# New research says wormholes may be a feasible shortcut through time and space

Sina science and technology news Beijing time on November 17, in a new study, the new theory proposed by scientists refuted the previous prediction that the wormhole will collapse rapidly. This bold new theory suggests that wormholes – or channels between black holes – may eventually be stable.

Wormhole, also known as Einstein Rosen bridge, is a narrow channel that may exist in the universe to connect two different time and space. Previous theories predicted that these hypothetical space-time “shortcuts” were fleeting and would collapse rapidly. The reason for such a different outcome in the new research is due to the small differences in the relativistic mathematics used to describe the wormhole, which finally dramatically changed our overall understanding of the wormhole.

Everything is related to the gauge

First, let’s learn some background knowledge about how general relativity works. Relativity is like a machine. When you put some objects – such as a group of chaotic or regularly distributed particles – in, the machine will show the changes of these objects under the action of gravity. Everything in general relativity is based on the movement of space and time: objects start from specific physical coordinates, move around, and finally reach other coordinates.

Although the rules of general relativity are fixed, the theory itself provides a large degree of freedom so that we can describe these coordinates mathematically. Physicists call these different descriptions “metrics”. You can think of a compass as a different way to describe going to a place for a dinner, perhaps according to the direction of the street, or based on the longitude and latitude of a satellite, or a landmark written on a napkin. In each case, your gauge is different, but no matter which gauge you choose, you will eventually have a full meal.

Similarly, physicists can use different yardsticks to describe the same situation. Sometimes one yardstick is more practical than another – similar to determining the direction of the street before switching to napkins to check again whether you have reached the correct landmark.

Expanding black hole

When we talk about black holes and wormholes, we will involve some potential metrics. The most well-known is the Schwarzschild metric, which is the first exact solution of general relativity that can be used to characterize black holes (i.e. Schwarzschild black holes). However, the Schwarzschild metric contains some strange mathematical functions. It is not so easy to use when it is at a certain distance from the black hole, that is, the Schwarzschild radius or event horizon as we know it today.

The “not so easy to use” here refers to the complete collapse of the Schwarzschild gauge, which can no longer distinguish the differences between space and time. However, we also have another metric, called the Eddington finkstein metric, which describes what happens when particles reach the event horizon: they pass directly through and fall into a black hole, and then disappear. So what does all this have to do with wormholes? The easiest way to build a wormhole is to “expand” the mirror concept of a black hole, that is, a white hole. This idea was originally proposed by Albert Einstein and Nathan Rosen, so the wormhole is sometimes called “Einstein Rosen bridge”. Black holes don’t let anything out, while white holes don’t let anything in. To make a wormhole, you just need a black hole and a white hole to combine their singularities (points with infinite density at the center). Thus, a tunnel through time and space was created.

However, the tunnel seems completely “impassable”.

Narrow path

If there is a theoretical wormhole, we have every reason to ask, what happens when we pass through this wormhole? Then general relativity comes into play: how do particles move in this (very interesting) case? The answer may be chilling. The white hole itself is unstable (or may not even exist at all), and the extreme forces inside the wormhole will force the wormhole itself to stretch and break, just like a rubber band. If you want to send something into the wormhole, I can only wish you good luck.

However, Einstein and Rosen built the wormhole using the Schwarzschild gauge, which is used in most wormhole analysis. Therefore, Pascal coyland, a physicist at Lyon Normal University in France, decided to try other methods. He changed to the Eddington finkstein gauge. In October this year, he described this in a paper published in the preprint database arXiv, which is expected to be published in the recently published journal of modern physics D.

Coyland found that by using the Eddington finkstein gauge, he could more easily track the path of particles through an imaginary wormhole. Particles can pass through the event horizon in a limited time, enter the wormhole tunnel, and then escape from the other end. At any point on the particle trajectory, the Eddington Finkelstein gauge did not fail.

Does this mean that the Einstein Rosen bridge is stable? Not exactly. General relativity only tells us the behavior of gravity, but does not describe the behavior of other natural forces. For example, thermodynamic theory (how heat and energy interact) tells us that white holes are unstable. If physicists try to create a combination of black holes and white holes in the real universe with real matter, it can be seen from other mathematical methods that the energy density of this combination will tear everything apart.

Of course, koylan’s research results are still interesting because he points out that wormholes are not as dangerous as predicted by the original theory, and there may be a stable path through wormhole tunnels under the framework of general relativity. (Ren Tian)