system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible for something to have negative mass?

Is there anything in the universe that has properties opposite of gravity resulting from having the opposite of mass?
gpt
The existence of negative mass would not cause any contradictions, and the mathematics work out in a self-consistent way, so it can't be ruled out. However, we currently have no reason to believe that anything with negative mass actually exists.