Philosophy invites consideration of many disturbing theses. Maybe everything we think we perceive is really just a hallucination. Maybe there’s ultimately nothing more to ethics than projecting our arbitrary sentiments on to the world. Maybe solipsism is true and I’m the only person who really exists. Maybe illusionism is true and not even my consciousness really exists. (OK, maybe I can rule out that last one.)

There are a lot of creepy ideas out there. (No doubt you could suggest more.) Some are more credible than others. I’m not seriously worried about solipsism, for example, for all that it would be horrifying if true. But below the fold, I’ll share the idea I find most viscerally appalling, after adjusting for credibility. I don’t think it’s true; but it easily could be—I don’t think we can confidently rule it out—and I find it incredibly disturbing to think about.