Wednesday, January 18, 2017

very heavy and very light

can you explain why the ratio between the Hubble mass (i.e. the mass inside the Hubble volume today for a critical universe) and the Planck mass is about $10^{60}$? why are stars roughly in the middle (on a logarithmic scale)? or even more puzzling: why's the ratio between Hubble and Planck-mass about equal to the ratio between stellar masses and the masses of nucleons?


  1. How's this? 10^60 is the square root of 10^120, which is the cosmological-constant-problem number. It is also the age of the universe in Planck units. Barrow and Shaw have written about this.

  2. In general, the chapter on large numbers in Edward Harrison's textbook Cosmology: The Science of the Universe is a good introduction to this topic. (I recommend his book as a good introduction to most topics in cosmology; it is better than most introductory books.)