The speed of light (more generally, the speed of propagation of electromagnetic radiation) in a vacuum, denoted c, is an important fundamental physical constant in many areas of physics. It has an exact value of 299,792,458 meters per second, because the meter length unit is redefined based on this constant and the standard second. According to special relativity, c is the maximum speed that all energy, matter, and information in the universe can reach. It is the speed at which every massless particle bound to physical fields (including electromagnetic radiation such as light photons) propagates in a vacuum. It is also the propagation speed of gravity (such as gravitational waves) predicted by current theories. Particles and waves travel with velocity c regardless of the motion of the source or of the observer’s inertial frame of reference. After Einstein founded relativity, it became known that the speed of light is indeed very fast, because this is the upper limit of the local speed in the universe, and no other speed can be exceeded. through it. Moreover, regardless of the medium in the frame of reference, the measured speed of light is exactly the same. Based on the principle of the constant speed of light in relativity and the highly accurate measurement of the speed of light, physicists have also determined the speed of light to be 299,792,458 meters/second without affecting the speed of light. affect the current physical quantity. In this way, people no longer have to worry about accurately measuring the speed of light, and can also solve the problem of errors in the equipment used to determine the clock. The speed of light propagating in a vacuum is independent of both the motion of the light source as well as of the observer’s inertial frame of reference. The constancy of the speed of light was postulated by Einstein in his 1905 paper on special relativity. Physicists can now only experimentally confirm the speed of light by methods above two Two-way speed of light is frame-independent, because the speed of light cannot be measured in one-way speed of light, ignoring some conventions of uniformity. synchronization between the clock at the source and the clock at the receiver. Whether it’s electron transition, nuclear fusion, nuclear fission, or the annihilation of yin and yang matter, these processes produce light. Once light is created, their speed will immediately reach the speed of light, and they will always travel at this speed. If light were not absorbed by matter, they would not be dissipated in the universe, and the speed would always remain at the speed of light. For example, the first photons created in the universe 13.8 billion years ago are still present today, and they travel through the universe at the speed of light. So, how did light reach the speed of light? How does light maintain the speed of light? What is the driving force that drives the light forward? If it is explained from the point of view of the particle nature of light, then light is composed of photons with no rest mass. According to special relativity, since the static mass of photons is zero, their speed can only be the speed of light. According to the Higgs mechanism of the Standard Model of Particle Physics, when photons without static mass pass through the Higgs field throughout the universe, the photons will not be coupled, so they will not gain static mass, and their speed will not decrease. Once the photons are generated, their speed will directly reach the speed of light, and there is no acceleration from zero to the speed of light. Propagation of photons does not require energy to propagate, if they were not absorbed by matter or a black hole, they would always travel aimlessly through a vacuum at the speed of light. On the other hand, if explained from the evaporation of light, the nature of light is electromagnetic wave. Maxwell’s equations of electromagnetism show that electricity and magnetic fields are essentially unified, that a changing electric field excites a magnetic field, and a changing magnetic field excites a repeated electric field, creating out electromagnetic waves. Since electromagnetic fields are formed at the speed of light, electromagnetic waves travel at the speed of light. The generation and existence of electromagnetic fields are independent of the medium, so light can travel at the speed of light in a vacuum. Although the spatial structure continues to expand, light propagating through space will appear redshift, but they will not completely disappear in the universe.

See through smoke and fog, map a person’s blood vessels while monitoring heart rate – without skin contact; look through the silicon wafers to check the quality and composition of the electronic board. Those are some of the many functions of infrared camera new, developed by a team of researchers led by electrical engineers at the University of California San Diego. The camera detects a part of the infrared spectrum known as shortwave infrared light (wavelengths between 1000 and 1400 nanometers), which lies just outside the visible spectrum (400 to 700 nanometers). Shortwave infrared imaging, unlike thermal imaging, detects much longer infrared wavelengths emitted by the body. The camera works by shining short-wave infrared light at an object or area of ​​interest, then converting the reflected low-energy infrared light back to the device into shorter, high-energy wavelengths. than the human eye can see. “It makes invisible light visible,” said Tina Ng, professor of electrical and computer engineering at UC San Diego Jacobs School of Engineering. When technology Infrared imaging has been around for decades, where most systems are expensive, cumbersome, and complex, often requiring a separate camera and monitor. They are also often made with inorganic semiconductors, which are expensive, hard, and contain toxic elements such as arsenic and lead. The infrared camera that Ng’s team has developed overcomes these problems. It combines sensors and display into a slim, compact and simple device. It is made of organic semiconductors, so it is low cost, flexible and safe for use in biomedical applications. It also offers better image resolution than some of its inorganic versions. The camera is made up of multiple layers of semiconductors, each hundreds of nanometers thin, stacked on top of each other. Three of these layers, each made of a different organic polymer, are the key elements of the image: the photodetector layer, the organic light-emitting diode (OLED) display layer, and the blocking layer. electrons in the middle. The photodetector layer absorbs shortwave infrared light (low energy photons) and then generates an electric current. This current flows to the OLED display layer, where it is converted into a visible image (high-energy photons). An intermediate layer, called an electron block, keeps the OLED display layer from losing any current. This is what allows the device to produce clearer images. Another special feature is camera effective in providing optical and electronic indicators. “This makes it multifunctional,” says Li. For example, when the researchers shined infrared light on the back of the subject’s hand, the camera provided an image of the subject’s blood vessels while recording the subject’s heart rate. The researchers also used their infrared camera to see through the fog and a silicon wafer. In one test, they placed an “EXIT” patterned photosphere in a small room filled with smog. In another setting, they placed a photorealist patterned “UCSD” behind a silicon wafer. Infrared light penetrates both smog and silicon, making it possible for the imagineer to see the letters in these illustrations. This would be useful for applications such as helping self-driving cars see in bad weather and checking for silicon faults. The researchers are currently working to improve the performance of this type of camera.

Dark matter is thought to be six times more abundant than normal matter. What is dark matter? First and perhaps most confusingly, researchers are still unsure what exactly dark matter is. Initially, some scientists surmised, the missing mass in the universe was made up of faint small stars and black holes. However, detailed observations have not shown enough evidence to explain the effects of dark matter. The current leading hypothesis is a hypothetical particle known as the weakly interacting mass particle, or WIMP. This particle would behave like a neutron and be 10-100 times heavier than a proton. However, this conjecture has opened a series of other unanswered questions. Is it possible to detect dark matter? In the 1930s, Swiss astronomer Fritz Zwicky discovered that galaxies in a distant cluster were orbiting each other much faster than they should have been visible. At the time, he suggested, an invisible substance, dark matter, could be pulling gravity on these galaxies. Since then, researchers have confirmed, this mysterious matter can be found throughout the universe. They are six times more abundant than ordinary matter. If dark matter were produced from WIMPs, they would be all around us, invisible and virtually undetectable. While they won’t interact much with normal matter, there’s always some small chance that a dark matter particle could bump into an ordinary particle like a proton or electron as it travels through space. So the researchers carried out a series of experiments to study the huge numbers of ordinary particles deep underground, where they are shielded from interfering radiation. These particles can behave like a collision between dark matter particles. After decades of searching, none of these detectors have made a reliable discovery. Earlier this year, China’s PandaX experiment reported failing to detect WIMP. According to physicist Hai-Bo Yu at the University of California, Riverside, it seems that dark matter particles are much smaller than WIMP, or lack properties that make them easy to study. Does it include more than one particle? Ordinary matter is made up of particles like protons and electrons, as well as more exotic particles like neutrinos, muons, and pions. So some researchers have wondered, could dark matter, which makes up 85 percent of the matter in the universe, be just as complex? “There is no good reason to assume that all dark matter in the universe is made up of one type of particle,” said Harvard physicist Andrey Katz. According to Katz, dark protons can combine with dark electrons to form dark matter. From there, create configurations as varied and interesting as those found in the physical world. However, this problem has not been elucidated so far by scientists. Does the dark force exist? Some researchers have been looking for “dark photons,” analogous to photons exchanged between ordinary particles that generate the electromagnetic force. However, dark photons will only be sensed by dark matter particles. Physicists in Italy are preparing to break a beam of electrons and their antiparticles, called positrons, into a diamond. If dark photons exist, electron-positron pairs could annihilate and create one of the strange force carriers. From there, it is possible to open up a whole new realm of the universe. Is it made up of axions? As physicists pay more and more attention to understanding WIMPs, other dark matter particles are starting to gain favor. One of the top substitutes is the axion. This hypothetical particle is very light, smaller than a proton. Axion is currently being searched for in a few trials. Recent computer simulations have raised the possibility that these axions can form star-like objects. At the same time, they can produce radiation that is easily detected, similar to the mysterious phenomenon known as fast radio bursts. What are the properties of dark matter? Astronomers have discovered dark matter through its gravitational interaction with ordinary matter. This is also an indication that it is the main way that the presence of dark matter is known in the universe. According to some theories, dark matter particles must be their own antiparticles. This means that the two dark matter particles will annihilate each other when they meet. The Alpha Magnetic Spectrometer (AMS) experiment aboard the International Space Station has been looking for amazing signs of this destruction since 2011. As a result, AMS detected hundreds of thousands of events. Scientists are still unsure if these come from dark matter, and have yet to determine exactly what dark matter is. Does it exist in every galaxy? Because of its greater mass than normal matter, dark matter is often thought to be the driving force that organizes large structures such as galaxies and galaxy clusters. So it was strange that earlier this year, astronomers announced that they had found a galaxy called NGC 1052-DF2. Surprisingly, this galaxy barely contains any dark matter. At the time, Pieter van Dokkum of Yale University said: “Dark matter does not seem to be a necessary element to form a galaxy.” However, another team of researchers analyzed and showed that van Dokkum and colleagues miscalculated the distance to the galaxy. This means that visible matter is much fainter and lighter than first detected.

Illustration. If the universe is filled with matter but there is no force of interaction between them, there would be no formation of nuclei, atoms, molecules… and galaxies, stars and planets. Basic interactions of nature Electromagnetic interaction or electromagnetic force is the interaction between charged particles, for example protons with the same positive charge repel each other, but attract electrons because electrons have a negative charge. This interaction is not only a matter of attraction or repulsion of the magnet poles due to the excess or lack of electrons, but the most important thing is that it is the attractive properties of this proton and electron that the electron can keep its orbit around the atomic nucleus. , and thus the atoms, molecules and, more generally, all the matter we see every day, that make us up. Electromagnetic interactions are transmitted by bosons or photons, or as we know them as light-transmitting particles. Light is precisely an electromagnetic wave of the right wavelength to produce images on the retina of the human eye. The photon itself has neither mass nor charge, it only plays the role of transmitting electromagnetic interactions through its oscillation frequency. The frictional force generated when one object slides over another is due to the electromagnetic interaction of the atomic particles of the contact surface, the elastic force of a spring or the tension of a string is also an electromagnetic interaction due to the change in the surface area. changing the distances of the atoms from each other leads to a change in the magnitude of the interaction from the initial steady state, the force produced by muscles when you lift a heavy object or any other movement that is elastic muscle bundles, so of course there’s also an electromagnetic interaction… Strong interaction (also known as strong nuclear force). The interaction is caused by bosons called gluons – a type of particle with no mass and no charge. This is the bonding interaction between quarks, the main components of the two types of baryons, protons and neutrons, which as we know are the particles that make up the nucleus of an atom. It is thanks to this type of interaction that new baryons are formed and also bind the protons and neutrons in the atomic nucleus together (protons carry the same charge, so they generate an electromagnetic force that repels each other, thanks to the presence of electrons). neutrons, so the nucleus of an atom can exist). The strong interaction is the strongest of the basic interactions of nature, but it also has the shortest range of effects. Simulation of forces in the universe. Outside the radius of the atomic nucleus, the strong interaction does not work and of course that is also the reason why matter can exist today because with the magnitude of this interaction it can act. As far as the electromagnetic interaction goes, there will be no existence of atoms with electron shells because they will be crushed by the attraction between the nuclei themselves (because this force is much stronger than the electromagnetic repulsion). between nuclei). The weak interaction (or weak nuclear force) plays a role in causing beta decay of neutrons, thereby causing nuclear decay such as radiation and fission. The neutrons themselves are unstable in isolation, they are stable only when bound to protons. Stand-alone, neutrons can absorb or emit W or Z bosons and undergo beta decay to form a proton, an electron, and a neutron fraction. The nuclei of heavy elements have many protons and, respectively, require many neutrons to keep the protons from repelling each other. But at the same time when there are many neutrons, there will be neutrons isolated from the proton, out of the range of the strong interaction. Then the weak interaction causes them to decay and make the nucleus unstable. Elements whose nuclei have this phenomenon are called radioactive elements. The heavier the nucleus, the more unstable it is, and so the weak interaction is what keeps the number of elements in the universe finite, not infinite. Standard model of particle physics These three types of interactions are now uniformly described in the standard model of particle physics. According to the standard model, at sufficiently high energies, these interactions are consistent, although as already stated they appear to be very different in mechanism. In the cosmological model based on the Big Bang theory, the first stage of the universe from the age of the universe is 10–43s to the time of 20-36s the universe undergoes a period known as the great unification epoch. , in which the three types of interactions mentioned above have not been separated from each other. Immediately after the great unification era is the electroweak era, when the strong interaction has separated but the remaining two interactions are still united, called the electroweak interaction. It wasn’t until the quark era, when the age of the universe was 10-12s, that the universe cooled down enough for the electromagnetic and weak interactions to separate. Illustration. Gravitational interaction (or gravity) Interactions tend to pull objects and particles of mass toward each other. This is the weakest of the four basic interactions of nature on a certain object, but it is the one with the furthest range of effects. It plays a major role in forming the great structures of the universe, from stars, planets, asteroids, satellites to galaxies, clusters and superclusters of galaxies. The Earth and the planets revolve around the Sun also due to the effect of this type of interaction. Despite being the weakest force, gravity has not only the longest range, but also an unstoppable force, every man-made weightless environment or gravitation-isolating material in sci-fi movies. thought is unscientific. It cannot happen not because of technology but because of the general principle of the universe. For the same reason, gravity is also the force that causes the most violent phenomena in the universe, typically the collapse of matter to form neutron stars or black holes and supermassive black holes. In this phenomenon, thanks to the large amount of matter, the gravitational force is enough to overcome the electromagnetic force and the strong interaction causes the structure of matter to be destroyed. Gravity is very common to everyday life as we can stand on the ground and objects that are thrown high fall because of gravity. Some so-called forces, such as the resistance of the ground when you are standing on it or the Archimedes earth force in a liquid, are just indirect manifestations of gravity. The reason this universal force is mentioned last in the article is because it is the only one of the four fundamental interactions of nature that is not included in the standard model. Is there a fifth fundamental interaction? The existence of a fifth interaction of nature is still believed by many scientists, especially since the presence of dark matter has been confirmed. To date, there have been a number of experiments showing the involvement of a strange variation that was thought to be such a small interaction that has never been known. But so far, the fifth interaction has not been described in any way. Thus, the number of fundamental interactions of nature is still only four, with three unified in the standard model and gravitational interactions standing independently of them.