Everyday repercussions of nuclear forces change I'm pretty sure that, if all of a sudden gravity just disappeared (someone just set $G=0$ by turning a magical knob) we would notice immediately, starting to float in the air and a bunch of other things. Same thing if $\alpha =0$, I guess contact forces wouldn't really work anymore and things would just... pass through other things. But what about the weak and strong forces? If their coupling constant were (magically) set to zero, how would we notice in everyday life?
 A: The neutrino is unaffected by strong or electromagnetic forces. So if these forces were “turned off” for all matter we can predict it would behave like a cloud of neutrinos with mass. All atoms would immediately break apart with a release of huge amounts of binding energy and you would simply be left with galaxy-sized clouds of fundamental particles (quarks, electrons, neutrinos) bound loosely by gravity, with very occasional weak force interactions.
And if you turn off the weak force too then essentially ordinary matter has become dark matter. Again, galaxy-sized clouds of fundamental particles.
A: I'm assuming you just want a general idea - I'll leave others to describe changes to the CKM matrix and Majorana equation...
If the strong force were to disappear, as Vadim hints, atomic nuclei would fall apart, since that force holds the neutrons and protons together. In fact, it would be worse than that; the strong force keeps the quarks inside the nucleons. So the universe would just dissolve into a soup of quarks, leptons and bosons.
The weak force is the funny one. It's not really a force in that it holds things together. It's more the mechanism that governs certain processes: $\beta$-decay, mainly, in which a neutron decays to a proton plus electron
$$
n \rightarrow p, e^{-}
$$
So if that stopped, the first to notice it would be physics students doing undergraduate experiments. They'd discover their beta-sources had stopped working.
The next thing we might notice is that the Sun had got awfully quiet in terms of its neutrino output.
This is because the weak force is responsible for the formation of deuterium in nuclear fusion ($p \rightarrow n, e^{+}$). So the Sun would stop producing energy. However, we might not notice this for a while - the Sun is very large and very hot; it would take a long time for it to cool enough to have any effect on our climate.
Long-term, it wouldn't be good, though.
A: No, the nuclei would disintegrate and there would be no one to notice the change.
