Scientists at the Max Planck Institute for Gravitational Physics have concluded that gravitational waves must bear the imprint of the extra dimensions of space predicted by string theory.
The 20th century gave the world two great physical theories - the general theory of relativity (GR) and quantum mechanics. The first deals with space, time and gravity. For example, she explains why clocks will run slightly slower on the surface of the Earth than in orbit. Such features have to be taken into account when creating GPS and GLONASS systems. General relativity also deals with black holes and other interesting things.
Quantum mechanics is the science of the behavior of the smallest constituents of matter, such as electrons. It became the basis for all modern electronics, which gave us computers, mobile phones, and in general everything that is smarter than a light bulb.
These two theories have an unfortunate flaw: they are incompatible with each other. If we apply them to the same object, then general relativity says one thing, and quantum mechanics says another, and the contradiction cannot be eliminated in any way. This is not so important in practice, because the effects of general relativity are noticeable only for very massive bodies (planets, stars, black holes), and quantum effects - for very small ones (elementary particles). But physicists have long been concerned about the incompatibility of the two greatest physical theories of our time. For this reason, scientists are looking for a more complete theory that will “reconcile” quantum mechanics and general relativity, and will also describe the micro- and macrocosm using uniform laws.
The most famous candidate for this role is string theory. It really shows how you can eliminate the contradiction and combine the two theories. But it has its drawback: unlike the general relativity and quantum mechanics themselves, it stubbornly defies experimental verification. Physicists joke bitterly that they would test string theory if they had an accelerator the size of a galaxy.
As David Andriot and Gustavo Lucena Gómez of Germany's Max Planck Institute for Gravitational Physics have found out, such a giant machine may not be needed. Confirmation of string theory can be obtained by observing gravitational waves - an amazing phenomenon long predicted by theorists, but experimentally discovered only in 2015.
Let us recall that some grandiose processes, for example, collisions of black holes, disturb the gravitational field, and waves run along it. From this, all objects caught in the gravitational wave begin to sway slightly with it in time. These fluctuations are too small to be noticed with the naked eye. In addition, in ordinary life, they are completely blocked by vibration from a car driving along the street or a cabinet moved by a neighbor. But specially created for these purposes, very sensitive detectors, hidden deep underground and extremely protected from all extraneous vibrations, can pick up a gravitational wave, which happened for the first time two years ago.
But, as it turns out, they are able to give not only this result. According to Andrio and Gomez's findings, observing gravitational waves could support string theory. The fact is that, according to this theory, space is not at all three-dimensional - it is nine-dimensional. We do not notice the six extra dimensions because they are too small. So, the mirror seems to us smooth, although it is worth looking at its surface through a microscope, and we will see whole “mountain ranges” and “gorges” on it.
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Gravitational waves, as the authors of the new work show, must “feel” these additional dimensions. If they are present in gravitational waves, a special rhythm should appear, which they call the "breathing mode". If "breathing" is detected by detectors, then this will be the first experimental confirmation of string theory. In addition, a set of high-frequency signals should appear, similar to several sudden high-pitched sounds - a kind of "screams" or "squeaks" that additional dimensions will herald about themselves.
As the authors of the study note, the pair of LIGO detectors lack the sensitivity to detect the "breathing mode". But in Italy, the third detector, VIRGO, is currently being upgraded. It will start operating at full capacity in 2018, and then, perhaps, the “breathing” of gravitational waves will be recorded. As for the second sign of additional measurements - high-frequency signals - their observation, alas, requires the creation of a new detector, since the existing devices are designed to study low-frequency, not high-frequency signals.
A scientific article with the results of the study was published in the Journal of Cosmology and Astroparticle Physics.
