It not only connects time and space fundamentally, but also guarantees the future.
Will not happen before the past. Therefore, some people say that we can stop the footsteps of light, which may be
It's amazing.
When you read this sentence, michael schumacher was driving his car.
Ferrari runs 300 meters, and light can travel back and forth between the earth and the moon. light
It moved so fast that for most of human history.
It's instantaneous. We now know that of course not. We have learned to control.
The speed of light We can slow down or even stop the movement of light, and then gently.
The switch makes it move again. We can see that the light beat it in the competition.
You can also use the speed of light to measure the age of the universe. It can even decide how much you are.
Tall man.
Ole Romer, a Danish astronomer, successfully calculated for the first time17th century.
Out of the light speed. He used the regular orbital motion of one of Jupiter's satellites as a timer.
Every time this satellite is covered by a giant planet (Jupiter), he records one.
Tick tock, tick tock. But he found that from the earth, the appearance of these ticks was not as expected.
Think about it regularly, sometimes a few minutes faster and sometimes a few minutes slower in a year.
Romer calculated that these delays are one of them when Jupiter and the Earth orbit the sun.
Caused by the change of the distance between them. By calculating that the earth, Jupiter and its satellites will be in a year
In the relative position of orbit, he calculated the speed of light through space. Romoyu
1676 submitted his results to the French Academy of Sciences, and the value is one of the currently recognized values.
The difference is not more than 30%.
The theoretical discussion on the nature of light also gives people an understanding of the speed of light. 19th century 60
In the mid-1990s, Scottish scientist james clerk maxwell set up a team.
Equation describing the behavior of space electromagnetic field. The solution of this equation shows that electricity
Magnetic waves must travel at a speed of about 300,000 kilometers per second in a vacuum, which is different from Romer and his.
The measurement results of later generations are quite close.
Michael faraday of the Royal Institute in London used the concepts of electric field and magnetic field to explain it.
Electrostatic force and magnetic field force, and show that light will be affected by magnetic field. This confirms the visible light thing.
In fact, it is part of the electromagnetic spectrum. For other parts of the electromagnetic spectrum-microwave, red
The direct measurement of the propagation velocity of external lines, ultraviolet rays, X rays and γ rays shows that,
They all have the same speed in a vacuum.
Experiments used to measure the speed of light are getting more and more accurate. By the 1950s,
Electronic timing devices have replaced ancient mechanical equipment. In the 1980 s, through
Measure laser and frequency (f) and wavelength (λ), and calculate light with formula c=fλ.
Speed (c). These calculations are based on the standard definition of meters and seconds, just like now.
1 meter is defined as 1, 650,763.73 times the wavelength of light generated by krypton -86 source, and it is determined as 1 second.
It means that the radiation frequency released by the ultra-fine transition of cesium-133 atom is 9, 192, 63 1, 770 times.
This makes C achieve very high accuracy, and the error is only a few parts per billion.
1983, the speed of light replaces the meter as the definition standard, and the agreement is as follows.
299,792,458 m/s, the value conforms to the definition of meters at that time. Definition of seconds and light speed
Value, representing 1 m, is defined as the distance that light travels in vacuum in1/299,792,458 seconds.
Leave. Therefore, since 1983, no matter how accurate we have measured the speed of light,
Correction will not affect the speed of light, but will affect the length of meters. How tall are you?
Is actually defined by the speed of light.
But the speed of light also defines something more basic than length. Albert Anse
Tan's works show the real importance of the speed of light. Because of his contribution, we know that,
The speed of light is not only the speed at which photons move in a vacuum, but also the relationship between time and space.
Basic constant.
When Einstein was young, he once asked himself whether people move fast enough.
To keep up with the footsteps of light, what light looks like. In theory, it looks like
There is a stationary peak around you, but Einstein knows Maxwell's equations don't allow it.
This kind of result occurs. His conclusion is that either Maxwell's theory is not applicable.
For the observer in motion, either the relative motion mechanics needs to be changed.
Einstein solved this problem in his special theory of relativity published in 1905.
This theory is based on a general principle: relative to any observer moving at a uniform speed,
Generally speaking, no matter what the speed is, the physical principle is the same as the speed of light. own
Stan's special theory of relativity completely changed our concept of time and space.
, emphasizing the fundamental position of the speed of light in physics.
Imagine you are in a rocket, rushing into space with laser pulses.
Observers on earth will see this pulse disappear at the speed of light. Are you relative to the earth
What is the speed of motion, such as 99% of the speed of light, and light still surpasses you at the speed of light.
It seems absurd, but it's true. The only way to achieve this is you.
Residents in rockets and observers on the earth's surface measure time and space in different ways.
Time and space certainly look different, depending on whether you are on the earth or not.
Is in space. Einstein's general theory of relativity describes gravity as space-time geometry.
Structural distortion. A corollary of this statement is to always follow the shortest possible path.
Light traveling through time and space will bend near a massive object. This is during the 19 19 solar eclipse.
It is proved that the starlight passing near the sun is bent by the mass of the sun. this
An observation made Einstein's theory finally accepted and won him worldwide recognition.
Fame.
But according to the basic mechanics principle, if the light is deflected, it will be accelerated. this is
Will it change the speed of light and shake the fundamental principle of relativity? In a sense, it is right.
Yes, the speed of light we observe from the earth is like this when passing near the sun.
Change. However, the theory of relativity and the principle of constant speed of light cannot be abandoned.
Gravitational prank-seeing is believing
Einstein realized that gravity was experienced by observers who could not move freely.
A little delusional. Imagine jumping off a wall. In the process of free fall, you won't feel it
Move the gravity around you, but anyone who watches you fall to the ground will understand.
It means that your movement is caused by gravity. The same is true for the space flight of the space station.
Members also apply: they are always mentioned as being in a "zero gravity" environment, but
Looking up from the earth's surface, we will explain their orbits around the earth by gravitational attraction.
Tao movement. So when we look from the earth, the light passing near the sun looks good.
Bending and accelerating, but if we fall to the sun freely, the light looks like
Will overtake us in a straight line at a constant speed. For any observer of free fall,
The light passing through him moves at a constant speed. However, when it passes through and distorts its neighborhood,
An empty object appears to bend and accelerate.
Another strange inference of relativity is that nothing can accelerate to the speed of light.
Unless we build powerful rocket ships, they will never reach the light.
Speed. This is because the faster an object moves, the greater its kinetic energy and inertia. own
In his E=mc2 formula, Stein pointed out that energy is related to mass or inertia.
Therefore, as the kinetic energy of an object increases, its inertia also increases, making it more and more difficult to continue.
Accelerate. This is a principle of diminishing returns: the more work you do on an object, the more it will be.
The heavier it becomes, the weaker the acceleration effect is.
Accelerating a single electron to the speed of light requires infinite energy, particle physicist.
Scientists are deeply touched by this restriction. Protons enter Fermi in Tawiah, Illinois, USA.
When the Tevatron accelerators in the laboratory are running, their speed has reached 99% of the speed of light.
The last stage of the accelerator increases the energy of protons by 100 times, but the speed is only increased to.
The speed of light is 99.99995%, which is less than 1% higher than their speed of entering the accelerator.
However, quantum theory, which has always been in conflict with relativity, seems to allow matter
Moving faster than the speed of light. In the 1920s, quantum theory showed a system.
Different components that are far apart can be connected immediately. For example, when a high-energy photon
When decaying into two low-energy photons, their states (for example, clockwise or counterclockwise).
Spin is uncertain until one of them is observed.
Another particle seems to perceive that its companion has been observed, and the result is Ren.
How to measure the second particle will always be consistent with the measurement of the first particle.
Result. Such a long-distance instantaneous connection looks like a message of infinite size.
Velocity is transmitted between particles. Einstein called it "ghost work at a distance."
"Use" sounds incredible, but it is a real phenomenon.
In 1993, Raymond Chiao of the University of California at Berkeley shows that,
Quantum theory also allows another kind of superluminal travel: quantum tunneling. Imagine facing a wall.
Play football on a solid wall. Newtonian mechanics predicts that it will bounce back, but quantum mechanics
It is predicted that it is unlikely to appear on the other side of the wall. Consider one of the following situations.
The way is to imagine that it can "borrow" enough energy to cross the wall to reach another wall.
Return the energy immediately after the face. This does not violate the laws of physics, because the final energy,
Momentum and other properties are preserved. Measurement by German physicist Wiener Heisenberg
The uncertainty principle shows that there are always some attributes in a system-in this case.
But the value of energy is uncertain, so the principle of quantum physics benefits the system.
With this uncertainty, we can borrow some extra energy in a short time. In the case of tunnels,
The need for particles to disappear from one side of the obstacle and reappear from the other side is almost negligible.
Obstacles can be arbitrarily thick-but with the increase of thickness, particle tunnels become less.
This ratio is rapidly falling towards zero.
Jiao Lizhong is proved by measuring the tunneling time of visible light photons through a specific filter.
Understand the existence of "superluminal" tunnel effect. To this end, he made these photons.
Photons passing through vacuum in similar time are compared. As a result, tunnel photons first reach the detection point.
Jiao Lizhong proved that their speed through the filter may be 1.7 times the speed of light.
1994, Ferenc Kraus of Vienna University of Technology shows that the tunneling time is as follows.
Independent of the upper limit of the thickness of the obstacle, it indicates the time for photons to pass through the obstacle.
There is no upper limit. Gunter Niemz of the University of Cologne also achieved this with microwaves.
He even modulated Mozart's Symphony No.40 on the signal.
4.7 times the speed of light to transmit it through an obstacle with a thickness of 12 cm.
Full speed ahead-the limit of information transmission
All these ideas seem to shake the relativistic principle of prohibiting superluminal. In that way
Neither, because what relativity forbids is actually the superluminal propagation of information.
Experiments show that the "instantaneous connection" between two quantum objects cannot be used to transmit letters.
Rest. The tunneling effect is also limited by the same. This is because quantum theory is intrinsic.
Statistical law, which depends on the nature of a large number of particle swarm. So when some photons exceed,
Time cannot be used to convey information. Tunnel effect distorts the input waveform and produces it.
Give birth to a peak that may be received earlier than expected. However, information is not made up of
A single wave peak carries it, but it is transmitted through the whole wave packet, and its moving speed is not faster than light.
Careful analysis of the tunneling effect seems to support that the information content of the signal is still influenced by light.
Speed limit, although it is still a controversial topic.
The speed limit of information transmission protects the law of causality, that is, the result of an event.
It can't have happened before this event. If not, observe the movement at different speeds.
Researchers will never come to the same conclusion about the sequence of a series of related events. have
Some people may bump into a teacup and see its fragments scattered, while another observer
But you may see the fragments first, and then you may see the cup fall. If there is no information transmission speed
With this limit, the universe will look strange.
Although it is impossible to make a massive particle move faster than light in a vacuum,
This is not the case for substances whose "refractive index" exceeds 1. For example, in water, light
The moving speed is 60% of its vacuum speed. The speed of light in different transparent materials will be
Slow down, it was discovered 300 years ago. It can explain the refraction of light and
Scattering is also the principle behind all optical instruments. Refraction occurs because of light.
Neutrons-independent energy units that make up light-interact with electrons inside atoms.
Use. Photons travel at full speed between atoms, but they will be repeated in the process of passing through materials.
They are absorbed and released again, so the speed at which they carry information will be reduced.
Therefore, particles such as high-energy electrons may be in the same medium as light in water.
Be quick. In this case, they generate electromagnetic waves, which do not move at the same speed.
When the speed of particles is very fast, they will gather along the direction of motion and form a violent shock wave, which is different from supersonic speed.
The mechanism of sonic boom in high-speed aircraft is the same. Particles moving faster than the speed of light in a material medium are produced.
This kind of radiation, called Cherenkov radiation, is often used to detect other movements faster than light.
Invisible particles, such as the Shengang Cosmic Particle Research Facility of Tokyo Cosmic Ray Research Institute.
Looking for neutrinos in a huge detector filled with water.
Most substances do not significantly slow down the speed of light. In ordinary matter, the speed of light can be reduced.
The decline does not exceed 50%. However, 1998 Lene of Harvard University in the United States.
Vestergaard Hou announced that she had reduced the speed of light to17m per second. 200 1, she
Completely extinguished the lights. Of course, her research team is not using ordinary materials, but
It is the so-called fifth substance (after solid, liquid, gas and plasma).
Mass state: Bose-Einstein condensate.
This unusual substance consists of a mass of atoms, which is cooled to.
One millionth of a degree above absolute zero, thus forming Bose-Einstein condensation. it
The essence is a single quantum object, a bit like a giant atom, all of which
All atoms are in the same quantum state and move in the same way as if they were a whole.
An object.
The trick to slow down the speed of light is to irradiate Bose-
Einstein condensate. One of them carries information, called probe light; The other is called.
Coupled light. When the coupled light strikes the condensate, it will become completely transparent, so
So that probe light can pass through.
There is an electron in the outermost orbit of the sodium atom, between the probe light and this electron.
The interaction between them is very important to this process. When an atom absorbs one from the detected speed of light.
When there are 10 photons, the outer electrons jump to a higher energy level. After a short time,
It falls back to its original energy level, releasing a photon. Unfortunately, this is too
This process is completely random, so all the information in the original beam is lost.
Components of probe light with different pulse frequencies have different velocities when passing through condensate,
The result is that the input pulse gathers in the sodium atom cloud and passes slowly.
At the same time, the spin of the atom changes under the influence of the pulse. If that couple light is removed at this time
Otherwise, the optical pulse (or at least the information in it) will be bound to the spin mode of the atom.
In the room, the light beam basically stopped. When the coupling lamp lights up again, the condensate is released again.
Light pulse.
Slowing down or stopping the speed of light may find practical application in operation. physics
Scientists have long wanted to make optical computers, using the speed of light instead of electrons to transmit letters.
Number, perform the operation. They also hope to use the quantum state of atoms to build a quantum computer.
And strange quantum principles to make processors with super computing power. Hou deals with light.
Technology may also help scientists simulate the behavior of light near black holes. In fact, research
Studying the speed of light may be the most profound mystery in the universe-those mysteries determined by the speed of light.
-The best way.
Supplement 1: pranks of light and hallucinations in space
There are many examples showing that objects seem to move faster than the speed of light. But in fact, they didn't
Do not violate the principle of relativity. For example, an electron beam sweeps across a line drawn by a TV screen.
Theoretically, it can move faster than the speed of light. The reason for this phenomenon is the continuous fluorescence on the screen.
Optical pixels are excited by different electrons. Therefore, it is nothing more than light in essence.
Move quickly from one point to the next simply because they are emitted in a certain order.
Bright, so it looks like this.
Astronomers have seen the illusion of faster than light in space: quasars sometimes blow out.
A jet that looks much faster than the speed of light. In order to measure the velocity of these jets,
Astronomers need to take two measurements of their positions to determine the time between these two measurements.
To calculate the speed of injection. But if this speed is much faster than the speed of light, it will be enough.
Reason: Because the jet bursts directly towards the observer. So, the next point of view
It is necessary to consider that the airflow is closer to the observer and the emitted light needs to reach the earth.
Time has been reduced. This makes the distance of jet movement appear to be in the interval between two observations.
It is higher than it really is.
Two American astronomers, Edwin Hubble and Vesto shriver, are 20 years old.
Another illusion was discovered in the 1920s. They found that the universe is expanding, and galaxies are like
The fragments produced by the explosion are far apart from each other. But in this case, between galaxies,
The farther the distance, the greater the separation speed. If galaxies are far enough away, they will retreat.
Travel is faster than light. So if this apparent expansion is caused by galaxies,
Running in space, nothing can run faster than light.
It is broken. But this is actually an illusion. The superluminal motion of galaxies is actually
The space between galaxies is expanding. No matter what people think they see,
The speed of light has not been surpassed.
Supplement 2: Is the speed of light uneven in a uniform universe?
In cosmology, there is a problem called "horizon problem"
Prolem). The speed of light may not always be as great as it is now. If over time,
Change, much faster than now, may help solve the universe.
The mystery of learning.
If the speed of light is the upper limit of any signal transmission speed, those far away in the universe
There is no reason for the region to reach thermal equilibrium. Simply put, it is because there is nothing.
-Including heat.-You can cover this distance in the time after the Big Bang.
And if the two areas can't exchange heat, they can't reach the same temperature.
However, the universe is quite uniform on a large scale, so it must have existed in the past.
To some extent, the most reasonable explanation for this is called inflation theory. This principle
Theoretically, the leisurely expansion was found in Harbin very early.
Before the beginning, the universe experienced a period of exponential expansion.
However, this rapid expansion faces its own light speed problem, which urges physics.
Scientists think that the speed of light in the early universe may be different from that now. If the speed of light used to be
Much faster than now, it will make the "horizon" spread further, so that heat can be realized.
Balance.
It is not clear whether this bold theory can be integrated into other physical theories.
However, it still shows that the speed of light occupies a core position in our understanding of the universe.