When tweaking values of physic's fundamental constants, how are outcomes observed?

Question

I often read about the concept of the "Fine-Tuned Universe". From my understanding, the universe's existence is sensitive to the values of certain fundamental physical constants, which are observed and measured.

How does the process of determining what our universe looked like, if those values were changed, work? How do we know that if the,e.g. speed of light, were faster or slower our universe would look much differently?

Answer 1

Typically, computer models are run which contain the fundamental constants. You run the model with the constants we have, then run it with the tweaked constants, and look for differences.

In some cases, estimates can be had by doing the calculations in simplified form "by hand".