How Would We Talk To Aliens About Size, Mass, and Time?

Measurements here on Earth make sense to us because of our surroundings--that's the point

made in this video from MinutePhysics. If we were trying to communicate with an alien race on a distant planet, our style of measurement wouldn't make much sense. Some of these problems of communication are easily solved, by referring to size, distance and time in terms of the number of neutrons and protons in atoms. That can't be misinterpreted. But mass is a whole other situation--because mass on Earth depends on gravity, it's meaningless elsewhere. Luckily, scientists have a clever idea for how to solve that.
http://www.popularmechanics.com/science/math/a28454/aliens-size-mass-and-time/