Anti-Matter, Anti-Gravity, Anti-Time....

[Mike42]

Question for the Learned and Wise...

So we don't have much anti-matter in the Universe. And we Don't know why, and we don't know if anti-matter has anti-gravity or Not....

But...

If Anti-Matter has Anti-Gravity... would it not also have Anti-Time???

and would that not explain why there is so little of it?

If Anti-Matter and Matter were made at the same instant in the Big Bang in equal amounts....

and If Anti-Matter had Anti-Time... It would proceed, from our perspective, backwards from the Big Bang and we would not be able to perceive it due to its "Speed Away" from us in time.

Any Anti-Matter observed will have been made in our future time... and of course those living in the Anti-Matter-Anti-Gravity-Anti-Time Universe would be wondering where all that strange matter stuff went to after the gnaB-giB....

[Beyond]

Pehaps with all that anti-time, the 'other' side of the Big Bang can't unfold into the gnaB giB, and it's just sitting there doing nothing, which is anti-all the somethings that are going on, on this side of it. There-fore, there wouldn't be anyone to wonder about 'strange' matter stuff, because there wouldn't be anything 'there', at all. There would be no time for anything to happen.http://www.youtube.com/watch?v=oqeSUAlI5uI

[Chris Peterson]

So we don't have much anti-matter in the Universe. And we Don't know why, and we don't know if anti-matter has anti-gravity or Not....

But...

If Anti-Matter has Anti-Gravity... would it not also have Anti-Time???

We do know that antimatter does not have "anti-gravity". In a sense, antimatter does have "anti-time", since an antimatter particle is just a normal matter particle that is moving backwards in time.

and would that not explain why there is so little of it?

There is pretty solid theory which explains why the balance between matter and antimatter is so lopsided. The idea is that this is the only stable result given an infinitesimal difference in the amount of each (which can be explained by quantum fluctuations) in the very early Universe, when matter densities were much higher.

[neufer]

So we don't have much anti-matter in the Universe. And we Don't know why, and we don't know if anti-matter has anti-gravity or Not....

• We do know that antimatter does not have "anti-gravity".

[c]Not really:[/c]

<<The gravitational interaction of antimatter with matter or antimatter has not been conclusively observed by physicists. While the overwhelming consensus among physicists is that antimatter will attract both matter and antimatter at the same rate that matter attracts matter, there is a strong desire to confirm this experimentally. The CPT theorem asserts that antimatter should attract antimatter in the same way that matter attracts matter. However, there are several theories about how antimatter gravitationally interacts with normal matter.

When antimatter was first discovered in 1932, physicists wondered about how it would react to gravity. Initial analysis focused on whether antimatter should react the same as matter or react oppositely. Several theoretical arguments arose which convinced physicists that antimatter would react exactly the same as normal matter. They inferred that a 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 the results of the Eötvös test of the weak equivalence principle. Many of these early theoretical objections were later overturned.

Antimatter's rarity and tendency to annihilate when brought into contact with matter makes its study a technically demanding task. Many scientists consider the best experimental evidence in favor of normal gravity to come from the observations of neutrinos from Supernova 1987A. In this landmark event, 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 may have been detected virtually simultaneously. If both were actually observed, then any difference in 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 the experiment any time soon. The last known supernova to occur at such a close range prior to Supernova 1987A was around 1867.

Physicist William Fairbank attempted a laboratory experiment to directly measure the gravitational acceleration of both electrons and positrons. However, their charge-to-mass ratio is so large that electromagnetic effects overwhelmed the experiment. Furthermore, antiparticles must be kept separate from their normal counterparts or they will quickly annihilate. Worse still, production methods typically result in high-energy antimatter particles which are unsuitable for observation of gravitational effects in a laboratory environment. In recent years, the production of cold antihydrogen has become possible at the ATHENA and ATRAP experiments at CERN. Antihydrogen, which is electrically neutral, should make it possible to directly measure the gravitational attraction of antimatter particles to the matter Earth. CERN is aiming to do this.
....................................................................................................................
In 1958, Philip Morrison argued that antigravity would violate conservation of energy. If matter and antimatter responded oppositely to 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 the photons yielded from annihilation. However, it was later found that antigravity would still not violate the second law of thermodynamics.

If one can invent a theory in which matter and antimatter repel one another, what does it predict for things which are neither matter nor antimatter? Photons are their own antiparticles, and in all respects behave exactly symmetrically with respect to matter and antimatter particles. In a large number of laboratory and astronomical tests, (gravitational redshift and gravitational lensing, for example) photons are observed to be attracted to matter, exactly in accordance with the theory of General Relativity. It is possible to find atoms and nuclei whose elementary particle contents are the same, but whose masses are different. For example, Helium-4 weighs less than 2 atoms of deuterium due to binding-energy differences. The gravitational force constant is observed to be the same, up to the limits of experimental precision, for all such different materials, suggesting that "binding energy"—which, like the photon, has no distinction between matter and antimatter—experiences the same gravitational forces as matter. This is again in accordance with the theory of General Relativity, and difficult to reconcile with any theory predicting that matter and antimatter repel.

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 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 the argument in terms of relative potentials, Gabriel Chardin found that it resulted in an amount of Kaon regeneration which agrees with observation. He argues that antigravity is in fact a potential explanation for CP violation. Antimatter antigravity [might also] explains two cosmological paradoxes. The first is the apparent local lack of antimatter: by theory antimatter and matter would repel each other gravitationally, forming separate matter and antimatter galaxies. These galaxies would also tend to repel one another, thereby preventing possible collisions and annihilations. These two facts combine to imply that the universe gradually arranges itself into a gravitational dipole at the largest scale.

This same galactic repulsion is also endorsed as a potential explanation to the observation of a flatly accelerating universe. If gravity was always attractive, the expansion of the universe might be expected to decelerate and eventually contract into a big crunch. Using redshift observations, astronomers and physicists estimate that instead, the size of the universe is expanding and the rate of expansion is accelerating at an approximately constant rate. Several theories have been proposed to explain this observation within the context of an always-attractive gravity. On the other hand, supporters of antigravity argue that if mutually repulsive, equal amounts of matter and antimatter would precisely offset any attraction.

CERN physicist Dragan Slavkov Hajdukovic has proposed an explanation for the problem of galaxy rotational speeds (currently explained by dark matter models) based on antimatter antigravity. Assuming that a particle and its antiparticle have the gravitational charge of the opposite sign, the physical vacuum may be considered as a fluid of virtual gravitational dipoles. Following this hypothesis, he presents indications that dark matter may not exist at all and that the phenomena for which it was invoked might be explained by the gravitational polarization of the quantum vacuum by the known baryonic matter.

Several authors have pursued the idea of antigravity, either assuming that antimatter has negative gravitational mass, and thus is self-attractive, or that it is even self-repulsive.

In a recent paper, Villata argued that there is no need to change the sign of the gravitational mass of antimatter (which would represent a violation of the weak equivalence principle) to get repulsion between matter and antimatter; but he showed that antigravity appears as a prediction of general relativity, once it is assumed that this theory is CPT invariant and that, consequently, matter is transformed into antimatter by these three joint operations (charge conjugation, parity, and time reversal). In general relativity, the equation of motion for a matter test particle in a matter-generated gravitational field is composed of four elements. If we CPT-transform all the four elements, we get an identical equation describing the motion of an antimatter test particle in an antimatter-generated gravity field, since all the four changes of sign cancel one another. Thus, this CPT symmetry ensures the same self-attractive gravitational behavior for both matter and antimatter. But, if we transform only one of the two components, either the field or the particle (represented by the remaining three elements), we get a change of sign that converts the original gravitational attraction into repulsion, so that matter and antimatter repel each other. The equation for a massless particle (e.g. a photon) is formally equal to that for material particles. Therefore, a (retarded) photon will be repelled by an antimatter gravity field, as well as a CPT-transformed photon, i.e. an advanced photon, will be repelled by matter. (As a consequence, the energy of a retarded-advanced photon pair in a gravitational field would be conserved, thus invalidating the Morrison argument against antigravity.) This may provide a test for the theory of antigravity: the presence of antimatter in cosmic voids suggested by Villata might be revealed by its gravitational effect on the radiation coming from background sources, in a sort of antigravitational lensing.>>

[Chris Peterson]

We do know that antimatter does not have "anti-gravity".

Not really

Of course, you are correct that we don't have experimental confirmation of that. Nevertheless, the theoretical support for the idea that antimatter and normal matter have the same sort of mass is very strong. To suggest otherwise is highly speculative, at best. So it is, by far, most reasonable to assume that antimatter does not have anything that might reasonably be called "anti-gravity".

[neufer]

We do know that antimatter does not have "anti-gravity".

Not really

Of course, you are correct that we don't have experimental confirmation of that. Nevertheless, the theoretical support for the idea that antimatter and normal matter have the same sort of mass is very strong. To suggest otherwise is highly speculative, at best. So it is, by far, most reasonable to assume that antimatter does not have anything that might reasonably be called "anti-gravity".

Science is ALL about speculation and experimental confirmation.

We claim "to know" things only after overwhelming experimental confirmation.

While it would be foolish to ignore the fact that CPT does insist that antimatter should gravitationally attract other antimatter, there are several (not unreasonable) theories about how antimatter interacts with normal matter gravitationally.

[Chris Peterson]

Science is ALL about speculation and experimental confirmation.

No. Speculation and experimentation are very important aspects of scientific investigation. But not all of it.

Saying an idea is "highly speculative" is not arguing against the role of speculation in science.

[Markus Schwarz]

We do know that antimatter does not have "anti-gravity".

Not really

Here are my reasons why matter and anti-matter do have the same mass (I specialize to the electron and its anti-particle, the positron).

In a magnetic field, electrons and positrons move on circles with the same radius, but with an opposite sense of rotation (that's how anti-matter was discovered in the first place). This means that the ratio between their charge and mass is equal in magnitude but opposite in sign. To prove that the different sign comes from a different sign of the electric charge, one can look at positronium. Positronium is the bound system of an electron and positron. It is the same as a hydrogen system, except for the mass difference (the proton is heavier than the electron/positron). This then implies that the positron must have the same electric charge as the proton. Furthermore, positronium decays into an electrically neutral photon, which is only possible if the original particles have opposite electric charge.

Combined, these findings lead to the conclusion that electrons and positrons have the same positive mass. Unless you start messing with things like charge conservation, I find it very hard to accompany negative mass with the above findings. I agree with Chris: it would be highly speculative.

By the way: from what we know of gravity, it implies that masses of opposite sign would still attract.

[orin stepanek]

Does antimatter really mater! After all; what are the chances that any of us will come in contact with it?

[Markus Schwarz]

Does antimatter really mater! After all; what are the chances that any of us will come in contact with it?

Chances are far from zero:

• In medicine, there exists Positron-Electron-Tomography. The patient is injected with a radioactive substance that emits positrons. These then annihilate with the electrons in the body. The resulting photons are then defected.
• Earth is constantly bombarded by highly energetic particles. During these collisions anti-matter is also produced. The resulting particles and radiation contribute to the natural radioactivity on Earth.

[neufer]

Does antimatter really mater [sic?]!
After all; what are the chances that any of us will come in contact with it?

• Do you take public transportation?

<<An antimacassar is a small cloth placed over the backs or arms of chairs, or the head or cushions of a sofa, to prevent soiling of the permanent fabric. The name is attributable to macassar oil, an unguent for the hair commonly used in the early 19th century – the poet Byron called it, "thine incomparable oil, Macassar." The fashion for oiled hair became so widespread in the Victorian and the Edwardian period that housewives began to cover the arms and backs of their chairs with washable cloths to preserve the fabric coverings from being soiled. Around 1850, these started to be known as antimacassars. They were also installed in theatres, from 1865.

• His accents mild took up the tale:
  He said "I go my ways,
  And when I find a mountain-rill,
  I set it in a blaze;
  And thence they make a stuff they call
  Rolands' Macassar Oil --
  Yet twopence-halfpenny is all
  They give me for my toil."

They came to have elaborate patterns, often in matching sets for the various items of parlour furniture; they were either made at home using a variety of techniques such as crochet or tatting, or purchased. The original antimacassars were usually made of stiff white crochet-work, but in the third quarter of the 19th century they became simpler and softer, usually fabric embroidered with a simple pattern in wool or silk. Annie Chapman, the second canonical victim of Jack the Ripper, was said to have made antimacassars for a living shortly before she was murdered.

By the beginning of the 20th century, antimacassars had become so associated in people's minds with the Victorian period that the word briefly became a figurative term for it. (See also, Doily). Antimacassars are also used on the seat headrests of commercial passenger transport vehicles, such as trains, buses and especially aircraft to extend the life of fabrics. Also refers to the cloth flap on a sailor's blouse, used to keep Macassar oil off the uniform.>>