Time portal

Time portals are doorways in time, employed in various fiction genres, especially science fiction and fantasy, to transport characters to the past or future.

They differ from time machines in being a permanent or semi-permanent fixture linking specific points in time, and thus are an especially useful plot device when the plot involves characters moving many times back and forth.

Time portals can be represented as vortices of energy, which allow matter to travel from one point in time to another by passing through the portal, or may appear as an ordinary doorway.

In most films, time portals are used to take a group of people or a single person back in time. The most popular of all time travels would be traveling back to the time of the dinosaurs. In some films time portals can also be set as a hazard, for example, they can begin to go haywire which makes them accidentally transport something or someone from a different time to the present; again the most popular is a dinosaur being accidentally brought into the present world.

The 1966-67 series The Time Tunnel.

In the 1967 Star Trek episode "The City on the Edge of Forever", a temporarily deranged Dr. Leonard McCoy runs into a time portal, an ancient sentient stone-like ring which calls itself the Guardian of Forever, and is transported back to 1930s Depression-era Earth and history is changed as shown when the Enterprise disappears from orbit. Captain James T. Kirk and Mr. Spock follow through the time portal to set things right.

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