No, but there are likes… 
Downvoting has been discussed a few times, but it’s believed that the risk for abuse is greater than any potential benefit. If something is merely “meh”, there’s no harm in letting it stay as it’ll quickly get replaced by new or more active topics; and if it’s actually offensive, it needs moderation attention and should get flagged.
(Actually, you could think of flags as Discourse’s downvotes; if enough members flag a post, it’ll get hidden automatically even without moderator intervention.)