What Is the Observable Universe?

Hubble Volume (also known as the Observable Universe, English: Hubble Volume) is a sphere space centered on the observer, which is small enough for the observer to observe objects in this range, that is, the light emitted by the object is sufficient Time reaches the observer. Hubble's volume radius is now about 46 billion light years .

Hubble Volume

Hubble volume is a

After the Big Bang, some parts of the universe may have been too far away from the earth, causing them to have not reached the earth until now. Therefore, this part of the universe may now be outside the observable universe. In the future, the light emitted by distant galaxies will have a longer time to travel through space and time, so a part of the universe that we cannot observe now will be observed in the future. However, due to Hubble's law, some areas of the universe far enough away from us will move away from us at speeds that exceed the speed of light (Special relativity prevents neighboring objects in the same local area from moving beyond the speed of light relative to another object, but for Distant objects in space and time that are expanding are not so limited), and dark energy has caused the universe to accelerate its expansion. Assuming that dark energy remains unchanged, the speed of expansion of the universe continues to increase, and there will be a "future visible limit" An object exceeding this limit will never be able to be observed by us, because the light emitted by this object is outside this limit. (A subtle situation is that, because Hubble parameters continue to decrease over time, there will be a scene where a galaxy that is just a bit faster than light away from us may just be able to pass light to us). The calculation of "Future Visible Limit" gives a total motion distance of 19 billion seconds (about 62 billion light years), which means that the number of galaxies we can see in the endless future can only be greater than the galaxies we see now. 2.36 times more. (Something that cannot be observed due to redshift, as described in the next paragraph). Although in principle more galaxies will be observed in the future, in fact more galaxies will be redshifted too much due to uninterrupted expansion so that they will appear to disappear in view and cannot be observed . A subtle point is that if we can identify a galaxy at a given co-movement distance in the observable universe, we must require that its past can emit light that we can receive. (Such as an early galaxy formed 500 million years after the Big Bang), but due to the expansion of the universe, the signal it sends out in the possible next historical period of the galaxy cannot reach us and be received in the infinite future. . Although it is still at the same co-movement distance, it is shorter than the co-movement distance of the observable universe. This phenomenon can be used to define a type of horizon of cosmic events that varies with time. For example, this horizon is only 16 billion light years, meaning that an event that currently occurs in 16 billion light years can be in the future. Accepted by us, but events beyond 16 billion light-years will never be known to us if they occur now. Whether in the popular and professional cosmology field, research literature often uses "universe" instead of "observable universe", and this has a fundamentally good reason: we may never know the universe we can't communicate with through direct experiments. Part of the information. Although quite a few feasible theories require an observable universe many times larger than the observable universe. There is no evidence explaining that the boundary of the observable universe is the de facto boundary of the entire universe. There is also no mainstream cosmological model. First, it is assumed that the universe has a recognized physical boundary. Although some models guess that the universe is finite but unbounded Like a two-dimensional sphere in three-dimensional space, it has a limited area but is boundless. It seems likely that galaxies in the observable universe represent only a tiny fraction of the galaxies in the universe. According to the theory of expansion of the universe and his founder Alan Guth, if it is assumed that expansion occurs 10 seconds after the birth of the universe, then according to this seemingly reasonable assumption, the size of the universe during this period is as large as the speed of light times its age. This means that the entire universe may be 10 times the size of the observable universe. If the universe is finite but unbounded, it means that the universe is smaller than the size of the observable universe. In this case, galaxies that we look far away may be the illusion of nearby galaxies, which are illusions caused by the light circle around the universe. This hypothesis is very difficult to detect because galaxies are different at different age stages, or even completely different. A 2004 document believed that the size of the universe was only 78 billion light-years. This may be the smallest cosmic scale, even smaller than the size of the observable universe. This result benefits from the data processing results for WMAP (an artificial astronomical satellite), and research in this area is being heatedly debated.

Usually people think that the diameter of the universe is 29 billion seconds, about 93 billion light years. Assuming the universe is smooth, this means that the volume of the universe is 3.5 × 10 cubic meters, which is about 4.1 × 10 cubic light years. . In cosmological time, these data are the current distance, not the distance at which the light is emitted. For example, the decoupled photons emitted by the cosmic microwave background radiation were emitted 380,000 years after the big bang, which occurred about 13.7 billion years ago. These radiations were emitted by some of the materials that later formed most galaxies, and these The galaxy is now 46 billion light years away. In order to estimate how far the rays came to us at the moment they were emitted. (The following is a brief derivation). Although they are now 46 billion light-years away from us through redshift and cosmological formulas, they were only 42 million light-years away from us at that time. (Additional content: The reason why astronomers will conclude that the radius of the universe is 47 billion light-years, is due to the expansion of space-time, the universe is constantly expanding, and this happens in every corner of the universe, like an expanding balloon On the surface, the distance between any two points is constantly increasing, so the distance between substances is increasing, and the speed of change is not the same at different times. This is because as the distance increases, the distance between two However, it s faster and faster to get away from it. Although it takes 13.7 billion years for light to travel to us, the light source that emits light at the same time has gone further away from us. If you want to calculate the light source at this time and our Distance requires some astronomical formulas and integral calculations. A simple approximation. For distant celestial bodies, you can simply think of the distance D = 3ct, so that you can roughly get D = 13.7 billion years * 3 * c is about 50 billion light years the result of.)