TRAVEL TO THE PAST

Every point in time has its alternatives...The future can be shaped - the actions of the present change the future. To a small extent a man can change the course of history. It takes a being of ... almost unlimited power to destroy the future.

When travelling to areas in one's personal past, the question most often asked is, ``has time travelled already happened?''. This is another way of asking whether or not the past in immutable. For example, has it already happened in history that a time-time traveller from the future has travelled back, or does travelling back change history? The two alternatives are usually summed up thus:

1. Time travel has already happened -- the past destination is really an extension of your present. Nothing you do will change history, and everything you do will fullfill history, barring abnormal interference. This is also described as a soft time-loop.

2. Time travel has not already happened. In this case the traveller risks the possibility of creating an alternative universe.

The distinction is far from academic. Let us consider an example:

Is there one version of this event? Do they concur on the details? Does Andy see Borak from the future? Certainly Borak should see Andy. Whilst travelling in a TARDIS one will find that a meeting such as the one described above simply cannot happen. Basically Andy would come and go, and Borak would not be there. Borak then would not be able to set his coordinate to day 100 12:10. In fact, the nearest coordinate would be day 101 12:00. This prevents the potential paradox mentioned above. The enforcement of time-streams creates urgency, as one cannot wait around and then act on an emergency distress call, as it may well preclude the ability to answer.

Without the TARDIS enforcing travel to within time-streams, the following may of happen:

If Borak were to attempt to contact Andy, he would find himself up against the Blinovitch limitation effect. As Andy has arrived ``first'' (See: for more on determing who arrives first at spatial-temporal destination) his version of the events are immutable. And since he didn't see Borak, Andy cannot do anything to change that.

To summarise, the past is ordinarily immutable. What has happened has happened. Everything one does in the present is recorded in the past. So what happens when someone tries to change history? Various phenomena occur as one battles with time. If one attempts to change the past of their own time-stream, the Blinovitch limitation effect comes into play. If one attempts to change the past of someone else's time-stream, they will find this immutable. It is possible, as the quote above suggests, for a being or machine of extraordinary power to distort space-time so much as to force the creation of an alternative reality which becomes the default reality for all time-travellers.