Time travel is taken no more seriously than the imagination of science fiction writers. In fact, this is a unique phenomenon - the direct derivation of equations that describe the physics of our world. What can make such travel a reality is in our material.
Our columnist and physicist Daria Zaremba believes that striving to translate the idea of time travel into practice in practice can contribute to scientific progress and unconventional discoveries. After all, this is how exotic matters, photonic rockets and new properties of astrophysical objects are born. She compiled a dictionary of mechanisms that could theoretically send humans on a journey through time.
B - Warp drive
A warp drive is a hypothetical technology for traveling to the future, in which, due to the deformation of the canvas of space-time, the effect of movement is created at a speed exceeding the speed of light.
Imagine that you are lying on a carpet and you need to, without moving, be beyond its front edge. One possible solution is to crumple the front of the carpet under you and then pull out by pulling on the back. Approximately the same can be done with the "carpet" of space-time: this is the principle used by a hypothetical starship powered by a warp drive.
He compresses the space in front of him and expands it behind, creating the illusion of movement at a speed several times the speed of light. In this case, there will be no tidal forces inside the spaceship, and the actual acceleration will be equal to zero.
The crew can easily sip cocktails from straws or even relax in the bubbling jacuzzi, while the starship will madly "rake" space-time under itself, taking travelers into the bowels of the Galaxy.
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One model of time machine based on warp drive technology is the Alcubierri Bubble, named after its Mexican inventor, Miguel Alcubierri.
The whole physics of traveling to the future on such a "unit" is based on the postulates of the Special Theory of Relativity, which say that after the bubble stops, the crew will find the outside world aged for many years, because for them the time inside the bubble slowed down.
In this case, there will be no violations of the principle of the absoluteness of the speed of light, because in this case, movement faster than light does not mean that the bubble itself moves at such a speed, but that the bubble will reach its destination faster than a ray of light moving outside the bubble.
But to create such an effect of deformation of space-time, a special matter is required, exhibiting unconventional physical properties - “exotic matter”, which will create a shell (bubble) around the spaceship and provide the very “raking” of space. While progress in the production of such matter has not been observed, reasoning about the suitability of a warp drive in practice is rather limited.
The theoretical mechanism of the warp drive.
D - Gravity
Gravity - in a broad sense - a manifestation of the curvature of space-time, in a narrow sense - the force that attracts objects.
The well-known employee of the patent office - Albert Einstein helped to open the gates to the world of "time management". To do this, he needed to establish only two things: first - that space and time are inextricably linked, second - that massive bodies with their mass are capable of deforming this space-time canvas, creating gravity.
In other words, Einstein proved that the Earth (like other similar massive bodies), "bending" the "trampoline" of space with its mass (creating circular orbits around itself), at the same time bends time, namely, slows down its course as it approaches to the surface (and deeper).
The revolutionary nature of this idea was that for the first time time was no longer perceived as an absolute value in classical mechanics. It was found that the wristwatch of a miner and a climber ticks differently (although it is imperceptible on such a scale), a twin brother who lives by the river is younger (again, not significantly) his brother who lives in a house on a mountain, and the core of the Earth is younger its surface.
Thus, a way was found to slow down "one's" time and thereby travel to the future, approaching, for example, a body whose mass is many times greater than the mass of the Earth, and then return to the home planet and contemplate the world of the future.
D - Black hole
A black hole is an object in space that has collapsed under the influence of its own gravitational forces to such an extent that even electromagnetic radiation cannot escape from its gravitational field.
The best object to travel to the future, if you choose the gravitational mechanism for influencing time, is definitely a black hole.
To scroll through such a journey, you will need to go into space directly to her. Descend there on a heavy-duty cable, but only so as not to cross the event horizon - the border in a black hole, followed by "spaghettification" - stretching and tearing of all objects that fall there under the influence of singular gravity.
As long as you hang in this position, time slows down for you. At the same time, it is completely imperceptible to yourself, because everything in your frame of reference slows down: metabolism, biological clock, heartbeat, movement of electrons in atoms, and so on.
But if in some miraculous way you could spy on earthlings from your black hole, then it would seem to you that they move with a tenfold accelerated rate! And they, looking at you, would think that they are watching a video with a slow-motion effect.
Thus, your one day near a black hole corresponds to almost three years of life on Earth (it also depends on how close you are to the horizon - time stops at it at all). And when you, hanging so little, return to your home planet, you will notice that the world is old enough in your absence. Voila - you are in the future!
The mechanism of travel to the future through the effect of time dilation near the event horizon of a black hole. The cones in the image are "light cones" - the hypersurface of space-time that limits the areas of the future and the past relative to a given event. The tilt of the cone demonstrates the change in time for the astronaut. More details about the structure of the light cone in the image below:
Light cone.
In addition to being used as a "gravitational moderator", rotating black holes can be useful for travel into the past. The fact is that, due to their gravitational field, they are able to create so-called "closed timelike curves", moving along which, the traveler can move back in time.
But the “usefulness” of black holes as time machines does not end there either. According to the English physicist and mathematician Roger Penrose, some black holes - namely those with charge or rotation - can serve as "gates" to the universes of the future.
According to the Penrose diagram, beyond the event horizon, spatial coordinates are swapped with temporal ones.
The unusual thing about black holes with a charge or with a moment of rotation is that they should have two such event horizons. Accordingly, the replacement of spatial and temporal coordinates will occur twice.
It turns out that, jumping into such a hole, the astronaut will first overcome one event horizon - the point of no return, and then the second, which will be followed by the universe of the future. But such daredevils are unlikely to be found, so the hypothesis remains shaky.
З - Closed timelike curve
A closed time-like curve is a world line (a curve in space-time that describes the movement of a body) in the structure of space-time, which returns an object to an event (a point in space-time) that it has already passed.
ZVK - one of the mathematical solutions of the equation of General Relativity. It is this physical phenomenon that is most often interpreted as the main mechanism of travel into the past.
According to gravitational equations, a closed time-like curve can be formed where a massive object or a powerful gravitational field moves and literally "pulls" space-time behind it. That is why, for example, only rotating black holes can create ZVK - the static gravitational field is not able to form them.
Moving along the CEC, the object returns to the same spatial coordinates from which it left, but with the time of arrival before its exit. That is, it actually makes a trip into the past.
L - Laser
A laser (from light amplification by stimulated emission of radiation) is a device that emits an intense monochromatic narrow electromagnetic beam of long-range propagation.
Due to its characteristics, the laser beam has an increased energy density, which can even exceed the energy density of a nuclear explosion (with a maximum reduction in the beam width).
The author of one of the most simple and sophisticated time machines in implementation is the theoretical physicist of the University of Connecticut, Ronald Mallett.
The idea of creating such a device came from the professor in early childhood, when his father unexpectedly died of a heart attack at the age of 33. The professor has repeatedly admitted that everything that he has achieved in the field of science is based on his endless love for his father and the desire to see him again.
For many years, Ronald worked on his model of a time machine, hiding it from colleagues and "hiding behind" the study of black holes. And at the age of about 70 he managed to get the desired result.
Mallet's model is based on the energy of a laser beam. And its creation was facilitated by the most famous Einstein's equation - E = mc2.
From this legendary formula, it follows that mass is equivalent to energy, which means that the space-time canvas should also be distorted under the influence of high energies.
Now let's talk about the energy of electromagnetic radiation (in the narrow sense - light). It is transferred, as you know, by means of photons - "portions" of electromagnetic radiation. The latter, in turn, have energy, which can be calculated using a special formula: E = hv, where h is the proportionality coefficient (Planck's constant), and nu is the photon frequency.
Thus, it turns out that a beam of light can also create a gravitational field, since it has energy. It was this thought that laid the foundation for the scientific works of Ronald Mallet.
The scientist took a powerful laser beam and with the help of a system of mirrors made it circulate in a circle, creating a so-called laser ring. The idea is that the space-time canvas inside this ring is distorted, twisting like a whirlpool.
We observe about the same when stirring tea with a spoon. Due to such "manipulations", along with space, time inside the ring closes into a loop, which makes it possible to move objects that have got inside into the past.
The geometry of the Ronald Mallett time machine.
According to the professor, such a unit will be able to send encoded messages to the past, transferring particles in time. True, such a message will be able to travel only until the creation of this time machine: it will serve both as a transmitter and a receiver.
Thus, it will be possible, for example, to warn people from the past about impending disasters. With regards to the movement of macro-objects in this way, here scientists will have, as they say, sweat.
But such a time machine is also not without its "pitfalls". For example, the theory was criticized by Allen Everett and Ken Olum for incorrectly chosen space-time geometry for the formation of the expected closed timelike curve (TLC).
Scientists were also embarrassed by the amount of energy required: according to their calculations, to provoke SEC in space-time, the diameter of the laser ring should exceed the size of the visible Universe. And although Ronald tried to reduce the amount of energy required by slowing the light output of his laser, the slow beams proved useless in the study.
O - negative energy
Negative energy is one of the varieties of "exotic matter" (or rather, "energy"), obtained through the Casimir effect, which can be used for travel into the past, as well as for maintaining wormholes.
In a simplified form, the "recipe" for obtaining such energy can be described as follows:
Take two uncharged metal platinum and place them in a vacuum. We bring the plates together as much as possible, but so that they do not touch.
We observe the attraction of the plates to each other. This is due to the fact that the vacuum actually has energy - although it does not contain particles familiar to us, pairs of virtual particles and antiparticles constantly arise and annihilate (mutually annihilate) in it.
Such processes generate pressure. But because we left a tiny gap between the plates, the concentration of antiparticle particles there is much less than in the space around. Therefore, stronger pressure from the outside begins to bring the plates closer together.
While pulling in, the plates reduce the vacuum energy between them below the normal zero point, thus creating a space of negative energy.
Casimir effect.
The phenomenon of the appearance of negative energy as a result of such an experiment is called the Casimir effect - in honor of the Dutch physicist Hendrik Casimir. Such energy can potentially cause the space-time curvature necessary for travel into the past.
However, the amount of negative energy generated in this way is negligible compared to how much it is needed for the proper deformation effect. But, as scientists note, the development of a mechanism is already a good progress.
R - Relativistic effects
Relativistic effects are physical phenomena observed when an object moves at near-light speeds. They are the object of study in relativistic mechanics based on the Special theory of relativity.
Among all the relativistic effects, such as an increase in mass, a decrease in the length of an object, the most interesting and practical, from the point of view of use in time travel, is the effect of time dilation.
According to the Special Theory of Relativity, for a body moving at a speed comparable to the speed of light, time slows down relative to bodies at rest.
This theory found its experimental confirmation in 1971, when two desperate physicists Hafele and Keating flew around the world twice with four atomic clocks on board. Upon landing, they discovered that the travel watch was indeed lagging behind the remaining hours at the United States Naval Observatory.
As a time travel opportunity, it might look like this. Let's say you've found a way to accelerate your spaceship to 99.5 percent the speed of light. In this case, you can get to one of the nearest stars in, say, a minute. Four years will pass on Earth.
Thus, on the way back and forth, you will spend two minutes of your subjective time - due to the effect of time dilation in the ship, and when you return to Earth, you will find it eight years older.
By the way, bless the great Einstein every time you search for a nearby burger shop in online maps: if GPS satellites did not take into account these speed decelerations of time (and they move at an orbital speed of 14,000 km / h), the marker of the location you need would be displayed with a kilometer error …
However, accelerating to a speed close to the speed of light is not an easy task. Einstein established that the speed of light is the maximum possible speed of movement and can only be achieved by something without mass. The greater the mass of an object, the less likely it is to reach near-light speed.
One of the reasons for this is the colossal increase in mass when reaching near-light speeds. That is why, for example, photons, particles of light that do not have a rest mass, can move with such a speed.
Although today there are ideas for the creation of so-called photonic rockets (like, for example, the rocket of the Norwegian Professor Haug), acceleration to such speeds is incompatible with life for the crew due to excessive overloads. So for now, we are talking about this way of traveling to the future only in theory.
H - Wormhole
A wormhole, or wormhole, is a theoretical passage in the structure of spacetime that connects two distant events (points in spacetime) in the universe.
Wormholes are like traversable black holes. They also have an event horizon, but only after passing through it does it not tear you apart under the influence of strong gravity, but only "spits out" from the opposite side, already at another point in space-time (the main thing is not to confuse a black hole with a mole, otherwise instead of traveling to another time you will move "to the next world").
Such entrances and exits are called mouths, and they are connected by a throat-tunnel passing through the Universe. A wormhole can connect both past and future events.
There is an assumption that our entire Universe is strewn with wormholes. Only now they exist in the form of "quantum foam" at incredibly microscopic levels: they are as many times smaller than the atomic nucleus, as much as the nucleus is smaller than the planet Earth (we are talking about the so-called foam of John Wheeler's space-time).
And there is a hypothesis that in the process of the expansion of the universe, these microscopic wormholes could have increased to a noticeable size.
Scientists also suggest that black holes may be the "entrance mouth" for some wormholes. According to the famous astrophysicist-theorist and cosmologist Igor Novikov, the nuclei of some galaxies may not be supermassive black holes, but the entrance to a wormhole.
That is why, as the professor notes, when searching for wormholes, one should first of all look at the center of the galaxy. According to the scientist, it is quite possible that some wormholes can connect events (points in space-time) of two different universes.
The problem with a wormhole, however, is that it collapses before anything can pass through it. And in order to make a wormhole passable and more or less stable, a field with negative energy density is needed, which will keep its mouths open.
The antigravity created by such matter will act against the forces of gravity ("squeezing") of the wormhole, and thus it will be possible to force it to stay longer in a passable state, and at the same time to increase its size.
The popular American physicist and astronomer Kip Thorne proposed a mechanism for maintaining a wormhole by placing parallel conducting plates on opposite sides of it.
This, according to the Casimir effect, will create negative energy on both sides, which will prevent the burrow from collapsing. At the same time, under the influence of negative energy, the wormhole will expand, which is very useful if you are used to traveling in time on an impressive spacecraft (continuing Thorne's hypothesis, astrophysicist from Cambridge University Luke Butcher proposed a more effective way to create negative energy inside a wormhole by generating its very wormhole, without the use of plates).
However, the amounts of this negative energy to maintain a wormhole must be enormous. At the same time, calculations show that this number has its own limit, which reassures science fiction writers a little.
Modeling by Kip Thorn of the appearance of the mouth of a wormhole depending on its length and lensing.
E - Exotic matter
Exotic matter is matter that in one way or another differs from the classical one and has “exotic” properties. This will be considered a matter that has a negative mass, or is capable of moving at superluminal speed, or consisting of particles that are different from our usual baryons (that is, protons and neutrons) - like dark matter, for example.
In the theory of time travel, exotic matter plays one of the key roles in realizing travel to the past. Theorists say that if an exotic substance is created or discovered that can deform space-time in an unconventional way, a time loop can form in the structure of the space-time continuum, suitable for moving backward in time.
This is evidenced, for example, by the author of one of the most accurate mathematical models of the time machine - Traversable acausal retrograde domains in spacetime (TARDIS) - Canadian mathematician and physicist Ben Tippett:
“The curvature effect of space-time with which we are most familiar is gravity: it pulls us towards the center of the Earth, and the planets towards the Sun.
But in Einstein's theory, the curvature of space-time can generate much more diverse effects: rotating massive bodies pull nearby objects in the direction of their rotation; The universe is expanding rapidly; massive objects can cause gravitational waves recently measured by the Ligo observatory,”the scientist notes.
According to him, Einstein's theory allows you to connect different types of curvature of space-time with a different nature of the matter involved. "Our spacetime geometry was designed to allow time travel, and Einstein's equation tells us the type of matter that will bend the universe in this way with its weight: exotic matter in particular."
So, according to Tippet's model, the time machine should be something like a "box" (a physically tangible structure) surrounded by exotic matter.
Moreover, negative energy density should impart “exoticism” to this matter: in other words, it should create something like an anti-gravitational field and bend space-time in an unusual way for us - so that the time line closes into a ring, forming a closed time-like curve.
Ben Tippett's TARDIS movement in space-time - along a closed timelike curve.
“It is enough to distribute it on the outside of the 'machine', and the universe will bend as desired in response to its presence,” explains Ben.
Ben presented all the calculations proving the possibility of creating such a time machine in his article published on March 31, 2017 in the journal Classical and Quantum Gravity.
Exotic matter with anti-gravity properties is also needed to maintain the permeability of wormholes. Today, the most suitable type of exotic matter is considered to be negative energy generated due to the Casimir effect.
Time travel doesn't seem so fantastic to you? In the next article by Daria Zaremba, read about what prevents humanity from dreaming about these displacements - about refuting thought experiments, paradoxes of travel into the past and their solutions.
Daria Zaremba