[Metric]

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There is also a theory that the universe will continue to expand, finally reaching a point where it starts to contract. The contraction will be slow at first but will accelerate as gravity increases. Finally contracting to the size of the initial "big bang". No real use in conserving energy if this is the case.

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Yes, always possible -- but the best evidence right now points to a cosmological constant that will ensure continued expansion and eventual heat death of the universe, making long-term conservation of resources a really good idea for intelligent life.