Negative Speed Force

"Breathe. You're reaching out and nobody's there. The loneliness is pain. Pain racing through your mind. Crushing you, wrecking you, shattering your soul into a million little pieces. And suddenly, you are no longer you. You're part of something different now. Part of a negative force."

- Eobard Thawne to Nora West-Allen

The Negative Speed Force is an extradimensional energy that was created by Eobard Thawne at some point after replicating the Flash's powers. Speedsters with a connection to the Speed Force can gain a connection to the Negative Speed Force by exercising their fear, hate, and anguish to such an extent that it corrupts them from the inside. Gaining a connection to the Negative Speed Force will turn a speedster's natural yellow lightning red. Team Flash has also found that users of the Negative Speed Force harness negative tachyons but, rather than slowing the speedster down, the negative tachyons allow a speedster to siphon tachyons from the normal Speed Force like a parasite in order to accelerate their own movement. Due to this, unlike normal Speed Force users, Negative Speed Force users produce a huge amount of tachyons that can be tracked.

History
At some point in the future, after Eobard Thawne discovered that his destiny was to become the exact opposite of the Flash, he created a Speed Force completely opposite to the one of the Flash and called it the "Negative Speed Force" so that he could time travel without the Flash knowing his presence in the timeline.

In 2049 when Nora West-Allen wanted to go back in time without her father feeling her presence, Eobard taught her how to use the Negative Speed Force. He regrets it since it has a negative side-effect.

Eobard later revealed to Barry and Nora that the connection Nora established to the Negative Speed Force was a part of his plan, as a means of preserving her existence after Cicada's dagger was destroyed, as that caused her timeline to be erased. Knowing that the Negative Speed Force had begun to make her more like Thawne and that wasn't who she wanted to be, Nora ultimately decided to accept her fate rather than continue to use it.

Lightning coloration

 * Red: Red lightning is typically the result of a speedster having a connection to the Negative Speed Force, which Eobard Thawne created at some point after recreating the accident that gave the Flash his powers. Red lightning is seen in Eobard himself as well as Edward Clariss. In addition, speedsters such as Hunter Zolomon who are taken by Time Wraiths into the Speed Force also have their lightning turned red.
 * Red and Purple: After Nora West-Allen managed to run into the Negative Speed Force to return to the present day, the yellow part of her lightning turned red while retaining the purple part of her lightning.

Eye transformation
When harnessing the Negative Speed Force, a speedster's eyes and the skin around the eyes can glow red.

Powers and abilities
The Negative Speed Force, like the Speed Force, enhances all movement, momentum, and force exerting capabilities of its user, down to a microscopic level, as well as giving the user conscious control over it. This enhances overall acceleration, agility, reflexes, coordination, balance, and reaction time to inhuman levels. In addition, the body becomes conditioned beyond human potential, allowing them to handle extreme physical exertion and performance, which is also enhanced. ''The only powers listed below are the ones that differ between the Negative Speed Force and the Speed Force. For all of the powers that a speedster can have, see Speed Force powers.''
 * Time travel: Users of the Negative Speed Force can travel through time like users of the Speed Force. What differs here is that users of the Negative Speed Force can time travel undetected by users of the Speed Force.
 * Time shelter: Since it exists outside the timeline, a speedster can prevent themselves from being erased from existence by running into and staying in the Negative Speed Force. However, their connection to the Negative Speed Force becomes the sole tether of their existence unless their timeline is restored.

Weaknesses
Like with the Speed Force, speedsters may show one or more weaknesses despite their connection to the Negative Speed Force. Whether this hints towards inherent limitations of the Negative Speed Force itself or just to limitations of its users' control over their connection to it, is not known for certain, but the latter seems more likely. ''The only weaknesses listed below are the ones that differ between the Negative Speed Force and the Speed Force. For all of the weaknesses that a speedster can have, see Speed Force weaknesses.''
 * Gravity: While deprived of gravity, a speedster's lack of weight prevents them from accessing their speed.
 * Tachyon production: Users of the Negative Speed Force produce huge traces of negative tachyons while running, which can easily be tracked.

Known users

 * Eobard Thawne/Reverse-Flash (creator)
 * Nora West-Allen/XS (formerly; erased from existence)

Trivia

 * According to Eobard Thawne, unlike the normal Speed Force, the Negative Speed Force is comprised of negative energy.
 * Eobard Thawne has stated that the Negative Speed Force is not meant to be used by every speedster since it has a negative side-effect.
 * According to Eobard Thawne, the Negative Speed Force is the only place that is immune to timeline changes. However, that isn't true as it has been mentioned several times that the temporal zone is also immune to timeline changes and the Speed Force has also been shown to be immune to timeline changes.
 * However, it has been seen that if an aberration is massive enough, things will be affected even inside the temporal zone. This suggests that Eobard may have meant that the Negative Speed Force is the only place that is completely immune to timeline changes.

Behind the scenes

 * In the DC comics, the Negative Speed Force was created by Eobard Thawne when he got his powers and he used it to leech off of the Flash's power throughout history.