Because Newton's classical mechanics has many unexplained problems in space, Einstein put forward the concept that time and space are not absolute and flat, but have curvature, and people's view of time and space was subverted for the first time. Curvature engine was first proposed by Mexican physicist Mingo Alku Bailey in 1994. Since then, it has often been quoted by various science fiction novels and movies, such as the novel Three-body and the movie Star Trek. The "curvature" of the curvature engine is the expression of the degree to which the space-time bending deviates from the straightness.
Alku Bailey's curvature engine is based on the fact that space-time is not flat under relativity (it has been verified so far). It holds that the universe is a curved (or locally uneven) space-time with curvature. The basic principle of the engine is to flatten the space behind the spacecraft and make the space in front of the spacecraft more curved (increase the curvature and contract the space-time) through a device that can generate extremely powerful energy (decrease the curvature and expand the space-time). In this way, the spacecraft can reduce the straight-line flight distance. From a distance, the spacecraft seems to be flying at "superluminal speed" and reaching its destination at a faster speed. Of course, in fact, the spacecraft did not exceed the speed limit of the universe, because the "bubble-like" space-time where the spacecraft is located is still flat and has no curvature. In this way, the speed of the spacecraft equipped with the curvature engine did not exceed the speed of light, but it achieved "superluminal" travel.
Very easy to understand. You can take a piece of curved paper by yourself. If the curvature at the back is flattened, will the curvature at the front be greater? This shortens the straight-line distance between two points on the plane, and the space becomes flat after the spacecraft flies over. Of course, you can't see the space bending from the outside, but you think the speed of the spacecraft has accelerated. Here's another interesting thing. Theoretically, when a spaceship is in a "bubble" that bends in time and space, it may not need its own power. The "bubble" will push the spaceship forward at a very high speed, just as waves push people forward when surfing.
At present, such an engine can be realized theoretically. Scientists used a set of laser device named "White-Judy Curvature Field Interferometer" in the laboratory, which realized the space-time disturbance on a millionth scale. Although this scale is far from the requirements of the curvature engine (perhaps larger), at least people can see this hope for the future.
The biggest problem in manufacturing curvature engine is how to realize such an engine. First, there is no clue about the material used to make this engine; Second, the energy needed to achieve space bending is far from being mastered by human beings. According to Alku Bailey's early curvature engine model, to realize this kind of flight through time and space, it is necessary to convert the entire mass of Jupiter into energy according to Einstein's mass-energy equation. This level of energy is beyond human reach. However, human beings have no other way. After research, scientists believe that if the shape of Alku Bailey engine is changed to a "cylindrical" shape like a doughnut, the energy required may be greatly reduced. Moreover, he also found that the intensity of space-time bending is not fixed, and there may be other ways to reduce energy demand. From this point of view, although the realization of curvature engine is still far away, we have seen the possibility of realization from fantasy, which is undoubtedly the gospel for mankind to move towards the sea of stars.
Of course, we are back to the current problem. At present, celestial bodies bend space-time because of their huge mass, resulting in ripples or bends in space-time. Man-made spacecraft will certainly not have the mass of a celestial body, so to realize the change of time and space, it needs to produce huge gravity, and negative energy may be the only choice to produce this gravity. Although negative energy has been proved in the laboratory, there is no concept of materials that can be used. Alku Bailey thinks that the Casimir effect discovered in the 1940s can meet the engine's demand for negative energy. However, the gravitational force generated by Simile effect is conservative, which means that the zero-point energy of vacuum must be borrowed and returned, which will not provide continuous power for the curvature engine, let alone the gravitational force that causes the space-time to bend obviously, which requires a big gap.
Another problem is that the spacecraft needs continuous strong power. A core concept of curvature engine is that mass is energy, and energy can only change curvature of spacetime if it produces pressure. Therefore, in order to produce sustained and powerful energy output, it is necessary to realize controlled nuclear fusion (that is, we often say artificial small sun) to provide energy. As things stand, controlled nuclear fusion is hopeless in 50 years. As for 50 years later, that's what G knows.
So at present, from the mathematical model, the curvature engine can be realized. According to the laws of physics, the Alku Bailey curvature engine does not violate the theory of relativity. It is a space-time metric based on the theory of relativity. Before the thorough study of quantum gravity, it can be considered that it also conforms to the current laws of physics. But as far as human cognition and technology are concerned, it is really far from making curvature engines.
But as long as there is hope, mankind will realize it one day. Just like humans hundreds of years ago, they didn't consider that humans could fly to space and the moon in a few years, did they?