The visible universe is so vast that if alien singularities developed and persisted, they may not have had sufficient time to affect us in any noticeable way, or indeed each other. If this is the case, intelligent aliens may be rare and those that persist beyond the turmoil of technological infancy rarer still. Under such circumstances physical laws as we've best determined them to be through scientific inquiry, could remain an insurmountable obstacle.
Including the scenario expanded upon above, there seem to be at least 3 plausible explanations for what we observe in the universe today.
1. Singularities are rare, seperated by vast distances, with a rate of progress and expansion limited by physical laws.
2. Singularities occur in unknown frequency and lead to transcension beyond our conventional means of detection, and perhaps beyond known physical laws.
3. Singularities don't occur, something impedes their development in all cases or in all cases as of yet.
I'd also add these seemingly less plausible explanations.
4. The minds involved in bringing about the first singularity manipulated conditions in this universe so as to prevent future singularities from forming and potentially posing a threat to them.
5. The minds that brought about their own singularity in an extra-universal location created this baby universe, setting it's conditions so as to reduce the threat posed by singularities developing within it. That could be accomplished by preventing the formation of singularities altogether, or in some way affecting physical laws so as to hinder their development.
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While all explanations seem plausible barring developments which render some impossible, our limited powers of observations do not allow us to adequately rule on the likelyhood of any of them beyond the acknowledgement of their currently indeterminate status. The singularity could be realized here before we detect alien life, let alone alien singularities. If the first scenario applies in our universe, we may not physically encounter other alien singularities for millions or billions of years.