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.

Up to now, the theory of relativity has become a classic theory. Many people think that Einstein’s brain development has reached the highest level, so he came up with these great theories. The famous theory of relativity The theory of relativity includes general relativity and special relativity. Special relativity has been applied by mankind with the famous formula E=mc2. Meanwhile, general relativity is related to the theory of the curvature of space and time, leading to the idea of ​​a hyperspace, time, connection between locations in the universe, or between two parallel universes – that is the way for people of the future to return to the past that readers are very familiar with in the “magic door” of Doraemon (popular fantasy comic book series). Description of gravitational waves created by a pair of stars (Image: Internet) With the continuous development of science and technology, many of Einstein’s theories have been confirmed. In 2016, scientists found gravitational waves proposed by Einstein. The finding of gravitational waves is believed to be the key to solving a series of questions about how the universe works. Einstein believed that the hyperspace tunnel was a medium based on two space-time. As long as we find the hyperspace tunnel (also known as the “wormhole”), we can complete the time travel shuttle. Traveling from one time and space to another can break the limits of distance and travel to distant planets. Simulation of hyperspace tunnel (Image: Internet) Unfortunately, scientists have yet to find the so-called hyperspace tunnel. We have discovered many habitable planets in the universe, but they are all too far away and the nearest ones are hundreds of light-years away. Time travel – advantages and disadvantages However, some scientists believe that time travel goes against the laws of the universe. Time travel seems to be a very practical tool that can realize human desires. And if we have the technology to travel through time and space, then we can make up for the mistakes we’ve made. But in fact, this advantage can also become a disadvantage, because knowing that the mistakes of the past can be corrected by people in the future, people in the present stage often do not work carefully. , which is harmful to the entire human civilization. (“Grandfather’s paradox” is said to be the theoretical basis for proving that it is impossible to travel to the past. If a person goes back to the past and kills his grandfather, that person will not be born, and there will be nobody back in time to kill the grandfather). Another point to consider is that if a time-traveling space shuttle does indeed exist, it could also be used by other “extraterrestrial life”. By then, if our technology is not as advanced as the other, then human civilization is likely to be destroyed. Simulating a super space tunnel from Earth to another planet (Image: Internet) Moreover, if humans abuse the hyperspace tunnel, it will lead to chaos in time and space. Time and space are like a tunnel, if thousands of people enter the tunnel, some will want to go forward and some will want to go back. Different paths will cause bottlenecks and each outcome will affect future growth. Therefore, it can be said that, whether the space tunnel or Doraemon’s “miracle door” really exists or not, we should still try to cherish the present and live well in the present. Future generations will certainly benefit as well.

Humans used to believe that the Earth was the center of the solar system until Nicolaus Copernicus, a Polish astronomer, proved that our Earth is just a planet revolving around the Sun. Later, Newton proved the principle behind the planets orbiting the Sun with the law of universal gravitation. He said the larger the objects, the greater the force of attraction between them, but the further apart they are, the weaker the attraction. Next came Albert Einstein’s theory of relativity, which suggested that all objects in the universe lie on “a cloth”, which is a four-dimensional continuum known as space-time and causes distortion. Massive objects like the Sun warp space-time around them, so Earth’s orbit is simply the result of our planet obeying this curvature, similar to gravity. Newton. Does quantum theory contradict the concept of space-time? Besides, we also have another concept that is quantum theory. In the quantum world, a physical system always has overlapping states. Specifically, a particle can exist in many places or have many velocities at the same time. In the 1930s, physicist Erwin Schrödinger devised a thought experiment that is still known today as “Schrödinger’s cat” to discuss this quantum theory. Suppose there is a sealed box, inside is a living cat with a vial of poison and a radioactive substance that will decay after about an hour (but also probably not). If decay occurs, it will be recorded by the quantum state meter and activate the counter causing the hammer to be dropped to break the vial of poison, which will kill the cat. If the potion hadn’t been broken, the cat was still alive. The problem here is that until the measurement is taken, the cat will be in two superpositions of life and death. Massive objects warp the structure of space and time around them, resulting in neighboring objects following a curve. Photo: Space. This cannot be reconciled with the space-time continuum. “The gravitational field cannot be in two places at once,” said Sabine Hossenfelder, a theoretical physicist at the Frankfurt Institute for Advanced Study. According to Einstein, space-time is warped by matter and energy, but according to quantum physics, matter and energy exist in many states simultaneously. “So where is the gravitational field?” Hossenfelder asked. However, no one has an answer to that question. Looking for a solution To be able to reconcile the two theories, physicists have tried to find a common theory that solves both quantum physics and space-time theory. Perhaps the most famous theory is the string theory of physicist Andrew Strominger. It’s the idea that subatomic particles like electrons and quarks are created from the continuous oscillations of microscopic filaments, not from collections of particles. However, the strings must vibrate in 11 dimensions, while Einstein’s fabric of space-time has only four. “String theory is interesting math, but whether it describes the space-time we live in, we need an experiment to prove it,” said Professor Jorma Louko from the University of Nottingham. know. String theory, a way to reconcile relativity and quantum theory, says that reality is made of vibrating strings. Photo: Spice. Evolving from the limitations of string theory, other physicists have turned to an alternative called Ring Quantum Gravity (LQG). They argue that space-time is made up of a series of interwoven loops structured on the smallest size scales, like a cloth. However, it is made of a network of stitches, or like a computer photo, made of individual pixels. According to physicists studying the LQG, these loops are so small that the number of rings in a cubic centimeter of space is more than the volume of the entire observable universe in cubic centimeters. “If space-time differs only on the Planck scale, this would be difficult to test in any particle accelerator,” says Louko. You’ll need an atom smasher 1,000 trillion times more powerful than the large particle accelerator (LHC) at CERN. To find the answer, scientists must use light from Gamma rays at a distance to look for evidence for LQG. The signals we receive from the universe may have traveled billions of light years, experiencing the influence of space-time. Cosmic flashes are emitted as stars reach the end of their lives, scientists are still trying to understand the meaning of these explosions in space. “Their spectral ranges have systematic distortion,” commented Hossenfelder. However, the problem now is to find the answer to the cause of this distortion. An alternate picture shows that space and time are not smooth, but are instead created by a series of small loops. Photo: Space. Quantum entanglement According to Einstein, space-time always exists even if there are no stars or planets around it. However, physicists Laurent Freidel, Robert Leigh and Djordje Minic argue that space-time does not exist independently of the objects in it. According to them, space-time is defined by the interactions between objects. “This may sound confusing, but it’s the best way to approach the problem,” Mr. Minic said. The theory mentioned above is called the modulus of space-time, which can explain a well-known phenomenon called “quantum entanglement”. Quantum entanglement is when two atomic particles are brought together and linked their quantum properties. Then, when the scientists separated them from each other, they found that the particles retained their property bonds. When the properties of a particle are changed, the particle at the other end will sense this change immediately, faster than the speed of light. Einstein was so confused by this phenomenon that he called it the ‘spooky effect at a distance’, because the speed of light is the fastest, according to him. Modularity of space-time theory can modify the properties of a particle by looking at the “separation” from a different perspective. If space-time emerges from the quantum world, it would be simpler to be closer in the quantum sense than in the physical sense. “Each person will have a different concept depending on the context,” says Minic. It’s like a person-to-person relationship. We can feel closer to our loved ones far away than to strangers around us,” added Hossenfelder. Albert Einstein presented a Newtonian picture of gravity as a force, replacing it with space-time. Photo: Science Photo Library. Freidel, Leigh and Minic have been working on their concept for the past five years and believe they are taking steps towards perfecting it. According to Minic, this would be a novel approach to bring the concept of gravity into the quantum world, instead of quantizing gravity as with the LQG theory. However, any scientific theory needs to be tested. For now, the trio is looking for a way to incorporate time into their model. This new discovery could have a more profound effect on our daily lives. “All of our current devices work solely on quantum theory. If we better understand the quantum structure of space-time, that will have an impact on future technologies – maybe in 200 years,” said Hossenfelder.