At his blog, Paul Knoepfler says that he sometimes lets himself dream big as a scientist. "The truth is that having a big-time, perhaps way 'out there' goal or even dream is important for both scientists and Science," he writes at the appropriately named blog, Confessions of a Stem Cell Scientist. Knoepfler notes that while those dreams may not come true tomorrow, but that those ideas serve as a starting point to get to that tomorrow. "When science has had its biggest impact it has been through achieving what pretty much everyone said was impossible," he says.
In the video clip below from Real Time with Bill Maher, astrophysicist Neil deGrasse Tyson worries that people, particularly politicians, have stopped dreaming. (HT: PZ Myers at Pharyngula)