A time machine is any device or object that allows a person using it engage in time travel. Time machines come in many varieties, but for story purposes they can be broadly classified into three groups.
Mobile Time Machine
Any time machine that moves itself through time along with the user. Time travel using supernatural abilities or artifacts falls under this category in terms of story ramifications, though there are usually less restrictions.
The large degree of freedom offered by this type of time machine is often undesirable from a story perspective; this can be addressed in a number of ways (these can also be applied to immobile time machines if needed):
- The time machine is prone to mechanical issues, so that those who don't return to the present often will likely get stranded.
- The time machine requires a prohibitive amount of energy to function, and thus can take only a few trips before needing a recharge.
- For a magical ritual, very rare ingredients may be required.
- The time machine can only be operated by a computer, and none of the travelers know how to program in a new destination.
- For magical time travel, each destination may require a separate spell or artifact.
- Security measures restrict the ways in which the time machine may be used.
An issue users may have to deal with is that the larger models tend to be highly conspicuous and prone to theft. Some models conveniently double up as vehicles, some others are too bulky for this to be practical.
Putting control in the hands of the travelers, this mode of time travel is mostly suited for stories where very few people know about time travel and those who do would rather use it themselves than trust anyone with the secret, even when there is a lot at stake.
Immobile Time Machine
Any time machine that itself remains in the present while the traveler is sent to another time period. This typically means that the return journey must be initiated by an operator who remains in the present. Returning to the present involves one of the following:
- The travelers carry a special beacon. When the operator in the present activates the return journey, whoever is in possession of the beacon will be brought to the present.
- The beacon may include an emergency button or monitoring functions to automatically send the traveler back if something goes wrong or if tampered with.
- The beacon may be a large capsule that the travelers must be inside. This may add any of the drawbacks of a mobile time machine (which is good, from a storytellers point of view).
- The operator in the present can (theoretically) bring to the present anything from and place and time without the need for a beacon. Usually some special technology allows the operator either to directly view or directly communicate with the travelers; otherwise, the return will have to be carefully planned and obvious risks apply.
- There might simply not be a possibility for a return journey (other than The Slow Path), though this is rare.
Putting control in the hands of the operator in the present, this mode of time travel is mostly suited for stories where time travel is controlled by no more than a handful of powerful organizations.
See Portal To The Past.
This mode of time travel is ideal for including a one-time time travel storyline in a larger narrative of a different kind: it avoids having the time travel capability destroy later plotlines while allowing a storyteller to avoid getting too deeply involved with paradoxes and the like.
Game and Story Use
- The nature of the time machine has a profound impact on a time travel story, and should be one of the first choices to consider.
- For mobile time machines, in particular, you'll need to decide whether or not the time machine stays within the Earth's frame of reference.
- Another important thing to consider / decide is how time travel looks and works within the setting.