It's Thursday again, so here come last week's best or most interesting popular science videos from Youtube:

Sixty Symbols: negative temperatures - I mean for real, below 0K!

Crash Course!: it's the fifth episode of the series, covering quantum mechanical bases of chemistry.

Veritasium: not-so-DIY double slit experiment, using a single photon now.

MinuteEarth: this is a brand new channel, and in their first video they go through the history of Earth, MinutePhysics-style.

Mental Floss: another new channel, this one's from the VlogBrothers. It's the Youtube channel of the Mental Floss magazine, and their first video debunks 50 common misconceptions in six minutes.

Numberphile: an amateur mathematician works out the squaring of the circle, and in the course of doing that he changes the value of pi to 3.2, then he protects the whole thing with copyright, and finally he (almost) convinces Indiana to pass a law on this.

TEDTalks: emotions, hyperactivity disorder, and fruit flies on coke.