Now people often use the universe to represent the vast space outside the earth's atmosphere. We know very little about this space, and even the farthest distance that humans can reach now is just leaving the solar system.
Man's study of the universe is limited to observation. We can use optical telescopes to see all celestial bodies that can transmit light to the earth, use radio telescopes to detect invisible electromagnetic waves emitted by all celestial bodies, and even use satellite detectors to collect microwave background radiation of the universe.
No matter which way we use, we can't really see the outside of the universe. The diameter of human Hubble volume is only 93 billion light years. There must be a lot of space beyond the observation of the universe, but we can't see it at all, so we can't know if there will be a boundary of the universe if we go further.
The best way to understand a thing or phenomenon is to observe. Through observation and experiment, human beings know all kinds of unknowns of the universe. When we can never observe a phenomenon, all we can do is to speculate according to the existing conditions.
First of all, we should all be very familiar with a theory of the birth of the universe-the Big Bang theory. In this theory, the universe was originally a singularity with infinite mass and infinitesimal volume. One day, the dot was crushed by its own pressure and exploded.
Before the explosion of the singularity, there was no active matter and no change of matter, so there would be no natural time, because time is actually a concept that will come into being after we perceive the change of matter.
After the explosion, the universe changed dramatically in a very short time. At this time, the diameter of the universe has expanded a lot. After the expansion, countless positive and negative substances began to appear under the strong energy impact.
Theoretically, both positive and negative matter appear in pairs, and all positive and negative matter can be restored to their original energy when they collide. But due to a little accident, more positive matter appeared, thus forming a cosmic environment dominated by matter in our eyes now.
After the Big Bang, the temperature of the universe began to drop, and the positive and negative substances converted from energy began to spread around, and the scope of the universe was gradually expanding.
In our idea, all phenomena in the world should be repeatable. Since there is a singularity that can evolve into our present universe through explosion, there should be another or even countless singularities exploding repeatedly outside the universe.
So these countless explosive singularities formed the universe, which may be completely different from our present universe, may even have completely different physical rules, and of course may be exactly the same as ours.
However, the multiverse can't reasonably explain what is outside the universe, because it is actually just a doll-like answer, which inevitably requires us to study the question of "what is outside the multiverse".
Some scientists believe that the size and mass of the universe are limited, but it has no boundaries. This statement is difficult to understand.
To put it simply, the direction of BIGBANG is 360 degrees without dead angle from the beginning, so the matter expands outward in the form of a sphere with the singularity as the center, just like blowing bubbles. For example, it may be like blowing a balloon.
In fact, the earth we live in can also be approximately regarded as a finite-size existence without boundaries. We start from any point on the earth and move in one direction. Finally, after a round-the-world trip, we will return to the original point. This so-called borderless theory probably means this, but the problem is that the earth actually has boundaries, and the boundaries are above the atmosphere.
Inflated balloons also have boundaries. Going up on the surface of the balloon is the boundary of the universe. So in this unexpanded universe, which direction is upward? No one can answer this question.
In the famous superstring theory and M theory, there is a branch that explains the existence of the universe, that is, film cosmology. According to the film cosmology, the universe we exist is actually like a bead embedded in a higher-dimensional film.
For this film, our universe is only its elementary particle, so there are countless three-dimensional universes in this film that are almost even the same as our universe.
This is actually an upgraded version of the multiverse theory. The only difference is that all universes exist in a higher dimensional space instead of the same three-dimensional space. In the membrane universe, if we can break through the boundary of the universe, we can enter a higher dimensional world.
According to the observation of scientists, it is believed that the life span of the universe should be about 65.438+0.373 billion years. However, from the Hubble volume with a diameter of 93 billion light years, we can quickly draw a conclusion that the universe is spreading faster than the speed of light.
But we also know that particles and matter with mass can never reach the speed of light, let alone surpass it. The reason why the universe is expanding faster than the speed of light is that, in fact, it is not the matter of the universe that is moving away from us at superluminal speed, but the space between celestial bodies is expanding at an extremely fast speed.
In Einstein's general theory of relativity, the space of the universe is not straight and can be twisted and pulled. For example, the space near the sun bends and deforms due to the weight of the sun itself.
This deformed space is like a stretched sheet that has been hit by a stone. When other objects enter this depression, there will be a relative velocity between all objects and the sun.
So these objects will always rotate along the inner wall of the depression and around the sun in the center of the depression. Because the friction in space is almost negligible, the planets around the sun can keep rotating for tens of billions of years without falling into the center of the depression.
Originally, the space was flat, but as long as there was substance in the space, the surrounding space would be curved, and BIGBANG made the substance appear, and at the same time the space became tortuous.
So first of all, we can get an answer, that is, in the space where the matter produced by the cosmic explosion has not yet reached, if there is space, then this space is at least straight.
If there is no space, the answer is simpler, which means that the universe has a boundary, and all substances in the universe cannot cross this boundary. Even though the diffusion of cosmic matter may make the boundary retreat, the boundary will still exist.
The world is divided into two worlds: the space with matter behind the border and the world without matter. So we can only say that there is nothing outside the universe, or even that the universe has no outside, because we can't understand what a world without space and matter looks like.
Of course, scientists still prefer to have space outside the universe. When matter diffuses into these flat spaces, the universe becomes distorted.
The universe described above expands faster than light, because the universe with matter is distorted, and the continuous distortion makes the matter outside the universe seem to be farther and farther away from us.
In a word, now we can draw two conclusions, either there is nothing outside the universe, or the universe has only a flat space without matter.
In fact, it is of little significance to study things outside the universe, because the universe we can't effectively observe is just a big sphere with a radius of 46.5 billion light years.
In the farther universe, due to the distortion and expansion of space, the speed of matter 46.5 billion light-years away from us has exceeded the speed of light, and the light they emit can no longer reach us, so we can't see or feel anything outside this range anyway.
So the horizon was formed. In fact, the horizon is more like our cosmic boundary than the cosmic boundary that doesn't necessarily exist and doesn't know in what form.
Everything that happens near us will not affect the universe beyond the horizon. There is a simple reason. Can't even send a message. Matter outside the Hubble volume is equivalent to non-existence for us.
Information generally travels at the speed of light, and matter can never exceed the speed of light, so the invisible world can't influence us and we can't influence them.
The existence of horizon also prevents us from studying the boundary of the universe. No matter how we guess the existence form of the boundary of the universe, we can never verify these guesses through observation or any other means, and the unverifiable views are always uncertain.
Because of the horizon, we can't study the real origin of the universe and the existence form of the universe. These questions have no answers, which will become the biggest obstacle to the development of our physics.
We humans have always been very good at observing phenomena and then using the principles of phenomena to improve our existing technology. So we can open a brain hole here, since the universe beyond the horizon is beyond the speed of light because of the distortion and expansion of space by matter. So as long as we can develop the technology of distorting space, does it mean that we can also achieve the effect of seemingly superluminal?
At present, the distorted space we know is to press it into distortion with a large mass. Is there any other way to distort space? For example, a straight plate can not only be pressed by stones, but also be distorted by clamps.
This brain hole is actually the general principle of curvature spacecraft. Of course, with the current technology of human beings, the function of space distortion can not be realized, and the curvature spacecraft can only exist in science fiction, but the existence of this brain hole can still make many people feel a glimmer of hope. Perhaps one day in the future, human beings can break through the horizon, reach the boundary of the universe, and see for themselves what the boundary of the universe really looks like.
In fact, thinking and studying the origin of the universe and the possible state of the boundary of the universe requires a huge knowledge reserve. Otherwise, it's just fantasy. What we should do more than guess is to know more about the existing knowledge, and then use this knowledge to study these unknown phenomena.
The origin of the universe and the boundary of the universe are actually the same problem. If we can get the answer, we can accurately understand the existing form of matter and the future development direction of the universe, which requires scientists to study hard.