The 20th century was marked by the greatest discoveries in the field of physics and cosmology. The foundations of these discoveries were theories developed by a galaxy of outstanding physicists. The most famous of them is Albert Einstein, on whose work modern physics is largely based. From the scientist’s theories it follows that the speed of light in a vacuum is the maximum speed of particle movement and interaction. And the time paradoxes arising from these theories are completely amazing: for example, for moving objects, time flows slower relative to those at rest, and the closer to the speed of light, the more time slows down. It turns out that for an object flying at the speed of light, time will completely stop.
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This gives us hope that with the proper level of technology, theoretically, a person is capable of reaching the most remote corners of the Universe within the lifetime of one generation. In this case, the flight time in the earth's reference frame will be millions of years, while on a ship flying at near-light speed, only a few days will pass... Such possibilities are impressive, and at the same time the question arises: if physicists and engineers of the future somehow accelerate the spacecraft to enormous values, even theoretically up to the speed of light (although our physics denies this possibility), will we be able to reach not only the most distant galaxies and stars, but also the edge of our Universe, look beyond the boundary of the unknown, about which scientists have no idea?
We know that the Universe was formed about 13.79 billion years ago and has been expanding continuously since then. One could assume that its radius at the moment should be 13.79 billion light years, and its diameter, accordingly, 27.58 billion light years. And this would be true if the Universe was expanding uniformly at the speed of light - the maximum possible speed. But the data obtained tells us that the Universe is expanding at an accelerating rate.
We observe that the galaxies most distant from us are moving away from us faster than those nearby - the space of our world is continuously expanding. At the same time, there is a part of the Universe that is moving away from us faster than the speed of light. In this case, no postulates and conclusions of the theory of relativity are violated - objects inside the Universe remain at sublight speeds. This part of the Universe cannot be seen - the speed of photons emitted by radiation sources is simply not enough to overcome the speed of expansion of space.
Calculations show that the part of our world visible to us has a diameter of about 93 billion light years and is called Metagalaxy. We can only guess about what lies beyond this boundary and how far the Universe extends. It is logical to assume that the edge of the Universe is moving away from us the fastest and far exceeds the speed of light. And this speed is constantly increasing. It becomes obvious that even if some object flies at the speed of light, it will never reach the edge of the Universe, because the edge of the Universe will move away from it faster.
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But really, what will happen? This question actually has no answer, because it contradicts all the laws of physics, and, as we know, experiments cannot be carried out. But no one will forbid you to think theoretically. So, let's say we got hold of a VAZ car that can accelerate, for starters, to the speed of light. Go…
As we know from the 11th grade physics course, the speed of light is a constant value and is neither more nor less, but 300,000 km per second. At near-light speeds, the usual laws of physics do not apply. The laws of relativistic physics apply here, so we will have to turn to Mr. Einstein and read his theory of relativity.
Applying the laws of classical physics, we can assume that the speed of photons (particles of light) will add up to the speed of the car, and the headlights will shine as always. But... It turns out that these same photons must fly at double the speed of light - the speed of the car and the speed of the photons are added up. But this is impossible, because back in 1905 Einstein proved that the speed of light is constant in any frame of reference. This means that the photon from the headlight will still have a speed of 300,000 km/sec. But the car also has the same speed. So, photons of light will fly next to the car? Then the driver will not see the headlights. An observer on the side of the road should appear to see a spot of light flying past. In fact, not quite like that.
Using the theory of relativity, one can imagine another picture, much more fantastic. Here many factors overlap each other and create something unimaginable.
For example, at a speed close to the speed of light, an object, that is, a car, must acquire unlimited mass. The result should be some kind of black hole, which, with its gravity, will not allow any photons to leave its surface. On the contrary, it, as befits an object of incredible mass, will draw into itself all the surrounding matter. At the speed of light, the mass of our car will be equal to infinity. Well, it’s no longer worth even guessing about even greater speed. In this case, the time in it will be equal to zero, that is, it will stop.
On the other hand, the movement of any particle is determined by the distance per unit time. And if time stands still, what kind of movement can there be? Everything freezes until the speed slows down. Theoretically, our car could fly across the entire Universe, and the clock in it wouldn’t even count a fraction of a second! And how would they count if all the molecules in them stopped. But the stopping of molecules means the temperature of the object is absolute zero! Imagine, for a person in a car, time goes slower and slower until it stops completely. He freezes and even the molecules in his body stand still - his temperature is absolute zero. But somehow the speed decreases and the person comes to life. He didn't even notice this stop. So he reaches out and spends seconds of his time on this, but hours, years, or even centuries pass by for us! Although everything is vague here, because the accumulation of matter increases pressure and temperature, and here it is absolute zero. No matter how supernova it turns out!
Let’s even say that our car remained a car and the driver turned out to be alive and was able to turn on the headlights. As is known, at high speeds the so-called Doppler effect operates. After all, light also has a wave nature. This means that the frequency, or spectrum, of visible light changes. If an object approaches, we will see a shift in the spectrum to the violet part, and if it moves away, to the red.
If we apply this to our near-light machine, then instead of headlights we can get hard gamma radiation, or simply radiation. The driver may not understand anything; this is a moot point, because for him nothing much has changed. But our observer is unlikely to live more than a split second after the car flies past. He will receive all types of radiation - the ultraviolet part while the car is approaching, and the infrared part while it is moving away. This can hardly be called headlights.
There is no answer to the question of what will happen to light at superluminal speeds. Just as there is no such thing for light. Near-light - please, the theory of relativity applies here. The light remains ordinary light. But when the speed of light is reached, such miracles begin that the brain would rather boil than find the answer or imagine all possible options. Changes in matter and time that are incredible to us begin there. Maybe it’s for the best that such speed can never be achieved. Not to mention superluminal...
Although it was not possible to answer the question due to the impossibility of explaining the impossible, it seems that the food for thought turned out to be tasty.
1) Does headlights illuminate other objects and reflect back into your eyes?
No. As you know, you cannot exceed the speed of light. This means that in one direction the light cannot shine at all because it is not able to exceed the speed of the car, so it will never come out of the headlights. However, we live in a multidimensional world and not all light shines in one direction.
Let's imagine a two-dimensional car with no mass (that is, moving at the speed of light) that emits two photons, one up and one down. Two beams separate from the car and remain behind it. They move at the same speed of light, but cannot move forward just as fast, since one of the speed vectors is directed up/down, so we overtake them. These photons then encounter some obstacle in their path, such as a road sign or a tree, and are reflected back. The problem is that they can no longer catch up with you. Other people walking on the sidewalk are able to see the reflected light, but you have already left and will never see it.
Here you go, everything can be explained by the mere fact that all light moves at the same speed, no matter where. This hardly has anything to do with the theory of relativity.
However, there is also a more hardcore version.
2) Can things moving at the speed of light have headlights? Can they even have vision?
This is where the crazy truth of relativity really comes into play, so there's no need to be ashamed if you don't understand something, but the answer is again no.
You may be familiar with the concept of relativistic time dilation. Suppose my friend and I get on different trains and travel towards each other. Driving past, if we look through the window at the wall clock in each other's compartment, then both Note that they are moving slower than usual. This is not because the clock is slowing down, but because the light between us comes into play: the faster we move, the slower we age relative to less moving objects. This is because time is not absolute for all objects in the Universe, it is different for each object and depends on its speed. Our time depends only on our speed in the Universe. You can think of this as moving in different directions on a space-time scale. There is a certain problem here, because our brain is not designed to understand the geometry of space-time, but tends to imagine time as some kind of absolute. However, after reading a little literature on this topic, you can normally accept as a natural fact: those who move quickly relative to you age more slowly.
Let's say your friend is sitting in a hypothetical car, traveling at the speed of light. So, let's plug his speed into our formula and see what the answer is.
Oh-oh! It looks like no time has passed for him at all! There must be something wrong with our calculations?! It turns out that no. Time. Not. Exists. For. Objects. On the. Speed. Sveta.
It simply doesn't exist.
This means that things at the speed of light cannot perceive “happening” events in the same way that we perceive them. Events cannot take place for them. They can perform actions, but cannot gain experience. Einstein himself once said, “Time exists so that everything doesn't happen at once.” It is a coordinate designed to arrange events into a meaningful sequence so that we can understand what is happening. But for an object that moves at the speed of light, this principle does not work, because All happens simultaneously. A traveler at the speed of light will never see, think or feel anything that we consider meaningful.
This is such an unexpected conclusion.
March 25th, 2017
FTL travel is one of the foundations of space science fiction. However, probably everyone - even people far from physics - knows that the maximum possible speed of movement of material objects or the propagation of any signals is the speed of light in a vacuum. It is designated by the letter c and is almost 300 thousand kilometers per second; exact value c = 299,792,458 m/s.
The speed of light in a vacuum is one of the fundamental physical constants. The impossibility of achieving speeds exceeding c follows from Einstein's special theory of relativity (STR). If it could be proven that transmission of signals at superluminal speeds is possible, 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 c. However, recent experimental studies have revealed some very interesting phenomena, indicating that under specially created conditions superluminal speeds can be observed without violating the principles of relativity theory.
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 precede the cause. No one has ever observed that, for example, a bear first fell dead and then the hunter shot. At speeds exceeding c, the sequence of events becomes reversed, the time tape is rewinded back. This is easy to verify from the following simple reasoning.
Let's assume 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 times. First, we would catch up with photons emitted, say, yesterday, then those 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. Causes and effects would then change places.
Although this discussion completely ignores the technical details of the process of observing light, from a fundamental point of view it clearly demonstrates that movement at superluminal speeds leads to a situation that is impossible in our world. However, nature has set even more stringent conditions: movement not only at superluminal speed is unattainable, but also at a speed equal to the speed of light - one can only approach it. From the theory of relativity it follows that when the speed of movement increases, three circumstances arise: the mass of a moving object increases, its size in the direction of movement decreases, 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 and more noticeable, and in the limit - at a speed equal to c - the mass becomes infinitely large, the object completely loses size in the direction of movement 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-penetrating” particle - a neutrino, which, like a photon, cannot move at a speed less than c.)
Now about the signal transmission speed. Here it is appropriate to use the representation of light in the form of electromagnetic waves. What is a signal? This is some information that needs 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 of movement of the phase of a sine wave - the so-called phase speed - can, under certain conditions, exceed the speed of light in a vacuum in a medium. There are no restrictions here, since the phase speed is not the speed of the signal - it does not exist 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 sine 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 speed usually coincides with the group speed, 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 therefore the signal speed, is less than the speed of light in vacuum. It is not by chance that the expression “under normal conditions” is used here, because in some cases the group velocity may exceed c or even lose its meaning, but then it does not refer to signal propagation. The service station establishes that it is impossible to transmit a signal at a speed greater than c.
Why is this so? Because the obstacle to the transmission of any signal at a speed greater than c is the same law of causality. Let's imagine such a situation. At some point A, a light flash (event 1) turns on a device sending a certain radio signal, and at a remote point B, under the influence of this radio signal, an explosion occurs (event 2). It is clear that event 1 (flare) is the cause, and event 2 (explosion) is the consequence, occurring later than the cause. But if the radio signal propagated at superluminal speed, an observer near point B would first see an explosion, and only then the cause of the explosion that reached him at the speed of a light flash. In other words, for this observer, event 2 would have occurred earlier than event 1, that is, the effect would have preceded the cause.
It is appropriate to emphasize that the “superluminal prohibition” of the theory of relativity is imposed only on the movement of material bodies and the transmission of signals. In many situations, movement at any speed is possible, but this will not be the movement of material objects or signals. For example, imagine two fairly long rulers lying in the same plane, one of which is located horizontally, and the other intersects it at a small angle. If the first ruler is moved downwards (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 desired, but this point is not a material body. Another example: if you take a flashlight (or, say, a laser producing a narrow beam) and quickly describe an arc in the air, then the linear speed of the light spot will increase with distance and at a sufficiently large distance will exceed c. The light spot will move between points A and B at superluminal speed, but this will not be a signal transmission from A to B, since such a spot of light does not carry any information about point A.
It would seem that the issue of superluminal speeds 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 be assigned 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 tachyon mass turns out to be real. There is some analogy here with photons: a photon has zero rest mass, but this simply means that the photon cannot be at rest - light cannot be stopped.
The most difficult thing turned out to be, as one would expect, to reconcile the tachyon hypothesis with the law of causality. The attempts made in this direction, although quite ingenious, did not lead to obvious success. No one has been able to experimentally register tachyons 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 described in detail in the article by A. N. Oraevsky “Superluminal waves in amplifying media” (UFN No. 12, 1998). Here we will briefly summarize the essence of 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 (lasting about 1 ns = 10-9 s) high-power light pulses. To do 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 sent to the amplifier, and the other propagated in the air and served as a reference pulse with which the pulse passing through the amplifier could be compared. 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 would experience some delay in it compared to the reference pulse, that is, the speed of light propagation in the amplifier would be less than in air. Imagine the amazement 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 higher than the speed of light in 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 this is what helped to find the correct explanation: if the principles of SRT are preserved, then the answer should be sought in the properties of the amplifying medium.
Without going into details here, we will only point out that a detailed analysis of the mechanism of action of the amplifying medium completely clarified the situation. The point was a change in the concentration of photons during the propagation of the pulse - a change caused by a change in the gain of the medium up to a negative value during the passage of the rear part of the pulse, when the medium already absorbs energy, because its own reserve has already been used up due to its transfer to the light pulse. Absorption causes not an increase, but a weakening of the impulse, and thus the impulse is strengthened in the front part and weakened in the back part. Let's imagine that we are observing a pulse using a device moving at the speed of light in the amplifier medium. If the medium were transparent, we would see the impulse frozen in motionlessness. In the environment in which the above-mentioned process occurs, the strengthening of the leading edge and the weakening of the trailing edge of the pulse will appear to the observer in such a way that the medium seems to have moved the pulse forward. But since the device (observer) moves at the speed of light, and the impulse overtakes it, then the speed of the impulse exceeds the speed of light! It is this effect that was recorded by experimenters. And here there really is no contradiction with the theory of relativity: the amplification process is simply such that the concentration of photons that came out earlier turns out to be greater than those that came out later. It is not photons that move at superluminal speeds, but the pulse envelope, in particular its maximum, which is observed on an oscilloscope.
Thus, while in ordinary media there is always a weakening of light and a decrease in its speed, determined by the refractive index, in active laser media there is not only an amplification of light, but also propagation of a pulse at superluminal speed.
Some physicists have tried to experimentally prove the presence of superluminal motion during the tunnel effect - one of the most amazing phenomena in quantum mechanics. This effect consists in the fact that a microparticle (more precisely, a microobject that under different conditions exhibits both the properties of a particle and the properties of a wave) is capable of penetrating through the so-called potential barrier - a phenomenon that is completely impossible in classical mechanics (in which such a situation would be an analogue : a ball thrown at a wall would end up on the other side of the wall, or the wave-like motion imparted to a rope tied to the wall would be transferred to a rope tied to the wall on the other side). The essence of the tunnel effect in quantum mechanics is as follows. If a micro-object with a certain energy encounters on its way an area with potential energy exceeding the energy of the micro-object, this area is a barrier for it, the height of which is determined by the energy difference. But the micro-object “leaks” through the barrier! This possibility is given to him by the well-known Heisenberg uncertainty relation, written for the energy and time of interaction. If the interaction of a microobject with a barrier occurs over a fairly certain time, then the energy of the microobject will, on the contrary, be characterized by uncertainty, and if this uncertainty is of the order of the height of the barrier, then the latter ceases to be an insurmountable obstacle for the microobject. It is the speed of penetration through the potential barrier that has become the subject of research by a number of physicists, who believe that it can exceed c.
In June 1998, an international symposium on the problems of superluminal motion was held in Cologne, where the results obtained in four laboratories were discussed - in Berkeley, Vienna, Cologne and Florence.
And finally, in 2000, reports appeared about two new experiments in which the effects of superluminal propagation appeared. One of them was performed by Lijun Wong and his colleagues at the Princeton Research Institute (USA). Its result is that a light pulse entering a chamber filled with cesium vapor increases its speed by 300 times. It turned out that the main part of the pulse exited the far wall of the chamber even earlier than the pulse entered the chamber through the front wall. This situation contradicts not only common sense, but, in essence, the theory of relativity.
L. Wong's message caused intense discussion among physicists, most of whom were not inclined to see a violation of the principles of relativity in the results obtained. The challenge, they believe, is to correctly explain this experiment.
In L. Wong's experiment, the light pulse entering the chamber with cesium vapor had a duration of about 3 μs. Cesium atoms can exist in sixteen possible quantum mechanical states, called "hyperfine magnetic sublevels of the ground state." Using 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 ° C). The length of the cesium chamber was 6 centimeters. In a vacuum, light travels 6 centimeters in 0.2 ns. As the measurements showed, the light pulse passed through the chamber with cesium in a time that was 62 ns less than in vacuum. In other words, the time it takes for a pulse to pass through a cesium medium has a minus sign! Indeed, if we subtract 62 ns from 0.2 ns, we get “negative” time. This "negative delay" in the medium - an incomprehensible time jump - is equal to the time during which the pulse would make 310 passes through the chamber in a vacuum. The consequence of this “temporal reversal” was that the pulse leaving the chamber managed to move 19 meters away from it before the incoming pulse reached the near wall of the chamber. How can such an incredible situation be explained (unless, of course, we doubt the purity of the experiment)?
Judging by the ongoing discussion, an exact explanation has not yet been found, but there is no doubt that the unusual dispersion properties of the medium play a role here: cesium vapor, consisting of atoms excited by laser light, is a medium with anomalous dispersion. Let us briefly recall what it is.
The dispersion of a substance is the dependence of the phase (ordinary) refractive index n on the light wavelength l. With normal dispersion, the refractive index increases with decreasing wavelength, and this is the case in glass, water, air and all other substances transparent to light. In substances that strongly absorb light, the course of the refractive index with a change in wavelength is reversed and becomes much steeper: with decreasing l (increasing frequency w), the refractive index sharply decreases and in a certain wavelength region becomes less than unity (phase velocity Vf > s ). This is anomalous dispersion, in which the pattern of light propagation in a substance changes radically. The group velocity Vgr becomes greater than the phase velocity of the 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. It should, however, be noted that the condition Vgr > c is purely formal, since the concept of group velocity was introduced for the case of small (normal) dispersion, for transparent media, when a group of waves almost does not change its shape during propagation. In regions of anomalous dispersion, the light pulse is quickly deformed and the concept of group velocity loses its meaning; in this case, the concepts of signal speed and energy propagation speed are introduced, which in transparent media coincide with the group speed, and in media with absorption remain less than the speed of light in vacuum. But here’s what’s interesting about Wong’s experiment: a light pulse, passing through a medium with anomalous dispersion, is not deformed - it exactly retains its shape! And this corresponds to the assumption that the impulse propagates with 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, while acknowledging that much remains unclear, believes that what is happening in his experimental setup can, to 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, adding up, reinforce each other and form an impulse. As they further propagate in space, the waves become dephased and thereby “cancel” 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 change accordingly. Once 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 in question again find themselves in phase at some point. Here they add up again and form a pulse of exactly the same shape as that entering the cesium medium.
Typically in air, and in fact in any transparent medium with normal dispersion, a light pulse cannot accurately maintain its shape when propagating over a remote distance, that is, all its components cannot be phased at any distant point along the propagation path. And under normal conditions, a light pulse appears at such a distant point after some time. However, due to the anomalous properties of the medium used in the experiment, the pulse at a remote 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 had passed through the medium!
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 during the spectral decomposition of a pulse, the spectrum contains components of arbitrarily high frequencies with negligibly small amplitude, the so-called precursor, going ahead of the “main part” of the pulse. The nature of establishment and the shape of the precursor depend on the law of dispersion 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 ahead of itself, approaches the camera. Before the peak of the incoming wave hits the near wall of the chamber, the precursor initiates the appearance of a pulse in the chamber, which reaches the far wall and is reflected from it, forming a “reverse wave.” This wave, propagating 300 times faster than c, reaches the near wall and meets the incoming wave. The peaks of one wave meet the troughs of another, so that they destroy each other and as a result there is nothing left. It turns out that the incoming wave “repays the debt” to the cesium atoms, which “lent” energy to it at the other end of the chamber. Anyone who watched only the beginning and end of the experiment would see only a pulse of light that "jumped" forward in time, moving faster than c.
L. Wong believes that his experiment is not consistent with the theory of relativity. The statement about the unattainability of superluminal speed, he believes, applies 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, according to Wong, is not the limit. However, Wong admits that the effect he discovered does not make it possible to transmit information at speeds greater than c.
“The information here is already contained in the leading edge of the pulse,” says P. Milonni, a physicist at Los Alamos National Laboratory in the United States. “And it can give the impression of sending information faster than light, even when you are not sending it.”
Most physicists believe that the new work does not deal a crushing blow to fundamental principles. But not all physicists believe the problem is settled. Professor A. Ranfagni, from the Italian research group that carried out another interesting experiment in 2000, believes that the question is still open. This experiment, carried out by Daniel Mugnai, Anedio Ranfagni and Rocco Ruggeri, discovered that centimeter-wave radio waves in normal air travel at speeds 25% faster than c.
To summarize, we can say the following.
Work in recent years shows that, under certain conditions, superluminal speed can actually occur. But what exactly is moving at superluminal speeds? The theory of relativity, as already mentioned, prohibits such speed for material bodies and for signals carrying information. Nevertheless, some researchers are very persistently trying to demonstrate overcoming the light barrier specifically for signals. The reason for this lies in the fact that in the special theory of relativity there is no strict mathematical justification (based, say, on Maxwell’s equations for the electromagnetic field) of the impossibility of transmitting signals at speeds greater than c. Such an impossibility in STR is established, one might say, purely arithmetically, based on Einstein’s formula for adding velocities, but this is fundamentally confirmed by the principle of causality. Einstein himself, considering the issue of superluminal signal transmission, wrote that in this case “... we are forced to consider possible a signal transmission mechanism, in which the achieved action precedes the cause. But, although this result from a purely logical point of view does not contain itself, in my opinion, there are no contradictions; it nevertheless so contradicts the nature of our entire experience that the impossibility of the assumption V > c seems to be sufficiently proven." The principle of causality is the cornerstone that underlies the impossibility of superluminal signal transmission. And, apparently, all searches for superluminal signals without exception will stumble over this stone, no matter how much experimenters would like to detect such signals, for such is the nature of our world.
But still, let's imagine that the mathematics of relativity will still work at superluminal speeds. This means that theoretically we can still find out what would happen if a body were to exceed the speed of light.
Let's imagine two spaceships heading from Earth towards a star that is 100 light years away from our planet. The first ship leaves Earth at 50% the speed of light, so it will take 200 years to complete the journey. The second ship, equipped with a hypothetical warp drive, will travel at 200% the speed of light, but 100 years after the first. What will happen?
According to the theory of relativity, the correct answer depends largely on the perspective of the observer. From Earth, it will appear that the first ship has already traveled a considerable distance before being overtaken by the second ship, which is moving four times faster. But from the point of view of the people on the first ship, everything is a little different.
Ship No. 2 moves faster than light, which means it can even outpace the light that it itself emits. This results in a kind of “light wave” (similar to a sound wave, but instead of air vibrations there are light waves vibrating) which gives rise to several interesting effects. Recall that the light from ship #2 moves slower than the ship itself. The result will be visual doubling. In other words, first the crew of ship No. 1 will see that the second ship has appeared next to them as if out of nowhere. Then, the light from the second ship will reach the first one with a slight delay, and the result will be a visible copy that will move in the same direction with a slight lag.
Something similar can be seen in computer games, when, as a result of a system failure, the engine loads the model and its algorithms at the end point of the movement faster than the movement animation itself ends, so that multiple takes occur. This is probably why our consciousness does not perceive that hypothetical aspect of the Universe in which bodies move at superluminal speeds - perhaps this is for the best.
P.S. ... but in the last example I didn’t understand something, why the real position of the ship is associated with the “light emitted by it”? Well, even if they see him in the wrong place, in reality he will overtake the first ship!
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In September 2011, physicist Antonio Ereditato shocked the world. His statement could revolutionize our understanding of the universe. If the data collected by the 160 OPERA Project scientists was correct, the incredible was observed. The particles - in this case neutrinos - moved faster than light. According to Einstein's theory of relativity, this is impossible. And the consequences of such an observation would be incredible. The very foundations of physics might have to be reconsidered.
Although Ereditato said he and his team were “extremely confident” in their results, they did not say that the data was completely accurate. Instead, they asked other scientists to help them figure out what was going on.
In the end, it turned out that OPERA's results were wrong. Due to a poorly connected cable, there was a synchronization problem and the signals from GPS satellites were inaccurate. There was an unexpected delay in the signal. As a result, measurements of the time it took neutrinos to travel a certain distance showed an extra 73 nanoseconds: it seemed that the neutrinos were traveling faster than light.
Despite months of careful testing before the experiment began and double-checking the data afterwards, the scientists were seriously wrong. Ereditato resigned despite the comments of many that such errors always occurred due to the extreme complexity of particle accelerators.
Why did the suggestion - just the suggestion - that something could travel faster than light cause such a fuss? How sure are we that nothing can overcome this barrier?
Let's look at the second of these questions first. The speed of light in a vacuum is 299,792.458 kilometers per second - for convenience, this number is rounded to 300,000 kilometers per second. It's quite fast. The sun is 150 million kilometers from the Earth, and its light reaches the Earth in just eight minutes and twenty seconds.
Can any of our creations compete in the race against light? One of the fastest man-made objects ever built, the New Horizons space probe whizzed past Pluto and Charon in July 2015. It reached a speed relative to the Earth of 16 km/s. Much less than 300,000 km/s.
However, we had tiny particles that were moving quite quickly. In the early 1960s, William Bertozzi at MIT experimented with accelerating electrons to even higher speeds.
Because electrons have a negative charge, they can be accelerated—more accurately, repelled—by applying the same negative charge to a material. The more energy is applied, the faster the electrons accelerate.
One would think that one would simply need to increase the applied energy to reach a speed of 300,000 km/s. But it turns out that electrons simply cannot move that fast. Bertozzi's experiments showed that using more energy does not lead to a directly proportional increase in electron speed.
Instead, enormous amounts of additional energy had to be applied to even slightly change the speed of the electrons. She came closer and closer to the speed of light, but never reached it.
Imagine moving towards the door in small steps, each step covering half the distance from your current position to the door. Strictly speaking, you will never reach the door, because after each step you take, you will still have a distance to cover. Bertozzi encountered approximately the same problem while dealing with his electrons.
But light is made up of particles called photons. Why can these particles travel at the speed of light, but electrons cannot?
"As objects move faster and faster, they become heavier - the heavier they become, the harder it is for them to accelerate, so you never reach the speed of light," says Roger Rassoul, a physicist at the University of Melbourne in Australia. “A photon has no mass. If it had mass, it couldn't move at the speed of light."
Photons are special. Not only do they have no mass, which provides them with complete freedom of movement in the vacuum of space, but they also do not need to accelerate. The natural energy they have moves in waves just like them, so when they are created they already have maximum speed. In some ways, it's easier to think of light as energy rather than as a stream of particles, although in truth light is both.
However, light travels much slower than we might expect. Although internet technologists like to talk about communications running at the "speed of light" in fiber optics, light travels 40% slower in glass fiber optics than in a vacuum.
In reality, photons travel at speeds of 300,000 km/s, but encounter a certain amount of interference caused by other photons emitted by glass atoms as the main light wave passes through. This may not be easy to understand, but at least we tried.
In the same way, within the framework of special experiments with individual photons, it was possible to slow them down quite impressively. But for most cases, 300,000 would be about right. We haven't seen or built anything that can move that fast, or even faster. There are special points, but before we touch on them, let's touch on our other question. Why is it so important that the speed of light rule be strictly followed?
The answer has to do with a man named Albert Einstein, as is often the case in physics. His special theory of relativity explores the many implications of his universal speed limits. One of the most important elements of the theory is the idea that the speed of light is constant. No matter where you are or how fast you are moving, light always moves at the same speed.
But this raises several conceptual problems.
Imagine the light that falls from a flashlight onto a mirror on the ceiling of a stationary spacecraft. The light goes up, reflects off the mirror and falls on the floor of the spacecraft. Let's say he covers a distance of 10 meters.
Now imagine that this spacecraft begins to move at a colossal speed of many thousands of kilometers per second. When you turn on the flashlight, the light behaves as before: it shines upward, hits the mirror and is reflected onto the floor. But to do this, the light will have to travel a diagonal distance, not a vertical one. After all, the mirror now moves quickly along with the spacecraft.
Accordingly, the distance that light travels increases. Let's say 5 meters. That turns out to be 15 meters in total, not 10.
And despite this, even though the distance has increased, Einstein's theories claim that light will still travel at the same speed. Since speed is distance divided by time, since speed remains the same and distance increases, time must also increase. Yes, time itself must stretch. And although this sounds strange, it has been confirmed experimentally.
This phenomenon is called time dilation. Time moves slower for people who travel in fast-moving vehicles compared to those who are stationary.
For example, time moves 0.007 seconds slower for astronauts on the International Space Station, which is moving at 7.66 km/s relative to Earth, compared to people on the planet. Even more interesting is the situation with particles like the aforementioned electrons, which can move close to the speed of light. In the case of these particles, the degree of deceleration will be enormous.
Stephen Kolthammer, an experimental physicist at the University of Oxford in the UK, points to the example of particles called muons.
Muons are unstable: they quickly decay into simpler particles. So fast that most muons leaving the Sun should decay by the time they reach Earth. But in reality, muons arrive on Earth from the Sun in colossal volumes. Physicists have long tried to understand why.
“The answer to this mystery is that muons are generated with such energy that they travel at close to the speed of light,” says Kolthammer. “Their sense of time, so to speak, their internal clock is slow.”
Muons "stay alive" longer than expected relative to us, thanks to a real, natural time warp. When objects move quickly relative to other objects, their length also decreases and contracts. These consequences, time dilation and length reduction, are examples of how space-time changes depending on the movement of things - me, you, or a spacecraft - that have mass.
What's important, as Einstein said, is that light is not affected because it has no mass. That's why these principles go hand in hand. If things could travel faster than light, they would obey the fundamental laws that describe how the universe works. These are the key principles. Now we can talk about a few exceptions and exceptions.
On the one hand, although we haven't seen anything going faster than light, that doesn't mean that this speed limit can't theoretically be beaten under very specific conditions. For example, take the expansion of the Universe itself. Galaxies in the Universe are moving away from each other at speeds significantly exceeding light speed.
Another interesting situation concerns particles that share the same properties at the same time, no matter how far apart they are. This is the so-called “quantum entanglement.” The photon will spin up and down, randomly choosing between two possible states, but the choice of spin direction will be exactly reflected in another photon elsewhere if they are entangled.
Two scientists, each studying their own photon, would get the same result at the same time, faster than the speed of light could allow.
However, in both of these examples, it is important to note that no information travels faster than the speed of light between two objects. We can calculate the expansion of the Universe, but we cannot observe objects faster than light in it: they have disappeared from view.
As for two scientists with their photons, although they could get one result at the same time, they could not let each other know it faster than the light travels between them.
"This doesn't create any problems for us, because if you can send signals faster than light, you get weird paradoxes whereby information can somehow go back in time," says Kolthammer.
There is another possible way to make faster-than-light travel technically possible: rifts in spacetime that would allow the traveler to escape the rules of normal travel.
Gerald Cleaver of Baylor University in Texas believes that one day we will be able to build a spacecraft that travels faster than light. Which is moving through a wormhole. Wormholes are loops in space-time that fit perfectly into Einshein's theories. They could allow an astronaut to jump from one end of the universe to the other via an anomaly in spacetime, some form of cosmic shortcut.
An object traveling through a wormhole will not exceed the speed of light, but could theoretically reach its destination faster than light that takes a "normal" path. But wormholes may be completely inaccessible to space travel. Could there be another way to actively distort spacetime to move faster than 300,000 km/s relative to someone else?
Cleaver also explored the idea of an "Alcubierre engine", proposed by theoretical physicist Miguel Alcubierre in 1994. It describes a situation in which spacetime contracts in front of the spacecraft, pushing it forward, and expands behind it, also pushing it forward. “But then,” says Cleaver, “the problems arose: how to do it and how much energy would be needed.”
In 2008, he and his graduate student Richard Obouzi calculated how much energy would be needed.
"We imagined a ship 10m x 10m x 10m - 1000 cubic meters - and calculated that the amount of energy required to start the process would be equivalent to the mass of the entire Jupiter."
After this, energy must be constantly “added” so that the process does not end. No one knows if this will ever be possible, or what the necessary technology will look like. “I don’t want to be quoted for centuries as if I predicted something that would never happen,” says Cleaver, “but I don’t see any solutions yet.”
So, traveling faster than the speed of light remains science fiction at the moment. So far, the only way to visit an exoplanet during life is to plunge into deep suspended animation. And yet it's not all bad. Most of the time we talked about visible light. But in reality, light is much more than that. From radio waves and microwaves to visible light, ultraviolet radiation, X-rays and gamma rays emitted by atoms as they decay, these beautiful rays are all made of the same thing: photons.
The difference is in energy, and therefore in wavelength. Together, these rays make up the electromagnetic spectrum. The fact that radio waves, for example, travel at the speed of light is incredibly useful for communications.
In his research, Kolthammer creates a circuit that uses photons to transmit signals from one part of the circuit to another, so he is well qualified to comment on the usefulness of the incredible speed of light.
“The very fact that we built the infrastructure of the Internet, for example, and radio before it, based on light, has to do with the ease with which we can transmit it,” he notes. And he adds that light acts as the communication force of the Universe. When the electrons in a mobile phone start to shake, photons are released and cause the electrons in another mobile phone to also shake. This is how a phone call is born. The trembling of electrons in the Sun also emits photons - in huge quantities - which, of course, form light, giving life on Earth heat and, ahem, light.
Light is the universal language of the Universe. Its speed - 299,792.458 km/s - remains constant. Meanwhile, space and time are malleable. Perhaps we should think not about how to move faster than light, but how to move faster through this space and this time? Go to the root, so to speak?