Time travel is the concept of movement between certain points in time, analogous to movement between different points in space by an object or a person, typically using a hypothetical device known as a time machine, in the form of a vehicle or of a portal connecting distant points in spacetime, either to an earlier time or to a later time, without the need for the time-traveling body to experience the intervening period in the usual sense. Time travel is a widely-recognized concept in philosophy and fiction. It was popularized by H. G. Wells' 1895 novel The Time Machine, which moved the concept of time travel into the public imagination. However, it is uncertain if time travel to the past is physically possible. Forward time travel, outside the usual sense of the perception of time, is possible according to special relativity and general relativity, although making one body advance or delay more than a few milliseconds compared to another body is not feasible with current technology. As for backwards time travel, it is possible to find solutions in general relativity that allow for it, but the solutions require conditions that may not be physically possible.