system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why did Vader sense Kenobi's presence, but not Luke's? Surely someone with that much potential with the force would cause a disturbance? Plus it was his son. Even though he didn't know that he had a son, wouldn't that disturbance be unique?
gpt
Vader knows what Obi Wans presence in the force feels like.  He was around it for most of his life.  Luke is someone pretty much unknown to him.  When Vader felt a large force presence on the Death Star he instantly recognised Obi Wan.  The addition force presence he probably just chalked up to Obi-wan having become more powerful and changing since the last time he saw him.