The Time Bubble was a time travel device used by the Legion of Super-Heroes.
The Time Bubble was invented by Brainiac 5 as a child. Due to the varying nature of Time travel the true origin of the time is complex as Brainiac invented the device in his childhood, but is Post Zero Hour contnuity RJ Brande requested the development so they could prove Superman was more than a myth. In both version this work is done prior to Brainiac 5 joining the Legion and when he was in the employ of Brande. The device was used regularly to bring Superboy and Supergirl to the 30th Century.
The Time Bubble has proven more durable than other time travel devices such as the Cosmic Treadmill of the Flashes which was obliterated when in a collison with Rip Hunter's Time Sphere. It also lacks the side effects of Rond Vidar's Time Cube, a technology that did the same as the bubble only it was portable.
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