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34-915: On 27 September 2023, ALPHA collaborators published findings suggesting that antimatter interacts with gravity in a way similar to regular matter, supporting a prediction of the weak equivalence principle . Working with antimatter presents several experimental challenges. Magnetic traps—wherein neutral atoms are trapped using their magnetic moments —are required to keep antimatter from annihilating with matter, but are notoriously weak. Only atoms with kinetic energies equivalent to less than one kelvin may be trapped. The ATHENA and ATRAP (AD-2) projects produced antihydrogen by merging cold plasmas of positrons and antiprotons . While this method has been quite successful, it creates antimatter atoms with kinetic energies too large to be trapped. Moreover, to do laser spectroscopy on these antimatter atoms, they need to be in their ground state , something that does not appear to be

68-473: A positron bound together as a long-lived metastable state. Positronium has been studied since the 1950s to understand bound states in quantum field theory . A recent development called non-relativistic quantum electrodynamics (NRQED) used this system as a proving ground. Pionium , a bound state of two oppositely-charged pions , is interesting for exploring the strong interaction . This should also be true of protonium . The true analogs of positronium in

102-431: A "minimum- B " magnetic trap. Once trapped, antihydrogen can be subjected to study, and the measurements compared to those of hydrogen. In order to detect trapped antihydrogen, ALPHA also includes a 'silicon vertex detector': a cylindrical detector composed of three layers of silicon strips. Each strip acts as a detector for the charged particles passing through. By recording how the strips are excited, ALPHA can reconstruct

136-404: A gravitational field, then it would take no energy to change the height of a particle–antiparticle pair. However, when moving through a gravitational potential, the frequency and energy of light is shifted. Morrison argued that energy would be created by producing matter and antimatter at one height and then annihilating it higher up, since the photons used in production would have less energy than

170-559: A matter–antimatter gravitational repulsion have been published by Marcoen Cabbolet. He introduces the Elementary Process Theory, which uses a new language for physics, i.e. a new mathematical formalism and new physical concepts, and which is incompatible with both quantum mechanics and general relativity. The core idea is that nonzero rest mass particles such as electrons, protons, neutrons and their antimatter counterparts exhibit stepwise motion as they alternate between

204-409: A particlelike state of rest and a wavelike state of motion. Gravitation then takes place in a wavelike state, and the theory allows, for example, that the wavelike states of protons and antiprotons interact differently with the earth's gravitational field. Further authors have used a matter–antimatter gravitational repulsion to explain cosmological observations, but these publications do not address

238-488: A repulsion of matter and antimatter. It has to be taken that the observed trajectories of antiparticles are projections on our spacetime of the true trajectories in the inverted spacetime. However, it has been argued on methodological and ontological grounds that the area of application of Villata's theory cannot be extended to include the microcosmos. These objections were subsequently dismissed by Villata. The first non-classical, non-quantum physical principles underlying

272-408: Is a bound state of a particle and its antiparticle . These states are usually named by adding the suffix -onium to the name of one of the constituent particles (replacing an -on suffix when present), with one exception for " muonium "; a muon–antimuon bound pair is called " true muonium " to avoid confusion with old nomenclature. Positronium is an onium which consists of an electron and

306-469: Is false, and only proves that an anti-ball falls down on an anti-earth – which is not disputed. Since repulsive gravity has not been refuted experimentally, it is possible to speculate about physical principles that would bring about such a repulsion. Thus far, three radically different theories have been published. The first theory of repulsive gravity was a quantum theory published by Mark Kowitt. In this modified Dirac theory, Kowitt postulated that

340-425: Is the deflection of a continuous particle trajectory due to the curvature of spacetime, but antiparticles 'live' in an inverted spacetime. The equation of motion for antiparticles is then obtained from the equation of motion of ordinary particles by applying the C, P, and T operators (Villata) or by applying isodual maps (Santilli), which amounts to the same thing: the equation of motion for antiparticles then predicts

374-450: Is wrong with the idea of gravitational repulsion: if a ball is thrown high up in the air so that it falls back, then its motion is symmetric under time-reversal; and therefore, the ball falls also down in opposite time-direction. Since a matter particle in opposite time-direction is an antiparticle, this proves according to 't Hooft that antimatter falls down on earth just like "normal" matter. However, Cabbolet replied that 't Hooft's argument

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408-451: The gravitational mass of antihydrogen atoms was between −65 and 110 times their inertial mass , leaving considerable room for refinement using larger numbers of colder antihydrogen atoms. ALPHA has succeeded in the laser cooling antihydrogen atoms, a technique known as that was first demonstrated on normal matter in 1978. On 27 September 2023, the ALPHA team published a paper supporting

442-428: The ALPHA magnet that creates the minimum B-field was designed to allow rapid and repeated de-energizing. The decay of current during de-energization has a characteristic duration of 9 ms, orders of magnitude faster than similar systems. In theory, the fast turn-off speed and the ability to suppress false cosmic rays signals allows ALPHA to detect the release of single antihydrogen atoms during de-energization. One of

476-507: The ALPHA trap set direct, i.e. freefall, coarse limits on antimatter gravity. These limits were coarse, with a relative precision of ±100%, thus, far from a clear statement even for the sign of gravity acting on antimatter. Future experiments at CERN with beams of antihydrogen, such as AEgIS, or with trapped antihydrogen, such as ALPHA and GBAR, have to improve the sensitivity to make a clear, scientific statement about gravity on antimatter. Onium Onia An onium (plural: onia )

510-491: The argument in terms of relative potentials, Gabriel Chardin found that it resulted in an amount of kaon regeneration which agrees with observation. He argued that antigravity is a potential explanation for CP violation based on his models on K mesons. His results date to 1992. Since then however, studies on CP violation mechanisms in the B mesons systems have fundamentally invalidated these explanations. According to Gerard 't Hooft , every physicist recognizes immediately what

544-439: The case for the majority of antimatter atoms created with this technique. Antiprotons are received from the antiproton decelerator and are 'mixed' with positrons from a specially-designed positron accumulator in a versatile Penning trap . The central region where the mixing and thus antihydrogen formation takes place is surrounded by a superconducting octupole magnet and two axially separated short solenoid "mirror-coils" to form

578-438: The creation of antimatter (specifically antihydrogen ) result in particles and atoms of high kinetic energy, which are unsuitable for gravity -related study. Antimatter is gravitationally attracted to matter. The magnitude of the gravitational force is also the same. This is predicted by theoretical arguments like the gravitational equivalence of energy and matter , and has been experimentally verified for antihydrogen. However

612-649: The difference between the properties of a matter particle and those of its antimatter counterpart is completely described by C-inversion. Since this C-inversion does not affect gravitational mass, the CPT theorem predicts that the gravitational mass of antimatter is the same as that of ordinary matter. A repulsive gravity is then excluded, since that would imply a difference in sign between the observable gravitational mass of matter and antimatter. In 1958, Philip Morrison argued that antigravity would violate conservation of energy . If matter and antimatter responded oppositely to

646-433: The equivalence of the gravitational acceleration of matter to matter vs antimatter to matter has an error margin of about 20% ( table 3). Difficulties in creating quantum gravity models have led to the idea that antimatter may react with a slightly different magnitude. When antimatter was first discovered in 1932, physicists wondered how it would react to gravity. Initial analysis focused on whether antimatter should react

680-605: The experiment any time soon. The last known supernova to occur at such a close range prior to Supernova 1987A was around 1867. Since 2010 the production of cold antihydrogen has become possible at the Antiproton Decelerator at CERN . Antihydrogen, which is electrically neutral, should make it possible to directly measure the gravitational attraction of antimatter particles to the matter of Earth. Antihydrogen atoms have been trapped at CERN , first ALPHA and then ATRAP ; in 2012 ALPHA used such atoms to set

714-450: The first free-fall loose bounds on the gravitational interaction of antimatter with matter, measured to within ±7500% of ordinary gravity, not enough for a clear scientific statement about the sign of gravity acting on antimatter. Future experiments need to be performed with higher precision, either with beams of antihydrogen ( AEgIS ) or with trapped antihydrogen ( ALPHA or GBAR ). In 2013, experiments on antihydrogen atoms released from

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748-477: The framework of the Standard Model , have in a large number of astronomical tests ( gravitational redshift and gravitational lensing , for example) been observed to interact with the gravitational field of ordinary matter exactly as predicted by the general theory of relativity . This is a feature that any theory that predicts that matter and antimatter repel must explain. The CPT theorem implies that

782-410: The gravitational interaction would have to be very small. However, neutrino detectors cannot distinguish perfectly between neutrinos and antineutrinos. Some physicists conservatively estimate that there is less than a 10% chance that no regular neutrinos were observed at all. Others estimate even lower probabilities, some as low as 1%. Unfortunately, this accuracy is unlikely to be improved by duplicating

816-407: The incompatibility of the Standard Model and gravitational repulsion. In 1961, Myron L. Good argued that antigravity would result in the observation of an unacceptably high amount of CP violation in the anomalous regeneration of kaons . At the time, CP violation had not yet been observed. However, Good's argument is criticized for being expressed in terms of absolute potentials. By rephrasing

850-436: The main challenges of working with antihydrogen is cooling it enough to be able to trap it. Antiprotons and positrons are not easily cooled to cryogenic temperatures , so in order to do this ALPHA has implemented a well known technique from atomic physics known as evaporative cooling . State-of-the art minimum-B traps such as the one ALPHA uses have depths of order 1 Kelvin. A preliminary experiment conducted in 2013 found that

884-523: The photons yielded from annihilation. Later in 1958, L. Schiff used quantum field theory to argue that antigravity would be inconsistent with the results of the Eötvös experiment . However, the renormalization technique used in Schiff's analysis is heavily criticized, and his work is seen as inconclusive. In 2014 the argument was redone by Marcoen Cabbolet, who concluded however that it merely demonstrates

918-617: The physical principles of gravitational repulsion. One source of experimental evidence in favor of normal gravity was the observation of neutrinos from Supernova 1987A . In 1987, three neutrino detectors around the world simultaneously observed a cascade of neutrinos emanating from a supernova in the Large Magellanic Cloud . Although the supernova happened about 164,000 light years away, both neutrinos and antineutrinos seem to have been detected virtually simultaneously. If both were actually observed, then any difference in

952-416: The positron is not a hole in the sea of electrons-with-negative-energy as in usual Dirac hole theory , but instead is a hole in the sea of electrons-with-negative-energy-and-positive-gravitational-mass: this yields a modified C-inversion, by which the positron has positive energy but negative gravitational mass. Repulsive gravity is then described by adding extra terms ( m g Φ g and m g A g ) to

986-645: The prediction that the gravitational interaction of antimatter is similar to that of regular matter. For the weak equivalence principle of general relativity to be correct, it is required that the two substances display identical gravitational properties. The findings rule out a 'repulsive [antigravity]', as previously theorized by some in the field. ALPHA collaborators include the following institutions: Record for ALPHA experiment on INSPIRE-HEP Gravitational interaction of antimatter Onia The gravitational interaction of antimatter with matter or antimatter has been observed by physicists. As

1020-450: The results of the Eötvös test of the weak equivalence principle . Many of these early theoretical objections were later overturned. The equivalence principle predicts that mass and energy react the same way with gravity, therefore matter and antimatter would be accelerated identically by a gravitational field. From this point of view, matter-antimatter gravitational repulsion is unlikely. Photons , which are their own antiparticles in

1054-477: The same as matter or react oppositely. Several theoretical arguments arose which convinced physicists that antimatter would react the same as normal matter. They inferred that gravitational repulsion between matter and antimatter was implausible as it would violate CPT invariance , conservation of energy , result in vacuum instability , and result in CP violation . It was also theorized that it would be inconsistent with

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1088-444: The traces of particles traveling through the detector. When an antiproton annihilates, the process typically results in the emission of 3 or 4 charged pions . By reconstructing their traces through the detector, the location of the annihilation can be determined. These traces are quite distinct from those of cosmic rays also detected, but due to their high energy they pass straight through the detector. To confirm successful trapping,

1122-479: The wave equation. The idea is that the wave function of a positron moving in the gravitational field of a matter particle evolves such that in time it becomes more probable to find the positron further away from the matter particle. Classical theories of repulsive gravity have been published by Ruggero Santilli and Massimo Villata . Both theories are extensions of general relativity , and are experimentally indistinguishable. The general idea remains that gravity

1156-567: Was the consensus among physicists previously, it was experimentally confirmed that gravity attracts both matter and antimatter at the same rate within experimental error. Antimatter's rarity and tendency to annihilate when brought into contact with matter makes its study a technically demanding task. Furthermore, gravity is much weaker than the other fundamental forces , for reasons still of interest to physicists, complicating efforts to study gravity in systems small enough to be feasibly created in lab, including antimatter systems. Most methods for

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