Pacific Rim is an interesting combination of several genres that have never been readily accepted by the American public; oversized monsters called Kaiju have been a part of Japanese entertainment for decades (Godzilla among them). Jaegers are a common name for very large robots. The movie also has elements of disaster films. Del Toro has bluntly stated that his creation is about overcoming differences of sex, race, and even prejudgment. All of them are great and nicely meshed into a seamless story. The director even sidestepped making it look like a war-glorifying film by giving ranks that belong more in a Western than a military film. But what made the movie intriguing for me was the concept of the Matter Bridge.
The Matter Bridge is not a new concept. I remember hearing of it first with The One, where two policemen patrol a "multiverse" where every person may have a counterpart in every other universe. The television programs Stargate SG-1 and Stargate Atlantis both also used matter bridges for various purposes. But the concept was always the same there; the cast was introduced to their counterparts from another dimension/reality.
In Pacific Rim, the Matter Bridge is used to transport an alien species' Kaiju, cloned war-monsters, to Earth as a prelude to conquest. This film is not about a neat way for characters to talk with each other, nor does it go into the well-traveled road of alternate timelines. It is an exploration of an alternate form of travel.
It's also a feasible. Recently, scientists have discovered that there may be Matter Bridges throughout the universe. They are discovering an increasing amount of evidence that dark matter may serve as a type of connector for the universe, helping to keep it tied together and structured even as the galaxies expand exponentially. According to the theory, Matter Bridges are composed of this dark matter. It is possible that they span not only galaxies but (perhaps) work on the smaller scale of solar systems as well. And, if there are other universes or dimensions (a big if), then it stands to reason the dark matter and therefore Matter Bridges would connect them together as well.
In effect, the movie brings to attention not only another hypothetical means of transportation across the stars but opens up another means of potential alien invasion. Better than that, the suggestion is made that the sea might be the end of the Matter Bridge just as easily as a point in space or on land.
I think that is perhaps the most brilliant detail in the movie; aliens launching an invasion from another dimension with a launching platform in the Pacific Ocean. There are large stretches of square miles in the Pacific that are so deep we have no ships built to withstand the intense pressures. The bottom of the Pacific would be a perfect place to launch an invasion. With our technology as it is, we would never be able to destroy their base.
To sum up, we could be attacked at any time, from a direction we would never expect and from which we might not have the technology to combat. NEAT! I can't wait for a sequel.