I got one question for you. In the book that I learn from (Physics textbook), I read that "at very small dimensions of the particles (like the molecules of the gases) the force of the light pressuring at small particles can reach the force of gravity which acts on the particles upon." If the light can "send" the gas particles out of the Earth I was wondering how gas particles exist on the Earth? Maybe, I misunderstood something, but how is possible that the pressure can be so "big"? For example: The Standard atomic weight of one atom of hydrogen is 1.00794(7) g·mol-1. To form the H2 gas it needs 2 atoms, so the mass of one molecule will be 2.00794(7) g·mol-1. If the "ordinary" light (the light that we see) has 600 nm wavelength, 2 eV (energy), 3,6*10-36 and a impulse of 1,1*10-27, how "big" force acting on the hydrogen molecule it needs to "counter" the force of gravity? Thanks in advance. P.S I am a total beginner so please use plain expressions and plain English as possible since I won't understand anything.