Yesterday morning I found myself in a shuttle with two of the world’s most eminent labor economists.  So I presented one of my favorite puzzles for human capital extremists: Why is the best education in the world already free?  Colleges do not card.  With a few exceptions, any presentable adult can simply show up on campus and learn to his heart’s content. 

Both labor economists simply denied my premise.  Yes, they’d allow an enrolled student to sit in on their courses.  But if a random person asked to attend one of their classes, they’d turn him down flat. 

Their answers contradict my entire experience with higher education.  From what I’ve seen, most professors are flattered if someone asks to unofficially study at their feet.  So what gives?  A few possibilities:

1. Professors at top schools are exceptionally unwelcoming of curious outsiders.

2. Economics professors at top schools are exceptionally unwelcoming of curious outsiders.

3. These two economics professors are exceptionally unwelcoming of curious outsiders.

What do you think?  Relevant first-hand experiences from professors and curious outsiders are especially welcome.