Ah I meant that a bit differently - a big difference between the 19th and 20th century are the technologies and scientific concepts it brought forth. This pic shows about 30 of the greatest physicists and scientists overall we ever had, a lot of great, revolutionary thoughts were thought by them and great inventions were done by them. Of course not nearly alone by them. They are symbols. And of course scientific progress is not the only thing which makes the 20century unique, a lot of things went along with it, art, philosophy, politics, religion - and all those topics are interwoven (is this an english word?), interdependent, connected, - but none of those topics has such a wonderful "group photo"(id est pic related, in my opinion, as science.