In terms of methods of time travel, we must first think about who has access to time travel. Is making a time travel object just like setting up a Portkey or do you need special privileges, perhaps even special powers to set it up?
So far, the only method of time travel we know about is the use of Time Turners. Hermione says in POA that Professor McGonagall had to write lots of letters to the Ministry for her to use the Time Turner. This raises two issues:
Is the use of a Time Turner kept down in records, like it is when an underage wizard uses magic outside of Hogwarts?
Are the Time Turners completely Ministry controlled or is there a way to acquire them from elsewhere?
If the Ministry does have complete control over time travel, then would they be able to alter all time? If this is the case, then if Fudge is, as many people believe, under the control of Voldemort, there may be serious time travel implications in future books.
If the people who make Time Turners can create them on demand, they have a lot of power. Assuming they can also refuse to sell them to others, they have the ability to alter time without anyone being able to do anything about it.
Another possibility is that there are a certain number of Time Turners that exist. If one Time Turner is broken, the number goes down one, and there is no way to replace it. This would make sense, as it seems very difficult to be able to artificially create a device that allows the person to go back in time. However, how would they have been created in the first place?
There may be a way of creating a Time Turner just like you can create a potion by using certain ingredients. This would mean Time Turners are freely available to anyone (if the ‘ingredients’ are indeed freely available). In POA, Hermione says that McGonagall had to write several letters to the Ministry to allow her to use a Time Turner. This makes it very unlikely that Time Turners can be freely made.
Also, in POA, Hermione throws the chain round Harry’s neck and it transports them both back in time. If a Time Turner can transport an infinite number of people back to one spot, Voldemort’s Death Eaters may be able to travel back and cause a lot of havoc. I realise this is branching somewhat onto theory now, but how did Voldemort get his wand back from Godric’s Hollow? Perhaps someone went back in time at a later date and got it for him.
According to Lupin in OOTP, Portkeys can be “set up.” They are designed to transport the person touching it to another place at the same time and date. There may be able to set them up so that they transport people to another place and another time. If setting up a Portkey depends on giving it a specific location, another factor may be brought in.
Say that the location the Portkey has to transport to is shown using two numbers, each one corresponding to a certain distance away from the starting point. Thus each Portkey could contain the information (23,98). This may be how many miles north and how many miles east the new location is from the original location. There may be a way of bringing a third factor in (a time factor) that allows the user to be transported to not only another place, but at another time.
This, however, seems quite unlikely. In all instances of a Portkey being used, the people have been transported at an almost instantaneous speed. According to Einstein, when people reach the speed of light, they transport forward in time. This may be a way of allowing time travel when using a Portkey.
I’m a little unsure as to what exactly these bell jars are. Unlike the Time Turners, which appear to transport the user back in time, the bell jar transports time to the user. In the Department of Mysteries, a Death Eater got stuck in a bell jar, and in doing so, got turned back into a baby . After this happens, Hermione says:
“It’s time,” said Hermione in an awestruck voice. “Time ”
This may be a way of telling us that in future books there will be a lot more time travel occurring but suffice to say, this is an example showing us that there are many more ways to interfere with time than just a Time Turner.
Throughout the books, there have been several references to ‘dark magic.’ We have seen the Unforgivable Curses, but not much else in the way of dark magic. I believe time travel could be a method of Dark Arts, perhaps used by Voldemort to help him in his quests. Messing with the time is a very serious thing indeed.
Since so far we have only seen two distinct ways of altering time (Time Turners and the bell jars), we can assume that there may be more ways of playing with time and that time travel will play a very important part in future books. Now that we have a way to travel, go to the How it Works section to see how time travel is performed.