Talk:Gravitational interaction of antimatter

LEP Observations

I don't know if it has ever been published, but in 1993 in LEP it was found we had to adjust our calculations for the beam orbits to take into account the moon. We actually observed tidal effects on the positron and electron beams. The calculated corrections where done assuming gravitational attraction of positrons, and noticeably improved the agreement between predictions and observation. I remember this was mentioned when they discovered a 1% correction to the beam energies. I'm not certain how much of the 1% correction was the tidal corrections... I doubt anyone at the time thought to run the calculations reversed to see if the effect was significant enough difference to prove the gravitational attraction of positrons to ordinary matter. In fact since the work was done by graduate students, I would not be surprised if they did the calculations and then just assigned the +/- sign to match the experimental results. However, chances are the answer to this question if positrons are attracted by matter exists within the LEP data.Bill C. Riemers, PhD. (talk) 21:42, 22 December 2010 (UTC)

• I'm not a physicist, but from my reading of the paper [1] I think that the change in beam energy was due to tidal forces deflecting the equipment, and not the beams directly. 74.183.177.42 (talk) 20:04, 13 November 2011 (UTC)

Measurement of antimatter's relationship with gravity?

Are you seriously suggesting that antiprotons and positrons (very common compared to anti-matter) have never been tested for susceptibility to gravity? The Antiproton page claims that they know that the antiproton interacts with gravity; is it true no one has demonstrated whether the sign of that interaction is positive or negative? Then one must assume they have never demonstrated any interaction at all.

Is anyone seriously suggesting that combining a positron with the antiproton will flip its sense of gravity?

This speculation about the gravitational interaction of antimatter is unserious. The interesting question is whether, once we know how gravity arises, we'll find a symmetrical set of particles (gravity reversed protons, anti protons, etc.). As for the sort of antimatter formed by antiproton-positron pairs, I'll think you'll find we already know the answers.

Someone with access to journals will have to find the relevant cites.

76.126.215.43 (talk) 17:40, 9 July 2009 (UTC)

These are extremely difficult experiments; I don't think any of them have been done. The antiproton article doesn't say that the gravitational interaction has been experimentally observed, just that it's predicted. From "antiprotons and positrons (very common compared to anti-matter)" it sounds like you think that antiprotons and positrons aren't antimatter. They are. -- BenRG (talk) 21:11, 20 July 2009 (UTC)

I do not have a source, but I seem to remember that anti-protons and positrons have been weighed and found to have positive weight. That is, they are attracted gravitationally to the Earth. But this only measures their passive gravitational charge. Measuring their active gravitational charge (whether matter is attracted to them) is probably effectively impossible. JRSpriggs (talk) 11:10, 21 July 2009 (UTC)

As far as I know, it should be a relatively simple (Though expensive) experiment - you get an antiparticle, put it in a vacuum and isolate it from any external electromagnetic fields, and 'drop' it (By removing the field supporting it, of course). Then whether it goes up or down (Detectable by the annihilation event, as it releases heat.) should present the answer for us. I'm surprised no one has apparently done this yet. Xander T. (talk) 08:07, 22 July 2009 (UTC)

The problem is that you need to cool individual atoms of antihydrogen to millikelvin temperatures in order to do this. Otherwise, they're moving quickly enough to swamp any gravitational effect on their motion. Last I heard, the best we could do was to cool antiprotons down to eV energy scales (thousands of K) to allow formation of antihydrogen.

The best way I can think of to test the response of antimatter to gravity would be to look at a cosmic ray source that produces both matter and antimatter and that appears to pass behind the Sun as Earth moves in its orbit. If the matter and antimatter parts of it cut off at the same time, they're affected the same way by the Sun's gravitational lensing effect. If antimatter is repelled by the Sun's gravity, lensing would cause the antimatter component to cut off earlier and the matter component to cut off later.

Moot point for now, though. What I'd really like to see is a citation attached to the statement claiming that it's been measured. If it's been measured reliably, there'll be papers about it. If there aren't any, then it probably hasn't been measured reliably. --Christopher Thomas (talk) 20:04, 22 July 2009 (UTC)

(Unindent) It's been a while since someone added a comment here. I'd like to refer anyone reading this to the exotic matter article, where one of the things talked about is "negative mass". It seems to me that that stuff would be a much better candidate for exhibiting gravitational repulsion with ordinary matter, than anti-matter. To better understand that involves two steps. First, remember that that standard equations for gravitation do not incorporate Quantum Mechanics, but almost certainly they some day will (that's the goal of Grand Unified Theories, after all). Anyway, when it happens that gravitational equations do incorporate QM, that's when they will incorporate Planck's Constant. The second step here is to closely examine the Definition of Planck's Constant. It has the "dimensional units" (see dimensional analysis) of "energy multiplied by time". Now look again at the Planck's Constant article, and notice that the first equation in it describes the association of the energy of a photon with its wavelength. That's a photon of ordinary energy, and so Planck's Constant includes ordinary energy in its dimensional units. Which means, if we wanted to equivalently describe a photon of negative energy, the energy "dimension" of Planck's Constant should be negative, not positive. The net effect of this is, when we get to the gravity equations that incorporates Planck's Constant, for negative mass, some key sign-reversals will occur. For example, with an ordinary Planck's Constant two negative masses are predicted to generate an attractive gravitational force between them, and will respond by accelerating away from each other. But with a negative Planck's Constant in the equations, two negative masses are predicted to generate a repulsive gravitational force between them, and will respond by accelerating toward each other. That "accelerating toward each other" is of course identical to the gravitational behavior of two ordinary masses. I leave open the question of what value of Planck's Constant to use when an ordinary mass gravitationally interacts with a negative mass, but the result of "accelerating away from each other" does not appear to be impossible. So, like I wrote near the start, negative mass could be a much better candidate than anti-matter, when one wants to explain such things as the accelerating expansion of the universe. Especially since, per the "E=mc² argument", anti-matter is very likely only ordinary, in terms of mass-energy, and General Relativity has a lot to say about the gravitational behavior of ordinary mass-energy. V (talk) 17:42, 30 December 2009 (UTC)

Maybe I am simple, and I am surely no physicist, but if antimatter produced an opposite to gravity, antimatter would gravitate together and would repel matter. paulbuchholz22 —Preceding unsigned comment added by Paulbuchholz22 (talk • contribs) 02:54, 27 May 2010 (UTC)

There is a discrepancy in terminology here. two groups use the term anti-matter in two slightly different ways. The article on antimatter describes it in analogy to the relation between regular matter to regular sub-atomic particles. That is, it is neutral stable matter which when brought into contact with regular matter will annhilate. I understand that some would say that antimatter was discovered in 1932 and pronounce that an anti-particle is antimatter. While I do not favor equating ANY sub-atomic particle with matter, it is certainly moot. What is NOT moot is that there are two different definitions of antimatter, one essentially sub-atomic (on up) and one restricted to atomic matter (on up) and clearly this difference should be explained in this article. It is especially important now that we are creating antihydrogen with significant life-times in the laboratories.71.31.152.112 (talk) 04:15, 4 October 2010 (UTC) I should add that it seems that no one commenting here has any idea how incompetent we are at creating a vacuum. Before people go off making wild claims about how easy it is to measure a antiatom's gravitational interaction by "just putting it into a vacuum" please check to see what the neutral atom density IS in the very best vacuums we are able to create. Some of you will be chagrined - at least SHOULD be.71.31.152.112 (talk) 04:23, 4 October 2010 (UTC)

Interesting analogy from semiconductors says anti-matter falls up.

General relativity predicts anti-matter falls down, and it probably does. However, I find the close analogy between electron/hole pairs and electron/positron pairs fascinating. Holes fall up, because the electrons above fall down. When electron/hole pairs meet, they annihilate each other, often giving off a photon, just like electron/positrons. Electron/holes are created in pairs, never just on their own, just like matter/anti-matter.

It's a weak analogy, but if gravity is caused by warping of space, can we compare that to how electrons and holes warp a crystal lattice? Electrons cause a crystal lattice to expand to make room for them, and this expansion causes other electrons to be weakly attracted to them. At very low temperatures this results in Cooper pairs, which likely explains super-conductivity. Holes in a silicon lattice similarly attract each other, because they cause the local lattice to contract. There are papers on the web that mention the possibility of Cooper pairs made of holes. Electrons are repelled by the lattice contraction caused by holes, just as holes are repelled by the lattice expansion caused by electrons. Could matter/anti-matter be similar? WaywardGeek (talk) 04:20, 8 March 2012 (UTC)