Martin Rees formulates the fine-tuning of the Universe in terms of the following six dimensionless constants:

  1. N = ratio of the strengths of gravity to that of electromagnetism;
  2. Epsilon (ε) = strength of the force binding nucleons into nuclei;
  3. Omega (ω) = relative importance of gravity and expansion energy in the Universe;
  4. Lambda (λ) = cosmological constant;
  5. Q = ratio of the gravitational energy required to pull a large galaxy apart to the energy equivalent of its mass;
  6. D = number of spatial dimensions in space time.

A Question of Origins - A Finely Tuned Universe (Dennis Prager)

What does a Fine-Tuned Universe Mean? (Robin Collins)

Is the Universe Fine-Tuned ... (Leonard Susskind)