I was thinking, would it have been more secure if the Precursors and had set-up the breach to Earth in such a way that it would allow a kaiju to enter earth but not return back.

Their aim was to destroy human population and in most of the fights shown in the movie, a kaiju fights till it dies. Secondly it does not make sense to bring a kaiju back after couple of fights, when it can cause more damage if it continued to attack human habitats. So is the feature which allows outsiders to pass through the breach a security failure?

closed as primarily opinion-based by user16696, Jason Baker, Joe L., Major Stackings, Null Mar 20 '15 at 2:44

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  • Maybe because they planned to use it themselves as a transportation method when humans where extinct, so you need to go in and out. And if it is one way there would be no plot. – Guillelon Mar 19 '15 at 16:22
  • Assuming there is only one Breach, how would the Precursors get back if they went to Earth and needed to return? This also assumes that the Precursors built The Breach, and it wasn't a naturally occurring phenomenon. – phantom42 Mar 19 '15 at 16:22
  • or that, even if they had wanted to, that they knew how to make a one-way breach – KutuluMike Mar 19 '15 at 16:24
  • 2
    Id say the simplest thing is, they could only make a 2way breach. – Himarm Mar 19 '15 at 16:28
  • (Also, just a note to writers of potential answers: please avoid pure speculation. Answer on SF&F should have some basis in canon, rather than merely your opinion.) – KutuluMike Mar 19 '15 at 16:38

The official novelisation deals with this quite neatly. The fundamental basis of The Breach is that it's a fold in spacetime, bringing two distant points (in this case separated dimensionally as well as spatially) into contact. That being the case, you could no more create a "one way breach" than you could poke a "one-way hole" in a piece of paper.

Harnessing the fundamental energies necessary to the creation of a passage such as the Breach — which essentially folds space-time around itself to bring two distant points into proximity — requires technology far beyond current human capabilities, as well as focused energies equivalent to the entire output of human civilization during the last century. Destroying the Breach, however, is likely easier than creating one.

Secondly, a uni-directional passage would defeat the aliens's battle plan; to learn from each Kaiju encounter and use that data to refine their attacks:

  • The kaiju are manufactured
  • Some of the repeated strands of DNA act as encoding mechanisms for a kind of species memory
  • The kaiju passing through the Breach transmit their experiences on Earth back to the Anteverse

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