What evidence can you cite that the universe is flat?

The possibility of the universe expanding and thus being infinite can be cited as evidence that the universe is flat because an infinite plane is believed to have zero curvature.

Explanation:

If an expanding object is given a curve in its course of expansion, it eventually ends up meeting itself at some point or the other. If something is believed to be 'ever-expanding', it can be broadly concluded that it has no curvature at all.

Answer metamorphic rock;