Who Americans spend their time with
Longitudinal data would be informative. I strongly suspect people spent less time alone in the past.  
(Note: The X-axis is age.)My theories:* Multitude of choices given to us by technology have led to fewer things we pay attention to in common with our friends and neighbors. Thus, fewer shared loci of interaction. Career specialization is another key contributing factor.* More recently, dopamine rush generated by endless new contents tailored to our preferences has made real-world interactions and activities dull by comparison. More people choose to spend time alone with that rush. In the long run, it might result in weaker social ties and less healthy psychology for some/many people.Research has shown that strong social ties are important for mental and even physical health.How do we design technologies and social institutions to help connect people in the real world and alleviate the problems?