As cool as it'd be, it wouldn't ever be like Half-Life or Stargate. Heres a few reasons why (I'm trying to ignore the actual physics involved. While I have a grasp of the concepts, I doubt I could explain them):
Half-Life
1. The portals created in Half-Life's 'Portal Storm' were interdimensional gateways that needed to be specifically locked to another dimension. The scientists at Black Mesa Research Facility (FTW) where experimenting with teleport technology when the discovered Xen, a 'world stretched thin across the membrane where dimensions intersect', sort of like a 'border world' between dimensions. It was near improbably that the BMRF team found a border world that was inhabited. However, according to the theory of infinite universe, it comes to 50/50 odds (That is a simplified version of the actual odds. The current theory is much different) of finding a world that is inhabited versus a world that isn't. Then, you figure in whether or not the world's life forms are hostile or not, which comes out to 25/25/50, and if you keep narrowing it down, it becomes a virtual impossibility.
2. The only reason the aliens got to Earth in the first place was the interferance of the portal's structure by the Nihilanth. Otherwise, the portals would be glimpsed for fractions of microseconds before they collapse within themselves.
-> I can use that same explination to debunk the 'Black hole' debate. Every black hole formed (and there will be a lot of them), will only exist at the sub-atomic level for incredibly small amounts of time, not large enough to do any damage.
3. The only reason the Combine got to Earth was for the same reason.
4. The odds of creating an interdimensional breach of even a sub-atomic scale is a virtual impossibility.
Stargate
1. The wormholes in Stargate require 2 seperate points in 3-dimensional space to create an effective wormhole. As the odds of creating the earth based wormhole at the same time of another wormhole is, again, a virtual impossibility.
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Actually, it may be more likely that we discover a 'Slip-space' like dimension than to create a 'Portal Storm' or 'Stargate'.
*Does a system check of his HEV suit*