QuoteWith Einstein and the models of modern physics the universe does not expand into anything.
This statement is misleading. As of current models and observations, both the universe and the space in which it exists are in accelerated expansion. The expansion of space seems to add so much that the distances between our galaxy and the most distant still observable galaxies seem to increase with more than the speed of light. The continued dilution of matter on the largest scale, the increase in entropy and the further development of stars will make the universe much different from now.