Ghosts were created in a last ditch effort by The Traveler before it went dormant in order to create Guardians to protect it before the Darkness could arrive. Since the Eliksni became dependent on The Traveler's Light to survive (Servitors are artificial Travelers and Ether is artificial Light), it's likely they spent a lot more time with their Great Machine then however long our Golden Age lasted.
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Servitors are not artificial Travelers and ether is not artificial light, it always existed on their homeworld the Traveler just made it more plentiful.
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<Actually it is looking like Servitors being based on the Traveler's imagery. But yeah Ether is in no way artificial Light.>
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Yes they may be based on the Traveler's shell, but that is pretty much it, not what I would call an artificial Traveler. I think people keep saying that ether is artificial light because they want the traveler to give the fallen light like it gave humanity, I never got a satisfactory reason why the Traveler would do that.