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Posted: Dec 19, 2013

Space-time - smooth or grainy?

(Nanowerk News) A paper by Stefano Liberati from SISSA has been selected as one of the 2013 Highlight papers (the best papers of the year) of the journal Classical and Quantum Gravity. The paper ("Tests of Lorentz invariance: a 2013 update") is a systematic review of the methods devised by scientists since the 90s to test Einstein’s laws of Special Relativity, up to the highest observable energies. These types of tests are important: deviations from Special Relativity could in fact indicate that space-time is not continuous but grainy.
Smooth" or grainy? Is space-time continuous or is it made up of very fine (10-35 metres on the “Planck scale”) but discrete grains, if we look at it very close up ? If the latter were true, scientists think, this would lead to deviations from the theory of special relativity formulated by Albert Einstein more than 100 years ago.
gravitational-lens
Gravitational lens: Light from an ancient galaxy 10 billion light-years away has been bent and magnified by the galaxy cluster RCS2 032727-132623. Without the help of this lensing effect, the distant galaxy would be extremely faint.
In some theoretical scenarios, the “non-continuity” of space-time implies violations to the invariance of the physical laws under the so-called Lorentz transformations (which establish that physical laws are the same for all inertial reference frames that are at the basis of special relativity). Since the 90s physicists have devised several methods (often based on phenomena connected to high-energy astrophysics) to test these deviations from standard physics. Stefano Liberati, coordinator of the Astroparticle Physics group of the International School for Advanced Studies (SISSA) of Trieste, recently published a systematic review to present the state of the art in this field and the constraints that can be placed on the various models that predict violations to Special Relativity.
The paper is an invited Topic Review published in the journal Classical and Quantum Gravity. This journal periodically asks leading world experts to “sum up” what is known in a specific field of study. The review has now been selected as one of the journal’s Highlight papers for 2013.
“Physicists have been wondering about the nature of space-time for years. We’ve been asking ourselves whether it is continuous at all scales, as we perceive it in our daily experience, or whether at very small sizes it presents an irregular grain that we, in our direct experience, are unable to perceive”, explains Liberati. “Imagine looking at a slab of marble from some distance: it will probably seem to have a uniform texture. However, on closer inspection, for example using a powerful microscope, you can see that the marble is porous and irregular”.
“In a certain sense physicists have been trying to do something similar with space-time: to find something that acts as a microscope to find out whether at very small length scales there is indeed some irregularity. In my paper I presented a systematic overview of the experiments and observations that can be exploited to investigate the existence of these irregularities. Special relativity is one of the cornerstones of modern physics and as such it is very important to test its validity, insofar as current observations allow us”.
Source: Sissa Medialab
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