Does the quantum gravity have energy

19.03.2012 12:58

See quantum gravity in the mirror?

Veronika Schallhart Public relations and event management
University of Vienna

On the Planck scale of extremely large energies and very small distances, the merging of quantum physics with Einstein's theory of gravity is expected. However, this scale is so far removed from experimental possibilities that it is considered impossible to test quantum gravity. A collaboration between Časlav Brukner and Markus Aspelmeyer, both quantum physicists at the University of Vienna, and Myungshik Kim from Imperial College London, has now proposed an experiment with mirrors on the Planck mass scale that could be used to test some quantum gravity theories in the laboratory . The results are currently published in "Nature Physics".

A task that has not been resolved for a long time

One of the most important and exciting tasks of modern physics is the search for a theory that combines quantum mechanics with Einstein's general theory of relativity. Quantum mechanics describes the physics that shows itself on the orders of magnitude of individual particles, atoms and molecules. On the other hand, Einstein's general theory of relativity is particularly evident in the case of large masses. A unified theory of quantum gravity is only expected on the so-called Planck scale of extremely large energies and very small distances. The Planck length is just 1.6 x 10-35 meters: If this length were defined as 1 meter, an atom would be as big as the entire visible universe. And the Planck energy is so great that even the Large Hadron Collider at CERN only achieves a tiny fraction of this energy. In order to get close to the Planck energy, a particle accelerator would have to be astronomical in size. The Planck scale can also be described by the Planck mass: A speck of dust has about this mass, which is extremely heavy compared to atoms, so that quantum effects are not considered to be observable for such masses. The Planck scale is so far removed from experiments that it is considered almost impossible to test theories of quantum gravity. Nevertheless, physicists have now found a way to test predictions of some theories of quantum gravity in experiments with massive mirrors.

The order makes the difference

Quantum mechanics forbids knowing the position and speed of a particle at the same time. Nevertheless, successive measurements of the location and the impulse are possible: Either you measure the location first and then the impulse or vice versa. In quantum physics you get different results, depending on which order you choose. However, many theories on quantum gravity say that this difference changes depending on the mass, because the Planck length limits the measurement accuracy of the location. The researchers in Vienna and London have now shown that despite this very small change, a measurable effect can occur in very massive quantum systems.

Testing new theories with moving mirrors

The researchers' idea is to test this difference between the two measurement sequences in new quantum systems: With new techniques and quantum technologies, it has recently become possible to bring massive, movable mirrors into quantum states and to measure them with very high precision. The researchers propose to use four interactions between a laser pulse and a moving mirror to investigate precisely this difference between the order of measurements of the location and the pulse. By coordinating the interactions precisely in terms of time and implementing them precisely, it is possible to transfer this effect to the laser pulse and then read it out using quantum optical methods. "Any deviation from the expected quantum mechanical result would be very exciting," says Igor Pikovski, lead author of the research, "and even if you do not measure any deviation, you get a restriction for possible new theories". Indeed, some of the theories on quantum gravity make different predictions from quantum mechanics about the outcome of the experiment. The researchers show with their work that it may be possible to test some predictions of the still unexplored quantum gravity directly on the laboratory bench.

Publication in "Nature Physics":
Probing Planck-scale physics with quantum optics: I. Pikovski, M. R. Vanner, M. Aspelmeyer, M. S. Kim and C. Brukner. Nature Physics (2012) DOI: 10.1038 / NPHYS2262

Scientific contact
Dipl.-Phys. Igor Pikovski
Quantum Optics, Quantum Nanophysics, Quantum Information
University of Vienna
1090 Vienna, Boltzmanngasse 5
T + 43-1-4277-725 83
M + 43-699-172 071 81
[email protected]

Consultation notice
Petra Beckmannova
(Office of Prof. Časlav Brukner)
Quantum Optics, Quantum Nanophysics, Quantum Information
University of Vienna
1090 Vienna, Boltzmanngasse 5
T + 43-1-4277-512 05
[email protected]

Features of this press release:
Physics / astronomy
Research results, research projects