Transcript: The existence of life in the universe also depends fairly sensitively on the ratios of certain fundamental particle masses. If the ratio of the proton to the neutron mass was not approximately one, in the early big bang the fusion processes would have created almost all neutrons or all almost protons, with the result being that there could have been no stable nucleides and no chemistry, and therefore no biology. If the proton to electron ratio were not roughly as large as it is, almost a factor of 2,000, once again the physics of the universe would have been such as to allow no chemistry or no solid matter. Gravity could be different and life could arise in a scaled-up or a scaled-down universe, but the general principle is that many of the fundamental ratios of particle masses in nature, and the strengths of the fundamental forces could, in principle, take a variety of values. Such universes would have different physics from our universe, but it would be plausible physics, realistic physics, and reasonable physics. The only difference would be that chemistry, biology, and life would not be possible.