Except the current Henry does seem to have lived those four years. Hm. I'm trying to find a way for both those things to be true.

Okay. 2006-Henry lived for a while without Kim, then went back in time to the critical moment, stopped the experiment and lived four years of bliss, with the memories of the "erased" timeline. Bad things start to happen; Jack's going back to stop him. Henry must know that if Jack succeeds, 2010-Henry with the memories of bliss will cease to exist, and the only Henry will be the one who only knows he failed, and knows nothing of the four years. This is unacceptable. He wants to remember, and to try again, hopefully without screwing up the fabric yadayada this time around. His only choice then is - to go back in time again, to the critical moment, arriving before HIMSELF. This moment has Jack in it, so it's already a different moment than the one he went back to before. So he arrives before he arrived last time, thus wiping out the first timeline in which he went back, tries again to stop the experiment (because what's he gonna do, stand there? and Jack would have been suspicious), and fails. But he has his memories of both previous timelines, he knows what's worked and what hasn't, so he can try again. And he knows Jack isn't savvy enough to realize immediately (who did?) that the Henry he stopped and is now living with shouldn't be remembering the same timeline he does. And now he's wiped Jack's memory, so now there's no chance he'll figure it out later.

This requires something to be true of Henry that wasn't mentioned in the show, but it's the only way I can think of to make it work out. And I've been typing this for an hour so someone else has probably already said something even better.

Time travel makes my head hurt.

"Time travel. That takes me back. Or is it forward?"

Pardon me as I butcher an old Who quote. There are some lovely ones from 2005 Who s3 too. "timey-wimey" (not plot-spoilery) comes immediately to mind, from Blink.

At first I thought askeye was right about how things are supposed to be, but Zenkitty makes a good point. For some reason, Henry seems to remember more of Timeline B than he should.

Henry should definitely remember Timeline A. Henry should remember the attempt at Timeline B. However, after Carter interferes, he should only remember up until the point that Carter stops him from saving Kim, generating Timeline C.

On the other hand, Henry knows that he was successful in saving Kim, but the universe began to unravel, requiring Carter to go back in time to stop Henry from saving Kim. And considering that supposedly they're best friends, maybe they've talked about what happened in the other timeline... a month did elapse. (Maybe this is the explanation?)

Then again... it could be an inconsistency. Wouldn't be the first time that a scifi show got it wrong.

Eureka. How I missed you!

I wonder if he will somehow keep that savvy, maybe subconsciously, or if he lost it with his memories?

It will be interesting to see if little bits come back from time to time.

Does Henry only blame Jack? Jack couldn't have gotten back to that timeline without other people's help, and presumably if there were no Jack, Stark or someone would have done it. Maybe going to work for General Dynamics is a plan to get all of them.

Perhaps the combined effect of all the things that happen by random chance perhaps not happening that way again would lead to fairly significant changes in short order?

That's a pretty common assumption in time-travel fiction, such as Ray Bradbury's "Sound of Thunder." Allyson being head of General Dynamics and the boy absorbing something from the Artifact are already big changes.

I came up with my theory at work when I should have been filing, so I forgot that Henry shouldn't remember Timeline B.

Then I also wondered if maybe Henry's messed with the time lines before this and we aren't really on Timeline E or G or something.

It will be interesting to see where the show takes this.

It would be totally cool if we find out later that Henry's actually tried many times to save Kim, and it never works out, and he's remembering a hundred years' worth of different expressions of those four years, and he's the only one who knows all the things that have happened/not happened. And he's wiped out Jack's memory like twelve times.

Cool, and scary.

It would be totally cool if we find out later that Henry's actually tried many times to save Kim, and it never works out...

Wouldn't he age? Time travel is so confusing.

If he were Teal'c, sure. Actually, I don't know. I think that's a wriggly bit that I would exploit however best fit my story. Just make up a different mechanism for travel.