What would happen if Col. O’Neil (Richard Dean Anderson) walked behind the star gate and went through it from behind? (so to speak)
Instead of going through a worm-hole would he go through a hole-worm? Time travel? Would he end up in a black hole?
I need to know before I finish building mine.
Can’t be to careful you know… 
He’d get his truck, his wife, and his dog back.
Yayyyy!
Hmmmm… What about Samantha? Better than the dog. Maybe.
He would die
Yep, that probably right. The gates have a tendency to disintegrate people or objects that use them improperly. I think that walking into an “incoming” wormhole disintegrates the subject (though radio waves can go through both ways just fine), and being in the path of that whoosh of a new wormhole definitely disintegrates the subject.
I realize that, but maybe the backside goes" hsoohw" ? Is one sucked into the “hsoohw” and perhaps, well, turns up on Fox News, or something worse? If that’s possible.
Might be the fourth way you can kill someone with the Stargate, the other three being:
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Have them stand in front of the Stargate when it opens, and have them get hit by the “wave” of “water” which briefly extends from the Gate.
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Have the iris closed on your Stargate when someone at another Stargate dials yours, and attempts to come through (the iris prevents them from rematerializing on your end).
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Stick part of them through an open Stargate, then shut it down. Slice!
As far as I can recall time travel would happen if a stargate was used during a solar flare, which would occur only when it was convenient for the plot.
He’d end up in the X-Files universe.
Oh god, anything but the X-Files!
ISTR that it’s irrelevant if one enters from the “front” or the “rear” of the event horizon. It’s not a “tunnel” in the physical sense, but rather a “threshold” that enters one into the wormhole.
I could be, and probably am, wrong…
Not doubting you, but in that case one wonders why the iris is only on one side. Or is it?
Not in Stargate physics. The wormhole is entirely artificial. You step through one side, and you are split up into your component molecules (ala the transporter) and then streamed through the real wormhole, which is very tiny. You come out the other end, and are rematerialized.
And, yes, a solar flare causes time travel–but you have to have the timing perfect, which requires knowing ahead of time when a flare is going to happen. And it has to be in a direct line between the two sides of the wormhole. It takes future tech, or at least future information.
Great question. Here’s one answer:
I always thought if you tried to go through the back it would just push you away, sort of like a trampoline, but I don’t know that anything in the show ever supports that theory. I have no idea where I came up with it.
Interestingly, in the original movie, there’s a little “tail” sticking out the backside when a wormhole opens.
Two quibbles.
Quibble the First: You do rematerialize. Of course, you’re a smear that’s considerably less than a molecule thick, but some kind of goo rematerializes. I’m rewatching it with a buddy, and Sam just explained that to either Daniel or Hammond (or both)
Quibble the Second: That only works on some Stargates. Others will either spit you out or stay open longer. (See: Stargate Universe, first couple of episodes). Stupid, STUPID inconsistant Ancients! 
Which episode was it that split people? I aways recall being able to keep a Stargate active longer by essentially sticking something into it. Whether it was a particle stream or something else, it was definitely possible.
Plus I am not sure there was a way to shut it down short of destroying the power source.
That’s the trouble with quibbles. No, wait … wrong show.
I believe that Kawalsky was killed in episode 3 (he had been taken by a goa’uld) when Teal’c held his head partway in the wormhole while they shut down the gate at the SGC. Basically just took off the back half of his head.