Peter doesn't know about the Sylar switcharoo, correct? At least he didn't at the end of volume 4. And the last thing he said to Nathan was "I love you too" so why is he avoiding him now?

Agrees, though it could also be because he may know that his brother, his mother and Noah is up to something - and he thought that that something, once again, is up to no good, and hence separates himself again.

Plus, he's not calling/replying to anyone at all, not his brother or mother or whomever, so who knows? From the looks of it, he seems to be very concentrated on his work and is in a mood right now, so maybe he just doesn't care about anything besides saving lives right now.

He's separating himself from everything in his past practically and devoting all his time to saving people. That's why he's not talking to Nathan.

While I like what I've seen of Peter so far I don't really understand the sudden change of attitude.

Last we saw he was finally forgiving everyone and wanted to make a "family" version of the company.

Maybe he knows that Sylar is posing as Nathan and he has the body stored in cold storage somewhere waiting for the right time to revive him or Nathan has already been revived and Peter's hiding him for some point in the future to be revealed again

I personally don't think knows what happened to Nathan. However I wonder if Peter noticed if something was off about Sathan. Maybe on an unconscious level he noticed Sylarish behavior that upset without him even realizing it.

THANK YOU!

They unfortunately changed this "family" version to a real company again and I think that's definately a additional point that makes him avoid these people.

Check his conversation with Noah again in which Noah is asking him to be his partner.

I agree that we have to employ a bit of conjecture here. And somehow I don't think that much more will be explained.

He might still have a grudge towards Nathan (which would indeed be odd after what happened in An Invisible Thread), but remember that Angela tells Nathan, when she comes to collect him for lunch, that Nathan hasn't been in touch with her either. It's not much of a stretch to assume that he wasn't in touch with Peter either. So first Nathan didn't call Peter, then Peter got caught up in his own quest for redemption and didn't call Nathan. I have an older brother too, I know how that happens... They both have rather busy lives too.

I can also see him keeping his distance again when it becomes clear that the new company is trying to emulate the old one in several ways.

I had a thought a while back that if a shape shifter spots another shape shifter, they will be able to see each other in their original forms. Like an invisible person can't hide from another invisible person. Although Sylar would have realised that Peter was posing as the President...

I wonder if Peter absorbs flight from 'Nathan' he'd realize it isn't Nathan at that point. Does it feel different absorbing powers from different people? Or at least from a multi powered person from a single powered one?

If I was Peter I wouldn't call him either

We're just discussing that here: http://boards.9thwonders.com/index.php?showtopic=69702