through the European "Enlightenment" through Cavendish, Rutherford, Chadwick and especially Dirac, who introduced the notion of antimatter. Then read some Feynman; he was extremely "accessible". It's a grand, relatively simple story. The "Standard Model" is just a theory, true, and even its proponents (most of them, anyway) suspect that it is ultimately wrong in some particulars (so to speak). But it is not just some handwaving "Anyone's guess is as good as anyone else's" invention. Countless lives have been devoted to testing and rejecting speculations about the makeup of matter, and it is an insult to their dedication and effort to just make stuff up out of ignorance that could easily be ameliorated by a little reading. This is no place for laziness. If you aren't willing to EARN an informed opinion, please keep yours to yourself; otherwise ResearchGate will just be another noise repository.

Hey! Please post the results of this experiment when it comes. Its really nice and awaited experiment.

No. Anyone want to make a bet?

Experiments on matter and anti-matter will prove which interacts with gravity more.

Oh my goodness... Look, the accepted view is that CP violation unbalanced the matter vs. antimatter of the Big Bang at the time of hardonic freezeout (more or less) so that by the time atoms formed (and the universe became transparent to light) the only heavy stuff (baryons) left was all one type -- what we now (naturally enough) refer to as "matter". Since CP violation only offers about a tenth of a percent asymmetry, and that only in the strange & beautiful meson sectors, what's left is probably only a teensy bit of what we started with -- but it's enough! As for gravity being different for matter & antimatter, we don't know for sure yet, but I'll give you 10 to 1 odds that it isn't. Any takers?

The extended standard model (SME) provides a theoretical framework for *possible* matter-antimatter gravitational asymmetry, see http://www.physics.indiana.edu/~kostelec/faq.html. So far the experiments have only provided upper bounds for such an asymmetry. It may be experimentally impossible to observe *possible* symmetry violations because of the weakness of the gravitational interaction.

With AEGIS we will do the same experiment with antihydrogen, produced through the interaction of Rydberg positronium with antiprotons.

see http://aegis.web.cern.ch/aegis/home.html

the results will presumably arrive next year

Antihydrogen could have a different g than matter, according to scalar and vector gravity theories, or be subject to antigravity

Antigravity ??? How so ???

Matter and antimatter should have the same mass but having different arrangement and quite different properties..

While there are theoretical reasons (and only theoretical so far) to expect that matter and antimatter *might* have a tiny asymmetry in their interaction with gravitation, there's no proof of antigravitational effects. All the experiments so far have given negative results. I would not bet my money on this horse :).

Prof. Jess is correct. The weight need not differ.

Discovery of positron led to the concept of antimatter and it is proved that positron has mass equal to that of electron. In this many other antiparticles have been postulated. As such from the discussions i came to know that there are no as such experiments to prove that antimatter is heavier than matter or vice versa.

So in my opinion matter and antimatter have same masses.

Antimatter? I need proofs more robust about it

Ok, thanks, if cosmic rays are antimatter, and high energy particles also. I agree, in this case. I wanted to be sure that there was another kind of mysterious entity

Daniel, existence of antimatter is an experimental fact, which can be theoretically explained and defined by the Standard Model. It's not a matter of personal opinion.

As you can easily check, antimatter has been experimentally created from antiparticles.

Some of the comments above are informed and interesting; others belong in the "Crank Science" Topic (which see). But quite a few (in no particular order) are just annoying. Please, folks, you are entitled to any opinion you choose; but if you want others to read your opinion and take it seriously, you need to do your homework and make sure you at least know a little of what you are talking about. Read up on the history of elementary particle physics, from the Greeks through the European "Enlightenment" through Cavendish, Rutherford, Chadwick and especially Dirac, who introduced the notion of antimatter. Then read some Feynman; he was extremely "accessible". It's a grand, relatively simple story. The "Standard Model" is just a theory, true, and even its proponents (most of them, anyway) suspect that it is ultimately wrong in some particulars (so to speak). But it is not just some handwaving "Anyone's guess is as good as anyone else's" invention. Countless lives have been devoted to testing and rejecting speculations about the makeup of matter, and it is an insult to their dedication and effort to just make stuff up out of ignorance that could easily be ameliorated by a little reading. This is no place for laziness. If you aren't willing to EARN an informed opinion, please keep yours to yourself; otherwise ResearchGate will just be another noise repository.

Look, before you post your own "opinions" about antiparticles or antimatter, please read at least the following simple descriptions of facts:

http://en.wikipedia.org/wiki/Antimatter

http://en.wikipedia.org/wiki/Baryogenesis

There's no excuse for intellectual laziness.

Thank you for the review of Kuhn, Daniel. I agree with all these fine principles, of course, and with most of what you say; but I have a big problem with what you leave out. If I make up an original theory to explain the difference between particles and antiparticles in terms of charge alone, it may be able to predict the annihilation of positrons and electrons and thereby meet your criteria listed above. But it does not explain why an electron will not annihilate with a positive muon, because it ignores the different flavors of lepton number. A multitude of other observations are inconsistent with that model as well. You can't just make a customized micro-theory to explain one observation and ignore all the others that are explained by the painstakingly assembled Standard Model, hidebound consensus though it may be. Such micro-theories are already wrong, in that they are inconsistent with existing observations. Therefore, if you want to propose a radical new theory, you must at least be aware of the existing observations. You cannot shrug off this responsibility by claiming that all the observations are contaminated by their interpretation within the conventional theory; that is just insulting. Academics my be arrogant, but they are not all fools.

Now, my previous comments were not really directed at you, but since you asked for dialogue, I have some things to say about your previous post. [It sure would be nice in ResearchGate automatically specified WHICH previous post each new entry was responding to. As it is, there is no dialogue unless one goes to the trouble to specify the recipient "manually".] Anyway, you said the following (in quotes; I will insert my comments as annotations):

"There is a distinction to be made between antiparticles and antimatter. The fact that an antiparticle has a charge opposite to that of its corresponding particle does not imply that it is made of antimatter."

Clearly there is a semantic problem here. Conventional terminology would have an antiparticle be a particle of antimatter and all antimatter be composed of antiparticles. What do YOU mean by these terms?

"If it were true, then we would observe complete proton-antiproton annihilation, complete neutron-antineutron annihilation, etc, and not only electron-positron annihilation."

In what sense do we NOT have complete proton-antiproton and neutron-antineutron annihilation? Baryon-antibaryon annihilation usually produces pions, but always in equal numbers of particles and antiparticles. Do you mean annihilation is not "complete" unless only self-adjoint particles like photons remain, as in positron-electron annihilation? In principle a positron and an electron can annihilate into a neutrino-antineutrino pair, but very very rarely (and of course never observed).

"All that we can say for certain, is that a particle can be positively or negatively charged, but not that they are made of matter and antimatter."

That is most certainly not the case. Neutrons and antineutrons are uncharged; are you seriously claiming that antineutrons are not what their name implies? If you reject "composite" particles like nucleons, then what about neutrinos and antineutrinos?

"My personal opinion is that there is no such thing as antimatter, that is, there no matter that is made of fundamentally different components. All matter, including what we call antimatter, should be made of the same fundamental blocks."

There is nothing here for me to disagree with, as you have clearly labelled your statement as a personal opinion and specified only how you feel matter and antimatter SHOULD be made.

Imagination, speculation and open-mindedness are among the best features of our species, but they should not be used as an excuse to ignore (experimental) facts. Anybody who claims that "generations of theorists are always ultimately proven wrong" knows nothing about the philosophy and history of natural sciences. Classical mechanics is not wrong; it can be derived from quantum mechanics. Thermodynamics is not wrong; it can be derived from statistical physics. General relativity and the standard model are not wrong; they are particular limits of a more fundamental unified theory (which we don't yet have). There's an effective physical theory for each relevant scale that we can observe and measure.

Hmm, obviously retirement has left me with far too much free time on my hands, and my argumentative nature finds plentiful ways to use it. :-)

Tapio, I have only a minor quibble with your defense of old theories. It is true that (for example) classical Newtonian mechanics is still valid within the domain for which it was developed; the discovery of relativity and quantum mechanics did not mean that bridges started falling down. However, it is economical and satisfying to declare that, while old theories my still be "approximately correct", they are "absolutely wrong". Newton made sweeping claims about ALL bodies under ALL circumstances; those claims are emphatically and dramatically incorrect when applied to atoms and cosmic rays. So, as a General Explanatory Theory, Newtonian mechanics is indeed "wrong". So, surely, will all theories become in the fullness of time. Daniel was right about that, I think.

Jess, you're of course right in saying that Newton overestimated the validity of his theory. The point I was trying to make is that physics is fundamentally an empirical science, and all these "effective" theories (such as classical mechanics or thermodynamics) were built on explaining all the experiments that could be done at that time. In that sense they all have a well-defined range of validity where they are "correct". I think of physical theories in terms of coarse-graining or "emergence" (term often misused in philosophy of science).

I think we have learned enough over the centuries not to repeat Newton's mistake. We know that our understanding of antimatter may not be perfect, but any future theory or "opinion" must explain the current experiments, too, which are in accord with the standard model (i.e. no negative mass, no difference in g-coupling between particles and antiparticles etc.).

The development of philosophy of science is perhaps even more interesting than that of science itself :), but often not very well-argumented...

@Daniel: There are no neutral muons. Positive muons can (and presumably do) decay into a neutrino-antineutrino pair -- in fact they MUST do this; I've calculated the branching ratio as a homework assignment in 1971. You speculate as if there were no data on rare decays of muons with which your theory must agree.

OK, I found out how to EDIT a post; now how can I DELETE this one?

@Tapio: I wish it were true that we have learned enough over the centuries not to repeat Newton's mistake, but when people claim that string theory is a ToE ("Theory of Everything") I have to conclude that not much has changed. Such naive reductionism is, as Anderson says, not a theory of anything.

I think the link given below will serve the purpose up to a certain extent regarding antimatter property questioned above.

http://www.sciencedaily.com/releases/2011/07/110727161135.htm

Ya definate

@Lal: Sorry, that experiment had nothing to do with gravitational mass, only with inertial mass. Of course, most folks (myself included) believe they are the same thing, or at least proportional to each other; but that's the question here: are they?

In reality mass of elementary particles is neither inertial nor gravitational.

@Jess:first thanks for ur comments.

agree on your point that experiments are measuring inertial mass. gravitational mass is measured using the force of gravity. no matter in which place (i.e similar environment) objects are, they will experience equal magnitude of gravity and weight will be decided by their mass. not easy to express. to me there seems to be no difference between the inertial and gravitational mass. that is why above link, to me, seems helpful. further the link given below may be of some help for us.

-------http://www.physlink.com/education/askexperts/ae305.cfm

----------http://en.wikipedia.org/wiki/Mass

i may be wrong, please comment on this.

http://www.physlink.com/education/askexperts/ae305.cfm

The difference between inertial and gravitational mass is conceptually fairly simple. Inertial mass describes how an object responds to an external force (how it accelerates with the force, or resists acceleration if you want). Gravitational mass is the response to a g-field. If future experiments were to show that particles and antiparticles have different gravitational coupling (as allowed in the extended standard model), there would probably be no simple relationship between inertial and gravitational masses.

Ok, sorry if this is not absolutely clear :). Inertial masses of particles and antiparticles are identical according to high-precision measurements (and the standard model). This makes it highly plausible that g-masses would also be identical, i.e. that matter and antimatter would have an equal "weight". However, the difficulty of measuring g-coupling to an extremely high precision has so far prevented this from being experimentally verified. We don't yet have a proper theory to know for sure.

I don´t know if these links have been posted previously in this thread, since Google Chrome does not seem work with Researchgates "Show full discussion" button, which hides earlier posts in the conversation from viewing. BTW, anyone else having this problem?

http://www.physorg.com/news/2012-01-repulsive-gravity-alternative-dark-energy_1.html

Interesting theory, but wouldn´t such large amounts of antimatter have been observed with telescopes?

That is the classical debunking of the theory of antimatter being the dark matter, as I understand it.

And the AEgIS project at CERN:

http://aegis.web.cern.ch/aegis/home.htm

Erik: Experiments have set strict limits to the relative amount of measurable antimatter beyond locally produced antiprotons (10^-9 by now?) and thus the theory above seems unlikely.

Tapio, that was my reason to doubt this otherwise interesting idea. Even if antimatter has negaitve gravity,( which hopefully will be disproved or proved by AEgIS), how could there possibly be enough antimatter in the universe to cause expansion of the universe comparable to the effects required of dark energy? It seems unlikely that we should not be able to observe such large amounts of antimatter if it is there, since it would interact with matter, obscure celestial objects and be far from dark etc. Or are there any plausible explanations for hiding the antimatter, should it be there?

Erik, you're quite right. As far as I understand it, the measurements I was referring to mean that if a significant amount of antimatter existed in the universe, it would have to be too far from us to be measurable (> 100 Mpc). This seems unlikely.

Nathan, we don´t know for sure until experimental evidence such as AEgIS settles the issue. I think Tapio and Daniel have posted good answers to Your questions above. The link I posted above is one example of an interesting idea about possible consequences if antimatter should behave differently than ordinary matter in gravitational fields. Regarding Your comment about dark matter and dark energy being confused with antimatter, I don't understand what You mean. We all probably know that classical cosmology predicts the required proportions of 70:25:5, that dark matter is clumped together with matter and that dark energy has to be evenly distributed trough the universe to fit the classical model. It was once believed that antimatter could be the dark matter, which now seems impossible since observations tell us that there is very little of it left in the universe, as noted above. The theory in the link is an attempt to revive that old idea, where if I understand it correctly, the effect ascribed to dark energy would instead be caused by antimatter with negative gravity causing accelerated expansion.

Chris, perhaps it's you who should read Russell, and I don't mean Walter but Bertrand. Maybe then you could appreciate the fundamental differences between beliefs (religion) and natural sciences :-).

Yes - anti-matter has mass and, for example, the mass of an anti-proton will be

the same as the mass of a proton

Proton and antiproton have the same mass but in many respects they are still evasive particles. For instance we don’ t know still with enough certainty how accelerated proton emits radiant energy. It seems that it emits energy in lower measure than the accelerated electron, but it isn’ t altogether evident.

@Susana: Please check out some of the earlier postings about different definitions of mass and possible matter-antimatter asymmetry.

Hi Hector, good points (and an excellent turn of phrase -- the Higgs bosom -- where theorists turn for comfort and reassurance? :-) Anyway, as a crusty, cynical experimentalist I can only say what I think I know from (sometimes second-hand) observation: the electron appears to be a point particle since no one has ever detected any signs of structure or size in electron-electron or electron-positron scattering, except of course in the various hadrons crated through virtual photoproduction in such collisions. Messy business, that high energy scattering. But until some of the predictions of the model (point electrons) turn up false, it's a nice simple idealization. [As an aside, the "classical" radius of an electron (its Compton wavelength, more or less) is finite, calculated from the assumption that its rest mass is the coulomb potential energy required to assemble a shell of charge at that radius totalling one electron charge; but that doesn't count.] As for "spinning a point", that's a really, really interesting topic! Spin, governed by the Lie algebra of SU(2), the Simple Unitary group of order 2, is not the same thing as orbital angular momentum, governed by O(3), the Orthogonal group of order 3. One of the things that means is that since you (as a whole) obey O(3), if you turn around 360 degrees, the world you see is the same as before you turned; but if you were a spin-1/2 particle like an electron, the phase of the world [whatever that is -- remember, I'm an experimentalist] would pick up a minus sign and would not be back to normal until you turned through another 360 degrees. I used to understand this stuff better.... Anyway, all that group theory doesn't help understand how a point particle can have true angular momentum; if you like, you can imagine starting with a cloud of "electron vapor" spinning at some finite rate, and then impose angular momentum conservation to have it spin faster and faster as it collapses (like the canonical figure skater) until it spins infinitely fast at zero size. Does that help? No, me neither. Some things you just have to get used to.... But it's important to realize that this outlandish picture was not arrived at arbitrarily, or even voluntarily -- a vast collection of precision experiments and careful interpretations, in which every imaginable avenue of error or alternative interpretation was meticulously explored, let to the formulation of this elegant but ultimately empirical Standard Model, which (in Einstein's words) is as simple as possible -- but no simpler! Is everyone smugly satisfied and happy with it? Hell no! Some are, of course; pity them. But anyone who want to propose another interpretation has to make sure it is also compatible with all those data, or it will be justly ignored. (Remember how omniscient you were at 13, and how you used to try to explain the workings of the world to idiotic adults who thought experience gave them insights you lacked? Something like that.)

Hector, I may be out on limb here, but one simple way to look at the problem of Your question in classical mechanics terms may be to imagine the spinning electron as a limit problem. When the radius goes down and becomes close to zero, the electron would then spin faster to conserve momentum. This can of course not happen in the real world, its just a thought experiment. But when the radius becomes small enough, the uncertainty principle kicks in and you need to switch from classical mechanics and instead describe the position of the point in terms of a probability function. The rate of spin therefore would not reach infinity, but is limited by the quantum uncertainty of the point. It therefore seem like an pointless exercise to try to run this thought experiment to a much smaller radius than the positional uncertainty. A quantum mechanical description is likely more appropriate at very small scale.

I believe the vector algebra usually used to describe 1/2 spin particles is the complex valued spinor algebra, which also models the somewhat unintuitive 720 degrees needed to rotate the particle back to its original spin state. It also provides a quantum probability function.

The spin is due to the rotation of the elementary particle around its own axis. If we consider the rotation of the electrodynamic mass we have the angular spin. If we consider the rotation of the electric charge we have the magnetic spin. The two spins don’ t coincide and the Zeeman effect allows to define a relation between the two spins. The photon mass deduced from the relation hf=mc^2 is an equivalent mass (virtual and not real). I think the probability theory can be considered anyway only a very provisional mathematical model and the questions of science and technology have to be solved by more convincing mathematical models.

Hector, even Einstein did not believe in Quantum mechanics (Or so the story is told at least...). So don´t give up.

As was pointed out previously in this thread, Your question of why a point particle can have angular momentum is a very good one. To come to terms intuitively with quantum concepts by reasoning from the viewpoint of classical mechanics is no easy task. It is a little akin to try to visualize 4 dimensional space time. It is next to impossible for our minds to do that. But we can see certain aspects of the concept that makes it intuitively understandable. Expanding balloons and breads with raisins are usually used, but hey are bad analogies since since they have a surface. But if You can accept the fact that looking far as we can out in to space with a radiotelescope, what You look at is the cosmic microwave background radiation. This radiation is believed to have been created during the recombination epoch when the tiny young universe first became transparent. So we can understand that by looking very far out in every direction in space, we will essentially look back at something very small instead of infinity. That if anything goes against our experience and intuition. But that way we can get some feel of what a finite but unbounded universe is like. What I wanted to say by that of topic rambling is that it is possible to intuitively get a feeling for quantum concepts as being the best explanation of very small scale phenomena by similar reasoning and examples. I remember 30 years ago when i studied group theory and electron physics at university, I had many, perhaps immature, intuitive objections to the theories. But the more reality seems to fit theories, the more intuitive it becomes. The electron spin is very real. Precession of electron spin is used in NMR measurements that You may be familiar with from medicine. The Planc radiation law depends on quantum physics. It would actually be sort of strange if we could define something with arbitrary precision in the real world as we can do in math. By counterexamples infinite precision gets us into trouble in many areas. Infinite information density would in principle be possible which is not good for thermodynamics among other hings. It seems counter intuitive that we will continue to find smaller and smaller particles indefinitely. There has to be some smallest element or structure that preferably is self sufficient in some sense to not warrant further division into smaller pieces. We believe the electron to be an indivisible particle. But the definition of it as a point particle is tricky. A spectral line that You mention has a certain bandwidth, or uncertainty. The simplest explanation for that is the theory of coupled oscillators. Even a number of simple coupled electric LC circuits tuned to exactly the same frequency will exhibit band broadening. Electric and magnetic fields will split atomic spectral lines by the Stark and Zeeman effect which depend on electron spin as previously mentioned. Virtual particles that are continously created and destroyed and have been detected. It is seems much more reasonable to assume that everything is sort of granular at a small enough scale, with a certain uncertainty that is definite.

if it so? there is no meaning for antimatter. Because the mass of the matter playing very impartent role in energy conversion, that if matter and antimatter get together anhilation takes place which in both matters disappears and in place enrgy is appears that is same amount matters are rewuired to nullify each other and to produce energy. which in turn rewuired same amount mass of matter and antimatter, hence massof matter and antimatter are same nat different.

Has this been experimentally verified?

The recent discussion on this topic has been based on a disappointingly naive view of elementary particle physics and quantum mechanics. As suggested by Tapio Ala-Nissila: "Look, before you post your own "opinions" about antiparticles or antimatter, please read at least the following simple descriptions of facts" (And I would add: "Read the earlier discussions'.)

Uninformed opinions are the lowest form of information, informed opinions rank slightly higher and expert opinion the highest in the spectrum of opinion and information transfer. Everyone is entitled to their own opinion. I would prefer that, unless you are an expert, you would keep your opinions to yourselves. However, feel free to ask questions as long as they are informed questions. I thought that Research Gate was for serious researchers, not for idle gossip and speculation from innocent bystanders. Perhaps I was mistaken.

The question of the weight of elementary particle of matter versus that of an antimatter particle has not been addressed substantially in the later responses. Earlier discussions dealt with this question to some extent. Weight is derived from the gravitational attraction between masses and does not depend solely on the intrinsic mass of the particle but also on the gravitational interaction which is supposedly (in the Principle of Equivalency ) invariant with respect to matter or antimatter. Any difference in the mass of matter and antimatter particles (not contained withing the Standard Model) has not yet been determined within the accuracy of experiments so far.

Now that it is possible to produce and maintain antimatter (anti-hydrogen) for a reasonable length of time, it should be possible to test whether the gravitational interaction between antimatter particles and the ordinary matter of the Earth is the same as that of ordinary matter particles and the Earth. The symmetry principle of equivalence implies that the gravitational interaction between antimatter and antimatter or antimatter and ordinary matter or ordinary matter with ordinary matter should all be equivalent. An experimental test of this principle may now be possible and is being planned for the near future.

"We have in 2012 then, two experiments, both different in their experimental make-up. Both are trying to measure the gravitational free-fall of antimatter: one using anti-hydrogen, one using positronium." - http://www.australianscience.com.au/physics/weighty-thoughts-on-antimatter/

Also see: http://www.ifraf.org/a-noter/article/antimatter-and-gravitation-first-630?lang=fr

Thanks. We shall see.

@all:-

the question we all are following/discussing is

Does antimatter weigh more than matter?

it will be nice if all remain specific to this for better understanding and fruitful results.