This article addresses questions of ideological polarization and the filter bubble in social media. It develops a theoretical analysis of ideological polarization on social media by considering a range of relevant factors. Over recent years, fake news and the effect of the social media filter bubble have become of increasing importance both in academic and general discourse. The article reviews the assumption that algorithmic curation and personalization systems place users in a filter bubble of content that decreases their likelihood of encountering ideologically cross-cutting news content. At the intersection of new media, politics and behavioural science, the article establishes a theoretical framework for further research and future actions by society, policymakers and industries.