Many research questions cannot be answered in the course of a single lifetime. Davide Castelvecchi, a contributing editor for Scientific American, has long-wondered what scientists would study if they could live for hundreds or thousands of years—or even indefinitely. Recently he put the question to leading investigators in their fields, reporting on their replies in "Questions for the Next Million Years," in our September 2012 issue.

A summary of the replies appears below. Which idea do you like best? Vote for one below. You can compare your answer with those of other voters here.

We'd also like to hear your ideas for other studies that would need centuries or more to carry out. Post your thoughts in the comments section below.