Source: Science and Technology Daily

The flat sphere with a huge plate is like a super large iron cake -this is the portrait of the galaxy we live in. So, what is the shape of the universe?

Numerous scientists have had a lot of conjectures, and this question has never been exactly an exact answer. After many years of observation and deduction, these conjectures have gradually converged into a mainstream view -the universe is the endless flat three -dimensional space.

Recently, Researcher Elionla Valentino, a researcher at the University of Manchester in the United Kingdom, pointed out through the observation data analysis of the Planck satellite that the universe may not be as flat as sheets, but a closed three -dimensional sphere, like a person, like a person The huge balloon bent as. The study was published in the magazine of Nature · Astronomy.

Two ideas to explore the mystery of the shape of the universe

The Newton cosmic concept based on Newton’s gravity believes that the universe is an infinite three -dimensional Our geometric space, that is, the universe is distributed in the three -dimensional geometric space we often say. Essence However, this assumption is not completely in line with gravity theory, but has some contradictions.

“Later, when people realized the concept of bending space, there was the possibility of the universe as a three -dimensional sphere.” Chen Xuelei, a researcher at the National Observatory of the Chinese Academy of Sciences, said in an interview with the Science and Technology Daily that Einstein constructed a limited and boundless universe Static model, he believes that the universe may be a limited and closed three -dimensional sphere.

According to the general theory of relativity, the existence of matter makes time and space bent. Near the huge quality of celestial bodies, the light does not “go” straight lines, but the “walk” curve. Later, with the further deepening of the cognition of the universe, people found that there were many possibilities in the real shape of the universe.

“There are three most common possibilities, that is, the straight three -dimensional Euki geometric space, the bended three -dimensional sphere and the bending three -dimensional bilateral surface.” Chen Xuelei said that the cosmic curvature is zero, positive and negative, respectively, and the universe, respectively, the universe presented, respectively, the universe presented in the universe, respectively. Three different forms.

Among these three possible cosmic shapes, only closed three -dimensional sphere is limited. The three -dimensional dual surface is like the shape of a saddle. The flat three -dimensional Our space is even more boundless.

So, which three possibilities are the real shape of the universe? What method do we use to calculate the shape of the universe?

“There are two main ideas, one is to measure in geometry, and the other is to define it by density.” Chen Xuelei introduced.

As we all know, in the Eushi geometry of the straight space, the inner angle of any triangle is 180 °. However, if on the surface of the sphere or on the curved surface, the inner corner will be more than 180 °. On the curved surface with bilateral or curvature, the inner corner of the triangle will be less than 180 °. The principle of the geometric measurement method is to use the observer as a vertex, and then select 2 points in the space to form a triangle. If we can measure the edge length of the three edges, we can determine this unique triangle in the Eushi geometry, and the size of the top angle can be calculated. On the other hand, we can also obtain the size of our top angle through direct observation. Compared with the calculation value, we can determine whether it is consistent, or larger or smaller.

If the observation value and calculation value (real value) of this top angle are equal, it indicates that the universe is a straight three -dimensional space space; if the observation value is greater than the calculation value, it indicates that the light walks on a positive curvature surface, that is, the universe is the sphere; If the observation value is less than the calculation value, it indicates that the universe is a bilateral surface of negative curvature.

Another idea depends on the relationship between the overall density and critical density of the expansion universe. Critical density depends on the speed of expansion. The higher the expansion speed at a certain moment, the higher the critical density.

According to the general theory of relativity, when the overall density of the universe (that is, the average density) is equal to the critical density, the shape of the universe is unlimited and flat. When the overall density is greater than the critical density, the geometric properties of the universe are spherical geometry; if the universe The total amount of material in the space is too small, making the density smaller than the critical density, the universe is manifested as the hyperbolic geometry.

Microwave background radiation set off the mysterious veil of the universe

However, if you measure the idea of ​​geometric measurement and at the scale of the universe, we cannot fly to a field detection at a long enough distance, because if it is only measured in the galaxy and even the surrounding galaxy, it is only a local curvature, not the entire universe, not the entire universe. Real curvature. It’s like there are high mountains and basins on the earth, which are uneven, but the earth is generally a sphere.

If you study along the idea of ​​cosmic density, it is also difficult to operate. The reason is that although we have calculated the critical density related to Hubble’s constant, the overall density of the universe is difficult to measure. There is a vast space between galaxies, and the space density between galaxies and galaxies is very different. What’s more, there is still an unpaid, so -called dark matter in the universe, and the number may far exceed the current visible substance, which brings great uncertainties to the determination of the overall density.

Cosmic microwave background radiation provides a lot of help to calculate the average density of the universe. In the millimeter -band balloon viewing plan at the end of the 1990s, people measured the ratio of the overall density of the cosmic and critical density through the relevant data of the universe microwave background radiation, which was close to 1. “Experiments are errors, so based on this result, people think that the universe has no obvious positive or negative curvature, which is almost a smooth and smooth space structure.” Chen Xueling said that this is also the flat universe predicted by the theory of the universe bloating theory. Coincidence.

In 2018, the European Space Agency (ESA) Planck’s Sky Tour Program announced more accurate observation data. “After eliminating the relevant experimental errors as much as possible, data from the European Space Agency show that the cosmic song rate may tend to be positive, that is, the shape of the universe is a closed sphere, although this ‘tendency’ is not very obvious.” Chen Xuelei said.

In this study, Valentino and others obtained the data basis of the degree of “gravitational mirrorization” by the cosmic microwave background radiation through Planck’s satellite observation, and analyzed a large amount of data. Different models were used to fit the data. The probability that the universe is about 99%of the universe is about 99%.

As a result, it is more reliable but the debate is far from dust.

Is this study reliable? Is the dispute between the shape of the universe settled?

“The statistical research adopted in this study is not impeccable, and there are certain errors. But if the facts are true, it will inevitably overturn a lot of traditional cognition.” Chen Xuelei told the Science and Technology Daily that researchers may underestimate the statistical errors. Therefore, the real probability may not be as high as 99%.

“It is worth noting that all parameters are deduced based on a certain model, such as the relationship between the three of them through time and speed. Among them, we are not sure whether the model it uses itself contains all physical effects, which is worth further studies. “Chen Xuelei pointed out that, for example, if certain effects are not considered or there are some unknown effects, it will affect us, which will affect us. Judgment of the real shape of the universe.

Researchers also said: “I don’t want to say I believe in a closed universe.” He believes that this result is only to indicate that there is a difference from previous research. As for why there is this difference, you should explore the reason carefully.

In the past, studies have also pointed out that the shape of the universe is not a flat three -dimensional Our space. Why is the academic circles more concerned about this study?

“In the past, the study of the universe was usually judged according to the thermal spot radiation of the universe microwave background.” Chen Xuelei told reporters that the temperature of the universe microwave background radiation is uneven. In the early days of the universe, there was an oscillation of sound waves, and the hottest spots produced for the first time. In the past, the study was equivalent to just drawing a triangle on the basis of this largest hot spots to measure cosmic song rate. In fact, if some parameters are changed, even different models may fit the same curve, so the accuracy is relatively low and the credibility is low.

“And this study is equivalent to not only the maximum hot spots, but also analyzes the triangles produced by the hot spots produced by other oscillations at the same time. It is not satisfactory to observations except the background radiation of the universe microwave background radiation, such as supernova, etc. This shows that there are still some things that we have not considered and we need to explore further. “

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