Text/Gan Xinfeng
The research object of relativity is the high-speed moving world and the vast universe beyond our daily experience, which is the main reason why it is difficult for us to understand relativity.
Since the birth of the theory of relativity, the revolution of time and space brought by it has greatly expanded human understanding of the universe. From the theory of relativity, people have discovered the mystery of time travel, the great energy of atomic fission, the origin and end of the universe, black holes and dark energy, and other wonderful phenomena. Almost all the mysteries of the universe are hidden in the simple formula of relativity.
Time travel
Time travel may mean that you can correct or change the development of your destiny, or witness great historical events with people in history; It is also possible for people to travel in the future, for example, to understand the stock market and explore new scientific discoveries. Time travel opens a door for us to go back to the past and step into the future.
It is a big mistake to think that time travel is only a science fiction theme, because the idea of relativity shows that time travel is possible.
Special relativity proves that high-speed travel will slow down time. Assuming that at some point in the future, people have solved all the technical problems and can build a spaceship flying at sub-light speed, then time travel in a sense becomes possible. If the spaceship flies from the earth to a distant galaxy at sub-light speed, the round-trip journey is only a few years (according to the time on the spaceship), but during this period, thousands of years have passed on the earth, and everything has changed dramatically. If human civilization
General relativity shows that space-time can be curved, not flat. We can cut a wormhole between the earth and the distant part of the universe, and then open this hole with some kind of "strange substance", making it a hyperspace pipeline that suddenly appears in the universe, allowing us to reach the distant shore in an instant. Then when we came back, the strange nature of the wormhole made us much younger.
According to the general theory of relativity, enough mass can change and distort space-time. Mathematician Frank Dipler conceived a time travel method of rolling up time and space. He believes that if a huge object in space rotates at half the speed of light, space-time will twist back. So in the future, as long as someone makes a huge cylinder, its length is about 10 times the diameter, and then the cylinder is rotated at the speed of150,000 km/s,
To use this cylinder as a time machine, the spacecraft must travel to the center of the cylinder and fly along the inner wall of the cylinder: sailing against the direction of cylinder rotation means driving into the past, and sailing along the direction of cylinder rotation means driving into the future. With each flight, the spacecraft will go deeper into the past or the future. When the time traveler arrives at the destination time, he will leave the cylinder. It must be understood that, like all theoretical time machines, it is impossible to reach an earlier time than making cylinders.
Time travel is a wonderful and fascinating topic. For a long time, scientists have put forward one scheme after another, and have also had a heated discussion on the problems that may be encountered in time travel. One day, the fascinating light of relativity will shine on us and start real-time travel.
Atomic fission
1905, 1 1 In June, Einstein also published a second article on special relativity in the German journal of physics: "Is the inertia of an object related to the energy it contains? This is a short essay. In this paper, he pointed out that the mass of an object is not constant, but increases with the increase of the speed of motion. This is the "mass increase effect" of moving objects.
Now let's imagine that we are pushing a small scooter, which is very light and has nothing on it. Suppose this is an "ideal" scooter in a vacuum without any friction and resistance, so as long as we keep pushing, its speed will get faster and faster, but as time goes on, its mass will get bigger and bigger. At first, it was like a car full of steel. Then there seems to be a Himalayan mountain, and then there seems to be an earth, a solar system and a galaxy ... When the scooter approaches the speed of light, it seems that the whole universe is mounted on it-its mass reaches infinity. At this time, no matter how hard you push it, no matter how long you push it, it can't go any faster.
Therefore, because a photon travels at the speed of light, its rest mass must be equal to zero, otherwise its moving mass will be infinite.
When an object moves close to the speed of light, we constantly apply external force to the object to supply energy, but the speed of the object becomes more and more difficult to increase. Where is the energy we use? In fact, energy has not disappeared, but has been transformed into mass. In other words, the increase of mass of an object is closely related to the increase of kinetic energy, or the mass of an object is closely related to energy. In the process of explaining this relationship, Einstein put forward the famous mass-energy relationship: E=mc2.
Energy equals mass times the square of the speed of light, which is thrilling even for pure theoretical physicists who don't care much about practical value. In most people's eyes, energy is equal to mass times the square of the speed of light, that is, energy is 9 million times the mass. What an attractive prospect! If the mass of a substance the size of a fingernail disappears completely, the energy released will be calculated as 10,000 tons of coal.
Unfortunately, no one can lose weight casually, such as a stone. We can break it into small pieces with a hammer and then grind it into pieces, but when you collect these pieces carefully, you will find that its quality has not changed.
However, more than ten years later 1939, three scientists-Aurio Curie, Fermi and szilard-independently discovered the chain reaction, which enabled mankind to find a way to release huge atomic energy. The nucleus of uranium -235 will split into two new nuclei with medium mass, releasing 1 ~ 3 neutrons, releasing huge energy, which can then trigger other uranium nuclei.
The chain reaction makes atomic energy a new weapon with great lethality. Only a few years later, the first atomic bomb exploded successfully in the United States, and then the Japanese suffered the most cruel punishment in human history, with hundreds of thousands of casualties, some of whom instantly became elementary particles, which really took their lives away. Before bringing hope to the world, E=mc2 brought fatal trauma, which was undoubtedly a heavy blow to Einstein who loved peace to the death.
BIGBANG
To our contemporary surprise, as late as 19 17, the smartest human brain still thinks that our galaxy is the whole universe. This galaxy-sized universe is always stable, neither growing nor shrinking. This is a steady-state cosmology that has been circulating for thousands of years.
19 17, Einstein tried to deduce the model of the whole universe according to the equation of general relativity, but he found that in such a model with only gravity, the universe was either expanding or contracting. In order to keep the model of the universe still, Einstein added a new concept to his equation-cosmological constant, which represents a repulsive force. Contrary to gravity, it increases with the distance between celestial bodies.
However, Einstein soon discovered that he was wrong. Because scientists soon discovered that the universe is actually expanding!
Hubble, the father of astronomy in the 20th century, 1889 was born in Missouri, USA, and graduated from the Astronomy Department of the University of Chicago. 1929, Hubble found that all galaxies are leaving us, which shows that the universe is expanding. This expansion is the uniform expansion of the whole space, so the observer at any point will see exactly the same expansion, from any point of view.
The expansion of the universe means that in the early days, the distance between stars was closer, and at some point in the more distant past, they seemed to be in the same small range.
When the news of the expansion of the universe reached the famous physicist Gamov, it immediately aroused the interest of the scholar. George gamow was born in Russia, and he was interested in poetry, geometry and physics since he was a child. He became a proté gé of physicist Friedman in college. Friedman once put forward an important model of the expansion of the universe after Einstein, and Gamov became one of the enthusiastic supporters of the theory of the expansion of the universe, and the first atomic bomb exploded successfully in human history. 18960/888617 Looking at the photo of the mushroom cloud rising, Gamov suddenly had an inspiration: isn't it a cosmic explosion to "enlarge" the size of the atomic bomb to infinity? He combined the knowledge of nuclear physics with the theory of cosmic expansion, and gradually formed his own theoretical system of the Big Bang universe.
1948, Gamov and his student Alpha wrote a famous paper, which systematically put forward the theory of the origin and evolution of the universe. Contrary to what we usually think, the big bang that created the universe did not happen at a certain point and then spread into the surrounding air, but the space itself was expanding, and the galactic matter separated with the expansion of the space.
According to the Big Bang cosmology, the very early universe was a huge homogeneous gas composed of microscopic particles, with extremely high temperature, extremely high density and extremely high expansion speed. Gamov also made an unusual prediction: our universe is still bathed in the residual radiation of the early high-temperature universe, but the temperature has dropped to about 6 K, just like a furnace, even without fire, it can emit a little hot air.
1964, penzias and Wilson, young engineers of American Bell Telephone Company, stumbled upon the residual radiation of the early universe predicted by Gamow. After measurement and calculation, it is found that the temperature of this residual radiation is 2.7K (lower than that predicted by Gamov), which is generally called 3K cosmic microwave background radiation. This discovery strongly supports the big bang theory.
The wisdom of general relativity lies in that it can describe the whole universe from its birth, even those unknown fields. It is really overqualified to deal with such a small and ordinary space-time field of the solar system.
Cosmic constant comes from dark energy.
After discovering the fact that the universe is expanding, Einstein hastily deleted the cosmological constant term from his equation, thinking that the cosmological constant was "the biggest mistake in his life". Subsequently, the cosmological constant was thrown into the garbage dump of history.
However, decades later, the cosmological constant revived like a ghost, thanks to the discovery of dark energy.
1998, astronomers found that the universe is not only expanding, but also expanding outward at an unprecedented acceleration, and all distant galaxies are moving away from us faster and faster. Then there must be some hidden force accelerating the tearing of galaxies in the dark. This is a repulsive energy, which scientists call "dark energy". In recent years, scientists have confirmed through various observations and calculations. Dark energy not only exists, but also dominates the universe. Its total amount accounts for about 73% of the universe, while dark matter accounts for about 23%, and ordinary matter only accounts for about 4%. We always think that there are enough stars in the sky. What else in the universe can compare with them? Now, we find that the stars in the sky are "vulnerable groups", and most of the rest are we know little or nothing. How can this not make people feel thrilling?
In fact, as early as 1930, astrophysicists pointed out that Einstein's cosmological equation with cosmological constant could not lead to a completely static universe: because gravity and cosmological constant are unstable balance, a small disturbance may lead to uncontrolled expansion and contraction of the universe. The discovery of dark energy tells us that Einstein's cosmological constant, as a counterbalance to gravity, not only really exists, but also greatly disturbs our universe, making the expansion speed of the universe serious.
Today, the cosmological constant appears in front of the world in the form of dark energy, and its surging repulsive force has discolored the whole universe! Since the birth of the universe, the struggle between dark energy and gravity has never stopped. In this long battle, the most important thing is the density of each other. The density of matter decreases with the increase of space caused by the expansion of the universe. However, when the universe expands, the density of dark energy changes very slowly or remains unchanged at all. Long ago, the density of matter was relatively high, so the universe at that time was in the stage of deceleration and expansion; At present, the density of dark energy is greater than that of matter, and repulsion has completely seized control from gravity, pushing the universe to expand at an unprecedented speed. According to some scientists' predictions, after more than 20 billion years, the universe will usher in the end of turmoil, and the horrible dark energy will eventually tear all the galaxies, stars and planets one by one, leaving endless cold and darkness for the universe.
The discovery of dark energy also fully reflects that the cognitive process of human beings has entered a "paradox circle": that is, the universe accounts for the largest proportion, but it is the latest and most difficult for us to know. On the one hand, human beings now know more and more about the mysteries of the universe, on the other hand, we have to face more and more unknowns, which constantly stimulates human beings to explore the truth behind the universe.
How does dark energy come from? How will it develop? This has always been one of the most important problems faced by cosmology in 2 1 century.
Black hole discovery
General relativity shows that gravitational field can cause space bending, and strong gravitational field can cause strong space bending. What will happen to the infinitely strong gravitational field?
Shortly after Einstein published his general theory of relativity in 19 16, German physicist karl schwarzschild used this theory to describe how the space and time around a hypothetical completely spherical star are curved. He proved that if the mass of a star is concentrated in a spherical area small enough, for example, the mass of a celestial body is the same as that of the sun, and the radius is only 3 kilometers, then the intense squeezing of gravity will increase the density of that celestial body infinitely, and then it will collapse catastrophically. Without the connection of optical signals, this space-time is divided into two areas with different properties from the outside space-time, and that divided sphere is the horizon.
This is the black hole we are familiar with today, but at that time, almost no one believed that such a strange celestial body existed. Even Einstein himself and relativist masters like Eddington clearly expressed their opposition to this behemoth. Einstein also said that he could prove that no star can reach infinite density. Even the name of the black hole was not named by American physicist Wheeler until 1967.
Of course, history will not stop because of this. In 1930s, American astronomer Chandraseka put forward the famous "Chandraseka limit", that is, when the mass of a star after its hydrogen nucleus is burnt out exceeds 1.44 times of the mass of the sun, it will not become a white dwarf, but will continue to collapse and become a star smaller and denser than a white dwarf. That is, neutron star. 1939, American physicist Oppenheimer further proved that when the mass of a star's hydrogen nucleus is more than three times that of the sun, its own gravity will prevent light from escaping from the star's range.
With the accumulation of experience, the theory about black holes has matured. People have completely rejected this monster and come to believe it. By the 1960s, people had generally accepted the concept of black hole, and the mystery of black hole was gradually studied.
Strictly speaking, a black hole is not a "star" in the usual sense, but just a region of space. This is a field that is out of touch with our daily world. The event horizon of the black hole separates these two regions. Outside the event horizon, they can be connected at any distance by optical signals. This is the normal universe in which we live. However, in the horizon, light cannot spread freely from one place to another, but all gather at the center, and the connection between events is strictly restricted. This is a black hole.
Inside the black hole, in the process of falling to the black hole, the tidal force gets bigger and bigger. In the central region, gravity and tidal force are infinite. So in the center of the black hole, except for mass, charge and angular momentum, other properties of matter are lost, and atoms, molecules and so on will cease to exist! In this case, it is impossible to talk about what part a black hole is, and a black hole is a unity!
At the center of a black hole, all matter is squeezed into a geometric point with infinite volume approaching zero, and no powerful force can separate them. This is the so-called "singularity" state. General relativity can't investigate this, but it must be replaced by a new correct theory-quantum theory. Ironically, general relativity gave us a black hole, but it failed at the singularity of the black hole, and quantum theory took its place, while quantum theory and relativity were fundamentally replaced.