system
Given the following post, respond as if you're commenting on Reddit:
human
If airships use helium to create lift. Would a vacuum create the same effect?
gpt
Yes, it would work even better with a vacuum than with helium, but you would need a very rigid shell to keep it from collapsing under atmospheric pressure. That is very, very difficult to achieve over large enough a volume without negating all the mass savings you've gained from swapping to the vacuum in the first place. 

Helium on the other hand is lighter than air at the same pressure, so it balances the atmospheric pressure and the balloon doesn't collapse.