Greetings! I'm new here and I think about this place as soon as I see what the statement asks. 1. The problem statement, all variables and given/known data Considering the volumetric density ρv=(e-2r/r2), figure the total charge (ℚ) of the universe. 2. Relevant equations ρv=ΔQ/ΔV -> (ΔQ ∝ ΔV) ℚ=∫v ρv dxdydz 3. The attempt at a solution I know you can figure it out ℚ when you've a pack of coordinates (bounds of the volume) in which you can calculate the total charge if you find some kind of symetry or not (i.e: cilindric, spherical coordinates and so on); but my mind just stacked overflow when the book asks the total charge of the universe... I wonder what system of coordinates and values should I use for the triple integral? I've read that the shape of the universe —or known one— is flat; but I'm pretty sure I haven't the proper knowledge and mathematical understanding to realize that; so I assume for early problems, the shape is spherical, so I would use the following: ℚ=∫vρv dv = ∫∫∫ρvr2Sin(Φ) drdΦdΘ Jacobian Determinant. I've found this problem at the second chapter of the book Electromagnetic Theory - Hayt. I'd appreciate some help with this problem. Thank you for your attention and keep this pantheon of physics alive! Congrats on this forum.