High-precision neutron experiment confirmed the validity of the law of gravity of Newton to the micro level and limited the possible characteristics of dark matter particles and energy. The law of universal gravitation formulated by Newton in 1687, is now known to every schoolboy: "two bodies attract each other with a force that is directly proportional to the mass of the objects and inversely proportional to the square of the distance between them." But, on the other hand, the gravitational force is the force of large bodies, and there is just such a law in the microcosm? The answer to this question has got an international team of scientists, which has Russian scientists currently working abroad.
Flight of the thrown stone seems smooth, but it's just an illusion. Gravitational energy is quantized, that is, has many quantum States. As it depends on height, it means that the body can be at any height, but only on certain levels. Stone at the movement jumps from one energy level to another, like from one step to another. But the difference between levels is very small, and the transition happens so fast that the trajectory looks smooth. The quantization of energy is impossible to miss for macroscopic bodies, but using ultracold neutrons, transitions between energy levels can be seen and measured.
Physics, opened a few years ago, the quantization of the gravitational energy of the neutrons now used this effect to test the laws of gravity at the micro level, on a scale which previously has gravity not studied. The results were published in the journal Physical Review Letters. Experiments were performed at the Institute Laue-Langevin in Grenoble, France.
To obtain neutrons with quantized gravitational energy States, the researchers used a technique gravity resonance spectroscopy, first described them in 2011. A nuclear reactor produces neutrons moving at a speed of 2200 meters per second. Then they slow down to less than 7 metres per second, cooled to a fraction of a degree above absolute zero and is directed between two horizontal plates.
The neutrons bounce off the lower plate, which is a perfectly smooth mirror, while the top plate is the absorber, which captures neutrons with high energies, leaving only the particles in the lower quantum state. Neutrons are ideal for this procedure because they do not have electric charge. They feel only gravity. The piezoelectric crystal is forced to shake the mirror, giving the neutron energy to reach a higher level. The required shock depends on the difference between the energy levels, which in turn depends on gravity and, accordingly, the height. By measuring the frequency of vibration, physicists have determined the strength of gravity range from micrometers to millimeters with very high accuracy. According to the experimenters, their results are 100 000 times greater precision than has been achieved previously.
The results showed that within the measuring range and accuracy of Newton's inverse square law for gravity is fair. The importance of this experimental fact is not actually the confirmation of the law – although this is interesting, but it was expected. The importance of the experiment is that it puts limits on the existence of other "exotic" forces, which, according to some predictions could be seen on these scales. Simply put, these forces were not found, which will affect the development of the theory, for example, the dark energy responsible for accelerated expansion of the universe.
The fact that some hypotheses related to dark energy, predicted the existence of a special fifth force, named "chameleon" (a hypothetical particle – the carrier of dark energy). This name it received because the range in which it operates, is dramatically reduced for solid objects, "masking" it. This helps to explain why we don't see it in observations of the Solar system. However, for microscopic neutron it should be substantial and result in different available energy levels from those levels that are associated only with gravity.
In this experiment, the "chameleon" was not found. This does not exclude the explanation of dark energy based on the theory of "chameleon", but limits a limit value of this force. To definitively abandon this hypothesis, it is necessary to increase the accuracy of another seven orders of magnitude, which poses a very difficult challenge.
The results of the experiment restricted the possible properties of and candidate for the dark matter, which according to modern views, is 85% of the matter in the Universe, but it seems imperceptible, except in the case of gravitational attraction on cosmic scales. Believe very light hypothetical particles called axions however, should cause a deviation from the ordinary law of gravitation at small distances. The lack of this effect in this experiment, limiting the amount of interaction.