What is space-time?

Physicists believe that at the smallest scales, space appears from quantum. So, what do these works look like?

People often consider space to be obvious. It is empty, the context for everything else. Time, likewise, is simply tickles. But if physicists find anything after a long process of research to unify their theories, it is space and time that creates such an amazingly complex system. it can challenge our most intense efforts just to make it clear.

In early November 1916, Albert Einstein saw what was about to happen. A year earlier he had developed general theory of relativity, arguing that gravity is not the force that works through space but is a characteristic of space-time itself . When you throw a ball high up, fly into the air, it returns to the ground because the Earth distorts the space around it, causing the paths of the ball and the ground to intersect again. In a letter to a friend, Einstein thought about the challenge of combining general relativity with another of his mental children, the primitive theory of quantum mechanics. That will not only distort space but also destroy it. Mathematically, he hardly knows where to start. "I have made myself difficult to know how many times this way!" , Einstein writes.

Einstein never went too far. Even today there are many competing ideas for a compelling quantum theory when scientists study this topic. The debate obscures an important fact: all competing methods assume that space originates from something deeper - a breakthrough idea with 2,500 years of scientific understanding and philosophy.

 

A normal magnet can clearly point out the problem that physicists face. It can suck a paper clip that does not fall due to Earth's gravity. The gravitational pull is weaker than the magnetic field or the electric or nuclear force. Despite the quantum effect, it is still weaker. The only tangible evidence that these processes are present is the spotted material model in the original universe (before) - thought to be due to the quantum fluctuations of the gravitational field.

Black holes are the best test case for quantum gravity. " It's the closest thing we have to test , " said Ted Jacobson of the University of Maryland, College Park. He and other theorists studied black holes as a theoretical fulcrum. What happens when you create an equation, work perfectly in laboratory conditions and extrapolate them into a completely imaginary situation? Does some small flaw can manifest itself?

Black holes are the best test case for quantum gravity.

The wide prediction of matter falling into the black hole will be unlimited compression when approaching the central area - in mathematics called singularity. Theorists cannot extrapolate the trajectory of an object beyond the singularity; Its timeline ends there. Even saying "there" is a problem because space-time itself will determine the end of the existence of singularity. Researchers hope that quantum theory can carefully analyze this singularity and see how things fall into black holes.

Outside the boundary of the pit, matter is not compressed, gravity is weaker. In short, known laws of physics should be preserved. Therefore, it becomes even more complicated than it is. The black hole is demarcated by the event horizon, a point that does not return: the material that falls into it cannot return. The irreversible fall. It is a problem because all known fundamental laws of physics, including quantum mechanics laws in general, can be reversed. At least in principle, you will be able to reverse the movement of all particles and restore what you have.

A conundrum is very similar to physicists' questions in the late 1800s, when they contemplated the mathematics of a "black object" , idealized as a cavity filled with electromagnetic radiation. James Clerk Maxwell's electromagnetism predicts such an object would absorb all the radiation acting on it and could never achieve equilibrium with surrounding matter. Rafael Sorkin of the Perimeter Institute for Theoretical Physics in Ontario explains: "It will absorb an infinite amount of heat from a reservoir maintained at a fixed temperature." In thermodynamic terms, it is possible that the object has an absolute zero temperature. This conclusion contradicts the observation of actual black objects (like an oven). Following Max Planck's research, Einstein showed that a black body could reach thermal equilibrium if radiant energy comes from discrete units, or from quantum itself.

Theoretical physicists have tried for nearly half a century to come up with a suitable explanation for black holes. Finally, Stephen Hawking of Cambridge University made a major advance in the mid-1970s, when he applied quantum theory to the radiation field around the black hole and showed that they had a different temperature. Thus, they not only absorb but also emit energy. Although his analysis puts black holes in thermodynamics, going deeper into the irreversible problem. Radiation comes from outside the pit boundary and there is no information on the inside of the pit. It is random thermal energy. If you reverse the process and recharge the power again, things that have fallen in won't pop out; You will get more heat. And you can't imagine that the original stuff is still there, just stuck inside the hole, because when the hole emits radiation, it shrinks and, according to Hawking's analysis, eventually disappears.

This problem is called the information paradox because the black hole rejects information about falling particles that allow you to rewind their motion. If physics black holes are really reversible, something must bring information back and our notion of space-time may need to change to allow that.

Atomic space-time

Heat is a random movement of microscopic parts, such as gas molecules. Because black holes can warm and cool, this explains why they have so many parts, in other words, that black holes have a micro structure. And because a black hole is just an empty space (according to general relativity, matter falls over the horizon but cannot linger), parts of the black hole must be parts of space.

Even the theories given to preserve a common concept of the space-time end point also conclude that there is a secret behind the flat facade. For example, in the late 1970s, Steven Weinberg, now working at the University of Texas, sought to describe gravity similar to other natural forces. He still obtained results basically zero-time changes in its smallest scope.

Early physicists envisioned microscopic space as a mosaic of small spaces. If you enlarge Planck's scale to an almost unimaginable small size of 10–35 meters, you'll see something like a chessboard. But that is not entirely true. Not only that, in the grid lines of the board space, there will be a number of ways to outweigh the remaining directions, causing asymmetry. This contradicts the theory of relativity. For example, the light of different colors can move at different speeds - like in a glass prism, causing light refraction into constituent colors. Conflicts with relativism are quite obvious.

The thermodynamics of black holes increase the skepticism about space imagery as a simple mosaic picture. By measuring the heat behavior of any system, you can count its parts, at least in principle. Extract energy and see the thermometer. If it shot up, that energy certainly covered the relatively few molecules.

If you experiment with a normal substance, the number of molecules increases compared to the volume of material. That means: If you increase the radius of a sea ball by a factor of 10, you will gain 1,000 times the molecule inside it. But if you increase the radius of a black hole by a factor of 10, the number of molecules collected increases only 100 times. The number of "molecules" it forms must be directly proportional to its mass but against the surface area. The black hole looks like a three-dimensional object, but its behavior is like two-dimensional.

This strange effect is called the three-dimensional principle because it conjures up the hologram. However, closer research, it became an image created by a two-dimensional film. If the three-dimensional principle counts the micro-components of space and its content, then the space-making time will be longer than the pairing of small pieces together.

However, the relationship of a part with the whole is rarely so simple. A molecule of H ₂ O is not simply a small water particle. See what liquid water does: it flows, forms droplets, ripple and waves, freezes and boils. A single H ₂ O molecule does not do that: it is collective behavior. Likewise with space. Daniele Oriti of the Max Planck Institute of Attractive Physics in Potsdam, Germany said: "The atoms of space are not the smallest parts of space. They are the constituents of space. Geometric properties of space is the new, collective, approximate attribute of a system made up of so many atoms ".

What exactly are the building blocks depends on different theories. In loop quantum gravity, they are quantum synthesized by applying quantum principles. In string theory, they are the same fields as electromagnetic fields that exist on the surface, detected by a moving fiber or energy loop - a string of characters. In M theory, which is related to string theory and may be its foundation, they are a special type of particle: from a shrinking membrane to a point. In causal set theory, they are events involving a causal network. In amplituhedron theory and some other approaches, there are no constituent blocks - at least not in the usual sense.

Although the organizational principles of these theories differ, they all try to maintain some versions of the so-called relational theory of 17th and 18th-century German philosophers Gottfried Leibniz. In a broad sense, relational theory suggests that space arises from a certain correlation model between objects. In this view, space is a jigsaw puzzle. You start with a huge pile of pieces, see how they connect and place them accordingly. If two parts are similar in nature, such as color, they may be close; If they differ drastically, you temporarily set them apart. Physicists often express this relationship as a network with a certain connection model. The relationships are determined by quantum theory or other principles, and the spatial arrangement follows.

Phase relay is another popular topic. If the space is assembled, it can also be disassembled; Then the building blocks can sort into something that looks like space. Thanu Padmanabhan of the Center for Astronomy and Astrophysics in India said: "Just as matter in many different states, like rocks, water and steam, the atoms of space can also be reconfiguration in different phases ". In this view, black holes may be places where space melts. Known theories are broken, but a more general theory will describe what happens in the new phase. Even if the space ends, physics continues.

Network entangled

Major discoveries in recent years are correlation relationships related to quantum entanglement. A kind of extraordinary relationship, intrinsic to quantum mechanics, entanglement seems more primitive than space. For example, an experimentalist can create two particles flying in opposite directions. If they are entangled, they are still coordinated no matter how far apart they are.

As usual, when people talk about quantum gravity, that is to refer to quantum uncertainty, quantum fluctuations and almost every other quantum effect in recording - but no one ever mentioned quantum entanglement. That changed with black holes. During the life of a black hole, particles get caught in, but after the hole evaporates completely, their outer components are not entangled with anything."Hawking should call it a problem , " said Samir Mathur of Ohio State University.

Even in a vacuum, there are no particles around, electromagnetic and other fields are entangled inside. If you measure a school in two different positions, the material you read will become disordered in a random but resonant way. And if you divide a region into two, the parts will be correlated, with the level of correlation depending on the number of unique geometry they have in common: their interface area. In 1995, Jacobson argued that entanglement brings a link between the presence of matter and the shape of space-time. That is, it can explain the law of gravitation. "Many problems imply weaker gravity - then, space-time is more harsh," he said.

Some quantum gravity methods now find entanglement very important. String theory applies the hologram principle not only to black holes but also to the universe in general, providing a formula for creating space - or at least part of it. For example, a two-dimensional space can be threaded according to the fields, when structured in the right way, creates an extra dimension of space. The original two-dimensional space will be the boundary of a wider field, called the bulk space. And entanglement is what weaves the cubic space into a whole.

In 2009, Mark Van Raamsdonk of the University of British Columbia made an argument for this process. Suppose the fields on the boundary are not entangled - they form a pair of unrelated systems. They correspond to two separate universes, there is no way to move between them. When systems become entangled, it is like a tunnel, or wormhole, opening between those universes, and a spaceship can travel from one to another. As the level of entanglement increases, the wormhole shrinks in length, dragging the universe together until no one calls them two universes anymore. When we observe correlations in electromagnetism and other fields, they are a residue of entanglement that binds space together.

Many other features of space, besides its contiguity, may also reflect entanglement. Van Raamsdonk and Brian Swingle, now at the University of Maryland, argue that entanglement exists everywhere to explain the universality of gravity - it affects all objects and cannot be screened. For black holes, Leonard Susskind of Stanford University and Juan Maldacena of the Institute of Advanced Studies in Princeton, argue that the entanglement between the black hole and the radiation it emits creates a wormhole. That can help preserve information and ensure that black hole physics can be reversed.

While string theory ideas only work with specific geometries and recreate only one dimension of space, some researchers have sought to explain how all spaces can appear. from the beginning. For example, ChunJun Cao, Spyridon Michalakis and Sean M. Carroll, at the California Institute of Technology, start with the minimal quantum description of a system, constituted without direct reference to space-time or even lice is material. If it has an appropriate correlation pattern, the system can be divided into sections that can be defined as different regions of space-time. In this model, the degree of entanglement defines a concept of spatial distance.

In physics and in natural science, space-time is the foundation of all theories. However, we never see space-time directly. Instead we deduce its existence from our daily experience. We think that the most economical aspect of the phenomenon we see is that some mechanisms work in spacetime. But the last lesson of quantum gravity is that not all phenomena fit in space-time. Physicists will need to find some new foundation structures, and when they do, they will complete the Einstein revolution that began more than a century ago.