Can Olivia move between worlds? Walter confronts her with that question in this clip from Fringe. She then tries to take some pills to get rid of Peter... as a symptom.
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Fringe Season 3 Episode 5 Quotes

Nature doesn't recognize good and evil Philip. Nature only recognizes balance and imbalance. I intend to restore balance to our world. Whatever it takes.

Walternate

Genetically you are exact replicas, you and the other Olivia. It means theoretically you both should be capable of the same things.

Walternate