How does flash time travel?
My answer is based on the DC comics, not on any other media.
There are multiple speedsters in the DC universe. There have been four different persons who have used the name "Flash". Chronologically they are: Jay Garrick, Barry Allen, Wally West (the original red-haired Wally, who was also Barry's sidekick as the Kid Flash; and then became Flash after Barry's death), and the fourth Flash is Bart Allen (aka Impulse, Kid Flash, and then Flash).
- Jay Garrick doesnt have the ability of travelling in time.
- Barry Allen does not travel in time by "running fast". He actually travels in time by changing "the vibrations of his body".
- The same vibration thing gives him ability to travel between different dimensions.
- It is not necessary for him to achieve a particular speed for travelling in time, but he requires to achieve a particular level of vibration, which he manages to do by running.
- He generally uses the "cosmic treadmill" to do this, but there are instances where he has done it without the cosmic treadmill.
- Wally West, unlike his uncle Barry, doesnt use treadmill. He generally runs faster than light to "break the time barrier", and then chooses his destination (past or present) while in the limbo.
- In few instances, Wally has also used the "Speed Force" to travel through time. That is, for a brief moment, he enters in the speed force, and exists in to the desired time and space. But as Wally said himself, it is risky as there are chances of getting trapped inside the speed force.
- On a side not, Wally West is the fastest human ever. He is even faster than Superman/girl/woman. And according to Max Mercury, he is "arguably the fastest being."
- Bart Allen also travels in time by running faster than light to "break the time barrier", and then chooses his destination (past or present) while in the limbo.
Speed force is a place through which flash gets his speed. It is a dimension which consists all the time in the world and by tapping into the speed force one can access time in past or can see the future. By running at higher speed flash taps in to the speedforce and therefore can time travel by focusing on the date and time that he wishes to visit. In comics flash uses cosmic trademil to time travel which he happens to build in future with the help of starlabs. The cosmic trademil can not only be used to travel through time but can also be use to travel to different earths, this is done by running on trademil which then vibrates and switches frequency from current earth to the destination earth therefore allowing flash to travel through earths.
If you watch flash the tv show or even read the comics you might have a little idea about what flash actually is.
If not then...he is a speedster (a term to define a person with peculiar speed)
Flash has speedforce around him which is an energy force of speed giving him immense power. Because of this he runs faster than the speed of light or sound or whatever is the fastest.
Now, to time travel he runs at a speed of more than mach 2 to go at such an immense speed that he breaks the time barrier and opens a worm hole through which he can travel to anywhere in time.
He runs faster than light speed.
According to Theory of Relativity.
- Speed of light remains constant irrespective of the observer
- It is observed that as the speed of object increases, time slows down
- At the speed of light, time stops
- And on further increment of speed greater than light, time reverses
- Thus to travel back in time we have to move faster than Light