Echo Chambers
The formation of echo chambers is not a strictly online phenomenon. Any belief or set of beliefs that self-perpetuates amongst a group of people via reciprocation of sentiment constitutes an echo chamber. An echo chamber is an example of confirmation bias actualized. It may be a symptom of limited access to information or opposing ideas, as settings like small towns have traditionally facilitated echo chambers. The antidote is active and civil participation in political discourse.
Echo chambers are dangerous because they may promote the spread of misinformation. In worst case scenarios, fallacious ideas promoted within an echo chamber may grow to the extent that a spiral of silence occurs within the opposition, and the status quo is consequently informed by falsehood.
Shown above: An educational video on what echo chambers are, and how they form
Social media platforms may exacerbate the extent to which echo chambers form, but this hasn't yet been empirically demonstrated. It has been demonstrated, however, that they do form online, and at different rates depending on the platform they develop. More research is needed.
It is also possible that the wide access to information the internet provides may, in some ways, hinder the formation of echo chambers. Future research could be geared towards identifying characteristics that differ from the average in groups prone to situating themselves in echo chambers. My hunch is that those who aren't generally receptive to new ideas will be more prone to stagnation in their opinions. If it is true that certain individuals are predisposed to settling in echo chambers, then the internet might not exacerbate the phenomenon significantly.