The year is 2400 and we have a steady alliance with another sapient species that is helping us on our dying planet. The problem? their planet is across the galaxy. How can we realistically (both economically and technologically) travel to their planet and back with their gifts? Their culture is the same as ours but their technology is 400 years more advanced. It's up to you to decide what technology is reasonable for that time. The solution will need to be able to carry a few tons of materials but doesn't need to carry personnel. We can assume that their planets gravity is equal to ours.
closed as too broad by TrEs-2b, Aify, Frostfyre, bilbo_pingouin, Gary Walker Oct 17 '15 at 20:51
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Use the same physical principles used in establishing and maintaining communication with the aliens. Since our Galaxy is 100k light years across, there is no way whatsoever we can communicate using contemporary physics. So just use whatever groundbreaking discoveries (most likely FTL and wormholes) happen in the following 400 or 800 years.