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Recently I was reading about CERN's upgrade to work on gravitational theories. But if most of the work has been done by General Theory of Relativity than with other theories are there that need to be tested.

But gravity term is used in terms of heavenly bodies than how will they simulate it using atomic level particles as both follow entirely different postulates ?

m0nhawk
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Pankaj Sejwal
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    Can you please give a link on what your read? If CERN is involved it might be testing models with quantized gravity that would predict effects in particle scattering, or use of its accelerator produced beams as gravitometers. – anna v Dec 19 '12 at 06:34
  • http://articles.timesofindia.indiatimes.com/2012-09-12/science/33788941_1_particle-collider-large-hadron-collider-european-organization is the link – Pankaj Sejwal Dec 19 '12 at 09:55
  • the fact that a 80km circumference accelerator is proposed does not imply that it actually will be built. People are free to study the benefits or need for new experiments and accelerators. However, such an accelerator would be very expensive, not to mention the fact that a whole new tunnel would have to be built. By simple scaling of the circumference of LHC, I would expect that the accelerator alone would be about three times more expensive than the LHC. – Andre Holzner Dec 20 '12 at 08:18

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There exists an experiment at CERN, an international collaboration called ALPHA which at the moment aims to check for differences between particles and antiparticles.

In a news bulletin the intent is stated to extend the experiment :

Though ALPHA-2 has only just arrived, discussions have already begun on a possible new experiment for the collaboration: ALPHA-3, which would investigate the properties of gravity. In order to make space for this possible expansion, a new platform was created over the experimental area for the ALPHA-2 electronics

There is no proposal pending for studying gravitational differences between hydrogen and antihydrogen. From their web page:

Eventually, we will use this technique to compare the structure of antihydrogen and hydrogen atoms, to search for difference between matter and antimatter, but In this first experiment, we do not yet have enough precision to test these fundamental symmetries. This is important, as the Universe has shown a preference for matter over antimatter as it has evolved, but so far, no measurements can explain why this came about. If matter and antimatter were truely identical, the Universe as we know it could not have come about. The next step at ALPHA is to construct an apparatus that will allow us to make these more precise measurements, using both microwave radiation, and laser light.

Maybe they aim at such a precision as to test how hydrogen and antihydrogen interact with gravity, but they have no open publication discussing this, except the cryptic sentence given with the CERN news bulletin.

Edit given the link in the comments above, it seems that the article is talking of a "gleam in the researcher's eye" . The only specific proposals of testing gravity in accelerators has come from the ALPHA collaboration as stated above, and the relevant papers are restricted to the collaboration, but have to do with using interferometry to test the gravitational field of hydrogen with respect to antihydrogen, old proposals (T. J. Philips, Hyp. Int. 109 (1997) 357. which is reference 3 in an older experiment.

The article in the Times of India was probably written by somebody who listened to the presentations, and is probably referring to the expectation of current physics models that the unification of all forces, including gravity, will allow to study the behavior of particles closer to the energies of the Big Bang . A verification of the theories, which predict a lot of new particles, would be a study of gravity.

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There also exists the Aegis experiment also at CERN using the beams.

> The principle of universality of free fall (or weak equivalence principle, WEP) states that all bodies fall with the same acceleration, independent of mass and composition. The WEP has been tested with very high precision for matter but never for antimatter. AEgIS is an experiment to test the WEP with antiprotons at the European laboratory CERN, using the antiproton decelerator (AD). AEgIS is a collaboration of physicists from all around the world.

anna v
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    From what I've heard from ALPHA, the simplest/first gravity experiment they'd like to try is just to make antihydrogen fall towards Earth. Surprisingly, there aren't any experimental bounds on this! My understanding is that, beyond this test, they would measure local gravity with antihydrogen as a test of the equivalence principle (everything accelerates under gravity the same, regardless of mass, charge, etc.). A failure of antihydrogen to fall the same as hydrogen would, I presume, indicate beyond-GR physics. – emarti Dec 20 '12 at 07:38
  • One of my few questions involved this problem, back when I first joined. http://physics.stackexchange.com/questions/5521/is-there-a-different-behavior-between-proton-and-antiproton-beams-at-the-tevatro .And yes, I had forgotten about the Aegis experiment :(. – anna v Dec 20 '12 at 07:47
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In fact, searches for Gravitons, the hypothetical particle mediating the gravitational force, have been performed at colliders such as the Tevatron and the LHC (by the ATLAS and CMS collaborations).

Some of the theories probed involve the postulate of the presence of a 4th, 5th etc spatial dimension which however would be very limited in size such that Newton's law of gravitation would still be valid at macroscopic scale while making gravity a much stronger force than we expect at the microscopic scale.

Andre Holzner
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