Speculation with portals
I would posit that, like most things where Earth's rotation is brought in as a counter-example, it has to do with frame of reference. We define "moving" and "still" in the frame of reference of our surroundings, which are also moving. On an absolute scale, we're all moving massively fast, away from the Big Bang, around the galaxy, around the Sun and so forth as you mention.
The thing is: physics doesn't care. It only cares about how fast you're moving relative to the system you're examining. See what I mean?
My guess is that the two portals have to keep the same velocity relative to each other to stay connected. If they were on both sides of a rocketship and the rocket changed velocities, maybe the portals would stay open. (However, my instinct is now telling me that if you put two portals side by side on a moving wall-section and moved it, both would close, despite maintaining identical momentums. Hmm.)
A couple pages back, somebody said that the universe is endless. I don't believe thats correct. I've read my share of scientific articles, and I'm pretty sure that the general scientific community agrees (for the most part) that the UNIVERSE was BORN out of an infinitely dense particle, blah blah blah. BUT! That particle had to be SOMEWHERE. That SOMEWHERE wasn't the universe, it was somewhere unnamed by human sciences (as far as I know). The universe is only as big as the oldest waves from the original expansion have traveled, which we know for a fact to be a limited number, as we HAVE measured the distance to the oldest particles, and they exhibit a red-shift, meaning that they [the boundary of the Universe] are moving away, but into what? It can't be farther into the universe, because that is where it ends. The universe is filled with sparsely spread (double-ftw) particles. Space is a NEAR-vacuum. There ARE, however, particles. "Space" as we know it only stretches as far as the afore-mentioned universal wall. The area beyond that wall is undefined, and is impossible to define unless we would manage to get there someday (unlikely), but is assumed to be a true vacuum, lacking in ANYTHING. Other hypotheses state that there may be other universes past our barrier, and that as we grow, they shrink, only to expand again when they have been forced into a single particle, causing our universe to begin to shrink. That is where the new theory, the big bounce, could fit in as well, but I believe (not sure) that the big bounce doesn't yet account for other universes.
Anyway, I like portals, and I think that, were it not for engine limitations (or practical ones), that they WOULD move with platforms. I'm working on a mod, and I have it explained to the Test Subject early on that only one thing cannot travel through them, sound.
Common sense tells us space is infinite nothingness. It's space. Nothin' out there. I don't get why we need all these retarded speculations of other universes. Seriously. It's Just SPAAAAAAAAAAACE. It doesn't ned to be created by a big bang, or be classified as infinite or finite, it's just NOTHINGNESS.
If space is pure nothingness then I have a lot of space where my brain is supposed to be... 
status: Mapping (map 1 of 10)
LOL I actually tried to make that impossible scenario, and I didn't fail at all 
I got managed to make two portals at same coordinate at same time without that another one fizzles. I actually faked it, I used two prop_portals and deactivated them. Then made 10-100 x trigger_multiple to open a new portal when last one is fizzled, this for both portals in two separated time layers, so they both will stay open and reopen so fast that human eye can't see the "secret". I used box to trigger the trigger. I have picture of it, it's kinda mindfuck 
This one fuckt up my pc pretty badly...
I got managed to make two portals at same coordinate at same time without that another one fizzles. I actually faked it, I used two prop_portals and deactivated them. Then made 10-100 x trigger_multiple to open a new portal when last one is fizzled, this for both portals in two separated time layers, so they both will stay open and reopen so fast that human eye can't see the "secret". I used box to trigger the trigger. I have picture of it, it's kinda mindfuck
This one fuckt up my pc pretty badly...
can you upload the map please? 
And a vmf?
sure
okay check the wip
okay check the wip
Thanks!
EDIT:
Lol, That's really cool! but i lagg alot when the portal's are open :p
I read this whole thread.
Yes, yes I did. And I few things to say that were already said, but I'd like to post something that shows I'm not a retard.
On the topic of portals bending 4space and "flatlanders" paper portals:
This is EXACTLY right. If you took a sheet of paper, and made two holes, and folded it over to line them up, WE'D see a folded piece of paper. A flatlander, would see a shortcut, you know, a portal, but nothing distorted. So portals, in our 3space, would be bent through 4space. (I'm not running the risk of "the 4th dimension is time"). We wouldn't notice, we'd see a shortcut.
At the rule of not placing a portal between portals (I'll go back and look for that post later) You could fold the paper the other way, so this could work. How many times, I don't know, but in your example, one in the cube one out of the cube works.
Another speculation with moving portals (Please don't bring up relative to each other or portals don't move. I don't really want to hear it. It's a cheap cop-out to thinking, and not what this post is for.)
Say there's 0 on something that's falling toward you, and 0 on a stationary object. When you go through 0 (Or more correctly, when it passes over you, do you leave 0 at the speed of 0?
My brains hurt after thinking about this, but I'd say yes.
Anyone ever seen Monsters, Inc or the animated short Presto? Both made by Pixar, both using the concept of portals, both freaking hilarious. You can see Presto on Youtube; since I'm not sure if it's there legally, I'm not supplying a link. Searching for "Pixar Presto" should do the trick.
"Duct Tape is the answer."