Additional energy / matter from parallel universes

If you transfer it through a GR wormhole, the consequence is that the wormhole mouth on your end gains negative mass to balance the positive mass of the stuff you are bringing in, while the mouth on the source end gains positive mass. If you don't keep the flow of material roughly balanced in each direction, the source mouth will eventually be enveloped by a black hole, turning the destination end into a white hole, and you will only be able to send material and information one-way.

My recommendation would thus be to not try to import large amounts of energy, but merely to import sources of low entropy, and dump your high entropy waste back into the other universe to balance the books.

Since direct interaction with parallel universes is totally out of bounds for current science, you can basically do whatever you want. Make up your own laws, because we currently have no way of scientifically determining what would happen in such a scenario.

If you’re completely stuck, here’s an idea for a way to preserve the zero-energy property of separate universes while still allowing matter transfer:

• The process of transferring matter from one universe to another requires as much energy as is stored in that matter, as calculated by the formula $E=mc^2$ (and this consumed energy is released into the universe from which the matter was taken).
  • Pro: this would mean that each universe maintains the zero-energy property, which is nice.
  • Con: moving even microscopic objects between universes will require an astronomical amount of energy, which probably isn’t feasible.
  • Pro: although moving matter between universes will be hard, you can certainly transfer information much more easily. So you might be able to Zoom with someone in an alternate universe, but not meet them in person.