Marvel Comics has just retconned Thor's immortality - and this idea potentially adds greater depth to his MCU arc, especially in Avengers: Endgame. When Asgardians were introduced in the MCU in 2011's Thor, they seemed to just be a race of ancient aliens with extended lifespans; as Thor explained to Jane Foster, he came from a realm where science and magic were one and the same. Marvel took that approach because they were unsure whether the supernatural would be a good fit for their science-based universe, but over the years they've become increasingly confident. Thor: Ragnarok certainly treated the Asgardians as gods, with Thor Odinson claiming his power as God of Thunder.

Marvel Comics' Thor #15, by Donny Cates and Michele Bandini, explores what it means to be a functional immortal. According to this issue, Thor's relationship with time is very different to that of a mortal. "A moment for you," he reveals, after demonstrating his power to the Avengers, "a battle, a war, a minute, a day... they are remembered as seconds to me. I remember them as a mortal would recall what he had for breakfast a year ago." Asgardians live in a perpetual present, and they cannot really tell whether the events they remember happened minutes ago, or millennia. It's a fascinating concept, making Thor the most tragic Avenger, for he has lost so many in his long life. What's more, it works surprisingly well in the MCU - notably in his Avengers: Endgame arc.

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If the MCU's Thor experiences time in the same way as his comic book counterpart, then his losses in Thor: Ragnarok and Avengers: Infinity War become even more crushing. Living in an eternal present, Thor is essentially defined by his latest experiences - in this case, by a crushing sense of loss and defeat. In the space of just weeks, Thor had seen his father die, lost his enchanted hammer Mjolnir, watched as his homeworld was destroyed, failed to prevent Thanos slaying half the surviving Asgardians - and then he had chosen not to go for the head, meaning Thanos had succeeded in his insane goal of erasing half the life in the universe. All Thor's other triumphs would have paled into insignificance in the face of this overwhelming reality. It is little wonder Thor retreated from the world in a state of PTSD - and, trapped in a perpetual present, that retreat consumed him.

This also explains how Thor's time travel escapades helped him begin to heal in Avengers: Endgame. When Thor traveled back in time to visit Asgard, his past glories would dominate his experiences - notably his relationship with his mother Frigga and the realization he was still worthy. These experiences would have had a powerful effect on any trauma victim, but on a man with Thor's relationship with time they were even more pronounced. That visit to Asgard was far more transformative than even the Avengers realized, beginning a process of healing for Thor, one that was completed by the Avengers' victory over Thanos in Avengers: Endgame's final battle.

Thor's immortality does not take away from the PTSD arc in the MCU; rather, it reinterprets it, because his experience of such trauma would not necessarily be the same as the experience of a human being. He is, after all, no mere mortal - he is Thor, the God of Thunder.

More: Love & Thunder Theory: Why Thor Has Stormbreaker & Jane Wields Mjolnir

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