In 1999, it was indicated that one of nature’s fundamental constants - a number that reflects how tightly atomic particles stick together - may be different now than in the distant past. This number is known as he fine structure constant or alpha. Recent data has shown hat statistical evidence that alpha has, in fact, changed by one part in 100,000 over the past 12 billion years.
I was nder the impression that atomic particles stick together by one of three ways: hydrogen bonding, valent bonding, or ionic bonding. So, what is this alpha that measures how tightly atomic particles stick together when how tightly they stick together would depend on the type of bonding?
This is pretty much true provided you take “atomic particles” to mean atoms rather than the likes of protons and neutrons. (Given that the latter are often called “subatomic particles”, yours is perfectly natural usage, though not a common one.) Atoms stick together to form molecules and crystals entirely as a result of electromagnetism. Ignoring a certain amount of quantum mechanics, it’s all a matter of atoms either swapping or sharing electrons and then being held together as a result of forces between electric charges.
So what’s alpha ? Crudely, it’s how strong electromagnetism is. Given two charges you can work out how strong the force between them is - if you’ve already measured alpha. Slightly more precisely, if you’ve two charges q1 and q2 (where electrons have q=-1) with separation R, then the force between them is (up to quibbles about units)
F = alpha x q1 x q2 / (R x R).
Very precisely, it’s the ratio of the electrostatic energy of repulsion between two elementary charges, separated by one Compton wavelength, to the rest energy of a single charge. If that helps. The neat thing about knowing alpha (it’s famously roughly 1/137) is that given just this single measured number you can in principle predict any quantities in electromagnetism.
If the equation above reminds you of Newton’s Law of Gravitation, then you’ll see that it’s analogous to big G, the gravitational constant. It’s a bit more complicated for the weak and strong forces, but you can define such a “coupling constant” for each of the four fundamental constants.
As far as interatomic forces are concerned, in general you’d expect that if alpha were bigger then atoms would squeeze closer together. Simeta’s example of it being involved in how light interacts with atoms is also very true. Changes would thus also impact on about every single everyday phenomena you can think of, including the colour of things.
I haven’t followed the recent controversy about variations in alpha inferred from astronomical observations. My impression is that the professionals are taking the issue seriously, but people are far from convinced. Controversies like this are the norm in research - sometimes the claims play out, sometimes they don’t.
It should also be noted that alpha isn’t a constant once you start worrying about quantum effects. The higher the energy involved in a process, the stronger electromagnetic forces appear to be, which is interpreted as alpha getting stronger at high energies. Such effects can get large: at CERN’s LEP accelerator the relevant value of alpha is more like 1/120 than the everyday 1/137. When someone talks about alpha changing in time, they’re really talking about a change in the value when there’s zero energy in the process (the fine structure constant).
There was a similar thread about G the other week.