I realize this film is not to be taken too seriously, but at the beginning, after the time trip, how on earth did the four of them get to the top of the mountain without passing through the ski lodge or seeing anyone else?
And they were all naked in the hot tub, where did they get their clothes/ski gear/etc without noticing their hotel room and things had changed?
Well, figure they were heavily hung over in the morning and possibly got up very early. If we assume that their clothes and gear were not identical but probably very similar, and they wound up getting up fairly early in the morning, they may have stumbled through getting dressed, gotten through a mostly empty lodge without looking at anyone very closely or talking to them other than a few vague mutters that wouldn't have had anything to do with the year ("Four tickets." "Five dollars, please." "Hnnh. (Only that much?)"), and so on. Basically it's only once they got up to the top that they started to be coherent enough to notice things.
Considering that the fact that they still have the Chernobyly energy drink with them, as well as their 2010s technology that makes the other guys think they're Russian spies, it's entirely possible the time travel magic that infected the tub has some sort of protective bubble around their room as well as them, so the room stayed the same. The magic isn't really well defined, but we do know that they look like they do in 2010 still to each other, while looking younger to everyone else, Jacob travelled with them, & their tech travelled with them, so it's entirely possible it transported their clothes, as well as them, back as well. Plus, the lodge hadn't really changed much in 20 years, so it's not like they would've noticed much beyond the other people there, so they probably assumed some other people checked in while they were in their room, depending on how early they woke up & went skiing.
In the past, the characters look like their older selves to each other but like their younger selves to everybody else. When they leave Lou back in the past should he not look like a 60 year old to the other characters in the modern day?
They're not time traveling anymore so that special effect isn't in place.
The time machine works like Kitty Pride's ability in X-Men: Days of Future Past, where their minds were sent back, but not their bodies, thus the effect on display.
What was the last 20 years in the new timeline like from Lou's perspective?
Pretty fucking sweet, from the looks of it.
Well, with his knowledge of the future, he was able to start a Hair Metal band of the Motley Crue variety, invest in some big name companies before they made it big, start similar companies before some of them came to be, get his friends' lives back on track, & charm his way to marrying Adam's sister & raising Jacob, & most likely a whole bunch of other stuff, so it's not too different, but different enough to where there are a lot of discontinuities in the other's memories.
When Adam, Nick and Jacob get back to the present, a lot of things are different but their family members and coworkers recognize them. Does that mean there were alternate versions of the characters walking around for 20 years who lost their memories in 2010?
I assumed that they would regain their memories of the "new" past after a while, or else that ending is not particularly happy, when you think about it.
Considering Lou planned for that contingency, it's most likely that they simply asked him about most of the details, or looked up stuff through the internet. There's also the possibility that they asked their loved ones about everything & explained themselves, otherwise they're looking at some awkward interactions.
Lou uses his knowledge of the future to preempt Google and redefine Motley Crue with himself as lead singer. How? Knowing that Google exists doesn't mean he has the wherewithal to actually invent it. He's not a programmer and wouldn't know who he'd have to torture to get the vast amount of information he'd need. And how did he manage to get into Motley Crue? Prove he could predict the future and promise to make them rich(er)? Might work...
He wouldn't have to be a programmer to preempt Google. He'd have to have money to buy the biggest share in Google and cause a name change to suit him. He didn't have to invent it, just fund it.
He could weasel his way into Motley Crue by joining their road crew after high school, using his knowledge of their future library of songs to become closer to the band by "contributing" their future songs to them before they wrote them & then replacing Vince Neil as singer in 1992, or even manipulating events so that he left the band earlier. With it becoming public knowledge that Lou "wrote" a large number of their songs even before he replaced Vince Neil as the singer, fans would likely view him as important to Motley Crue as Mick Mars & Nikki Sixx.
On the Google end, he could've gone to college, or met up with actual programmers over the years that knew how to do that, or he could've funded it with his earnings from being in Motley Lue. As for the band itself, he could've started a tribute band that later overtook them in popularity by "writing," practicing, & recording songs they wouldn't have until years later after, as well as some other Hair Metal songs from other future bands' albums, as well as originals he'd write with his bandmates after getting a recording contract. Hair Metal bands, especially Motley Crue, were really big in the 80s, thus if they were marketed to record companies as "the next Motley Crue," due to similar stylings & writing techniques, as well as being a tribute band that covers their earlier material, it's entirely possible he could've broken into the mainstream through his own releases. Either that, or what they guy above me said, though with the added bonus of Lou having his own band & eventually working with the band on writing their material.
Shouldn't there be an alternate timeline where Adam and Nick went missing for 20 years? I am assuming when the main characters traveled to the past, they took over the bodies of their past selves. When 3 of the characters returned to the present, Adam and Nick's young bodies remained in the past, regaining their memories.
Yep, essentially "X-Men" logic here, where the time travel displaced their minds in time, though with the added confusion of transporting Jacob, as well as their belongings, back with them & keeping them from seeing each other as younger while in the past. When they travelled back to the present, it's easy to conclude that their younger selves walked out of the tub completely confused & Lou would explain what happened to them, otherwise they'd be confused about what happened the last few days. It'd certainly explain what they were still doing at the lodge in the present, despite not needing to go there because of the timeline changes, though that could easily be chalked up to most of the guys wanting to do a minivacation with Jacob, or the fact that they knew could've caused them to go to the lodge & wait, but then again, it's probably best not to think about that part of it, as it's confusing without a direct answer from the characters.