Many politicians, journalists and scholars suggest that echo chambers and filter bubbles are chiefly responsible for the emergence of communities, particularly online, that espouse contrarian and counterfactual perspectives and ideologies, and for their disconnect from the societal mainstream. Echo chambers are said to enable these groups to reinforce their views by connecting with like-minded others; filter bubbles to shield them from encountering contrary perspectives. They are assumed to result from a combination of individual choice, in selecting the news sources to consult or the social media accounts to follow, and the algorithmic shaping of such choices, as search engines, news portals and social media platforms highlight and recomme...