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If space is infinite- as science tells us- which means there are more galaxies out there than grains of sand on the beach- and each of those galaxies has numerous solar systems & each solar system has numerous planets- then how could we be alone?

Very unlikely we're alone. Their must be some life out there.
But in what form ? Conditions vary from planet to planet.
More planets just like earth is possible ,
Probably we never get the answer while we're alive. :-)