There are several online forums and discussion groups that can be helpful for UPSC Physics optional subject preparation. These platforms provide a space for aspirants to connect with each other, share resources, discuss important topics, and seek guidance from experts. Here are some recommended forums and discussion groups:

1. EduRev UPSC Physics Community:
EduRev is a popular online platform that offers a dedicated UPSC Physics community. This community allows aspirants to access study materials, previous years' question papers, practice tests, and interact with fellow UPSC aspirants. It provides a comprehensive platform for discussions and doubt-solving.

2. Quora:
Quora is a widely used question-and-answer platform where you can find a dedicated UPSC section. Many UPSC aspirants and experts actively participate in discussions related to various subjects, including Physics. You can ask questions, find relevant answers, and engage in discussions with like-minded individuals.

3. ClearIAS Forum:
ClearIAS is a well-known website for UPSC preparation, and they also have a dedicated forum section. Here, aspirants can discuss Physics as an optional subject, seek guidance, share strategies, and exchange study resources. The platform is moderated by experts who provide valuable insights and suggestions.

4. UPSC Forum on InsightsIAS:
InsightsIAS is another popular platform for UPSC preparation. They have a dedicated forum section where aspirants can engage in discussions related to Physics optional subject. This forum allows you to post queries, get answers from experts, and interact with fellow aspirants to enhance your understanding of the subject.

5. UPSC Forum on ForumIAS:
ForumIAS is a comprehensive platform for UPSC preparation. Their forum section features discussions on various subjects, including Physics. Here, you can join threads, seek guidance, and interact with UPSC experts and fellow aspirants to gain valuable insights and knowledge.

These online forums and discussion groups provide a platform for UPSC Physics optional subject aspirants to connect, collaborate, and learn from each other's experiences. It is essential to actively participate in these platforms to make the most out of the shared resources and discussions. Remember to verify the accuracy of information and cross-check with reliable sources before incorporating them into your preparation strategy.