The 'Magic number' everyone knows but no one understands!

Drum roll, please.... 1/137.

No units. A value one gets by combining the speed of light, Planck's constant, and the charge of an electron or proton. It appears in electromagnetic theory, relativity, and quantum mechanics. It is connected with all the pillars of physics, and is necessary to understand how atoms work.

But NO ONE has a clue as to why it is so important, or if it holds the key to a unified theory of physics and nature. Physicists, especially theorists, often write the number on their chalkboards, so it is always there and always on their minds.

Does this number hold the key to understanding the entire universe???? Perhaps, but we don't know. It is given the name fine structure constant in textbooks, because it was connected early on over a century ago to a particular feature of the electromagnetic spectrum (which has to do with the nature of how atoms emit light). But it is a puzzle waiting to be solved, even though all of the great physics geniuses over the past 100+ years have taken a shot at trying to figure it out.

For more, check this. For a little more technical information, check here.