Quora Physics - Another question and answer community, which is especially good for meta questions and opinion questions, which are not allowed at Stackexchange.
/r/Physics/ - The physics subreddits mostly focuses on discussions of recent news.
CosmoCoffee - Another nice physics forum with a focus on cosmology.
sci.physics - The oldest physics community, which is however no longer very active. However many great discussions can be found in the archives.
resources/communities.1525527970.txt.gz ยท Last modified: 2018/05/05 13:46 (external edit)