The greatest scientific discoveries of the 20th century are the theory of cosmic expansion—the neighboring galaxies and distant galaxies are far away from us, and the distant galaxies are moving faster, as if the entire universe is expanding and stretching. From a macro perspective, the facts are also true. If we can see far enough, we will find that the distant galaxies seem to be wrapped in tremendous power and pushed farther and farther at a very fast speed. Any signals we emit cannot reach these galaxies, even if they are signaled. The speed of propagation is the speed of light.
However, if the universe is expanding at a speed faster than the speed of light, why can’t we feel it? The atoms, animals, the earth, and the solar system and the Milky Way around us still have a constant size and do not become fat. Moreover, the distance between the various planets in the solar system has not changed, and the distance between the Earth and the Sun is still as far as before. If our feelings are correct, what is the expansion in the universe?
The universe has never stabilized
Initially, human understanding of the universe originated from Newton. He regarded the universe as a completely fixed grid. The matter was filled in this grid, maintaining an absolute balance through gravitation and material motion. Later, Einstein discovered that the mesh of the universe is not fixed as described by Newton. As time goes by, it can twist and stretch, constantly changing, and it is the fluid in the grid that determines the change of the universe. Astral matter and radiant energy. However, if the distorted universe has only matter in space and time, then they will inevitably collapse together because of gravity, forming a black hole until the entire universe is swallowed up. Einson does not like the result of such deduction. He specially introduced an anti-gravitational “cosmological constant” to study the tendency of the cosmic contraction in the study of the gravitational field equation of the universe, so that the universe can be placed in a near-constant state. .
But not all scientists feel that the universe is not stable. Soviet physicist Alexander Friedman believes that Einstein’s “cosmological constant” is really superfluous. Later, Friedman mathematically proved that if the “cosmological constant” is not introduced and the universe is filled with dynamic matter such as radiation and fluid, then the universe will either shrink or expand.
Mathematical deduction can only provide a variety of possible “solutions”. Scientists still have to make real-world observations in the physical world to understand the direction of the evolution of the universe. In the 1920s, Edwin Hubble observed 46 constellations and galaxies and found that their spectra were red-shifting, indicating that they were moving away. Moreover, Hubble also found that the ratio of the speed at which the galaxy moves away and the distance between them is a constant, that is, the farther they are apart, the faster the separation. This relationship, known as Hubble’s law, was born.
We don’t feel the grand scale change
According to Hubble’s law, the way the universe expands seems to be a bit counter-intuitive—the cosmic mesh itself is constantly stretching, and the distance between objects is pulled further and further. If the object is farther away from the other, the stretching between them is The more you move away from each other, the faster. In this case, if the matter in the universe is evenly distributed, the density of the matter will become smaller and smaller, and we will naturally become fat. However, the matter in the universe is not evenly distributed, with densely populated areas such as galaxies and clusters of galaxies, as well as areas of dense density, such as huge cosmic voids, which have almost no mass. The reason why the universe is like this is because there are many physical effects between matter in the universe. On small scales, such as animal-sized layers, electromagnetic and nuclear forces play a major role; on large scales, such as stars and galaxies, gravitation plays a major role; on very macroscopic scales, galaxies are far away, clusters of galaxies In the decomposition, the expansion of the universe plays a major role. According to research, the motive force of the universe comes from the mysterious dark energy. So far, scientists know very little about this mysterious dark energy.
Therefore, in the universe, the expansion of the universe and the gravitation of gravity are the biggest competitors of each other. Even the Virgo Galaxy, which is only 50 million light-years away from us, cannot attract the solar system through gravity because the universe expands. The solar system and even the stars in the Milky Way have solved the expansion of the universe through gravitation and are stably tied together. Only through such competition can the earth and humans survive for a stable and long-term life, and even the expanding universe can do nothing to us.