‘The Girl Who Waited’ demonstrates that it isn’t only the Time Lords who are well versed in temporal physics. While the Doctor is impressed by their facility that controls multiple time streams he is far from shocked or surprised. It would seem that there are many races who can achieve this level of technology.
The Two Streams facility is remarkable. It can create 40,000 time streams at the same time, which the time mirror later shows occupy the same space. The residents blurred ghosts living their lives in fast forward.
Here it is used to quarantine the diseased, to give them a full life in 24 hours, but there are plenty of other ways that the facility could be used. The biggest drawback is the isolation, but there could be a way around that. We see something close to this with the Doctor folding the time stream to allow young and old Amy to co-exist.
The isolation might not be an issue if it was used to incarcerate prisoners. They could serve out their sentence in a single day, depending on the speed of the time stream. Rather than a collection of pleasure zones the prisoner might have to undergo re-education and spend thinking about their crimes with the handbots acting as wardens. Time mirrors could be used to evaluate whether they had made amends.
Over-population could be solved using a Twin Stream facility. Those living inside won’t consume the planets resources, free to live a peaceful life. This would be ideal for those who wish to live alone but might be a problem for those who want to have a family sometime in the future.
If multiple people can share the same time stream then there is still the advantage of not needing food but with the added bonus of being able to procreate. We see that people still age within the Stream so it is possible that several generations could come into existence in only a few days. Potentially this could benefit a society that is suffering a low population.
Along similar lines a baby could be placed inside a fast moving time stream to be cared for by the handbots and educated. When the child comes of age they could exit the facility and join the general population.
This would be useful in a society where there is an urgent demand for trained professionals. This could be used to rapidly train medics to cope with a plague or to produce soldiers for a war.
The facilities could also have recreational uses. Instead of people going on holiday, which would impact on the economy, they could spend several weeks from their perspective enjoying themselves whenever work got too much or they just wanted a break.
We saw that a time stream could be faster than normal time but there is no reason to believe that the reverse couldn’t be true. This would be a good way to send people on a one way trip to the future.
This would make a good alternative to placing people in hibernation if some great disaster was foreseen. As long as the stream could be maintained survivors could wait for the planet to recover, even if it took hundreds of years only minutes would have passed for those inside the stream.
There is the potential that the facility could be used for time travel purposes. The Doctor demonstrates how the technology in the facility can create a rip in time, allowing different versions of the same person to co-exist.
The moment the TARDIS demateralized the paradox of the two Amy’s resolved, with the older version having no long existed. Presumably the Doctor, Rory and Amy would still remember the encounter, indicating that information could still be gathered from these temporal duplicates.
There are two ways this could be used. Firstly a person could occupy an accelerated time stream, working on a project until it is complete or they have solved a problem. The time stream could then be folded and the older version gives their younger selves their work.
The young version could then exit the stream, benefiting from the work that they’ll never do while their older self fades out of existence. This prevents the potential paradox but there would need to be a way to stop the older version from trying to avoid their erasure.
Alternatively someone could act as a fail safe, existing in a time stream which is separate but synchronised with normal time. Should disaster fall or an event need to be altered they can be informed of the situation via a Time Mirror.
The person only has to fold the time stream, travelling to an earlier point and then either use the Time Mirror to relay the information from the future or exit so they can make the changes themselves. This would approximate the time travel seen in the film ‘Primer’ and ‘Time Crimes’, where the time machine can only take you back to the point it was first turned on.
Amy learnt first hand that not everything is perfect within the facility. In her case the robots programming was lacking. In other time streams there could be other technical problems that might make the situation hellish.
Amy didn’t need to sleep or eat over several years but what if you did, yet couldn’t die? Or if you aged more quickly than the time you experienced? What if the time stream began to contract, the space which you could move through getting smaller and smaller?
Time travellers could find themselves helping people trapped in just a situation. They might also find that it was their TARDIS landing in a time stream that caused the problem in the first place.
A whole campaign could be centred on problem shooters working at various Twin Stream facilities. The fact that several mechanised parts of the facility are within the time streams themselves would require employees to enter in order to fix the problem.