An investigation led by the Institute for Corpuscular Physics (Joint center for Scientific Research Council and the University of Valencia), in the Science Park of the academic institution, has announced a crucial discovery in the laws of physics: has obtained evidence of symmetry breaking in time. The discovery, that will be published this week in the journal ‘Physical Review Letters’, was conducted by the international collaboration BABAR, laboratory SLAC (Stanford Linear Accelerator Center) from the Department of Energy of United States in the University of Stanford (California).
Time passes inexorably. In the history of the universe and complex systems, the time evolution is associated with an increase of entropy. In other words, over time the disorder always grows from an initial situation more orderly.
To explain it, we can imagine that we look back a movie in which a vase falls to the ground and breaks into pieces. We will be aware very fast that what we are observing it is impossible from the point of view of physical laws because we know it is not possible that the pieces fly from the ground and form the vase. This is because, from our point of view, ‘the arrow of time’ passes without interruption from past to future.
However, for a single, isolated particle, the time looks the same forwards and backwards, that is, its movement is reversible or temporary symmetrical. Suppose that we are watching a film in which appears a billiard ball that hits a corner. If we are not told, we will not know if the screening of the film is going forward or backwards. This is because in both temporary movements, the movement of the billiard ball has the same physical laws. This concept is known as ‘time reversal symmetry’ and explain to us, that in the world of particles, the physics theories are valid for both senses of movement, which is to say that they move forward and backward indistinctively in time.
Time has a preferential direction
José Bernabeu explains that “the breaking of temporal symmetry o symmetry T in physics of particles is related with CP asymmetry that exists between matter and antimatter, required for generating the current universe of matter at any moment of its history. Symmetry C, he says, knowing that each particle of nature belongs an antiparticle with opposite charge, the laws of physics would be the same exchanging those with positive charge with those with negative charge”.
The symmetry P states that the laws of physics remained unchanged under inversions, i.e., the universe behaves like its image in a mirror. These two symmetries combined give rise to the charge-parity symmetry or CP symmetry. Previous experiments with particles known as mesons B and K have revealed that CP symmetry is not fulfilled. And the CPT theorem states that for any system of particles, symmetries must remain balanced. Or what is the same, if CP symmetry is not fulfilled symmetry T either”.
The researcher Fernando Martínez Vidal adds: “BABAR experiment, which was designed for a depth study of the asymmetry between matter and antimatter, has permitted us to observe for the first time the breaking of symmetry T”.
Between 1999 and 2008, were produced more than 500 million of B mesons at SLAC particle accelerator and their antimatter counterparts, called B-bar. Thus, the scientists observed how these particles violate the CP symmetry. The problem for observing the breaking of symmetry T resided in that B mesons are irreversibly disintegrated in a few billionth of a second, preventing to reverse its initial and final position. The solution was found through the quantum correlation between the two B, which allows that the information of the first particle disintegrated can be used to determine the state of the partner particle which is still alive. The researchers have discovered that the state of this last B meson is transformed in another six times more often in one direction than in the reverse.
Bernabéu explains that “this demonstrates unequivocally the breaking of symmetry under time reverse in the fundamental laws of physics”. These results are so convincing that the probability that they are a coincidence is similar to obtain the same side of a dice if you throw it 55 times in a row, 14 sigma in language of statics. Particle physicists believe that from 5 sigma can be considered a discovery.
The research is supported by the Ministeri D’Economia I Competitivitat, through the Programa Nacional de Física de Partícules, and the Generalitat Valenciana, through the Programa d’Excel.lencia PROMETEU.
More information:
BaBar Collaboration, Phys. Rev. Lett.
The Economist, The arrow of time: Backward ran sentences…
Bernabéu, Martínez-Vidal, Villanueva-Pérez, JHEP 1208, 064 (2012)
Bernabéu, Bañuls, Phys. Lett. B 464,117 (1999); Nuclear Physics B 590,19 (2000)
http://www-public.slac.stanford.edu/babar/Nobel2008.aspx
http://ific.uv.es/
Last update: 19 de november de 2012 12:28.
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