What limits the speed of light propagation, GZK blocking is only one of the reasons.
The nature of light and the speed of light propagation.
Through many of the chapters above, we have analyzed many experiments with light. Includes light reflection, refraction, dispersion, interference, diffraction, photoelectric effects and Michelson Morley experiments. In this chapter, we will have an overall summary and divergent thinking about light knowledge.
Without light, the human world is unimaginable, but it seems really difficult for us to understand light and catch up with light. From the birth of mankind to today, optical research is still very hot, which is enough to illustrate this point. Some people even say that light is something that "connects the upper and lower", connecting the macroscopic world and the quantum world, and whoever understands the essence of light will have a deep understanding of this world.
What do you think of light? What does light mean to you? Today we will enter the world of light together to unveil its most magical veil.
First of all, everyone must know that "light" is a special word, why do you say this? Because the essence of light is electromagnetic waves. Maxwell was the first to predict that light is an electromagnetic wave, and Hertz was the first to confirm it experimentally.
What we usually call light, light source, is the electromagnetic wave that we can see. The visible spectral range of electromagnetic waves is about 390~760nm, which is only a very small part of the entire electromagnetic spectrum, so light is special. Other spectral ranges are electromagnetic waves invisible to humans, with ultraviolet, infrared, X-rays, gamma rays, and so on.
So the important thing is emphasized again - light is an electromagnetic wave! So let me now ask you a question.
Does light have refraction, reflection, interference, and photoelectric effects, as well as X-rays, gamma rays, ultraviolet rays, etc.? The answer is certain, all the properties of light, electromagnetic waves in other bands also have. It's just that our human eyes can't see it, and we can observe it with the help of other instruments.
However, electromagnetic waves in different spectral ranges will have different differences. For example, X-rays, gamma rays have strong penetrating properties and are harmful to the human body. But it is emphasized here that this difference is mainly for humans. Because for a stone, any kind of electromagnetic wave is the same. A stone cannot see electromagnetic waves in any spectral range, and the word "harm" does not exist for it.
Light is an electromagnetic wave, which leads to another question - what is the nature of electromagnetic waves? Only by understanding the nature of electromagnetic waves can we understand the nature of light. Electromagnetic waves are a form of motion of electromagnetic fields. Electricity and magnetism can be said to be two sides of the same coin, a changing electric field will produce a magnetic field (that is, the current will produce a magnetic field), and a changing magnetic field will produce an electric field. The changing electric field and the changing magnetic field constitute an inseparable unified field, which is the electromagnetic field. The propagation of the changing electromagnetic field in space forms electromagnetic waves, and the changes in electromagnetism are like water waves generated by a breeze blowing the surface of the water, so it is called electromagnetic waves.
The official definition of electromagnetic waves is as follows: electromagnetic waves are oscillating particle waves derived and emitted in space by electric and magnetic fields that are in phase and perpendicular to each other, and are electromagnetic fields that propagate in the form of fluctuations and have wave-particle duality. Electromagnetic waves are electric and magnetic fields that oscillate in phase and are perpendicular to each other moving in space in the form of waves, and their propagation direction is perpendicular to the electric field. Electromagnetic waves have a fixed rate in a vacuum, at the speed of light.
So the essence of electromagnetic waves is electromagnetic field radiation. Then, according to the theory of radiation, absolute zero is unattainable, which means that everything has radiation. Radiating energy outward, this radiation is electromagnetic radiation.
In another popular saying, electromagnetic waves are an energy, and light is naturally an energy. In this way we extend the general understanding of light to all matter, and any matter is energy.
At this time, everyone will think of a mass-energy formula of Einstein: E=MC2. Does light appear in this formula? Is this accidental? Obviously I wouldn't think so. Deriving here, let's summarize that light is an electromagnetic wave, electromagnetic wave is an energy radiation, that is, light is an energy.
The mass-energy formula is universal, it is a formula applicable within the universe, and the appearance of light in this formula itself represents that it is an indispensable "factor" for measuring the material energy of the universe.
Whether you are a junior high school student or a scientific researcher, if you have never thought this way, you can think about this problem now.
I emphasized in the first chapter that "the world is certain, but we cannot grasp the certainty of the world." The deeper meaning of this sentence includes that the contingency of any connection is certain. So the appearance of light in this mass-energy formula is not accidental.
It is also with this guidance in mind that I boldly redefine inertia in Change. That is to say, the fact that the inertial mass and gravitational mass are strictly equal does not seem to me to be accidental, so I deduce that gravity is the source of inertia.
Similarly, the many inverse squared laws in the universe are not accidental in my eyes and are worth exploring. If you see all these similarities as accidents, we will inevitably lose the opportunity to get closer to the truth.
Coincidentally, light also appears in Einstein's field equations. Newtonian mechanics is the limit of Einstein's special theory of relativity at low speeds, including the law of universal gravitation. So the gravitational formula is actually a factor that hides "light". When you think of low speed, you immediately think of the word "speed." But when you think of speed, you think of the speed of light! That's right, that's it. The impact of speed is still new to us humans. A new view of time and space, a new view of the universe, as if everything is new.
Our chapter is a summarizing and enlightening understanding of light, so we must focus on light. So now let's talk about the movement of light, about the movement of light, the foreshadowing of the previous chapters, is already the result of modern experiments.
First of all, the first impression of our ordinary people is that light travels in a straight line, and secondly, the speed of light is fast and is the fastest. One involves the direction of movement, the other involves the speed of movement, and now we analyze these two points.
A more rigorous understanding would be that light propagates in a straight line in a vacuum, or it can be expressed as light traveling in a straight line in the same homogeneous medium. But the strictest vacuum and homogeneous medium do not exist. 】
In the real world, light does not travel in a straight line most of the time. When light propagates in the medium, due to the interaction of the light, its propagation path will be deflected when it encounters a smooth object, resulting in reflection and refraction.
There are also interference, diffraction and other phenomena under different conditions. In addition, according to general relativity, when light propagates near a massive object, the propagation path of light will also be deflected accordingly due to the influence of the strong gravitational field of the object.
So I have a problem again now? Are we correct in saying that light travels in a straight line? The answer is yes. Light travels in a straight line in the same homogeneous medium. For example, white light is in the same medium before entering the prism, so it propagates in a straight line. After entering the prism, it is also considered in the same medium in the prism [but it is refracted ], and after exiting the prism, it is in the same medium, so it propagates along a straight line.
The question can also be translated into light traveling along a straight line, but why is the rainbow arc-shaped? That's probably the reason above, but the situation is more complicated. The formation of a rainbow is a drop of water from the sun hitting the sky, refracted → reflected→ refracted ... It is formed after shooting towards our eyes.
Our problems will never have the last one! Next, I will ask you another question: "Since light travels in a straight line, why is it said that it is a wave, and there are peaks, troughs?" "Professionals don't laugh, there are indeed many friends who have such doubts. Since it is popular science, it is necessary to tell everyone's doubts.
The answer is indeed not difficult, we say that light travels in a straight line, but no one tells you that light is a straight line! Remember that light travels in a straight line, but light is not a straight line! Light has peaks, troughs, and frequencies, so it has the property of "waves".
As for our eyes seeing that the light is a straight line, that is the eyes deceiving us.
If you read my first few chapters on optics, it should be clear that at the beginning the particle of light was dominant, and Newton's influence was great. Later, with experiments and explanations of interference and diffraction phenomena, the particle theory was broken, and the wave theory began to be taken seriously. Later, Ai's explanation of the photoelectric effect led to the wave-particle duality of light.
Inspired by the wave-particle duality of light, the French physicist De Broglie proposed a hypothesis in 1924, pointing out that wave-particle duality is not only unique to photons, and all microscopic particles, including electrons and protons, and neutrons, have wave-particle duality.
He generalized the relationship between the momentum of a photon and the wavelength p=h/λ to all microscopic particles, pointing out that moving particles with mass m and velocity v also have fluctuations, and the wavelength of such waves is equal to the ratio of Planck's constant h to the momentum mv of the particles, that is, λ = h/(mv). This relation came to be called de Broglie's formula.
Many people may not have the patience to look at the entire foreshadowing, so here again I will tell you about the process of human understanding of light, first Huygens, and then Newton.
According to Huygens' principle, the linear propagation of waves and spherical propagation. The more complete theory of light was first developed by Christian Huygens, who proposed a theory of light fluctuations. Using this theory, it is possible to explain how light waves interfere with each other to form a wavefront, at each point of the wavefront can be considered to be the source of the spherical wave, and at any subsequent moment the wavefront can be regarded as the envelope of these waves. From his principle, he can give a qualitative explanation of the linear propagation of waves and spherical propagation, and derive the law of reflection and refraction, but he cannot explain why when the light wave encounters an edge, aperture or slit, it will deviate from the straight line propagation, that is, the diffraction effect will occur.
Huygens hypothesized that the secondary wave would only propagate forward, not rear. He did not explain why this physical behavior occurred. Later, Isaac Newton proposed the theory of light particles. He believed that light was composed of very mysterious particles that obeyed the laws of motion. This can reasonably explain the linear propagation and reflection nature of light. However, Newton's explanation of the refractive and diffraction properties of light was not satisfactory.
Because of Newton's unparalleled academic standing, his theory of light particles was unchallenged for more than a century, and Huygens's theory was gradually forgotten. It was not until the discovery of diffraction in the early nineteenth century that the wave theory of light was re-recognized. The debate over the volatility and particle nature of light has never subsided. Later, Thomas Young, Fresnel, Maxwell, Hertz, Einstein and others perfected the theory of light. In the early nineteenth century, Thomas Young and Augustin Fresnel made significant contributions respectively. The double-slit experiment completed by Thomas Young showed that diffracted light waves obeyed the superposition principle, a wave behavior that Newton's theory of light particles could not predict.
Huygens
This experiment confirmed the fluctuating nature of light with certainty. Augustine Fresnel proposed the Huygens-Fresnel principle, which assumes that secondary waves will interfere with each other on the basis of Huygens principle, and assumes that the amplitude of secondary waves is related to direction.
The Huygens-Fresnel principle explains the forward propagation and diffraction of light waves. The light fluctuation theory did not immediately replace the light particle theory. However, by the mid-nineteenth century, the light fluctuation theory began to dominate scientific thought because it could explain the mechanism of polarization phenomena, which the light particle theory could not do.
Later in the same century, James Maxwell integrated the theory of electromagnetism and proposed Maxwell's equations. This system of equations enables the analysis of phenomena in electromagnetism. From this system of equations, he derived the equation of electromagnetic waves. The electromagnetic wave velocity obtained by applying the electromagnetic wave equation is equal to the optical wave velocity measured experimentally. So Maxwell guessed that light waves are electromagnetic waves, and electromagnetism and optics were thus linked into a unified theory.
In 1888, Heinrich Hertz conducted experiments to transmit and receive electromagnetic waves predicted by Maxwell, confirming that Maxwell's guess was correct. From this time on, the light fluctuation theory began to be widely recognized.
After reading the above introduction and explanation, do you have any questions about the movement of light? I asked, "Is the propagation of light assumed by Huygens' principle the case of real light?" That is, about spherical waves, secondary waves, envelopes, etc., is it the true appearance of light? ”
Obviously, these "secondary waves", "spherical waves", and "envelopes" are all acquired words, and it is difficult for the ancestors. Without a good imagination, it is not good to create these words.
Obviously, Huygens is a very pioneering person, but everyone must know that his principle starts from the phenomenon, not that he observed "envelope" and "secondary wave" and so on, in order to explain the movement of light, in order to conform to the observed phenomenon, and created these words.
The imaginary component is large, but it is combined with actual imagination, so it is useful. Without these words, it is difficult to explain to you the many phenomena of light.
Now that we know that light has wave-particle duality, then the view of secondary waves must be correct, and there is a kind of "differential" thinking in it. As for the envelope, the radian is a characteristic of "wave" and can also be considered correct. So the answer is obvious, this is describing the real situation of light.
If there were people on another planet, the words they used to describe the phenomenon of light movement were certainly not these. But we know that no matter what words they use, what we describe is a thing. Just like language, "good morning" has many different expressions, different pronunciations, and different fonts, but we know that we mean the same thing.
Then Fresnel is undoubtedly correct in his explanation of diffraction and interference. Because he developed the theory on the basis of Huygens.
The mathematical proof of Huygens and Fresnel 's theory was given by Fermat. This has been said in this previous chapter.
Explanations of diffraction and interference of light are also the basis of quantum mechanics. A familiar experiment is also the single-electron interference experiment. A rather bizarre experiment, it is generally believed that an electron passes through two gaps at the same time, and the relationship between the electron and the experimental observer and so on. This chapter will not be discussed here, but it will be explained and elaborated for you in a later article. Now move on to the explanation of the speed of light.
It is no exaggeration to say that "speed of light" appears in many of the most common physical formulas. The Einstein field equation is such an equation. I have done a lot about the Eye's field equations in my physics book Change. There is no doubt that the field equation is the correct theory, and its difficulty lies in the nonlinear fluctuation of the field equation.
The speed of light cannot be surpassed, this is what we know now. But why can't the speed of light be surpassed? Why is the speed of light 300,000 meters per second? Answering these questions is important to us.
In fact, I have dealt with this problem in Chapter 26 of "Change", "Explanation of the Quality and Speed of Motion". I will explain it to you today.
In the true sense, the speed of an object does not exceed the speed of light, and photons have no rest mass, and light has no rest mass. I agree with Aiji on this.
Let's start with why objects don't exceed the speed of light? Let's look at this formula m=m0/sqrt(1-v^2/c^2). If the speed V of an object is greater than the speed of light, then there must be 1 under the root number minus a number larger than it to get a negative number. Even if it is opened, it does not make any sense. That's why superluminal speeds don't theoretically exist.
With the same formula, we assume that the mass of the object is 1 and the speed of the object reaches the speed of light. Then the mass of the object becomes 1 divided by 0. Dividing 1 by zero has no mathematical meaning, but in the real universe, it means infinity. That is, the mass of the object tends to infinity. You can enter 1 divided by 0 on your mobile phone, and infinity will be displayed.
So that's why the mathematical explanation that objects can't reach the speed of light. Whether the mass is 1, 2, 3, or any other positive number, divided by zero, is an infinity tendency.
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This is the mathematical explanation, are you satisfied? I also have to ask at a deeper level, what is the reason why objects cannot move at the speed of light? All number formulas will become powerful when they return to reality!
Let me reply to you like this, Ai's use of space-time curvature to explain the cause of gravity, I think it needs to be corrected. That is, the cause of gravity is space-time, not space-time curvature. And time, space, matter are one thing. This kind of integration can be measured in terms of space-time energy. So any object must be in a gravitational field, an object in the universe.
Then an object must overcome the nature of space-time in order to exceed the speed of light. This space-time nature refers to the cosmic environment, after all, time, matter, and space are integrated things, and space-time is viscous and elastic.
Moreover, if a mass object moves at the speed of light, the mass will tend to infinity, and time will stop. It's as if the object acts as a "force point" trying to influence and pull the entire universe. So this is an impossible situation. Because the energy of a single object is not beyond the energy of the entire universe. So if you explain it this way, the speed of light is actually a law, that is, the speed of light is a bound state, a bound state law, a space-time bound state law. That's why objects don't move faster than the speed of light!
Another popular explanation could be this: the universe requires the speed of light to be at a limit of 300,000 meters per second, and it is not allowed to break through.
As early as 1966, scientists discovered that in addition to the speed of light, there is a speed limit in the universe, which is called "GZK cut off".
According to the Big Bang theory, our universe was born at an extremely hot and dense "singularity". Due to the limitation of the speed of light, photons from the early days of the universe are still propagating in the universe, but because of the expansion of the universe, they have now entered the microwave band, and in our opinion, no matter which direction, we receive the same microwave radiation, so this is called "microwave background radiation" (CMB).
The photons of "microwave background radiation" fill the entire universe, and all matter moving in space will inevitably meet them, usually, the photons of "microwave background radiation" will not affect the motion state of matter, but scientists have found that when the speed of the matter exceeds a critical value, it will interact with the photons of the "microwave background radiation", and the energy corresponding to this critical value is called the "GZK limit" (GZK limit).
For example, the "GZK limit" of a proton is 5 x 1019eV (note: eV is electron volts), if the energy corresponding to the speed of a proton moving in space exceeds this value, it will interact with the photons of the "microwave background radiation" and generate π mesons, which will cause the proton to lose energy and its speed will be reduced.
It is generally believed that whether it is a microscopic particle or a macroscopic object in the universe, it will be limited by the "GZK truncation", which means that to fly faster than light, you must first break the "GZK limit".
Our problems are not over! Since light can be deflected by the gravitational pull of a massive object, it should have mass. If there is no mass, gravity will not act on it.
Let's look at two formulas, the mass-energy formula E=MC^2, and Planck E=hv. Assuming that photons have mass, different transition jump photons correspond to different velocities, but this does not match the observations, and the observed photon velocities are all uniform speeds. Moreover, the absence of m in Planck's formula in itself indicates that the rest mass of photons is zero. Or it can also be said that there is no static mass, which is more accurate.
The fact that we know that a photon has a rest mass of zero is a theoretical requirement, and none of us have measured its mass as "zero", nor can we measure it, because you can't find a photon at rest. So it is accurate to say that photons have no rest mass. It can also be said that photons must have mass and have motion quality.
Eyche once questioned that Newton's first law was suspected of circular argumentation, and here I found that his theory was also suspected of circular argumentation. We can't find an inertial frame in real life, but we have to show that in an inertial frame, objects always maintain a uniform linear motion and rest.
Similarly, to prove that a photon has zero rest mass, we must first find the photon at rest. But we can't find a stationary photon, but we also say that the photon has zero rest mass. Or that photons have no rest mass. The discussion here may seem pointless, but it is actually very interesting.
We then assume that photons have no rest mass, and that photons with different transitions correspond to a fixed spectrum, consistent with observations, so we say that photons have no rest mass.
Then the question arises again, there is a movement quality alone, why is the movement process, the mass is not infinite? General books show that photons have no rest mass, but we still don't understand it. There is a quality of movement, why not comply with the theoretical content!
A similar question arises: Why does the speed of light travel at the speed of light? What is the nature of the principle of the speed of light and the mechanism of the laws of the universe?
Let's answer the first question first, light has a moving mass, but it can travel at the speed of light. I think it has something to do with wave-particle duality. The energy of a photon is transmitted in parts, and it exhibits the property of a "wave" when it is deflected by a massive object.
Mass and energy are two concepts, two sides of the same body of an object. Photons are often described in terms of energy. That is, how much energy a photon moves at the speed of light, not how much mass it is. The energy is not infinite, and the mass is naturally not infinite. So the photon, a special particle moving at the speed of light, has no infinite mass.
Otherwise, the sunlight that hits us will directly wipe out the ashes we beat! But the sunlight is warm, indicating that it carries energy. In our visible words, it is "warm", and who have you ever seen would say give me two pounds of "warmth". This description is actually inaccurate, just to make everyone intuitive.
And an object with mass, to move at the speed of light, needs unlimited energy to maintain its movement at the speed of light. If energy is infinite, then mass is naturally infinite, so it is impossible for an object with mass to reach the speed of light.
In fact, wave-particle duality itself is a combination of "macro" and "quantum". It can also be said to be a transitional embodiment of the "mass" and "energy" of an object. We generally say that mass refers to macroscopic, but energy can point to microscopic. Therefore, after discovering the photoelectric effect and establishing the theory of relativity, Ai's idea of unifying the four basic forces has always been in his mind, which is correct and can be unified. The development of physics itself proves this, but the last section of the Great Wall is still missing!
As for the last question: why does light move at the speed of light? There was an answer above just now, in fact, it is still due to the "stickiness" of time and space. This viscosity is a space-time property that hinders the movement of objects at the speed of light, which in turn allows photons to move at the speed of light.
Speaking of the circular argument above, I think of Gödel's incompleteness theorem.
1. Any formal system containing first-order predicate logic and elementary number theory has a proposition in which it can neither be proven true nor proved to be false.
2. If the system S contains elementary number theory, its non-contradiction cannot be proved in S when S is not contradictory.
So you see, the great Gödel revealed a philosophical inspiration for us. Any circular argument, paradox and theory wants to say this with this, prove the other with the other, follow up layer by layer, and the final result is unfifiable and unspeakable.
This tells us that the universe exists in an interconnected form, but it cannot prove itself. Yes, the universe does not need truth or pseudo, but humans do!
We don't have the last one of our problems! In fact, about light, no amount of problems is superfluous, and the real problem has not yet been solved.
Maxwell originally calculated that the speed of electromagnetic waves is the speed of light, and boldly predicted that light is electromagnetic waves. But who can explain why the speed of light is 300,000 kilometers per second, not 290,000 kilometers per second. Electromagnetic waves in a vacuum are 300,000 kilometers per second, which is the product of frequency and wavelength. But the speed of a single photon is also 300,000 kilometers per second, does a single photon also have a frequency and wavelength?
You can understand why our problem will never be the last, right?
More questions, more answers. My answer is not the best, you can scold, but I hope that your answer will always be better than mine, more enlightening than mine.
Excerpted from the independent scholar and writer's popular science book "Seeing the Micro-Knowledge". "Seeing the Little" is one of the four parts of the popular science series of the spirit escape. The other three books are "Change", "Exploring Life", and "Reconstructing the World".