In science fiction wormholes, or wormholes , is a method often used to travel very long distances in space. Can these magical bridges really exist?
For all my enthusiasm for the future of humanity in space, there is one obvious problem. We are soft meat sacks made up mostly of water, and those others are so far away from us. Even with the most optimistic spaceflight technologies, we can imagine that we will never reach another star in a time equal to the duration of a human life.
Reality tells us that even the closest stars to us are incomprehensibly far away, and it will take a huge amount of energy or time to make this journey. Reality tells us what we need spaceship, which can somehow fly for hundreds or thousands of years, while astronauts are born on it, generation after generation, live their lives and die while flying to another star.
Science fiction, on the other hand, leads us to methods for building advanced engines. Engage the warp drive and watch the stars rush past, making the journey to Alpha Centauri as fast and enjoyable as cruising on a ship somewhere out at sea.
Frame from the movie "Interstellar".
And you know what's even easier? Worm-hole; a magical tunnel that connects two points of space and time with each other. Just set a destination, wait for the stargate to stabilize, and just fly... fly half the galaxy to your destination.
Yes, it's really cool! Someone should have invented these wormholes, ushering in a bold new future of intergalactic travel. What are wormholes, and how soon can I use them? You ask...
A wormhole, also known as an Einstein-Rosen bridge, is a theoretical method for folding space and time so that you can connect two points in space together. Then you could instantly move from one place to another.
We'll use the classic demo from , where you draw a line between two points on a piece of paper, and then fold the paper and insert a pencil at those two points to cut the path. This works great on paper, but is it real physics?
Albert Einstein photographed in 1953. Photographer: Ruth Orkin.
As Einstein taught us, gravity is not a force that attracts matter like magnetism, it is actually a curvature of space-time. The moon thinks it's just following a straight line through space, but it's actually following a curved path created by Earth's gravity.
And so, according to physicists Einstein and Nathan Rosen, you could twist a ball of space-time so tight that two points would be in the same physical location. If you could keep the wormhole stable, you could safely separate these two regions of space-time so that they are still in the same location, but separated by the distance you like.
We go down the gravity well on one side of the wormhole, and then appear at lightning speed in another place at a distance of millions and billions of light years. While the creation of wormholes is theoretically possible, they are practically impossible from what we currently understand.
The first big problem is that wormholes are impassable, according to the General Theory of Relativity. So keep that in mind, the physics that predicts these things forbids their use as a method of transportation. Which is a pretty serious blow to them.
Artistic illustration of a spaceship moving through a wormhole into a distant galaxy. Credit: NASA.
Second, even if a wormhole could be created, it would most likely be unstable, shutting down instantly upon creation. If you tried to go to one end of it, you might just fall through the .
Thirdly, if they are traversable and can be kept stable, as soon as any matter tries to pass through them - even photons of light - it would destroy the wormhole.
There is a glimmer of hope, as physicists still haven't figured out how to combine the theories of gravity and quantum mechanics. This means that the universe itself may know something about wormholes that we do not yet understand. It is possible that they were created naturally as part of when the space-time of the entire universe was pulled into a singularity.
Astronomers have proposed looking for wormholes in space by watching how their gravity distorts the light of stars behind them. None have shown up yet. One possibility is that wormholes look natural, like the virtual particles we know exist. Only they would be incomprehensibly small, of the Planck scale. You will need a smaller spaceship.
One of the most interesting implications of wormholes is that they could also allow you to travel through time. Here's how it works. First, create a wormhole in the lab. Then take one end of it, put a spaceship in it, and fly at a significant fraction of the speed of light, so that the time dilation effect takes effect.
For people on a spaceship, it will only take a few years, while hundreds or even thousands of generations of people will change on Earth. Assuming you could keep the wormhole stable, open, and traversable, then traveling through it would be very interesting.
If you went in one direction, you would not only travel the distance between the wormholes, but you would also move forward in time, and on the way back: back in time.
Some physicists, such as Leonard Susskind, believe this won't work because it would violate two fundamental principles of physics: the law of conservation of energy and the Heisenberg uncertainty principle of energy-time.
Unfortunately, it seems that wormholes will have to remain in the realm of science fiction for the foreseeable future, maybe forever. Even if it were possible to create a wormhole, you would need to keep it stable, open, and then figure out how to allow matter to pass through without collapsing. Still, if you could figure it out, you would make space travel very convenient.
The title of the article you read "What are wormholes, or wormholes?".
- Sergey Vladilenovich, what is a wormhole?
There is no strict definition. Such definitions are needed when you are proving some theorems, and there are almost no strict theorems, therefore, they are mainly limited to figurative concepts, pictures. Imagine that we took out a ball from our three-dimensional space in one room and took out exactly the same ball in another room, and glued the resulting boundaries of these holes. Thus, when in one room we step inside this former ball that has become a hole, we emerge in another room - from a hole that was formed in the place of another ball. If our space were not three-dimensional, but two-dimensional, it would look like a piece of paper with a pen glued to it. A three-dimensional analog and its development in time is called a wormhole.
How are wormholes generally studied?
This is a purely theoretical activity. No one has ever seen wormholes, and, in general, there is no certainty yet that they even exist. Wormholes began to be studied, starting from the question: are there any mechanisms in nature that would guarantee us that such holes cannot exist in nature? These mechanisms have not been found, so it can be assumed that wormholes are a real phenomenon.
- Is it possible, in principle, to see a wormhole?
Of course. If a person suddenly crawls out of nowhere in a locked room, then you are observing a wormhole. Wormholes as an object of study were invented and promoted by the American theoretical physicist John Wheeler, who, with their help, wanted to explain, neither more nor less, electric charges. Let's explain. Free Description electric field from the point of view of theoretical physics - not very difficult task. But to describe the electric charge from the same point of view is very difficult. Electric charge appears in this sense as a very mysterious thing: some kind of substance, separate from the field, of unknown origin, and it is not clear how to deal with it in classical physics. Wheeler's idea was as follows. Let's say we have a microscopic wormhole, which is riddled with lines of force - from one end these lines enter it, and from the other they exit. An outside observer who does not know that these two ends are connected by lines of force will perceive such an object as a simple sphere in space, will examine the field around it, and it will look like the field of a point charge. It will only seem to the observer that this is some kind of mysterious substance that has a charge, etc., and all because he does not know that in fact it is a wormhole. Of course, this is very elegant idea, and many tried to develop it, but did not make much progress, because electrons are, after all, quantum objects, and no one, of course, knows how to describe wormholes at the quantum level. But if we assume that the hypothesis is correct, then wormholes are more than an everyday occurrence, everything related to electricity will ultimately be tied to them.
Exotic matter is a classical physics concept that describes any (usually hypothetical) matter that violates one or more of the classical conditions, or does not consist of known baryons. Such substances may have properties such as negative energy density or repel rather than be attracted by gravity. Exotic matter is used in some theories, for example, in the theory of the structure of wormholes. The most famous representative of exotic matter is the vacuum in a region with negative pressure produced by the Casimir effect.
- What are wormholes?
In terms of theoretical travel, there are traversable and impassable wormholes. Impassable - these are those through which the passage is destroyed, and this happens so quickly that no object simply has time to go from one end to the other. Of course, the second type of wormholes, traversable, is the most interesting to study. There is even a beautiful theory that says that what we used to think of as supermassive black holes in the centers of galaxies are actually the mouths of wormholes. This theory is almost not developed and has not found, of course, so far no confirmation, it exists, rather, as a kind of idea. Its essence is that outside of the wormhole you only see that in the center of the galaxy there is a certain spherically symmetrical object, but what it is - a wormhole or a black hole - you cannot say, because you are outside this object.
In fact, they can be distinguished only by one parameter - mass. If the mass turns out to be negative, then this is probably a wormhole, but if the mass is positive, then additional information is needed here, because a black hole can also turn out to be a wormhole. Negative mass in general is one of the central moments of the whole story with wormholes. Because in order to be passable, a wormhole must be filled with what is called an exotic substance, a substance whose energy density is negative at least in places, at some points. At the classical level, no one has ever seen such a substance, but we know for sure that it can, in principle, exist. Quantum effects have been registered that lead to the appearance of such a substance. This is a fairly well-known phenomenon and is called the Casimir effect. It has been officially registered. And it is connected precisely with the existence of negative energy density, which is very inspiring.
The Casimir effect is an effect consisting in the mutual attraction of conducting uncharged bodies under the action of quantum fluctuations in vacuum. Most often we are talking about two parallel uncharged mirror surfaces placed at close range, but the Casimir effect also exists for more complex geometries. The cause of the effect is the energy fluctuations of the physical vacuum due to the constant birth and disappearance in it. virtual particles. The effect was predicted by the Dutch physicist Hendrik Casimir in 1948 and later confirmed experimentally.
In general, in quantum science, negative energy density is a fairly common thing, which is associated, for example, with Hawking's evaporation. If such a density exists, we can ask the following question: how big is the mass of a black hole (the parameter of the gravitational field it creates)? There is a solution to this problem that is applicable to black holes - that is, objects with positive mass, and there is a solution that is applicable to negative mass. If there is enough exotic matter in the wormhole, then the outside mass of this object will be negative. Therefore, one of the main types of "observations" of wormholes is the tracking of objects that can be assumed to have negative mass. And if we find such an object, then with enough big share probability it will be possible to say that this is a wormhole.
Wormholes are also divided into intra-world and inter-world. If we destroy the tunnel between the two mouths of the second type of holes, we can see two completely unrelated universes. Such a wormhole is called interworld. But if we do the same and see that everything is fine - we have remained in the same Universe - then we have an intraworld wormhole. These two types of wormholes have a lot in common, but there is also an important difference. The fact is that an intraworld wormhole, if it exists, tends to turn into a time machine. Actually, it was against the background of this assumption that the last surge of interest in wormholes arose.
Wormhole as imagined by an artist
©depositphotos.com
In the case of an intraworld wormhole, there are two different ways look at a neighbor: directly through the tunnel or in a roundabout way. If you start moving one mouth of the wormhole relative to the other, then, in accordance with the well-known twin paradox, the second person, returning from the trip, will be younger than the remaining one. And on the other hand, when you look through the tunnel - both of you are sitting in laboratories that are motionless, from your point of view, nothing happens to you, your clocks are synchronized. Thus, you have a theoretical possibility to dive into this tunnel and get out at a moment that, from the point of view of an external observer, precedes the moment when you dived. The delay brought to an appropriate degree will give rise to the possibility of such a circular travel in space-time, when you return to your original place of departure and shake hands with your previous incarnation.
The twin paradox is a thought experiment that tries to "prove" inconsistency special theory relativity. According to SRT, from the point of view of "stationary" observers, all processes of moving objects slow down. On the other hand, the principle of relativity declares the equality of inertial frames of reference. Based on this, an argument is built that leads to an apparent contradiction. For clarity, the story of two twin brothers is considered. One of them (a traveler) goes on a space flight, and the second (a homebody) stays on Earth. Most often, the "paradox" is formulated as follows:
From the homebody's point of view, the moving traveler's clock has a slow running time, so when returning, it should be behind the homebody's clock. On the other hand, the Earth was moving relative to the traveler, so the homebody's clock should be behind. In fact, the brothers are equal, therefore, after returning, their watches should show the same time. However, according to SRT, the traveler's watch will be lagging behind. In such a violation of the apparent symmetry of the brothers, a contradiction is seen.
What is the fundamental difference between a wormhole and a black hole?
First of all, it must be said that there are two types of black holes - those that were formed as a result of the collapse of stars, and those that existed originally, arose along with the emergence of the Universe itself. These are two fundamental different types black holes. At one time there was such a thing as a "white hole", now it is rarely used. A white hole is the same black hole, but evolving backwards in time. Matter only flies into a black hole, but can never escape from there. From a white hole, on the contrary, matter only flies out, but it is impossible to get into it in any way. In fact, this is a very natural thing, if we remember that the General Theory of Relativity is symmetrical in time, which means that if there are black holes, there must be white ones. Their totality is a wormhole.
Black hole in the representation of the artist
©VICTOR HABBICK VISIONS/SPL/Getty
- What is known about the internal structure of wormholes?
So far, models are only being built in this sense. On the one hand, we know that the appearance of this exotic matter can be detected even experimentally, and still there are a lot of questions. The only model of a wormhole known to me that is more or less consistent with reality is the model of an initially evaporating (since the origin of the Universe) wormhole. Due to this evaporation, such a hole remains passable for a long time.
- What exactly are you working on?
I am engaged in purely theoretical activity, what can be generally called the causal structure of space-time is the classical Theory of Relativity, sometimes semi-classical (quantum, as we know, does not yet exist).
In the classical non-relativistic theory, one can come up with fairly convincing evidence that time travel cannot exist, but in general relativity there is no such evidence. And Einstein, when he was just developing his theory, was aware of this. He wondered if there was some way to eliminate that possibility. Then he did not cope with this task, as he himself later said. And although Einstein created a language to study this issue, the task remained academic. A surge of interest in it occurred in the late 1940s, when Gödel proposed a cosmological model containing such closed curves. But since Gödel always offered something exotic, it was treated with interest, but without serious scientific consequences. And then, somewhere at the end of the last century, thanks mainly to science fiction - for example, the film "Contact" with Jodie Foster - interest in the topic of time travel using wormholes was revived again. The author of the novel, on which the film script was written, is a very famous astronomer, popularizer of science, Carl Sagan. He took the matter very seriously and asked his friend, also a very famous relativist, Kip Thorne, to see if everything described in the film was possible from the point of view of science. And he published a semi-popular article in the magazine for American physics teachers "Wormholes as a tool for studying the General Theory of Relativity", where he considered the possibility of time travel through wormholes. And I must say that at that time the idea of traveling through black holes was popular in science fiction. But he understood that a black hole is an absolutely impassable object - travel through them is impossible, so he considered wormholes as an opportunity for time travel. Although this was known before, but for some reason people perceived his conclusions as a completely fresh idea, and rushed to investigate it. Moreover, the emphasis was on the presumption that a time machine cannot exist, but we decided to find out why. And quite quickly the understanding came that there were no obvious objections to the existence of such a machine at all. Since then, more large-scale studies began, theories began to appear. Basically, I've been doing this ever since.
Contact is a 1997 science fiction film. Directed by Robert Zemeckis. Main story: Ellie Arroway (Judy Foster) devoted her whole life to science, she becomes a member of a project to search for extraterrestrial intelligence. All attempts to search for extraterrestrial signals are fruitless, and the future of her project is in jeopardy. Ellie despairs of finding support, but unexpectedly receives help from the eccentric billionaire Hadden. And here is the result - Ellie picks up the signal. Signal decoding shows that it contains a description of a technical device. Its purpose is not clear, but a place for one person is planned inside.
After building and launching the device, Ellie travels through a wormhole system and is transported, presumably to a planet in another star system. Waking up there, on the seashore, she meets a representative of another civilization, who chose the image of her late father. Looking around, the heroine realizes that this area is recreated by an alien mind in her mind in the image of a drawing she drew as a child. The alien tells her that the device allows you to organize a system of interstellar communications, and the Earth from now on becomes a member of the community of civilizations of the Universe.
Ellie returns to Earth. From the point of view of outside observers, nothing happened to her after the launch of the installation, and her body did not leave our planet. Ellie finds herself in a paradoxical situation. Being a scientist, from the point of view of rigorous science, she cannot confirm her words in any way. It also turns out one more circumstance: the video camera attached to Ellie during the trip did not record anything, but the duration of the empty recording was not a few seconds, but 18 hours ...
Is it possible to "make" a wormhole?
Just about this there is a rigorous scientific result. This is due to the fact that there are no exact results on the study of wormholes. There is a theorem that has been proven for a very long time, and it says this. There is such a thing as global hyperbolicity. In this case, it doesn’t matter at all what it means, but the point is that while and since space is globally hyperbolic, it is impossible to create a wormhole - it can exist in nature, but it will not work to make it yourself. If you manage to break the global hyperbolicity, then maybe you can create a wormhole. But the fact is that this violation in itself is such an exotic thing, so poorly understood and poorly understood, that the side effect of the birth of a wormhole is already a relatively minor thing compared to the very fact that you managed to violate global hyperbolicity. There's a very famous thing going on here called the "strict cosmic censorship principle" which says that space is always globally hyperbolic. But this, in principle, is nothing more than a wish. There is no proof that this principle is true, there is simply some inner certainty, common to many people, that space-time must be globally hyperbolic. If this is so, it is impossible to create a wormhole - you need to look for an existing one. Meanwhile, severe doubts about the fidelity of the principle of cosmic censorship were expressed by the author himself - Roger Penrose, but that's another story.
- That is, some serious energy costs are required to create a wormhole?
It's very difficult to say something here. The trouble is that when your global hyperbolicity is violated, predictability is also violated at the same time - this is practically the same thing. You can somehow geometrically change the space around you, for example, take a bag and put it in a different place. But there are certain limits to which you can do this, in particular the limit imposed by predictability. For example, sometimes you can tell what will happen in 2 seconds, and sometimes you can't. The edge of what you can or cannot predict lies precisely in global hyperbolicity. If your space-time is globally hyperbolic, you can predict its evolution. If we assume that at some point it violates global hyperbolicity, everything becomes very bad with predictability. Therefore, an amazing thing arises, for example, such that right here and now a wormhole can materialize, through which a lion will jump out. It will be an exotic phenomenon, but it will not violate any laws of physics. On the other hand, you can spend a lot of effort, money and resources to somehow facilitate this process. But the result will still be the same - in both cases, you do not know whether a wormhole will appear or not. In classical physics, we can’t do anything about it - if it wants, it will arise, if it doesn’t want, it won’t arise - but quantum science does not give us any clues in this matter yet.
The principle of "cosmic censorship" was formulated in 1969 by Roger Penrose in the following figurative form: "Nature abhors the naked singularity." It says that space-time singularities appear in places that, like the interior of black holes, are hidden from observers. This principle has not yet been proven, and there are reasons to doubt its absolute correctness (for example, the collapse of a dust cloud with a large angular momentum leads to a “naked singularity”, but it is not known whether this solution of the Einstein equations is stable with respect to small perturbations of the initial data).
Penrose's formulation (a strong form of cosmic censorship) suggests that spacetime as a whole is globally hyperbolic.
Later, Stephen Hawking proposed another formulation (a weak form of cosmic censorship), where only the global hyperbolicity of the "future" component of space-time is assumed.
The text of the work is placed without images and formulas.
Full version work is available in the "Files of work" tab in PDF format
Fantasy novels describe entire transport networks connecting star systems and historical eras, the so-called portals, time machines. But much more surprising is the fact that time machines and tunnels in space are quite seriously, as hypothetically possible, actively discussed not only in articles on theoretical physics, on the pages of reputable scientific publications, but also in the media. There have been many reports about the discovery by scientists of some hypothetical objects called "wormholes".
Selecting material for the NPC on the topic "Black Holes", we came across the concept of "Wormholes". This topic interested us, and we made a comparison between them.
Objective: Comparative analysis of black holes and wormholes.
Tasks: 1. Collect material about black holes and wormholes;
2. Make detailed analysis received information;
3. Compare black holes and wormholes;
4. Create an educational film for students.
Hypothesis: Is space-time travel possible thanks to wormholes.
Object of study: literature and other resources about wormholes and black holes.
Subject of study: version of the existence of wormholes.
Methods: study of literature; use of Internet resources.
Practical significance of this work is to use the collected material for educational purposes in physics lessons and in extracurricular activities in this subject.
In the presented work, materials of scientific articles, periodicals, Internet resources were used.
Chapter 1. Historical background
In 1935, physicists Albert Einstein and Nathan Rosen, using the theory of general relativity, suggested that there are special "bridges" across space-time in the universe. These paths, called Einstein-Rosen bridges (or wormholes), connect two completely different points in spacetime by theoretically creating a warp in space that shortens travel from one point to another.
Theoretically, a wormhole consists of two entrances and a neck (that is, the same tunnel). The entrances to wormholes are spheroidal in shape, and the neck can be either a straight segment of space or a spiral one.
For a long time, this work did not arouse much interest among astrophysicists. But in the 1990s, interest in such objects began to return. First of all, the return of interest was associated with the discovery of dark energy in cosmology.
The English term that has taken root for "wormholes" since the 90s has become "wormhole", but the first to propose this term back in 1957 were American astrophysicists Mizner and Wheeler. In Russian, "wormhole" is translated as "worm hole". This term was not liked by many Russian-speaking astrophysicists, and in 2004 it was decided to vote on various proposed terms for such objects. Among the proposed terms were such as: "wormhole", "wormhole", "wormhole", "bridge", "wormhole", "tunnel", etc. Russian-speaking astrophysicists with scientific publications on this topic participated in the voting. As a result of this vote, the term "wormhole" won.
In physics, the concept of wormholes arose in 1916, just a year after Einstein published his great work, the general theory of relativity. The physicist Karl Schwarzschild, then serving in the Kaiser's army, found the exact solution of Einstein's equations for the case of an isolated point star. Away from a star, its gravitational field is very similar to that of an ordinary star; Einstein even used Schwarzschild's solution to calculate the deflection of light around a star. Schwarzschild's result had an immediate and very powerful effect on all branches of astronomy, and today it is still one of the most famous solutions to Einstein's equations. Several generations of physicists have used the gravitational field of this hypothetical point star as an approximate expression for the field around a real star with a finite diameter. But if we consider this point solution seriously, then in its center we will suddenly find a monstrous point object that has amazed and shocked physicists for almost a century - a black hole.
Chapter 2
2.1. Mole Hole
A wormhole is a supposed feature of space-time, representing at any moment of time a "tunnel" in space.
The area near the narrowest section of the molehill is called the "throat". There are passable and impassable molehills. The latter include those tunnels that collapse (destroy) too quickly for an observer or signal to get from one entrance to another.
The answer lies in the fact that, according to Einstein's theory of gravity - the general theory of relativity (GR), the four-dimensional space-time in which we live is curved, and gravity, familiar to everyone, is a manifestation of such curvature. Matter “bends”, warps the space around it, and the denser it is, the stronger the curvature.
One of the habitats of "wormholes" is the centers of galaxies. But here the main thing is not to confuse them with black holes, huge objects that are also located in the center of galaxies. Their mass is billions of our Suns. At the same time, black holes have a powerful force of attraction. It is so large that even light cannot escape from there, so it is impossible to see them with an ordinary telescope. The gravitational force of wormholes is also enormous, but if you look inside the wormhole, you can see the light of the past.
Wormholes through which light and other matter can pass in both directions are called traversable wormholes. There are also impenetrable wormholes. These are objects that outwardly (at each of the entrances) are, as it were, a black hole, but inside such a black hole there is no singularity (a singularity in physics is an infinite density of matter that breaks and destroys any other matter that enters it). Moreover, the property of singularity is obligatory for ordinary black holes. And the black hole itself is determined by the presence of its surface (sphere), from under which even light cannot escape. Such a surface is called the black hole horizon (or event horizon).
Thus, matter can get inside an impenetrable wormhole, but can no longer get out of it (very similar to the property of a black hole). There may also be semi-passable wormholes, in which matter or light can pass through the wormhole only in one direction, but cannot pass in the other.
Features of wormholes are the following characteristics:
A wormhole must connect two non-curved regions of space. The junction is called the wormhole, and its central section is the neck of the wormhole. The space near the neck of the wormhole is quite strongly curved.
A wormhole can connect either two different universes, or the same universe in different parts. In the latter case, the distance through the wormhole may be shorter than the distance between the entrances measured from the outside.
The concepts of time and distance in a curved space-time cease to be absolute values, i.e. such as we subconsciously always accustomed to consider them.
The study of wormhole models shows that exotic matter is necessary for their stable existence within the framework of Einstein's theory of relativity. Sometimes such matter is also called phantom matter. For the stable existence of a wormhole, an arbitrarily small amount of phantom matter is sufficient - say, only 1 milligram (or maybe even less). In this case, the rest of the matter supporting the wormhole must satisfy the condition: the sum of the energy density and pressure is zero. And there is nothing unusual in this anymore: even the most ordinary electric or magnetic field satisfies this condition. This is exactly what is needed for the existence of a wormhole with an arbitrarily small addition of phantom matter.
2.2. Black hole
A black hole is a region in space-time. The gravitational attraction is so strong that even objects moving at the speed of light, including quanta of light itself, cannot leave it. The boundary of this region is called the event horizon.
Theoretically, the possibility of the existence of such regions of space-time follows from some exact solutions of the Einstein equations. The first was obtained by Karl Schwarzschild in 1915. The exact inventor of the term is unknown, but the designation itself was popularized by John Archibald Wheeler and first used publicly in the popular lecture "Our Universe: Known and Unknown". Previously, such astrophysical objects were called "collapsed stars" or "collapsars", as well as "frozen stars".
There are four scenarios for the formation of black holes:
two realistic ones:
gravitational collapse (compression) of a fairly massive star;
collapse of the central part of the galaxy or protogalactic gas;
and two hypotheses:
the formation of black holes immediately after the Big Bang (primordial black holes);
the emergence of high energies in nuclear reactions.
The conditions under which the final state of the evolution of a star is a black hole have not been studied well enough, since for this it is necessary to know the behavior and states of matter at extremely high densities that are inaccessible to experimental study.
Collision of black holes with other stars, as well as collision neutron stars, causing the formation black hole, leads to the most powerful gravitational radiation, which, as expected, can be detected in the coming years with the help of gravitational telescopes. Currently, there are reports of collisions in the X-ray range.
On August 25, 2011, a message appeared that for the first time in the history of science, a group of Japanese and American specialists were able in March 2011 to record the moment of the death of a star that is being absorbed by a black hole.
Black hole researchers distinguish between primordial black holes and quantum ones. Primordial black holes currently have the status of a hypothesis. If at the initial moments of the life of the Universe there were sufficient deviations from the homogeneity of the gravitational field and the density of matter, then black holes could form from them by means of collapse. At the same time, their mass is not limited from below, as in the case of stellar collapse - their mass could probably be quite small. The detection of primordial black holes is of particular interest in connection with the possibility of studying the phenomenon of black hole evaporation. As a result of nuclear reactions, stable microscopic black holes, the so-called quantum black holes, can arise. For a mathematical description of such objects, a quantum theory of gravity is needed.
Conclusion
If a wormhole is impenetrable, then outwardly it is almost impossible to distinguish it from a black hole. To date, the theory of the physics of wormholes and black holes is a purely theoretical science. Wormholes are topological features of space-time, described in the framework of the special theory of relativity by Einstein in 1935.
The general theory of relativity mathematically proves the probability of the existence of wormholes, but so far none of them have been discovered by man. The difficulty in detecting it lies in the fact that the alleged huge mass of wormholes and gravitational effects simply absorb light and prevent it from being reflected.
After analyzing all the information found, we found out how wormholes differ from black holes and came to the conclusion that the world of space is still very little studied, and humanity is on the verge of new discoveries and opportunities.
On the basis of the research done, an educational film "Wormholes and Black Holes" was created, which is used in astronomy lessons.
List of used sources and literature
Bronnikov, K. Bridge between worlds / K. Bronnikov [Electronic resource] // Around the world. 2004. May. - Access mode // http://www.vokrugsveta.ru/vs/article/355/ (09/18/2017).
Wikipedia. Free Encyclopedia [Electronic resource]. - Access mode // https://ru.wikipedia.org/wiki/%D0%9A%D1%80%D0%BE%D1%82%D0%BE%D0%B2%D0%B0%D1%8F_% D0%BD%D0%BE%D1%80%D0%B0 (09/30/2017);
https://en.wikipedia.org/wiki/%D0%A7%D1%91%D1%80%D0%BD%D0%B0%D1%8F_%D0%B4%D1%8B%D1%80%D0 %B0 (09/30/2017).
Zima, K. "Wormhole" - the corridor of time / K. Zima // Vesti.ru [Electronic resource]. - Access mode // http://www.vesti.ru/doc.html?id=628114 (20.09.2017).
Wormholes and Black Holes [Electronic resource]. - Access Mode // http://ru.itera.wikia.com/wiki/%D0%9A%D1%80%D0%BE%D1%82%D0%BE%D0%B2%D1%8B%D0% B5_%D0%BD%D0%BE%D1%80%D1%8B_%D0%B8_%D0%A7%D0%B5%D1%80%D0%BD%D1%8B%D0%B5_%D0%B4% D1%8B%D1%80%D1%8B (09/30/2017).
Wormholes. Popular Science with Anna Urmantseva [Electronic resource]. - Access mode // http://www.youtube.com/watch?v=BPA87TDsQ0A (09/25/2017).
Wormholes of space. [Electronic resource]. - Access mode // http://www.youtube.com/watch?v=-HEBhWny2EU (09/25/2017).
Lebedev, V. Man in a wormhole (review) / V. Lebedev // Lebed. Independent almanac. [Electronic resource]. - Access mode // http://lebed.com/2016/art6871.htm (09/30/2017).
Through a wormhole, Is there an end to the universe. [Electronic resource]. - Access mode // https://donetskua.io.ua/v(25.09.2017).
Black hole [Electronic resource]. - Access mode // http://ru-wiki.org/wiki/%D0%A7%D1%91%D1%80%D0%BD%D0%B0%D1%8F_%D0%B4%D1%8B% D1%80%D0%B0 (09/30/2017).
Black holes. Universe [Electronic resource]. - Access mode // https://my.mail.ru/bk/lotos5656/video/_myvideo/25.html (09/25/2017).
What is a wormhole. Pulp [Electronic resource]. - Access mode // http://hi-news.ru/research-development/chtivo-chto-takoe-krotovaya-nora.html (09/18/2017).
Shatsky, A. Wormholes: what is it - a myth, a gate to other worlds or a mathematical abstraction? [Electronic resource]. - Access mode // http://www.znanie-sila.su/?issue=zsrf/issue_121.html&r=1 (09/18/2017).
Encyclopedia for children. T. 8. Astronomy [Text] / Chapter. ed. M. Aksenova; method. ed. V. Volodin, A. Eliovich. - M.: Avanta, 2004. S. 412-413, 430-431, 619-620.
A wormhole or wormhole is a hypothetical topological feature of space-time, which is a “tunnel” in space at every moment of time (a space-time tunnel). Thus, the wormhole allows you to move in space and time. The areas that a wormhole connects can be areas of a single space or be completely disconnected. In the second case, the wormhole is the only link between the two regions. The first kind of wormholes is often called “intraworld”, and the second kind is “interworld”.
As you know, the General Theory of Relativity prohibits movement in the Universe at a speed exceeding the speed of light. On the other hand, general relativity allows the existence of space-time tunnels, but it is necessary that the tunnel be filled with exotic matter with a negative energy density, which creates a strong gravitational repulsion and prevents the tunnel from collapsing.
Tachyons are most often referred to as such particles of exotic matter. Tachyons are hypothetical particles that travel faster than the speed of light. In order for such particles not to violate general relativity, it is assumed that the mass of tachyons is negative.
Currently, there is no reliable experimental confirmation of the existence of tachyons in laboratory experiments or astronomical observations. Physicists can only boast of a “pseudo-negative” mass of electrons and atoms, which are obtained with high density electric fields, special polarization of laser beams or ultra-low temperatures. In the latter case, the experiments were carried out with a Bose-Einstein condensate, an aggregate state of matter based on bosons cooled to temperatures close to absolute zero (less than a millionth of a kelvin). In such a highly chilled state, it is enough big number atoms are in their minimum possible quantum states, and quantum effects begin to manifest themselves at the macroscopic level. The Nobel Prize in Physics was awarded in 2001 for the production of the Bose-Einstein condensate.
However, a number of experts suggest that they can be tachyons. These elementary particles have a non-zero mass, which was proved by the detection of neutrino oscillations. The last discovery was even awarded Nobel Prize in physics for 2015. On the other side exact value neutrino masses have not yet been determined. A number of experiments to measure the speed of neutrinos have shown that their speed can slightly exceed the speed of light. These data are constantly questioned, but in 2014 a new job on this occasion.
String theory
In parallel, some theorists suggest that special formations (cosmic strings) with negative mass could have formed in the early Universe. The length of relic cosmic strings can reach at least several tens of parsecs with a thickness less than the diameter of an atom at an average density of 10 22 grams per cm 3 . There are several works that such formations were observed in the events of gravitational lensing of light from distant quasars. In general, it is currently the most likely candidate for a “theory of everything” or a unified field theory that combines the theory of relativity and quantum field theory. According to it, all elementary particles are oscillating threads of energy about 10 -33 meters long, which is comparable to (minimum possible size object in the universe).
The unified field theory suggests that there are cells in the space-time dimensions with a minimum length and time. The minimum length should be equal to the Planck length (approximately 1.6 x 10 −35 meters).
At the same time, observations of distant gamma-ray bursts indicate that if space graininess exists, then the size of these grains is no more than 10 −48 meters. In addition, he could not confirm some of the consequences of string theory, which became a serious argument for the fallacy of this fundamental theory of modern physics.
Potentially significant on the road to a unified field theory and space-time tunnels is the discovery in 2014 of a theoretical connection between quantum entanglement and wormholes. In a new theoretical work, it was shown that the creation of a space-time tunnel is possible not only between two massive black holes, but also between two quantum entangled quarks.
Quantum entanglement is a phenomenon in quantum mechanics in which the quantum states of two or more objects become interdependent. This interdependence persists even if these objects are separated in space beyond any known interactions. Measurement of the parameter of one particle leads to an instantaneous (above the speed of light) termination of the entangled state of the other, which is in logical contradiction with the principle of locality (in this case, the theory of relativity is not violated and information is not transmitted).
Kristan Jensen from the University of Victoria (Canada) and Andreas Karch from the University of Washington (USA), described a quantum entangled pair consisting of a quark and an antiquark that rush away from each other at near-light speeds, making it impossible to transmit signals from one to the other. Researchers believe that the three-dimensional space in which quarks move is a hypothetical facet of the four-dimensional world. In 3D space, quantum entangled particles are connected by a kind of "string". And in 4D space, this "string" becomes a wormhole.
Julian Sonner from the Massachusetts Institute of Technology (USA) has presented a quantum-entangled quark-antiquark pair, born in a strong electric field that separates oppositely charged particles, causing them to accelerate into different directions. Sonner also concluded that particles quantumly entangled in 3D would be connected by a wormhole in 4D. In the calculations, physicists used the so-called holographic principle - the concept according to which the entire physics of the n-dimensional world is fully reflected on its "facets" with the number of dimensions (n-1). With such a “projection”, a quantum theory that takes into account the effects of gravity in four-dimensional space is equivalent to a quantum theory “without gravity” in three-dimensional space. In other words, black holes in 4D space and a wormhole between them are mathematically equivalent to their 3D holographic projection.
Prospects for gravitational wave and neutrino astronomy
The greatest prospects in studying the properties of matter at the most microscopic and high-energy level for a better understanding of quantum gravity are gravitational-wave and neutrino astronomy due to the fact that it studies waves and particles with the highest penetrating power. So if the microwave background radiation of the Universe was formed 380 thousand years after, then the relict neutrinos in the first few seconds, and the relict gravitational waves in just 10 -32 seconds! In addition, registration of such radiation and particles from black holes or from catastrophic events (mergers and collapses of massive stars) has great prospects.
On the other hand, traditional astrometric observatories are actively developing, which now cover the entire electromagnetic spectrum. Such observatories can detect unexpected objects or phenomena in the early universe (the first interstellar clouds,
wormhole - 1) astrophysicist. The most important concept of modern astrophysics and practical cosmology. "Wormhole", or "molehole", is a trans-spatial passage that connects a black hole and its corresponding white hole.
An astrophysical "wormhole" pierces the space folded in extra dimensions and allows you to move along a really short path between star systems.
Studies conducted using the Hubble Space Telescope have shown that every black hole is the entrance to a "wormhole" (see Hubble's LAW). One of the largest holes is located in the center of our Galaxy. It has been theoretically shown (1993) that it is from this central hole that the Solar System originated.
According to modern concepts, the observable part of the Universe is literally all riddled with "wormholes" going "back and forth." Many leading astrophysicists believe that travel through "wormholes" is the future of interstellar astronautics. "
We are all used to the fact that the past cannot be returned, although sometimes we really want to. For more than a century, science fiction writers have been painting all sorts of incidents that arise due to the ability to travel through time and influence the course of history. Moreover, this topic turned out to be so burning that at the end of the last century, even physicists far from fairy tales began to seriously look for such solutions to the equations that describe our world, which would allow creating time machines and overcoming any space and time in the blink of an eye.
Fantasy novels describe entire transport networks connecting star systems and historical eras. I stepped into a booth stylized, say, as a telephone booth, and ended up somewhere in the Andromeda Nebula or on Earth, but - visiting long-extinct tyrannosaurs.
The characters of such works constantly use zero-transportation of the time machine, portals and similar convenient devices.
However, fans of science fiction perceive such trips without much trepidation - you never know what can be imagined, referring the implementation of the invented to an uncertain future or to the insights of an unknown genius. Much more surprising is the fact that time machines and tunnels in space are quite seriously discussed as hypothetically possible in articles on theoretical physics, on the pages of the most reputable scientific publications.
The answer lies in the fact that, according to Einstein's theory of gravity - the general theory of relativity (GR), the four-dimensional space-time in which we live is curved, and gravity, familiar to everyone, is a manifestation of such curvature.
Matter "bends", warps the space around it, and the denser it is, the stronger the curvature.
Numerous alternative theories of gravitation, the number of which goes to hundreds, differing from general relativity in details, retain the main thing - the idea of space-time curvature. And if space is curved, then why not take, for example, the shape of a pipe, short-circuiting regions separated by hundreds of thousands of light years, or, say, eras far from each other - after all, we are talking not just about space, but about space- time?
Remember, the Strugatskys (who also, by the way, resorted to zero-transportation): “I absolutely don’t see why the noble don shouldn’t ...” - well, let’s say, not fly to the XXXII century? ...
Wormholes or black holes?
Thoughts about such a strong curvature of our space-time arose immediately after the advent of general relativity - already in 1916, the Austrian physicist L. Flamm discussed the possibility of the existence of spatial geometry in the form of a kind of hole connecting two worlds. In 1935, A. Einstein and the mathematician N. Rosen drew attention to the fact that the simplest solutions of the GR equations, describing isolated, neutral or electrically charged sources of the gravitational field, have a spatial structure of a “bridge” that almost smoothly connects two universes - two identical, almost flat, space-time.
Such spatial structures were later called "wormholes" (rather loose translation English word"wormhole" - "wormhole").
Einstein and Rosen even considered the possibility of using such "bridges" to describe elementary particles. Indeed, the particle in this case is a purely spatial formation, so there is no need to specifically model the source of mass or charge, and with the microscopic dimensions of the wormhole, an external, distant observer located in one of the spaces sees only a point source with a certain mass and charge.
Electric lines of force enter the hole from one side and exit from the other, without beginning or ending anywhere.
In the words of the American physicist J. Wheeler, it turns out "mass without mass, charge without charge." And in this case, it is not at all necessary to believe that the bridge connects two different universes - the assumption that both "mouths" of the wormhole open into the same universe, but at different points and at different points, is no worse. different times- something like a hollow "handle", sewn to the usual almost flat world.
One mouth, into which the lines of force enter, can be seen as a negative charge (for example, an electron), the other, from which they exit, as a positive one (positron), the masses will be the same on both sides.
Despite the attractiveness of such a picture, it (for many reasons) did not take root in elementary particle physics. It is difficult to attribute quantum properties to the "bridges" of Einstein - Rosen, and without them there is nothing to do in the microcosm.
At known values masses and charges of particles (electrons or protons), the Einstein-Rosen bridge is not formed at all, instead, the "electric" solution predicts the so-called "naked" singularity - the point at which the curvature of space and electric field become endless. The concept of space-time, even if it is curved, loses its meaning at such points, since it is impossible to solve equations with infinite terms. The general relativity itself quite clearly states where exactly it stops working. Let us recall the words said above: "almost smoothly connecting ...". This "almost" refers to the main flaw of the "bridges" of Einstein - Rosen - a violation of smoothness in the narrowest part of the "bridge", on the neck.
And this violation, it must be said, is very non-trivial: on such a neck, from the point of view of a distant observer, time stops...
By modern concepts, what Einstein and Rosen saw as the throat (that is, the narrowest point of the "bridge") is in fact nothing more than the event horizon of a black hole (neutral or charged).
Moreover, from different sides of the “bridge”, particles or rays fall on different “sections” of the horizon, and between, relatively speaking, the right and left parts of the horizon, there is a special non-static area, without which it is impossible to go through the hole.
For a distant observer, a spaceship approaching the horizon of a sufficiently large (compared to the ship) black hole seems to freeze forever, and signals from it reach less and less. On the contrary, according to the ship's clock, the horizon is reached in a finite time.
Having passed the horizon, the ship (a particle or a ray of light) soon inevitably rests on a singularity - where the curvature becomes infinite and where (still on the way) any extended body will inevitably be crushed and torn apart.
This is the harsh reality internal device black hole. The Schwarzschild and Reisner-Nordstrom solutions describing spherically symmetric neutral and electrically charged black holes were obtained in 1916-1917, but physicists fully understood the complex geometry of these spaces only at the turn of the 1950s-1960s. By the way, it was then that John Archibald Wheeler, known for his work in nuclear physics and the theory of gravity, proposed the terms "black hole" and "wormhole".
As it turned out, there really are wormholes in the Schwarzschild and Reisner-Nordström spaces. From the point of view of a distant observer, they are not completely visible, like black holes themselves, and are just as eternal. But for a traveler who dared to penetrate beyond the horizon, the hole collapses so quickly that neither a ship, nor a massive particle, nor even a ray of light will fly through it.
In order, bypassing the singularity, to break through "to the light of God" - to the other mouth of the hole, it is necessary to move faster than light. And physicists today believe that superluminal speeds of movement of matter and energy are impossible in principle.
Wormholes and time loops
So, the Schwarzschild black hole can be considered as an impenetrable wormhole. The Reisner-Nordstrom black hole is more complicated, but also impassable.
However, it is not so difficult to come up with and describe traversable four-dimensional wormholes, choosing the desired type of metric (a metric, or metric tensor, is a set of quantities that are used to calculate four-dimensional distances-intervals between event points, which fully characterizes the geometry of space-time, and gravitational field). Traversable wormholes are, in general, geometrically even simpler than black holes: there should not be any horizons leading to cataclysms with the passage of time.
Time at different points can, of course, go at a different pace - but it should not infinitely accelerate or stop.
I must say that various black holes and wormholes are very interesting micro-objects that arise by themselves, as quantum fluctuations of the gravitational field (at lengths of the order of 10-33 cm), where, according to existing estimates, the concept of classical, smooth space-time is no longer applicable.
On such scales, there should be something similar to water or soap foam in a turbulent stream, constantly “breathing” due to the formation and collapse of small bubbles. Instead of calm empty space, we have mini-black holes and wormholes of the most bizarre and intertwining configurations appearing and disappearing at a frantic pace. Their sizes are unimaginably small - they are as many times smaller than the atomic nucleus, how much this nucleus is smaller than the planet Earth. There is no rigorous description of space-time foam yet, since a consistent quantum theory of gravity has not yet been created, but in general terms, the described picture follows from the basic principles of physical theory and is unlikely to change.
However, from the point of view of interstellar and intertemporal travel, wormholes of completely different sizes are needed: “I would like” a spaceship of reasonable size or at least a tank to pass through the neck without damage (it would be uncomfortable among tyrannosaurs without it, right?).
Therefore, to begin with, it is necessary to obtain solutions to the equations of gravity in the form of traversable wormholes of macroscopic dimensions. And if we assume that such a hole has already appeared, and the rest of the space-time has remained almost flat, then consider that there is everything - a hole can be a time machine, an intergalactic tunnel, and even an accelerator.
Regardless of where and when one of the mouths of a wormhole is located, the second one can be anywhere in space and at any time - in the past or in the future.
In addition, the mouth can move at any speed (within the limits of light) with respect to the surrounding bodies - this will not prevent the exit from the hole into the (practically) flat Minkowski space.
It is known to be unusually symmetrical and looks the same at all its points, in all directions and in any inertial frames, no matter how fast they move.
But, on the other hand, assuming the existence of a time machine, we are immediately faced with the whole "bouquet" of paradoxes such as - flew into the past and "killed grandfather with a shovel" before grandfather could become a father. Normal common sense suggests that this, most likely, simply cannot be. And if a physical theory claims to describe reality, it must contain a mechanism that prohibits the formation of such "time loops", or at least makes them extremely difficult to form.
GR, no doubt, claims to describe reality. Many solutions have been found in it that describe spaces with closed time loops, but as a rule, for one reason or another, they are recognized as either unrealistic or, let's say, “non-dangerous”.
Yes, very interesting solution Einstein's equations were pointed out by the Austrian mathematician K. Godel: this is a homogeneous stationary universe, rotating as a whole. It contains closed trajectories, traveling along which you can return not only to the starting point in space, but also to the starting point in time. However, the calculation shows that the minimum time length of such a loop is much longer than the lifetime of the Universe.
Traversable wormholes, considered as "bridges" between different universes, are temporary (as we said) to assume that both mouths open into the same universe, as loops appear immediately. What then, from the point of view of general relativity, prevents their formation - at least on macroscopic and cosmic scales?
The answer is simple: the structure of Einstein's equations. On their left side there are quantities that characterize the space-time geometry, and on the right - the so-called energy-momentum tensor, which contains information about the energy density of matter and various fields, about their pressure in different directions, about their distribution in space and about state of motion.
One can "read" Einstein's equations from right to left, stating that they are used by matter to "tell" space how to curve. But it is also possible - from left to right, then the interpretation will be different: geometry dictates the properties of matter, which could provide it, geometry, existence.
So, if we need the geometry of a wormhole, we will substitute it into Einstein's equations, analyze and find out what kind of matter is required. It turns out that it is very strange and unprecedented, it is called “exotic matter”. So, to create the simplest wormhole (spherically symmetric), it is necessary that the energy density and pressure in the radial direction add up to a negative value. Is it necessary to say that for ordinary types of matter (as well as for many known physical fields) both of these quantities are positive?..
Nature, as we see, has indeed put up a serious barrier to the emergence of wormholes. But this is how a person works, and scientists are no exception: if the barrier exists, there will always be those who want to overcome it ...
The work of theorists interested in wormholes can be conditionally divided into two complementary directions. The first, assuming in advance the existence of wormholes, considers the consequences that arise, the second tries to determine how and from what wormholes can be built, under what conditions they appear or can appear.
In the works of the first direction, for example, such a question is discussed.
Suppose we have a wormhole at our disposal, through which one can pass in a matter of seconds, and let its two funnel-shaped mouths "A" and "B" be located close to each other in space. Is it possible to turn such a hole into a time machine?
The American physicist Kip Thorne and his collaborators showed how to do this: the idea is to leave one of the mouths, "A", in place, and the other, "B" (which should behave like an ordinary massive body), to disperse to speed comparable to the speed of light, and then return back and brake near "A". Then, due to the SRT effect (deceleration of time on a moving body compared to a stationary one), less time will pass for the mouth “B” than for the mouth “A”. Moreover, the greater was the speed and duration of travel of the mouth "B", the greater will be the time difference between them.
This, in fact, is the same “twin paradox” well-known to scientists: a twin who returned from a flight to the stars turns out to be younger than his homebody brother ... Let the time difference between the mouths be, for example, half a year.
Then, sitting near the mouth of "A" in the middle of winter, we will see through the wormhole a vivid picture of the past summer and - really this summer and return, having passed through the hole through. Then we will again approach the funnel "A" (it, as we agreed, is somewhere nearby), once again dive into the hole and jump straight into last year's snow. And so many times. Moving in the opposite direction - diving into funnel "B", - let's jump half a year into the future ...
Thus, having performed a single manipulation with one of the mouths, we get a time machine that can be "used" constantly (assuming, of course, that the hole is stable or that we are able to maintain its "operability").
The works of the second direction are more numerous and, perhaps, even more interesting. This direction includes the search for specific models of wormholes and the study of their specific properties, which, in general, determine what can be done with these holes and how to use them.
Exomatter and dark energy
Exotic properties of matter that must be possessed construction material for wormholes, as it turns out, can be realized due to the so-called vacuum polarization of quantum fields.
This conclusion was recently reached by Russian physicists Arkady Popov and Sergey Sushkov from Kazan (together with David Hochberg from Spain) and Sergey Krasnikov from the Pulkovo Observatory. And in this case, vacuum is not a void at all, but a quantum state with the lowest energy - a field without real particles. Pairs of "virtual" particles constantly appear in it, which again disappear earlier than they could be detected by devices, but leave their very real trace in the form of some energy-momentum tensor with unusual properties.
And although the quantum properties of matter manifest themselves mainly in the microcosm, the wormholes generated by them (under certain conditions) can reach very decent sizes. By the way, one of the articles by S. Krasnikov has a "frightening" title - "The Threat of Wormholes." The most interesting thing about this purely theoretical discussion is that the real astronomical observations recent years seem to greatly undermine the positions of opponents of the possibility of the very existence of wormholes.
Astrophysicists, studying the statistics of supernova explosions in galaxies billions of light years away from us, concluded that our Universe is not just expanding, but is expanding at an ever-increasing speed, that is, with acceleration. Moreover, over time, this acceleration even increases. This is quite confidently indicated by the latest observations made with the latest space telescopes. Well, now is the time to remember the connection between matter and geometry in general relativity: the nature of the expansion of the Universe is firmly connected with the equation of state of matter, in other words, with the relationship between its density and pressure. If the matter is ordinary (with positive density and pressure), then the density itself falls over time, and the expansion slows down.
If the pressure is negative and equal in magnitude, but opposite in sign to the energy density (then their sum = 0), then this density is constant in time and space - this is the so-called cosmological constant, which leads to expansion with constant acceleration.
But for the acceleration to grow with time, and this is not enough - the sum of pressure and energy density must be negative. No one has ever observed such matter, but the behavior of the visible part of the Universe seems to signal its presence. Calculations show that this kind of strange, invisible matter (called "dark energy") in the present era should be about 70%, and this proportion is constantly increasing (unlike ordinary matter, which loses density with increasing volume, dark energy behaves paradoxically - the Universe is expanding, and its density is growing). But after all (and we have already talked about this), it is precisely such exotic matter that is the most suitable “building material” for the formation of wormholes.
One is drawn to fantasize: sooner or later, dark energy will be discovered, scientists and technologists will learn how to thicken it and build wormholes, and there - not far from the "dream come true" - about time machines and about tunnels leading to the stars ...
True, the estimate of the density of dark energy in the Universe, which ensures its accelerated expansion, is somewhat discouraging: if dark energy is distributed evenly, a completely negligible value is obtained - about 10-29 g/cm3. For an ordinary substance, this density corresponds to 10 hydrogen atoms per 1 m3. Even interstellar gas is several times denser. So if this path to the creation of a time machine can become real, then it will not be very, very soon.
Need a donut hole
Until now, we have been talking about tunnel-like wormholes with smooth necks. But GR also predicts another kind of wormholes - and in principle they do not require any distributed matter at all. There is a whole class of solutions to Einstein's equations, in which the four-dimensional space-time, flat far from the source of the field, exists, as it were, in duplicate (or sheets), and common to both of them are only a certain thin ring (the source of the field) and a disk, this ring limited.
This ring has a truly magical property: you can “wander” around it for as long as you like, remaining in “your own” world, but once you pass through it, you will find yourself in a completely different world, although similar to “your own”. And in order to go back, you need to go through the ring again (and from any side, not necessarily from the one you just left).
The ring itself is singular - the curvature of space-time on it turns to infinity, but all points inside it are quite normal, and the body moving there does not experience any catastrophic effects.
It is interesting that there are a great many such solutions - both neutral, and with an electric charge, and with rotation, and without it. Such, in particular, is the famous solution of the New Zealander R. Kerr for a rotating black hole. It most realistically describes black holes of stellar and galactic scales (the existence of which most astrophysicists no longer doubt), since almost all celestial bodies experience rotation, and when compressed, the rotation only accelerates, especially when collapsing into a black hole.
So, it turns out that rotating black holes are "direct" candidates for "time machines"? However, black holes that form in stellar systems are surrounded and filled with hot gas and harsh, deadly radiation. In addition to this purely practical objection, there is also a fundamental one related to the difficulties of getting out from under the event horizon to a new spatio-temporal “sheet”. But it is not worth dwelling on this in more detail, since, according to general relativity and many of its generalizations, wormholes with singular rings can exist without any horizons.
So there are at least two theoretical possibilities for the existence of wormholes connecting different worlds: burrows can be smooth and consist of exotic matter, or they can arise due to a singularity, while remaining passable.
Space and strings
Thin singular rings resemble other unusual objects predicted by modern physics - cosmic strings that were formed (according to some theories) in the early Universe when superdense matter cooled and its states changed.
They really do resemble strings, only extraordinarily heavy - many billions of tons per centimeter of length with a thickness of a fraction of a micron. And, as was shown by the American Richard Gott and the Frenchman Gerard Clement, several strings moving relative to each other at high speeds can be used to create structures containing time loops. That is, moving in a certain way in the gravitational field of these strings, you can return to the starting point before you flew out of it.
Astronomers have long been looking for this kind of space objects, and today there is already one “good” candidate - the CSL-1 object. These are two surprisingly similar galaxies, which in reality are probably one, only bifurcated due to the effect of gravitational lensing. Moreover, in this case, the gravitational lens is not spherical, but cylindrical, resembling a long thin heavy thread.
Will the fifth dimension help?
In the event that space-time contains more than four dimensions, the architecture of wormholes acquires new, previously unknown possibilities.
Thus, in recent years, the concept of "brane world" has become popular. It assumes that all observable matter is located on some four-dimensional surface (denoted by the term "brane" - a truncated word for "membrane"), and in the surrounding five or six-dimensional volume there is nothing but a gravitational field. The gravitational field on the brane itself (and this is the only one we observe) obeys the modified Einstein equations, and they have a contribution from the geometry of the surrounding volume.
So, this contribution is capable of playing the role of exotic matter that generates wormholes. Burrows can be of any size and still not have their own gravity.
This, of course, does not exhaust the whole variety of "constructions" of wormholes, and the general conclusion is that, for all the unusual nature of their properties and for all the difficulties of a fundamental, including philosophical, nature, to which they can lead, their possible existence is worth treated with full seriousness and due attention.
It cannot be ruled out, for example, that large holes exist in interstellar or intergalactic space, if only because of the concentration of the very dark energy that accelerates the expansion of the Universe.
There is no unequivocal answer to the questions - how they can look for an earthly observer and whether there is a way to detect them - yet. Unlike black holes, wormholes may not even have any noticeable attraction field (repulsion is also possible), and therefore, one should not expect noticeable concentrations of stars or interstellar gas and dust in their vicinity.
But assuming that they can “short-circuit” regions or epochs that are far from each other, passing the radiation of the luminaries through themselves, it is quite possible to expect that some distant galaxy will seem unusually close.
Due to the expansion of the Universe, the farther away the galaxy, the greater the shift of the spectrum (toward the red side) its radiation comes to us. But when looking through a wormhole, there may not be any redshift. Or will be, but - another. Some of these objects can be observed simultaneously in two ways - through the hole or in the "usual" way, "past the hole."
Thus, the sign of a cosmic wormhole can be as follows: the observation of two objects with very similar properties, but at different apparent distances and with different redshifts.
If wormholes are nevertheless discovered (or built), the area of philosophy that deals with the interpretation of science will face new and, I must say, very difficult tasks. And for all the seeming absurdity of time loops and the complexity of the problems associated with causality, this area of \u200b\u200bscience, in all likelihood, sooner or later will figure it all out somehow. Just as at one time "handled" with conceptual problems quantum mechanics and Einstein's theory of relativity...
Kirill Bronnikov, Doctor of Physical and Mathematical Sciences
