An introduction to the physics of time travel

Spacetime tunnels are such physical objects that allow any bodies to move very large distances in space in an instant or to move from one moment in time to another. In Albert Einstein's theory of general relativity, these tunnels are derived from the geometry of curved spacetimes in which mathematical differential equations and tensors occur. However, this work shows that spacetime tunnels cannot be described by Albert Einstein's theory of general relativity alone. This means that relativity is not sufficient to describe all aspects of a tunnel in spacetime. This requires new approaches and understandings of the physics of the universe. The new understanding is the physical theory of time travel, which, according to the best current knowledge, describes spacetime tunnels in the most accurate and objective way. The physics of spacetime tunnels is a part of the physics theory of time travel, which is briefly presented in this paper. In this work, the focus is not on the technical possibility of creating spacetime tunnels, but on those aspects that determine the lengths and directions of spacetime tunnels. For example, the length of the tunnels depends on how far the bodies move in a moment in space or time. However, the directions of the tunnels determine whether the bodies move in space or time to the past/future. These aspects must be known if we want to technically create the world's first tunnel in spacetime.