People always take the space for granted. In the end, it’s just emptiness — the capacity for anything else. Time is also ticking continuously. But physicists are people, they always need something to complicate it. Regularly trying to combine their theory, they found that space and time merge into a system so complex that an ordinary person would not understand.

Albert Einstein realized that we were waiting for back in November 1916. The year before he formulated the General theory of relativity according to which gravity is not a force that is distributed in space, but a property of space-time. When you throw the ball in the air, it flies in an arc and returns to the earth, because the Earth warps space-time around itself, so the track of the ball and the earth will cross again. In a letter to a friend Einstein considered the problem of merging General relativity with its offspring, the nascent theory of quantum mechanics. But his math skills are just not enough. “I tortured myself with this!”, he wrote.

Einstein never came to this. Even today, the idea of creating a quantum theory of gravity seems extremely distant. Disputes hide an important truth: a competitive approach all as one say that the space is born somewhere deeper — and this idea breaks the established 2500 years of scientific and philosophical perception of it.

## Down a black hole

An ordinary magnet on the fridge perfectly illustrates the problem faced by physics. He can pin a piece of paper and to resist the gravitation of the whole Earth. Gravity is weaker than magnetism or other electric or nuclear forces. Whatever quantum effects it stood, they will be weaker. The only tangible proof that these processes actually happen, this motley picture of matter in the early Universe — which is thought to have been painted by the quantum fluctuations of the gravitational field.

Black holes — the best way to test quantum gravity. “This is the best that you can find for experimentation,” says Ted Jacobson from the University of Maryland, College Park. He and other theorists studying black holes as a theoretical fulcrum. What happens when you take the equations that work perfectly in the laboratory, and placed in the most extreme situations imaginable? Not whether there will be some barely noticeable blemishes?

Regarding the General theory predicts that matter falling into a black hole of infinitely compressed as it approaches the center, the mathematical cul — de-SAC called the singularity. Theorists can’t imagine the trajectory of an object outside the singularity; all lines converge in it. Even to talk about it, as problematic, because the very space-time that determines mestopolojenie singularity ceases to exist. Scientists hope that quantum theory may provide us with a microscope, which will allow us to consider this infinitely small point of infinite density and to understand what is going on with getting to her matter.

On the border of a black hole the matter is not so constrained, the gravity is weaker and, as far as we know, all laws of physics should work. And the more discouraging the fact that they don’t work. A black hole is limited by the event horizon, point of no return: the substance emerging from the event horizon, will not return. The descent is irreversible. This is a problem because all the known laws of fundamental physics, including quantum mechanical, are reversible. At least in principle, in theory, you should be able to reverse the movement and restore all the particles that you have.

With similar physics puzzle collided in the late 1800s, when mathematics was considered the “black body”, idealized as a cavity filled with electromagnetic radiation. The theory of electromagnetism James Clerk Maxwell predicted that such an object will absorb all radiation that falls on it, and will never come into equilibrium with the surrounding matter. “He can absorb infinite amount of heat from a reservoir which is maintained at a constant temperature,” explains Rafael Sorkin from the Institute for theoretical physics Perimeter in Ontario. From the thermal point of view, it will have a temperature of absolute zero. This conclusion is contradicted by observations of real black bodies (such as oven). Continuing work on the theory of max Planck, Einstein showed that the black body can reach thermal equilibrium, if the radiation energy will be supplied in discrete units, or quanta.

Theoretical physicists for nearly half a century tried to reach these solutions for black holes. The late Stephen Hawking of Cambridge University have taken an important step in the mid-70s, applying quantum theory to the field of radiation around black holes and showed that they have nonzero temperature. Consequently, they can not only absorb but also emit energy. Although his analysis was screwed up black holes in the area of thermodynamics, it has also exacerbated the problem of irreversibility. The outgoing radiation is emitted at the border of a black hole and does not transfer information from the bowels. This random thermal energy. If you reverse the process and feed this energy to the black hole, nothing comes up: you just get more heat. And it is impossible to imagine that in a black hole is something left, just trapped, because as soon as the black hole emits radiation, it is reduced and, according to Hawking’s analysis, in the end disappears.

This problem is called the information paradox, as the black hole destroys the information about the trapped particles, which you could try to recover. If the physics of black holes is indeed irreversible, something must carry the information back and our concept of space-time may have to change to fit this fact.

## Atoms of space-time

Heat is the random movement of microscopic particles, like gas molecules. Since black holes can heat up and cool down, it would be reasonable to assume that they consist of parts or, if in General, from the microscopic structure. And since a black hole is just empty space (according to General relativity falling into a black hole, the matter passes through the event horizon, not stopping), part of the black hole should be a piece of space itself. And under the deceptive simplicity of a flat empty space hides enormous complexity.

Even theories which were supposed to preserve the traditional idea of space-time, came to the conclusion that something is hiding under that smooth surface. For example, in the late 1970-ies Steven Weinberg, now working at the University of Texas at Austin, tried to describe gravity as well as describe other forces of nature. And found that space-time is radically modified in its smallest scale.

Physics originally visualized the microscopic space as a mosaic of small pieces of space. If you increase them to the Planck scale, infinitely small in dimensions 10^{-35} meters, scientists believe that it is possible to see something like a chess Board. But maybe not. On the one hand, such a network of lines, chess space, will prefer some other direction, creating an asymmetry that contradicts the special theory of relativity. For example, light of different colors will move at different speeds — as in a glass prism that splits light into its component colors. And although the manifestation on a small scale would be difficult to notice, violations of General relativity will be openly obvious.

Thermodynamics of black holes puts into question the picture of the space in the form of simple mosaic. Measuring the thermal behavior of any system, you can count part of it, at least in principle. Discard a energy and look at the thermometer. If the mercury soared, the energy should apply to relatively few molecules. In fact, you measure the entropy of the system, which represents its microscopic complexity.

If you do it with ordinary matter, the number of molecules increases with the volume of the material. So, in any case, it should be: if you increase the radius of the beach ball 10 times inside it fit 1000 times more molecules. But if you increase the radius of a black hole 10 times the number of molecules in it will be multiplied by just 100 times. The number of molecules of which it is composed, must be proportional not to its volume and surface area. A black hole can appear three-dimensional, but behaves as a two dimensional object.

This strange effect is known as the holographic principle because it resembles a hologram that seems to us like a three-dimensional object, and on closer inspection, the image produced by the two-dimensional film. If the holographic principle takes into account the microscopic components of space and its content — what physics allow, though not all — to create space will not be enough simple pairing its tiny pieces.

## The intricate network

In recent years, scientists have realized that this all needs to be involved quantum entanglement. It is a deep property of quantum mechanics, an extremely powerful type of communication, it seems much more primitive space. For example, experimenters can create two particles flying in opposite directions. If they are confused, they will remain linked regardless of the distance separating them.

Traditionally, when people talked about “quantum” gravity, they mean quantum discreteness, quantum fluctuations, and all other quantum effects — but not quantum entanglement. Everything changed for black holes. Over the lifetime of the black hole fall in it entangled particles, but when the black hole evaporates completely, the partners outside of the black hole remain confusing — with nothing. “Hawking should have called it a problem of confusion,” says Samir Mathur of Ohio state University.

Even in vacuum, where no particles of electromagnetic and other fields internally confusing. If you measure the field in two different places, your readings will fluctuate slightly, but remain in coordination. If you divide the area into two parts, these parts will be in correlation, and the degree of correlation will depend on the geometrical property that they have: the area of the interface. In 1995, Jacobson said that the involvement provides a link between the presence of matter and geometry of space-time — and thus could explain the law of gravity. “More confusion — gravity is weaker,” he said.

Some approaches to quantum gravity — especially string theory — consider involvement as an important cornerstone. String theory the holographic principle applies not only to black holes, but the universe as a whole, providing a recipe to create space — or at least some part of it. The original two-dimensional space will serve as the border of the vast volume of space. And the confusion is to associate three-dimensional space in a single and continuous whole.

In 2009, mark van Raamsdonk from the University of British Columbia has provided an elegant explanation of this process. Suppose a field on the border of not confusing — they form a couple of systems out of correlation. They correspond to the two separate universes, between which there is no method of communication. When systems become entangled, formed like a tunnel, a wormhole, between universes and space ships can move between them. The higher the degree of entanglement, the less length of the wormhole. The universes merge into one and no longer two separate. “The emergence of a large space-time directly links the entanglement of these degrees of freedom in field theory,” says van Raamsdonk. When we observe correlations in the electromagnetic and other fields, they are a remnant adhesion that binds the space together.

Many other features of the space, in addition to its connectivity, can also reflect confusion. Van Raamsdonk and Brian record layer, working at the University of Maryland, argues that the ubiquity of entanglement explains the universality of gravity — that it affects all objects and penetrates everywhere. As for black holes, Leonard Susskind and Juan Maldacena believe that the entanglement between the black hole and she emitted radiation creates a wormhole back into a black hole. Thus information is stored and the physics of a black hole is irreversible.

Although these ideas of string theory work only for specific geometries and rekonstruiruet only one dimension of space, some scientists are trying to explain the emergence of space from scratch.

In physics, and in General, in the natural Sciences, space and time are the basis for all theories. But we never notice the space-time directly. Rather, we derive its existence from our everyday experience. We assume that the most logical explanation of the phenomena that we see, is some mechanism that operates in space-time. But quantum gravity tells us that not all phenomena fit perfectly into this picture of the world. Physicists need to understand that is even deeper ins and outs of the space, the reverse side of a smooth mirror. If they succeed, we will finish the revolution begun more than a century ago by Einstein.