That can move faster than light. How NASA scientists are going to exceed the speed of light in space. Simple examples of FTL travel
Physicists have discovered that particles of light (photons) can live for about 1 trillion years, and after decay, they in turn emit very light particles that can travel faster than light! Over time, many particles naturally decay. For example, unstable radioactive atoms at a certain moment decay into small particles and release a burst of energy.
Just recently, scientists were convinced that photons do not decay, since they were believed to have no mass. However, scientists currently assume that photons have a mass, it is just so small that it cannot be measured with modern instruments.
The current upper limit for the mass of a photon is so small that it is less than one billionth, billionth, billionth of the mass of a proton. Based on this indicator, scientists have calculated that a photon in the visible spectrum can live for about 1 trillion years. However, this extremely long lifespan does not apply to all photons, it is calculated on average. There is a possibility that some photons live very shortly. Our Big Bang Universe is currently about 13.7 billion years old. And currently ongoing research projects are designed not only to measure the afterglow of the Big Bang, but also to possibly detect signs of early decay of photons.
If a photon is broken, as a result of the decay, even lighter particles should be released, those that are able to travel in our Universe faster than the speed of light. These ghostly particles (neutrinos) very rarely interact with ordinary matter. Countless streams of neutrinos rush every fraction of a second not only through space, stars and bodies, but also through every person living on Earth, without affecting our matter.
When decaying, each photon emits two light neutrinos, which, being lighter than light, move faster than photons. The discovery of neutrinos would seem to violate Einstein's theory of relativity that nothing can travel faster than light, but this is not the case, since the theory is based on the fact that a photon has no body mass. And the theory says that no particle can move faster than a massless particle.
In addition, Einstein's theory of relativity suggests that particles move extremely fast while in warped time space. That is, if they had consciousness, they would have the impression that everything that happens around them is in a very “slow motion” mode. This means that in our time space, photons should live for about 1 trillion years, and in their time stream - only about three years.
Sergey Vasilenkov
A group of scientists from the OPERA experiment, in collaboration with the European Organization for Nuclear Research (CERN), published the sensational results of an experiment to overcome the speed of light. The results of the experiment refute the special theory of relativity of Albert Einstein, on which the whole modern physics... The theory says that the speed of light is 299 792 458 m / s, and elementary particles cannot move faster than the speed of light.
Nevertheless, scientists recorded an excess of 60 nanoseconds by a neutrino beam while traveling 732 km. It happened on September 22 during an experiment conducted by an international group of nuclear physicists from Italy, France, Russia, Korea, Japan and other countries.
The experiment proceeded as follows: the proton beam was accelerated in a special accelerator and hit with it in the center of a special target. This is how mesons were born - particles composed of quarks.
When mesons decay, neutrinos are born, ”RAS Academician Valery Rubakov, Chief Researcher at the RAS Institute for Nuclear Research, explained to Izvestia. - The beam is located so that the neutrino flies 732 km and falls into the Italian underground laboratory in Gran Sasso. It contains a special detector that records the speed of the neutrino beam.
The research results split the scientific world. Some scientists refuse to believe the results.
What was done at CERN is impossible from the modern point of view of physics, - Academician of the Russian Academy of Sciences Spartak Belyaev, scientific director of the Institute of General and Nuclear Physics, told Izvestia. - It is necessary to check this experiment and its results - perhaps they were just wrong. All the experiments carried out before this fit into the existing theory, and because of one experiment carried out once, it is not worth raising a panic.
Academician Belyaev at the same time admits: if it is possible to prove that the neutrino can move faster than the speed of light, it will be a coup.
We will then have to break all physics, ”he said.
If the results are confirmed, this is a revolution, - academician Rubakov agrees. - It's hard to say how this will turn out for the townsfolk. In general, it is, of course, possible to change the special theory of relativity, but it is extremely difficult to do this, and what kind of theory will crystallize as a result is not entirely clear.
Rubakov noted that the report says that over the three years of the experiment, 15 thousand events were recorded and measured.
The statistics are very good, and an international group of reputable scientists took part in the experiment, - sums up Rubakov.
Academicians stressed that the world regularly attempts to experimentally refute the special theory of relativity. but positive results none of them have given it so far.
But it turned out that it is possible; now they believe that we will never be able to travel faster than light ... ". But in fact, it is not true that someone once believed that it is impossible to move faster than sound. Long before supersonic aircraft appeared, it was already known, that bullets fly faster than sound. guided supersonic flight, and that was the mistake. The SS movement is another matter entirely. It was clear from the outset that supersonic flight was hampered by technical problems that simply had to be resolved. But it is completely unclear whether the problems that hinder the SS movement can ever be resolved. The theory of relativity has a lot to say about this. If SS travel or even signal transmission is possible, causality will be disrupted, and completely incredible conclusions will follow from this.
We will first discuss simple cases of STS motion. We mention them not because they are interesting, but because they come up again and again in discussions of the SS movement and therefore have to be dealt with. Then we will discuss what we consider to be difficult cases of STS movement or communication and consider some of the arguments against them. Finally, we look at some of the more serious speculations about the true STS movement.
Simple SS movement
1. The phenomenon of Cherenkov radiation
One way to travel faster than light is to slow down the light itself first! :-) In a vacuum, light flies at a speed c, and this value is a world constant (see the question Is the speed of light constant), and in a denser medium like water or glass it slows down to the speed c / n, where n is the refractive index of the medium (1.0003 for air; 1.4 for water). Therefore, particles can move in water or air faster than light moves there. As a result, Vavilov-Cherenkov radiation arises (see question).
But when we talk about the SS motion, we, of course, mean the excess over the speed of light in a vacuum c(299 792 458 m / s). Therefore, the phenomenon of Cherenkov cannot be considered an example of the SS movement.
2.From a third party
If the rocket BUT flies away from me at a speed 0.6c to the west and the other B- from me with speed 0.6c east, then the total distance between BUT and B in my frame of reference increases at a rate 1,2c... Thus, the apparent relative velocity greater than c can be observed "from the third side".
However, this speed is not what we usually mean by relative speed. Real rocket speed BUT regarding the rocket B is the rate of growth of the distance between missiles, which is observed by an observer in a rocket B... Two velocities must be added according to the relativistic formula for the addition of velocities (see the question How to add velocities in partial relativity). In this case, the relative speed is approximately 0.88c, that is, it is not superluminal.
3. Shadows and bunnies
Think about how fast the shadow can move? If you create a shadow on a distant wall from your finger from a nearby lamp, and then move your finger, then the shadow moves much faster than your finger. If the finger moves parallel to the wall, then the speed of the shadow will be in D / d times the speed of the finger, where d is the distance from the finger to the lamp, and D- the distance from the lamp to the wall. And even higher speed can turn out if the wall is located at an angle. If the wall is very far away, then the movement of the shadow will lag behind the movement of the finger, since the light will still have to travel from the finger to the wall, but still the speed of the movement of the shadow will be as many times higher. That is, the speed of the shadow is not limited by the speed of light.
In addition to shadows, bunnies can also move faster than light, for example, a speck from a laser beam aimed at the moon. Knowing that the distance to the Moon is 385,000 km, try to calculate the speed of the light by moving the laser slightly. You can also think of a sea wave slanting against the shore. How fast can the point at which the wave breaks move?
Similar things can happen in nature. For example, a light beam from a pulsar can sweep through a cloud of dust. A bright flash creates an expanding shell of light or other radiation. When it crosses the surface, a ring of light is created that grows faster than the speed of light. In nature, this occurs when an electromagnetic pulse from lightning reaches the upper atmosphere.
These were all examples of things moving faster than light, but which were not physical bodies. With the help of a shadow or a bunny, it is impossible to transmit an SS message, so communication cannot be faster than light. And again, this, apparently, is not what we want to understand by ST motion, although it becomes clear how difficult it is to determine what exactly we need (see the question Superluminal scissors).
4. Solids
If you take a long, hard stick and push one end of it, does the other end move right away or not? Is it possible to carry out the SS transmission of the message in this way?
Yes it was would can be done if such rigid bodies existed. In reality, the impact of a blow to the end of the stick propagates along it at the speed of sound in a given substance, and the speed of sound depends on the elasticity and density of the material. Relativity imposes an absolute limit on the possible hardness of any bodies so that the speed of sound in them cannot exceed c.
The same thing happens if you sit in the field of attraction, and first hold the string or pole vertically by the upper end, and then release it. The point that you let go will start moving immediately, and the lower end cannot begin to fall until the influence of the release reaches it at the speed of sound.
It is difficult to formulate a general theory of elastic materials within the framework of relativity, but the main idea can be shown using the example of Newtonian mechanics. The equation of longitudinal motion of an ideally elastic body can be obtained from Hooke's law. In variables, masses per unit length p and Young's modulus of elasticity Y, longitudinal displacement X satisfies the wave equation.
Plane wave solution moves at the speed of sound s, and s 2 = Y / p... This equation does not imply the possibility of a causal influence spreading faster. s... Thus, relativity imposes a theoretical limit on the magnitude of elasticity: Y < pc 2... There are practically no materials that even come close to it. By the way, even if the speed of sound in the material is close to c, matter by itself is not at all obliged to move with relativistic velocity. But how do we know that, in principle, there can be no substance that overcomes this limit? The answer is that all substances are composed of particles, the interaction between which obeys the standard model of elementary particles, and in this model no interaction can travel faster than light (see below about quantum field theory).
5. Phase velocity
Look at this wave equation:
He has solutions of the form:
These solutions are sine waves moving at a speed
But this is faster than light, so we have the equation of the tachyon field in our hands? No, this is just the usual relativistic equation for a massive scalar particle!
The paradox will be resolved if you understand the difference between this speed, also called the phase speed v ph from another speed called group v gr which is dated by the formula,
If the wave solution has a frequency spread, then it will take the form of a wave packet that moves with a group speed not exceeding c... Only wave crests move with phase velocity. It is possible to transmit information with the help of such a wave only with a group velocity, so the phase velocity gives us another example of superluminal velocity, which cannot carry information.
7. Relativistic rocket
A dispatcher on Earth is watching a spacecraft departing at a speed of 0.8 c... According to the theory of relativity, even after taking into account the Doppler shift of the signals from the ship, he will see that the time on the ship is slowed down and the clock there goes slower by a factor of 0.6. If he calculates the quotient of dividing the distance traveled by the ship by the elapsed time measured by the ship's clock, then he will receive 4/3 c... This means that the passengers on the spacecraft travel through interstellar space at an effective speed greater than the speed of light they would have received if it were measured. From the point of view of the ship's passengers, interstellar distances are subject to Lorentzian contraction by the same factor of 0.6, and therefore they must also admit that they cover the known interstellar distances at a rate of 4/3 c.
This is a real phenomenon and, in principle, it can be used by space travelers to overcome huge distances during their life. If they accelerate with a constant acceleration equal to the acceleration of gravity on Earth, then they will not only have an ideal artificial gravity on their ship, but they will still have time to cross the Galaxy in just 12 of their years! (see the question What are the equations of a relativistic rocket?)
However, this is not a real STS movement either. The effective speed is calculated from distance in one frame of reference and time in another. This is not real speed. Only the passengers on the ship benefit from this speed. The dispatcher, for example, will not have time in his life to see how they fly a gigantic distance.
Difficult cases of SS movement
9. Paradox of Einstein, Podolsky, Rosen (EPR)
10. Virtual photons
11. Quantum tunneling
Real Candidates for SS Travelers
This section provides speculative, but serious assumptions about the possibility of FTL travel. These will not be the things that are usually posted in the FAQ, as they raise more questions than they answer. They are presented here mainly to show that serious research is being carried out in this direction. Only a brief introduction is given in each direction. More detailed information can be found on the Internet.
19. Tachyons
Tachyons are hypothetical particles that locally travel faster than light. To do this, they must have an imaginary mass, but their energy and momentum must be positive. It is sometimes thought that such SS particles should be impossible to detect, but in fact, there is no reason to think so. Shadows and bunnies tell us that stealth does not yet follow from the SS movement.
Tachyons have never been observed and most physicists doubt their existence. Somehow it was stated that experiments were carried out to measure the mass of neutrinos emitted during the decay of Tritium, and that these neutrinos were tachyonic. This is highly doubtful, but still not excluded. There are problems in tachyon theories, since from the point of view of possible violations of causality, they destabilize the vacuum. It may be possible to bypass these problems, but then it will be impossible to use tachyons in the SS message we need.
The truth is that most physicists consider tachyons a sign of error in their field theories, and interest in them on the part of the broad masses is fueled mainly by science fiction (see Tachyon's article).
20. Wormholes
The most famous hypothesized possibility of SS travel is the use of wormholes. Wormholes are tunnels in space-time that connect one place in the universe to another. It is possible to travel along them between these points faster than light would do its usual way. Wormholes are a phenomenon of classical general relativity, but to create them, you need to change the topology of space-time. The possibility of this can be included in the theory of quantum gravity.
To keep the wormholes open requires huge amounts of negative energy and. Misner and Thorn suggested that the large-scale Casimir effect can be used to generate negative energy and, while Visser proposed a solution using space strings. All of these ideas are highly speculative and may simply be unrealistic. An unusual substance with negative energy may not exist in the form necessary for the phenomenon.
Thorne discovered that if wormholes can be created, they can be used to create closed time loops that make time travel possible. It has also been suggested that the multivariate interpretation of quantum mechanics suggests that time travel will not cause any paradoxes, and that events will simply unfold differently when you enter the past. Hawking says that wormholes can simply be unstable and therefore not applicable in practice. But the topic itself remains a fruitful area for thought experiments, allowing you to figure out what is possible and what is not possible on the basis of both known and assumed laws of physics.
refs:
W. G. Morris and K. S. Thorne, American Journal of Physics 56
,
395-412 (1988)
W. G. Morris, K. S. Thorne, and U. Yurtsever, Phys. Rev. Letters 61
, 1446-9 (1988)
Matt Visser, Physical Review D39, 3182-4 (1989)
see also "Black Holes and Time Warps" Kip Thorn, Norton & co. (1994)
For an explanation of the multiverse see, "The Fabric of Reality" David Deutsch, Penguin Press.
21. Motors-deformers
[I have no idea how to translate this! Original warp drive. - approx. translator;
translated by analogy with the article on Membrane]
The deformer could be a mechanism for twisting spacetime so that an object can travel faster than light. Miguel Alcabier became famous for developing the geometry that describes such a deformer. The distortion of spacetime makes it possible for an object to travel faster than light while remaining on a time-like curve. The obstacles are the same as when creating wormholes. To create a deformer, you need a substance with negative energy density and. Even if such a substance is possible, it is still unclear how it can be obtained and how to make the deformer work with it.
ref M. Alcubierre, Classical and Quantum Gravity, 11
, L73-L77, (1994)
Conclusion
First, it turned out to be difficult to define at all what the SS travel and the SS message mean. Many things, such as shadows, perform an STS division, but in such a way that it cannot be used, for example, to transmit information. However, there are also serious possibilities for real SS movement, which are proposed in the scientific literature, but their implementation is not yet technically possible. The Heisenberg Uncertainty Principle makes it impossible to use the apparent STS motion in quantum mechanics. In general relativity there are potential means of STS motion, but they may not be possible to use. It seems that it is extremely unlikely that in the foreseeable future, or in general, technology will be able to create spaceships with SS engines, but it is curious that theoretical physics, as we now know it, does not permanently close the door for SS movement. The SS movement in the style of science fiction novels is apparently completely impossible. For physicists, the question is interesting: "why, in fact, is it impossible, and what can be learned from this?"
Doctor of Technical Sciences A. GOLUBEV.
In the middle of last year, a sensational report appeared in magazines. A group of American researchers found that a very short laser pulse travels in a specially selected medium hundreds of times faster than in a vacuum. This phenomenon seemed absolutely incredible (the speed of light in a medium is always less than in a vacuum) and even gave rise to doubts about the validity of the special theory of relativity. Meanwhile, a superluminal physical object - a laser pulse in an amplifying medium - was first discovered not in 2000, but 35 years earlier, in 1965, and the possibility of superluminal motion was widely discussed until the early 1970s. Today the discussion around this strange phenomenon has flared up with renewed vigor.
Examples of "superluminal" motion.
In the early 1960s, high-power short light pulses began to be obtained by passing a laser flash through a quantum amplifier (medium with inverse population).
In the amplifying medium, the initial region of the light pulse causes stimulated emission of the atoms of the amplifier medium, and its final region causes the absorption of energy by them. As a result, it will seem to the observer that the pulse is moving faster than light.
Lijun Wong's experiment.
A light beam passing through a prism made of a transparent material (for example, glass) is refracted, that is, undergoes dispersion.
A light pulse is a set of vibrations of different frequencies.
Probably everyone - even people far from physics - knows that the maximum possible speed the movement of material objects or the propagation of any signals is the speed of light in a vacuum. It is denoted by the letter with and is almost 300 thousand kilometers per second; exact value with= 299 792 458 m / s. The speed of light in a vacuum is one of the fundamental physical constants. Impossibility to reach speeds exceeding with, follows from Einstein's special theory of relativity (SRT). If it were possible to prove that signals can be transmitted at superluminal speeds, the theory of relativity would fall. So far, this has not happened, despite numerous attempts to refute the ban on the existence of speeds greater than with... However, in recent experimental studies, some very interesting phenomena have been discovered, indicating that under specially created conditions, superluminal velocities can be observed without violating the principles of the theory of relativity.
To begin with, let us recall the main aspects related to the problem of the speed of light. First of all: why is it impossible (under normal conditions) to exceed the light limit? Because then the fundamental law of our world is violated - the law of causality, according to which the effect cannot outstrip the cause. No one has ever watched, for example, that first a bear fell dead, and then a hunter fired. At speeds exceeding with, the sequence of events is reversed, the tape of time is rewound. This is easy to verify from the following simple reasoning.
Let's suppose that we are on some kind of space miracle ship, moving faster than light. Then we would gradually catch up with the light emitted by the source at earlier and earlier points in time. First, we would catch up with the photons emitted, say, yesterday, then the ones emitted the day before yesterday, then a week, a month, a year ago, and so on. If the light source were a mirror reflecting life, then we would first see the events of yesterday, then the day before yesterday, and so on. We could see, say, an old man who gradually turns into a middle-aged man, then into a young man, into a youth, into a child ... That is, time would turn back, we would move from the present to the past. The causes and effects would be reversed.
Although this reasoning completely ignores the technical details of the process of observing light, from a fundamental point of view, it clearly demonstrates that movement with superluminal speed leads to an impossible situation in our world. However, nature has set even more stringent conditions: it is unattainable to move not only with superluminal speed, but also with a speed equal to the speed of light - you can only approach it. From the theory of relativity it follows that with an increase in the speed of movement, three circumstances arise: the mass of a moving object increases, its size decreases in the direction of movement, and the flow of time on this object slows down (from the point of view of an external "resting" observer). At ordinary speeds, these changes are negligible, but as they approach the speed of light, they become more noticeable, and in the limit - at a speed equal to with, - the mass becomes infinitely large, the object completely loses its size in the direction of motion and time stops on it. Therefore, no material body can reach the speed of light. Only light itself has such speed! (And also an "all-pervading" particle - a neutrino, which, like a photon, cannot move at a speed less than with.)
Now about the signal transmission speed. It is appropriate here to use the representation of light in the form of electromagnetic waves. What is a signal? This is some kind of information to be transmitted. An ideal electromagnetic wave is an infinite sinusoid of strictly one frequency, and it cannot carry any information, because each period of such a sinusoid exactly repeats the previous one. The speed at which the phase of a sine wave moves - the so-called phase speed - maybe in an environment with certain conditions exceed the speed of light in a vacuum. There are no restrictions here, since the phase velocity is not the signal velocity - it is not there yet. To create a signal, you need to make some kind of "mark" on the wave. Such a mark can be, for example, a change in any of the wave parameters - amplitude, frequency or initial phase. But as soon as the mark is made, the wave loses its sinusoidality. It becomes modulated, consisting of a set of simple sinusoidal waves with different amplitudes, frequencies and initial phases - a group of waves. The speed at which the mark moves in the modulated wave is the speed of the signal. When propagating in a medium, this velocity usually coincides with the group velocity, which characterizes the propagation of the above-mentioned group of waves as a whole (see Science and Life, No. 2, 2000). Under normal conditions, the group velocity, and hence the signal velocity, is less than the speed of light in a vacuum. It is not by chance that the expression "under normal conditions" is used, because in some cases the group velocity can also exceed with or even lose its meaning, but then it does not apply to signal propagation. In the service station it is established that it is impossible to transmit a signal at a speed greater than with.
Why is this so? Because an obstacle to the transmission of any signal with a speed of more with the same law of causality serves. Let's imagine the following situation. At some point A, a light flash (event 1) turns on a device that sends a certain radio signal, and at a remote point B, an explosion occurs under the action of this radio signal (event 2). It is clear that event 1 (flash) is a cause, and event 2 (explosion) is a consequence that occurs later than the cause. But if the radio signal propagated at a superluminal speed, an observer near point B would first see an explosion, and only then - reaching it with a speed with light flash, the cause of the explosion. In other words, for this observer, event 2 would occur earlier than event 1, that is, the effect would be ahead of the cause.
It is pertinent to emphasize that the "superluminal prohibition" of the theory of relativity is imposed only on the movement of material bodies and transmission of signals. In many situations, movement at any speed is possible, but it will not be movement of material objects or signals. For example, imagine two fairly long rulers lying in the same plane, one of which is horizontal, and the other intersects it at a small angle. If the first ruler is moved down (in the direction indicated by the arrow) at high speed, the point of intersection of the rulers can be made to run as fast as you want, but this point is not a material body. Another example: if you take a flashlight (or, say, a laser giving a narrow beam) and quickly describe an arc in the air with it, then the linear velocity of the light spot will increase with distance and at a sufficiently large distance will exceed with. The light spot will move between points A and B at a superluminal speed, but this will not be a signal transmission from A to B, since such a light spot does not carry any information about point A.
It would seem that the question of superluminal velocities has been resolved. But in the 60s of the twentieth century, theoretical physicists put forward the hypothesis of the existence of superluminal particles called tachyons. These are very strange particles: theoretically they are possible, but in order to avoid contradictions with the theory of relativity, they had to ascribe an imaginary rest mass. Physically imaginary mass does not exist, it is a purely mathematical abstraction. However, this did not cause much alarm, since tachyons cannot be at rest - they exist (if they exist!) Only at speeds exceeding the speed of light in a vacuum, and in this case the mass of the tachyon turns out to be real. There is some analogy here with photons: a photon has zero rest mass, but this simply means that a photon cannot be at rest - light cannot be stopped.
The most difficult, as expected, was to reconcile the tachyon hypothesis with the law of causality. Attempts in this direction, although they were quite ingenious, did not lead to obvious success. Nobody succeeded in registering tachyons experimentally either. As a result, interest in tachyons as superluminal elementary particles gradually faded away.
However, in the 60s, a phenomenon was experimentally discovered that initially confused physicists. This is discussed in detail in the article by A. N. Oraevsky "Superluminal waves in amplifying media" (Phys. Phys. No. 12, 1998). Here we will briefly summarize the matter, referring the reader interested in details to the specified article.
Soon after the discovery of lasers - in the early 60s - the problem arose of obtaining short (with a duration of the order of 1 ns = 10 -9 s) high-power light pulses. For this, a short laser pulse was passed through an optical quantum amplifier. The pulse was split into two parts by a beam-splitting mirror. One of them, more powerful, was directed to the amplifier, while the other propagated in the air and served as a reference pulse with which one could compare the pulse that passed through the amplifier. Both pulses were fed to photodetectors, and their output signals could be visually observed on the oscilloscope screen. It was expected that the light pulse passing through the amplifier will experience a certain delay in it compared to the reference pulse, that is, the speed of light propagation in the amplifier will be less than in air. Imagine the surprise of the researchers when they discovered that the pulse propagated through the amplifier at a speed not only greater than in air, but also several times faster than the speed of light in a vacuum!
Having recovered from the first shock, physicists began to look for the reason for such an unexpected result. No one had even the slightest doubt about the principles of the special theory of relativity, and it was this that helped to find the correct explanation: if the principles of special relativity are preserved, then the answer should be sought in the properties of the amplifying medium.
Without going into details here, we only point out that a detailed analysis of the mechanism of action of the amplifying medium has completely clarified the situation. The matter consisted in a change in the concentration of photons during pulse propagation - a change due to a change in the gain of the medium up to a negative value during the passage of the back of the pulse, when the medium already absorbs energy, because its own reserve has already been spent due to its transmission to the light pulse. Absorption causes not amplification, but a weakening of the impulse, and thus the impulse is enhanced in the front and weakened in the rear. Let's imagine that we are observing a pulse with the help of a device moving at the speed of light in an amplifier medium. If the medium were transparent, we would see an impulse frozen in immobility. In the environment in which the above-mentioned process takes place, the amplification of the leading and weakening of the trailing edge of the pulse will appear to the observer in such a way that the environment, as it were, moved the pulse forward. But since the device (observer) moves at the speed of light, and the pulse overtakes it, then the speed of the pulse exceeds the speed of light! It is this effect that was registered by the experimenters. And here there really is no contradiction with the theory of relativity: just the amplification process is such that the concentration of photons that came out earlier turns out to be greater than that of those that came out later. It is not photons that move with superluminal speed, but the pulse envelope, in particular, its maximum, which is observed on the oscilloscope.
Thus, while in ordinary media there is always an attenuation of light and a decrease in its speed, determined by the refractive index, in active laser media, not only light amplification is observed, but also the propagation of a pulse with a superluminal velocity.
Some physicists have tried to experimentally prove the existence of superluminal motion in the tunneling effect - one of the most amazing phenomena in quantum mechanics. This effect consists in the fact that a microparticle (more precisely, a microobject, exhibiting both the properties of a particle and the properties of a wave under different conditions) is able to penetrate through the so-called potential barrier - a phenomenon that is completely impossible in classical mechanics(in which the analogue would be the following situation: the ball thrown into the wall would be on the other side of the wall, or the undulating motion imparted to the rope tied to the wall would be transmitted to the rope tied to the wall on the other side). The essence of the tunneling effect in quantum mechanics is as follows. If a micro-object with a certain energy meets on its way a region with a potential energy exceeding the energy of the micro-object, this region is a barrier for it, the height of which is determined by the energy difference. But the micro-object "seeps" through the barrier! This possibility is given to him by the well-known Heisenberg uncertainty relation, written for the energy and interaction time. If the interaction of the micro-object with the barrier occurs for a sufficiently definite time, then the energy of the micro-object will, on the contrary, be characterized by uncertainty, and if this uncertainty is of the order of the barrier height, then the latter ceases to be an insurmountable obstacle for the micro-object. This is the rate of penetration through a potential barrier and has become the subject of research by a number of physicists, who believe that it can exceed with.
In June 1998, an international symposium on FTL problems was held in Cologne, where the results obtained in four laboratories were discussed - in Berkeley, Vienna, Cologne and in Florence.
And finally, in 2000, there were reports of two new experiments in which the effects of superluminal propagation were manifested. One of them was performed by Lijun Wong and co-workers at a research institute in Princeton (USA). Its result is that a light pulse entering a chamber filled with cesium vapor increases its speed 300 times. It turned out that the main part of the pulse leaves the far wall of the chamber even earlier than the pulse enters the chamber through the front wall. This situation contradicts not only common sense, but, in essence, the theory of relativity.
L. Wong's message provoked intense discussion among physicists, most of whom are not inclined to see in the results obtained a violation of the principles of relativity. The challenge, they believe, is to correctly explain this experiment.
In L. Wong's experiment, a light pulse entering the chamber with cesium vapor had a duration of about 3 μs. Cesium atoms can be in sixteen possible quantum-mechanical states called "magnetic hyperfine ground state sublevels." With the help of optical laser pumping, almost all atoms were brought into only one of these sixteen states, corresponding to almost absolute zero temperature on the Kelvin scale (-273.15 o C). The cesium chamber was 6 centimeters long. In a vacuum, light travels 6 centimeters in 0.2 ns. The measurements showed that the light pulse passed through the chamber with cesium in 62 ns less time than in vacuum. In other words, the transit time of the pulse through the cesium medium has a minus sign! Indeed, if 62 ns is subtracted from 0.2 ns, we get a "negative" time. This "negative delay" in the medium - an incomprehensible time jump - is equal to the time during which the pulse would have made 310 passes through the chamber in a vacuum. The consequence of this "temporary coup" was that the impulse leaving the chamber had time to move away from it by 19 meters before the incoming impulse reached the near wall of the chamber. How can you explain such an incredible situation (if, of course, there is no doubt about the purity of the experiment)?
Judging by the unfolding discussion, an exact explanation has not yet been found, but there is no doubt that unusual dispersion properties of the medium play a role here: cesium vapors, consisting of atoms excited by laser light, are a medium with anomalous dispersion. Let us briefly recall what it is.
The dispersion of a substance is the dependence of the phase (conventional) refractive index n on the wavelength of light l. With normal dispersion, the refractive index increases with decreasing wavelength, and this occurs in glass, water, air and all other substances transparent to light. In substances that strongly absorb light, the course of the refractive index changes to the opposite with a change in the wavelength and becomes much steeper: with a decrease in l (an increase in the frequency w), the refractive index sharply decreases and in a certain region of wavelengths becomes less than unity (the phase velocity V f> with). This is the anomalous dispersion, in which the picture of the propagation of light in matter changes radically. Group speed V gr becomes greater than the phase velocity of waves and can exceed the speed of light in vacuum (and also become negative). L. Wong points to this circumstance as the reason underlying the possibility of explaining the results of his experiment. However, it should be noted that the condition V gr> with is purely formal, since the concept of group velocity was introduced for the case of small (normal) dispersion, for transparent media, when the group of waves almost does not change its shape during propagation. In regions of anomalous dispersion, on the other hand, the light pulse is rapidly deformed and the concept of group velocity becomes meaningless; in this case, the concepts of signal velocity and energy propagation velocity are introduced, which in transparent media coincide with the group velocity, and in media with absorption remain less than the speed of light in vacuum. But here is what is interesting in Wong's experiment: a light pulse, having passed through a medium with anomalous dispersion, is not deformed - it exactly retains its shape! And this corresponds to the assumption about the propagation of the pulse with the group velocity. But if so, then it turns out that there is no absorption in the medium, although the anomalous dispersion of the medium is due precisely to absorption! Wong himself, admitting that much is still unclear, believes that what is happening in his experimental setup can, in a first approximation, be clearly explained as follows.
A light pulse consists of many components with different wavelengths (frequencies). The figure shows three of these components (waves 1-3). At some point, all three waves are in phase (their maxima coincide); here they add up, reinforce each other and form an impulse. As the waves propagate further in space, the waves are out of phase and thereby "extinguish" each other.
In the region of anomalous dispersion (inside the cesium cell), the wave that was shorter (wave 1) becomes longer. Conversely, the wave that was the longest of the three (wave 3) becomes the shortest.
Consequently, the phases of the waves also change accordingly. When the waves have passed through the cesium cell, their wavefronts are restored. Having undergone an unusual phase modulation in a substance with anomalous dispersion, the three waves under consideration are again in phase at a certain point. Here they add up again and form a pulse of exactly the same shape as entering the cesium medium.
Usually in air and in virtually any transparent medium with normal dispersion, a light pulse cannot accurately maintain its shape when propagating over a distant distance, that is, all of its components cannot be phased at any distant point along the propagation path. And under normal conditions, a light pulse at such a distant point appears after some time. However, due to the anomalous properties of the medium used in the experiment, the pulse at a distant point turned out to be phased in the same way as when entering this medium. Thus, the light pulse behaves as if it had a negative time delay on its way to a distant point, that is, it would arrive at it not later, but earlier than it passed the environment!
Most physicists are inclined to associate this result with the appearance of a low-intensity precursor in the dispersive medium of the chamber. The fact is that in the spectral decomposition of a pulse, the spectrum contains components of arbitrarily high frequencies with negligible amplitude, the so-called precursor that goes ahead of the "main part" of the pulse. The nature of the establishment and the form of the precursor depend on the dispersion law in the medium. With this in mind, the sequence of events in Wong's experiment is proposed to be interpreted as follows. The incoming wave, "stretching" the harbinger in front of itself, approaches the camera. Before the peak of the incoming wave hits the near wall of the chamber, the precursor initiates an impulse in the chamber, which reaches the far wall and is reflected from it, forming a "backward wave". This wave, spreading 300 times faster with, reaches the near wall and meets the incoming wave. The peaks of one wave meet the troughs of another, so they destroy each other and nothing is left as a result. It turns out that the incoming wave "returns the debt" to the cesium atoms, which "lent" energy to it at the other end of the chamber. Anyone who would only observe the beginning and end of the experiment would see only a pulse of light that "jumped" forward in time, moving faster with.
L. Wong believes that his experiment does not agree with the theory of relativity. The statement about the unattainability of superluminal speed, he believes, is applicable only to objects with rest mass. Light can be represented either in the form of waves, to which the concept of mass is generally inapplicable, or in the form of photons with a rest mass, as is known, equal to zero. Therefore, the speed of light in a vacuum, Wong believes, is not the limit. Nevertheless, Wong admits that the effect he discovered does not make it possible to transmit information at a faster speed. with.
"The information here is already in the leading edge of the pulse," says P. Milonny, a physicist at Los Alamos National Laboratory, USA. "And you can get the impression of sending information faster than light even when you are not sending it."
Most physicists believe that the new work does not strike a crushing blow to fundamental principles. But not all physicists believe the problem is solved. Professor A. Ranfagni of the Italian research group, which carried out another interesting experiment in 2000, believes that the question is still open. This experiment, conducted by Daniel Mugnai, Anedio Ranfagni and Rocco Ruggeri, found that centimeter-band radio waves in normal air travel at a speed exceeding with by 25%.
Summarizing, we can say the following. The work of recent years shows that under certain conditions, superluminal speed can actually take place. But what exactly is traveling at superluminal speed? The theory of relativity, as already mentioned, prohibits such a speed for material bodies and for signals carrying information. Nevertheless, some researchers are very persistently trying to demonstrate how to overcome the light barrier just for signals. The reason for this lies in the fact that in the special theory of relativity there is no rigorous mathematical justification (based, say, on Maxwell's equations for electromagnetic field) the impossibility of transmitting signals at a speed greater than with... Such impossibility in SRT is established, one might say, purely arithmetically, proceeding from the Einstein formula for the addition of velocities, but this is fundamentally confirmed by the principle of causality. Einstein himself, considering the question of superluminal signal transmission, wrote that in this case "... we are forced to consider a signal transmission mechanism, when using which the achieved action precedes the cause. But, although this result from a purely logical point of view does not contain in to myself, in my opinion, no contradictions, it still contradicts the nature of all our experience so much that the impossibility of assuming V> c seems to be sufficiently proven. "The principle of causality is the cornerstone that underlies the impossibility of superluminal signal transmission. And this stone, apparently, will stumble all, without exception, searches for superluminal signals, no matter how much experimenters would like to find such signals , for this is the nature of our world.
In conclusion, it should be emphasized that all of the above refers specifically to our world, to our Universe. This reservation was made because recently new hypotheses have appeared in astrophysics and cosmology, which admit the existence of many Universes hidden from us, connected by topological tunnel-bridges. This point of view is shared, for example, by the famous astrophysicist NS Kardashev. For an outside observer, the entrances to these tunnels are marked by anomalous gravitational fields, like black holes. Movements in such tunnels, as hypothesized by the authors of the hypotheses, will make it possible to bypass the limitation of the speed of movement imposed in ordinary space by the speed of light, and, consequently, to realize the idea of creating a time machine ... things. And although so far such hypotheses are too reminiscent of plots from science fiction, one should hardly categorically reject the fundamental possibility of a multi-element model of the structure of the material world. It's another matter that all these other Universes are likely to remain purely mathematical constructions of theoretical physicists living in our Universe and trying to find worlds that are closed to us by the power of their thoughts ...
See the issue on the same topic
... According to Antonio Ereditato, an employee of the center for particle physics on the French-Swiss border, after three years of measurements, it turned out that a beam of neutrinos launched from Geneva into the Italian laboratory of Gran Sasso covered a distance of 730 km, 60 nanoseconds faster than light."We have high confidence in the results. But it is necessary for other colleagues to do their tests and confirm our results.", - he noted. According to the scientist, the measurement error does not exceed 10 ns.
If the research results are confirmed, then this may call into question the basis of Albert Einstein's special theory of relativity (1905), which states that nothing in the universe can move faster than light, i.e. with a speed higher than 299,792 km / s.
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It is written here, alas, complete nonsense. The Reuters agency is certainly a solid organization, but science news must still not be drawn from the same hands that bring news of politics and social life.
"the basis of Albert Einstein's special theory of relativity (1905), which states that nothing in the universe can travel faster than light"
The theory of relativity does not assert anything like that. The theory of relativity states that nothing can travel faster than light IN VACUUM. And particles that move faster than light were found a long time ago, more precisely, such media were found in which some particles can move faster than photons.
How the neutrino beam went from Geneva somewhere there is not clear to me, but certainly not in a vacuum. If, for example, he walked through the air, then there is nothing surprising in the fact that the photons scattered by the air reached the end point later than neutrinos that hardly interact with matter.
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In fact, neutrinos will always move faster than light :) Simply because they practically do not interact with matter, and light (photons) interacts perfectly. And only in a vacuum do photons finally accelerate to a full buzz :)
But it was interesting to find such an environment in which electrons could move faster than the speed of light. And such an environment was found long ago. And in doing so, amazing effects occur. Look at Wikipedia "Vavilov-Cherenkov radiation".
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Another post on the topic:
Physicists at the research center of the European Organization for Nuclear Research (CERN) during the experiment found that subatomic particles can move at a speed exceeding the speed of light.
The neutrino beam, sent from CERN to the Gran Sasso underground laboratory in Italy at a distance of 732 km, arrived at its destination, reportedly a few billionths of a second earlier than if traveling at the speed of light.
If the experimental data are confirmed, then Einstein's theory of relativity, according to which the speed of light is 299 792 458 meters per second, will be refuted.
According to scientists, beams of neutrinos outrun it by 60 nanoseconds, which contradicts the postulate that elementary particles cannot move faster than the speed of light.
The BBC Russian Service spoke to Ruben Sahakyan, professor of physics at University College London, about the results of the experiment.
BBC BBC: You worked in the Gran Sasso laboratory, and are probably very familiar with the Opera experiment.
Ruben Sahakyan: I left the Gran Sasso laboratory more than 10 years ago, when the Opera was just being built. Opera is an experiment that searches for such a phenomenon as neutrino oscillations, that is, the transformation of one type of neutrino into another.
Neutrinos are fundamental particles, the so-called building blocks of the universe. They have a number of interesting properties, including converting from one type to another. Opera is meant to study this problem.
That result (data that neutrinos are moving faster than the speed of light) was a byproduct of the experiment they were doing.
BBC: Are the results presented by scientists convincing?
RS: The published results look convincing. In experimental science, there is a numerical measure of confidence in the result, that is, your measurement must exceed the measurement error by at least five times. And for them it exceeds six times.
On the other hand, it is a complex dimension, there are many elements in it, and at each stage there are many ways to get it wrong. And so you need to take it with healthy skepticism. To the credit of the authors, they do not interpret the result, but simply state the data obtained during the experiment.
BBC: How did the world scientific community react to this data?
RS: The international community has reacted with healthy skepticism and even conservatism. After all, this is a serious experiment, not a populist statement.
The consequences, if these data are proven to be true, are too serious to be easily perceived.
Our fundamental understanding of the world will change. Now people will wait for further publications of experimental bias and, most importantly, data from independent experiments.
BBC: Which ones, for example?
RS: There is an American experiment "Minus", which can confirm this measurement. It is very similar to "Opera". A neutrino beam is produced at the accelerator, then sent to 730 kilometers and measured in an underground laboratory. The essence of the measurement is simple: you know the distance between your source and your detector, you measure the time it took, and thus determine the speed.
The devil is in the details. "Minus" made a similar measurement four years ago, but then they had the same value that they measured, and the error was commensurate with each other. Their key problem was that they did not have an accurate distance.
The 730 kilometers between the source and the detector are difficult to measure with absolute precision, and Opera has recently been able to measure this distance up to 20 centimeters using geodetic methods. Minus will try to do the same, and then he will be able to verify the data of this experiment.
BBC: If the result of the experiment is confirmed, how will this affect traditional ideas about the world?
RS: If this is confirmed, then the result will be serious. Now there are two theories that scientifically explain the whole world that surrounds us: the quantum theory of the microworld and Einstein's theory of relativity.
The result of the experiment (neutrinos move at a speed exceeding the speed of light) directly contradicts Einstein's theory of relativity, which states that at any point of reference the speed of light is constant and nothing can overtake the speed of light.
There are a huge number of dizzying consequences, in particular the possibility of time travel (for particles).
Http://www.bbc.co.uk/russian/science/2011/09/110923_interview_expert_neutrino_discovery.shtml
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There will be a lot of publications, but it is pointless to discuss them by 10, since you cannot even imagine how much physics has gone ahead since 1905 :), when Einstein only formulated the principles of the theory of rel. There are many completely unexpected aspects to all of this, and if they are neglected, then it is easy to suck the sensations. The experimenters did not suck anything, apparently, but it is only characteristic that neither they themselves nor the scientists who deal with these problems emit any screams - they simply recorded such and such a result and now propose to check it and either refute, or confirm, and “to confirm” does not mean that the theory of relativity should be corrected, since there can be a variety of explanations for these data in the conditions of the existing model.
For example, imagine - a certain particle is so accelerated that its speed is almost equal to the speed of light - well, very close. in this case, if its coordinate is sufficiently weakly undefined, then according to the Heisenberg uncertainty principle, the uncertainty of its velocity becomes such that there is a nonzero probability that the particle moves faster than the speed of light. This is a well-known paradox, from which, in particular, follows the hypothesis of the existence of antimatter, which is fine in the end and explains everything within the framework of the existing model.
Well, remember such a fucking thing as the Casimir vacuum - a vacuum is not a void, it is an oblate of space, which is teeming with countless numbers of born and dying virtual particles. They are named virtual because they are born and annihilate faster than you can detect it, in order to fix the violation of conservation laws. Nevertheless, with certain mental experiments, it is possible, as it were, to "move apart" pairs of virtual particles, and they will not be able to collapse. In addition, if we take an extremely small size of the region of space, then only one particle will appear in it, and the second will be on the other side of the "wall". The Casimir effect has already been experimentally proven, but its study is practically unchanged due to the fact that it is extremely difficult to conduct experiments in such small regions of space.
I'm not even talking about the theory of tachyons, which can also calmly be called upon to support the theory of relativity (if we add it to the explanation of the mysterious transformations of neutrinos from one type to another and the possible this gtuke with exceeding the speed of light
In general, there are so many details that there is a hell of a lot of possibilities to keep the theory of relativity intact. But some of the possible interpretations can nevertheless move physics forward significantly.
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It is also not clear to me: from what I read and saw, it follows that scientists launched a neutrino beam at a distance of 700 km to a recording device .. But the earth is constantly, every second, pierced by neutrino huelions, which do not interact with matter in any way. How did they determine that it was "their" neutrino that was recorded on the recorder, and not the one that came from space?
