The continual progress of physics provides an insight ever deeper of the Universe, and also to have new technologies, but at the same time place us in front to new and new demands. One of the open questions in physics is to reconcile the two most successful theories of physics, Einstein's general relativity and quantum physics, which work perfectly, but in completely different fields. General relativity explains gravity and the universe at large scale, astronomical and cosmological, and at the same time has allowed us to achieve very precise GPS; quantum physics explains the universe at a microscopic scale of atomic distances (less than a billionth of a meter) or even smaller, and his understanding is the basis of all electronic devices that we use daily.
But no one knows how to do when we want to apply the two theories together, for example to explain what happens near a black hole. Or rather, there are many theories that aspire to achieve this unification and to become the "theory of everything", but none of them is convincing and above all it is not clear how they can be verified experimentally. A common feature of these theories is that the space-time changes nature, become "granular" at a very small length, called "Planck scale" (10 to 35 meters, or billion billion times smaller than an atomic nucleus) . A "microscope" able to see these ultra-small scale can be achieved by crashing particles at higher and higher energies, as is done at CERN, or by observing with detectors or telescopes the high-energy astrophysical phenomena.
The HUMOR experiment uses a new method for probing the space-time to these extreme dimensions: a table-top experiment, at very low energies, but permitting measurements of displacements and times with the highest precision. In particular the microscopic vibrations of oscillators of different sizes and masses, from a few nanogram up to a few milligrams, are measured with great accuracy, using lasers and / or electromagnetic sensors. In the article it is shown that the presence of a granularity of space-time at the Planck scale should be reflected in a nonlinear behavior of the oscillators, up to the dimensional scale currently measurable in the laboratory.
Some of the oscillators, electromechanical and optomechanical, have been specially designed and produced by IMEM-CNR, where also were made measurements with electromechanical readout. The optomechanichal measurements were instead conducted by INO-CNR and by the University of Camerino. Currently no effects of "granularity" have been observed, but the work could set limits, much more stringent than those currently available, to a large class of theories that seek to unify gravity and quantum physics.
The first scientific results of the experiment HUMOR (Heisenberg Uncertainty Measured with Opto-mechanical resonators) were published last June 19 in the journal Nature Communications ("Probing deformed commutators with macroscopic harmonic oscillators", doi: 10.1038/ncomms8503). These measurements set new limits for the unification of Einstein's general relativity and quantum mechanics, and were made by a partnership including the National Institute of Nuclear Physics, the CNR (IMEM + INO), the LENS of Florence, FBK of Trento and the University of Florence, Trento and Camerino.
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