The Mood Experiment

Facebook tuned 689,000 feeds to see if sadness spreads. It does. They published it.

The 2014 PNAS paper 'Experimental evidence of massive-scale emotional contagion' reported Facebook's 2012 manipulation of 689,003 users' feeds to test mood transmission — without specific consent, drawing an editorial expression of concern and regulatory complaints. It is the platform-ops file's smoking gun: not that manipulation is possible, but that it was run, measured, published, and worked.