In many sci-fi works, there are often some crossing bridges, and the most common one may be going back to the past at faster than light, but in previous articles, we have refuted this (the original sci-fi works, especially some film and television dramas, are mostly third-rate).

Secondly, wormholes are used for crossing. In fact, wormhole crossing was a "cosmic passage" discovered by Einstein and Rosen when they were studying Schwarzschild space-time. Unfortunately, the wormhole they found at that time could not achieve the function of crossing.

Later, Thorne and others made contributions to wormholes in the 1980s. Theoretically, some wormholes have been found that can be crossed. The cause of the incident also originated from a novel named Contact written by Sagan, a famous astronomer and novelist at that time. In the novel, there is a plot in which the hero crosses through a black hole to Vega. Sagan was not sure about this process at that time, so he asked Thorne to see if it was feasible to cross the black hole.

As an expert in relativity, Thorne thinks it is almost impossible to cross a black hole. However, if black holes are replaced by some special wormholes, it seems that things have changed. So Thorne studied this matter carefully, and finally published a paper (this plot seems to be the same as Thorne was invited to be the scientific consultant of the sci-fi movie Interstellar a few years ago, and designed a black hole model for the movie, and finally published a paper considering its scientific nature).

Before introducing this special wormhole in detail, it is necessary for us to explain a picture of relativistic science that we often see, as follows:

Looking at this picture, do you feel familiar? Isn't this the schematic diagram of matter bending time and space? What is there to introduce? In fact, this picture really needs to be introduced, because many people will have some preconceived associations when they see the picture after hearing the word time-space bending. For example, they think that the curved grid lines in the picture are the real objective time-space, but in fact the real time-space is invisible.

The reason why the picture is depicted in this way is that the word bending can be depicted intuitively enough. I even want to tell you that the curved grid lines in the picture are actually just the space geometry on the equatorial plane of the celestial body. Yes, it's just the spatial situation on the equatorial plane. Because the radial coordinate difference of the spatial scale is not equal to the actual length, it is a sunken image. Therefore, this unequal length can be drawn with a Euclidean cylindrical coordinate, thus showing the abstraction of space bending.

For this kind of picture, scientists call it an embedded picture. In order to better introduce the embedded graph (introducing the necessary preparation before wormhole), let's introduce a simple embedded graph.

Assuming that there is an isolated spherical celestial body in the universe, and the celestial body does not rotate, and the overall charge it carries is neutral, then the space-time where the celestial body exists is called Schwarzschild space-time.

If it is wider, we will use boekhoff's theorem, which tells us that the spherically symmetric solution of vacuum Einstein equation must be Schwarzschild's solution, that is, as long as the celestial body is spherical, there is no other matter, no rotation and no charge in the nearby space, then the solution of gravitational field equation is Schwarzschild's solution. It should be noted that this theorem tells us that as long as matter is spherically symmetric, celestial bodies can move radially, such as expanding or collapsing along the radius.

This theorem is very useful, for example, our sun, from the main sequence star to the red giant star, we can use Schwarzschild solution to describe the surrounding time and space (although there are many substances around the sun, and it has additional factors such as rotation, we can still use Schwarzschild solution approximately).

So how can such a celestial body show its influence on time and space through an embedded figure?

Please see the next article for related content.

This article ends here.

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