Types of time travel

To the future

In this case the traveler arrives to a point in time that hasn’t happened yet. Could be near or far future.

To the past

In this case the traveler arrives to a point in time that has already happened. Could be near or far past.

Time loops

In this case the traveler continuously arrives to the same point in time in the past. The loop can have different durations and ending points, eg. falling asleep or dying, before starting over.

Without fixed points

In this case of past time travel it is possible to change any events that have already happened or create events that haven’t been there before. Because this differs from what has already happened though, a new timeline is created by these changes and the present the traveler goes back to becomes a different present from the one they have left from.

With fixed points

In this case of past time travel it is possible to change events but there are fixed points that cannot be changed because they have to happen in one way or another, it’s impossible to avoid them. Despite these minor changes, there is no new timeline created, because the events that change have no impact on the flow of time as it was before.

In this case of past time travel whatever can happen has happened already. No events can be changed because the traveler was already there the first time around and caused events to be just as they turned out to be. Because of that there is only one timeline and it’s impossible to create another one with different outcomes.

With a time machine

Time travel usually happens with a machine and it can have various forms. The device is able to deliver information, objects or a person to another point in time, to the past or to the future. More about devices and their mechanisms’s here.

Without a time machine

Time travel can also happen without a machine. This type of travel is usually involuntary, but not necessarily unpleasant. Cases of machine-less time travel can occur in many ways, like falling asleep or unconscious and waking up in a different time, or finding a magical portal.

Travel close to the speed of light

One of the more scientific ways of time travel happens where one travels at the speed of light, or close to that. This type of time travel can only happen to the future because as time slows down and even stops for the traveler being very-very fast, years can go by at normal speed that feel like a second for the traveler. When the traveler leaves the state of being at lightspeed, they will arrive at a point in time that they perceive as the future.

Travel close to huge gravitiy

Another scientific way of traveling to the future is being close to huge amounts of gravity. Because time-space is curved in such a way around these objects – planets or black holes – the traveler perceives time spent there to be less, than around smaller gravities. When the traveler leaves the state of being close to huge gravities, they will arrive to a point in time that they perceive as the future.