Antimatter gravity could explain Universe's expansion

[Bill USA]

http://www.physorg.com/news/2011-04-antimatter-gravity-universe-expansion.html


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).
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hm-m-m-m-m.

[laconicsax]

1. Dupe.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=228x78010

[Possumpoint]

2. Then

Harnessing anti matter could well provide a propulsion method we could utilize.

[Lionel Mandrake]

3. This summary is inaccurate.

Villata does NOT claim that "the current formulation of general relativity predicts that ... matter and antimatter mutually repel each other." He claims only that the gravitational force between matter and antimatter could be either attractive or repulsive according to general relativity. He gives symmetry arguments in favor of a repulsive force. As a physicist I do not find his arguments convincing.

Consider that a particle and its antiparticle can annihilate each other, producing gamma rays (photons). We know that photons are attracted by normal matter. That's what Einstein predicted and Eddington confirmed by observing stars near the sun during a total eclipse. Would photons be attracted or repelled by antimatter? Either answer leads to a theoretical conundrum.