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Thread: Antimatter Gravity Could Explain Universe's Expansion

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    WeVie's Avatar
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    Antimatter Gravity Could Explain Universe's Expansion


    (PhysOrg.com) -- In 1998, scientists discovered that the Universe is expanding at an accelerating rate. Currently, the most widely accepted explanation for this observation is the presence of an unidentified dark energy, although several other possibilities have been proposed. One of these alternatives is that some kind of repulsive gravity – or antigravity – is pushing the Universe apart. As a new study shows, general relativity predicts that the gravitational interaction between matter and antimatter is mutually repulsive, and could potentially explain the observed expansion of the Universe without the need for dark energy.

    Ever since antimatter was discovered in 1932, scientists have been investigating whether its gravitational behavior is attractive – like normal matter – or repulsive. Although antimatter particles have the opposite electric charge as their associated matter particles, the masses of antimatter and matter particles are exactly equal. Most importantly, the masses are always positive. For this reason, most physicists think that the gravitational behavior of antimatter should always be attractive, as it is for matter. However, the question of whether the gravitational interaction between matter and antimatter is attractive or repulsive so far has no clear answer.

    In the new study, Massimo Villata of the Osservatorio Astronomico di Torino (Observatory of Turin) in Pino Torinese, Italy, has shown that an answer can be found in the theory of general relativity. As Villata explains, the current formulation of general relativity predicts that matter and antimatter are both self-attractive, yet matter and antimatter mutually repel each other. Unlike previous antigravity proposals – such as the idea that antimatter is gravitationally self-repulsive – Villata’s proposal does not require changes to well-established theories. The study is published in a recent issue of EPL (Europhysics Letters).

    “The significance of this study is actually twofold,” Villata told PhysOrg.com. “On one side, that of physics in general, it is to have shown that one of the most heretical concepts debated in the last several decades, i.e., that of antigravity, can be found as a prediction of the coupling of two of the best-established theories of the last century, providing the extension of general relativity to antimatter, considered as space-time-reversed matter, as requested by CPT symmetry. On the other side, the cosmological implications of this finding have shown antigravity as an alternative to (or explanation of) the wooly concept of dark energy for the accelerated expansion of the Universe.”

    Repulsive gravity

    At first, the idea of repulsive gravity between matter and antimatter seems to go against intuition, since we usually consider mass to be the only component determining an object’s gravitational behavior. But as Villata explains, there is more than just mass involved in gravity. In this case, time and parity are involved.

    The idea is based on the concept that all physical laws have CPT (charge, parity, and time) symmetry. CPT symmetry means that, in order to transform a physical system of matter into an equivalent antimatter system (or vice versa) described by the same physical laws, not only must particles be replaced with corresponding antiparticles (C operation), but an additional PT transformation is also needed.

    From this perspective, antimatter can be viewed as normal matter that has undergone a complete CPT transformation, in which its charge, parity and time are all reversed. Even though the charge component does not affect gravity, parity and time affect gravity by reversing its sign. So although antimatter has positive mass, it can be thought of as having negative gravitational mass, since the gravitational charge in the equation of motion of general relativity is not simply the mass, but includes a factor that is PT-sensitive and yields the change of sign.

    As Villata explains, CPT symmetry means that antimatter basically exists in an inverted spacetime (the P operation inverts space, and the T operation inverts time). He gives the following analogy: if an anti-apple falls onto the head of an anti-Newton sitting on an anti-Earth, it would fall in exactly the same way as if all of these objects were made of normal matter. But if an anti-apple falls on the (normal) Earth, or a (normal) apple falls on an anti-Earth, then the result is different. In both cases, a minus sign arises in the equation of motion, which reverses the gravitational interaction between the anti-apple and Earth, or apple and anti-Earth, making it repulsive.

    Observations and experiments

    The theoretical prediction of antigravity between matter and antimatter could have significant consequences, if it’s true. Whenever matter and antimatter meet, they annihilate and produce photons. But if matter and antimatter repel each other, then they would tend to isolate themselves apart from each other and not annihilate. The force of this matter-antimatter repulsion could explain why the Universe is expanding at an accelerating rate, eliminating the need for dark energy and possibly dark matter.

    Villata suspects that antimatter could exist in the Universe in large-scale voids that have been observed in the distribution of galaxy clusters and superclusters. Previous studies have found that these voids can originate from small negative fluctuations in the primordial density field, which repel surrounding matter – as if they have a negative gravitational mass. With diameters of tens of megaparsecs (about a hundred million light years), these voids are the largest structures in the Universe. The problem is that, so far, researchers have not observed antimatter in these locations. Villata plans to investigate this question in a future study on the invisibility of antimatter in voids.

    “The relevant ideas are there, but I'm looking for the best way to formalize them,” he said. “However, you can find anticipations on this and many other features of matter traveling backwards in time in the novel by Max Wells (which is my literary pseudonym, in honor of J. C. Maxwell and H. G. Wells), The Dark Arrow of Time, which is currently published only in Italian (La freccia oscura del tempo), but I hope to find an English publisher soon.”

    As for testing the possibility of antigravity between matter and antimatter, the upcoming AEGIS experiment at CERN could provide some answers. The experiment will compare how the Earth’s gravity affects hydrogen and antihydrogen atoms, and could give scientists a better understanding of antimatter’s gravitational properties.

    “Antigravity has always been controversial, and likely it will still be so until we can get an experimental (or observational) response,” Villata said. “However, I hope that my work, in the meantime, can at least dissipate some prejudices against antigravity.”
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    Rafiki's Avatar
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    But wouldn't this imply that there is a great deal of antimatter remaining in our universe?

    If I am not mistaken, it is generally understood that the antimatter content that was created by the big bang was shortly thereafter destroyed by the matter. But since the matter created by the big bang was one billionth of a percent more abundant than the antimatter, we have our universe today.

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    NY8123's Avatar
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    Quote Originally Posted by Rafiki View Post
    But wouldn't this imply that there is a great deal of antimatter remaining in our universe?

    If I am not mistaken, it is generally understood that the antimatter content that was created by the big bang was shortly thereafter destroyed by the matter. But since the matter created by the big bang was one billionth of a percent more abundant than the antimatter, we have our universe today.
    Not really there is a 50/50 split about Anti-matter and the amount of it in the known universe. Some believe that it was destroyed after the big bang and might only remain in the confines of a black hole or neutron star but there are many others that are slowly presenting evidence that Anti-Matter maybe as abundant or actually exceeds the amount of matter in the universe.

    Almost like a north/south magnetic attraction that is leading to the expansion of the universe, something has to be accelerating the matter if you think of the big bang like a round of ammunition the expansion of the universe should be slowing down and not speeding up.

    Anti-matter would explain why it is accelerating and not decceleration.
    Last edited by NY8123; 04-25-2011 at 10:56 AM.
    "I am free of all prejudice. I hate everyone equally" ~ W.C. Fields

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    Makes decent theoretical sense. Dark stuff is not only repulsing outward, but repulsing inward on the flip side making that matter move at a decelerated rate than the outward. Creating the added increasing distance between the inward movement and outward expansion and thus weakening the pull of of gravity between them. But then again with the ever growing distance the force of the initial anti-matter repulsion is going to weaken too...unless the amount of anti-matter is increasing?
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    Rafiki's Avatar
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    I still doubt it's antimatter. I haven't seen any evidence that there is a significant amount in the universe.

    Here is the accepted and supported theory:

    The current hypothesis that explains the lack of antimatter is that matter and antimatter are not symmetric. This created an imbalance during the big bang and resulted in the creation of about .0001% more matter than antimatter. After one second almost all of the matter and antimatter had annihilated each other, which would have left that .0001% of matter to from the current universe.
    http://ffden-2.phys.uaf.edu/212_fall...an/bigbang.htm

    So I'll believe this until there is evidence to the contrary.

    One interesting thought I've had is this, we understand that space can travel faster than the speed of light. If this expansion of space is "dragging" us along, perhaps we will continue to accelerate until we reach the speed of light and are converted to energy, and then the universe will end as it began- suddenly.
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    Dogbone34's Avatar
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    i'm anti antimatter


    i think
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    Quote Originally Posted by Rafiki View Post
    I still doubt it's antimatter. I haven't seen any evidence that there is a significant amount in the universe.

    Here is the accepted and supported theory:



    http://ffden-2.phys.uaf.edu/212_fall...an/bigbang.htm

    So I'll believe this until there is evidence to the contrary.

    One interesting thought I've had is this, we understand that space can travel faster than the speed of light. If this expansion of space is "dragging" us along, perhaps we will continue to accelerate until we reach the speed of light and are converted to energy, and then the universe will end as it began- suddenly.
    I'm not sure that Relativity allows for that scenario. Theortically when you reach the speed of light, mass becomes infinite as well. If every piece of matter in the universe is accelarating to the speed of light, then that is going to take a very, very, VERY long time. At point which every star in the universe would have stopped and everything would have spread out.

    I've never been happy with the whole "dark matter/energy" theory. It seems more like a stab in the dark than an actual theory.
    Insert pithy saying here.

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    Rafiki's Avatar
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    Quote Originally Posted by LouPhinFan View Post
    I'm not sure that Relativity allows for that scenario. Theortically when you reach the speed of light, mass becomes infinite as well. If every piece of matter in the universe is accelarating to the speed of light, then that is going to take a very, very, VERY long time. At point which every star in the universe would have stopped and everything would have spread out.

    I've never been happy with the whole "dark matter/energy" theory. It seems more like a stab in the dark than an actual theory.
    Yeah, maybe you're right. But things can go in excess of the speed of light with the expansion of space. It's why we can look into the past billions of years. The universe expanded at faster than the speed of light at one point, and may be still expanding at that speed:

    Some of the misunderstandings surrounding this topic might come from confusion over what is meant by the universe "expanding faster than the speed of light." However, for the simplest interpretation of your question, the answer is that the universe does expand faster than the speed of light, and, perhaps more surprisingly, some of the galaxies we can see right now are currently moving away from us faster than the speed of light! As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be heard from again.
    http://curious.astro.cornell.edu/que...php?number=575

    But you're probably correct that the objects themselves are unable to move at the speed of light within their own area of space.
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    Most of this stuff is just way over my head. I wish I were smart enough to be a physicist though. It would be awesome to be in that field and having my "work" be learning new things about the universe.




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    From what I have read and comprehend, I can simplify it.
    The universe is simply a large sponge curtain comprised of matter and anti matter.
    The curtains hang parallel to each other and occasionally interact with each other creating holes in time/space.
    Essentially, humans are just a tiny spinning microbes. Republicans spin to the right, liberals spin to the left.
    Any questions?
    lol
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