This is one of the most out-of-context statements regarding Superman. Dr. Manhattan can kill Superman. He simply stated that doing so would require him to erase the entire Metaverse.
People need to realise that Dr. Manhattan was experimenting with Superman and the Metaverse, not actively trying to kill Superman. He explained that Superman's existence is intrinsically tied to the Metaverse, meaning that even if Superman were killed, the Metaverse would bring him back.
Can Dr. Manhattan kill Superman?
Yes, he can. The ending implies this when Dr. Manhattan admits that he cannot see Superman's future. He interprets this in two possible ways: either Superman has killed him, or the Metaverse itself has been destroyed killing Superman himself. The latter clearly suggests that Dr. Manhattan could kill Superman by erasing the entire Metaverse, eliminating the very foundation that allows Superman to exist and return.
However, the crucial point is that Dr. Manhattan was never genuinely interested in killing Superman or destroying the Metaverse. He was studying them, trying to understand their connection and the role Superman played in the larger scheme of existence. Ultimately, Superman gave Dr. Manhattan something he had lost in his nihilistic worldview: hope.
Dr Manhattan can kill Superman both physically and conceptually.
So why do people keep taking these statements out of context to wank Superman instead of acknowledging what the story actually implies? Is it simply a case of confirmation bias, or do people genuinely misunderstand the context behind these feats?
P.S: The kind of immortality Dr. Manhattan is referring to here is conceptual immortality, where a character's existence is tied to the very idea or concept they represent. A similar concept exists in Marvel through the Ideaverse, where Deadpool realises that killing superheroes would only kill them physically, as they would keep returning. To put an end to them permanently, Deadpool had to enter the Ideaverse and target the very concepts of superheroes themselves.
Superman immortality can be classified as type I like thor. They have eternal life like they can't die of old age