Time travel is the concept of moving between different moments in time in a manner analogous to moving between different points in space, either sending objects or information backwards in time to a moment before the present, or sending objects forward from the present to the future without the need to experience the intervening period at the normal rate.
Time travel has not been proven to be impossible nor possible. Any technological device, whether fictional or hypothetical, that is used to achieve time travel is known as a time machine.
Some interpretations of time travel also suggest that an attempt to travel backwards in time might take one to a parallel universe whose history would begin to diverge from the traveler’s original history after the moment the traveler arrived in the past. Although time travel has been a common plot device in fiction since the 19th century, and one-way travel into the future is arguably possible given the phenomenon of time dilation based on velocity in the theory of special relativity, it is currently unknown whether the laws of physics would allow backwards time travel.
Several experiments have been carried out to try to entice future humans, who might invent time travel technology, to come back and demonstrate it to people of the present time. Events such as Perth’s Destination Day or MIT’s Time Traveler Convention heavily publicized permanent advertisements of a meeting time and place for future time travelers to meet.
In 1982, a group in Baltimore, identifying itself as the Krononauts, hosted an event of this type welcoming Visitors from the Futures. These experiments only stood the possibility of generating a positive result demonstrating the existence of time travel, but have failed so far. No time travelers are known to have attended these events.
It is theoretically possible that future humans have traveled back in time, but have traveled back to the meeting time and place in a parallel universe. Another factor is that for all the time travel devices considered under current physics, it is impossible to travel back to before the time machine was actually made.