Time travel is the concept of movement (such as by a human) between certain points in time, analogous to movement between different points in space, typically using a hypothetical device known as a time machine, in the form of a vehicle or of a portal connecting distant points in time. Time travel is a recognized concept in philosophy and fiction, but traveling to an arbitrary point in time has a very limited support in theoretical physics, and usually only connected with quantum mechanics or wormholes, also known as Einstein-Rosen bridges. In a more narrow sense, one-way time travel into the future via time dilation is a well-understood phenomenon within the frameworks of special relativity and general relativity, but advancing a large amount of time is not feasible with current technology. The concept was touched upon in various earlier works of fiction, but was popularized by H. G. Wells' 1895 novel The Time Machine, which moved the concept of time travel into the public imagination, and it remains a popular subject in science fiction.