Between is a dark dimension through which @Dragons, @Watch-Whers, and @Fire-Lizards have the ability to travel to teleport from one location to another. This process is referred to as going between.
Between is universally described as a place of nothingness. It is characterized by extreme cold (far below zero, possibly colder than outer space) and near-total sensory deprivation for humans who travel through it on @Dragonback. Since there appears to be no breathable air between, riders who made exceptionally long journeys (usually the result of traveling between Times) suffer the effects of oxygen deprivation. Because of the extreme cold of between, dragons and @Fire-Lizards deliberately travel between and back when they come into contact with threadfall, freezing and destroying the organism almost instantly.
The cold of between can also cause health problems, such as kidney chills, for @Dragonriders. Riding gear is designed to keep the wearer warm. Female riders risk developing cystitis from frequent journeys between and the low temperature can also abort or prevent pregnancies. The exact length of time a rider needs to be between for these things to happen is debatable and not fully determined.
The length of time it takes for a dragon to travel from one location to another via between is generally described as the time it takes to cough three times and generally considered eight to ten seconds. This time frame can vary depending on if the travel includes going between times as well.
Failing to envision a destination properly can result in a @Dragon and @Dragonrider failing to emerge from between and perishing as a result. It can also lead to a dragon and rider emerging from between but arriving in the same place as an existing object instead of near it. @F'lar once mentioned to @Lessa during her training that a dragon and rider had once been found entombed in the rock of @Benden Weyr. Envisioning a destination too well, with details that correspond to a location at a specific point in time, can result in a dragon and rider travelling between times. If a dragon sustains a fatal injury or believes that its rider is deceased, the dragon will go between forever by not envisioning a destination because the dragon cannot mentally sustain the breaking of the bond between dragon and rider.
@Dragonriders are able to guide their @Dragons between time by envisioning a destination so vividly that they can arrive at the exact point in time the location looked that way. This is often done by using the positions of stars in the night sky or the location of the Red Star, but it is also done by using a memory of a place to create an image. While @Lessa was learning how to go between on Ramoth, she attempted to travel to @Ruatha Hold. She accidentally thought of the hold as she remembered it immediately prior to the invasion of Fax and as a result, went between times to that day.
Time travel between operates under the stable time loop principle, where a person cannot change the course of history when travelling backward or forward in time, but their actions might create a chain of events that cause the reason for them travelling through time in the first place. One example is "Lessa's Ride". In the beginning of the Ninth Pass, @Benden Weyr is the only inhabited Weyr on Pern. @Lessa went back in time 400 turns to the Eighth Interval and brought the inhabitants of the other five existing weyrs forward to her time. This action left the other five weyrs abandoned with Benden Weyr being the only inhabited weyr through the Eighth Interval, leading to the decline of Benden Weyr and necessitating Lessa's trip through time to begin with.
Attempts to go between times to try to alter a historical event were known to be futile. Due to the obvious dangers, the ability is generally kept a secret between the queen and bronze riders of the Weyr. Despite this, riders have been known to accidentally discover the ability for themselves. Travelling between times is fairly exhausting to both rider and dragon, both often requiring rest, and food in the dragon's case, after returning to their own time.
Travelling between times also takes far longer than a normal trip between, with the trip taking longer to travel further back in time. Riders will often suffer from oxygen deprivation when the trip is an especially long one, as happened to Lessa. Since dragons are able to hold their breaths for far longer, they are not affected by this.
A @Dragonrider who remains for any length of time in the same period of time with another version of themselves are known to experience incredible exhaustion. Some become irritable and cross. This is thought to be caused by the telepathic link between a rider and their @Dragon inadvertently becoming duplicated and overwhelming the minds of both incarnations of rider and dragon.
Going between forever or forever between is something that can happen by accident or intentionally, in both cases resulting in the death of the dragon
A dragon and their rider might end up going between forever by accident if they fail to envision their destination properly.
A dragon will go between forever by choice if they either sustain injuries from which they cannot recover, such as a fatal thread scoring, or as occurred in the Third Pass, severe infection with the Dragon Plague, or if their rider perished or was believed dead by the dragon. The latter of these scenarios can prove dangerous. If a rider sustains an injury that renders them unconscious to the point where the dragon cannot feel their presence, their dragon might believe them dead and go between forever, leaving the rider broken upon recovery.
Dragonets that fail to Impress on the Hatching Grounds will also go between forever, though this is an incredibly rare occurrence that is thought to have only happened in the First Pass or First Interval and has been mitigated by having a large number of candidates present at each Hatching.
Very few things are known to have prevented a dragon from going between forever after the death of their rider. Almost every known instance in recorded history is a situation where a golden queen was bound to the Hatching Grounds with her clutch at the time of her rider's death. The queen remained after the death of her rider until after the clutch hatched and impressed, going between shortly after.