What it is? Why do you need? And whether it is necessary?

Probably, before talking about quantum gravity, just have to talk about gravity.

Gravity, or gravity, attraction (to earth) – It `s that, that everyone learns from their own experience as soon as they are born. At school we learn, that on this topic turns out and theories exist. Perhaps everyone can tell a story about Newton and the apple.. Many, if not all, heard about Einstein, who managed to confuse such a simple and understandable thing like this, that I achieved universal worship.

What is gravity in ordinary, everybody understands? Like what – wherever we are, or any item was not found, power is everywhere, seeking to bring us into direct contact with the surface of the earth, gender – with all that, what's between us and the earth. Yes, and standing on the surface, we will not forget about the presence of this power. She presses down – and point. In theory Newton this force is called gravitational and is available at any point (different, of course) outside any massive body. It is she who holds such bodies, eg, planets and stars next to each other. so, the first and familiar point of view on gravity – this idea of ​​her as a force. Moreover, about the power of universal, which affects everything and everyone near the Earth. And quite special, because she never repels, but only attracts.

We are familiar with different forces. The most common idea of ​​them arises from the need to apply this very force, to budge something, move. What does it mean to move? So this – change the position of one object relative to others, change distances to them. It turns out, what change in the distance between objects and there is an indication of the presence, the action of forces between them?

In everyday life, we also very often encounter one special force., which is called the force of inertia. It manifests itself most clearly when meeting with some kind of obstacle., which suddenly (maybe not very suddenly) arises in the way of our movement. Think, few people have escaped stars in their eyes or even a bump on their foreheads after an unexpected meeting with some pillar, wood or wall. And again we have (very fast) changing the distance between objects. But how good it is before a meeting – movement may not require any strength at all. how Galileo managed to establish, even if the distances from the subject to others change, but change in a certain way, then no forces act on this object. Namely, if the body moves evenly and in a straight line. And if uniformly and / or non-linearly, then the forces act.

Figured out? It wasn’t there. Let's admit, move evenly and in a straight line along the train carriage, which is accelerated by rail, enveloping the mountain. Whether forces act on you or not? This and that. Movement by nature relatively. About what you need to move evenly and in a straight line, so that no forces are guaranteed to act on you?

Initial, in Newton's time, the answer to this question was as follows: There are some, the best frames of reference (that is, bodies, relative to which all movements need to be measured). They are called inertial. Here, with a uniform and rectilinear movement relative to these, and only these frames of reference and no forces act on objects. If relative to such frames of reference the body moves unevenly and / or not rectilinearly, then this means, that forces are acting on him. Real, correct forces. If the object moves relative to some objects, which in turn are used as reference bodies, but do not constitute an inertial reference frame, then fictitious, inertial forces. And this is in addition to the real, correct forces, which, in general, may not be. And what are the real forces? for instance, electromagnetic. And also gravitational. Those same, which we are interested in here. Like this.

But mind you, bogus inertial forces can provide you with a very real full-fledged bump on your forehead, if you forget about them! but, the theory said just that. Divided forces into “real” and “bogus”, frames of reference on “good ones” and “bad”. AND, naturally, the question arose – well, what kind of bodies make up good, true inertial reference frame? Nobody found the answer to this question.! Yes, many reference systems claimed to be a fairly good approximation to the inertial. At the beginning of the twentieth century, distant stars were considered the best approximation to a truly inertial reference frame.. But it was still clear enough, what is it no more, than an approximation. Someone will say – idle question. And the strength? After all, it is precisely with the solution of this issue that the division of forces into real and fictitious is connected., forces of inertia. So this question is by no means an idle one., but the most critical. General Theory of Relativity is an attempt to answer this question. This answer sounds like this: An inertial frame of reference does not need to be looked for somewhere far away. At each point in space time there is a whole set of inertial systems, locally inertial systems. And this is one of the postulates of the theory. This postulate is based on observation, that gravity (remind, one of “real” forces!) is not observed at all in the frame of reference, freely falling in a gravitational field. Einstein usually explained this statement by experiments, held in a falling elevator.

So what happens, according to Einstein, gravity is not real force, but just the force of inertia, easily destroyed by simply choosing the correct frame of reference? So, and not so. Although gravity, and the forces of inertia turn out to be practically indistinguishable in very small regions of space-time, locally (ie. in this place), there are two possibilities to distinguish between them. The first of them, less principled, related to, that in most cases, by choosing a suitable frame of reference, the inertial forces can be removed from consideration (to zero) not only at the point, but also in some area. The second, fundamental, related to, that gravity has its sources, ie. singular points in space time, in which the masses are, creating these forces, attracting other masses. AND “verily” inertial forces of such sources do not have. But still, then, that the force of gravity turned out to be at least locally destroyed by choosing a suitable coordinate systems, is a fundamental fact. And this fact is not the last to understand the answer to the question., which is in the title of this article.

The General Theory of Relativity connects the manifestation of gravitational interaction with the difference in the values ​​of the components of the metric tensor from those values, which the metric tensor has in the case (pseudo)Euclidean space. Special metrics (pseudo)In this case, the Euclidean space is put in correspondence with just the same, ideal, the best inertial reference frame. The relationship here is one-to-one – in inertial reference frame (coordinates) metric always (pseudo)Euclid, and vice versa, if the metric in some coordinate system (pseudo)Euclid, then it is inertial. Such frames of reference must be extremely distant from any gravitating masses.. And the closer to some mass we are, the more the metric at this point differs from (pseudo)Euclidean. What does it mean, metric is different from (pseudo)Euclidean? This means, what if we fill the entire area under consideration with a continuous coordinate grid of the lines of existence of test bodies, points of reference body, then it will not consist of parallel and perpendicular lines. Somewhere the lines will be thicker, somewhere thinner. Notice, the metric is the image of the reference body, with the help of which the frame of reference is formed.

I emphasize, the classical description of gravity is a description of the difference between the frame of reference and a certain standard, inertial, euclidean (more precisely, pseudo-Euclidean).

How, then, to describe the gravitational forces in the quantum case? After all, no one canceled Bohr's complementarity principle., who formulated a very natural thing – all measurements, which we produce, are made classic appliances. It's nothing else, as statement that, that any of our frame of reference is classical. This is why all attempts “quantize” metric are doomed to fail. Metric concept is purely classical. There is still no “quantum gravity”.

Where is the exit? Electromagnetic forces are well described in the quantum approximation. Moreover, in the quantum approximation ( there and then, when a relatively small number of particles interact) there were also other forces, or rather interactions – the so-called weak and strong. They, too, are already well described in the quantum approximation.. How about gravitational? After all, we must also learn to describe gravitational in this approximation, is not it so?

Whether it is necessary? Let's take a closer look at the picture we have.. In the classical approximation, only two forces are well known to us. Electromagnetic and gravitational. Moreover, the second is in a sense more general, than the first. In the sense, that the presence of electromagnetic energy-momentum in a certain region necessarily means that the metric in this region differs from the pseudo-Euclidean, and hence the presence of gravity in it. And vice versa – not! Gravity, described by the metric tensor, according to Einstein, it is an indispensable attribute of energy-momentum. Electromagnetic forces leave some mark on the metric, but they themselves are not described by the metric. Einstein's attempts, and not only him, to construct a description and electromagnetic forces using geometric structures were unsuccessful. The reason, in my opinion, there was initially a wrong interpretation of the physical meaning of the metric, which was identified with the potential of the gravitational field. Inevitably appearing in theory affine connection identified with power. But it should be just the opposite. Besides, due to its successful application to describe gravity, the metric began to seem primary, absolutely necessarily existing under any circumstances structure. With a shift in attention in theory to the properties of affine connection, it is easy and natural to include in the general scheme of the classical description and electromagnetism. And the metric in this case turns out to be in an obvious way a purely classical (existing and working only in the classical approximation) field.

so, electromagnetic (better to say – electroweak) interactions are classic. Strong interactions in the classical approximation have no analogue at all. And gravitational – have no analog in the quantum approximation. It says something?

In the quantum approximation, all that, which, upon passing to the classical, generates a metric and an electromagnetic potential, already not described by the metric. But continues to be described by affine connection. And the classification of the connection properties is somewhat different.. These properties are just those, what are now called strong interactions. As a matter of fact, we actually have some description of quantum gravity already now. We only call the best model used for this quantum chromodynamics..

© Gavryusev V.G.
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