A time machine is a device capable of transporting its user forwards or backwards through time. Although such an idea is theoretically possible under the right circumstances, such a machine has not yet been created. In fiction, however, time machines are a popular method of sending heroes and villains on adventures in different time periods.

Examples of time machines

• Professor Frank N. Stein worked on a time portal that could send him and his companions into the past. There was no evidence of the professor being able to alter the controls on the device and the only known destination he visited was Medieval Swansea. On the first occasion, Frank fell on top of Doctor Daffyd Leek and knocked him unconscious. Believing he had killed the man responsible for ending poopleism, Frank returned to the present and fetched Chuck D. Head, Igor and his medical bag before going back to Swansea. Fortunately, Leek was not dead and was able to continue his work. A time limit was imposed on this method of travel, with the time machine pulling them back to Castle Frank N. Stein after a few minutes. The machine has not been seen again.

• Colonel Granite built himself a time machine, diverting military funds into Operation Starwatch. His plan was to take modern technology into 1860s Kansas and take over the world. Amy Rose and Tekno the Canary witnessed Granite's plan first-hand and forced Granite (and themselves) back to Earth. Once there, Tekno used the machine to travel through space as well as time, setting co-ordinates to Mobius before making it self-destruct.

With the location backed up, Granite oversaw creation of a new machine, before using to invade the Emerald Hill Zone. A stream of infantry and heavy weapons travelled across space to Mobius, until Sonic the Hedgehog blocked the gateway by using a Spin Attack on an arriving tank. After seeking advice from the Prime Minister, Sonic used Granite's second time machine in Scotland to return home. It was then down to nature itself to blow Granite and his men back through the machine and into the arms of the Military Police.

• In a world torn apart by the Iblis, G.U.N. had developed a time machine. Dr. Gerald and his team salvaged the remains of the Omni-Viewer and, with the power of 3 Chaos Emeralds, was able to send Silver the Hedgehog back in time to avert the disaster.

Alternative methods of time travel

Time machines are not the only way of navigating time. Several characters have been able to travel through time without the means of a purpose-built machine. The Omni-Viewer is one such sentient being that acts like a time machine, able to follow a "chronotron trail" to carry his passengers (such as Sonic and the Chaotix Crew) back to a certain moment. The Ring of Eternity was a very similar concept, until it was later destroyed.

Time Stones are another way of heading into the past or future. By running at high speeds, the holder of a stone can move into a different time period. The stones can be found on the Miracle Planet, itself a world detached from normal time.

Tikal and Pochacamac are two echidnas who have differing means of pulling people into the past or sending them home. Tikal could merely lock on to her target if they were infused with the power of the Chaos Emeralds, bringing them right next to her. Pochacamac required the Emeralds to do the same, using their power to send Sonic into the equivalent location in the future. Shadow the Hedgehog can also use the Emeralds to transport himself and any surrounding people into the past, although it is unclear whether or not they can be seen by that time's versions of them.

Tails also took part in an adventure that saw him watch as the Echo City Zone went through a disaster - in reverse. Only by waiting until the Zone's destruction was undone could Tails destroy the Troopers that had caused it, correcting the direction of time in the process.

Blaze the Cat has also been seen to travel through time, although she has no idea how it happened.