It is also one of the most seemingly esoteric interactions, because its effects are little-felt in the everyday world. We predominantly feel the effects of the strong interaction (the sun's smashing of protons together to fuse hydrogen is a release of energy due to the strong interaction), the electromagnetic (the light we see from the sun, and our computers), and the gravitational (Earth keeps us on it this way).

The weak interaction, by contrast, is generally known mainly for its presence in certain kinds of radioactive decay, known as beta decay. Other expressions and characteristics of the weak interaction seem abstractly theoretical or unimportant.

Really?

Let's start with something we call parity nonconservation. This aspect of the weak interaction imprints a kind of "handedness" on the universe - the first clue that maybe the universe doesn't obey a perfect left-right symmetry. In effect, you can tell the real thing from its mirror image.

So we have something that can tell the difference between a particle and an antiparticle.

Hmm. We're onto something here.

The weak interaction is also known to do something called "mixing generations of quarks". This has an important, and fundamental, effect on the kinds of stable particles we see around us. If the weak interaction did not do this, things containing strange quarks would be stable.

Gosh. Maybe this weak interaction thing is actually a lot more fundamental than we thought.

Ending the detour, we can restore the symmetry in the weak interaction by imposing something called "CP conservation". If you swap all the particles with antiparticles ("C" means "Charge conjugation") and then swap all the parities, everything looks the same.

Now what? There still doesn't seem to be any way to explain how to get more matter than antimatter in the universe from the Big Bang.

Enter the K meson.

It turns out that the K meson violates CP symmetry, and can thus decay preferentially to slightly more antimatter over matter. Other mesons which may have been created in the Big Bang might show an asymmetry in favor of matter (as yet there is no theoretical reason to reject this possibility, the problem is in getting the experimental apparatus and time to study them).

In this way it can be shown that without CP violation, the universe as we know it simply would not exist. So this weak interaction thing turns out to be pretty gosh-darn important.

As to the handedness of the universe, there is a great popular book by Martin Gardner called 'The Ambidextrous Universe' in which 'handedness is examined in detail. A great read.

As to the speed of light, I think it usually is referred to as the maximum speed something can travel, Schrodinger's cat aside.