Question: (Probably related to [this one](https://physics.stackexchange.com/questions/721), and probably should be CW.)

A very long time ago, I had the good fortune to read George Gamow's excellent series of *Mr. Tompkins* books. That introduced me to the idea of a world where the usual physical constants (e.g. the speed of light and Planck's constant) were changed such that "paradoxical" effects became apparent in the macroworld.

My memory is hazy now, but I do recall the concepts of relativity (e.g. dilation) becoming more pronounced when the speed of light is reduced to "human-sized" speeds.

In this vein, I ask this: assuming all other physical constants being fixed, what exactly can be expected to happen if (*physical constant of your choice*) is increased/or decreased?

One physical constant per answer, please.

Answer: 
See Smolin's book "The Life of the Cosmos", [here](http://en.wikipedia.org/wiki/The_Life_of_the_Cosmos) and [here](http://books.google.com/books?id=EF5jZ_eev-cC&printsec=frontcover&dq=smolin+The+Life+Cosmos&source=bl&ots=pICurxIw2S&sig=yeuUzglCG92kKkNClBiEkpy77ak&hl=en&ei=yk_5TP2_HcX7lweJvdjhBw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CDwQ6AEwBA#v=onepage&q&f=false), wherein he suggests common descent and Darwinian selection amongst multiverses for peturbed physical constants maximizing black hole formation in that universe. His most recent paper on arxiv on this topic is <http://arxiv.org/abs/hep-th/0612185>, where he argues that this is still a live hypothesis, which has already survived several experimental tests.
Increasing the value of $\hbar$ significantly would be pretty interesting, as matter has a wavelength proportional to it. Walking through a doorway might become a new experience as you get diffracted into a wall. 

However, this is all backwards thinking. The physical constants calibrate our mathematical models of the universe, like $\lambda = h/p$, not the other way around. So it is better to say that if you got diffracted every time you walked through a doorway, you would need a large $\hbar$ to model that. 

Additionally, since constants like $\hbar$ have units, their value is somewhat arbitrary anyway. Which brings us to dimensionless constants... here's a good one:

$F\_{\rm{grav}} / F\_{\rm{em}} \propto \frac{\frac{G m m}{r^2}}{\frac{K q q }{ r^2}} \propto \frac{G}{K}$

the ratio of the gravitational to electromagnetic force for a unit charge and mass at a unit distance.

Currently the electromagnetic force kicks gravity's butt, but I wonder what life would be like if that weren't the case.