The principle of constant speed of light: the speed of light in a vacuum is the same for any observer.The principle of light speed invarianceSpecial relativityIn, it means that no matter in which inertial frame（Inertial frame of reference）Observed in thevacuumThe propagation speed in is a constant and does not change with the relative motion of the reference system where the light source and the observer are located.This value is 299792458 meters/second.
Chinese name
Principle of invariance of light speed
Overview
Principle of light speed invariance: light speed in vacuum
Introduction
The principle of light speed invariance is solved by Max
The principle of light speed invariance is solved by simultaneousMaxwell's equationsAnd isMichelson Morey experimentConfirmed.The principle of constant speed of light isEinsteinCreate narrow senserelativityOne of the basic starting points of.
Einstein's famous relativity paper published in the German Physics Yearbook in September 1905《On Electrodynamics of Moving Bodies》There are four paragraphs about the speed of light:
"Light always travels at a certain speed V in the empty space, which is the same as that of the emittermotion state Not relevant. "
"The following considerations are based on the principle of relativity and the principle of invariance of light speed, which are defined as follows:
1. The laws by which the states of the physical system change have nothing to do with which of the two coordinate systems that describe these state changes is moving in parallel at a uniform speed.
2. Any ray is moving at a certain speed V in the 'stationary' coordinate system, no matter whether it is emitted by a stationary or moving object. "
"For the speed greater than the speed of light, our discussion becomes beyond doubt; in future discussions, we will find that the speed of light plays an infinite role in our physical theory."
"Thus, when ν=V, W becomes infinite.Just like our previous results,Superluminal speedThe speed of is not possible. "
(Einstein's Miracle Year - Five Papers Changing the Face of Physics [US] John StarrHullEdited by Fan DainianXu LiangyingTranslated by Shanghai Science and Technology Education Press, 2001 edition, page 97-98, page 100-101, page 109, page 127
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The fourth solution is the mass velocity solution, which is derived from the mass velocity relationship.Einstein mass velocity relation:
M=m0/√ 1 - ν 2/c2 (m is the moving mass, m0 isStatic mass, ν is the speed of motion of the object, and c is the speed of light), indicating that when the object moves at a speed much lower than the speed of light (at the human scale), the change of mass is not obvious, and the increased mass is negligible, so the mass can be considered unchanged, and the classical mechanical laws can meet the needs of calculation.But when moving close to the speed of light, the mass of the object increases more. With the speed of light approaching, the mass tends to be infinite.The big and small poles are connected, and the mass is infinite. Since the two poles are the same, the mass is infinitesimal, and the mass is infinitesimal, it can be regarded as zerophotonNo static mass.As a limiting object, light has the same size, motion and statics, and no static mass means no moving mass.From the mass velocity relation, it can also be concluded that when m0=0, m=0, ν=c, this formula is not valid.Some people think that how can there be energy without mass?It should be noted that the electromagnetic field is an energy field, and the photon is also an energy particle. Because the photon has no mass, any energy value is infinite when compared with the mass. Because there is no mass, no energy is consumed in motion. In addition to transmitting energy to other objects, the photon energy is enough to maintain its speed unchanged.
The photon without mass is not allowed by the intellect, and people look everywhere for the basis of mass.Some people think that onlyLight pressureFor quality performance, but the light pressure is unknownphotoelectric effectThe expression is light quantumLight energy conversionIs the performance of electric energy.Einstein was also quotedMass energy formula: E=mc ^ 2 (E is energy, m isInertial mass, c is the speed of light). It is believed that only when there is mass, there is energy, which conflicts with the aforementioned mass speed formula. This conflict shows that light, as the limiting object, is independent of the two formulas.According to another energy formula: E=h ν (E is energy, h is Planck constant, ν is light frequency), we can calculate the light of a certain frequencyphotonEnergy, so that m=h ν/c2 derives the photon potential mass.Note that this means that a certain energy must correspond to a certain mass, but for a photon, this is only its potential mass rather than its real mass, which is why there is no mass photon in the experiment. The potential mass only indicates how much mass can be transformed.If it is not recognized that light has quality according to classical mechanics,electromagnetic fieldWith mass, vacuum, as a light quantum field, will show huge mass. All places with light will also have heavy mass pressure. The mass of particles containing electromagnetic fields will be doubled. The law of gravity will also deform vacuum.Reasoning continues. The stronger the light is, the greater the mass is, and the greater the gravity is, the stars become black holes. Isn't that ridiculous!The electromagnetic field is an energy field,gravitational fieldIt is a quality field, and only when they are further identical will the potentialMass energy relationSublation is the real relationship, which is not the topic of this article.OtherslightBend in the gravitational field to prove that light has mass, and only things with mass are attracted by gravity.We know that energy is a repulsive force and is not affected by gravity. We will understand why it bends in the future.The electromagnetic field has energy but no mass, and the gravitational field has mass but no energy. The physical objects have both of them. We need to walk a little more to really understand them.
The fifth solution of the constant speed of light is the space-time solution, which comes fromEinstein's Theory of Relativity。The theory of relativity tells us that when an object moves at a high speed, it will become shortClock slowness”This phenomenon has very little change in low speed movement. PressNewtonian mechanicsAccording to the law, there is no change, but the change is obvious at high speed.For example, if a scale of 1 meter is taken along the direction of motion, and the earth time is 1 second, when the speed per second is 30000 kilometers, 1 meter is 0.995 meters, and 1 second is 1.01 seconds;At 150000 km, one meter is 0.866 meters and one second is 1.15 seconds;At 297000 km, one meter is 0.141 meters and one second is 7.1 seconds;At 299900 km, one meter is 0.02 meters and one second is 50 seconds.When the speed of the object movement reaches the speed of light, the scale of the object along the space direction will be reduced to zero, and the time will be slow to stop.
Explanation of "short ruler, slow clock" effectSpace and timeYesMaterial movementIt is applicable to all substances, including light.At the speed of light, the clock stops, and zero time means that light does not consume time in the process of propagation.Space is the extensibility of matter, and time is the continuity or extensibility of material changes.No time means that matter is still and unchanged, so the speed of light is unchanged.Zero spacetimeAlthough it is a reasonable inference, a natural phenomenon and natural law, it is also not allowed by intellectual metaphysics.Some people believe that motion is absolute and static is relative, which not only separates and opposes motion and static, but also reduces the corresponding category that should be used together - relative and absolute - to the lower level in metaphysics.
Dialectics holds that there is no identity.Zero spacetime does not mean that we really have nothing, but that we cannot measure this spacetime.Countless light quanta dissolve into a whole and form a unified field, regardless of each other. This light is that light. Because you can't separate a single light quanta, you can't give a specific quantumSpace and time。This phenomenon is similar to the problem of ownership by the whole people in economics: the means of production belong to all the people, and everyone has the means of production, which is only symbolic;Everyone does not own the means of production, which is practical. It is impossible to determine which means of production belong to one person. As a result, the proletariat is still the proletariat.When the world is declining, selfishness will become yours and mine. If you don't take it for nothing, everyone will take it.
Compared with the universe, the field of human life is as small as dust and is not worth mentioning.People live in the field of human scale for a long time, and their life experience and knowledge are limited here. The two poles of the world - the largest and smallest - are outside our world.If it were not for the survival crisis faced by modern mankind, which forced us to step into the mysterious realm of the two poles and seek new living space, we would never understand the dialectical thoughts of Laozi and Hegel.
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principle
Principle of light speed invariance: no matter what inertial frame (inertial reference frame) is observed, the propagation speed of light in vacuum is a constant, which is 299792.458 km/s.
fact
Four facts proving that the speed of light is constant.
The aberration of any star remains unchanged for a long time, which proves that the aberration does not change with time, so the speed of light does not change with time.The optical aberration of all stars is 20.5 ″ angular distance, which proves that the light speed of all stars is the same.
"Systematic analysis of star aberration" has demonstrated in detail that "the speed of light is constant", so it will not be repeated.
Stars are small dots one by one, which proves that all the light speed of any star is the same, that is, there is no light with different light speed.
Suppose: a star sends light of two speeds of light;The light whose speed of light is c is represented by c;The light whose speed of light is C is represented by C;Speed of light c>C
Because c and C are continuousObserverCan receive c and C at the same time;But the c and C that the observer receives at the same time must not be emitted from the star at the same time.
Therefore, suppose that the time of c sending is zero;The time when C is sent is t;The position of the star at zero time is A;The position at time t is B;Because of the starDiurnal visual movementAngular velocity ω=15.0411 ″/s, so the angular distance between A and B φ=ω t
Then: φ=10 '(1/3 of the sun's diameter);Star distance L=30 light-years.
Then: t=φ/ω=10 × 60 ÷ 15.0411 ≈ 40 (seconds)
C Propagation time T1=L/c=30 (year) ≈ 86400 × 365=946080000 (seconds)
C propagation time T2=L/C
According to the question, T2=T1+t=L/c+t=946080000+40=946080040 (seconds)
So: C=L/T2=946080000c/946080040 ≈ 0.9999999577c ≈ 2999999.987 (km/s)
That is, if φ=10 ', then c － C=30000-29999.987=0.013 (km/s)=13 (m/s)
That is to say, if the light speed difference between the two lights is 13 meters/second, the star with a distance of 30 light years will be at both A and B positions with an angular distance of 10 '.
It is much more likely that the speed of light changes continuously than intermittently. If the speed of light of a star changes continuously within the range of C and c, it seems that the star should be a line segment with a length of 10 'angular distance.
Because it has never been seen that stars have multiple positions and any elongated phenomenon, the conclusion is correct.
All stars are stationary, proving that the speed of light of all stars does not change with time, and is always constant c.This is because if the speed of light changes constantly, it seems that the stars must be moving.Method of proofIt is similar to the above and will not be repeated.
The Michelson Morey experiment of sunlight proves that the speed of light of sunlight is constant.
The Michelson Morey experiment is based on the speed of light=wavelength×frequency
The light wavelength and frequency are determined according to the light interference fringe.According to 'Yang ShiDouble slit interferenceThe distance between interference fringes in the experiment can independently calculate the 'light wavelength', and naturally determine the 'light frequency'.
In this way, the product of the determined light wavelength and frequency is a constant, that is, the product of the wavelength and frequency of light with different colors is equal;And the product value is equal to the detected 'speed of light';This fully proves that 'speed of light=wavelength × frequency' is true.
Michelson and Morey have tested the light speed of sunlight from different directions for many times over a long period of time, fully proving that the light speed of sunlight does not change.
Discrimination
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one
Cherenkov effect: the speed of light in the medium is smaller than that in vacuum.The propagation speed of particles in the medium may exceed the speed of light in the medium.In this case, radiation will occur, which is called Cherenkov effect.This is not the true superluminal speed. The true superluminal speed means that it exceeds the speed of light in vacuum.
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Third observer: If A moves eastward at a speed of 0.6c relative to C, B moves westward at a speed of 0.6c relative to C.For C, the distance between A and B increases at a rate of 1.2c.This "speed" -- the speed between two moving objects relative to a third observer -- can exceed the speed of light.But the speed of two objects relative to each other does not exceed the speed of light.In this example, in A'sCoordinate systemThe speed of B in is 0.88c.In the coordinate system of B, the speed of A is also 0.88c.
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Shadow and light spot: shake your hand under the lamp, and you will find that the speed of shadow is faster than that of hand.The ratio of the speed of the shadow and the hand shaking is equal to the ratio of their distance to the lamp.If you shake your flashlight towards the moon, you can easily make the light spot falling on the moon move faster than the speed of light.Unfortunately, information cannot be transmitted faster than light in this way.The ratio of the speed of the shadow to the speed of the hand shaking is really equal to the ratio of their distance to the lamp, but the fastest speed of the shadow will not exceed the speed of light. The same is true of the light spot. Suppose there is a slope with an elevation of 60 degrees, and an object is at a speed of 0.6CHorizontal movementIn theory, the projection speed on the slope is 1.2C. In fact, the maximum shadow speed is C. The phenomenon is that the shadow will not appear in the vertical projection direction of the object, but will lag
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Rigid body: if you hit one end of a stick, will the vibration immediately spread to the other end?Doesn't this provide a super light speed communication mode?unfortunately,idealThe rigid body ofsound velocityIn the final analysis, the speed of sound is the result of electromagnetic action, so it is impossible to exceed the speed of light.(An interesting question is, holding the upper end of a stick vertically and suddenly letting go, whether the upper end of the stick starts to fall first or the lower end of the stick starts to fall first? The answer is the upper end.)
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Phase velocity: The phase velocity of light in the medium can exceed that in vacuum in some frequency bands.The phase velocity refers to the "propagation velocity" corresponding to the phase lag of a continuous sine wave (assuming that the signal has been propagating for a long enough time to reach a stable state) after propagating for a certain distance in the medium.Obviously, a simple sine wave cannot transmit information.To transmit information, it is necessary to modulate the slow changing wave packet on the sine wave. The propagation speed of such wave packet is called group velocity, which is less than the speed of light.(Note: Sommerfeld and Brillouin's research on the propagation of pulse in the medium proves that the signal with a starting time [the signal that is zero before a certain time] cannot travel faster than the speed of light in the medium.)
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Superluminal galaxies: galaxies moving towards us may have an apparent speed exceeding the speed of light.This is an illusion, because there is no correction for the reduction of time from the galaxy to us.For example, if we measure a galaxy 10 light years away from us, its velocity is 2/3c.Now, the measured distance is 30 light-years, because when the light it emitted arrived, the galaxy reached 10 light-years, 3 years later, and the galaxy reached 8 light-years, so the apparent distance was three times of 8 light-years, that is, 24 light-years.As a result, the visual distance decreased by 6 light years in 3 years
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Relativity rocket: people on the earth see the rocket moving away at a speed of 0.8c, and the clock on the rocket is slower than people on the earthEarth clock0.6 times.If you divide the distance the rocket moves by the time on the rocket, you will get a "speed" of 4/3 c.(There is a problem here. First, take the rocket as the reference system, and the speed of the rocket is 0. At this time, only the speed of the earth away from the rocket can be calculated. The time of the rocket reference system is 0.6 times that of the earth, and the distance is 0.6 times that of the earth. The speed of the earth away from the rocket=0.6 * 0.8c/0.6=0.8c)Therefore, the people on the rocket move at a speed "equivalent to" the speed of superlight.For the people on the rocket, time has not slowed down, but the distance between galaxies has shrunk to 0.6 times of the original, so they also feel that they are moving at a speed equivalent to 4/3c.The problem here is that the number obtained by dividing the distance in one coordinate system by the time in another coordinate system is not the real speed.
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The propagation speed of gravity: Some people think that the propagation speed of gravity exceeds the speed of light.In fact, gravity travels at the speed of light.
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EPR paradox: Einstein, Podolski and Rosen published a thought experiment in 1935 to try to show thatquantum mechanicsIncompleteness of.They believe that there is an obvious over distance effect when measuring two separated particles in the entangled state.Ebhard proved that it is impossible to use this effect to transmit any information, so superluminal communication does not exist.But there is still controversy about the EPR paradox.
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Virtual particleIn quantum field theory, force is transmitted through virtual particles.becauseHeisenberg Uncertainty These virtual particles can travel at superluminal speed, but virtual particles are only mathematical symbols, and superluminal travel or communication still does not exist.
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Quantum tunnel: quantum tunnel is the effect of a particle escaping from a potential barrier higher than its own energy, which is impossible in classical physics.Calculate the time when particles pass through the tunnel, and it will be found that the particle speed exceeds the speed of light.[1]A group of physicists made use ofQuantum tunneling effectExperiment of superluminal communication: they claim to have transmitted through 11.4cm wide barrier at 4.7cMozartSymphony No. 40.Of course, this has caused great controversy.Most physicists believe that because of Heisenberg uncertainty, it is impossible to use this quantum effect to transmit information at superluminal speed.If this effect is true, it is possible to use similar devices to transmit information to the past in a high-speed coordinate system.[2-3]Terence Tao believes that the above experiment is not convincing.It takes less than 0.4 nanoseconds for a signal to travel 11.4 cm at the speed of light, but it can predict an acoustic signal up to 1000 nanoseconds through simple extrapolation.Therefore, it is necessary to conduct experiments on faster than light communication over a longer distance or on high-frequency random signals.
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Casimir effect: when two uncharged conductor plates are very close, there will be very weak but still measurable force between them, which is the Casimir effect.The Casimi effect is caused by vacuum energy.Scharnhorst's calculation shows that between two metal platesLateral movementThe speed of a photon must be slightly greater than the speed of light (for a gap of one nanometer, this speed is 10-24 greater than the speed of light).Under certain cosmological conditions (such as near the cosmic string [if they exist]), this effect will be much more significant.However, further theoretical research shows that it is impossible to use this effect for superluminal communication.[4-6]
thirteen
Cosmic expansionHubbleThe theorem says that galaxies at distance D separate at the speed of HD.H is a constant independent of galaxies, called the Hubble constant.Galaxies far enough away may separate from each other at a speed faster than the speed of light, but this is relative to the separation speed of a third observer.
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The moon revolves around me at a speed faster than light: when the moon ishorizonAt the time of going up, let's assume that we circle at the speed of half a cycle per second, because the moon is 385000 kilometers away from us, and the speed of the moon relative to us is 1.21 million kilometers per second, about four times the speed of light!This sounds quite ridiculous, because in fact, we are rotating ourselves, but we say that the moon is circling around us.But according toGeneral relativityAny coordinate system, including the rotating coordinate system, is available. Isn't it that the moon is moving at superluminal speed?The problem is that in general relativity, the speed of different places cannot be directly compared.The speed of the moon can only be compared with other objects in its local inertial system.In fact, the concept of speed is not very useful in general relativity, and it is difficult to define what is "superluminal speed" in general relativity.In general relativity, even“Constant speed of light”They all need to be explained.EinsteinI said on page 76 of Relativity: Special and General Theory that "the speed of light is constant" is not always correct.When there is no absolute definition of time and distance, how to determine the speed is not so clear.Nevertheless, modern physics believes that the speed of light in general relativity is still constant.When the unit of distance and time are linked by the speed of light, the invariance of the speed of light is defined as an axiom that goes without saying.In the above example, the speed of the moon is still less than the speed of light, because at any time, it is located in thefutureInside the light cone.
fifteen
Clarify the definition of superluminal speed: The various plausible examples of superluminal speed listed in the first part show the difficulty in defining superluminal speed.For example, the "superluminal speed" of shadows and light spots is not the real superluminal speed, so what is the real superluminal speed?In relativity“World line”It is an important concept, and we can use the "world line" to give a clear definition of "superluminal speed".What is "World Line"?We know that all objects are composed of particles. If we can describe the position of particles at any time, we will describe the whole "history" of objects.Imagine a three-dimensional space and a one-dimensional timeFour-dimensional space。Since a particle can only be in a specific position at any time, its entire "history" is a continuous curve in this four-dimensional space, which is called "world line".The world lines of an object are a collection of the world lines of all the particles constituting it.Not only the history of particles can form world lines, but also the history of some artificially defined "things" can form world lines, such as shadows and light spots.The shadow can be defined by the points on its boundary.These points are not real particles, but their positions can be moved, so their "history" also constitutes a world line.Four-dimensional space-timeA point in represents an "event", that is, three spatial coordinates plus a time coordinate.Space time distance can be defined between any two "events". It is the square of the space distance between two events minus the square of the product of the time interval and the speed of light and then the root sign.The narrow relative argument shows that this space-time distance is independent of the coordinate system, so it is of physical significance.Space time distance can be divided into three categories: time like distance: the space interval is less than the light like distance multiplied by the time interval and the speed of light;Light like distance: space interval is equal to the product of time interval and light speed;Space like distance: space interval is greater than the product of time interval and light speed. We need to introduce the concept of "local".OneSmooth curve, "locally", very similar to a straight line.Similarly, four-dimensional spacetime is flat locally, and the world line is similar to a straight line locally, that is, it can be described by uniform motion, which is the speed of particlesInstantaneous velocity。photonLocally, the distance between adjacent events is light like.In this sense, we can say that the world line of photons is light like.The world line of any particle moving at a speed lower than the speed of light. Locally, the distance between adjacent events is timelike.In this sense, we can say that this kind of world line is timelike.InsteadSuperluminal motionThe world line of particles or artificially defined "points" is empty like.The word "world line" here is spacelike, which means that the space-time distance of adjacent events is spacelike when viewed locally.Because there may be curved space-time, there may be such a world line: locally, the distance between adjacent events is time like, and particles do not move faster than light speed;But there are two events that are far apart, and their space-time distance is empty.Is this a superluminal situation?The significance of this problem is that it can define both local "superluminal speed" and global "superluminal speed".Even if local superluminal speed is impossible, the possibility of global superluminal speed is not ruled out.Global superluminal speed is also worth discussing.In a word, "superluminal speed" can be defined by the spacelike world line. The advantage of this definition is that it excludes the situation that two objects move at "superluminal speed" relative to the third observer.Now let's consider what is the "thing" we want to transmit at superluminal speed. The main purpose is to exclude useless things such as "shadow" and "light spot".particle, energy, chargespinInformation is what we want to transmit.One question is: How do we know whether the thing being transmitted is the original thing?This problem is relatively easy. For a particle, we observe its world line. If the world line is continuous and no other particles are separated from this particle, we can generally think that this particle is still the original particle.Obviously, transmitting the whole object is technically more difficult than transmitting information.Now we can transmit information at the speed of light without any difficulty.Essentially, we just put information on the time series of photons and retrieve human readable information from the time series of photons, and the speed of photons is naturally the speed of light.Similarly, ifTachyon(Tachyons, predicted in theoryTachyon）If it really exists, we only need to find a technology that can control its generation and transmission direction to achieve superluminal communication.It is very likely that the cost of transporting different particles is very different, and the more economical way is to use replication technology.If we can get all the information about an object, and we have mastered the technology of copying the original object from this information, then superluminal communication and superluminal travel are equivalent.Science fiction has had this idea for a long time, which is called remote fax.To put it simply, it is like faxing a copy of the original and then destroying the original, which is equivalent to sending the person over.Of course, the question is whether a conscious complex object like human can be duplicated.
sixteen
Infinite energy: E=mc ^ 2/sqrt (1 - v ^ 2/c ^ 2) The above formula is the energy of a particle with a static mass of m moving at the speed v.Obviously, the higher the speed, the greater the energy.Therefore, to accelerate the particles, it is necessary toWorkThe work done is equal to the increase of particle energy.Note that when v approaches c, the energy tends to infinity, so it is impossible to accelerate particles to the speed of light in the usual way, let alone exceed the speed of light.But this does not rule out the possibility of making particles faster than light in other ways.Particles candecayOther particles, including photons moving at the speed of light (the static mass of photons is zero, so although they move at the speed of light, their energy can also be finite, and the above formula is invalid for photons).The details of the decay process cannot be described by classical physics, so we cannot deny the possibility of producing superluminal particles through decay (?).Another possibility is particles whose speed is always higher than the speed of light.Since there are photons always moving at the speed of light and particles always moving at a speed lower than the speed of light, why can't there be particles always moving at a speed higher than the speed of light?The problem is that if v>c in the above formula, either the energy is imaginary or the mass is imaginary.If there are such particles, does the imaginary energy and mass have any physical significance?How should they be interpreted?Can we deduce observable predictions?As long as we find the evidence of the existence of such particles, find the method to detect such particles, and find the method to deflect the movement of such particles, we can achieve superluminal communication.[7]
seventeen
Quantum field theory: so far, all physical phenomena except gravity conform to the standard model of particle physics.The Standard Model is a relativistic quantum field theory, which can describeElectromagnetic interaction, weak interaction, strong interaction and all observed particles.According to this theory, any pair of operators corresponding to two physical observations at the event location with a spacelike distance is commutative (any pair ofoperators corresponding to physical observables at space-time events which are separated by a space like interval commute）。In principle, this means that no action can travel faster than the speed of light.However, no one can prove that the standard model is self consistent.It is very likely that it is actually not self consistent.In any case, it cannot guarantee that particles or interactions that it cannot describe will not be found in the future.No one has extended it to include general relativity and gravity.Many people who study quantum gravity doubt whether such simple statements about causality and locality can be generalized in this way.In a word, in the future more perfect theories, there is no guarantee that the speed of light is still the upper limit of speed.
eighteen
Grandfather's paradox (causality): The best evidence against superluminal speed is probably the Grandfather's paradox.According to special relativity, particles moving faster than light in one reference system may return to the past in another coordinate system.Therefore, superluminal travel and superluminal communication also mean returning to the past or transmitting information to the past.If time travel is possible, you can go back and kill your own grandfather.This is a strong rebuttal to superluminal speed.But it cannot rule out the possibility that we may travel at a limited superluminal speed but cannot go back to the past.Another possibility is that when we travel faster than light speed, causality is destroyed in a consistent way.In a word, time travel and superluminal travel are not the same but related.If we can go back to the past, we can also travel faster than light in general.
nineteen
Tachyon: tachyon is a particle predicted in theory.It has a local velocity that exceeds the speed of light（Instantaneous velocity）。Its mass is imaginary, but its energy andmomentumIs a real number.Some people think that such particles cannot be detected, but this is not necessarily the case.The examples of shadows and light spots show that things that exceed the speed of light can also be observed.At present, there is no experimental evidence for the existence of tachyons, and most people suspect their existence.It is claimed that the Tritium Beta decayneutrinoThere is evidence in mass experiments that these neutrinos are tachyons.This is very doubtful, but it cannot be completely ruled out.The problem of tachyon theory is that it violates causality, and the existence of tachyons makes vacuum unstable.The latter can be avoided in theory, but then we cannot achieve the superluminal communication we want.In fact, most physicists believe that tachyons are the manifestation of the pathological behavior of field theory, and the public's interest in tachyons is mostly due to their many appearances in science fiction.
twenty
Wormhole: A famous suggestion for global superluminal travel is to useWormhole。Wormholes areCurved spacetimeAs a shortcut to connect two places in, the time ratio required to cross the wormhole from place A to place BlightIt takes a shorter time to propagate from A to B along the normal path.Wormholes are the corollary of classical general relativity, but creating a wormhole needs to change space-timetopologyStructure.This isQuantum gravity theoryIs possible.Opening a wormhole requires a negative energy area. Misner and Thorn suggest that the Casimir effect be used to generate a negative energy area on a large scale.Visser recommends using cosmic strings.These suggestions are almost unrealistic.Strange materials with negative energy may not exist in the form they require.Thorn found that if wormholes can be created, they can be used to construct closed timelike world lines in space-time, so as to realize time travel.Some people think yesquantumThe multiple interpretation of mechanics can be used to eliminate the paradox of causality, that is, if you go back to the past, history will occur in a different way from the original.Hawking believes that wormholes are unstable and therefore useless.But wormholes are still a fruitful area for thought experiments, which can be used to clarify what is possible and what is impossible under the known and proposed physical laws.[8-12]
twenty-one
Warp drive: Warp drive refers to makingSpace-time curvatureSo that the objectSuperluminal motion。Miguel Alcubierre is famous for proposing a space-time geometric structure that can realize curved phase propulsion.The curvature of space-time allows objects to travel at the speed of superlight while maintaining a time likeWorld lineOn.Like wormholes, curvilinear propulsion requires strange materials with negative energy density.Even if such substances exist, it is unclear how they should be arranged to achieve curved phase propulsion.
