Como @brianOrtiz disse em seu comentário, a resposta para isso é encontrada no romance stargate licenciado Moebius Squared . No universo principal, George Hammond (sabendo que ele sobreviveu aos seus 50 anos e era, portanto, efetivamente imortal) colocou-se em risco extremo ao salvar o pai de Sam, Jacob. O pai dela e o exemplo de bravura conspícua de Hammond levaram-na a juntar-se à USAF.
No universo alternativo, seu pai morreu no Vietnã, ela mal conhecia George Hammond e sua mãe a desencorajou de entrar para o serviço.
“You remind me of my dad,” Carter said, without thinking.
“Really?” Sam looked faintly embarrassed. “I never knew mine. He was killed in Vietnam when I was a baby. My mom raised me.”
“My mom died when I was in my teens,” Carter said slowly. “Dad took care of us as best he could. That’s part of why I went into the Air Force.”
“Mom would have had a heart attack if I’d even suggested it,” Sam said. “I had the hardest time talking her into letting me get a car, never mind flying a plane. I can’t imagine…” She shook her head. “She was determined to keep me safe. She wasn’t going to lose me like she lost Dad.”
“Did you ever know George Hammond?” Carter asked, and Sam nodded.
“He was my father’s wingman, the one who brought back his body. Danyel said that in your time he commanded the SGC?”
“Yes.”
“I remember when I was little he used to send me Christmas presents,” Sam said. “But Mom didn’t like having him around — too many bad memories, I think. She lost touch. That — I’m sorry about that, from what Danyel’s said. He must have been an amazing man.”
And that was more of what the Stargate had done, Carter thought. The time loop that had thrown the team back to 1969, when they’d given Lieutenant Hammond a note from his future self in order to get back to their own time — she’d wondered how that had changed him, and if it had, indirectly, changed her father. And now she knew. In her time, Hammond had saved Jacob Carter’s life that day in Vietnam, and maybe he had taken a crazy risk because he knew that somehow he was going to survive.