The universe we see has many common characteristics with black holes. A black hole has an event horizon, where gravity is so strong that even light cannot escape. The theory of cosmic inflation has also created a similar horizon. Space-time expands faster than the speed of light, so we can't see space-time outside Hubble's volume. There is also a singularity in the center of the black hole, where the density is infinite; BIGBANG was also a singularity before, and it also had infinite density.

Therefore, some scientists suggest that black holes may be other universes. And the multiverse theory makes many people believe that black holes are other universes. It has also become a favorite theory of many science fiction works.

Recently, a group of scientists published a paper on the preprint server. Relying on the idea of string theory, they proved that the singularity of a black hole may be connected with a multi-dimensional space-time called "membrane", and a new universe will be born in the next "Big Bang". Although no spaceship can take us through the horizon of a black hole alive, we can use mathematics to get close to the inside of the black hole.

Einstein's gravitational equation tells us that the space-time around a black hole is curved, and its curvature is beyond our imagination. Around the black hole, Newton's classical theory of gravity began to fail. In the era of BIGBANG, classical physics will also "collapse". Einstein's theory of relativity can explain black holes well, but it also creates internal singularities that are difficult to understand.

Quantum theory can explain the microscopic situation well, and it also tries to explain the singularity in black holes. However, it is very difficult to integrate the gravity theory into the quantum model. Hawking radiation is a successful example, but other attempts have failed.

In the new paper, scientists put forward methods to solve the singularity of black holes and big bang. They added an object to the effective field theory of space-time and matter, and this object is a "membrane". It is a relativistic object, occupying one-dimensional space-like hyperspace. This object violates the usual energy conditions, so it can analyze the singularity of space-time

In fact, this is not the first time that scientists have put forward the theory of black hole universe. However, many scientists who put forward this theory rely on general relativity to combine black holes with cosmological penrose diagram, but this will create new problems.

In order to solve this problem, researchers put forward the superstring theory, which holds that all forces in nature can be unified, and the birth of this theory is likely to solve the problems that relativity and quantum mechanics cannot solve. But the space-time of this theory needs more than 10 dimension, and our environment is three-dimensional space plus one-dimensional time. How to find other dimensions is a problem.